Volume 31, Issue 3

An analytical method for estimating the bulk melt temperature in the injection molding process by means of in-mold temperature sensors was presented in Part A of this article. This method was validated using a transient cooling simulation of an injection molding process. The simulation considered the heat flux and heat accumulation in the mold starting from process startup until steady state was achieved. For the simulation, a full 3D model of the mold geometry was developed. The average coolant temperature and the initial cavity wall temperature were evaluated as boundary conditions. The first was found to provide a more accurate prediction of the bulk melt temperature although it increases the sensitivity of the method to the temperature measurement. Overall, the trends correlated well for both simulated and experimental data as well as the bulk temperature measurements.

Electrospinning is a fascinating technology for producing nanoscale fibers. In this study, jet velocities were investigated for the full jet range using microparticles as tracers. Significant differences were observed in the jet velocities as a function of the measuring position and direction. This suggests that the jets drive toward the collector and undergo jet separation after forming jet entanglements. The visual evidence confirmed the jet elongation data.

Four PET samples of different intrinsic viscosity values based on diverse manufacturing processes were characterized for their linear viscoelasticity using a parallel plate rheometer. Thermal stability and frequency sweep experiments were performed in the melt state at 270 °C. The influences of drying temperature, testing atmosphere (air or nitrogen), and preparation (granules vs. samples cut from compression molded sheets) were investigated. Results indicated that a higher drying temperature promoted complex viscosity significantly and compression molded sheets generated irreversible structural changes in harsh conditions. The samples measured in air decreased because of thermo-oxidation degradation, whereas that in nitrogen unexpectedly increased slightly because of polycondensation without surface renewal. The role of carboxyl end group towards PET thermal stability was found to be influenced by the atmosphere.

The ethylene methyl acrylate copolymer (EMA), for the first time, was melt blended with poly(lactic acid) (PLA) by a twin-screw extruder to toughen PLA. The phase morphologies, mechanical, and rheological properties of the PLA/EMA blends with six weight ratios were investigated. The results showed that the addition of EMA improves the toughness of PLA at the expense of the tensile strength, flexural strength and modulus to a certain degree, and results in the transition from brittle fracture of PLA into ductile fracture. The droplet-matrix morphology is observed in the PLA/EMA blends, in which the mean diameter of EMA droplets increases and its distribution widens gradually with increasing the EMA content. The PLA/EMA blends with three weight ratios (90/10, 80/20, and 70/30) display different characteristic linear viscoelastic properties in the low frequency region, which were investigated in terms of their complex viscosity, storage modulus, and Cole-Cole plots. The interfacial tension between the PLA and EMA is calculated using the Palierne model conducted on the 80/20 PLA/EMA blend, and the calculated result is 3.3 mN/m.

To improve the impact toughness of short glass fiber (SGF) reinforced polypropylene (PP) composite foams, maleic anhydride grafted ethylene-α-octene copolymer (mEOC) was employed as impact modifier and interfacial compatibilizer. And for comparison, mEOC was also introduced into PP/EOC/SGF composite foams. Then, the foaming qualities, interfacial structures and mechanical properties of samples against varying mEOC contents were examined and compared in detail. Results showed that adequate mEOC significantly improved the foamabilities of the composites, while the optimized mass fraction was 8% for PP/SGF composite foams and 3% for PP/EOC/SGF system. Increased mEOC facilitated the higher impact toughness, which was increased by 77% for PP/SGF composite foams, whereas only 5% for PP/EOC/SGF foams. However, the flexural strengths were just improved slightly, while compressive strengths decreased monotonically with mEOC for the investigated composite foams.

Styrenic copolymers comprising styrene, methyl methacrylate, and maleic anhydride were developed to improve the heat-resistance property of poly(methyl methacrylate) (PMMA). The optical, thermal, and mechanical properties were examined for the blend specimens prepared by an injection-molding machine using melt-mixed samples. It was found that the copolymers, which were miscible with PMMA, increase the glass transition temperature and therefore the Vicat Softening temperature. Furthermore, the blends were completely transparent as similar to PMMA.

The creeping flow of a polymeric melt in a converging pipe is analyzed using an in-house finite element code. An introduced power-law model considers the shear thinning behavior of the viscous liquid. Furthermore, distributive and dispersive mixing processes are evaluated with the mean strain function and the Manas-Zloczower mixing index, respectively. Using a parametric study, the dependency of the mixing criteria on the rheological and geometrical factors is investigated. Finally, a new analytical expression for the evaluation of the distributive mixing is suggested, based on simplifying assumptions and a curve fitting method.

This study investigates the abrasive water jet turning (AWJT) process of commonly used plastics, such as polytetrafluoroethylene (PTFE), castamide, and polyamide (PA), in engineering. Machining parameters were used as follows: nozzle feed rate (10, 30, and 50 mm min −1 ), abrasive flow rate (50, 250, and 450 g min −1 ), and spindle speed (1 000, 2 000, and 3 000 min −1 ). The effects of the machining parameters on the average surface roughness and material removal rate were investigated. According to results, average surface roughness and material removal rate were affected by the nozzle feed rate by 87.15 % and 82.48 %, abrasive flow rate by 9.84 % and 13.49 %, and spindle speed by 1.09 % and 0.08 %, respectively. Optimization results that the nozzle feed rate should be 10 mm min −1 , while the abrasive flow rate is 450 g/min and spindle speed is 3 000 min −1 in order to obtain the minimum surface roughness and maximum material removal rate.

