微孔注射成型PPS及其性能研究

以超临界氮气(SC N2)作为发泡剂,采用注射成型法制备了微孔化聚苯硫醚(PPS)泡沫塑料,研究了模具流道、SC N2含量、PPS熔胶量位置对微孔化PPS泡沫塑料泡孔特性、相对密度、力学性能及介电性能的影响。结果表明,随着模具流道的延长,微孔化PPS泡沫塑料的泡孔孔径逐渐变大,泡孔密度降低;SC N2含量对泡孔孔径、力学性能及介电性能影响不大,但泡孔密度随SC N2含量的增大而增大;随着PPS熔胶量位置的降低,微孔化PPS泡沫塑料的泡孔孔径增大,泡孔密度降低,力学性能及介电常数也相应逐渐降低。     

Batch foaming of carboxylated multiwalled carbon nanotube/poly(ether imide) nanocomposites: The influence of the carbon nanotube aspect ratio on the cellular morphology

A series of microcellular poly(ether imide) (PEI) foams and nanocellular carboxylated multiwalled carbon nanotube (MWCNT‐COOH)/PEI foams were prepared by the batch foaming method. MWCNT‐COOHs with different aspect ratios were introduced into the PEI matrix as heterogeneous nucleation agents to improve the cell morphology of the microcellular PEI foams. The effect of the aspect ratio of the MWCNT‐COOHs on the cellular morphology, and gas diffusion is discussed. The results show that with the addition of MWCNT‐COOH, the sorption curve showed a slight reduction of carbon dioxide solubility, but the gas diffusion rate could be improved. The proper aspect ratio of MWCNT‐COOH could improve the cellular morphology under the same foaming conditions, in which m‐MWCNT‐COOH (aspect ratio ≈ 1333) was the best heterogeneous nucleation agent. When the foaming temperature was 170°C, the cell size and cell density of nanocellular m‐MWCNT‐COOH reduced to 180 nm and increased to 1.58 × 10¹³ cells/cm³, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42325.     

Effects of processing conditions on foaming behaviors of polyetherimide (PEI) and PEI/polypropylene blends in microcellular injection molding process

Foaming behaviors of both neat polyetherimide (PEI) and PEI/polypropylene (PP) blends were studied in this article in microcellular injection molding (Mucell) process. The study mainly focused on the comparison of two materials' foaming behaviors under different processing conditions which took a critical effect on the morphologies of foams. The results indicated that the different characteristics of PEI and PEI/PP blends, such as melt strength, gas dissolvability, and solubility, induced different nucleation ability of PEI and PEI/PP blends. The addition of PP could obviously improve the cell density and reduce the cell size. With the processing conditions changing, the morphologies of PEI/PP altered more variously, and their distribution of cell density was wider. This suggested that foaming behaviors of PEI/PP blends was more flexible to be controlled by the processing conditions than neat PEI. The effects of shot size, gas injection, and injection rate on foam morphologies were studied in detail. Shot size determined the weight reduction of samples and affected the cell density and size significantly. Gas dosing time and dosing rate determined the gas ratio which effected on foam morphologies of the PEI and PEI/PP foams. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41443.     

Effect of crystalline structure on the cell morphology and mechanical properties of polypropylene foams fabricated by core-back foam injection molding

Foam injection molding (FIM) is an advanced technology for preparing lightweight plastic foams, but its inferior mechanical performance remains a challenge. In this study, microcellular injection-molded β-polypropylene (β-PP) foams with high ductility were successfully prepared by combing the β-nucleating agent with controllable temperature field. Foaming results showed that the microcellular β-PP foams exhibiting a cell size of about 8 μm and cell density over 10⁸ cells/cm³ were prepared with a crystalline diameter approximately 5 μm, while PP foams had a rather large cell size approximately 150 μm and low cell density of 10⁵ cells/cm³ with 30 μm crystalline size. As a result, this significant improvement in cell structure as well as the crystalline size lead to a significant increment of 86% for the ductility of β-PP foams. This work offers a facile strategy to prepare injection-molded foams with desirable mechanical properties for their wide range of applications, such as automotive construction and consumer electronics.     

