Effects of SCF content,injection speed,and CF content on the morphology and tensile properties of microcellular injection‐molded CF/PP composites

Carbon fiber/polypropylene composite foams were prepared by microcellular injection molding using nitrogen as a foaming agent. The effects of nitrogen content, injection speed, and CF content on the morphology and tensile properties of the composite foams were investigated. A three‐layer structure was formed in the microcellular foams: the skin layer was solid, the intermediate layer contained stretched cells parallel to the flow direction, and the core layer consisted of spherical cells. The average cell diameter of the machine direction decreased from 41 to 34 μm as the nitrogen content increased from 0.5 to 1 wt%, increased from 34 to 43 μm as the injection speed increased from 50 to 150 mm/s, and decreased from 34 to 25 μm as the CF content increased from 10 to 30 wt%. Thus, the microcellular structure was improved by increasing the nitrogen and CF content and by decreasing the injection speed. Furthermore, when the CF content increased from 10 to 30 wt%, the Young's modulus of the solids and foams increased by 78% and 113%, respectively. Thus, the Young's modulus of the foams improved by 35% due to the improvement in the cellular structure. POLYM. ENG. SCI., 59:1371–1380 2019. © 2019 Society of Plastics Engineers     

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.     

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.     

The effect of nanoclay on the crystallization behavior,microcellular structure,and mechanical properties of thermoplastic polyurethane nanocomposite foams

The effects of nanoclay on the crystallization behavior, microcellular structure, and mechanical properties of thermoplastic polyurethane (TPU)/clay nanocomposite (TPUCN) foams were investigated using differential scanning calorimetry, rheometry, scanning electron microscope, transmission electron microscopy, and X‐ray diffraction. It was found that the nanoclay acted as an effective nucleating agent for both crystal nucleation and cell nucleation. As a result, it significantly enhanced the crystallization behavior of the hard segment (HS) domains in TPU while refining the foamed structure of the microcellular injection molded parts. In particular, the average cell diameter of TPUCN foams decreased from 45 µm for neat TPU to 27 µm for TPUCN5 (5 wt% clay) and 18 µm for TPUCN10 (10 wt% clay). Furthermore, the cell density increased from 0.7 × 10⁷ cell/cm³ for neat TPU to 1.4 × 10⁷ cell/cm³ and 3.1 × 10⁷ cell/cm³ for TPUCN5 and TPUCN10, respectively. In addition, the tensile strength also increased by 56.3% and 89.2% with 5 and 10 wt% clay content, respectively. By controlling the cell nucleation behavior through uniformly dispersed nanoclay, this study demonstrates that it is feasible to produce TPUCN foams via microcellular injection molding with desirable microcellular structures and improved mechanical properties. POLYM. ENG. SCI., 56:319–327, 2016. © 2015 Society of Plastics Engineers     

Lightweight investigation of long chain branching polypropylene/cellulose nanofiber composite foams

Long chain branching polypropylene (LCBPP)/cellulose nanofiber (CNF) composite foams were prepared by short shot foam injection molding method and their morphological, mechanical, and thermal properties were also investigated. The cellular structure of LCBPP/CNF composite foams was improved with weight reduction (WR) ratios increasing. The cell densities of LCBPP/CNF composite foams were dramatically increasing with WR ratios rising. More, the fine and uniform cellular structures were obtained due to the incorporation of CNF. The highest cell density, specific flexural strength, and modulus could achieved 20 × 10³ cell/cm², 65 MPa/(g/cm³) and 2.7 GPa/(g/cm³), respectively. Furthermore, the specific Charpy impact strengths were also higher than the ones of solid samples. At last, the thermal insulation properties were discussed accordingly.     

