Polymer Nanocomposite Foams Prepared by Supercritical Fluid Foaming Technology

The effect of process parameters of foam injection molding on the morphologicalproperties of acrylonitrile butadiene styrene (ABS)-nanoclay polymeric foam has been investigated. Polymethyl methacrylate (PMMA) was used as the compatibilizer between polymeric matrix and nanoclay. Different nanocomposite polymeric foam samples were produced in a chemical foam injection molding process. X-ray diffraction (XRD) test was carried out to analyze the dispersion of nanoclays with different percentages in the polymeric matrix and scanning electron microscopy (SEM) pictures were used to study the cellular structure of nanocomposite foamed samples. The effect of input parameters including nanoclay weight percentage (0, 2, and 4%), Injection Pressure (110, 125, and 140 MPa), and Holding pressure (110, 125, and 140 MPa) on cell density, cell size and expansion ratio of foamed samples have been investigated. Taguchi approach was used for the design of experiments and statistical analysis of results. Based on the results, 2 wt % of nanoclay and injection and holding pressures of 140 MPa is beneficial in order to have polymeric foam with small cell size. On the other hand, to achieve foams with higher cell density, 2 wt % of nanoclay, injection pressure of 140 MPa, and holding pressure of 110 MPa should be used.

As a substitute for conventional polymers for the preparation of biodegradable microcellular polymeric foams, polybutylene succinate (PBS) presents one of the most promising alternatives. However, the low melt strength of PBS makes it difficult to produce high-performance microcellular foams. This study aimed to improve the melt strength of PBS and explore the mechanical, thermal, crystalline, rheological, and supercritical CO2 foaming properties of PBS nanocomposites by using carbon nanofibers (CNFs). This study found that nanocomposites containing 7 wt% CNF exhibited the highest tensile strength, Young's modulus, and bending strength. Moreover, the CNF nanofillers were well dispersed in the PBS matrix without significant agglomeration, even at high filler concentrations. Furthermore, the nanocomposites demonstrated improved melting temperature and crystallinity compared with pure PBS. The rheological analysis showed that the addition of CNFs significantly increased PBS viscosity at low frequencies due to the interaction between the PBS molecular chains and CNFs and the entanglement of CNFs, resulting in a more complete physical network formation when the CNF content reached above 3 wt%. During the supercritical CO2 foaming process, the addition of CNFs resulted in increased cell density, smaller cells, and thicker cell walls, with good laps formed between the fibers on the cell walls of nanocomposite foams. Moreover, the electrical conductivity and electromagnetic interference (EMI) shielding properties of the foamed material were studied, and a nanocomposite foam containing 7 wt% CNF showed good electrical conductivity (4.5 × 10-3 S/m) and specific EMI shielding effectiveness (EMI SE) (34.7 dB/g·cm-1). Additionally, the nanocomposite foam with 7 wt% CNF also exhibited good compression properties (21.7 MPa). Overall, this work has successfully developed a high-performance, multifunctional PBS-based nanocomposite foam, making it suitable for applications in various fields.

Lightweight, high-strength and electrically conductive poly(butylene succinate) (PBS)/ carbon black (CB) nanocomposite foams with a density of 0.107–0.344 g/cm3 were successfully fabricated by a solid-state supercritical CO2 (ScCO2) foaming process. The morphology, thermal and dynamic mechanical properties, and rheological behavior of the PBS/CB nanocomposites were studied. The results indicate that the CB nanofiller was well dispersed in the PBS matrix and the presence of a proper CB nanofiller can accelerate the rate of crystallization, improve the thermal stability, enhance the stiffness, and increase the complex viscosity of PBS/CB nanocomposites. These improved properties were found to play an important role in the foaming process. The results from foaming experiments showed that the PBS/CB nanocomposite foams had a much smaller cell size, a higher cell density, and a more uniform cell morphology as compared to neat PBS foams. Furthermore, the PBS/CB nanocomposite foams also possessed low density (0.107–0.344 g/cm3), good electrical conductivity (~0.45 S/cm at 1.87 vol % CB loading), and improved compressive strength (108% increase), which enables them to be used as lightweight and high-strength functional materials.

Poly(butylene adipate‐co‐terephthalate) (PBAT) has attracted considerable attention in the field of porous materials due to its excellent mechanical properties and biodegradability. However, PBAT foams often exhibit poor cell morphology as well as limited cell size and density during batch foaming, which severely restricts their practical applications. In this study, a synergistic modification strategy combining polymer blending and chain extension was proposed based on the mold‐opening microcellular injection molding (MOMIM) process. Under a target weight reduction of 15%, the effects of packing time and supercritical fluid (SCF) content on cell morphology and size distribution were systematically investigated. Meanwhile, poly(butylene succinate) (PBS) was incorporated into PBAT to enhance its crystallization behavior and regulate melt strength, while 1 wt% of chain extender ADR was introduced to improve interfacial compatibility and suppress foam shrinkage. The results demonstrated that when the PBS content reached 40 wt% with 1 wt% ADR, uniform PBAT microcellular foams with an average cell size below 3 μm and a cell density of 10 10 cells/cm 3 were successfully fabricated, representing a two‐order‐of‐magnitude increase in cell density compared with neat PBAT foam. In terms of mechanical performance, the modified foams exhibited a 196.3% increase in Young's modulus and a 77.5% improvement in tensile strength relative to pure PBAT foams. This work provides valuable insights for the industrial‐scale preparation of biodegradable PBAT‐based microcellular foams via injection molding.