Microstructure and Properties of Microcellular Poly (phenylene sulfide) Foams by Mucell Injection Molding

A series of microcellular poly (phenylene sulfide) (PPS) foams were prepared by Mucell injection molding. The cell structure, mechanical properties, crystallization behavior and dielectric property of microcellular PPS foams were systemically investigated. The results showed that the longer the length of flow passage of injection mold, the larger cell size of microcellular PPS foams. The injection parameter of shot size played an important role in relative density of microcellular PPS foams. When the relative density of microcellular PPS foam reached to 0.658, the tensile strength, flexural strength and impact strength of PPS foam materials achieved 10.82 MPa, 52.99 MPa and 0.305 J/cm², respectively. Meanwhile, with the relative density decreasing, the dielectric constant of PPS foam materials reduced, while the volume resistivity of its uprated.     

A new microcellular foam injection‐molding technology using non‐supercritical fluid physical blowing agents

A new foam injection‐molding technology was developed to produce microcellular foams without using supercritical fluid (SCF) pump units. In this technology, physical blowing agents (PBA), such as nitrogen (N₂) and carbon dioxide (CO₂), do not need to be brought to their SCF state. PBAs are delivered directly from their gas cylinders into the molten polymer through an injector valve, which can be controlled by a specially designed screw configuration and operation sequence. The excess PBA is discharged from the molten polymer through a venting vessel. Alternatively, additional PBA is introduced through the venting vessel when the polymer is not saturated with PBA. The amount of gas delivered into the molten polymer is controlled by the gas dosing time of the injector valve, the secondary reducing pressure of the gas cylinder and the outlet (back) pressure of the venting vessel. Microcellular polypropylene foams were prepared using the developed foam injection‐molding technology with 2–6 MPa CO₂ or 2–8 MPa N₂. High expansion foams with an average cell size of less than 25 μm were prepared. The developed technology dispels arguments for the necessity to pressurize N₂ or CO₂ to the SCF to prepare microcellular foams. POLYM. ENG. SCI., 57:105–113, 2017. © 2016 Society of Plastics Engineers     

Influence of cell structure parameters on the mechanical properties of microcellular polypropylene materials

Microcellular polypropylene (PP) was prepared through chemical microcellular injection under different processing parameters. The effects of cell structure parameters on the mechanical properties of PP materials were analyzed by the microsphere model. The results show that the mechanical properties of microcellular PP with a smaller cell size and more uniform size distribution were enhanced. The relationship between the mechanical properties and cell structure parameters correlated well with the theoretical model. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Boosting solubility performance of supercritical CO2 via ethanol toward fabrication of polyetherimide/carbon fiber composite foam with three-dimensional geometry shape

The demand for light-weight, high-performance polymeric foam material, and part soars to meet the requirements of the national economy and the high-tech industries. Currently, foaming technologies are inadequate to fabricate these advanced materials. In this study, polyetherimide/carbon fiber (PEI/CF) foam was prepared by pressure-induced batch foaming technology with the supercritical CO₂ (scCO₂) and ethanol (EtOH) as the physical foaming agent and co-foaming agent, respectively. The presence of EtOH was verified to enhance the solubility of scCO₂ and increase the interaction energies between PEI molecular chain and CO₂/EtOH foaming agent, the expansion ratio of PEI pellets, as a result, was effectively improved from 1.3 to 7.5. Using the stainless mold-assisted sinter molding, numerous PEI or PEI/CF pellets was simultaneously foamed and squeezed into three-dimensional (3D) geometry shape. The cell morphology tests indicated that the CF, served as the nucleating agent, cannot only facilitate the formation of denser microcellular structure, but also improve the mechanical performance of the final foam product. As a model system, PEI/CF foam product with a density of 320 kg/m³ was successfully obtained, the compression and tensile strength of which were 11.6 and 9.7 MPa, respectively, as proved by the mechanical performance measurements.     

Influence of compatibilizers and processing temperature on microcellular injection‐molded polypropylene/(waste tire powder) composites

Nowadays the economic recycling of waste tires has become a global challenge. The use of waste tire powder as a dispersed elastomeric phase in a polypropylene (PP) matrix offers an interesting opportunity for recycling of waste tire rubber. Compatibilized PP/(waste tire powder) composites are microcellularly processed to create a new class of materials with unique properties. Recent studies have demonstrated the feasibility of developing microcellular structures in PP/waste ground rubber tire (WGRT) composites. Microcellular PP/WGRT composites are prepared by an injection‐molding process using a chemical blowing agent. In this study, cell sizes, cell density, void fraction, and mechanical properties of the composite foams were measured, as well as the shear viscosity of the unfoamed composites. The influence of various compatibilizers and processing temperatures on cell morphology and the mechanical properties of injection‐molded PP/WGRT composites were investigated. It was seen that the addition of maleic anhydride‐grafted styrene‐ethylene‐butylene‐styrene (SEBS‐g‐MA) increased the shear viscosity of the composites. The void fraction and cell density of the PP/WGRT composites increased with addition of compatibilizers, whereas the average cell sizes decreased. A processing temperature range of 180–195°C gave finer microcellular structure and regular cell distribution. The SEBS‐g‐MA enhanced the elongation properties and acted as an effective compatibilizer in this particular system. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Study of injection molded microcellular polyamide‐6 nanocomposites

