Volume 25, Issue 3

The ability of engineering polymers to resist scratching action has rapidly become a vital requirement for diverse industrial applications because scratches may greatly reduce the life cycle of the components. Therefore, the present work aims to study the possibility of using roller burnishing process to enhance the scratch resistance of polymers to a single pass scratching action. The effects of burnishing feed rate and roller contact width on the scratch hardness of poly(oxymethylene) and polyurethane were considered. The results revealed that low burnishing feed rate and smaller roller contact width led to an increase in scratch hardness for both polymers. The scratch fractures were also observed using SEM to study the changes in wear modes.

We present the preparation of polyamide 6 (PA6)/Vapor Grown Carbon Fiber (VGCF) composites by melt compounding. Two commercialized forms of PA6 with different melt flow rates (herein named PA6-low and PA6-high.) and two VGCF, VGCF-H (aspect ratio: 40) and VGCF-S (aspect ratio: 100) were used in this study. Young's modulus and the yield strength increased when small amount of VGCF (e.g. 1 wt.%) was added to PA6, and the properties of PA6-low/VGCF composites increased with a decrease in the aspect ratio of VGCF. According to scanning electron microscopy (SEM) observations, the dispersion state of VGCF in PA6-low/VGCF-S composites is superior to the PA6-low/VGCF-H composites. This may be due to the weakening of tensile properties caused by cracks between the adjoining crystals generated by the large amount of VGCF that act as nucleants. Hence, the aspect ratio of VGCF has an influence on the tensile properties of PA6/VGCF composites. The mechanical properties were shown to increase with VGCF-H length. Matrix viscosity and the screw rotation speed were also found to influence the mechanical properties of PA6/VGCF-H composites.

A model of agglomerate break-up, incorporating both rupture and erosion, is employed to predict the dynamics of filler size distribution in a plasticating single screw extruder. Filler spatial distribution along the extruder length was also ascertained and direct comparison of experimental and computational data proved to be satisfactory. The method was also used to investigate the effect of material properties, operating conditions and extruder geometry on the dynamics of agglomerate dispersion along a single screw extruder. Generally, dispersion levels were primarily governed by the magnitude of the hydrodynamic stresses developed in the extruder and the residence time in the melt.

This paper deals with the study of poly(ethylene terephthalate) (PET) fiber modification by antimicrobial substances following the crazing mechanism. The highest mean number of crazes and their maximal degree of opening in PET fibers subjected to tension in surface-active bactericidal liquids are reached when the plastic flow of PET begins and necks appear on the fibers. Further straining of the fibers results in a gradual transformation of the material into a fibrillar structure of strands that close the crazes. It is established that the amount of the bactericidal liquid captured by the crazes is 0.9 to 3.3 wt.% of the PET material and that the liquid localizes predominantly in the polymer amorphous phase. PET fibers treated by the developed liquids using the procedure developed preserve their antimicrobial properties after 10 to 50 cycles of heat-wet treatment.

The present work describes the processing and studies the erosion wear characteristics of bamboo fiber reinforced epoxy composites filled with SiC particulate. The mechanical properties of these composites are evaluated and are then compared with those of a similar set of SiC filled glass-epoxy composites. The solid particle erosion characteristics of the bamboo-epoxy composites have also been studied and the experimental results are compared with the reported erosion test results on glass-epoxy composites under similar test conditions by Biswas and Satapathy (2009). The influence of particulate filler on the erosion wear response of composites has been critically analyzed using Taguchi experimental design. This systematic experimentation has led to determination of significant process parameters and material variables that predominantly influence the wear rate of the particulate filled glass-epoxy and bamboo-epoxy composites. The comparative study indicates that although the bamboo based composites exhibit relatively inferior mechanical properties, their erosion wear performance is better than that of the glass-epoxy composites.

A composite model has been developed to simulate the extrusion process for intermeshing counter-rotating twin-screw extruders. An experimentally based melting model, solids conveying model, and new improved metering model, were combined to develop this formulation. The procedure for global design of a flood feed intermeshing counter-rotating twin screw extruder is presented. Illustrative calculations are made for polyvinyl chloride and high density polyethylene in this type of machines with different screw designs. Computations are made for axial variation of the fill factor, pressure, temperature and melting profiles. Simulations were found to match with experimental results well. The model was also applied to scale-up.

The injection molding of an optical grating was studied using two different polycarbonates. The grating had period 10 μm and peak-to-valley distance ∼1 μm. Parts were molded using different holding pressures and mold temperatures. After production, the parts were annealed at 100°C. The replication was investigated using white light interferometry (WLI) before and after annealing. WLI was performed using high definition vertical-scanning interferometry (HDVSI) to resolve the details of the molded gratings with a noise level below 2 nm. It was observed that increasing the holding pressure could have either a positive or a negative effect on the replication. When the microfeatures were not fully filled, an increased holding pressure improved the definition of the features. However, for both polymers, it was observed that the replication as a function of holding pressure started to drop when the holding pressure was increased above an optimal value. This could be due to an elastic recoil occurring after releasing the holding pressure. The peak-to-valley distance of the grating was reduced after annealing. This effect was larger for parts molded using a low mold temperature. This is probably due to a higher cooling rate giving higher internal stresses, which will relax during annealing.

The peroxide-initiated degradation of polypropylene is simulated by means of a one-dimensional (1D) reactive extrusion (REX) model. Two scale-up rules, namely, constant thermal time and specific energy consumption (SEC) are evaluated for co-rotating intermeshing twin screw extruders (COITSEs) of various sizes. The weight-average molecular weight (Mw) and the polydispersity index (PDI) are selected as the evaluation parameters for testing the scale-up procedures being analyzed. The results for the simulated operating conditions show that when the REX operation is scaled-up under constant thermal time, very good agreement is obtained between the Mw and PDI of the larger extruders and the values of these parameters corresponding to the reference extruder. For the constant SEC approach, more significant variations are observed for both of the aforementioned parameters. In the case of the constant thermal time scale-up approach, the effect of operating conditions of the reference extruder on the scaled-up operation is further analyzed. For a constant screw speed, when the reference mass throughput increases the predicted time of extrusion increases. Regarding the temperature of reaction, the higher increase of this parameter corresponds, in general terms, to the lower mass throughputs and higher screw speeds specified for the reference extruder.

A model for solid agglomerate dispersion in single screw extruders is proposed. The model combines numerical simulations of flow patterns in the metering section of a single screw extruder with a Monte Carlo method of clusters rupture and erosion mediated by a local fragmentation number. Particle size distributions and Shannon entropy are used for mixing characterization. The model is quite general and can be adapted for different polymer-additive systems as well as for different processing equipment.