Lightweight and High Impact Polypropylene Foam Fabricated via Ultra-Low Gas Pressure Injection Molding

Foamed materials play an important role in a lightweight design. Foam injection molding (FIM) is an advanced and convenient way to fabricate lightweight structural materials. Recently, a new foam injection molding machine is developed, which only needs ultra-low gas pressure to fabricate microcellular foam. As a universal plastic, polypropylene (PP) is widely used due to its good mechanical properties. But after foaming, the toughness of the PP tends to decrease. Herein, a lightweight and high-impact polypropylene foam is fabricated via the new FIM technology with an ultra-low nitrogen pressure of 6.5 MPa. PP/polyolefin elastomer (POE) foam with a tiny cell size of 4.13 µm and high cell density of 2.7 × 10⁹  cm⁻³ is successfully obtained. Owing to the superior cellular structure, compared with the pure PP foam, after adding the POE component, the maximum impact performance is increased by 465%. In this work, an easy-to-industrialized method for preparing lightweight and high-impact injection-molded PP foams are presented.     

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.     

Cell morphology and mechanical properties of microcellular mucell® injection molded polyetherimide and polyetherimide/fillers composite foams

Microcellular polyetherimide (PEI) foams were prepared by microcellular injection molding using supercritical nitrogen (SC‐N₂) as foaming agent. The effects of four different processing parameters including shot size, injection speed, SC‐N₂ content, and mold temperature on cell morphology and material properties were studied. Meanwhile, multiwalled carbon nanotube (MWCNT), nano‐montmorillonoid (NMMT), and talcum powder (Talc) were introduced into PEI matrix as heterogeneous nucleation agents in order to further improve the cell morphology and mechanical properties of microcellular PEI foams. The results showed that the processing parameters had great influence on cell morphology. The lowest cell size can reach to 18.2 μm by optimizing the parameters of microcellular injection molding. Moreover, MWCNT can remarkably improve the cell morphology of microcellular PEI foams. It was worth mentioning that when the MWCNT content was 1 wt %, the microcellular PEI/MWCNT foams displayed optimum mechanical properties and the cell size decreased by 28.3% compared with microcellular PEI foams prepared by the same processing parameters. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4171–4181, 2013     

Effects of clay dispersion on the foam morphology of LDPE/clay nanocomposites

Intercalated and exfoliated low‐density polyethylene (LDPE)/clay nanocomposites were prepared by melt blending with and without a maleated polyethylene (PE‐g‐MAn) as the coupling agent. Their morphology was examined and confirmed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The effects of clay content and dispersion on the cell morphology of nanocomposite foams during extrusion foaming process were also thoroughly investigated, especially with a small amount of clay of 0.05–1.0 wt%. This research shows the optimum clay content for achieving microcellular PE/clay nanocomposite foams blown with supercritical CO₂. It is found that < 0.1 wt% of clay addition can produce the microcellular foam structure with a cell density of > 10⁹ cells/cm³ and a cell size of ～ 5 μm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2129–2134, 2007     

Application of a novel organic nucleating agent: Cucurbit[6]uril to improve polypropylene injection foaming behavior and their physical properties

In this study, polypropylene (PP) foams were prepared with cucurbit[6]uril (Q[6]) used as a novel nucleating agent through a microcellular injection molding foaming process. The effect of Q[6] content (0.5–2.0 wt %) on the foaming behavior, as well as thermal, rheological and mechanical characterizations of the PP/Q[6] (PQ) samples were performed. According to scanning electron microscopy (SEM) images, the microstructure of foams exhibited a smaller cell size, higher cell density, and more homogeneous distribution of cells at a higher Q[6] content. It was found that the peak temperature of crystallization, the crystallinity and the crystallization rate of PP can be obviously improved by adding a low content of Q[6] (0.25–1.0 wt %), whereas further increasing the content of Q[6] (2.0 wt %) would disfavor the effect. With increasing the Q[6] concentration, the PQ composites had higher complex viscosities at low frequencies and higher modulus than that of PP except the content of 2.0 wt %. Furthermore, the introduction of Q[6] into PP can produce a mild increase in tensile strength, flexural strength and impact strength of PQ foams. This can be due to the well dispersion of Q[6], good compatibility between PP and Q[6], as well as the improvement of the cell morphology. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44538.     

