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  • 201.
    Källrot, Martina
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Covalent Vapor-Phase Grafting of Degradable Polymers2007Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Vapor-phase grafting is a step in the modern strategy of optimizing the molecular architecture of biomaterials. Covalent surface modification with hydrophilic vinyl monomers and the coupling of bioactive moieties improves the biocompatibility and bioactivity of the biomaterials.

    This thesis describes a new non-destructive, single-step method that has been developed for the surface modification of degradable polymers. The technique is solvent-free, performed at low temperatures, and utilizes low energy irradiation. Substrates are subjected to a vapor-phase atmosphere of photoinitiator (benzophenone) and a vinyl monomer in a closed reactor at very low pressure and low temperature under UV irradiation.

    Four of the most commonly used degradable polymeric biomaterials; poly(L-latide) (PLLA), poly(ε-caprolactone) (PCL), poly(trimethylene carbonate) (PTMC), and poly(L-lactide-co-glycolide) PLGA were functionalized with N-vinylpyrrolidone (VP). PLLA was surface modified with different vinyl monomers; VP, acrylamide (AAm), maleic anhydride (MAH), or acrylic acid (AA). The chemical composition of the surface changed upon grafting, and the wettability, assesed by static contact angle measurements, increased markedly. A cell seeding test showed that VP-functionalized PLLA, PTMC, and PLGA substrates are good materials for keratinocyte and fibroblast cells to adhere and proliferate on. Complex structures such as porous scaffolds of poly(ε-caprolactone-co-L-lactide) and poly(1,5-dioxepan-2-one-co-L-Lactide) with interconnected pores, and submicron-patterned PCL were surface modified by vapor-phase grafting. Their topographies were well preserved after grafting, indicating that the grafted layer was very thin. The wettability of the grafted substrates increased after grafting, especially in the case of porous scaffolds. Some porous scaffolds were covalently coupled with hyaluronic acid to demonstrate the concept of coupling bioactive moieties onto the grafted substrates to further improve the biocompatibility.

    Masked grafting, a simultaneous chemical and topographical surface modification technique for degradable polymers, was developed. The analyses showed a change in the surface chemistry in sub-micron pattern, and an increase in the wettability.

    The influence of vapor-phase grafting with hydrophilic monomers on the in vitro degradation rate has also been investigated. PLLA substrates were functionalized with VP, AAm, and AA and degraded in a buffered saline solution for various time periods. The results showed a change in the degradation rate in terms of mechanical characteristics and weight loss. Grafted monomers remained attached after 154 days of in vitro degradation which confirmed that the grafted layer was covalently attached to the surface.

  • 202.
    Le Normand, Myriam
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Ek, Monica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Extraction and valorization of spruce bark hemicelluloses and pectins2011In: The third Nordic Wood Biorefinery Conference: 22-24 March, 2011 Stockholm, Sweden, 2011, p. 274-275Conference paper (Other academic)
  • 203.
    Le Normand, Myriam
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Holmbom, Bjarne
    Åbo Akademi University, Finland.
    Ek, Monica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Hot-water extraction and characterization of spruce bark non-cellulosic polysaccharides2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 1, p. 18-23Article in journal (Refereed)
    Abstract [en]

    Non-cellulosic polysaccharides (NCP) from bark offer large potential as a class of natural raw materials for functional materials development and production of biochemicals. We have elaborated a process for sequential extraction of NCP from industrial Norway spruce bark using an accelerated solvent extraction (ASE) with water at 100 to 160°C. Carbohydrates, Klason lignin and ash content as well as size-exclusion chromatography (SEC) analyses were performed for all hot-water extracts. NCP were mainly composed of glucose, arabinose and galacturonic acid units which revealed the presence of starch, arabinose-rich hemicelluloses and pectins. In total, the industrial bark of Norway spruce contained up to 20% of NCP which were extracted with pressurized hot water. NCP were mainly extractable at 140°C and started to undergo degradation at higher temperature.

  • 204. Lu, Ting
    et al.
    Xiang, Tao
    Huang, Xue-Lian
    Li, Cheng
    Zhao, Wei-Feng
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology. Sichuan University, China.
    Zhang, Qian
    Zhao, Chang-Sheng
    Post-crosslinking towards stimuli-responsive sodium alginate beads for the removal of dye and heavy metals2015In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 133, p. 587-595Article in journal (Refereed)
    Abstract [en]

    Post-crosslinking as a new strategy to prepare sodium alginate (SA) beads with controllable swelling behavior, pH sensitivity and adsorption capacity was developed by using the solution of glutaraldehyde (GA), acetic acid and hydrochloric acid as the coagulating agent, for which could be used to fabricate polysaccharide beads in a large scale. Fourier transform infrared spectroscopy and thermogravimetric analysis convinced the successful cross-linking of SA by GA. The macro-porous structures of the beads were observed by scanning electron microscopy. Both acetic acid and hydrochloric acid had great effects on the swelling behavior and pH sensitivity of the SA beads. The SA beads could adsorb cationic dye (methylene blue) as high as 572 mg/g and other metal ions (Cu2+, Ag+ and Fe3+). The adsorption processes fitted well with the pseudo-second-order kinetic model and the Freundlich isotherm. The large-scale production of SA beads with tunable properties opens a new route to industrially utilize polysaccharide beads in wastewater treatments, intelligent separation and so on.

  • 205.
    Luttropp, Conrad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Strömberg, Emma
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Eco Quality Polymers-EQP2011In: Glocalized Solutions for Sustainability in Manufacturing - Proceedings of the 18th CIRP International Conference on Life Cycle Engineering, 2011, p. 482-485Conference paper (Refereed)
    Abstract [en]

    Polymers are materials worth recycling rather than incinerate. This calls for higher efficiency in recycling. To take a stepin this direction a study is made on how much of the polymer fraction of an electric product that is allocated to thehousing of the product.The study showed that a presorting of products according to polymer content of the shell and afterwards a fragmentingprocess where polymers and metals are separated would give a polymer fraction dominated by the housing polymer.

  • 206.
    Maleki, Laleh
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Chemical Pathways to Hemicellulose-rich Biomass Hydrogels2015Licentiate thesis, comprehensive summary (Other academic)
  • 207.
    Maleki, Laleh
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Synthesis of AcGGM Polysaccharide Hydrogels2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Lignocellulosic biomass is believed to serve a prominent role in tomorrow’s sustainable energy and material development. Among the polysaccharide fractions of lignocellulosic biomass, the potential of hemicelluloses as a valuable material resource is increasingly recognized. Thanks to their hydrophilic structure, hemicelluloses are suitable substrates for hydrogel design. The work summarized in this thesis aims to develop feasible strategies for the conversion of O-acetyl galactoglucomannan (AcGGM), an ample hemicellulose in softwood, into hydrogels. Within this framework, four synthetic pathways targeting the formation of crosslinked hydrogel networks from pure or unrefined AcGGM fractions were developed.

     

    Aqueous AcGGM-rich and lignin-containing side-stream process liquors of forest industry, known as softwood hydrolysates (SWHs) were formulated into highly swellable hydrogels by: i) allyl-functionalization of AcGGM chains of crude SWH to obtain a viable precursor for hydrogel synthesis via free-radical crosslinking, ii) directly incorporating unmodified SWH fractions into semi-interpenetrating polymer networks (semi-IPNs). SWH hydrogels and semi-IPNs were characterized with appreciable maximum swelling ratios of Qeq = 170 and Qeq = 225, respectively.

     

    Rapid crosslinking of AcGGM through thiol-click chemistry was addressed by first imparting thiol functionality onto pure AcGGM chains in a one-pot procedure. The thiolated AcGGM proved to be a suitable substrate for the synthesis of hemicellulose hydrogels via thiol-ene and thiol Michael addition reactions. Finally, sequential full IPNs were developed by subjecting single network hydrogels of pure AcGGM to a second network formation. IPNs obtained through either free radical crosslinking or thiol-ene crosslinking exhibited higher shear storage moduli than their single network counterparts. 

