The purpose of this report was to experimentally study the water-assisted injection molding process of poly-butylene-terephthalate
(PBT) composites. Experiments were carried out on an 80-ton injection-molding machine equipped with a lab scale water injection sys-
tem, which included a water pump, a pressure accumulator, a water injection pin, a water tank equipped with a temperature regulator,
and a control circuit. The materials included virgin PBT and a 15% glass fiber filled PBT composite, and a plate cavity with a rib across
center was used. Various processing variables were examined in terms of their influence on the length of water penetration in molded
parts, and mechanical property tests were performed on these parts. X-ray diffraction (XRD) was also used to identify the material
and structural parameters. Finally, a comparison was made between water-assisted and gas-assisted injection molded parts. It was found
that the melt fill pressure, melt temperature, and short shot size were the dominant parameters affecting water penetration behavior.
Material at the mold-side exhibited a higher degree of crystallinity than that at the water-side. Parts molded by gas also showed a higher
degree of crystallinity than those molded by water. Furthermore, the glass fibers near the surface of molded parts were found to be ori-
ented mostly in the flow direction, but oriented substantially more perpendicular to the flow direction with increasing distance from the
skin surface.
2006 Elsevier Ltd. All rights reserved.
Keywords: Water assisted injection molding; Glass fiber reinforced poly-butylene-terephthalate (PBT) composites; Processing parameters; B. Mechanical
properties; Crystallinity; A. Polymer matrix composites; Processing
An experimental study of the water-assisted injection molding of
glass fiber filled poly-butylene-terephthalate (PBT) composites
Shih-Jung Liu *, Ming-Jen Lin, Yi-Chuan Wu
Polymer Rheology and Processing Lab, Department of Mechanical Engineering, Chang Gung University, Tao-Yuan 333, Taiwan
Received 12 September 2005; received in revised form 29 June 2006; accepted 11 September 2006
Available online 7 November 2006