Preparation and balanced mechanical properties of solid and foamed isotactic polypropylene/SEBS composites

This study presents a self-designed foaming apparatus and routes to manufacture foamed isotactic polypropylene (iPP) blends with uniform and dense cells, using styrene-ethylene-butadiene-styrene (SEBS) block copolymer as toughening additive. The addition of SEBS can clearly enhance the impact strength of solid iPP, iPP blends with a 20 wt% SEBS has obtained high notched impact strength of 75 kJ/m², which is ca. 16 times larger than that of neat iPP. Relatively fine microcellular iPP-SEBS foams with the average cell size of several micrometers, and the cell density of 10⁹ cells/cm³ were fabricated using a batch foaming procedure. Moreover, using our self-designed mold and compression foaming method, iPP-SEBS foams with balanced mechanical properties were produced. With the increasing of SEBS, tensile strength and flexural strength were slightly decreased, but the impact strength was increased clearly. The balanced mechanical properties between stiffness and toughness were achieved after compression foaming.     

Thermoplastic polyurethane (TPU) modifier to develop bimodal cell structure in polypropylene/TPU microcellular foam in presence of supercritical CO2

Currently, the fabrication of microcell and bimodal cell structures (BCS) in polymer foams by using supercritical fluids has become a hot as well as a challenging research area worldwide. In this work, an environmentally friendly, effective, facile, and CO₂-based foaming technique was presented to fabricate microcellular polypropylene (PP) foams with BCS via blending with thermoplastic polyurethane (TPU). The toughness, thermal properties, rheological properties, and foamability of PP were systematically investigated with gradual incorporation of TPU. Representative sea-island structure was observed in the scanning electron microscopy (SEM) images for the fracture surface of various PP/TPU samples. Rheological measurement results demonstrated that the viscoelasticity of various PP/TPU samples was improved remarkably compared with that of pure PP and pure TPU. The impact strength of various PP/TPU samples possessed the highest value as 12.4 kJ/m² with the TPU content of 15 wt%. After the addition of TPU, an ameliorative cellular morphology was observed in the SEM micrographs of various PP/TPU samples and their volume expansion ratio was enhanced significantly thanks to their improved melt elasticity. Moreover, it is worth noting that BCS appeared in various PP/TPU foams when the TPU content exceeded 5 wt%.     

Microcellular Crosslinked Silicone Rubber Foams: Influence of Nucleation Agent (Polyhedral Oligomeric Silsesquioxane) on the Rheological,Vulcanizing, Cell Morphological Properties

A series of microcellular silicone rubber/silica/polyhedral oligomeric silsesquioxane (POSS) foams were prepared by supercritical carbon dioxide. The effect of POSS particles on the rheological behavior, vulcanizing, and cellular morphology of the composites was investigated. The results showed that the POSS grafted carboxylic acid group can improve the matrix strength of silicone rubber. POSS grafted carboxylic acid group act as inhibiting agent in the vulcanizing process. POSS particles play an important role in the microcellular structure formation. When the POSS content was 2.0?wt%, the cell size and cell density can reach to 3.77?µm and 7.99?×?10⁹ cell/cm³, respectively.     

Effect of solvent plasticization on polypropylene microcellular foaming process and foam characteristics

In this research, the effect of crystalline fraction of polypropylene (PP) on cell nucleation behavior was overcome by an introduction of solvent‐plasticized step to the microcellular foaming in a solid‐state batch‐foaming process. Utilizing the plasticization performance of the solvent facilitated the PP to be foamed at the temperatures lower than its melting point with the dramatic development in the cellular morphology of the final foams. In consequence of the heterogeneous cell nucleation sites induction and the crystalline loss, which were induced by solvent, a high cell density (i.e., 10⁹–10¹⁰ cells/cm³) was promoted without the cell sacrificing at the elevated temperatures (155 and 165°C) and favorable PP microcellular foams were accomplished. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Rheological properties of injection molded LDPE and mPE foams