A large amount of cork powder (CP) produced by cork industry ended up in landfills, they are the result of the crushing of natural floor (bark) cork oak, hence the need to recycle these wastes to prevent environmental problems. To this end, the work is to combine the powdered cork recovered with a thermoplastic material to provide a cork based composite (CPC) having physico-mechanical characteristics and thermal very interesting. Several formulations of composite materials based on PVC (as matrix), cork powder (as a charge) and a PVC-g-MA coupling agent, have been the subject of experimental study to evaluate the physical-mechanical and thermal properties. To investigate the combined effect of cork powder and PVC-g-MA on composite properties, the samples were manufactured by varying the content of PC (30 %, 40 % and 50 %) with two PVC-g-MA concentrations. Improving the stability of PVC which is accentuated in the presence of the coupling agent. In addition, it was found that the incorporation of the coupling agent has enabled the elimination of the adverse effect of cork powder, improving the tensile strength. The composite obtained in this study yielded some promising properties, even if building strategies to achieve greater strength and rigidity could beings needed for specific applications.

Polymer bonded magnets with a multipolar structure can be economically produced using the injection molding process for applications such as electric drives or sensor modules. Depending on the specific application, certain requirements of the multipolar bonded magnets, such as a high peak flux density or accurate pole length of each pole, must be assured. The multipolar magnetic structure of the parts can be applied during the injection molding process by incorporating a magnetic field inside the mold. Thus, the hard magnetic particles are oriented and magnetized directly in the injection molding process. The final properties of the multipolar molded magnets are affected by different parameters, such as the magnetic compound, the mold design and the processing parameters. This paper addresses the effects processing parameters have during the injection molding process. Additionally, the role the filler volume content plays with the properties of pole-oriented molded multipolar rings is also investigated. In particular, the magnetic characteristics, such as the maximum radial flux density, the pole length and the rate of the course of the flux density, were investigated. Further, the orientation of the particles and the influence of the varied parameters on the geometry of the rings were analyzed. It was found that the varied parameters do not significantly influence the accuracy of the pole length. The slope of the flux density curve is influenced by the peak maxima and varies slightly due to the high peak flux densities.

Micro-pillars forming in micro channels have been implemented by hot embossing. With dry etching and chrome photo mask, the silicon mold was fabricated using lithography process for manufacturing micro-pillars in micro channels. The hot embossing experiments are executed on the embossing machine by embossing the PMMA substrate and the silicon mold. Making the polymer filling in the concave cavity of the silicon mold is a difficulty, so the laws of polymer filling in the concave cavity were researched. The effects of three key embossing parameters including pressure, temperature and time on the PMMA replication accuracy were studied, and the optimal molding parameters were obtained. This work is instructive to fabricate microfluidic chips with micro-pillars.

Health regulations are becoming increasingly restrictive which leads to develop solvent free laminating processes. Hot melt adhesives represent an interesting solution to bond two pre-printed substrates of polymer for packaging applications for example, but their high viscosities require extruding the polymer formulation through important die gaps (between 0.5 mm and 1 mm) in order to limit the extrusion pressure. Thus, delivering a final very thin layer of hot melt (a few μm) between the polymer substrates requires applying very high draw ratios between the die and the contact point on the substrate. These high draw ratios would result in marked thickness and width instabilities (called draw resonance) when using usual stretching distances as in cast film (a few cm) or in coating thermoplastic layers on a metal or paper substrate (more than 10 cm). Surprisingly, reducing drastically the stretching distance (around 1 mm) and applying a differential pressure between the two sides of the melt allow postponing the instability occurrence. Nevertheless the processing window is narrow and the objective of the present paper is to describe the cotformatating process developed at Bostik Company, to characterize the drawing instabilities and to investigate the influence of different processing parameters. In addition, a numerical model explaining these surprising stabilizing conditions is proposed. This model results in the definition of a high speed coating processing window.

The aim of this study is to assess the effects of different parameters of the injection molding process in warpage, shrinkage, and mechanical properties of the plastic parts using the Taguchi method and the Analysis of Variance (ANOVA). The polyacetal copolymer (POM) and acrylonitrile-butadiene-styrene copolymer (ABS) were injected; and then the following processing parameters were analyzed: the mold temperature, holding pressure, holding time, melt temperature, cooling time, mold water flow, and injection speed. According to the results, statistically the most significant parameters in shrinkage were the mold temperature and cooling time for the POM molded parts; and the holding time and holding pressure for the ABS molded parts. The most significant parameters in warpage and flexural strength were the holding time and holding pressure for the POM and ABS parts, respectively. A multiple linear regression analysis was carried out to predict a theoretical ideal experiment to maximize the results.

To obtain the “high infrared radiation (IR) transmittance and low visible ray (VR) transmittance” necessary for a high-performance IR lens, cavity thickness and molding conditions were investigated experimentally for disk-shaped high-density polyethylene (HDPE). When injection molding and injection press molding were done using different cavity thicknesses, results showed that the molded part using the thinner cavity thickness maintained a semitransparent state. Simultaneously, they showed that higher IR transmittance was obtained. For high mold temperature and long cooling time, the increased core-layer thickness improved the IR transmittance. The VR transmittance decreased because crystallinity became higher. Furthermore, when injection press molding was conducted, the VR transmittance decreased because crystallinity became higher. IR transmittance and VR transmittance were obtained respectively as 65.4% and 6.4% when injection press molding was conducted at higher mold temperatures with longer cooling times.