  • 208.
    Maleki, Laleh
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Thiolated hemicellulose as a versatile platform for one-pot click-type hydrogel synthesis2015In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 16, no 2, p. 667-674Article in journal (Refereed)
    Abstract [en]

    A one-pot synthetic methodology for the thiolation of O-acetyl-galactoglucomannan (AcGGM) was developed to merge hemicellulose chemistry with "click" chemistry. This was realized by the AcGGM-mediated nucleophilic ring-opening of γ-thiobutyrolactone via the activation of the polysaccharide pendant hydroxyl groups. The incorporation of thiol functionalities onto the hemicellulose backbone was visualized by 1H and 13C NMR spectroscopy and was assessed by an Ellman's reagent assay of the thiol groups. The versatility of the thiolated AcGGM was elaborated and demonstrated by conducting several postmodification reactions together with hydrogel formation utilizing thiol-ene and thiol-Michael addition "click" reactions. The one-pot synthesis of thiolated AcGGM is a straightforward approach that can expand the applications of hemicelluloses derived from biomass by employing "click" chemistry.

  • 209.
    Maleki, Laleh
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Unrefined wood hydrolysates are viable reactants for the reproducible synthesis of highly swellable hydrogels2014In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 108, no 1, p. 281-290Article in journal (Refereed)
    Abstract [en]

    A value-adding robust and sequential synthetic pathway was elaborated to produce hydrogel structures with ionic character from crude acetylated galactoglucomannan-rich wood hydrolysate (WH). The WH was first-step liquor originating from a sulphite cracking pulp process for dissolving pulp. The synthetically modified WH fractions were verified at each step by NMR and FTIR, and the hydrogels were characterized with respect to their swelling and mechanical properties. Altering the crosslinking chemistry and the content of ionic moieties resulted in hydrogels with various swelling ratios and mechanical properties. Renewable hydrogel formulations with swelling ratios as high as Qeq = 270 were achieved.

  • 210.
    Malmström, Eva
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Bruce, Carl
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Fogelström, Linda
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Johansson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Carlmark, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Polymer-grafting or adsorption of amphiphilic block copolymers - different approaches to compatibilization in CNF-based nanocomposites2015In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 249Article in journal (Other academic)
  • 211. Meszynska, Anna
    et al.
    Pollet, Eric
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Averous, Luc
    Effect of Oligo-Hydroxyalkanoates on Poly(3-Hydroxybutyrate-co-4-Hydroxybutyrate)-Based Systems2015In: Macromolecular materials and engineering (Print), ISSN 1438-7492, E-ISSN 1439-2054, Vol. 300, no 6, p. 661-666Article in journal (Refereed)
    Abstract [en]

    This study presents the utilization of oligo-hydroxyalkanoates obtained from controlled degradation of poly(3-hydroxybutyrate) as additives in a poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer matrix (P(3HB-co-4HB)). These oligomers are compared to a conventional biobased plasticizer, used as reference, based on a monoglyceride acetate obtained from hydrogenated castor oil. Different multiphase systems are elaborated with these additives and characterized. Thermal and mechanical properties demonstrate that the monoglyceride acetate is as an efficient plasticizer increasing the elongation of the P(3HB-co-4HB) films while decreasing their maximum strength and elastic modulus. On the contrary, the addition of oligo-PHB results in an increased crystallinity of the matrix, thus improving the maximum strength and elastic modulus of the corresponding films. The oligomers act as an efficient reinforcing agent. Mobility brought by the oligomers induces a rearrangement of the P(3HB-co-4HB) with an increase of the chain rearrangement. Interestingly, the simultaneous addition of both additives results in significantly reduced T-g and improved elongation at break, as expected from an efficient plasticizer, but it also leads to P(3HB-co-4HB) films retaining relatively high strength and modulus values, thanks to the reinforcement ability of the oligo-PHB additive. Thermal characterization finally demonstrated that such mixed additives system results in greatly improved thermal stability of the polyhydroxyalkanoate copolymer matrix.

  • 212.
    Michalak, M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Recycling Oxidized Model Polyethylene Powder as a Degradation Enhancing Filler for Polyethylene/Polycaprolactone Blends2016In: ACS Sustainable Chemistry and Engineering, ISSN 2168-0485, Vol. 4, no 1, p. 129-135Article in journal (Refereed)
    Abstract [en]

    Polyethylene (PE) powder with different degrees of oxidation was prepared to model end-of life polyethylene that has been oxidized during processing and/or service-life. The nonoxidized and preoxidized PE powders were blended with PCL to evaluate the possibility to recycle PE powder in PCL blends. Good elongation at break was reached for all 25/75 (w/w) PE/PCL films and the elongation at break correlated well with the carbonyl index of the original PE powder, indicating that the oxidation of PE increased the interfacial adhesion with PCL and improved the blend properties. The preoxidized PE powder in combination with surfactant and pro-oxidant greatly accelerated the degradation rate of PCL as measured by molecular weight decrease during low temperature thermo-oxidative aging. This coincided with the fast initial increase in PE carbonyl index. The degradation accelerating effect was larger when preoxidized PE was blended with PCL as compared to when nonoxidized PE was added. However, the degree of preoxidation had minor impact on PCL degradation rate. Without PE powder the degradation rate of PCL was not enhanced by the addition of pro-oxidant and surfactant alone.

  • 213. Murdany, D.
    et al.
    Chen, X.
    Liu, Dongming
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Gedde, Ulf
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Suwarno, Suwarno
    Gubanski, S. M.
    Electrical treeing in polyethylene-alumina-filled nanocomposites for HVDC applications2015In: Proceedings - 5th International Conference on Electrical Engineering and Informatics: Bridging the Knowledge between Academic, Industry, and Community, ICEEI 2015, 2015, p. 213-216Conference paper (Refereed)
    Abstract [en]

    Electrical tree formations under DC pre-stress followed by an application of voltage pulses of opposite polarities were observed in low density polyethylene and its nanocomposite filled with 1.0 wt% and 3.0 wt% alumina nanoparticles. A special wire-plane electrode geometry were manufactured for the test. The obtained experimental results indicate that the addition of the nanoparticles has a positive impact on the resistance to electrical treeing. In addition to the reported above results, a thermal ageing and electro-thermal experiment is presently being conducted and the results comparing the treeing behavior after it will also be presented.

  • 214.
    Målberg, Sofia
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Macromolecular synthesis of functional degradable aliphatic polyesters and porous scaffold design2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    There is an increasing demand for new materials in biomedical applications with material properties that are highly specific for each application area. The search for new materials requires the creation of materials with suitable mechanical properties, functionalities, three-dimensional structures and a controlled degradation profile. The focus of the work described in this thesis has been on the synthesis of functional degradable aliphatic polyesters, on the design of porous scaffolds and on their synthesis with bio-safe catalyst/initiator systems.  

    An unsaturated aliphatic polyester has been synthesized by condensation polymerization to produce poly(but-2-ene-1,4-diyl malonate) (PBM), which was applicable as a cross-linked network and as a macro-co-initiator for the ring-opening polymerization (ROP) of cyclic ester monomers. The method of preparation of PBM was simple and straightforward and there was no need to purify the monomers or add a catalyst. PBM was successfully cross-linked with UV-radiation to form a transparent, colorless, flexible and strong film. When PBM was used as a macro-co-initiator, a triblock copolymer was formed with PBM middle blocks and poly(L-lactide) (PLLA) or poly(ε-caprolactone) side blocks. The ductility of the triblock copolymer of PLLA was greatly enhanced and the strength was maintained compared to the polymer obtained when PLLA was polymerized with ethylene glycol as co-initiator. The triblock copolymers were easily cross-linked to give materials with greater strength and higher modulus as a result. When these polymers were subjected to hydrolysis, a rapid initial hydrolysis of the amorphous PBM middle block changed the microstructure from triblock to diblock, with a significant reduction in ductility and number average molecular weight. Highly porous scaffolds were created from these functional materials and the mechanical properties were evaluated by a cyclic compression test under mimicked physiological conditions.