This study aims to explore the processing benefits and property improvements of combining nanocomposites with microcellular injection molding. The microcellular nanocomposite processing was performed on an injection‐molding machine equipped with a commercially available supercritical fluid (SCF) system. The molded samples produced based on the Design of Experiments (DOE) matrices were subjected to tensile testing, impact testing, Dynamic Mechanical Analysis (DMA), and Scanning Electron Microscope (SEM) analyses. Molding conditions and nano‐clays have been found to have profound effects on the cell structures and mechanical properties of polyamide‐6 (PA‐6) base resin and nanocomposite samples. The results show that microcellular nanocomposite samples exhibit smaller cell size and uniform cell distribution as well as higher tensile strength compared to the corresponding base PA‐6 microcellular samples. Among the molding parameters studied, shot size has the most significant effect on cell size, cell density, and tensile strength. Fractographic study reveals evidence of different modes of failure and different regions of fractured structure depending on the molding conditions. Polym. Eng. Sci. 44:673–686, 2004. © 2004 Society of Plastics Engineers.     

Effect of microstructure induced by microcellular injection molding on electromagnetic interference shielding properties

Preparing lightweight and versatile products is the unremitting goal of industry to save resources and energy. Lightweight carbon fiber reinforced polypropylene (CF/PP) composite foams with high-performance electromagnetic interference (EMI) shielding materials were fabricated by microcellular injection molding (MIM) technology. The average length and distribution of CF in CF/PP composite foams were examined. Thanks to the introduction of foaming process, the average CF length of composite foams was 33.98% longer than that of solids, which effectively enhanced the electrical conductivity and EMI shielding properties. The effect of shot size, gas content, and injection rate on the electrical conductivity and EMI properties was investigated. With melt shot size of 2/3 of the cavity volume, gas content of 0.5 wt% N₂ and injection rate of 100 mm/s, optimal cellular structure of the composite material was obtained. The EMI shielding effectiveness (SE) reaches 36.94 dB, which is the highest value achieved by using MIM technology to the best of the authors' knowledge. In addition, the mechanical properties of cellular structure can still maintain good values, with the tensile strength and impact strength improved by 15.3% and 14.03%, respectively.     

Effects of processing parameters and thermal history on microcellular foaming behaviors of PEEK using supercritical CO2

In this study, we mainly investigate the solid‐state foaming of polyether ether ketone (PEEK) with different crystallinities using supercritical CO₂ as a physical blowing agent. The gaseous mass‐transfer and thermophysical behaviors were studied. By altering the parameters of the foaming process, microcellular foams with different cell morphologies were prepared. The effect of crystallization on the cell morphology was also investigated in detail. The results indicate that the crystallization restricts gas diffusion in the material, and the thermophysical behaviors of the saturated PEEK sample with low crystallinity presents two cold crystallization peaks. The cell density decreases and the cell size increases as the saturation pressure increases. The cell density of the microcellular foams prepared under 20 MPa is 1.23 × 10¹⁰ cells/cm³, which is almost 10 times compares to that under 8 MPa. The cell size increases as the foaming time extends or the foaming temperature increases. It is interesting that the cell morphology with a bimodal cell‐size distribution is generated when the samples are foamed at temperatures higher than 320°C for a sufficient time. Additionally, nanocellular foams can be obtained from a highly crystallized PEEK after the decrystallization process. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42576.     

