A new plasticizer for poly(L-lactide) (PLA)-poly(propylene glycol) (PPG) is proposed. The advantage of using PPG is that it does not crystallize, has low glass transition temperature, and is miscible with PLA. PLA was plasticized with PPGs with nominal Mw of 425 and 1000 g/mol. Poly(ethylene glycol) (PEG), long known as a plasticizer for PLA, with nominal Mw of 600 g/mol, was also used to plasticize PLA for comparison. The thermal and tensile properties of PLA and PLA with 5-12.5 wt % of the plasticizers were studied. In blends of PLA with PPGs the glass transition temperature was lower than that of neat PLA. Both PPGs enhanced the crystallizability of PLA albeit less than PEG. All of the plasticizers increased also the ability of PLA to plastic deformation which was reflected in a decrease of yield stress and in an increase of elongation at break. The effect was enhanced by the higher PPG content and also by lower molecular weight of PPG. A phase separation occurred only in the blend containing 12.5 wt % of PPG with higher molecular weight. The evidences of crazing were found in deformed samples of PLA with low plasticizer content, whereas the samples with higher content of plasticizers crystallized due to deformation.

Green composites of PLA with micropowders derived from agricultural by-products such as oat husks, cocoa shells, and apple solids that remain after pressing have been prepared by melt mixing. The thermal and mechanical properties of the composites, including the effect of matrix crystallization and plasticization with poly(propylene glycol), have been studied. All fillers nucleated PLA crystallization and decreased the cold-crystallization temperature. They also affected the mechanical properties of the compositions, increasing the modulus of elasticity but decreasing the elongation at break and tensile impact strength although with few exceptions. Plasticization of the PLA matrix improved the ductility of the composites.

Samples of linear polyethylene, neat and crosslinked by irradiation with electron beam, were subjected to heavy plastic deformation by plane-strain compression up to the true strain exceeding 2 (deformation ratio l > 8) at room temperature. Structural studies of deformed samples and investigation of long-term strain recovery demonstrated that the deformation of the neat, non-crosslinked HDPE is completely reversible above the melting point of the crystalline phase, provided that the applied true strain does not exceed e ¼ 1.0 (l ¼ 2.7). At higher applied strains, e > 1, an irreversible deformation component emerged gradually, and at e ¼ 2.1 (l ¼ 8.2), the permanent, truly irreversible, residual strain was approx. e res ¼ 0.36 (l ¼ 1.4). In contrast, samples of crosslinked HDPE above T m exhibited complete reversibility of deformation, irrespectively of an applied strain, and e res z 0. The source of permanent irreversible strain component in neat HDPE is a deformation-induced partial destruction of the molecular network of entangled chains within amorphous interlamellar layers. The principal mechanism found was chain disentanglement, which was supplemented by a very limited chain scission. In the case of crosslinked materials, the dense and relatively homogeneous molecular network appeared robust enough to avoid any damage. Consequently, the strain appeared here fully reversible upon melting of crystalline phase.