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  • 1.
    Wu, Duo
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Xu, Huan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    From starch to polylactide and nano-graphene oxide: fully starch derived high performance composites2016In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, no 59, p. 54336-54345Article in journal (Refereed)
    Abstract [en]

    A delicate closed-loop strategy for valorization of starch to value-added products was developed. Carbon sheets, formed of carbon spheres, were obtained by microwave-assisted hydrothermal degradation of starch and then further transformed into nano-sized graphene oxide (nGO, 20 x 30 nm(2)) under oxygen-rich acidic conditions. The synthesized nGO exhibited self-assembly in solution. Furthermore, nGO strongly attached to the surface of starch granules by hydrogen bonding (nGO@ starch, 0.1 wt%) and allowed easy and highly efficient interfacial engineering in PLA/starch composites. After combining with polylactide (PLA), the composites could incorporate up to 30 wt% nGO@ starch, while retaining excellent properties. nGO was capable of facilitating PLA crystallization in the composites by providing a number of nucleation sites. Moreover, the interfacial adhesion between PLA and starch was significantly improved by nGO. Though its content was extremely low, nGO improved the mechanical and barrier properties and thermal stability of the PLA/starch composites. The results demonstrate a facile route to value-added starch-derived nGO and further to fully starch derived high performance PLA/starch biocomposites.

  • 2. Xie, L.
    et al.
    Xu, Huan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Li, Z. -M
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Structural Hierarchy and Polymorphic Transformation in Shear-Induced Shish-Kebab of Stereocomplex Poly(Lactic Acid)2016In: Macromolecular rapid communications, ISSN 1022-1336, E-ISSN 1521-3927, Vol. 37, no 9, p. 745-751Article in journal (Refereed)
    Abstract [en]

    The realization of hierarchical shish-kebab structures for stereocomplex poly(lactic acid) (PLA) is achieved by the application of a shear flow (100 s-1 for 1 s) mimicking what can be expected during polymer processing. Compared to the normal shearing scenarios, this transient and strong shear flow enables the creation of dense shish precursors in time- and energy-saving manner. The distribution of crystal form associated with the hierarchical structure is revealed by 2D Fourier transform infrared spectroscopy imaging, creating a unique visualization for both spatial resolution and polymorphism identification. Interestingly, in the shear stereocomplex chains are preferentially extended and crystallized as stable central cores with weak temperature dependence, whereas the development of lateral kebabs is defined by the distinct relation to the crystallization temperature. Below the melting point of homocrystals, both homo and stereocomplex crystallization are engaged in lamellar packing. Above that, exclusive stereocomplex crystals are organized into ordered lamellae. Combining the direct observations at multiscale, the ordered alignment of stereocomplex chains is recognized as the molecular origin of fibrillar extended chain bundles that constitute the central row-nuclei. The proposed hypothesis affords elucidation of shish-kebab formation and unique polymorphism in sheared stereocomplex PLA, which generates opportunities for engendering hierarchically structured PLA with improved performance. A transient and strong shear mimicking the typical melt processing scenario is used to create compact shish-kebab superstructures for stereocomplex poly(lactic acid). The highly oriented fibrillar extended chains are found to constitute the central shish, while 2D Fourier transform infrared spectroscopy imaging offered a direct visualization for determination of polymorphic transition that is associated with spatial hierarchy.

  • 3.
    Xu, Huan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Graphene Oxide Technology to Advance the Performance of Poly(lactic acid) Materials2016Doctoral thesis, monograph (Other academic)
    Abstract [en]

    In the past two decades, a burgeoning biorefinery concept has grown in concert with the materials science, contributing to the rise of biobased materials that respect environment and are versatile for various applications. An excellent example is poly(lactic acid) (PLA) that exhibits high strength and desirable degradability. Unfortunately, PLA suffers from poor mechanical ductility and toughness, and low resistance to heat and water/gas permeation. In order to promote the performance of PLA and thus to broaden the application areas, this study brings to light the morphological and structural specificities for fabrication of high-performance PLA films. The proposed strategy hinges on innovative uses of graphene oxide (GO) nanostructures, giving the possibility to simultaneously tailor the crystalline morphology, mechanical and barrier properties, and degradation behavior for PLA.

    While recognizing the GO-enabled function in controlling the crystalline morphology of racemic PLA, the nucleation mechanism induced by GO nanosheets was elucidated as a first step. In addition to the observation of random lamellae induced by the basal planes of GO nanosheets, it was of particular interest to reveal that the ultrathin edges of nanosheets were ready to trigger the ordered alignment of PLA lamellae. The high nucleation activity of GO was further employed to preferentially accelerate the stereocomplex crystallization of PLA, which subsequently suppressed the development of homo-crystals by generation of spatial hindrance. As a result of the decoration of GO nanosheets with sterecomplex crystals, an impressive combination of barrier and thermal properties, and mechanical strength and ductility was achieved for the racemic PLA/GO composites.

