Direct In-Mold Impregnation of Glass Fiber Fabric by Polypropylene with Supercritical Nitrogen in Microcellular Injection Molding Process

Combining microcellular injection molding and insert injection molding, an injection molding technique for glass fiber fabric (GFF) reinforced polypropylene (PP) composite foams was proposed. The GFF was directly set in the mold cavity, and then the PP with supercritical nitrogen (SCN) was injected into the cavity for in-mold impregnation. The impregnation effects of two types of GFFs (EWR300 and EWR600) by the PP/SCF solutions at different injection temperatures (230, 240, and 250 °C) were investigated. The results of the morphological and tensile properties of the samples showed that the interfacial bonding was not good, because of the heterogeneity between the GFF and PP. In comparison with solid PP, the unfoamed GFF/PP did not present a higher tensile strength and presented a lower specific tensile strength. However, the increased tensile strength of the GFF/PP composite foams indicated an improvement in the impregnation effect and interfacial bonding. The SCN decreased the viscosity, which benefited the direct in-mold impregnation of the GFF. Increasing the temperature can improve the interfacial bonding, but it also influenced the foaming and thus led to a decrease in the tensile strength. According to the temperature distribution, the samples from different positions in the mold cavity had different properties.

Mechanical Response of Fiber-Filled Automotive Body Panels Manufactured with the Ku-FizzTM Microcellular Injection Molding Process

To maximize the driving range and minimize the associated energy needs and, thus, the number of batteries of electric vehicles, OEMs have adopted lightweight materials, such as long fiber-reinforced thermoplastics, and new processes, such as microcellular injection molding. These components must withstand specific loading conditions that occur during normal operation. Their mechanical response depends on the fiber and foam microstructures, which in turn are defined by the fabrication process. In this work, long fiber thermoplastic door panels were manufactured using the Ku-Fizz^TM microcellular injection molding process and were tested for their impact resistance, dynamic properties, and vibration response. Material constants were compared to the properties of unfoamed door panels. The changes in mechanical behavior were explained through the underlying differences in their respective microstructures. The specific storage modulus and specific elastic modulus of foamed components were within 10% of their unfoamed counterparts, while specific absorbed energy was 33% higher for the foamed panel by maintaining the panel's mass/weight.

Tailoring Multifunctional and Lightweight Hierarchical Hybrid Graphene Nanoplatelet and Glass Fiber Composites

In this work, hybrid polypropylene (PP)-based composites reinforced with graphene nanoplatelets (GnPs) and glass fiber (GF) were fabricated by injection molding to elucidate how the hybrid approach can produce synergistic effects capable of achieving properties and functionalities not possible in biphasic composites. Synergism between the reinforcements translated to improved mechanical performance, which was attributed to the chemically and/or electrostatically assembled hierarchical structure that facilitates load transfer at the interface while simultaneously tailoring the crystalline microstructure of the matrix by inducing transcrystallization and β-crystal formation. It was demonstrated that there exists an optimal concentration of 0.5 wt % GnP, producing the greatest mechanical properties and synergistic effect, corresponding to the highest degree of crystallinity (∼6% greater than Neat PP) and peak formation of β-crystals within the PP matrix. The greatest synergistic effect was found to be ∼52 and ∼39% for the specific tensile strength and flexural strength, respectively. The same optimal concentration of GnPs was found to produce the highest synergistic effect for thermal conductivity of ∼68% due to the volume exclusion effect induced by the GFs combined with the higher crystallinity of the microstructure, promoting the formation of thermally conductive pathways. Ultimately, the mechanisms contributing to the synergistic effect presented in this work can be used to maximize the performance of hybrid composite systems, giving them the potential to be tailored for a variety of high-performance industrial applications to meet the rising demands for ultra-strong, thermally conductive, and lightweight materials.