    Copolymers of L-lactide (LLA) and ε-caprolactone (CL), trimethylene carbonate (TMC) or 1,5-dioxepane-2-one (DXO) have been synthesized with a low stannous-2-ethyl hexanoate  (Sn(Oct)2) ratio and used to fabricate porous tubular scaffolds. The tubes were designed to have a range of mechanical properties suitable for nerve regeneration, with different porosities and different numbers of layers in the tube wall. The adaptability of an immersion-coating and porogen-leaching technique was demonstrated by creating tubes with different dimensions.

    Although a low amount of residual tin (monomer-to-initiator ratio of 10000:1) is accepted in biomedical applications, an efficient bio-safe catalyst/initiator system would be favored. The catalytic activities of bio-safe Bi (III) acetate and creatinine towards the ROP of LLA have been compared with those of Sn(Oct)2-based systems and with those of a system catalyzed by enzymes. All these systems were shown to be suitable catalysts for the synthesis of high and moderate molecular weight PLLAs.

  • 215.
    Målberg, Sofia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Basalp, Dildare
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Finne Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Bio-Safe Synthesis of Linear and Branched PLLA2010In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 48, no 5, p. 1214-1219Article in journal (Refereed)
    Abstract [en]

    The catalytic activities of Bi(III) acetate (Bi(OAc)(3)) and of creatinine towards the ring-opening polymerization of L-lactide have been compared with those of a stannous (II) ethylhexanoate ((SnOct)(2))-based system and with those of a system catalyzed by enzymes. All four were suitable catalysts for the synthesis of high and moderate molecular weight poly(L-lactide)s and the differences in reactivity and efficiency have been studied. Linear and branched poly(L-lactide)s were synthesized using these bio-safe initiators together with ethylene glycol, pentaerythritol, and myoinositol as coinitiators. The polymerizations were performed in bulk at 120 and 140 degrees C and different reactivities and molecular weights were achieved by adding different amounts of coinitiators. A molecular weight of 105,900 g/mol was achieved with 99% conversion in 5 h at 120 degrees C with a Bi(OAc)(3)-based system. This system was comparable to Sn(Oct)(2) at 140 degrees C. The reactivity of creatinine is lower than that of Bi(OAc)(3) but higher compared with enzymes lipase PS (Pseudomonas fluorescens). A ratio of Sn(Oct)(2) M-o/I-o 10,000:1 was needed to achieve a polymer with a reasonable low amount of tin residue in the precipitated polymer, and a system catalyzed by creatinine at 140 degrees C has a higher conversion rate than such a system.

  • 216.
    Målberg, Sofia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Finne Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    The environmental influence in enzymatic polymerization of aliphatic polyesters in bulk and aqueous mini-emulsion2010In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 51, no 23, p. 5318-5322Article in journal (Refereed)
    Abstract [en]

    The catalytic effect of enzymes in different environments has been compared. Biodegradable polyesters and corresponding nanoparticles have been synthesized by an "eco-friendly" technique; enzyme-catalyzed ring-opening polymerization of lactones in bulk and in an aqueous mini-emulsion. Lipases from Burkholderia cepacia (lipase PS), B. cepacia immobilized on ceramic, Pseudomonas fluorescens and Candida Antarctica have been used as catalysts in the polymerization of L-Lactide (LLA), pentadecanolide (PDL) and hexadecanolide (HDL). The reaction conditions during the bulk polymerization of LLA were varied by adding different amounts of ethylene glycol at 100 degrees C or 125 degrees C. A number average molecular weight (M-n) of 78,100 was obtained when lipase PS was used at 125 degrees C. Lipase PS had a high catalytic activity in an aqueous environment with 100% conversion in 4 h, and the nanoparticles obtained from mini-emulsion polymerization were between 113 and 534 nm in size. The amount of hydrophobe affected the size of the PDL nanoparticles produced, less than the amount of surfactant in both systems.

  • 217.
    Målberg, Sofia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Höglund, Anders
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Macromolecular Design of Aliphatic Polyesters with Maintained Mechanical Properties and a Rapid, Customized Degradation Profile2011In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, no 6, p. 2382-2388Article in journal (Refereed)
    Abstract [en]

    An innovative type of triblock copolymer that maintains and even increases the mechanical properties of poly(L-lactide) (PLLA) and poly(epsilon-caprolactone) (PCL) with a controlled, predictable, and rapid degradation profile has been synthesized. Elastic triblock copolymers were formed from the hydrophobic and crystalline PLLA and PCL with an amorphous and hydrophilic middle block of poly(but-2-ene-1,4-diyl malonate) (PBM). The polymers were subjected to degradation in PBS at 37 degrees C for up to 91 days. Prior to degradation, ductility of the PLLA-PBM-PLLA was approximately 4 times greater than that of the homopolymer of PLLA, whereas the modulus and tensile stress at break were unchanged. A rapid initial hydrolysis in the amorphous PBM middle block changed the microstructure from triblock to diblock with a significant reduction in ductility and molecular weight. The macromolecular structure of the triblock copolymer of PLLA and PBM generates a more flexible and easier material to handle during implant, with the advantage of a customized degradation profile, demonstrating its potential use in future biomedical applications.

  • 218.
    Målberg, Sofia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Plikk, Peter
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Finne Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Design of Elastomeric Homo- and Copolymer Networks of Functional Aliphatic Polyester for Use in Biomedical Applications2010In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 22, no 9, p. 3009-3014Article in journal (Refereed)
    Abstract [en]

    An unsaturated aliphatic polyester was synthesized by condensation polymerization to yield the pre-polymer, poly(but-2-ene-1,4-diyl malonate) (PBM), which is applicable as an elastomeric network and as a macroinitiator for the polymerization of cyclic ester monomers. The method of preparation was simple and straightforward with no need to purify the monomers or add a potentially harmful catalyst. The number average molecular weight of the pre-polymer could easily be increased from 5000 to 12000 by extending the reaction time. The pre-polymer PBM was successfully cross-linked with UV-radiation to form a clear, transparent, colorless, flexible, and strong film. PBM as a macroinitiator for L-lactide (LLA) and epsilon-caprolactone (CL) polymerizations highly increased the ductility of the LLA-polymer, while maintaining the strength, compared to PLLA polymerized with common initiators. The tensile properties of PCL were also improved. The linear PCL-PBM and PLLA-PBM polymers were easily cross-linked to give polymers with greater strength and higher modulus as the result.

  • 219.
    Navarro, Julien R. G.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Lerouge, Frederic
    From gold nanoparticles to luminescent nano-objects: experimental aspects for better gold-chromophore interactions2017In: NANOPHOTONICS, ISSN 2192-8606, Vol. 6, no 1, p. 71-92Article, review/survey (Refereed)
    Abstract [en]

    Gold nanoparticles have been the center of interest for scientists since many decades. Within the last 20 years, the research in that field has soared with the possibility to design and study nanoparticles with controlled shapes. From spheres to more complex shapes such as stars, or anisotropic architectures like rods or bipyramids, these new systems feature plasmonic properties making them the tools of choice for studies on light-matter interactions. In that context, fluorescence quenching and enhancement by gold nanostructures is a growing field of research. In this review, we report a non-exhaustive summary of the synthetic modes for various shapes and sizes of isotropic and anisotropic nanoparticles. We then focus on fluorescent studies of these gold nano-objects, either considering "bare" particles (without modifications) or hybrid particles (surface interaction with a chromophore). In the latter case, the well-known metal-enhanced fluorescence (MEF) is more particularly developed; the mechanisms of MEF are discussed in terms of the additional radiative and non-radiative decay rates caused by several parameters such as the vicinity of the chromophore to the metal or the size and shape of the nanostructures.

