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Polymer foams have low density, good heat insulation, good sound insulation effects, high specific strength, and high corrosion resistance, and are widely used in civil and industrial applications. In this paper, the classification of polymer foams, principles of the foaming process, types of blowing agents, and raw materials of polymer foams are reviewed. The research progress of various foaming methods and the current problems and possible solutions are discussed in detail.

With economic development, environmental problems are becoming more and more prominent, and achieving green chemistry is an urgent task nowadays, which creates an opportunity for the development of supercritical foaming technology. The foaming agents used in supercritical foaming technology are usually supercritical carbon dioxide (ScCO2) and supercritical nitrogen (ScN2), both of which are used without environmental burden. This technology can reduce the environmental impact of polymer foam production. Although supercritical foaming technology is already in production in some fields, it has not been applied on a large scale. Here, we present a detailed analysis of the types of foaming agents currently used in supercritical foaming technology and their applications in various fields, summarizing the technological improvements that have been made to the technology. However, we have found that today’s supercritical technologies still need to address some additional challenges to achieve large-scale production.

Polylactide (PLA) is known as one of the most promising biopolymers as it is derived from renewable feedstock and can be biodegraded. During the last two decades, it moved more and more into the focus of scientific research and industrial use. It is even considered as a suitable replacement for standard petroleum-based polymers, such as polystyrene (PS), which can be found in a wide range of applications—amongst others in foams for packaging and insulation applications—but cause strong environmental issues. PLA has comparable mechanical properties to PS. However, the lack of melt strength is often referred to as a drawback for most foaming processes. One way to overcome this issue is the incorporation of chemical modifiers which can induce chain extension, branching, or cross-linking. As such, a wide variety of substances were studied in the literature. This work should give an overview of the most commonly used chemical modifiers and their effects on rheological, thermal, and foaming behavior. Therefore, this review article summarizes the research conducted on neat and chemically modified PLA foamed with the conventional foaming methods (i.e., batch foaming, foam extrusion, foam injection molding, and bead foaming).

The anti-foaming protection is designed to prevent the oil from overheating due to intense oil churning and to reduce torque losses. The numerical simulation will be performed on gearbox housing in the SolidWorks Flow module in two variants: without anti-foaming protection and with anti-foaming protection, both for 3 values of the speed: 1000, 1200, 1400 rpm and 3 values of the oil height: 70, 100, 126 mm. The aim of the paper is to quantify by simulation the torque losses in the gearbox housing for different values of speed and oil level.

The microcellular injection molding (MuCell®) process, which uses supercritical fluid (SCF) as a foaming agent, is considered an important green molding solution to reduce product weight, molding energy, and cycle time and to improve the foam quality. However, maximizing the foaming density while keeping size uniformity in the foaming cell requires further attention. In this study, H2O and the SCF N2 were employed as cofoaming agents in the MuCell® process of polypropylene (PP). Owing to the different critical points of N2 and H2O, bubble nucleation was expected to occur in interactive ways. Various process parameters were investigated, including the SCF N2 content, the moisture content adsorbed within the resin under targeted PP weight reductions of 30% and 40%, the melt and mold temperature conditions, and the gas counter pressure. The resulting foaming morphology was examined to evaluate the foam quality in terms of the foaming density and bubble size distribution. The bubble coalescence, particularly in the skin layer, was examined, and the associated gas permeability flow rate was measured. The results indicated that H2O-assisted foaming led to bubble coalescence and allowed for gas penetration in the direction of the part thickness direction, resulting in an overall increase in foaming density, particularly in the skin layer. Under high SCF N2 and H2O contents, the solid skin layer disappeared, regulating the gas permeability from one surface side to the other. Under the optimized process parameters, the gas permeability flow rate in the filter-like foaming PP material reached 300–450 mL/min. The application of gas counter pressure also helped increase the foam density and bubble coalescence, enhancing the gas permeability in the PP material to about 500 mL/min. These results demonstrate the potential application of microcellular injection molding using water as a cofoaming agent in moisture-release devices.

HighlightsA layered segregated shielding network was organized in porous PBAT/Fe3O4@MWCNTs/Ag composite by scCO2 foaming and scraping techniques.The composite foam achieved an electromagnetic interference (EMI) shielding effectiveness (SE) of up to 68.0 dB and a reflectivity of as low as 23% due to the “absorption-reflection-re-absorption” shielding mechanism.The solid and foamed PBAT/Fe3O4@MWCNTs/Ag composites displayed superior retention (> 92%) of EMI SE even after peeling experiment of 500 times under 100 g weight pressure.The utilization of eco-friendly, lightweight, high-efficiency and high-absorbing electromagnetic interference (EMI) shielding composites is imperative in light of the worldwide promotion of sustainable manufacturing. In this work, magnetic poly (butyleneadipate-co-terephthalate) (PBAT) microspheres were firstly synthesized via phase separation method, then PBAT composite foams with layered structure was constructed through the supercritical carbon dioxide foaming and scraping techniques. The merits of integrating ferroferric oxide-loaded multi-walled carbon nanotubes (Fe3O4@MWCNTs) nanoparticles, a microcellular framework, and a highly conductive silver layer have been judiciously orchestrated within this distinctive layered configuration. Microwaves are consumed throughout the process of “absorption-reflection-reabsorption” as much as possible, which greatly declines the secondary radiation pollution. The biodegradable PBAT composite foams achieved an EMI shielding effectiveness of up to 68 dB and an absorptivity of 77%, and authenticated favorable stabilization after the tape adhesion experiment.

