Effect of the annealing procedure and the molecular weight on the crystalline phase morphology and thermal properties of polylactide

Abstract

The thermomechanical properties of poly(lactide) (PLA) are strongly related to its semicrystalline microstructure and morphology. Thermal annealing is a strategy to improve the crystallinity of PLA. However, the different techniques and specimen types needed for each kind of characterization could lead to misleading conclusions. In this work, annealed samples of three PLA grades with different molecular weights were studied by DSC, wide angle X‐ray scattering and polarized optical microscopy (POM) and the results are related to their thermomechanical and impact properties. Special focus is put on the POM results obtained by different approaches and the suitability of each of them to be related to the thermomechanical properties. By annealing medium molecular weight PLA specimens at 140 °C an important increase of the heat distortion temperature was obtained, which was not related to the spherulite size but to the combination of high crystallinity degree together with high α/α′ crystal type ratio. However, the impact properties of annealed PLA decreased with increase in the annealing temperature according to an increment in crystallinity and in the α/α′ crystal ratio. © 2019 Society of Chemical Industry

Lamellae orientation and structure evolution of reinforced poly(lactic acid) via equal channel angular extrusion

“…An endothermic shoulder peak before the melting peak was observed. This shoulder peak can be considered to be related to the α ′ to α phase transition, and the main peak is thought to be the melting of α form 33,34 . Compared with the annealed one, this shoulder peak increased to a higher temperature and became less pronounced.…”

“…This shoulder peak can be considered to be related to the α 0 to α phase transition, and the main peak is thought to be the melting of α form. 33,34 Compared with the annealed one, this shoulder peak increased to a higher temperature and became less pronounced. The melting temperature (T m ) shifted slightly to a higher temperature.…”

Effect of crystallinity and related surface properties on gene expression of primary fibroblasts

“… 32 Similar trend was observed for high molecular weight semicrystalline PLLA, which exhibited limited crystallisation due to high density of chains entanglement presented lower chain mobility. 38 Authors suggested that, the lower the molecular weight was, the higher the crystallisation rate of PLLA. Under an annealing process, chain mobility increased with temperature resulting in an increase of crystallinity (PCL45w, PCL80w).…”