  • 220.
    Navarro, Julien R. G.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Wennmalm, Stefan
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Godfrey, Jamie
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Breitholtz, Magnus
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Luminescent Nanocellulose Platform: From Controlled Graft Block Copolymerization to Biomarker Sensing2016In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 17, no 3, p. 1101-1109Article in journal (Refereed)
    Abstract [en]

    A strategy is devised for the conversion of cellulose nanofibrils (CNF) into fluorescently labeled probes involving the synthesis of CNF-based macroinitiators that initiate radical polymerilation of methyl acrylate and acrylic acid N-hydroxysuccinimide ester producing a graft block copolymer modified CNF. Finally, a luminescent probe (Lucifer yellow derivative) was labeled onto the modified CNF through an amidation reaction. The surface modification steps were :verified with solid-state C-13 nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy. Fluorescence correlation spectroscopy (FCS) confirmed the successful labeling of the CNF; the CNF have a hydrodynamic radius of about 700 nm with an average number of dye molecules per fibril of at least 6600. The modified CNF was also imaged with confocal laser scanning microscopy. Luminescent CNF proved to be viable biomarkers and allow for fluorescence-based optical detection of CNF uptake and distribution in organisms such as crustaceans. The luminescent CNF were exposed to live juvenile daphnids and microscopy analysis revealed the presence of the luminescent CNF all over D. magna's alimentary canal tissues without any toxicity effect leading to the death of the specimen.

  • 221.
    Nawaz, Sohail
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Nordell, Patricia
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Azhdar, Bruska
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Hillberg, Henrik
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Gedde, Ulf
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Stabilizer activity in Al2O3/ poly(ethylene-co-butylacrylate) nanocompositesIn: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321Article in journal (Other academic)
    Abstract [en]

    The stabilizer activity of polymer nanocomposites based on poly(ethylene-co-butylacrylate) and 0.5 - 3 vol. % of two different types of Al2O3 nanoparticles was investigated. The nanoparticles were either functionalized using octyl- or amino-terminated silanes, or used as received. The nanocomposites also contained 0.2 wt. % of Irganox 1010, a hindered phenolic stabilizer. The activity of the stabilizer in the samples was analyzed by Differential Scanning Calorimetry (assessment of Oxidation Induction Time (OIT)), and compared those obtained for the pristine polymers. The stabilizer was adsorbed to the untreated Al2O3 nanoparticles resulting in a significant reduction in OIT. The reduction increased with increasing total surface area of the particles. Surface silanization of the nanoparticles resulted in an increase in OIT, compared to the untreated particles. The activity of the stabilizer was evaluated by OIT after thermal ageing of the nanocomposites in hot-air oven at 90C up to 30 days. No surface oxidation was observed on any of the samples using reflection infrared spectroscopy. The ageing showed that the stabilizer was not irreversibly adsorbed to the particle surfaces, resulting in a gradual release with the ageing time. This resulted in a slower reduction in OIT as function of aging time for the nanocomposites, compared to the pristine polymer. In order for the nanocomposites to exhibit similar or higher OIT values after thermal ageing, compared to unfilled EBA, > 0.5 mg of stabilizer per m2 of octyl- or amine-coated Al2O3 nanoparticles was needed. The loss of stabilizer was controlled by the evaporation rate of the stabilizer from the surface of the samples to the surrounding air.

  • 222. Ndazi, B.
    et al.
    Tesha, J. V.
    Karlsson, S.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Bisanda, E. T. N.
    Production of rice husks composite panels based on acacia mimosa resin2003In: Journal of Material Science and Engineering A, p. 15-Article in journal (Refereed)
  • 223.
    Ndazi, Bwire
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Karlsson, Sigbritt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Characterization of the potential of soda cooking to extract fibrous residues from rice hulls2010In: Polymers from Renewable Resources, ISSN 2041-2479, Vol. 1, no 3, p. 143-160Article in journal (Other academic)
    Abstract [en]

    In this paper, the potential of soda cooking to extract fibrous residues from rice hulls was investigated. Soda cooking was carried out at 170oC for 60 minutes using 5 to 13% NaOH. The goal was to selectively degrade silica and lignin from the structure of the rice hulls and produce fibrous carbohydrates that could be used as fillers in polymer biocomposites. This was studied by characterizing the physical and chemical properties of the fibrous residues and the spent liquor products. Results of scanning electron microscopy have revealed a substantial fragmentation of rice hulls above 7.5% NaOH charge. The fragmentation was accompanied with a significant removal of silica and lignin and the reduction of fibrous residues yield to 57% at 13%NaOH. Wet chemical composition analyses, infrared spectroscopy and x-ray spectroscopy have also revealed that lignin and silica were partly retained in the fibrous residue while the carbohydrates content were not affected. It is therefore concluded that soda cooking could be among the best processes for dissolving lignin and silica from rice hulls if the cooking conditions are optimized

  • 224.
    Ndazi, Bwire Sturmius
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Karlsson, S.
    Characterization of hydrolytic degradation of polylactic acid/rice hulls composites in water at different temperatures2011In: EXPRESS POLYMER LETTERS, ISSN 1788-618X, Vol. 5, no 2, p. 119-131Article in journal (Refereed)
    Abstract [en]

    Hydrolytic degradations of polyactic acid/rice hulls (PLA/RH) composites with various rice hulls contents due to water absorptions at 23, 51 and 69 degrees C were investigated by studying the thermal properties, chemical composition, molecular weight, and morphology of the degraded products. The results have attested that the stability of PLA/RH composites in water depends slightly on rice hulls contents but it is significantly influenced by water temperature. Water adsorption in 30 days at 23 degrees C was between 0.87 and 9.25% depending on rice hull contents. However, at thermophilic temperatures, the water adsorption and degradation of these products were increased significantly. Saturations were achieved in less than 25 and 9 days at 51 degrees C and 69 degrees C, respectively, while hydrolytic degradation was demonstrated by an increase in fragility and development of crystallinity. At 69 degrees C, there were significant reductions of the decomposition and glass transition temperatures of the polymer by 13 degrees C. These changes were associated with the reduction of the molecular weight of PLA from 153.1 kDa to similar to 10.7 kDa due to hydrolysis of its ester group.

  • 225.
    Nugroho, Robertus Wahyu N.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Höglund, Anders
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Highlighting the Importance of Surface Grafting in Combination with a Layer-by-Layer Approach for Fabricating Advanced 3D Poly(L-lactide) Microsphere Scaffolds2016In: CHEMISTRY OF MATERIALS, ISSN 0897-4756, Vol. 28, no 10, p. 3298-3307Article in journal (Other academic)
  • 226.
    Nugroho, Robertus Wahyu N.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Höglund, Anders
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Nondestructive Covalent "Grafting-from" of Poly(lactide) Particles of Different Geometries2012In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 4, no 6, p. 2978-2984Article in journal (Refereed)
    Abstract [en]

    A nondestructive "grafting-from" method has been developed using poly(lactide) (PLA) particles of different shapes as substrates and three hydrophilic monomers as grafts. Irregularly shaped particles and spheres of PLA were covalently surface functionalized using a versatile method of photoinduced free radical polymerization. The preservation of the molecular weight of the PLA particle bulk and the retention of the original particle shape confirmed the negligible effect of the grafting method. The changes in surface composition were determined by FTIR for both spherical and irregular particles and by XPS for the irregular particles showing the versatility of the method. Changes in the surface morphology of the PLA spherical particles were observed using microscopy techniques showing a full surface coverage of one of the grafted monomers. The method is applicable to a wide set of grafting monomers and provides a permanent alteration of the surface chemistry of the PLA particles creating hydrophilic PIA surfaces in addition to creating sites for further modification and drug delivery in the biomedical fields.

