Authors Du, M. ; Jariyavidyanont, K. ; Boldt, R. ; Tariq, M. ; Fischer, M. ; Spörer, Y. ; Kühnert, I. ; Androsch, R.
Title Crystal-nuclei formation during injection-molding of poly (l-lactic acid)
Date 26.05.2022
Number 60187
Abstract Injection-molding of rather slow crystallizing poly (l-lactic acid) (PLLA) was analyzed regarding the formation of crystal nuclei at different distances from the skin in a standard test bar. The relative number of nuclei in the various regions of fully amorphous test bars was estimated by evaluation of the kinetics of cold-crystallization, being faster in the skin than in the core region of the component. Simulation of the cooling-rate- and shear-rate-profiles along the cross-section of the molded bar suggests that the different nuclei numbers in skin and core mainly are caused by the higher shear rate in surface-near regions, though being supercritical for shear-induced nuclei formation also in the core. The latter conclusion is derived by comparing both the cold-crystallization kinetics and semicrystalline morphology with those of non-injection molded PLLA. The simulated shear-rate data, after conversion into specific-work-of-flow data, were found significantly exceeding the critical specific work of flow for shear-induced nuclei formation, being around 25 kPa, in all regions of the component. The results of the present study successfully demonstrate that knowledge about the crystallization kinetics of the sheared and quiescent melt of PLLA can be used to predict structure formation in industrial processing.
Publisher Polymer
Citation Polymer 250 (2022) 124897

Back to list