Studies on why the heat deflection temperature of polylactide bioplastic cannot be improved by overcrosslinking

Abstract

The high temperature application of polylactide (PLA) has been greatly limited by its low heat deflection temperature (HDT). As a slow crystallizing material, the HDT of amorphous PLA is mainly determined by its low T g value, near 55°C. In this work, PLA was chemically crosslinked, and the HDT of the crosslinked PLA was evaluated from two aspects—crystallization ability improvement and chain mobility limitation at T g of the PLA. The crystallization rate is improved by crosslinking because of the increased nucleation efficiency, and reached the highest level at moderate crosslinking. The final crystallinity is, however, still far lower than the crystallinity threshold for enhancing HDT of PLA. More importantly, T g of the PLA is not influenced by the crosslinking, even the average molecular weight between the crosslink points reaches as low as 1654 g/mol. The experimental research and theoretical calculations indicate that, to improve the HDT of the PLA, conformational restriction on the PLA chains should be focused on the segments with less than, at least, 14 repeating units. The fundamental reason why the HDT of PLA cannot be improved by crosslinking is investigated to guide the future structure design for high HDT PLA products.

The Effect of Surface Treatment with Isocyanate and Aromatic Carbodiimide of Thermally Expanded Vermiculite Used as a Functional Filler for Polylactide-Based Composites

“…The list of mean HDT values obtained for PLA and its composites is presented in Figure 11 . According to Wu et al, the possibility of improving HDT due to the partial crosslinking of the PLA structure as an effect of interactions with CE bonded to filler may be neglected [ 66 ]. An increase in HDT value in PLA is usually associated with an increased share of the crystalline phase [ 67 ].…”

The Use of Agricultural Waste in the Modification of Poly(lactic acid)-Based Composites Intended for 3D Printing Applications. The Use of Toughened Blend Systems to Improve Mechanical Properties

“…In addition to compounds such as SAGM, which are functionalized with oligomers, peroxides or isocyanates are also used. However, problems with the proper dosing of many compounds and the possibility of blend structure cross-linking [28] make chain extenders gain popularity as effective compatibilizers. Reactive CE compatibilizers significantly improve the toughness and elongation at the break of the PLA-based blends, which was already confirmed by many studies [18,[29][30][31][32].…”

Temperature Influence on Additive Manufactured Carbon Fiber Reinforced Polymer Composites

“…Several studies have shown that PLA, the polymer matrix employed in this FDM process, has a deflection temperature (HDT) near 55 • C [52,53]. HDT is a measure of the resistance of a polymer to deformation (stiffness of material) when subjected to stress loading at elevated temperatures.…”