Iranian Journal of Polymer Science and Technology
Year:2004 | Volume:17 | Issue:4 (ISSUE NO.72)|Papers Count:7

Extruders are by far the most important machines in polymer processing. Of these processes the reaction extrusion has recently attracted new interests. Reaction extrusion of thermosets has presented new difficulties in process uniformity and production continuity. To achieve a required degree of stability a special design of self-wiping screws for a co-rotating twin screw extruder has to be made. In this work such a screw has been designed and manufactured, and its performance has been checked for a reaction extrusion of melamine formaldehyde. The results of the stability of the process and the quality of the products are reported.

In this study, physical properties of high density poly ethylene such as degree of crystalline, softening point and its blends with paraffin wax were investigated. DSC Studies show two endothermic and exothermic peaks. The endothermic peak of polyethylene is narrow and that of the wax is broad. Rheological studies show a pseudo-plastic behavior for all the blends and as the wax content increases, the viscosity of blend at high shear rate decreases and the impact strength and softening point of blends decrease due to low strength of paraffin wax. The effect of wax content on shrinkage of the blends was also investigated. It was observed that an increase in wax content results in a decrease in shrinkage of the blend.

In this study, a linear carboxy-terminated polyester has been prepared from 1,6-hexanediol (HDO), neopentyl glycol (NPG), ethylene glycole (EG) and a terephthalic/adipic acid (93:7, TPA/APA) combination using a two-stage process. FTIR Spectroscopy was employed for structural characterization, gel permeation chromatography (GPC) was used for determination of number average molecular weight (Mn) and DSC technique was employed to investigate thermal behavior of the prepared resin. A hybrid polyester/epoxy powder coating was then formulated using the prepared resin and some physical and chemical properties of which were investigated. The results revealed that prepared resin is cured with epoxy resins in the presence of suitable catalyst, with reasonable mechanical properties for indoor applications.

To study tire tread compound extrudability is a very demanding process. Complicated flow geometry, and a broad range of operating parameters make predictions of process ability a difficult task. In this work the viscoelastic parameters, which affect the rheology of tire tread compound such as relaxation time, lk, and viscosity index, lk in generalized Maxwell model using two-parallel plates rheometer are determined. Then to simulate the flow of rubber compound through a capillary die a Fastflo software which works on mixed finite element (MFE) method is used. After calculation of the generalized viscoelastic Maxwell model parameters, the Fastflo software was used to simulate the flow of compound through a capillary die and laboratory extruder die. Comparisons between the simulation prediction and actual data show a good agreement between capillary die and laboratory extruder die. Numerical simulation in the Fastflo software was based on penalty method algorithm in FEM (finite element method).

Drying of solid particles is a process that is widely applied in industry. Since ester groups are very sensitive to hydrolysis, drying of polyester chips in production of polyester fibers is an important stage. In this study the effects of different drying temperatures of polyester chips in temperature range of 170-185ºC on the structure and properties of partial orientation yarns (e.g, tenacity, elongation, etc) have been investigated. Solution viscosities of polyester chips and fiber were also measured. The results showed that the drying temperature has some influence on the properties of yarn. In the case of lower temperatures (e.g, 170ºC) a loss of product quality such as deterioration in tensile strength and uneveness of yarn was observed. By increasing the drying temperature, the solution viscosity and dusting of polyester chips was increased and these dust particles caused in homogeneity in the melt flow.

The effect of an optical brightening agent (OBA) on optical properties of unbleached and bleached hardwoods CMP pulp bleached with different quantities of hydrogen peroxide and sodium borohydride was studied. The results indicated that the positive effect of OBA is higher with brighter pulps. Also, the effect of accelerated photo and thermal aging showed that OBA causes brightness stabilization during thermal aging, but it has no effect on photoaging. Bleaching with sodium borohydride could increase the brightness stability during photoaging.