  • 227.
    Nugroho, Robertus Wahyu N.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Höglund, Anders
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    The nature of polymer grafts and substrate shape on the surface degradation of poly(l-lactide)2015In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628Article in journal (Refereed)
    Abstract [en]

    Surface grafting of functional polymers is an effective method to alter material properties and degradation behavior. Two different substrate shapes of poly(l-lactide) (PLLA), i.e., films and microparticles, were surface-grafted with hydrophilic monomers, and their surface degradation was monitored. Surface grafting with a hydrophilic and acidic polymer graft [acrylic acid (AA)] induced large alterations in the surface morphology and topography of the films. In contrast, hydrophilic and neutral polymer grafts [acrylamide (AAm)] had no significant effect on the surface degradation behavior, while the PLLA reference and co-monomeric (AA/AAm) polymer-grafted samples exhibited intermediate surface degradation rates. The grafted PAA chains induced a local acidic environment on the surface of the substrates, which in turn catalyzed the surface degradation process. This effect was more pronounced in the films than in the microparticles. Thus, the nature of the grafted chains and substrate geometry were shown to affect the surface degradation behavior of PLLA substrates.

  • 228.
    Nugroho, Robertus Wahyu N.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Pettersson, Torbjörn
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Höglund, Anders
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Force interactions of grafted polylactide particles2014In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 248Article in journal (Other academic)
  • 229.
    Nugroho, Robertus Wahyu Nayan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Modification of polymeric particles via surface grafting for 3D scaffold design2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Surface modification techniques have played important roles in various aspects of modern technology. They have been employed to improve substrates by altering surface physicochemical properties. An ideal surface modifying technique would be a method that is applicable to any kind of materials prepared from a wide range of polymers and that can occur under mild reaction conditions. The work in this thesis has utilized four main concepts: I) the development of a ‘grafting-from’ technique by covalently growing polymer grafts from particle surfaces, II) the presence of steric and electrosteric forces due to long-range repulsive interactions between particles, III) a combined surface grafting and layer-by-layer approach to create polyelectrolyte multilayers (PEMs) on particle surfaces to fabricate strong and functional materials, and IV) the roles of hydrophilic polymer grafts and substrate geometry on surface degradation.

    A non-destructive surface grafting technique was developed and applied to polylactide (PLA) particle surfaces. Their successful modification was verified by observed changes to the surface chemistry, morphology and topography of the particles. To quantify the aggregation behavior of grafted and non-grafted particles, force interaction measurements were performed using colloidal probe atomic force microscopy (AFM). Long-range repulsive interactions were observed when symmetric systems, i.e., hydrophilic polymer grafts on two interacting surfaces, and asymmetric system were applied. Electrosteric forces were observed when the symmetric substrates interacted at pH 7.4. When PEMs were alternately assembled on the surface of poly(L-lactide) (PLLA) particles, the grafted surfaces played a dominated role in altering the surface chemistry and morphology of the particles. Three-dimensional scaffolds of surface grafted particle coated with PEMs demonstrated high mechanical performance that agreed well with the mechanical performance of cancellous bone. Nanomaterials were used to functionalize the scaffolds and further influence their physicochemical properties. For example, when magnetic nanoparticles were used to functionalize the scaffolds, a high electrical conductivity was imparted, which is important for bone tissue regeneration. Furthermore, the stability of the surface grafted particles was evaluated in phosphate buffered saline (PBS) solution. The nature of the hydrophilic polymer grafts and the geometry of the PLLA substrates played central roles in altering the surface properties of films and particles. After 10 days of PBS immersion, larger alterations in the surface morphology were observed on the film compared with microparticles grafted with poly(acrylic acid) (PAA). In contrast to the PAA-grafted substrates, the morphology of poly(acrylamide) (PAAm)-grafted substrates was not affected by PBS immersion. Additionally, PAAm-grafted microparticulate substrates encountered surface degradation more rapidly than PAAm-grafted film substrates.

  • 230.
    Nugroho, Robertus Wahyu Nayan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Steric Stabilization of Polylactide particles achieved by Covalent 'grafting-from' with Hydrophilic Polymers2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Despite numerous advantages of using particles in a wide range of applications, they have one drawback that is their tendency to agglomerate. One way to overcome this problem is to sterically  stabilize the particles by introducing polymeric  chains covalently attached to the surface. Surface modification by covalently attaching polymer chains to the particle surface can be achieved by e.g. a ‘grafting-from’ technique under UV irradiation.

    In this thesis, polylactide (PLA) particles were surface modified, under UV irradiation, with the hydrophilic monomers: acrylamide (AAm), acrylic acid (AA), and maleic anhydride (MAH). The developed ‘grafting-from’ technique was shown to be nondestructive method for surface modification of PLA particles of two different geometries. The change in surface chemistry of the PLA particles was confirmed by FTIR and XPS, indicating the success of the surface grafting technique. Force interaction between two surface grafted PLA substrates was measured by colloidal probe AFM in different salt concentrations. In order to understand the repulsive force, the AFM force profiles were compared to the DLVO theory and AdG model. Long range repulsive interactions were mainly observed when hydrophilic polymers were covalently attached to the surface of PLA particles, leading to steric interaction. Attractive force dominated the interaction when neat PLA particle was approaching each other, resulting in particle aggregation, even though short range repulsion was observed at small separation distance, i.e. approximately 10 nm. Attractive interaction was also observed when neat PLA was approaching to PAA-grafted PLA substrate. This attractive interaction was much greater than force interaction between two neat PLA substrates.

     The surface grafted particles can be used in biomedical application where secondary interactions are important to overcome particle agglomeration such as particle-based drug delivery.

  • 231.
    Nugroho, Robertus Wahyu Nayan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Pettersson, Torbjörn
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Höglund, Anders
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Force Interactions of Nonagglomerating Polylactide Particles Obtained through Covalent Surface Grafting with Hydrophilic Polymers2013In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 26, p. 8873-8881Article in journal (Refereed)
    Abstract [en]

     Nonagglomerating polylactide (PLA) particles with various interaction forces were designed by covalent photografting. PLA particles were surface grafted with hydrophilic poly(acrylic acid) (PAA) or poly(acrylamide) (PAAm), and force interactions were determined using colloidal probe atomic force microscopy. Long-range repulsive interactions were detected in the hydrophilic/hydrophilic systems and in the hydrophobic/hydrophilic PLA/PLA-g-PAAm system. In contrast, attractive interactions were observed in the hydrophobic PLA/PLA and in the hydrophobic/hydrophilic PLA/PLA-g-PAA systems. AFM was also used in the tapping mode to determine the surface roughness of both neat and surface-grafted PLA film substrates. The imaging was performed in the dry state as well as in salt solutions of different concentrations. Differences in surface roughness were identified as conformational changes induced by the altered Debye screening length. To understand the origin of the repulsive force, the AFM force profiles were compared to the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory and the Alexander de Gennes (AdG) model. The steric repulsion provided by the different grafted hydrophilic polymers is a useful tool to inhibit agglomeration of polymeric particles. This is a key aspect in many applications of polymer particles, for example in drug delivery.

  • 232.
    Odelius, Karin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Höglund, Anders
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Kumar, Sanjeev
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Ghosh, Anup K.
    Bhatnagar, Naresh
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Porosity and Pore Size Regulate the Degradation Product Profile of Polylactide2011In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, no 4, p. 1250-1258Article in journal (Refereed)
    Abstract [en]

    Porosity and pore size regulated the degradation rate and the release of low molar mass degradation products from porous polylactide (PLA) scaffolds. PLA scaffolds with porosities above 90% and different pore size ranges were subjected to hydrolytic degradation and compared to their solid analog. The solid film degraded fastest and the degradation rate of the porous structures decreased with decreasing pore size. Degradation products were detected earlier from the solid films compared to the porous structures as a result of the additional migration path within the porous structures. An intermediate degradation rate profile was observed when the pore size range was broadened. The morphology of the scaffolds changed during hydrolysis where the larger pore size scaffolds showed sharp pore edges and cavities on the scaffold surface. In the scaffolds with smaller pores, the pore size decreased during degradation and a solid surface was formed on the top of the scaffold. Porosity and pore size, thus, influenced the degradation and the release of degradation products that should be taken into consideration when designing porous scaffolds for tissue engineering.

