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Towards a retro-structural design of degradable aliphatic polyester-based materials
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The increasing amount of accumulated plastic waste has led to a continuous search for degradable materials for use in a variety of applications. This eco-friendly approach contemplates the use of degradable alternatives to the inert polymers (the main components in plastics) used today and further engineering of their degradation pathways. The most extensively investigated group of degradable polymers is the poly(α-esters), due to their tailorable thermo-mechanical properties and degradability. However, degradation of these polymers can be undesirable or desirable depending on the time of occurrence. Thus, by controlling the degradation process, it is possible to predict and, consequently, tailor the materials’ lifetime for specific needs.Herein, a methodology to allow for a retro-structural design of degradable materials based on aliphatic polyesters is presented. Insights into the degradation behavior of the systems were obtained and further translated to different levels of structural designs to achieve desired macroscopic properties in terms of performance and degradability. Several combinational strategies based on polymer morphology, polymer structure and block design, were developed. As a result, homopolymers and block copolymers with projected degradation for different instances were created. Apart from bulk modifications in the material, it was shown that it was possible to tailor degradation pathways by means of specific interactions between polymer pairs in block copolymers and also in polymer blends. Furthermore, well-defined structure-property relationships are crucial when designing materials with specific degradability properties. In light of this, degradable polyester-based particles with tunable crystalline structures and, hence, physical properties, were developed. These particles proved to function as reinforcing agents in the creation of “green” homocomposites. These composites are promising alternatives in the search for materials that are completely degradable and sustainable.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , 95 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:62
Keyword [en]
Hydrolysis, polyesters, polylactide, hydrophobicity, crystallinity, miscibility, nanoparticles, stereocomplex, homocomposites
National Category
Polymer Chemistry
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-177187ISBN: 978-91-7595-748-7 (print)OAI: oai:DiVA.org:kth-177187DiVA: diva2:871837
Public defence
2015-12-11, Kollegiesalen, Brinellvägen 2, KTH, Stockholm, 13:30 (English)
Opponent
Supervisors
Note

QC 20151117

Available from: 2015-11-17 Created: 2015-11-17 Last updated: 2015-11-17Bibliographically approved
List of papers
1. Tuning the Degradation Profiles of Poly(L-lactide)-Based Materials through Miscibility
Open this publication in new window or tab >>Tuning the Degradation Profiles of Poly(L-lactide)-Based Materials through Miscibility
2014 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 15, no 1, 391-402 p.Article in journal (Refereed) Published
Abstract [en]

The effective use of biodegradable polymers relies on the ability to control the onset of and time needed for degradation. Preferably, the material properties should be retained throughout the intended time frame, and the material should degrade in a rapid and controlled manner afterward. The degradation profiles of polyester materials were controlled through their miscibility. Systems composed of PLLA blended with poly[(R,S)-3-hydroxybutyrate] (a-PHB) and polypropylene adipate (PPA) with various molar masses were prepared through extrusion. Three different systems were used: miscible (PLLA/a-PHB5 and PLLA/a-PHB20), partially miscible (PLLA/PPA5/comp and PLLA/PPA20/comp), and immiscible (PLLA/PPA5 and PLLA/PPA20) blends. These blends and their respective homopolymers were hydrolytically degraded in water at 37 degrees C for up to I year. The blends exhibited entirely different degradation profiles but showed no diversity between the total degradation times of the materials. PLLA presented a two-stage degradation profile with a rapid decrease in molar mass during the early stages of degradation, similar to the profile of PLLA/a-PHB5. PLLA/a-PHB20 presented a single, constant linear degradation profile. PLLA/PPA5 and PLLA/PPA20 showed completely opposing degradation profiles relative to PLLA, exhibiting a slow initial phase and a rapid decrease after a prolonged degradation time. PLLA/PPA5/comp and PLLA/PPA20/comp had degradation profiles between those of the miscible and the immiscible blends. The molar masses of the materials were approximately the same after 1 year of degradation despite their different profiles. The blend composition and topographical images captured at the last degradation time point demonstrate that the blending component was not leached out during the period of study. The hydrolytic stability of degradable polyester materials can be tailored to obtain different and predetermined degradation profiles for future applications.

Keyword
Hydrolytic Degradation, Atactic Poly(3-Hydroxybutyrate), Mechanical-Properties, Enzymatic Degradation, Aliphatic Polyesters, Poly(Dl-Lactic Acid), Poly(Lactic Acid), Phase-Structure, Blends, Polylactide
National Category
Biochemistry and Molecular Biology Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-141304 (URN)10.1021/bm401667b (DOI)000329879800042 ()2-s2.0-84892601347 (Scopus ID)
Funder
Swedish Research Council, A0347801EU, European Research Council, 246776
Note

QC 20140214

Available from: 2014-02-14 Created: 2014-02-13 Last updated: 2017-12-06Bibliographically approved
2. Nano-Stereocomplexation of Polylactide (PLA) Spheres by Spray Droplet Atomization
Open this publication in new window or tab >>Nano-Stereocomplexation of Polylactide (PLA) Spheres by Spray Droplet Atomization
2014 (English)In: Macromolecular rapid communications, ISSN 1022-1336, E-ISSN 1521-3927, Vol. 35, no 22, 1949-1953 p.Article in journal (Refereed) Published
Abstract [en]

A direct, efficient, and scalable method to prepare stereocomplexed polylactide (PLA)-based nanoparticles (NPs) is achieved. By an appropriate combination of fabrication parameters, NPs with controlled shape and crystalline morphology are obtained and even pure PLA stereocomplexes (PLASC) are successfully prepared using the spray-drying technology. The formed particles of varying D- and L-LA content have an average size of approximate to 400 nm, where the smallest size is obtained for PLA50, which has an equimolar composition of PLLA and PDLA in solution. Raman spectra of the particles show the typical shifts for PLASC in PLA50, and thermal analysis indicates the presence of pure stereocomplexation, with only one melting peak at 226 degrees C. Topographic images of the particles exhibit a single phase with different surface roughness in correlation with the thermal analysis. A high yield of spherically shaped particles is obtained. The results clearly provide a proficient method for achieving PLASC NPs that are expected to function as renewable materials in PLA-based nanocomposites and potentially as more stable drug delivery carriers.

