A simultaneous increase of both stiffness and extensibility ofpoly（ethylene glycol-co-cyclohexane-1,4-dimethanol terephthalate） （PETG）/polycarbonate （PC） blends prepared through the slit die extrusion-uniaxial c...A simultaneous increase of both stiffness and extensibility ofpoly（ethylene glycol-co-cyclohexane-1,4-dimethanol terephthalate） （PETG）/polycarbonate （PC） blends prepared through the slit die extrusion-uniaxial cold stretching process was observed. The stretched sheets have a unique mechanical character that an increased tensile modulus is accompanied by an increased extensibility with increasing the draw ratio. Especially, a sharp increasing of the extensibility is observed for PETG/PC （70/30 wt%） blends at draw ratios between 8.2 and 20.0, where a nine times increase of extensibility is achieved. The mechanism of stretching-induced superior extensibility is investigated via micrograph observation, rheometry and calorimetric analysis. The observed superior extensibility could be tentatively explained by the bridging effect of the PC microfibrils on the crack development during tensile failure.展开更多
The strain-induced crystallization behaviors of ultrasonic micro-injection molded poly(L-lactic acid)/poly(D-lactic acid)(PLLA/PDLA)samples from an amorphous state were investigated by stress-strain relations and in s...The strain-induced crystallization behaviors of ultrasonic micro-injection molded poly(L-lactic acid)/poly(D-lactic acid)(PLLA/PDLA)samples from an amorphous state were investigated by stress-strain relations and in situ wide angle X-ray diffraction(WAXD) measurements.The formation of direct strain-induced stereocomplex(SC) was evident.In samples molded at 50 and 80℃,this phenomenon can be attributed to the acceleration of the ordered structures due to the existence of a large number of SC nuclei.The SC nuclei are assumed to serve as the transient physical cross-links to initiate the strain-induced crystallization.The onset of strain-induced crystallization is analogous to the heating induced structural reorganization.Consequently,the observed strain-induced SC process can be considered a pseudo process,which is actually thermally induced.Upon further stretching,the actual strain-induced crystallization occurs with the exclusive formation of the homocrystallite(HC),while the preceding formed SC crystals undergo slight fragmentation during subsequent tensile deformation.At 120 ℃,due to the reduced number of SC nuclei within the sample,the occurrence of cold crystallization during stretching plays a more significant role than SC nuclei with respect to the strain-induced SC process,as demonstrated by in situ WAXD measurements upon annealing in both the static and stretched states.展开更多
基金supported by the National Natural Science Foundation of China(Nos.50533050,20874064 and 50873063)
文摘A simultaneous increase of both stiffness and extensibility ofpoly（ethylene glycol-co-cyclohexane-1,4-dimethanol terephthalate） （PETG）/polycarbonate （PC） blends prepared through the slit die extrusion-uniaxial cold stretching process was observed. The stretched sheets have a unique mechanical character that an increased tensile modulus is accompanied by an increased extensibility with increasing the draw ratio. Especially, a sharp increasing of the extensibility is observed for PETG/PC （70/30 wt%） blends at draw ratios between 8.2 and 20.0, where a nine times increase of extensibility is achieved. The mechanism of stretching-induced superior extensibility is investigated via micrograph observation, rheometry and calorimetric analysis. The observed superior extensibility could be tentatively explained by the bridging effect of the PC microfibrils on the crack development during tensile failure.
基金finicially supported by the National Natural Science Foundation of China (No. 52103047)。
文摘The strain-induced crystallization behaviors of ultrasonic micro-injection molded poly(L-lactic acid)/poly(D-lactic acid)(PLLA/PDLA)samples from an amorphous state were investigated by stress-strain relations and in situ wide angle X-ray diffraction(WAXD) measurements.The formation of direct strain-induced stereocomplex(SC) was evident.In samples molded at 50 and 80℃,this phenomenon can be attributed to the acceleration of the ordered structures due to the existence of a large number of SC nuclei.The SC nuclei are assumed to serve as the transient physical cross-links to initiate the strain-induced crystallization.The onset of strain-induced crystallization is analogous to the heating induced structural reorganization.Consequently,the observed strain-induced SC process can be considered a pseudo process,which is actually thermally induced.Upon further stretching,the actual strain-induced crystallization occurs with the exclusive formation of the homocrystallite(HC),while the preceding formed SC crystals undergo slight fragmentation during subsequent tensile deformation.At 120 ℃,due to the reduced number of SC nuclei within the sample,the occurrence of cold crystallization during stretching plays a more significant role than SC nuclei with respect to the strain-induced SC process,as demonstrated by in situ WAXD measurements upon annealing in both the static and stretched states.
