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Tuning the polylactide hydrolysis rate without introducing new migrants
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The possibility to control and tune the hydrolytic degradation rate of polylactide without introducing any new degradation products was investigated by subjecting polylactide with cyclic or linear oligolactic acid additives, and a stereocomplex between the L- and D-enantiomers of polylactide to hydrolytic degradation at 37 and 60 °C for up to 39 weeks. The degradation was monitored by measuring mass loss, molar mass changes, water uptake, changes of surface structure, crystallinity and thermal properties. The degradation product pattern was followed through pH measurements and by electrospray ionization-mass spectrometry (ESI-MS).

Rapid migration of additives from the material into the aging medium was observed in the case of the more hydrophilic linear oligolactic acid additives. The mass loss at 37 °C was generally 10-20 % greater for the material containing linear additives instead of cyclic additives. The hydrolysis accelerating effect of the linear additives may be counteracted by the facilitated crystal formation of the short chains. Micrographs showed formation of holes on the surface of the material containing linear additives during degradation. This may be a result of migration of phase separated linear additives. Phase separation might take place in the material as the crystallinity increases. The stereocomplex had a higher hydrolytic stability, which is explained by the strong interactions between the complementary chain structures. At 37 °C, the observed mass loss was generally 15 % lower for the stereocomplex compared to the material containing the cyclic additives. However, a larger amount of short hydroxy acids was released from the stereocomplex material, as shown by the large pH drop and the degradation product pattern analysed using ESI-MS. This can be explained by increased intermolecular stereocomplex crystallisation, which results in a larger number of tie-chains between crystals which are susceptible to hydrolysis and facilitate the formation of shorter hydrolysis products. Hydrolysis at 60 °C, i.e. above the glass transition temperature, was drastically faster and the differences between the materials were not as obvious as at the lower temperature. A large advantage using different forms of lactide or lactic acid as additives is that no new migrants are introduced into the degradation product pattern.

Abstract [sv]

Möjligheten att kunna kontrollera och anpassa nedbrytningsbeteendet hos nedbrytbara material är av yttersta vikt för att kunna framställa mångsidiga material och då ha möjlighet att använda nedbrytbara material i ett större antal kommersiella tillämpningar. Både vid användning som förpackningsmaterial och i biomedicinska applikationer är det viktigt att materialet bryts ner på ett kontrollerat och säkert sätt. 

I denna studie undersöktes möjligheten att styra och reglera den hydrolytiska nedbrytningen av polylaktid utan att införa nya nedbrytningsprodukter. Tre material, polylaktid med tillsats av cykliska laktidoligomerer, polylaktid med tillsats av linjära mjölksyraoligomerer och ett stereokomplex av L- och D-enantiomerna av polylaktid, utsattes för nedbrytning i vatten och i fosfatbuffert vid två olika temperaturer, 37 och 60 °C, i upp till 39 veckor. Nedbrytningsprocessen följdes genom mätningar av massförlust, vattenabsorption, ytförändringar samt förändringar av molekylvikt, kristallinitet och av termiska egenskaper. Nedbrytningsprodukterna undersöktes med pH-mätningar och elektrospray jonisering-mass spektrometri (ESI-MS). De linjära, och följaktligen mer hydrofila, mjölksyraoligomererna migrerade snabbt från materialet och massförlusten för materialet modifierat med linjära mjölksyraoligomerer var generellt 10-20 % högre jämfört med materialet modifierat med cykliska laktidoligomerer. De linjära mjölksyraoligomererna bidrog till en ökad hydrolyshastighet, detta kan dock motverkas något av att de korta kedjorna kan underlätta kristalltillväxt under hydrolys. Det stereokomplexa materialet hade bättre hydrolytisk stabilitet. Detta beror på de starka interaktionerna mellan de komplementära L- och D-kedjorna. Massförlusten var cirka 15 % lägre för stereokomplexet jämfört med materialet modifierat med cykliska laktidoligomer. En större mängd korta hydroxysyror lämnade det stereokomplexa materialet vid nedbrytning. Detta observerades genom en stor sänkning av pH-värdet och genom profilen av nedbrytningsprodukterna via analys med ESI-MS. Förklaringen till detta kan vara en ökad mängd intermolekylära stereokomplexa kristaller som resulterar i ett stort antal korta kedjor som binder samman kristallerna. Dessa kedjor är mest mottagliga för hydrolys vilket resulterar i att korta kedjor avges som hydrolysprodukter. Den hydrolytiska nedbrytningen vid 60 °C, alltså över glastransitionstemperaturen, var betydligt mycket snabbare, och skillnaden mellan materialen var inte lika stor som vid den lägre temperaturen.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute ot Technology , 2011. , 35 s. p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:25
Keyword [en]
polylactide, sterocomplex, plasticizer, degradation, degradation products, ESI-MS
National Category
Biochemistry and Molecular Biology Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-32348ISBN: 978-91-7415-921-9 (print)OAI: oai:DiVA.org:kth-32348DiVA: diva2:410124
Presentation
2011-04-29, 13:00
Opponent
Supervisors
Note
QC 20110412Available from: 2011-04-12 Created: 2011-04-12Bibliographically 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

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