Keyword
biodegradable, nanoparticles, polylactides, spray-drying, stereocomplexes
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-158321 (URN)10.1002/marc.201400374 (DOI)000345443600006 ()
Note

QC 20150126

Available from: 2015-01-26 Created: 2015-01-07 Last updated: 2017-12-05Bibliographically approved
3. Selective degradation in aliphatic block copolyesters by controlling the heterogeneity of the amorphous phase
Open this publication in new window or tab >>Selective degradation in aliphatic block copolyesters by controlling the heterogeneity of the amorphous phase
Show others...
2015 (English)In: Polymer Chemistry, ISSN 1759-9954, E-ISSN 1759-9962, Vol. 6, no 17, 3271-3282 p.Article in journal (Refereed) Published
Abstract [en]

Controlling the course of the degradation of aliphatic polyesters is a key question when designing new degradable materials. It is shown herein that it is possible to predetermine the degradation path of aliphatic block copolyesters by controlling the heterogeneity of the amorphous phase, which in turn regulates the availability of the hydrolyzable groups in the polyester backbone. To demonstrate these processes, we synthesized a set of degradable materials based on poly(l-lactide) (PLLA), poly(ε-decalactone) (PεDL) and poly(ε-caprolactone) (PCL) with varying compositions. The materials were subjected to hydrolysis for a six months period. The materials composed of PLLA and PεDL exhibited a heterogeneous amorphous phase, whereas the materials composed of PCL and PεDL presented a more homogeneous phase. The kinetics of the degradation indicated that the slowest degradation rate was observed for the more homogeneous compositions. The degradation path of the heterogeneous amorphous phase materials was driven by a random chain scission process, whereas the more homogeneous composition presented a degradation path driven by a more selective chain scission. The confinement of the amorphous phase by the more hydrolytically stable PεDL permitted a selective degradation of the available hydrolyzable groups. The random and more selective chain scission processes were further verified by using previously determined molecular modeling based on Monte Carlo procedures. Topographical images and thermal analyses of the materials under different degradation periods correlated with the proposed degradation paths. Detailed insights and the ability to predetermine the degradation pathways of aliphatic polyesters will continue to expand the great potential of renewable materials and their use in specific applications for a future sustainable society.

Keyword
Chains, Degradation, Organic polymers, Polyesters, Thermoanalysis, Aliphatic polyester, Degradation pathways, Homogeneous composition, Monte Carlo procedures, Poly (epsiloncaprolactone), Random chain scissions, Selective degradation, Topographical images, Amorphous materials
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-167775 (URN)10.1039/c5py00136f (DOI)000353348700010 ()2-s2.0-84928485535 (Scopus ID)
Funder
Swedish Research Council, A0347801EU, European Research Council, 246776
Note

QC 20150526

Available from: 2015-05-26 Created: 2015-05-22 Last updated: 2017-12-04Bibliographically approved
4. Homocomposites of Polylactide (PLA) with Induced Interfacial Stereocomplex Crystallites
Open this publication in new window or tab >>Homocomposites of Polylactide (PLA) with Induced Interfacial Stereocomplex Crystallites
2015 (English)In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 3, no 9, 2220-2231 p.Article in journal (Refereed) Published
Abstract [en]

The demand for “green” degradable composite materials increases with growing environmental awareness. The key challenge is achieving the preferred physical properties and maintaining their eco-attributes in terms of the degradability of the matrix and the filler. Herein, we have designed a series of “green” homocomposites materials based purely on polylactide (PLA) polymers with different structures. Film-extruded homocomposites were prepared by melt-blending PLA matrixes (which had different degrees of crystallinity) with PLLA and PLA stereocomplex (SC) particles. The PLLA and SC particles were spherical and with 300–500 nm size. Interfacial crystalline structures in the form of stereocomplexes were obtained for certain particulate-homocomposite formulations. These SC crystallites were found at the particle/matrix interface when adding PLLA particles to a PLA matrix with d-lactide units, as confirmed by XRD and DSC data analyses. For all homocomposites, the PLLA and SC particles acted as nucleating agents and enhanced the crystallization of the PLA matrixes. The SC particles were more rigid and had a higher Young’s modulus compared with the PLLA particles. The mechanical properties of the homocomposites varied with particle size, rigidity, and the interfacial adhesion between the particles and the matrix. An improved tensile strength in the homocomposites was achieved from the interfacial stereocomplex formation. Hereafter, homocomposites with tunable crystalline arrangements and subsequently physical properties, are promising alternatives in strive for eco-composites and by this, creating materials that are completely degradable and sustainable.

National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-173245 (URN)10.1021/acssuschemeng.5b00498 (DOI)
Note

QC 20150910

Available from: 2015-09-08 Created: 2015-09-08 Last updated: 2017-01-11Bibliographically approved

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