Elucidating the effect of chain orientation on the dimensional change of a poly(lactic acid) composite containing a flexible fiber

Shrinkage is a major problem for plastic production after post-process annealing. The present study proposes a new method for controlling the dimensional change of poly(lactic acid) (PLA) during post-process annealing. A commercially available acrylic-modified poly(tetrafluoroethylene) (PTFE) was blended with PLA at 190 °C. It was dispersed to form a fibrous network structure in molten PLA. During extrusion and strand stretching, the PTFE fibers were easily oriented in the flow direction because of the hydraulic force. During post-process annealing, a PLA strand shrank once it was annealed beyond its glass transition temperature owing to orientation relaxation and isotropic crystallization with spherical texture. In contrast, the PLA/PTFE strand exhibited anomalous expansion in the machine direction, i.e., increases in length of approximately 9.3%, 4.0%, and 1.3% when annealed for 50 min at 65, 70, and 75 °C, respectively. The mechanism for this anomalous expansion was explained by anisotropic crystallization, i.e., trans-crystallization from the oriented PTFE fibers. This finding highlights a promising approach for controlling the dimensions of PLA products by manipulating molecular orientation during post-process annealing. • PTFE fibers with thickness of 130 nm were fabricated using an internal mixer. • PTFE fibers were easily oriented in flow direction to form pseudo-shish structure. • The highly-oriented structures of PLA developed from PTFE fibers during annealing. • The molecular orientation enhancement induced the expansion of PLA/PTFE fiber and film.