    As a parallel approach, the morphology and structure of GO were tailored to enhance PLA-GO interactions and to improve GO dispersion: (1) few-layer nanosheets were firmly immobilized onto microsized starch particles by hydrogen bonding, permitting the creation of strong and active nanointerfaces in PLA biocomposites that enhanced interfacial interactions and facilitated filler dispersion; (2) the planar dimensionality of GO was shrunk to quasi-zero, conferring the generation of higher density of oxygen functional groups and enhanced interactions with PLA matrix, and resulting in higher nucleation activity and accelerated hydrolytic degradation.

    In addition to the fundamental insights into the PLA-GO interaction mechanisms, the methodologies proposed here can shape new routes to high-performance PLA materials with promising potential in a diversity of applications.

  • 4.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Bai, Yuge
    Xie, Lan
    Li, Jinlai
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Heat-Resistant and Microwaveable Poly(Iactic acid) by Quantum-Dot Promoted Stereocomplexation2017In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 5, no 12, p. 11607-11617Article in journal (Refereed)
    Abstract [en]

    Nanofiller-tailored stereocomplexation signifies a promising and feasible pathway to develop heat-resistant poly (lactic acid) (PLA) materials. However, this pathway is thwarted by the potential adverse environmental issues of traditional nanofillers and the challenges in facilitating the nanofiller dispersion and selective formation of stereocomplex crystals (SCs). Here we unravel a microwave-assisted approach to exploit biobased quantum dots (QDs) featuring excellent capability to preferably nucleate PLA SCs. The combination of ultrasmall dimension and high oxygenation degree of QDs conferred intimate interactions with stereocomplexed PLA chains, readying complete exfoliation and uniform dispersion of QDs to promote stereocomplexation. The well-dispersed QDs provided perfect UV shielding for PLA composites, while sustaining high transmission to visible light comparable to pure PLA. Strong interfacial interactions and high concentration of SCs were created around the nanoscale surfaces of QDs, accounting for the greatly increased resistance to oxygen permeation, thermal deformation, and microwave heating. This was accompanied by substantial rise in tensile modulus and elongation at break (up to 74 and 51%) compared to that of pure PLA, affording the demonstration of unusual reinforcing and toughening mechanisms imparted by the PLA-affinitive QDs. The robust structural integrity under harsh usage environments, coupled with high gas barrier, prominent light management and evasion of flexibility and extensibility sacrifices, may prompt low-cost and ecofriendly PLA nanocomposites suitable for diverse applications including microwaveable food packaging.

  • 5.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology. College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, China.
    Feng, Zhaoxuan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Xie, L.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Graphene Oxide-Driven Design of Strong and Flexible Biopolymer Barrier Films: From Smart Crystallization Control to Affordable Engineering2016In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 4, no 1, p. 334-349Article in journal (Refereed)
    Abstract [en]

    Development of multifunctional, versatile biobased polymers can greatly benefit from the discovery and application of 2D sheet-like materials. For instance, the hybrid system integrating graphene oxide (GO) nanosheets with enantiomeric poly(lactic acid) (PLA) showcases several key properties that can address emerging multifunction needs such as good gas barrier and high thermal resistance. Here we revealed that large specific surface area and homogeneous dispersion of GO conferred the construction of interconnected networks in PLA even with relatively low GO contents (0.1 and 0.5 wt %). These well-extended GO nanosheets were ready to provide enormous and active platforms to nucleate preferentially the neighboring stereocomplex chains, prompting the prevailing development of stereocomplex crystals (SCs). The notable scenario associated with the GO distribution was imaged by 2D Fourier transform infrared spectroscopy, and was further elucidated by dynamic crystallization. More importantly, the nanosheets decorated with ordered PLA lamellae, in turn, contributed to the impressive enhancement in barrier and mechanical properties and chemical resistance. For example, a distinct decrease of 98.5% in oxygen permeability coefficient was observed for the composite films containing 0.5 wt % GO (6.264 × 10-17 cm3 cm cm-2 s-1 Pa-1) compared to the control sample crystallized at 150 °C (4.214 × 10-15 cm3 cm cm-2 s-1 Pa-1). The performance distinction was accompanied by the unusual combination of high tensile strength (73.5 MPa) and high elongation (13.6%), displaying an increase of 31.7% and 183.3% compared to the counterpart, respectively. This may provide a broader context for exploiting 2D nanosheets as robust cells to advance the function and property of PLA, which helps to outline the roadmap for fashioning high-performance, affordable bioplastics.

