Lignocellulosic Polymer Composites Research Articles

Optimization and numerical simulation analysis for molded thin‐walled parts fabricated using wood‐filled polypropylene composites via plastic injection molding

Plastic injection molding is discontinuous and a complicated process involving the interaction of several variables for control the quality of the molded parts. The goal of this research was to investigate the optimal parameter selection, the significant parameters, and the effect of the injection‐molding parameters during the post‐filling stage (packing pressure, packing time, mold temperature, and cooling time) with respect to in‐cavity residual stresses, volumetric shrinkage and warpage properties. The PP + 60 wt% wood material is not suitable for molded thin‐walled parts. In contrast, the PP + 50 wt% material was found to be the preferred type of lignocellulosic polymer composite for molded thin‐walled parts. The results showed the lower residual stresses approximately at 20.10 MPa and have minimum overpacking in the ranges of −0.709% to −0.174% with the volumetric shrinkage spread better over the part surface. The research found that the packing pressure and mold temperature are important parameters for the reduction of residual stresses and volumetric shrinkage, while for the reduction of warpage, the important processing parameters are the packing pressure, packing time, and cooling time for molded thin‐walled parts that are fabricated using lignocellulosic polymer composites. POLYM. ENG. SCI., 55:1082–1095, 2015. © 2014 Society of Plastics Engineers

Numerical Simulation on Moulded Thin-Walled Parts via Injection Moulding Process

The current trend in the industry is to produce thin, light weight, and environmental products. In this project, flat or shallow thin-walled parts were designed and moulded lignocellulosic polymer composites (PP + 50 wt% wood) to visualize the processability via moulding simulation. This studied focused on the filling, shear stress at wall, and in-cavity residual stresses behaviors. The shallow thin-walled part is preferable in moulding PP + 50 wt% wood due to economically in processing, low shear stress distribution and low residual stresses than the flat thin-walled part.

Numerical simulation analysis of the in-cavity residual stress distribution of lignocellulosic (wood) polymer composites used in shallow thin-walled parts formed by the injection moulding process

In this paper, a numerical analysis of in-cavity residual stress formation in the thin-walled parts of injection-moulded parts is presented by considering the residual stresses produced during the post-filling stage. Injection moulding of shallow thin-walled parts with a thickness of 0.7mm was performed using lignocellulosic polymer composites (PP+50wt% wood), and the parts have been systematically investigated using simulation results from Autodesk MoldFlow Insight® software. In-cavity residual stresses constitute the primary stage for analysis because of the need to control the quality of moulded parts to prevent problems with shrinkage and warpage. The analysis showed that the cooling times and packing times had a less significant effect; nevertheless, the optimal levels that are required to be used in the moulding process for thin-walled parts yielded better results. The in-cavity residual stress results show that the stress variation across the thickness exhibits a high tensile stress at the part surface, which changes to a low tensile stress peak value close to the surface, with the core region experiencing a parabolic tensile stress peak. The optimum parameter ranges for obtaining the minimum in-cavity residual stresses are as follows: a mould temperature of 40–45°C, a cooling time of 20–30s, a packing pressure of 0.85Pinject, and a packing time of 15–20s.

Shrinkages and warpage in the processability of wood-filled polypropylene composite thin-walled parts formed by injection molding

Reducing volumetric shrinkages and warpage during the injection molding process is a challenging problem in the production of molded thin-walled parts. In this study, the injection molding of shallow, thin-walled parts (thickness 0.7mm), composed of lignocellulosic polymer composites (polypropylene (PP)+50wt% wood), was simulated. The volumetric shrinkages and warpage in the thin-walled parts were evaluated under different process conditions, with varying post-filling parameters, such as mold temperature, cooling time, packing pressure and packing time. The analysis showed that the cooling time and packing time had less of an effect on the shrinkage and warpage; nevertheless the optimal levels for both parameters are required in the molding process for the thin-walled part to achieve the best results. The volumetric shrinkage was lower near the gate than at the end-of-fill location along the flow path. The results also showed that the volumetric shrinkage correlates with the warpage measured on the molded part. The optimum parameters ranges is 40–45°C for the mold temperature; 20–30s for cooling time; 0.85 from injection pressure (Pinject) for packing pressure; and 15–20s for the packing time to achieve the best results with the least amount of volumetric shrinkage and warpage.

An investigation of the processability of natural fibre reinforced polymer composites on shallow and flat thin-walled parts by injection moulding process

Currently, many industries are trending towards producing products exhibit such properties as small thickness, lightweight, small dimensions, and environmental friendliness. In this project, flat or shallow thin-walled parts were designed to compare the advantages and disadvantages of lignocellulosic polymer composites (PP+50wt% wood) in terms of processability. This study focused on the filling, in-cavity residual stresses and warpage parameters associated with both types of thin-walled moulded parts. Thin-walled parts 0.7mm in thickness were suitably moulded using lignocellulosic composite materials to determine the effects of filling. The analysis showed, the shallow thin-walled part is preferable in moulding lignocellulosic polymer composite material due to the low residual stress and warpage measured. The results also indicate that the shallow thin-walled part is structurally rigid, such that it can be used in applications involving small shell parts, and can be processed more economically using less material than the flat thin-walled part.

Optimal Substitution of Cotton Burr and Linters in Thermoplastic Composites

A study was conducted to evaluate various substitutions of cotton burr and linters from cotton gin waste (CGW) as natural fiber reinforcements in ligno-cellulosic polymer composites (LCPC). Samples were fabricated with approximately 50 percent natural fiber, 40 percent high-density polyethylene, 4 percent mineral filler, and 6 percent lubricant, by weight. The experiment included substituting wood fiber in LCPC with 25, 50, 75, and 100 percent (by weight) cotton burr (CB) and cotton burr mixed with 2 percent (by weight) second-cut linters (CBL), respectively, with the remaining fraction as wood fiber and comparing it against the control (100% wood). Samples were extruded into rectangular profiles and tested for physical and mechanical properties such as specific gravity (SG), water absorption, thickness swelling, coefficients of linear thermal expansion (CLTE), flexural strength and modulus, compressive strength, hardness, and nail withdrawal force (NWF). The CB and CBL treatments exhibited SG, CLTE, hardness, and NWF comparable to the control. However, the water absorption and thickness swelling, flexural strength and modulus, and compressive strength all deteriorated at high substitution rates of CB and CBL. The favorable properties of cotton burr included its tendency to decrease CLTE and increase hardness of LCPC.