Recently, functional applications of thermoplastic foams have received extensive attention from the research and materials communities, focusing on their various applications, key challenges, material systems designs, processing methods, and cellular structure characteristics needed for specific functional applications. This review paper starts with consideration of the microcellular foaming mechanism and basic concepts of microcellular foam processing, followed by polymer modification methods, and crucial factors that determine the performance of thermoplastic foams. Special emphasis has been placed on the synergies between foaming and reinforcements, including functional fillers and polymer blends; improvements in homogeneous, functional properties by achieving uniform cell structure and cell dispersion in polymer systems; and comparison of melt processing and solvent-based methods. Then, a wide array of advanced functional applications for foams-such as lightweight applications, heat and sound insulation, electromagnetic shielding, tissue engineering, oil spill cleanup, shape memory, and flexible materials-will be presented. In particular, the relationships between cellular structure and anticipated properties-including mechanical, barrier, dielectric, biomedical, and other properties required in advanced functional applications-will be discussed. Finally, we will outline a future perspective of lightweight and functional foams and suggest recommended future work regarding functional microcellular foams.

Injection molding machines are widely used to fabricate plastic products with complex geometries and structures. They consist of an injection unit and a clamping unit. To withstand the pressure of the mold cavity, the clamping unit needs a high clamping force to hold the mold halves. Unfortunately, the clamping force is among the overlooked parameters of the injection molding parameters. Setting the clamping force at max is needed in practice to avoid flash defects for most operators. However, excessive clamping force creates problems for the machine. This study proposes a verification method for determining optimal clamping force based on the clamping force change ΔCF. When ΔCF becomes zero, the current set value of the clamping force is appropriate. A positive and negative ΔCF corresponds to an excessive and insufficient set value of the clamping force, respectively. Verification experiments are implemented on an electric injection molding machine with polypropylene (PP). The experimental results show that the novel strategy can basically calculate and identify the optimal clamping force with iteration method. The optimal clamping force value for current working conditions (620kN) is acquired after several automatic molding trials, which provides a direction for further research.

Recent trends in energy and environmental protection have led to many studies of highperformance microcellular foams. Polymer blends provide an effective way to improve foamability, microstructure, and performance versus single component thermoplastics. However, challenges remain for morphological control of polymer blends because the reinforcing effect depends upon the morphology of the dispersed phase. In this work, we present a feasible method for attaining microfibrils with high aspect ratios based on the in situ fibrillation of immiscible polymers to improve the morphology and distribution of the blend phase and improve the microcellular structure and mechanical properties of composite foams. Composite foams of polypropylene (PP)/thermoplastic polyester elastomer (TPEE)/ polytetrafluoroethylene (PTFE) were fabricated, which were the polymer matrix, blend phase, and in situ fibrillation phase, respectively. The presence of PTFE and its effect on crystallization, rheology behavior, cellular structure, and mechanical properties were investigated. The results showed that PTFE microfibrils can promote melt strength, crystallization, and rheology properties. Thus, the multi-composite foams achieve improved microcellular structure and mechanical properties, and improvements in these properties indicate the positive effects of an in situ fibrillation phase on the polymer blend foams.

Injection molding (IM) is one of the essential forming methods for thermoplastic polymers, which is widely used in modern industries such as automobiles, electronics, and medical industries. At present, the machine parameters of the IM machine (IMM) have achieved sufficient high control accuracy and repeatability. However, the viscosity of thermoplastic melt is still easily influenced by the external environment, such as the fluctuations in batches, the compounding in recycled materials, and so on. Conventional IM equipment cannot sense and conduct adjustments correctly, which leads to the production of rejects. A real-time monitoring and controlling model employed for viscosity compensation was established in this article, which could monitor viscosity fluctuations and implement self-adjustment in the IM process. Three kinds of polypropylenes (PP) with different viscosity and materials with different percentages of recycled pellets were randomly added into the barrel for comparison. The results revealed that the pressure integral relative to time is able to monitor the melt viscosity and illustrate the IMM to optimize the V/P switchover and packing pressure in the current molding cycle. The part weight could achieve a higher stability and the model could bring about a decrease in weight fluctuations of 50% to 70%.

In order to solve the application restrictions of deterministic-based topology optimization methods arising from the omission of uncertainty factors in practice, and to realize the calculation cost control of reliability-based topology optimization. In consideration of the current reliability-based topology optimization methods of continuum structures mainly based on performance indexes model with a power filter function. An efficient probabilistic reliability-based topology optimization model that regards mass and displacement as an objective function and constraint is established based on the first-order reliability method and a modified economic indexes model with a composite exponential filter function in this study. The topology optimization results obtained by different models are discussed in relation to optimal structure and convergence efficiency. Through numerical examples, it can be seen that the optimal layouts obtained by reliability-based models have an increased amount of material and more support structures, which reveals the necessity of considering uncertainty in lightweight design. In addition, the reliability-based modified model not only can obtain lighter optimal structures compared with traditional economic indexes models in most circumstances, but also has a significant advantage in convergence efficiency, with an average increase of 44.59% and 64.76% compared with the other two reliability-based models. Furthermore, the impact of the reliability index on the results is explored, which verifies the validity of the established model. This study provides a theoretical reference for lightweight or innovative feature-integrated design in engineering applications.