Dynamic Melt Manipulation During Injection Molding Process for Enhancement of Semi-crystalline Material Properties

Shear rates are known to have significant effect on crystallization development of polymeric materials during processing and performance of the parts fabricated therefrom. The primary objective of this research was to gain fundamental insight on the effect of imposed shear rates by dynamic melt modulation during injection molding on the crystallinity development of PLA and the associated properties. The dynamic melt modulation was achieved by a Dynamic & Intelligent Shear-Controlled Injection Molding (DISC-IM) instrument that utilized an in-house developed control system capable of oscillating the injection screw. The melt modulation process proved to be an efficient processing technique for enhanced properties in a particular commercial grade of PLA that contained various additives. The cycle time was reduced by 40 % and total crystallinity was increased by ~50% during DISC-IM as compared to the conventional injection molding under similar conditions. The oscillatory movements also promoted the formation of α phase crystalline structures on the surface layer of the samples. The crystallization behavior of neat PLA was dramatically enhanced by 1wt.% of orotic acid. Introduction of DISC-IM enhanced the crystallinity of PLA-OA blends from 25% to 56% at a mold temperature of 70℃. Although, the overall crystallinity was relatively similar for different DISC-IM conditions, the crystalline phases that were formed was different. DISC-IM process promoted the formation of ά phases for PLA-OA blends.