In this study, the foaming of nonwoven fabrics and bulk polymers was investigated. Four different polymers that are commonly used for textiles including polyethylene terephthalate, thermoplastic polyurethane, thermoplastic polyether ester elastomer and polypropylene were foamed by batch foaming. Among the polymers, thermoplastic polyurethane seems to be the most promising material since it possesses the highest cell density and smallest cell size. In addition, nanoclay was added to thermoplastic polyurethane to promote cell nucleation and to increase the cell density. The results showed that well dispersed nanoclay in thermoplastic polyurethane served as an excellent nucleation agent and the cell structure was improved. The cell size of thermoplastic polyurethane nanocomposite foam decreased to 1 µm while the cell density increased to 3 × 1011 cells/cm3.

Batch foaming of SAN/clay nanocomposites with scCO2: A very tunable way of controlling the cellular morphology

Polystyrene microcellular foams blowing with supercritical CO2 were prepared with a novel polymer foam processing simulator. Key parameters influencing Polystyrene cell morphology were investigated. The effect of processing temperature and saturation pressure on cell morphology was observed by scanning electron microscope and the average cell diameter and cell size distribution was calculated. The results show that the cell density decrease and cell size increase with the increase of foaming temperature. The cell density increase and cell size decrease with the increase of saturation pressure. And the cell size distribution shows a narrow distribution at lower foaming temperature and higher saturation pressure.

A novel microcellular processing experimental setup was developed in which various nucleation agents were added to foaming material (Polystyrene). The effect of the nucleation agents on cell morphology of foam plastics was studied in the vibration field. The effects of the processing conditions such as nucleating agents, particle size of the nucleating agents, content of the nucleating agents, and the vibration parameters on polystyrene cell morphology were investigated. The cell morphology was analyzed with a scanning electron microscope. The results showed that the samples blown with nucleating agents, in general, had larger cell density and much smaller cell size than the ones without nucleating agents. It is believed that the smaller nucleating agents will be helpful for the larger bubble densities and the smaller cell size. There is the optimum content range for the maximum bubble densities and the minimum average cell diameter in foaming processing with nucleating agents. In the range of vibration parameter, the cell density increases with an increase of frequency and amplitude, and the cell size is the reverse.

In the brain, microglia are involved in immune responses and synaptic maturation. During early development, these cells invade the brain, proliferate, and morphologically mature to achieve coverage of the surrounding tissue with their fine processes. Their developmental proliferation overlaps with the postnatal development of neuronal circuits. Within the superior olivary complex (SOC), an auditory brainstem structure, microglia, and their early postnatal development have been documented. A quantification over the full developmental profile of the arrangement and morphological changes in single microglia cells is missing. Here, we used immunofluorescence labeling to quantify their distribution, morphological changes, and coverage during early and late postnatal development in the SOC of Mongolian gerbils. Microglia distributed rather homogenously within each nucleus with a bias to the nucleus borders at postnatal day (P) 5 and more centrally in the nucleus in mature stages. We found a nucleus-specific transient increase in microglia cell number and density reaching its peak at P17 with a subsequent decline to P55 values. Length and branching of microglia protrusions increased especially after P12. The stronger ramification together with the increase in cell density allows coverage of the surrounding tissue from P5 to mature stages, despite the large developmental increase in nucleus size. The transient increase in density during synaptic refinement in SOC nuclei suggests that microglia are important during the pruning period, compensating for developmental increase in tissue volume, and that in mature stages their main function appears tissue surveillance.

The relationship between diffusion heterogeneity and microstructural changes in high-grade gliomas using Monte Carlo simulations

The biodegradable nanocomposite foams can be developed using different fabrication techniques where the use of various kinds of bio-based nanofillers helps in tailoring the foam properties. A brief discussion on different techniques of fabrication, their economic viability, and industrial feasibility in regards to the polymeric foams is made in this chapter. Moreover, the available different biodegradable polymeric foams and their processing in the recent past years is detailed. However, the chapter mainly focuses on the biodegradable poly (lactic acid) (PLA)-based nanocomposite foams and their recent developments and breakthroughs. The addition of nanofillers for fabricating the foam greatly affects various foam properties such as cell size, cell density, and porosity. Other important properties such as thermal properties, mechanical properties, and wettability are also affected by the nanofiller materials. The degradation of PLA-based nanocomposite foams is greatly influenced due to the addition of various bio-based nanofiller materials. In this regard, the tailor-made properties of various biodegradable foams make them promising candidate in different areas of research.

Biomass chemical upcycling of waste rPET for the fabrication of formamide-free TPEE microcellular foams via scCO2 foaming

Simultaneous enhancements in electrical conductivity and toughness of selectively foamed polycarbonate/polystyrene/carbon nanotube microcellular foams

The influence of foam morphology of multi-walled carbon nanotubes/poly(methyl methacrylate) nanocomposites on electrical conductivity

Since the appearance of the continuous extrusion process, the section shape of the feedstock is round. The shape of the feedstock directly affects metal deformation and metal flow characteristics during the continuous extrusion process. Based on finite element method (FEM), using the Deform-3D software, this paper simulates continuous extrusion forming process for copper bus bar, and analyzes the effect of different feedstock shape on metal flowing temperature, velocity, rotating torque. The results show that: the size of the rectangular feedstock must be within a reasonable range, otherwise the continuous extrusion process can not be established; the rectangular feedstock is benefit to the flow uniformity comparing with the round feedstock; the temperature of the billet and tooling with rectangular feedstock is lower than that with round feedstock, as the feedstock width increases, the temperature decreases and the area of high temperature becomes smaller; the change of the feedstock shape and size has no effect on the extrusion wheel torque value.