Effects of compatibilizers on the physico‐mechanical and foaming properties of polyproylene/wood‐fiber composites

Polypropylene (PP)/wood‐fiber (WF) composites were prepared by intermeshing co‐rotating twin screw extruder, and microcellular closed cell PP/WF composite foams were prepared by using pressure‐quenched batch process method. The effect of various compatibilizers on the mechanical properties, morphology, crystallinity, rheological properties, and foamability of PP/WF composites were investigated. The results showed that PP/WF composite with addition of PP‐g‐MA as compatibilizer had the highest tensile strength, stiffness, and crystallinity, after foaming, it showed highest relative density and cell density, as well as the smallest cell size. Higher crystallinity of PP/WF composites, showed higher stiffness and higher relative density. J. VINYL ADDIT. TECHNOL., 19:250–257, 2013. © 2013 Society of Plastics Engineers     

Preparation of micro/nanocellular polypropylene foam with crystal nucleating agents

Open‐cell, porous microcellular foams with nanofibrillated structures were prepared from high tacticity isotactic polypropylene (i‐PP) with a crystal nucleating and gelling agent. The 1,3:2,4 bis‐O‐(4‐methylbenzylidene)‐d ‐sorbitol gelling agent (Gel‐all MD) was used as the crystal nucleating and gelling agent, which enhanced the crystallization and gelation of i‐PP with a three‐dimensional network of highly connected nanofibrils. The core‐back foam injection molding technique was employed to foam the i‐PP with nitrogen (N₂) at a high expansion ratio, where the crystal nucleating agent induced bubble nucleation and bubble growth in the inter‐lamella region and opened the cell walls with a nanoscale‐fibrillated structure. The effects of the nucleating agent on the open cell content (OCC), density and crystallinity were thoroughly investigated. We prepared open‐cell micro/nanocellular foams with an average cell size of microscale voids of < 5 μm. Nanometer‐scale fibrillated structures were formed on the cell wall of the microscale void, the expansion ratio was five‐fold and the open cell content was over 90%. POLYM. ENG. SCI., 54:2075–2085, 2014. © 2013 Society of Plastics Engineers     

Fabrication and cell morphology of a microcellular poly(ether imide)–carbon nanotube composite foam with a three-dimensional shape

The preparation of microcellular poly(ether imide) (PEI) based foams with three-dimensional geometry remains a great challenge worldwide. In this study, we fabricated microcellular PEI–carbon nanotube (CNT) bead foams with a batch rapid depressurization method in a self-designed mold with supercritical carbon dioxide (scCO₂) as a blowing agent. The effects of the saturation time, foaming temperature, foaming pressure, and depressurization rate on the microcellular structures of the PEI foam were analyzed by the Taguchi approach to determine the optimum foaming conditions, and the influence of the CNT content on the cell structure was analyzed. The results show that the depressurization rate and foaming temperature were the key factors influencing the cell size and cell density (N _f); that is, the high depressurization rate and low foaming temperature favored a small cell size and high N _f. The foaming temperature also influenced the foaming ratio (ϕ), and a high ϕ was obtained at a high foaming temperature. Under optimal foaming conditions, PEI with 2.0 wt % CNTs presented the best cell structure; N _f, cell size, and ϕ were 6.14 × 10¹⁰ cell/cm³, 2.43 μm, and 2.08, respectively. The mechanical properties of the final parts were related more to the foaming time and CNT concentration, and the maximum tensile and compression strength were reached at 3 h foaming time and 2.0 wt % CNT, that is, at 2.75 and 15.1 MPa (10% strain), respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47501.     

Microcellular and nanocellular solid-state polyetherimide (PEI) foams using sub-critical carbon dioxide I. Processing and structure

In this study we investigate the solid-state batch foaming of polyetherimide (PEI) using sub-critical CO₂ as a blowing agent. We report on the gas diffusion for various saturation pressures in this system. Foaming process characterization is reported detailing conditions used to create microcellular and nanocellular PEI foams of 40% and higher relative density. Gas sorption, foaming, and resultant morphologies are analyzed and compared to previously reported results on PEI thin films. It was found that equilibrium gas concentrations for PEI sheet begin to significantly exceed that of films for CO₂ pressures above 3 MPa. A large solid-state foaming process window has been identified that allows for the creation of either microcellular or nanocellular structures at comparable density reductions. A transition from micro-scale cells to nano-scale cells was observed at gas concentrations in the range of 94–110 mg CO₂/g PEI. Additionally, a hierarchical structure was observed which consisted of nanocellular structures internal to microcells. The PEI–CO₂ system offers the unique opportunity to compare and contrast the bulk properties of nanofoams and microfoams.     

