• Structure and Property of Microinjection Molded Poly(lactic acid) with High Degree of Long Chain Branching

      Zhao, Z.-G.; Yang, Q.; Coates, Philip D.; Whiteside, Benjamin R.; Kelly, Adrian L.; Huang, Y.-J.; Wu, P.-P. (2018-08-22)
      Long chain branches (LCB) are successfully grafted to linear poly(lactic acid) (PLA) using functional group reactions with pentaerythritol triacrylate (PETA) and tetraethylthiuram disulfide (TETDS). Results show a high branching degree of PLA (∼49.5%) can be effectively obtained with adding only 1 wt % PETA, contributing remarkably to enhancing strain hardening. The density of the nuclei formed during nonisothermal crystallization for LCB-PLA samples is markedly increased contrasted with PLA, resulting in significantly enhancing crystallinity from 13.3% to 41%, the onset crystallization temperature (∼20 °C), and the crystallization rate. Interestingly, compared with mini-injection molding, the elevated wall shear rates (and corresponding shear stresses) prove to be beneficial to the creation of special crystalline morphologies (β-crystal form) and oriented structures under microinjection molding conditions, resulting in the improvement of tensile strength by ∼45 MPa.