Various polyurethane foams (i.e., rigid, flexible, and spray polyurethane foams) offer diverse applications due to their unique properties, including thermal insulation, cushioning, and seamless gap filling. These foams provide solutions across industries such as construction, automotive, and refrigeration. However, the foaming process presents several challenges that may result in various defects in the final products. This work provides innovative predictive techniques for polyurethane foam expansion and applications in advanced manufacturing processes. The foaming height of the third polyurethane foaming agent (PU-3) closely aligned with the experimentally measured values. The relationship between foaming height and time is influenced by the type and concentration of catalysts, as well as the blowing agents used. However, simulations using Moldex 3D Version 2024 revealed a nonlinear relationship between foaming height and time, characterized by three distinct foaming rates. Zone B demonstrated the highest foaming rate, followed by Zone C, while Zone A showed the lowest rate. The foaming height and rate were significantly influenced by the foaming angle, with smaller angles enhancing both parameters. At a mold temperature of 30 °C and with an expansion coefficient of 35, the predicted foaming height of the polyurethane agent achieved an average accuracy of approximately 96% across four foaming angles. Based on these experimental findings, this study introduces three mechanisms involved in the foaming process of polyurethane foam components.

Foaming ability of oat protein isolate (OPI) was analysed at pH 4 and 7. Foaming properties were influenced by partial hydrolysis with trypsin (OPT) and alcalase (OPA). The viscoelasticity of the protein film, the interactions between the protein molecules, and the network forming within the protein film were analysed by interfacial rheology. At pH 7, foams made of OPI and OPT were found to be stable with OPI showing the fastest foaming ability. At pH 4, the foaming properties of OPI were found to be poor due to limited solubility. The specific cleavage pattern of trypsin resulted in peptides with improved foaming properties, especially at pH 4, resulting in a homogenous foam structure, a fast foaming ability, and a highly viscoelastic interfacial film. The formation of a thick steric protein layer at pH 7 and the formation of strong hydrophobic interactions at pH 4 were found to be the dominating foam stabilisation mechanisms. In conclusion, oat protein may serve as a food ingredient with targeted functional properties.

Conventional solvent-based methods widely used for isolating plant proteins may deliver an unsatisfactory protein yield and/or result in protein degradation. The present study started with the optimization of pumpkin seed protein from press cake by alkaline extraction and subsequent isoelectric precipitation. Subsequently, extraction was supported by ultrasound under three conditions: ultrasonic treatment followed by alkaline extraction (US+AE), concomitant ultrasonic treatment and alkaline extraction (UAE), and alkaline extraction followed by ultrasonic treatment (AE+US). Compared to the control group, an increase in protein yield was achieved after ultrasonic treatment, while the highest protein yield was obtained with AE+US (57.8 ± 2.0%). Isolates with a protein content of 94.04 ± 0.77 g/100 g and a yield of 43.6 ± 0.97% were obtained under optimized conditions. Following ultrasonic treatment applied during extraction, solubility, foaming capacity, foam stability, and denaturation enthalpy of the isolated protein increased, and water binding capacity decreased as compared to non-sonicated samples. The d90 particle size percentile of the extracted suspensions was 376.68 ± 38.32 µm for the control experiments, and particle size was significantly reduced in ultrasound-assisted treatments down to d90 = 179.93 ± 13.24 µm for the AE+US treatment). Generally, ultrasonication resulted in a significant increase in protein yield and improved techno-functional properties of the isolates.

This study determines the possibilities of synthesis of porous glass-ceramic materials based on Bioglass 45S5 using different methods obtained porous materials. In this work used foaming with sintering method for the set: bioglass 45S5 + glass cullet (CRT) + glass water (WG) and method sintering with forming-pore agents for the: bioglass + glass water (WG) + dried banana peels. The sets were melting and the next step sintering process. The resulting foams were examined and analysed for structural, microstructural, and physical properties. The research allowed for a quantitative and qualitative assessment of the foaming process generated by the presence of WG with the addition of CRT cullet and WG together with dried banana peel. It was found that WG with the addition of CRT cullet was a solution that offered the possibility of obtaining a large number of evenly distributed pores and higher total porosity compared the second set (WG + banana peel). Moreover, the use of CRT cullet and banana peel allowed the introduction of biogenic elements such as strontium, barium and potassium into the obtained materials, which have a positive effect on the stimulation of osteogenesis.