  • 233.
    Odelius, Karin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Ohlson, Madelen
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Höglund, Anders
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Polyesters with small structural variations improve the mechanical properties of polylactide2013In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 127, no 1, p. 27-33Article in journal (Refereed)
    Abstract [en]

    Improving the properties of biodegradable polymeric materials is needed to obtain materials competitive with current bulk plastics. Low-molecular weight polyesters with small differences in their backbone were synthesized using a straight-forward method and were subsequently blended with polylactide (PLA). The materials showed an improved ductility of up to 100% points and otherwise retained material properties. The changes in mechanical properties were shown to match the miscibility range of the materials and can be predicted by the solubility parameters of the materials up to a polyester content of roughly 10% w/w. The thermal stability of all the low-molecular weight polyesters was higher than that of PLA, and most 25% w/w blends showed a thermal degradation behavior similar to that of neat PLA. Low-molecular weight polyesters were demonstrated as being potential enhancers of the properties of PLA, while the materials degradability was maintained.

  • 234.
    Odelius, Karin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Olsén, Peter G.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Improving PLA-based material properties2012In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 244Article in journal (Other academic)
  • 235.
    Olsen, Peter
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Undin, Jenny
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Functional degradable polymers - simplified2014In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 248Article in journal (Other academic)
  • 236.
    Olsén, Peter
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Functional Degradable Polymers: from the monomeric point of view2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Degradable polymers is key, within the future vison, of creating a sustainable society were all aspects, cradle to grave, can be realized in a sustainable way. It is imperative to consider, how the monomer is formed, its polymerization, the material properties created and the final degradation behavior. In this thesis, the major focus will be placed on the three former aspects from the vantage point of the monomer. The immense variety of different monomers available within the realm of polymer chemistry necessitates a logical division among them. Herein, we make such a division according to their respective inherent thermodynamic properties and how these translate into the synthetic behavior of the corresponding polymers. These divisions are as follows: stable monomers (monomers that resist becoming polymers), meta-stable monomers (monomers for which temperature is of immense importance during polymer formation), and unstable monomers (monomers that desire to be in the polymeric state). From this viewpoint, three different investigations were conducted, thereby demonstrating the inherent advantages and disadvantages of each type together with the importance of using the “right” catalyst for the “right” monomer.

  • 237.
    Olsén, Peter
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Main-chain functionalization of poly(l-lactide) with pendant unsaturations2012In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 50, no 15, p. 3039-3045Article in journal (Refereed)
    Abstract [en]

     Main-chain-functionalized poly(L-lactide) (PLLA) with pendant unsaturations was synthesized through a one-pot postpolymerization procedure with the PLLA homopolymer as the starting material. The material was functionalized through a-hydrogen abstraction by a sterically hindered strong base, lithium diisopropylamide, followed by the addition of an acid chloride. Two different acid chlorides were examined, lauroyl chloride as a concept electrophile and oleoyl chloride to provide the pendant unsaturations. The semisolvated system, together with branching reactions from the alpha position of the acid chloride, yielded a high molar amount of the incorporated reactant in the material. The unsaturations were preserved under the chosen conditions and the material exhibited surfactant-like properties in blends with oleic acid and PLLA.

  • 238.
    Olsén, Peter
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Ring-Closing Depolymerization: A Powerful Tool for Synthesizing the Allyloxy-Functionalized Six-Membered Aliphatic Carbonate Monomer 2-Allyloxymethyl-2-ethyltrimethylene Carbonate2014In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 47, no 18, p. 6189-6195Article in journal (Refereed)
    Abstract [en]

    Ring-dosing depolymerization is demonstrated to be a powerful synthetic methodology for the formation of six-membered functional aliphatic carbonate monomers, providing a rapid, straightforward, inexpensive, and green route for obtaining six-membered functional aliphatic carbonate monomers at a scale greater than 100g. The utility of this technique was observed via the synthesis of the allyloxy-functionalized six-membered cyclic carbonate monomer 2-allyloxymethyl-2-ethyltrimethylene carbonate (AOMEC). The synthesis was performed in a one-pot bulk reaction, starting from trimethylolpropane allyl ether, diethyl carbonate, and NaH, resulting in a final AOMEC yield of 63%. The synthetic methodology is based upon the reversible nature of this class of polymers. The anionic environment produced by NaH was observed to mediate the monomer equilibrium concentration; thus, an additional catalyst is not required to induce depolymerization. 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) was demonstrated to be a very active catalyst for the ring-opening polymerization (ROP) of AOMEC, resulting in a rapid (k(p)(aPP) =28.2 s(-1)) and controlled polymerization with a low dispersity D = 1.2). The availability and activity of the functionality of poly(AOMEC)s were established through subsequent postpolymerization functionalization via the UV-initiated thiol-ene chemistry of poly(AOMEC) with 1-dodecanethiol and benzophenone as a radical initiator. The functionalization proceeded with high control and with a linear relation between the molecular weight and conversion of the unsaturation, revealing the high orthogonality of the reaction and the stability of the carbonate backbone. Hence, as a synthetic methodology, depolymerization provides a straightforward and simple approach for the synthesis of the highly versatile functional carbonate AOMEC. In addition, formation of the monomer does not require any solvents, reactive ring-dosing reagents, or transition-metal-based depolymerization catalysts, thereby providing a "greener" route for obtaining functional carbonate monomers and polymers.

  • 239.
    Olsén, Peter
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Undin, Jenny
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Establishing α-bromo-γ-butyrolactone as a platform for synthesis of functional aliphatic polyesters-bridging the gap between ROP and SET-LRP2014In: Polymer Chemistry, ISSN 1759-9954, E-ISSN 1759-9962, Vol. 5, no 12, p. 3847-3854Article in journal (Refereed)
    Abstract [en]

    Utilizing a-bromo-g-butyrolactone (aBrgBL) as a comonomer with 3-caprolactone (3CL) or L-lactide (LLA)produces copolymers with active and available grafting sites, e.g., for SET-LRP, where the choice of thegrafting monomers is limited only by one's imagination. This was deduced by utilizing a wide range ofdifferent acrylates of varying polarities and was realized with the aid of a fluorinated alcohol, 2,2,2-trifluoroethanol, which acts as a universal solvent for both the hydrophobic macroinitiators and thegrafting monomers. Using aBrgBL successfully provides a simple route to merge the two polymerizationmethodologies, ROP and SET-LRP. aBrgBL inherently meets all of the prerequisites to act as a platformmonomer for the synthesis of functional aliphatic polyesters, i.e., it is inexpensive, available, and able toform isolated grafting sites along the polymer chain. The copolymerization of aBrgBL together with twoof the most commonly used cyclic ester monomers, 3-CL and LLA, proceeds with a high degree ofcontrol and a linear relationship between the feed ratio of aBrgBL and its composition in the copolymer.The formation of isolated units of aBrgBL in the copolymer is visualized by the reactivity ratios of thecopolymerization reactions and confirmed by 13C-NMR spectroscopy. The incorporation of isolatedaBrgBL is the feature that makes this class of copolymers unique, and it can be considered to provide aroute to the “perfect graft copolymer” with a degradable backbone.

  • 240. Pal, Jit
    et al.
    Wu, Duo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Srivastava, Rajiv K.
    The viscoelastic interaction between dispersed and continuous phase of PCL/HA-PVA oil-in-water emulsion uncovers the theoretical and experimental basis for fiber formation during emulsion electrospinning2017In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 96, p. 44-54Article in journal (Refereed)
    Abstract [en]

    Emulsion electrospinning was recently introduced to minimize the amount of organic solvent during electrospinning process. Here, we uncover the theoretical and experimental basis for the fiber formation in emulsion electrospinning by revealing the viscoelastic interaction between dispersed and continuous phase. Composite electrospun matrices of poly(epsilon-caprolactone) (PCL) with or without hydroxyapatite were devised from an oil-in-water emulsion. The fiber formation and uniformity were clearly governed by the viscoelastic interaction between the continuous and dispersed phase. Caging of droplets by optimal quantity of poly(vinyl alcohol) (PVA) in continuous phase resulted in uniform stretching and coalescence of droplets. An increased storage and loss modulus for emulsions containing optimum PVA manifested desired viscoelastic interaction between dispersed and continuous phase, which further resulted in uniform jet stretching. The visthelasticity of the emulsion could be tailored by changing the polymer concentration in dispersed or continuous phase, which enabled production of electrospun fibers with desired fineness.

