Volume 31, Issue 6-7

A melt blending process was used to prepare poly(lactic acid) (PLA)/metallocene catalyzed polyethylene octene copolymer (POE) blends in order to toughen PLA. A commercialized ethylene-glycidyl methacrylate copolymer (EGMA) was applied as a compatibilizer to improve the dispersion and interaction of dispersed POE to the PLA matrix. The results showed that chemical interaction seems to be the driving force for reinforcing the compatibility between PLA and POE, and also the dispersion of POE into the PLA matrix domain. With the incorporation of 10 phr EGMA in the blends, POE was well-dispersed at a sub-micrometer scale within the PLA matrix, indicating better interfacial compatibility between PLA and POE. The impact strength test revealed that POE could significantly toughen PLA containing EGMA in the blends, up to no-break level regarding unnotched Izod impact strength at 10 phr EGMA content. With the increase of EGMA content, the blends showed lower tensile strength, but higher elongation at break due to the elastomeric characteristics of EGMA. When 10 phr of the EGMA was incorporated into the blends, its elongation at break reached 54.5%, 10.7 times that of neat PLA at 5.1%. The melt viscosity of compatibilized blends containing 10 phr EGMA increased by more than 50% in comparison with the non-compatibilized blend, which implied a good interfacial interaction between the PLA and POE interface.

Melt temperature in the injection molding process directly affects the quality of the molded plastic product. The injection molding process is a periodic dynamic process. Many factors affect the barrel melt temperature, so precise control of the melt temperature is difficult. This paper introduces this industrial problem and presents a combined strategy using a feedback controller and an iterative learning controller to resolve the problem. Results show that this method has a high dynamic control accuracy and improves molded part mass repeat accuracy.

This article deals with the further processing of a compounded metal/thermoplastic hybrid material through injection molding. By synergistically combining two fillers, short copper fibers and a low melting alloy, in a thermoplastic matrix, it is possible to achieve extremely high electrical conductivities comparable to those of steel. At the same time, it is possible to manufacture complex parts directly using (multi-component) injection molding. The filling and solidification behavior of this highly filled material is significantly changed due to the amount of metal. The maximum flow lengths and the resulting electrical properties of the compound are investigated based on small conductor paths in 2C injection molding. Constant high mold temperatures significantly improve the maximum flow length of conductor paths without having any significant effects on electrical conductivity. With an additional dynamic mold tempering, using an external inductive heating system, the flow ability can be further improved within the injection molding process.

Part quality and manufacturing cost are the key concerns of injection molding designers. The desired design can produce high quality parts with minimum manufacturing cost. The factors affecting part quality and manufacturing cost are discussed and a multi-objective optimization methodology presented to optimize runner sizes and process conditions simultaneously to achieve high quality parts with low manufacturing cost. This methodology optimizes a population of solutions and promotes individuals within the population according to Pareto-optimal criteria. A set of Pareto solutions was obtained, whereby each solution was both better and worse in at least one objective compared to another individual of the population. A weighted sum approach was employed to select the appropriate design parameters from the Pareto set.

We studied three-dimensional transient large coupled thermomechanical deformations of a polycarbonate (PC) plate with a through-the-thickness inhomogeneity at its centroid. The PC exhibits strain softening followed by strain hardening and its elastic moduli are taken to be functions of strain rate and temperature. The inhomogeneity is either a void or a region of initial temperature higher than that of the rest of the plate. The nonlinear initial-boundary-value problem is solved numerically by the finite element method. It is found that deformations localize into narrow regions that we call bands. For a plate deformed in tension, the maximum principal stretch within the band is almost twice that of the maximum shear strain and for a plate deformed in shear the two have approximately the same magnitude. For the PC deformed in uniaxial compression, we call the minimum slope of the effective stress vs. the effective strain curve in the strain softening regime as the softening modulus, E s , and find values of E s and the defect strength needed for the deformations to localize. These values are found to be different for the plate deformed in shear from that deformed in tension and the minimum value of E s for the localization of deformation also depends upon the defect type and the defect strength (e.g., the ratio of the major to the minor axes of the elliptic void).

The World Health Organization (WHO) is promoting the use of insecticide treated nets (ITNs) in order to roll back malaria. Long-life netting (LLIN) is preferred and this study investigated the possibility of incorporating the insecticide in the fiber polymer. Multifilament polypropylene (PP) yarn, containing up to 0.76% of pyrethroid insecticide, was successfully produced on a conventional production-scale fiber-spinning machine. The insecticides were incorporated via masterbatches that contained up to 18.8% active with low-density polyethylene (LDPE) as the carrier. Nets knitted from the yarns were tested using bioassays with mosquitoes. Initial efficacy complied with WHO specifications but the performance deteriorated with the number of wash cycles. Crystalline insecticides, featuring a melting point above the wash temperature of 60°C (e.g., β-cyfluthrin), provided better wash resistance than amorphous insecticides (e.g., cyfluthrin).

In this study, waste cotton cloth (RC) was bonded with soluble starches as an adhesive, then dried, cut into particles and filled into polylactic acid (PLA) to achieve resource efficiency. The mechanical, thermal and crystallization properties of the composites were characterized. The results indicated that with the addition of RC, the tensile strength, impact strength and flexural strength of PLA composites improved. Also, the heat distortion temperatures increased slowly, indicating that RC filled into PLA can be turned back into useful items without the degradation of PLA composites. This is a good way to give direction to the resource utilization of waste clothing. The addition of RC could significantly reduce the spherulitic size of PLA.