Tailoring the thermal and mechanical properties of injection‐molded poly (lactic acid) parts through annealing

Abstract

The effect of cold‐crystallization on poly (lactic acid) (PLA) injection‐molded parts was systemically investigated at different annealing temperatures (80/100/120°C) and annealing times (0.5/1/1.5/2 hr). The relative crystallinity (Xc) and crystal form (α' and α) of samples was investigated by differential scanning calorimetry (DSC) and wide X‐ray angle diffraction (WAXD). The dependence of the thermal and mechanical performance on relative crystallinity and crystal form/morphology was discussed in detail. A linear relationship between the increment of heat distortion temperature (HDT) and that of Xc was found. The tensile strength, tensile modulus and storage modulus all increased with annealing time and annealing temperature, while the tensile toughness presented a different behavior. The elongation at break for specimens reached a maximum value of 16.9% after annealing at 80°C for 2 hr, which is a threefold improvement compared to PLA samples prepared without annealing. This work suggests that annealing is an effective method for tailoring the physical properties of PLA products.

Extrusion and Injection Molding of Poly(3-Hydroxybutyrate-co-3-Hydroxyhexanoate) (PHBHHx): Influence of Processing Conditions on Mechanical Properties and Microstructure

“…These results differ from a study on PLA, where almost no crystallization was observed after molding at room temperature or up to 50 °C [60,61]. Crystal formation and enlargement in PLA was achieved by post-annealing at temperatures of 80-120 °C, with a maximal increase of elongation at break when annealing occurred at 80 °C for 0.5 and 2 hours [61]. As the mold temperature M has no effect on the crystallinity of the injection molded PHBHHx, other differences in microstructure, orientation effects, in particular, are investigated hereafter to account for the observed variations in mechanical properties.…”

“…The crystallinity remains constant with increasing mold temperature M, around ±38-39% (Table 10). These results differ from a study on PLA, where almost no crystallization was observed after molding at room temperature or up to 50 °C [60,61]. Crystal formation and enlargement in PLA was achieved by post-annealing at temperatures of 80-120 °C, with a maximal increase of elongation at break when annealing occurred at 80 °C for 0.5 and 2 hours [61].…”

Biodegradation evaluation of poly (lactic acid) for stent application: Role of mechanical tension and temperature

“…Intramolecular transesterification reaction is the main reason of thermal degradation of PLA, which leads to creation of cyclic oligomers of lactic acid. Applying heat stresses on PLA leads to unrecoverable changes in chemical and physical properties of the material 50,51 . This chemical processes that occurs during degradation can affect the polymer chemical composition and physical parameters.…”

Nonisothermal crystallization behavior and mechanical properties of poly(lactic acid)/ramie fiber biocomposites

“…The loading stress was 0.455 MPa and the heating rate was 2 C/min. The temperature at which the samples deflected by 0.2% (ε = 0.2%) [26,27] was defined as the HDT.…”

“…The melt temperature was set to 200 C, and the mold temperature was 50 C. The detailed dimensions of the samples and processing parameters were reported in our previous work. [26] For convenience, the RF reinforced PLA composites are defined as xRF, where x represents the RF content or percentage.…”