  • 241. Pedersen, T. O.
    et al.
    Xing, Z.
    Finne-Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Hellem, S.
    Mustafa, K.
    Hyperbaric oxygen stimulates vascularization and bone formation in rat calvarial defects2013In: International Journal of Oral and Maxillofacial Surgery, ISSN 0901-5027, E-ISSN 1399-0020, Vol. 42, no 7, p. 907-914Article in journal (Refereed)
    Abstract [en]

    Hyperbaric oxygen (HBO) therapy is used to treat or prevent tissue necrosis in patients undergoing irradiation. Many such patients require reconstructive surgery, but little is known of the effects of HBO on bone vascularization and regeneration. In this study, copolymer poly(L-lactide-co-1,5-dioxepan-2-one) (poly(LLA-co-DXO)) scaffolds were implanted into critical-sized calvarial defects in Wistar rats. The animals were randomly allotted to hyperbaric or normobaric oxygen groups. The treatment group received five sessions weekly for 90 min at increased atmospheric pressure, for up to 4 weeks. Samples were retrieved at weeks 2 and 8, i.e. after a total of 10 and 20 sessions, respectively. The samples were analyzed by real-time reverse transcriptase polymerase chain reaction (RT-PCR) and histology at week 2, and radiographically and histologically at week 8. At week 2, defects treated with HBO exhibited greater numbers of cells positive for the endothelial marker CD31, up-regulated gene expression of osteogenic markers, and down-regulated expression of pro-inflammatory cytokines. At week 8, radiographic examination revealed that calvarial defects subjected to HBO exhibited a higher percentage of radiopacities than normobaric controls, and histological examination disclosed enhanced bone healing. These results confirmed that HBO treatment was effective in stimulating vascularization and bone formation in rat calvarial defects.

  • 242. Pedersen, Torbjorn O.
    et al.
    Blois, Anna L.
    Xing, Zhe
    Xue, Ying
    Sun, Yang
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Finne-Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Akslen, Lars A.
    Lorens, James B.
    Leknes, Knut N.
    Fristad, Inge
    Mustafa, Kamal
    Endothelial microvascular networks affect gene-expression profiles and osteogenic potential of tissue-engineered constructs2013In: STEM CELL RES THER, ISSN 1757-6512, Vol. 4, p. 52-Article in journal (Refereed)
    Abstract [en]

    Introduction: A major determinant of the potential size of cell/scaffold constructs in tissue engineering is vascularization. The aims of this study were twofold: first to determine the in vitro angiogenic and osteogenic geneexpression profiles of endothelial cells (ECs) and mesenchymal stem cells (MSCs) cocultured in a dynamic 3D environment; and second, to assess differentiation and the potential for osteogenesis after in vivo implantation. Methods: MSCs and ECs were grown in dynamic culture in poly(L-lactide-co-1,5-dioxepan-2-one) (poly(LLA-co-DXO)) copolymer scaffolds for 1 week, to generate three-dimensional endothelial microvascular networks. The constructs were then implanted in vivo, in a murine model for ectopic bone formation. Expression of selected genes for angiogenesis and osteogenesis was studied after a 1-week culture in vitro. Human cell proliferation was assessed as expression of ki67, whereas a-smooth muscle actin was used to determine the perivascular differentiation of MSCs. Osteogenesis was evaluated in vivo through detection of selected markers, by using real-time RT-PCR, alkaline phosphatase (ALP), Alizarin Red, hematoxylin/eosin (HE), and Masson trichrome staining. Results: The results show that endothelial microvascular networks could be generated in a poly(LLA-co-DXO) scaffold in vitro and sustained after in vivo implantation. The addition of ECs to MSCs influenced both angiogenic and osteogenic gene-expression profiles. Furthermore, human ki67 was upregulated before and after implantation. MSCs could support functional blood vessels as perivascular cells independent of implanted ECs. In addition, the expression of ALP was upregulated in the presence of endothelial microvascular networks. Conclusions: This study demonstrates that copolymer poly(LLA-co-DXO) scaffolds can be prevascularized with ECs and MSCs. Although a local osteoinductive environment is required to achieve ectopic bone formation, seeding of MSCs with or without ECs increases the osteogenic potential of tissue-engineered constructs.

  • 243. Pedersen, Torbjorn O.
    et al.
    Blois, Anna L.
    Xue, Ying
    Xing, Zhe
    Sun, Yang
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Finne-Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Lorens, James B.
    Fristad, Inge
    Leknes, Knut N.
    Mustafa, Kamal
    Mesenchymal stem cells induce endothelial cell quiescence and promote capillary formation2014In: Stem Cell Research & Therapy, ISSN 1757-6512, Vol. 5, p. 23-Article in journal (Refereed)
    Abstract [en]

    Introduction: Rapid establishment of functional blood vessels is a prerequisite for successful tissue engineering. During vascular development, endothelial cells (ECs) and perivascular cells assemble into a complex regulating proliferation of ECs, vessel diameter and production of extracellular matrix proteins. The aim of this study was to evaluate the ability of mesenchymal stem cells (MSCs) to establish an endothelial-perivascular complex in tissue-engineered constructs comprising ECs and MSCs. Methods: Primary human ECs and MSCs were seeded onto poly(L-lactide-co-1,5-dioxepan-2-one) (poly(LLA-co-DXO)) scaffolds and grown in dynamic culture before subcutaneous implantation in immunocompromised mice for 1 and 3 weeks. Cellular activity, angiogenic stimulation and vascular assembly in cell/scaffold constructs seeded with ECs or ECs/MSCs in a 5:1 ratio was monitored with real-time RT-PCR, ELISA and immunohistochemical microscopy analysis. Results: A quiescent phenotype of ECs was generated, by adding MSCs to the culture system. Decreased proliferation of ECs, in addition to up-regulation of selected markers for vascular maturation was demonstrated. Baseline expression of VEGFa was higher for MSCs compared with EC (P < 0.001), with subsequent up-regulated VEGFa-expression for EC/MSC constructs before (P < 0.05) and after implantation (P < 0.01). Furthermore, an inflammatory response with CD11b + cells was generated from implantation of human cells. At the end of the 3 week experimental period, a higher vascular density was shown for both cellular constructs compared with empty control scaffolds (P < 0.01), with the highest density of capillaries being generated in constructs comprising both ECs and MSCs. Conclusions: Induction of a quiescent phenotype of ECs associated with vascular maturation can be achieved by co-seeding with MSCs. Hence, MSCs can be appropriate perivascular cells for tissue-engineered constructs.

  • 244.
    Persson, Johanna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Birch xylan modification by lactide grafting2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The wood based biorefinery concept has led to an increasing interest in the possibility of using hemicelluloses as a source for value added products. Hemicelluloses are dissolved in large amounts in the process liquor during kraft pulping. In particular, hardwood 4-O-methylglucuronoxylan (xylan) has been shown to be highly stable towards the harsh conditions used in kraft pulping procedures and it can therefore be isolated with intact polymeric features. Xylan is the most abundant hemicellulose found in plant cells and this makes it very interesting as a novel biorefinery product. Some of the challenges of utilizing xylan in value-added applications lie in its lack of both film-forming ability and thermal processability. Chemical modification of the hardwood hemicellulose is one way to overcome these weaknesses.

    In this work, birch xylan, isolated from a kraft cooking liquor, has been modified by grafting with lactide. Only a small degree of modification was sufficient to give a film-forming ability. Thin films of the modified xylan had a tensile strength of up to 48 MPa. The lactide-grafted xylan also had properties suitable for thermal processing.

