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Controlling Polylactide Degradation through Stereocomplexation and Lactic Acid Based Additives
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
2013 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , 53 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:14
Keyword [en]
Polylactide, stereocomplex, plasticizer, degradation, degradation products, ESI-MS
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-120120ISBN: 978-91-7501-687-0 (print)OAI: oai:DiVA.org:kth-120120DiVA: diva2:613571
Public defence
2013-04-26, K2, Teknikringen 28, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130403

Available from: 2013-04-03 Created: 2013-03-28 Last updated: 2013-04-03Bibliographically approved
List of papers
1. Polylactide Stereocomplexation Leads to Higher Hydrolytic Stability but More Acidic Hydrolysis Product Pattern
Open this publication in new window or tab >>Polylactide Stereocomplexation Leads to Higher Hydrolytic Stability but More Acidic Hydrolysis Product Pattern
Show others...
2010 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 11, no 4, 1067-1073 p.Article in journal (Refereed) Published
Abstract [en]

Poly-L-lactide/poly-D-lactide (PLLA/PDLA) stereocomplex had much higher hydrolytic stability compared to plain PLLA, but at the same time shorter and more acidic degradation products were formed. Both materials were subjected to hydrolytic degradation in water and in phosphate buffer at 37 and 60 C, and the degradation processes were monitored by following mass loss, water uptake, thermal properties, surface changes, and pH of the aging medium. The degradation product patterns were determined by electrospray ionization-mass spectrometry (ESI-MS). The high crystallinity and strong secondary interactions in the stereocomplex prevented water uptake and resulted in lower mass loss and degradation rate. However, somewhat surprisingly, the pH of the aging medium decreased much faster in the case of PLLA/PDLA stereocomplex. In accordance, the ESI-MS results showed that hydrolysis of PLLA/PDLA resulted in shorter and more acidic degradation products. This could be explained by the increased intermolecular crystallization clue to stereocomplexation, which results in an increased number of tie chains. Because mainly these short tie chains are susceptible to hydrolysis this leads to formation of shorter oligomers compared to hydrolysis of regular PLLA.

Keyword
structure-property relationships, ionization mass-spectrometry, degradation-products, poly(l-lactide), morphology, poly(lactide)s, polymerization, polyesters, copolymers, resistance
National Category
Polymer Chemistry Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-19392 (URN)10.1021/bm100029t (DOI)000276557300031 ()2-s2.0-77950805148 (Scopus ID)
Note

QC 20100525

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Tuning the Polylactide Hydrolysis Rate by Plasticizer Architecture and Hydrophilicity without Introducing New Migrants
Open this publication in new window or tab >>Tuning the Polylactide Hydrolysis Rate by Plasticizer Architecture and Hydrophilicity without Introducing New Migrants
2010 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 11, no 12, 3617-3623 p.Article in journal (Refereed) Published
Abstract [en]

The possibility to tune the hydrolytic degradation rate of polylactide by plasticizer architecture and hydrophilicity without introduction of new degradation products was investigated by subjecting polylactide with cyclic oligolactide and linear oligolactic acid additives to hydrolytic degradation at 37 and 60 degrees C for up to 39 weeks. The more hydrophilic oligolactic acid plasticizer led to larger water uptake and rapid migration of plasticizer from the films into the aging water. This resulted in a porous material more susceptible to further hydrolysis. During hydrolysis at 37 degrees C the mass loss was generally 10-20% higher for the material containing linear oligolactic acid plasticizers. The hydrolysis accelerating effect of the linear oligolactic acid is probably counteracted by the higher degree of crystallinity in the films containing oligolactic acid additives. The degradation process was monitored by measurements of mass loss, water uptake, molar mass changes, material composition changes, surface changes, and thermal properties. The water-soluble degradation products were analyzed by following pH changes and identified by electrospray ionization-mass spectrometry (ESI-MS). The time frame for formation of water-soluble products was influenced by the architecture and hydrophilicity of the plasticizer. Furthermore, the advantage with oligolactide and oligolactic acid plasticizers was clearly demonstrated as they do not introduce any new migrants into the degradation product patterns.