  • 6.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Hua, Geng
    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.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Stereocontrolled Entanglement-Directed Self-Alignment of Poly(lactic acid) Cylindrites2016In: Macromolecular Chemistry and Physics, ISSN 1022-1352, E-ISSN 1521-3935Article in journal (Refereed)
    Abstract [en]

    The concept of stereocontrolled entanglements, in which the tunable H-bonded chiral pairs serve as crosslinks to create topological constraints on the local chain dynamics, is introduced to tailor the crystalline morphology of stereocomplex poly(lactic acid). For the entanglements to be interconnected and activated, poly(d-lactic acid) with statistical branched architecture is incorporated, enabling the construction of 3D association with linear poly(l-lactic acid) chains. With thermodynamically graded disentanglement relaxation for the blends, the profound influence of entanglements on the crystalline morphology is revealed during isothermal crystallization. Orderly aligned cylindrites some with an exceptional length of over 500 μm, resembling the structural features of the classical shish-kebab superstructure, are observed in the blends penetrated with dense entanglement constraints. By contrast, only dendritic spherulites are formed in the highly disentangled blends. The selectively suppressed homo-crystallization by the entanglements offers insights into the contribution of constraints. This bottom-up strategy opens up pathways to engender oriented crystals of long-range order under quiescent conditions, which has potential implications for other chiral polymers.

  • 7.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wu, Duo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Yang, Xi
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Feng, Zhaoxuan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Adolfsson, Karin H.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Xie, Lan
    Sichuan Univ, Dept Polymer Sci & Engn, Chengdu, Sichuan, Peoples R China..
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Enhancing the function of graphene oxide nanosheets by crystallization control: Unexpected harvest of strength, ductility and thermal stability for poly(lactic acid) barrier films2016In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 251Article in journal (Other academic)
  • 8.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wu, Duo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Yang, Xi
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Xie, L.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Thermostable and impermeable "nano-barrier walls" constructed by poly(lactic acid) stereocomplex crystal decorated graphene oxide nanosheets2015In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 48, no 7, p. 2127-2137Article in journal (Refereed)
    Abstract [en]

    In contrast to the relatively clear understanding of epitaxial crystallization induced by one-dimensional nanofillers, the underlying interfacial interactions between polymer crystals and two-dimensional graphene oxide (GO) nanosheets are something of a mystery. Here, the GO-assisted formation of poly(lactic acid) (PLA) stereocomplex crystals (SCs) is disclosed from the quantitative structural analysis to the direct morphological observations at multiscale and the interaction mechanism at the molecular level. It is unexpected to observe that the edges of GO featuring rich grooves and ultralow thickness were ready to induce a layer of ordered lamellae, in clear contrast to the random growth of lamellae on the basal planes. The origin of GO-induced crystallization was appraised from the interaction point of view as indicated by the evident red-shift of a set of functional groups in the Fourier transform infrared spectroscopy spectra. More importantly, the GO nanosheets, albeit presented at an extremely low content (0.05 wt %), decorated by the preferred formation of SCs enabled the simultaneous enhancement of gas barrier properties and resistance to heat distortion. Specifically, the unique combination of greatly improved heat deformation temperature (HDT) and low oxygen permeability coefficient (P<inf>O</inf><inf>2</inf>) for the composite crystallized at 165 °C was demonstrated (146.5 °C and 0.95 × 10-15 cm3 cm cm-2 s-1 Pa-1), outperforming pure PLA with an increment of 75% and a decrease of 77% in HDT and P<inf>O</inf><inf>2</inf>, respectively. The proposed methodology affords elucidation of well-tailored thermal and barrier properties, which may motivate further extension of this rational design to other material combinations.

  • 9.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology. College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, China.
    Xie, Lan
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Beyond a Model of Polymer Processing-Triggered Shear: Reconciling Shish-Kebab Formation and Control of Chain Degradation in Sheared Poly(L-lactic acid)2015In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 3, no 7, p. 1443-1452Article in journal (Refereed)
    Abstract [en]