A simple method for preparation of polymer microcellular foams by in situ generation of supercritical carbon dioxide from dry ice

In this work, poly(methyl methacrylate) (PMMA) and PMMA/nanoclay nanocomposite microcellular foams were successfully prepared using a simple method based on in situ generation of supercritical carbon dioxide (CO₂) from dry ice. The method was compared with conventional methods exempted from high pressure pump and a separate CO₂ tank. Effect of various processing conditions such as saturation temperature and pressure and clay concentration on cellular morphology and hardness of the prepared microcellular foams was examined. State of the clay dispersion in the prepared PMMA/clay nanocomposites was characterized using X-ray diffraction and transmission electron microscopy techniques. Field emission scanning electron microscopy was used to study cellular morphology of the prepared foams. It was observed that elevation of saturation temperature from 85 to 105 °C at constant saturation pressure increased cell density and decreased average cell size of the prepared PMMA foams. Furthermore, an increase in saturation pressure from 120 to 180 bar resulted in a reduction in average cell diameter and an increase in cell density of the prepared PMMA foams. On the basis of the gathered results, optimum conditions for preparation of PMMA microcellular foams were determined and applied for preparation of PMMA/nanoclay microcellular foams. It was shown that incorporation of clay into the polymer matrix resulted in a finer and more uniform cellular morphology in the final microcellular foams. It was also observed that incorporation of nanoclay into the prepared foams, up to 3 wt%, led to a moderate increase in the foam hardness.     

N2‐filled hollow glass beads as novel gas carriers for microcellular polyethylene

N₂‐filled hollow glass beads (HGB) were first used as novel gas carriers to prepare microcellular polymers by compression molding. Dicumyl peroxide was acted as crosslink agent to control the produced microcellular structure of low density polyethylene (LDPE)/HGB. The effect of temperature, pressure and the content of gel on the embryo‐foaming, and final‐foaming structure are investigated. Scanning electronic microscopy shows that the average cell size of microcellular LDPE ranges from 0.1 to 10 μm, and the foam density is about 10⁹–10¹¹ cells/cm³. A clear correlation is established between preserving desirable micromorphologies of microcellular LDPE in different processing stage and tuning processing factors. The pertinent foaming mechanism of microcellular materials foamed with HGB is proposed. Because of the good mechanical strength, low density, weak water‐absorption, and excellent heat insulate ability, microcellular LDPE has great potential application in energy building materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal‐Insulation,Electrical, and Mechanical Properties of Highly‐Expanded PMMA/MWCNT Nanocomposite Foams Fabricated by Supercritical CO2 Foaming

Foaming behavior of poly(methyl methacrylate) (PMMA)/multi‐walled carbon nanotubes (MWCNTs) nanocomposites and thermally‐insulating, electrical, and mechanical properties of the nanocomposite foams are investigated. PMMA/MWCNT nanocomposites containing various amounts of MWCNTs are first prepared by combining solution and melt blending methods, and then foamed using CO₂. The foaming temperature and MWCNT content are varied for regulating the structure of PMMA/MWCNT nanocomposite foams. The electrical conductivity measurement results show that MWCNTs have little effect on the electrical conductivity of foams with large expansion ratio. Thermal conductivities of both solid and foamed PMMA/MWCNT nanocomposites are measured to evaluate their thermally insulating properties. The gas conduction, solid conduction, and thermal radiation of the foams are calculated for clarifying the effects of cellular structure and MWCNT content on thermal insulation properties. The result demonstrates that MWCNTs endowed foams with enhanced thermal insulation performance by blocking thermal radiation. Moreover, the compressive testing shows that MWCNTs improve the compressive strength and rigidity of foams. This research is essential for optimizing environmentally friendly thermal insulation nanocomposite foams with enhanced thermal‐insulation and compressive mechanical properties.     

Relationship between the cell structure and mechanical properties of chemically crosslinked polyethylene foams

The main objective of this work was to study the effect of the controlling parameters on the morphology and mechanical properties of the peroxide crosslinked low‐density polyethylene foams. The relationship between the morphology and mechanical properties was also considered. Using different Dicumyl peroxide (DCP) and azodicrbonamide (ADCA) concentrations, various foams with different cell structures were prepared. Gel content and density of the foams were measured according to the standard methods. The morphology was examined using SEM technique. The mechanical properties of the foams were evaluated by means of compression and creep recovery tests. The results showed that the gel content and the density are mainly controlled by DCP and ADCA concentration, respectively. The results also showed that the cell size distribution is mainly controlled by DCP concentration. Increasing of DCP increased the gel content and decreased the cell size and cell size distribution. Foam density was mainly controlled by ADCA concentration, whereas the morphology was less affected with ADCA concentration. The foams with small cell size and narrow cell size distribution showed higher mechanical strength and lower plastic strain. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012