Keyword
degradation-product patterns, poly(lactic acid), mechanical-properties, poly(l-lactic acid), copolymers, caprolactone, pla
National Category
Polymer Chemistry Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-28604 (URN)10.1021/bm101075p (DOI)000285267500049 ()2-s2.0-78650288294 (Scopus ID)
Note

QC 20110117

Available from: 2011-01-17 Created: 2011-01-17 Last updated: 2017-12-11Bibliographically approved
3. Customizing the Hydrolytic Degradation Rate of Stereocomplex PLA through Different PDLA Architectures
Open this publication in new window or tab >>Customizing the Hydrolytic Degradation Rate of Stereocomplex PLA through Different PDLA Architectures
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2012 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 13, no 4, 1212-1222 p.Article in journal (Refereed) Published
Abstract [en]

Stereocomplexation of poly(L-lactide) (PLLA) with star shaped D-lactic acid (D-LA) oligomers with different, architectures and end-groups clearly altered the degradation rate and affected the degradation product patterns. Altogether, nine materials were studied: standard PLLA and eight blends of PLLA with either 30 or 50 wt % of four different D-LA. oligomers. The influence of several factors, including temperature, degradation time, and amount and type of D-LA oligomer, on the hydrolytic degradation process was investigated using a fractional factorial experimental design. Stereocomplexes containing star shaped D-LA oligomers with four alcoholic end-groups underwent a rather slow hydrolytic degradation with low release of degradation products. Materials with linear D-LA oligomers exhibited similar mass loss but released higher concentrations of shorter acidic degradation products. Increasing the fraction of D-LA oligomers with a linear structure or with four alcoholic end-groups resulted in slower mass loss due to higher degree of stereocomplexation. The opposite results were obtained after addition of D-LA oligomers with carboxylic chain-ends. These materials demonstrated lower degree of stereocomplexation and larger mass and molar mass loss, and also the release of degradation products increased. Increasing the number of alcoholic chain-ends from four to six decreased the degree of stereocomplexation, leading to faster mass loss. The degree of stereocomplexation and degradation rate were customized by changing the architecture and end-groups of the D-LA oligomers.

Keyword
Enantiomeric Poly(Lactic Acid)S, Bio-Based Polymers, Polylactide Stereocomplex, Crystallization Behavior, Poly(L-Lactic Acid), Spherulite Growth, Product Patterns, End-Group, Melt, Hydrophilicity
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-95108 (URN)10.1021/bm300196h (DOI)000303076200032 ()22394150 (PubMedID)2-s2.0-84860711835 (Scopus ID)
Funder
EU, European Research Council, NMP2-CT-2007-026515
Note
QC 20120522Available from: 2012-05-22 Created: 2012-05-14 Last updated: 2017-12-07Bibliographically approved
4. Long-term properties and migration of low molecular mass compounds from modified PLLA materials during accelerated ageing
Open this publication in new window or tab >>Long-term properties and migration of low molecular mass compounds from modified PLLA materials during accelerated ageing
2012 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 97, no 6, 914-920 p.Article in journal (Refereed) Published
Abstract [en]

The durability of polylactide during accelerated ageing and the entire degradation process were significantly altered by different low molecular mass additives and stereocomplexation. The samples were aged in air at 60°C and 90°C and the degradation process was followed by monitoring mass loss, molar mass, presence and formation of low molecular mass compounds, changes in surface structure and thermal properties. Stereocomplexation increased the long-term durability of polylactide materials. Mass loss and molar mass changes also indicated that addition of TiO 2 nanoparticles had a stabilizing effect at higher temperature and during longer exposure times. Interestingly addition of linear lactic acid oligomers resulted in lower mass loss compared to materials containing cyclic lactide oligomers. This is interpreted as a result of stronger interactions between the linear oligomers and PLLA chains, resulting in slower migration rate, which was also shown by ESI-MS analysis. However, the linear oligomer additives accelerated the molar mass decrease, probably due to the catalytic effect of the end groups. The stereocomplex displayed the greatest resistance towards degradation, a consequence of strong secondary interactions.

Keyword
Degradation, Degradation products, ESI-MS, Polylactide, Stereocomplex
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-96177 (URN)10.1016/j.polymdegradstab.2012.03.028 (DOI)000304641300011 ()2-s2.0-84860358383 (Scopus ID)
Note
QC 20120611Available from: 2012-06-11 Created: 2012-05-31 Last updated: 2017-12-07Bibliographically approved
5. Stereocomplexation between PLA-Like Substituted Oligomers and the Influence on the Hydrolytic Degradation
Open this publication in new window or tab >>Stereocomplexation between PLA-Like Substituted Oligomers and the Influence on the Hydrolytic Degradation
(English)Manuscript (preprint) (Other academic)
Keyword
Polylactide, degradation, stereocomplex, degradation products, ESI-MS
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-120119 (URN)
Note

QS 2013

Available from: 2013-03-28 Created: 2013-03-28 Last updated: 2013-04-03Bibliographically approved

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