    Here we disclose an unprecedented methodology toward high-performance poly(L-lactic acid) (PLLA) through generation of dense shish-kebabs, while the normal shear stress-induced chain degradation is controlled. The key elements involve the application of a pulse of strong shear and controlled crystallization. Specifically, the shear featuring a short duration of 1 s and a shear rate high to 100 s(-1) was employed to create shish precursors, which was followed by high-temperature crystallization (at 130, 135, and 140 degrees C) to render the prevailing development of shish-kebabs rather than spherulites. The direct observation of the overgrown shish afforded the demonstration of its origin from shear-aligned bundles of fibrillar chains, implying the crucial importance of chain entanglements in driving the alignment of neighboring chains along the transient shear. For the first time, the shear-aligned shish was revealed to present much higher conformational order, compared to the neighboring kebabs or spherulites. It is of great interest that the application of transient shear flow prevented PLLA from shear-induced degradation, although the PLLA chains are inherently sensitive to external shear stress. The proposed pathway, thus, creates PLLA rich in shish-kebabs with well-preserved high-molecular-weight chains. This signifies a new scenario with respect to previous studies where strong and long-acting shear was required for the formation of oriented structures in PLLA and the property enhancement was to large part hampered by simultaneous chain scissions. Of immense significance is the possibility to utilize these findings during common processing such as extrusion, spinning, and blowing, in which a transient and intensive shear flow is normally generated.

  • 10.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Xie, Lan
    Li, Jinlai
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Coffee Grounds to Multifunctional Quantum Dots: Extreme Nanoenhancers of Polymer Biocomposites2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 33, p. 27972-27983Article in journal (Refereed)
    Abstract [en]

    Central to the design and execution of nanocomposite strategies is the invention of polymer-affinitive and multifunctional nanoreinforcements amenable to economically viable processing. Here, a microwave-assisted approach enabled gram-scale fabrication of polymer-affinitive luminescent quantum dots (QDs) from spent coffee grounds. The ultrasmall dimensions (approaching 20 nm), coupled with richness of diverse oxygen functional groups, conferred the zero-dimensional QDs with proper exfoliation and uniform dispersion in poly(L-lactic acid) (PLLA) matrix The unique optical properties of QDs were inherited by PLLA nano composites, giving intensive luminescence and high visible transparency, as well as nearly 100% UV-blocking ratio in the full-UV region at only 0.5 wt % QDs. The strong anchoring of PLLA chains at the nanoscale surfaces of QDs facilitated PLLA crystallization, which was accompanied by substantial improvements in thermomechanical and tensile properties. With 1 wt % QDs, for example, the storage modulus at 100 degrees C and tensile strength increased over 2500 and 69% compared to those of pure PLLA (4 and 57.3 MPa), respectively. The QD-enabled energy-dissipating and flexibility-imparting mechanisms upon tensile deformation, including the generation of numerous shear bands, crazing, and nanofibrillation, gave an unusual combination of elasticity and extensibility for PLLA nanocomposites. This paves the way to biowaste-derived nanodots with high affinity to polymer for elegant implementation of distinct light management and extreme nanoreinforcements in an ecofriendly manner.

  • 11.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Xie, Lan
    Wu, Duo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Immobilized Graphene Oxide Nanosheets as Thin but Strong Nanointerfaces in Biocomposites2016In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 4, no 4, p. 2211-2222Article in journal (Refereed)
    Abstract [en]

    Graphene oxide (GO) nanosheets featuring high surface activity and large planar dimension may function as robust nanointerfaces in biocomposites, contributing to simultaneous promotion of mechanical and gas barrier properties. Here, a solution-processed, additive-free approach to immobilize few-layer GO nanosheets on starch granule surfaces (GO@starch) by hydrogen bonding is demonstrated. This approach enabled a straightforward pathway to remove the intersheet van der Waals forces (pi-pi stacking) that generally cause reaggregation and poor dispersion of GO in polymer matrices. Incorporation of GO@starch into poly (lactic acid) (PLA) allowed an interesting structure with few-layer nanosheets firmly immobilized at the PLA-starch interfaces. Inheriting the high aspect ratio and surface energy of GO, GO@starch distinctly strengthened the interfacial interactions with PLA, albeit present at ultralow GO concentrations (up to 0.03 wt %), facilitating the dispersion of GO@starch and nucleation of PLA. The morphological regulation rendered composite films with an impressive combination of high thermal stability, mechanical strength and oxygen resistance. A substantial increase of 280% in tensile strength (58.2 MPa) and a prominent decline of 82% in oxygen permeation coefficient (4.0 cm(3) mm cm(-2) day(-1) atm(-1)) were achieved in the composites loaded with 30 wt % GO@starch in comparison with the counterpart. The cost-performance ratio for the nanostructured biocomposites was excellent even compared to the established packaging materials. The multiscale morphological regulation of sheet-like nanofillers by controlled exfoliation and immobilization of GO on microsized starch particle surfaces, the simplicity of manufacturing, together with the versatility of the engineered composites should make our strategy broadly applicable to other material combinations.

