Volume 24, Issue 4

Water assisted injection molding technology has become one of the most important methods to manufacture hollow plastic parts in recent years, due to its light weight, relatively lower resin cost per part and faster cycle time. This report aims to present a review of the development and progress of the water assisted injection molding technology. The tooling used for the process is introduced. The interaction between the assisting water and the polymer melt during molding is discussed, and insight into the penetration behaviors of the fluid is summarized. In addition, comparisons have been made between the gas-assisted injection molding and water assisted injection molding processes.

Rubber compounds have high viscoelastic property. One of the viscoelastic behaviors shown in profile extrusion is an extrudate swell and circulation flow at the corner of inside of die. Application of viscoelastic model to a capillary extrusion has been investigated in this study. Experiments and simulations have been performed using Fluidity Tester and commercial computational fluid dynamics (CFD) code, Polyflow respectively. Die swell of rubber compounds in a capillary die were predicted using a non-linear differential viscoelastic model, Phan-Thien and Tanner (PTT) model for various relaxation times and relaxation modes. As relaxation time and number of relaxation mode increase, die swell increases. The results of simulations were compared with the experiment. Pressure and velocity distributions, and circulation flows at the corner of reservoir have been analyzed through computer simulation. Two and three relaxation modes with large range of relaxation time examined in this study showed good agreement with experimental results of die swell and well represented circulation flow at the corner of reservoir in the capillary die.

We have studied the structural characteristics of the cross-sections of injection molded parts of various crystalline polyolefins including polyethylene (PE), isotactic polypropylene (PP), isotactic poly(butene-1) (PB1) and isotactic poly(4-methylpentene-1) (P4MP1). Polarized light microscopy, birefringence and wide angle x-ray diffraction pole figure analysis were used to investigate the samples. In most cases, high orientations were observed near the mold wall and isotropic molded part cores were found. However, highly oriented mold core regions were found in P4MP1. Significantly different types of crystalline orientation near the mold wall were observed among the various polyolefins. We represent the development of these differences through the components of a crystalline orientation tensor which represent changes in the state of orientation between melts in the mold prior to crystallization and the final crystalline molded part.

Rheological and mechanical properties of extruded wood plastic composites have been investigated for the purpose of providing a better understanding of processing conditions in profile extrusion for this novel class of thermoplastics composites. The basic formulations prepared for the study were comprised of 60 wt.% HDPE, with or without LLDPE-MAH as coupling agent, compounded with up to 40 wt.% of wood flour and lubricant. Capillary and rotational rheometers were employed to measure the rheological properties of the melt composite. A cooled die at the end of a single screw extruder was used for the extrusion of rectangular profiles having smooth surfaces and edges. Finite element flow simulation was used for the interpretation of the experimental data. Once extrusion steady conditions were achieved in the die, linear output was monitored and profile samples were cut for determination of flexural modulus and strength. The results showed that flexural properties can be influenced by many factors such as, coupling agents, lubricants, processing conditions, die pressure drop and cooling at the die. Linear speed of HDPE wood-plastic profile extrusion and end-use properties are strongly influenced by combination of these factors.

The miscibility of poly(vinyl chloride) (PVC) and poly(ethylene oxide) (PEO) blends was investigated by using differential scanning calorimetry (DSC), refractive index measurements and x-ray diffraction (XRD) analysis. The negative Flory-Huggins interaction parameter, χ 12 from the melting point depression of PEO by the blending of PVC shows that the interaction between PVC/PEO occurs. A refractive index measurement was performed to show that the miscibility of PVC/PEO blends occurs not only in solid form but also in solution form. The linear variation with composition of the refractive index of the polymer blend solutions in THF at 28°C, 40°C and 50°C indicates the miscibility of PVC with PEO. The shift in peaks in XRD of PEO by the blending of PVC is a characteristic evidence of complexation between PVC and PEO.

Zinc surfactant (ZS) is added into natural rubber (NR)/silica/TESPD (bis (triethoxysilyl propyl) disulfide) and silicone rubber (SR)/NR/silica/TESPD compounds and these compounds are vulcanized. The addition of the ZS shows significant improvements on mechanical properties on both compounds. It increases the torque maximum values of the compounds as well as the tan values, which is an indirect implication that the vibration isolation property is increased. It shows the presence of zinc ion in the ZS helps silane coupling with double bond in the rubber chain. This results in improved mechanical properties such as the modulus, tensile strength, elongation at break, and hardness.