Based on the PVT (pressure–volume–temperature) behavior of polymer, a novel process control methodology for injection molding is presented in this study. With the present control method, the process pressure is controlled by cavity temperature instead of time, which is used in a conventional injection‐molding process; thus the relationship between P (pressure) and T (temperature) can be controlled, which means that the V (volume) or part weight can be controlled because of the invariable PVT relationship of polymer. The objective of this study is to validate the feasibility of this process control methodology and examine its consistency. Experiments were conducted on an injection‐molding machine with an opened‐loop microprocessor controller. The weight of the molded parts serves as the main measure to probe the process capabilities. The variation of the mold temperature was monitored. The experimental results reveal that the present PVT control method yields much better part quality and uniform part weight than the conventional P–time (pressure–time) control method. It is also proved that the novel process control methodology can be used to accommodate the product weight change due to variation of the melt or mold temperature. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E474–E485, 2013; View this article online at http://wileyonlinelibrary.com. DOI 10.1002/adv.21294

The hot compaction process is still the principle method to produce single-polymer composites (SPCs) at present, which limits the industrial mass production of SPCs. In this article, an approach of preparing SPCs by injection molding was demonstrated. Polypropylene (PP) SPCs were prepared at different temperature and pressure. The flexural properties of the PP SPCs were tested. The optimum processing parameters, injection pressure of 140 MPa and nozzle temperature of 220 C were obtained. Flexural strength of the PP SPCs reached up to 43.3 MPa, which is 54.2% higher than that of nonreinforced PP. Flexural strength can be promoted by raising the injection pressure and nozzle temperature. The morphology of the fibers in the PP SPCs was investigated by optical microscope and scanning electron microscopy techniques. The matrix melt was able to penetrate into fiber webs under appropriate temperature and pressure, good interfacial compatibility and bonding properties were obtained. As the injection and holding pressure increased, the penetration capacity could be improved and the arrangement of fibers tended to be closer.

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The reinforcement and matrix of a polymer material can be composited into a single polymer composite (SPC), which is light weight, high strength, and has easy recyclability. The insert injection molding process can be used to realize the multiple production of SPC products with a short cycle time and wide processing temperature window. However, injection molding is a very complicated process; the influence of several important parameters should be determined to help in the future tailoring of SPCs to specific applications. The effects of varying barrel temperature, injection pressure, injection speed, and holding time on the properties of the insert-injection molded polypropylene (PP) SPC parts were investigated. It was found that the sample weight and tensile properties of the PP SPCs varied in different rules with the variations of these four parameters. The barrel temperature has a significant effect, followed by the holding time and injection pressure. Suitable parameter values should be determined for enhanced mechanical properties. Based on the tensile strength, a barrel temperature of 260 °C, an injection pressure of 127.6 MPa, an injection speed of 0.18 m/s, and a holding time of 60 s were determined as the optimum processing conditions. The best tensile strength and peel strength were up to 120 MPa and 19.44 N/cm, respectively.

A process for making high-density polyethylene (HDPE) single-polymer composites (SPCs) by insert injection molding was investigated. HDPE SPCs with relatively good tensile and interfacial properties were prepared within a short cycle time within a temperature range of 408C. Melt-spun HDPE fibers were made from the same resin as the matrix. The fibers were heat treated in silicone oil, with and without tension, to study the changes of fiber properties upon exposure to high temperature. HDPE SPCs containing about 30 wt% lab-made HDPE fabric achieved a tensile strength of 50 MPa, 2.8 times that of neat HDPE. The peel strength of HDPE SPCs increased with increasing injection temperature and achieved a maximum value of 16.7 N/cm. Optical micrographs of polished transverse cross-sections of the SPC samples showed that higher injection temperature is beneficial to the wetting and permeation properties of the matrix. Scanning electronic microscope photographs suggested good bonding and compatibility between the fibers and the matrix. POLYM. ENG. SCI., 55:2448-2456, 2015