Conventional and Microcellular Injection Molding of a Highly Filled Polycarbonate Composite with Glass Fibers and Carbon Black

Conventional solid injection molding (CIM) and microcellular injection molding (MIM) of a highly filled polycarbonate (PC) composite with glass fibers and carbon black were performed for molding ASTM tensile test bars and a box-shape part with variable wall thickness. A scanning electron microscope (SEM) was used to examine the microstructure at the fractured surface of the tensile test bar samples. The fine and uniform cellular structure suggests that the PC composite is a suitable material for foaming applications. Standard tensile tests showed that, while the ultimate strength and elongation at break were lower for the foamed test bars at 4.0–11.4% weight reduction, their specific Young’s modulus was comparable to that of their solid counterparts. A melt flow and transition model was proposed to explain the unique, irregular “tiger-stripes” exhibited on the surface of solid test bars. Increasing the supercritical fluid (SCF) dosage and weight reduction of foamed samples resulted in swirl marks on the part surface, making the tiger-stripes less noticeable. Finally, it was found that an injection pressure reduction of 25.8% could be achieved with MIM for molding a complex box-shaped part in a consistent and reliable fashion.

A Design of Experiment Approach for Surface Roughness Comparisons of Foam Injection-Moulding Methods

The pursuit of polymer parts produced through foam injection moulding (FIM) that have a comparable surface roughness to conventionally processed components are of major relevance to expand the application of FIM. Within this study, 22% talc-filled copolymer polypropylene (PP) parts were produced through FIM using both a physical and chemical blowing agent. A design of experiments (DoE) was performed whereby the processing parameters of mould temperatures, injection speeds, back-pressure, melt temperature and holding time were varied to determine their effect on surface roughness, Young’s modulus and tensile strength. The results showed that mechanical performance can be improved when processing with higher mould temperatures and longer holding times. Also, it was observed that when utilising chemical foaming agents (CBA) at low-pressure, surface roughness comparable to that obtained from conventionally processed components can be achieved. This research demonstrates the potential of FIM to expand to applications whereby weight saving can be achieved without introducing surface defects, which has previously been witnessed within FIM.

Advances in microcellular injection moulding

Injection moulding is a well-established replication process for the cost-effective manufacture of polymer-based components. The process has different applications in fields such as medical, automotive and aerospace. To expand the use of polymers to meet growing consumer demands for increased functionality, advanced injection moulding processes have been developed that modifies the polymer to create microcellular structures. Through the creation of microcellular materials, additional functionality can be gained through polymer component weight and processing energy reduction. Microcellular injection moulding shows high potential in creating innovation green manufacturing platforms. This review article aims to present the significant developments that have been achieved in different aspects of microcellular injection moulding. Aspects covered include core-back, gas counter pressure, variable thermal tool moulding and other advanced technologies. The resulting characteristics of creating microcellular injection moulding components through both plasticising agents and nucleating agents are presented. In addition, the article highlights potential areas for research exploitation. In particular, acoustic and thermal applications, nano-cellular injection moulding parts and developments of more accurate simulations.

Lightweight High-Performance Polymer Composite for Automotive Applications

The automotive industry needs to produce plastic products with high dimensional accuracy and reduced weight, and this need drives the research toward less conventional industrial processes. The material that was adopted in this work is a glass-fiber-reinforced polyamide 66 (PA66), a material of great interest for the automotive industry because of its excellent properties, although being limited in application because of its relatively high cost. In order to reduce the cost of the produced parts, still preserving the main properties of the material, the possibility of applying microcellular injection molding process was explored in this work. In particular, the influence of the main processing parameters on morphology and performance of PA66 + 30% glass-fiber foamed parts was investigated. An analysis of variance (ANOVA) was employed to identify the significant factors that influence the morphology of the molded parts. According to ANOVA results, in order to obtain homogeneous foamed parts with good mechanical properties, an injection temperature of 300 °C, a high gas injection pressure, and a large thickness of the parts should be adopted.

Study on Foaming Quality and Impact Property of Foamed Polypropylene Composites

In the present work, foamed polypropylene (PP) composites were prepared by chemical foaming technology, and the foaming quality and impact property of the foamed PP composites were studied. The results showed that the foaming quality was significantly improved after the introduction of thermoplastic rubber (TPR) and polyolefin elastomer (POE). Meanwhile, it was found that the impact property depended on the intrinsic toughness and contribution of foams (cells) to the PP composites. Furthermore, the data regarding impact property in low temperature showed that when the temperature was between -80 and -20 °C, the impact properties of the foamed PP composites were higher than that of the unfoamed sample, which was due to the impact property being completely contributed by cells under this condition. Meanwhile, when the temperature ranged from -20 to 20 °C, the impact property of the unfoamed sample was higher, which was due to the PP matrix contributing more to the impact property under this temperature. This work significantly improved the foaming quality of foamed PP composites and provided reliable evidence for the improvement of impact property.