  • 12.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Sichuan University, Chengdu, China.
    Yang, Xi
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Xie, Lan
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Conformational Footprint in Hydrolysis-Induced Nanofibrillation and Crystallization of Poly(lactic acid)2016In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 17, no 3, p. 985-995Article in journal (Refereed)
    Abstract [en]

    The origin of hydrolysis-induced nanofibrillation and crystallization, at the molecular level, was revealed by mapping the conformational ordering during long-term hydrolytic degradation of initially amorphous poly(lactic acid) (PLA), a representative model for degradable aliphatic polyesters generally displaying strong interplay between crystallization and hydrolytic erosion. The conformational regularization of chain segments was essentially the main driving force for the morphological evolution of PLA during hydrolytic degradation. For hydrolysis at 37 degrees C, no significant structural variations were observed due to the immobilization of frozen PLA chains. In contrast, conformational ordering in PLA was immediately triggered during hydrolysis at 60 degrees C and was responsible for the transition from random coils to disordered trans and, further, to quasi-crystalline nanospheres. On the surfaces, the head-by-head absorption and joining of neighboring nanospheres led to nanofibrillar assemblies following a gluttonous snake-like manner. The length and density of nanofibers formed were in close relation to the hydrolytic evolution, both of which showed a direct rise in the initial 60 days and then a gradual decline. In the interior, presumably the high surface energy of the nanospheres allowed for the preferential anchoring and packing of conformationally ordered chains into lamellae. In accordance with the well-established hypothesis, the amorphous regions were attacked prior to the erosion of crystalline entities, causing a rapid increase of crystallinity during the initial 30 days, followed by a gradual fall until 90 days. In addition to adequate illustration of hydrolysis-induced variations of crystallinity, our proposed model elucidates the formation of spherulitic nuclei featuring an extremely wide distribution of diameters ranging from several nanometers to over 5 mu m, as well as the inferior resistance to hydrolysis observed for the primary nuclei. Our work fuels the interest in controlling nanofibrillation mechanism during hydrolysis of PLA, opening up possibilities for straightforward nanofiber formation.

  • 13.
    Yang, Xi
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Clénet, Jocelyn
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Xu, Huan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Two step extrusion process: From thermal recycling of PHB to plasticized PLA by reactive extrusion grafting of PHB degradation products onto PLA chains2015In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 48, no 8, p. 2509-2518Article in journal (Refereed)
    Abstract [en]

    A green and industrially viable two-step process was demonstrated for toughening polylactide (PLA) without compromising the biobased and biodegradable nature. First, poly(3-hydroxybutyrate) (PHB) biopolymer was thermally degraded in an extruder to create PHB oligomers (dPHB) with functional end-groups suitable for further reactions. Second, a reactive extrusion process was developed to covalently anchor dPHB onto the main chain of PLA. PLA with 20% (w/w) grafted dPHB demonstrated an impressive elongation at break of 538%, 66 times higher than that of pure PLA and significantly higher than the elongation at break of the corresponding physical blend. At the same time WAXD measurements illustrated that grafting significantly increased the crystallization ability of PLA. We present a viable recycling route for PHB and a highly promising approach for fully biobased toughened PLA with covalently anchored PHB plasticizers.

  • 14.
    Yang, Xi
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Xu, Huan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Poly(lactide)-g-poly(butylene succinate-co-adipate) with High Crystallization Capacity and Migration Resistance2016In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 9, no 5, article id 313Article in journal (Refereed)
    Abstract [en]

    Plasticized polylactide (PLA) with increased crystallization ability and prolonged life-span in practical applications due to the minimal plasticizer migration was prepared. Branched plasticized PLA was successfully obtained by coupling poly(butylene succinate-co-adipate) (PBSA) to crotonic acid (CA) functionalized PLA. The plasticization behavior of PBSA coupled PLA (PLA-CA-PBSA) and its counterpart PBSA blended PLA (PLA/PBSA) were fully elucidated. For both PLA-CA-PBSA and PLA/PBSA, a decrease of Tg to around room temperature and an increase in the elongation at break of PLA from 14% to 165% and 460%, respectively, were determined. The crystallinity was increased from 2.1% to 8.4% for PLA/PBSA and even more, to 10.6%, for PLA-CA-PBSA. Due to the inherent poor miscibility between the PBSA and PLA, phase separation occurred in the blend, while PLA-CA-PBSA showed no phase separation which, together with the higher crystallinity, led to better oxygen barrier properties compared to neat PLA and PLA/PBSA. A higher resistance to migration during hydrolytic degradation for the PLA-CA-PBSA compared to the PLA/PBSA indicated that the plasticization effect of PBSA in the coupled material would be retained for a longer time period.

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