Regulating Mesophase via Melt Volume Pulsation on an Industrial Scale for Self-Toughening and Self-Reinforcing of Polyethylene Terephthalate

The enhanced toughness and balanced strength without sacrificing transparency can be achieved in polyethylene terephthalate (PET) injection-molded products by constructing ordered mesophase, but it is difficult for the present approaches to directly fabricate injection-molded products with ordered mesophase from melt because of the metastable microstructure of ordered mesophase. To address the challenge, this study employs volume-pulsation injection molding (VPIM) to introduce a vibration force field to achieve ordered mesophase formation of PET directly from melt via melt volume pulsation. According to wide-angle X-ray diffraction, differential scanning calorimetry, small-angle X-ray scattering, and dynamic mechanical analysis, molecular chains are induced to form ordered mesophase below 1 Hz, while the ordered mesophase is further developed into crystallite above 1 Hz. The ordered mesophase formed below 1 Hz is ascribed to the moderate collision of disentangled oriented PET chains under the low-frequency force field. Mechanical properties were improved, resulting from the formation of ordered mesophase. The tensile modulus and toughness of VPIM samples at 0.7 Hz are increased by 11.11 and 149.74%, respectively, compared with those of conventional injection molding specimens. The ductile–brittle transformation was observed above 1 Hz because of the transition from ordered mesophase to crystallite. This paper provides new insights into the precise regulatory mechanism of the condensed state structure and gives scientific guidance in the advanced processing of polymeric materials.