Supertoughened Polylactide Binary Blend with High Heat Deflection Temperature Achieved by Thermal Annealing above the Glass Transition Temperature

Abstract

Through thermal annealing above the glass transition temperature, a supertoughened binary blend with the highest notched Izod impact strength of 98 KJ/m 2 was achieved, which was about 52 times of that of neat polylactide (PLA; 1.9 KJ/m 2 ). The binary blend was composed of biocompatible and biodegradable PLA and ethylene−acrylic ester−glycidyl methacrylate terpolymer (EGMA) elastomer at the composition of 80/20 PLA/EGMA. For one toughened binary blend with the notched Izod impact strength of 94 KJ/ m 2 , its tensile elongation at break was kept above 120%. Moreover, this supertoughened binary blend also displayed a much higher heat deflection temperature for application. Thermal annealing induced crystallization of the PLA matrix in the blend, and a linear correlation between the notched Izod impact strength and crystallinity was revealed. The possible toughening mechanism for the PLA/EGMA 80/20 blend with thermal annealing was analyzed from the viewpoint of negative pressure effects, as imposed on EGMA elastomeric particles during the quench process and thermal annealing thereafter. Decreases of the glass transition temperatures for the EGMA elastomeric particles in the blend were observed for both the quench and thermal annealing processes, which originated from asymmetric thermal shrinkages between the EGMA elastomeric phase and PLA matrix phase.

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

“…Melt blending PLA with high HDT polymers such as PMMA and PC has been reported to obtain high HDT blends, but with the sacrifice of the biodegradability of PLA. Normally, the PLA content in these blends is controlled at a low level, and sometimes annealing is also needed to increase the HDT . Introduction of fillers such as layered silicate has been reported to be able to improve the HDT of PLA, but only for annealed samples …”

Improvement in Low Temperature Izod Impact Strength of SAN/ASA/HNBR Ternary Blends Considering Competing Effects of Glass Transition Temperature and Compatibility

“…Those T g s shift to low temperature about 4°C ~ 5°C than that of pure HNBRs. The same phenomenon has taken place constantly in the system of elastomer toughened polymers . It results from the mismatch of thermal expansion coefficients between elastomer and polymer matrix .…”

“…The same phenomenon has taken place constantly in the system of elastomer toughened polymers . It results from the mismatch of thermal expansion coefficients between elastomer and polymer matrix . The different thermal expansion coefficients of elastomer and polymer matrix will lead to a tensile force (i.e., negative pressure) on elastomer, which will increase the free volume fraction of elastomer.…”

Super‐Toughened Heat‐Resistant Poly(lactic acid) Alloys By Tailoring the Phase Morphology and the Crystallization Behaviors

“…The low crystallization rate makes that the PLA products produced from conventional molding processes like injection molding with a high cooling rate is nearly amorphous. Therefore, great efforts are devoted to toughening and heat‐resistant modification of PLA in recent decades …”

“…The amorphous parts of PLA will soften when the ambient temperature reaches its glass transition temperature ( T g , around 60 °C), and only the PLA crystal region melting at around 170 °C can withstand the high temperature . Therefore, increasing the crystallinity of PLA is the key to enhance its heat resistance, which can be effectively realized by annealing treatment above the T g of PLA . For example, the HDT of the PLA/EGMA blend was increased from 54.2 to 61.0 °C (under the loading stress of 1.8 MPa) with an annealing treatment at 90 °C for 2.5 h …”