Microstructure, Tensile Property, and Surface Quality of Glass Fiber-Reinforced Polypropylene Parts Molded by Rapid Heat Cycle Molding

Abstract

The microstructure of a molded product considerably influences its macroscopic properties. In this study, the influence of molding process on microstructure, tensile property, and surface quality was explored on the glass fiber-reinforced polypropylene (GFRPP) parts molded by rapid heat cycle molding (RHCM) and conversion injection molding (CIM). Tensile strength and surface gloss were chosen to measure macroscopic properties of the molded parts. The microstructure including multilayer, fiber orientation, crystallinity, and fiber-matrix bonding strength were analyzed by simulations, scanning electron microscopy, wide-angle X-ray diffraction, and dynamic mechanical analysis. The relationship between the macroscopic properties and microstructure of the RHCM samples was also discussed. The results indicate that as the mold cavity surface temperature increases, the tensile strength increases firstly and decreases thereafter. The tensile strength of RHCM parts reached the maximum at the mold heating temperature of 60°C. It is also observed that the surface gloss of the sample increases as the mold cavity surface temperature rises, and the increase of surface gloss decreases distinctly with the mold heating temperature higher than 90°C.

Application of Physical Methods for the Detection of a Thermally Degraded Recycled Material in Plastic Parts Made of Polypropylene Copolymer

“…It clearly follows from the results for the tensile properties, which were obtained from the samples exposed to conditions of 150 °C/500 h, that with the addition of the recycled material up to 10 wt.%, these properties change, e.g., the yield stress decreases by 60% (see Figure 14 ), the breaking stress decreases by up to 67% (see Figure 15 ), and the nominal relative elongation at yield point and at break point (i.e., also the total elongation; see Figure 16 and Figure 17 decreases by almost 80%. The results also confirm the conclusions made in the studies of Liu et al [ 24 ] and Atagur et al [ 25 ].…”

“…It clearly follows from the results for the tensile properties, which were obtained from the samples exposed to conditions of 150 °C/500 h, that with the addition of the recycled material up to 10 wt.%, these properties change, e.g., the yield stress decreases by 60% (see Figure 14), the breaking stress decreases by up to 67% (see Figure 15), and the nominal relative elongation at yield point and at break point (i.e., also the total elongation; see Figures 16 and 17 decreases by almost 80%. The results also confirm the conclusions made in the studies of Liu et al [24] and Atagur et al [25]. It clearly follows from the results for the tensile properties, which were obtained from the samples exposed to conditions of 150 • C/500 h, that with the addition of the recycled material up to 10 wt.%, these properties change, e.g., the yield stress decreases by 60% (see Figure 14), the breaking stress decreases by up to 67% (see Figure 15), and the nominal relative elongation at yield point and at break point (i.e., also the total elongation; see Figures 16 and 17 decreases by almost 80%.…”

Potential of Rapid Tooling in Rapid Heat Cycle Molding: A Review

“…Some important factors which may have an impact on the finishing are the process parameters, mold design, and properties of plastic materials [ 52 , 73 , 74 ]. One of the factors that determines the quality of injection molded parts is the weld line [ 50 , 75 , 76 ]. The weld line refers to the process in which the liquid material is divided into two or more flows in the cavity during the injection process and merged together after a period of time [ 51 , 77 , 78 , 79 ].…”

“…The heating and cooling system designs of electric heating molds are critical for RHCM with electric heating because they directly affect the heating/cooling efficiency and temperature uniformity, which have a decisive influence on the molding cycle and part quality [ 127 ]. Electric heating in RHCM can be accomplished through the deployment of electrical heating rods and cooling tunnels in the stationary mold, which can be rapidly heated via electric heating prior to filling and cooled via circulating water after filling [ 50 , 88 ]. In another study, Wang et al [ 54 ] investigated the thermal response of the electric heating with the deployment of a cartridge heater in rapid heat cycle molding, as well as its impact on the surface appearance and tensile strength of the molded part.…”

“…The results of production showed that the RHCM process completely eliminates the weld lines on the surface of the parts, and the surface gloss of the parts is also greatly improved. The influence of the RHCM process on part surface quality has been studied [ 40 , 42 , 50 , 53 , 54 ]. The results showed that the high cavity surface temperature near to the polymer’s glass transition temperature can assist in reducing surface roughness, significantly enhancing surface gloss, and eliminating the weld line.…”