A study of the cell morphology and mechanical properties of bumper material PP-T-EPDM composite foam

In this study, cellular polypropylene based composite foams were prepared using an universal injection moulding machine. The chemical foaming agent was added to neat polypropylene (PP) polymer, talc filled polypropylene (PP-T) composite and talc filled polypropylene/ethylene-propylene-diene blend (PP-T-EPDM) composite materials at the ratio of 1% and 2% by weight. The influence of foaming agent content on the mechanical and cellular properties of both neat PP polymer and PP composites was investigated. The results showed that the tensile strength, tensile modulus, impact strength, hardness, cell diameter, foam density and viscosity values and skin layer thickness decreased while volume expansion ratio increased with the increment in chemical blowing agent content.

Effect of Cell Morphology on Flexural Behavior of Injection-Molded Microcellular Polycarbonate

The quantitative study of the structure and properties relationship in cellular materials is mostly limited to cell diameter, cell density, skin layer thickness, and cell size distribution. In addition, the investigation of the morphology is generally carried out in two dimensions. Therefore, the interrelation between morphological properties and mechanical characteristics of the foam structure has remained in an uncertain state. In this study, during the physical foaming process, a foam morphology is locally created by using a mold equipped with a core-back insert. The variation in morphology is obtained by modifying the mold temperature, injection flow rate, and blowing agent content in the polymer melt. X-ray microtomography (μCT) is used to acquire the 3D visualization of the cells structure. The Cell Distribution Index (CDI) is calculated to represent the polydispersity in cell size distribution. The relationship between the wide range of morphological qualities and relevant flexural properties is made explicit via a statistical model. According to the results, the morphology, particularly cell shape, characterizes the mechanism of the linear elastic deformation of the closed-cell foams. IR-thermography reveals the bending failure of cellular structures in the tensile region despite the differences in cell diameter.

Backpressure Optimization in Foam Injection Molding: Method and Assessment of Sustainability

Inspired by the Industry 4.0 trend towards greater user-friendliness and self-optimization of machines, we present a novel approach to reducing backpressure in foam injection molding. Our method builds on the compressibility of polymer-gas mixtures to detect undissolved gas phases during processing at insufficient backpressures. Identification of a characteristic behavior of the bulk modulus upon transition from homogeneous to heterogeneous polymer-gas mixtures facilitated the determination of the minimum pressure required during production to be determined, as verified by ultrasound measurements. Optimization of the pressure conditions inside the barrel by means of our approach saves resources, making the process more sustainable. Our method yielded a 45% increase in plasticizing capacity, reduced the torque needed by 24%, and required 46% less plasticizing work and lower pressures in the gas supply chain. The components produced exhibited both improved mechanical bending properties and lower densities. From an economic point of view, the main advantages of optimized backpressures are reduced wear and lower energy consumption. The methodology presented in this study has considerable potential in terms of sustainable production and offers the prospect of fully autonomous process optimization.

Effect of Mold Opening Process on Microporous Structure and Properties of Microcellular Polylactide⁻Polylactide Nanocomposites

Cell structure is a key factor that determines the final properties of microcellular polylactide (PLA) product. In the mold opening process, adjusting the rate of mold opening can effectively control cell structure. PLA and PLA composites with a void fraction as high as 50% were fabricated using the mold opening technique. The effects of mold opening rate and the addition of nanoclay on the cell structure, mechanical properties, and surface quality of microcellular PLA and PLA composites samples were investigated. The results showed that finer cell structure was received in the microcellular PLA samples and the surface quality was improved effectively when decreasing the rate of mold opening. The effect of mold opening rate on the foaming behavior of microcellular PLA⁻nanoclay was the same as that of microcellular PLA. The addition of 5 wt % nanoclay significantly improved the foaming properties, such as cell density, cell size, and structural uniformity, which consequently enhanced the mechanical properties of foams and the surface quality.

Evolution of cellular morphologies and crystalline structures in high-expansion isotactic polypropylene/cellulose nanofiber nanocomposite foams

The development of cell morphology and crystalline microstructure of high expansion injection-molded isotactic polypropylene/cellulose nanofiber (PP/CNF) nanocomposite foams was understood.

Injection molded components with functionally graded foam structures – Procedure and essential results

In the past few years, foam injection molding has increasingly gained significance in the field of technical plastic components. This is due to the development of new processes and processing combinations and efforts to produce lightweight products. In this article, a special tool technology will be introduced, which aids the process of expanding the existing areas of applications. The technology enables the production of foam injection molded components with different foaming ratios. This is made possible by core movements in the closed injection mold after the cavity has been filled volumetrically with plastic melt containing blowing agent. In doing so, functionally graded components with locally differing properties can be produced in one processing step. The method (pull and foam method) is based on the idea of equipping thin-walled components with locally foamed thick-volume elements – i.e. to increase the stiffness, create spacers, or joining surfaces. Simultaneously this method aims to exceed the limitations of conventional foam injection molding, especially with regard to scope for design. This article describes the procedure and characteristics of the process. Results with regard to the density in the differentially foamed areas, the morphology and the mechanical properties in correlation with the essential processing parameters are given.

