Simulation of Injection Molding Using a Model with Delayed Fiber Orientation
(331-339) International Polymer Processing #3 (2011)
Vélez-García et al of Virginia Tech, Virginia proposed a simple alternative to the delay in fiber orientation evolution based on the Folgar-Tucker model to improve predictions of fiber orientation in injection molded parts.  Predictions based on this model and model parameters fitted to data from simple shear experiments were compared with experimentally determined fiber orientation in a center-gated disk. Three methods of fitting to simple shear data were assessed to obtain the isotropic diffusivity and the slip parameter. The model parameters and orientation data evaluated at the entry, lubrication and near-end-of fill regions in a center-gated disk for 30 wt.% short glass fiber-filled polybutylene terephtalate (PBT) were obtained from earlier efforts in our laboratory. Simulation results based on the Folgar-Tucker model with the slip correction using customarily assumed inlet orientation being random and experimentally measured at the gate disagreed with measured orientation values at certain positions along the disk. However, improvement in the prediction of orientation due the slip correction was found at the core and transition layers in the lubrication region.  The use of inlet conditions washes out quickly in the absence of the slip correction and induced a general reduction of orientation towards the center of the sample causing underestimation of orientation at the entry and lubrication region. Model predictions combining the slip correction and experimentally determined orientation at the gate are in agreement with the experimental data for the core layers near the end-of-fill region.  (RDC 7/5/2011)

Fiber length, thermal, mechanical, and dynamic mechanical properties of injection-molded glass-fiber/polyamide 6,6: plasticization effect
(488-498) Journal of Reinforced Plastics and Composites 30 #6 (2011)
Abstract
Hassan et al of the University of Malaya, Malaysia, showed that more fiber degradation occurred during processing of the composites with higher fiber loading.  With moisture uptake, there were no significance changes in the melting temperature, crystallization temperature, and enthalpy of crystalline; however, degree of crystallinity and enthalpy of melting decreased. Tensile strength, tensile modulus, flexural strength, and flexural modulus decreased with moisture uptake, while tensile strain and flexural displacement increased. DMA study showed that tan delta at room temperature and tan delta maxima increased with moisture absorption, while temperatures at maximum tan delta in α- and β-transition regions decreased.  (RDC 5/25/2011) (See  Polyamides)