Comparative Effects of mEOC on the Structures and Properties of PP/SGF and PP/EOC/SGF Composite Foams

To improve the impact toughness of short glass fiber (SGF) reinforced polypropylene (PP) composite foams, maleic anhydride grafted ethylene-α-octene copolymer (mEOC) was employed as impact modifier and interfacial compatibilizer. And for comparison, mEOC was also introduced into PP/EOC/SGF composite foams. Then, the foaming qualities, interfacial structures and mechanical properties of samples against varying mEOC contents were examined and compared in detail. Results showed that adequate mEOC significantly improved the foamabilities of the composites, while the optimized mass fraction was 8% for PP/SGF composite foams and 3% for PP/EOC/SGF system. Increased mEOC facilitated the higher impact toughness, which was increased by 77% for PP/SGF composite foams, whereas only 5% for PP/EOC/SGF foams. However, the flexural strengths were just improved slightly, while compressive strengths decreased monotonically with mEOC for the investigated composite foams.

Study on reducing sink mark depth of a microcellular injection molded part with many reinforcing ribs

As a novel injection molding process, microcellular injection molding process has the characteristics of saving material, decreasing warpage and surface sink mark, improving dimensional accuracy, etc. But for the plastic part with thick reinforcing ribs, if selection of process parameters are not reasonable, foaming quality of melt will be affected and obvious sink mark defects will appear on the surface of plastic part. This paper selected a medical appliance shell with many reinforcing ribs as research object. Simulation experiments of microcellular injection molding process were performed by using orthogonal experiment method. The influence of different process parameters, such as mold cavity surface temperature, melt temperature, injection rate, cooling time, weight reduction ratio and supercritical fluid level, on the surface sink mark of microcellular injection molding part was studied by using signal-to-noise ratio analysis and analysis of variance . The results showed that mold cavity surface temperature was the most important influence factor on surface sink mark depth of microcellular injection molding part, followed by weight reduction ratio, cooling time, supercritical fluid level, injection rate and melt temperature. Meanwhile, the optimal combination of process parameters was obtained for minimizing sink mark depth of microcellular injection molding part. The average surface sink mark depth of microcellular injection molding part molded by using the optimized process parameters was only 2.62 µm, compared to 4.87 µm of average surface sink mark depth of microcellular injection molding part molded by using the process parameters before optimization, the average sink mark depth of microcellular injection molding part was reduced by 46.2%. Finally, the forming mechanism of sink mark of microcellular injection molding part at locations of reinforcing ribs was discussed, and the influence mechanism of different process parameters on surface sink mark defects of microcellular injection molding part was also analyzed.

Effect of a cross-linking agent on the foamability of microcellular injection molded thermoplastic polyurethane

Thermoplastic polyurethane is one of the most versatile thermoplastic materials being used in a myriad of industrial and commercial applications. Thermoplastic polyurethane foams are finding new applications in various industries including furniture, automotive, sportswear, and packaging because of their easy processability and desirable, customizable properties. Low bulk density and a good foam microstructure are important properties that affect the mechanical properties, economics, and performance of the final product. In this study, the effect of a cross-linking agent on the foamability of microcellular injection molded thermoplastic polyurethane was studied with an aim to reduce the bulk density while achieving a consistent microstructure. Gel permeation chromatography showed an increase in the weight average molecular weight by 5.0% with the addition of a cross-linking agent. Rheological studies on the materials showed that the addition of a cross-linking agent increased the storage modulus and viscosity, while reducing the tan δ value. Using microcellular injection molding, cross-linked thermoplastic polyurethane could be foamed to a minimum density of 0.159 g/cc at the higher end of the processing window, as compared with a minimum density of 0.193 g/cc for pure thermoplastic polyurethane foam. Scanning electron microscope analyses of the foamed parts showed a bimodal foam structure for thermoplastic polyurethane with a cross-linking agent and a more integral foam structure with less cell coalescence even at higher density reductions.