Fabrication of porous synthetic polymer scaffolds for tissue engineering

Tissue engineering provides a novel and promising approach to replace damaged tissue with an artificial substitute. Porous synthetic biodegradable polymers are the preferred materials for this substitution due to their microstructure, biocompatibility, biodegradability, and low cost. As a crucial element in tissue engineering, a scaffold acts as an artificial extracellular matrix (ECM) and provides support for cell migration, differentiation, and reproduction. The fabrication of viable scaffolds, however, has been a challenge in both clinical and academic settings. Methods such as solvent casting/particle leaching, thermally induced phase separation (TIPS), electrospinning, gas foaming, and rapid prototyping (additive manufacturing) have been developed or introduced for scaffold fabrication. Each method has its own advantages and disadvantages. In this review, the commonly used synthetic polymer scaffold fabrication methods will be introduced and discussed in detail, and recent progress regarding scaffold fabrication—such as combining different scaffold fabrication methods, combining various materials, and improving current scaffold fabrication methods—will be reviewed as well.

Microcellular injection molding of polypropylene and glass fiber composites with supercritical nitrogen

Microcellular injection molding of polypropylene and glass fiber composites (PP-1684/GF-950) was performed using supercritical nitrogen as the physical blowing agent. Based on design of experiment matrices, the influences of glass fiber content and operating conditions on cell structure, glass fiber orientation and mechanical properties of molded samples were studied systematically. The results showed the cell morphology and glass fiber orientation of foaming parts were definitely influenced by the cooling and shear effects. The mechanical properties of foamed polypropylene–glass fiber composites could be effectively enhanced by improving the cell morphology, dispersion state and orientation of the glass fiber at optimal weight percentage [Formula: see text]. And the optimal conditions for injection molding were obtained by analyzing the signal-to-noise ratio analysis of the mechanical properties of the molded samples, which were a shot size of 36 mm, a supercritical N2 weight percentage of 0.4%, an injection speed of 60%, a melt temperature of 190℃ and a mold temperature of 70℃. The molded specimens of polypropylene–glass fiber composites, produced under those optimal conditions, exhibited very uniform fiber dispersion and microcellular structures with an average cell size less than 30 µm. And the mechanical properties normalized by weight ratio of the microcellular samples were increased significantly, especially the impact strength.

Bulk Density Reduction of Injection Molded Thermoplastic Foams via a Mold Design Approach

This study investigates the inter-relationships amongst processing parameters and mold design and their effects on relative density of injection molded foams. The limitation in lowering the overall bulk density of polymeric foams is one of the main drawbacks in injection foaming process. A sheet mold with a rectangular cavity was designed and manufactured which, includes an overflow channel connected with the main cavity via a secondary gate, the size of which was varied in this research. The effects of three parameters including chemical blowing agent weight percentage, gate width, and part thickness on reduction of relative density were investigated. Full factorial test experiments were applied in this research work. The results were used to determine the optimum conditions in terms of low foam bulk density and high cell density. The results showed that enhanced cell structure can be achieved at a larger part thickness and adjusting the secondary gate to an optimum thickness. The conclusions revealed that part thickness and secondary gate width were the most influential factors on reduction of relative density and part weight.

Influence and prediction of processing parameters on the properties of microcellular injection molded thermoplastic polyurethane based on an orthogonal array test

Thermoplastic polyurethane is a commonly used polymer in our daily lives. Microcellular injection molding (a.k.a. MuCell) is an emerging method capable of mass-producing thermoplastic polyurethane foams with tunable microstructures and properties. This study investigated the effects of four main processing parameters—namely, plasticizing temperature, carbon dioxide (CO2) content, injection volume, and injection speed—on microcellular injection molded thermoplastic polyurethane ASTM tensile test bars. Property variables of interest included the cell diameter, cell density, skin layer thickness, and Young’s modulus. Influence sequences of parameters on each variable were obtained via the orthogonal array test method. It was found that the CO2 content primarily affected the cell diameter and cell density, whereas the temperature mainly influenced the skin layer thickness and Young’s modulus. Surface fitting of each dependent variable was done by combining its two most influential parameters from the experiment data. The value of each property variable within the processing window could then be predicted from the fitted surface. In addition, microcellular injection molding of thermoplastic polyurethane was simulated by a commercial software package, and the simulated results confirmed the reliability of the cell diameter prediction.

Influence of the injection moulding parameters on the microstructure and thermal properties of microcellular polyethylene terephthalate glycol foams

Microcellular injection moulding is capable of producing lightweight polymeric products. The present study analyses the influence of several representative injection moulding parameters on the foam’s morphology, apparent density and thermo-mechanical properties of PETG, poly(ethylene terephthalate-co-1,4-cyclohexylene-dimethylene terephthalate) specimens. A strong variation of the cell morphology along the melt flow direction has been found, as well as a dependence on the shot volume. The most homogeneous microcellular structure is achieved when low shot volume, intermediate injection speed and low mould temperature are employed. The skin–core structure of the injected parts, determined the thermo-mechanical features of the specimen, which are ruled by the skin layer.

Effect of Weld Lines on Injection Moulded Fibreglass Reinforced Structural Foams. 2 - Impact and Flexural Properties

In the second part of this investigation, the effects of weld lines on impact strength and flexural properties of injection moulded glass fibre reinforced structural polypropylene foams are reported. The results show that Charpy impact strength decreases with density and presence of a weld line. For three-point bending tests, a linear decrease of the flexural modulus and flexural strength as density decreases was found, the latter being more important. There is also a significant decrease of flexural properties for samples with a weld line compared to samples without one of the same density. Also, to evaluate the weakness of the weld line region, off-centre flexural tests were performed to determine the minimum distance at which load should be applied for the failure to no longer occur at the weld line. The results obtained indicate that this distance decreases as density decreases.