Influence of stereo regularity on mechanical and thermal properties of poly(lactic acid)
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
The influence of stereo regularity in poly(lactic acid) (PLA) have been investigated, using poly(L-lactic acid) (PLLA) and poly(D,L-lactic acid) (PDLLA) with 4% D-lactide, to determine fatigue resistance. Samples were strain crystallized above Tg and studied with differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile testing. Both polymers exhibit heterogeneous characteristics in the amorphous phase observed by DSC and DMA, comprised according to the three phase model; of a mobile amorphous fraction (MAR, XMA), a rigid amorphous fraction (RAF, XRA) and a crystalline fraction (Xc). The effect of L/D ratio on crystallization kinetics and specific MAF was characterized with DSC. Its implications on mechanical properties after hydrated thermal conditioning, was observed on tensile stress-strain curves and alterations in glass transition dynamics with DMA. Enthalpy relaxation and fictive temperature was also studied with DSC to correlate structural relaxation with mechanical properties over time.
Place, publisher, year, edition, pages
PLA, glass transition, crystal structure, fatigue, relaxation behaviour
IdentifiersURN: urn:nbn:se:kth:diva-150790OAI: oai:DiVA.org:kth-150790DiVA: diva2:745016