    The grafting was achieved by ring-opening polymerization of lactide onto the xylan backbone. Two different catalysts were employed: stannous octoate and triazabicyclodecene. With stannous octoate, the xylan could be modified into lactidegrafted xylan with oligolactide branches. By optimizing the synthesis procedure with triazabicyclodecene as catalyst, the yield was almost quantitative. This also enabled polylactide-graft-xylan copolymers with a specific branch length to be produced.

  • 245.
    Persson, Johanna
    et al.
    Innventia AB.
    Dahlman, Olof
    Innventia AB.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Birch xylan grafted with pla branches of predictable length2012In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 7, no 3, p. 3640-3655Article in journal (Refereed)
    Abstract [en]

    Birch xylan (4-O-methylglucuronoxylan) isolated from a kraft cooking liquor was delignified and grafted with polylactide of predictable branch length. This graft copolymerization resulted in very high total yields, greater than 90%, and with less than 10% polylactide homopolymer byproducts. Mild reaction conditions (40 degrees C, 5 to 120 minutes) were used, which was believed to limit transesterification reactions and thus make it possible to reach good predictability of the polylactide branch length. The thermal properties of the polylactide-grafted xylan depended on the branch length. Short branches resulted in fully amorphous materials with a glass transition temperature of about 48 to 55 degrees C, whereas long polylactide branches resulted in semi-crystalline materials with melting points of about 130 degrees C. Using mixtures of L-lactide and D/L-lactide in the monomer feed further altered the thermal properties. The degradation temperatures of the polylactide-grafted xylans were higher than that of the unmodified xylan, with degradation temperatures of about 300 degrees C and 250 degrees C, respectively. Tensile testing showed increased elongation at break with increasing branch length. The proposed method thus enables tailor-making of copolymers with specific thermal and mechanical properties.

  • 246.
    Persson, Johanna
    et al.
    Innventia AB.
    Dahlman, Olof
    Innventia AB.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Modification of birch xylan by lactide-grafting2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 3, p. 518-524Article in journal (Refereed)
    Abstract [en]

    4-O-methylglucuronoxylan, isolated by ultrafiltration from a birch kraft cooking liquor, was delignified and subsequently modified by grafting lactide-chains onto the hydroxyl groups via ring opening polymerization with L-lactide. The structures and average molar masses of the lactide-grafted xylan polymers were characterised by NMR and SEC respectively. By varying the lactide-to-xylan feed ratio, graft polymers with different graft levels were synthesized. The degree of substitution of the hydroxyls in the xylan back-bone ranged from 0.7 to 1.7 with lactide side-chains having an average length of 1.2 to 2.5 lactide units. The side-chain length and degree of substitution influenced the hydrophobicity, thermal properties and tensile strength properties. A glass transition could be detected for lactide-grafted xylan polymers with lactide chains longer than 1.8 lactide units. Solution-cast thin films prepared from lactide-grafted xylans exhibited strong tensile strength and high modulus with decreasing strength and increasing elongation at break as the lactide chain length was increased.

  • 247. Poveda-Reyes, Sara
    et al.
    Rodrigo-Navarro, Aleixandre
    Gamboa-Martinez, Tatiana C.
    Rodiguez-Cabello, Jose C.
    Quintanilla-Sierra, Luis
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Ferrer, Gloria Gallego
    Injectable composites of loose microfibers and gelatin with improved interfacial interaction for soft tissue engineering2015In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 74, p. 224-234Article in journal (Refereed)
    Abstract [en]

    Poly(L-lactic acid) (PLLA) microfibers were surface functionalized by graft photopolymerization of 2-hydroxyethyl methacrylate (HEMA) onto the fiber surface. Grafted fibers were easily dispersed in enzymatically gelling tyramine-substituted gelatin, forming a homogeneous dispersion without hindering subsequent gelatin crosslinking. The obtained injectable hydrogels showed improved mechanical properties compared to analogues based on non-modified fibers. The composite with 1% (w/v) of surface modified fibers had a three-fold higher shear storage modulus (535.2 +/- 90 Pa) than pure gelatin (184.9 +/- 32 Pa) while no significant increase was observed in the case of non-grafted fiber composites. Moreover, PHEMA grafting on PLLA fibers did not compromise cell viability and proliferation within the hydrogel. The new injectable hydrogels offer improved potential as substrates for the regeneration of soft tissues.

  • 248.
    Rajkhowa, Ritimoni
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Varma, I. K.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Enzyme-catalyzed copolymerization of oxiranes with dicarboxylic acid anhydrides2005In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 97, no 2, p. 697-704Article in journal (Refereed)
    Abstract [en]

    Ring-opening copolymerizations of the oxiranes glycidyl phenyl ether (GPE) and diglycidyl ether of bisphenol A (DGEBA) with a dicarboxylic acid anhydride [methyl hexahydrophthalic anhydride, nadic anhydride, maleic anhydride (MA), or itaconic anhydride (IA)] were carried out with the lipases Candida cylindracea (CCL), Lipozyme TL-IM (LIM), and Novozyme 435 (N435) as catalysts. The CCL-catalyzed reaction of DGEBA with MA or IA (at a 1:2 molar ratio) at 80 degrees C resulted in only partial curing. We monitored the reactions by Fourier transform infrared spectroscopy and by following the changes in the intensities of carbonyl stretching frequencies of the anhydride and ester groups. The reactivity of the oxirane group in GPE was higher than that in DGEBA; this may have been due to the higher viscosity of DGEBA. The reactivities of the enzymes for the copolymerization of the oxiranes and dicarboxylic acid anhydride were in the order LIM > CCL > N435.

  • 249. Ramkumar, D.
    et al.
    Vaidya, U.R.
    Bhattacharya, M.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Karlsson, Sigbritt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Properties of injection moulded starch/synthetic polymer blends-I. Effect of processing parameters on physical properties1996In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 32, p. 999-1010Article in journal (Refereed)
  • 250.
    Regnell Andersson, Sofia
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Controlling Polylactide Degradation through Stereocomplexation and Lactic Acid Based Additives2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The successful use of degradable materials in new applications depends on our ability to control the degradation process. A number of aspects need to be evaluated including degradation rate, the onset of degradation and the nature, formation and release of degradation products. In this study, the possibility of tuning the properties and degradation of polylactide (PLA) through stereocomplexation between the L- and D-enantiomers of PLA was investigated. The influence of the oligo(D-lactic acid) architecture on the stereocomplexation and subsequent degradation rate was evaluated. The dependence of stereocomplex formation on the structure of the side-group and the effect of oligo(L-lactide) additives on hydrolytic degradation and thermal aging were also investigated. One advantage of these additives is that no foreign migrants are introduced into the degradation product pattern. This reduces the risk of a harmful impact on the environment. The degradation process was monitored through analyses of the remaining material and the released degradation products. Depending on the modification, both increased and decreased degradation rates could be obtained. Resistance against degradation was increased by stereocomplexation, which is explained by the strong interactions between the complementary L- and D- chain structures. On the other hand, even though the mass loss was low, larger amounts of short hydroxy acids were released from the stereocomplex materials, resulting in a faster decrease in the pH. This can be explained by an increase in the amount of intermolecular stereocomplex crystallites resulting in a large number of tie-chains connecting the crystallites. These chains are more exposed to hydrolysis, and hence short degradation products are released. The architecture of the added oligo(D-lactic acid) had a considerable impact on material properties such as crystallinity and degradation. Acidic end-groups increased the degradation rate, while alcoholic end-groups had the opposite effect. The addition of hydrophilic linear oligo(L-lactide) to poly(L-lactide) (PLLA) resulted in a rapid migration of additives from the material during hydrolytic aging and a faster loss of mass and molar mass than from a material containing cyclic analogues. During thermal aging, however, the opposite effect was observed as the linear oligo(L-lactide) additives interacted more strongly with PLLA, which resulted in smaller mass loss. Stereocomplexation was also revealed to take place between oligomers of the two enantiomers of the lactic acid-like monomer α-hydroxyisovaleric acid.

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