The rheological properties of molten LDPE and mPE foams have been measured for small‐amplitude oscillatory shear flow. The foam samples were prepared by injection molding, and the effect of injection conditions on the resultant cell structure is discussed. In all cases cellular foams with closed cells were obtained with cell densities in the range of 4 × 10⁵ ? 7 × 10⁶ cells/cm³ and cell diameters in the range of 30–110 μm. The viscoelastic behavior of the foams is shown to be well described by the emulsion model proposed by Palierne (1) without using any fitting parameter. The linear viscoelastic properties of LDPE and mPE foams depend only on the properties of the polymer matrix and of the gas volume fraction. The Palierne model is also used to predict the linear properties of microcellular foams. Polym. Eng. Sci. 44:2158–2164, 2004. © 2004 Society of Plastics Engineers.     

Microcellular foaming of polypropylene containing low glass transition rubber particles in an injection molding process

Microcellular foams in polypropylene containing rubber particles were produced in an injection molding process. The foams are generated because of the thermodynamic instability and are controlled by formation process. The effect of processing parameters on microcellular foaming was investigated in the injection molding process. Injection speed and pressure are less important factors but packing pressure plays an important role in controlling the foam density. A critical packing pressure, about 5 × 10⁶ Pa, was found to generate microcellular foams in our polypropylene material system. Rubber particles inside the polypropylene seem to stabilize the microcellular foams.     

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     

Microcellular foaming of low‐density polyethylene using nano‐CaCo3 as a nucleating agent

In this study, microcellular foaming of low‐density polyethylene (LDPE) using nano‐calcium carbonate (nano‐CaCO₃) were carried out. Nanocomposite samples were prepared in different content in range of 0.5–7 phr nano‐CaCO₃ using a twin screw extruder. X‐ray diffraction and scanning electron microscopy (SEM) were used to characterize of LDPE/nano‐CaCO3 nanocomposites. The foaming was carried out by a batch process in compression molding with azodicarbonamide (ADCA) as a chemical blowing agent. The cell structure of the foams was examined with SEM, density and gel content of different samples were measured to compare difference between nanocomposite microcellular foam and microcellular foam without nanomaterials. The results showed that the samples containing 5 phr nano‐CaCO₃ showed microcellular foam with the lowest mean cell diameter 27 μm and largest cell density 8 × 10⁸ cells/cm³ in compared other samples. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Influence of PTFE as a solid lubricant on the mechanical,electrical, and tribological properties of CF-reinforced PC composites

The objective of this research was to study the effects of polytetrafluoroethylene (PTFE) as a solid lubricant on the mechanical, electrical, and tribological properties of carbon fiber (CF)-reinforced polycarbonate (PC) composites. Samples were prepared by means of single-screw extrusion and injection molding processes. The mechanical tests included tensile, flexural, and failing weight impact tests, while the electrical tests consisted of surface and volume resistivity tests. The tribological testing was conducted under dry sliding conditions using pin-on-disk configuration. The results showed that the addition of CF managed to significantly reduce the electrical resistivity as the CF loading approached 10–15 wt%. The addition of PTFE managed to reduce the resistivity of the composite, that is, from 4.51 to 0.53 × 10 (Ωcm). The incorporation of 15 wt%. CF resulted with an increase of 45% in tensile strength and 51.5% in flexural strength, while the addition of PTFE had a negative impact on both properties. It was shown that PTFE was able to reduce the friction coefficient, μ and wear rate, K up to 0.257 and 6.35 × 10⁶ (mm³/Nm), respectively, which can be attributed to the excellent abilities of PTFE to form transfer film. The composite consisting of 15 wt% CF and 10 wt%. PTFE showed highest improvement in term of electrical resistivity, and is deemed the most suitable composition for this study. Scanning electron microscopy was also carried out to further elucidate the fracture and wear mechanism of the PC/CF/PTFE composites.     

Improving polypropylene microcellular foaming through blending and the addition of nano‐calcium carbonate

This article reports an attempt to improve polypropylene (PP) microcellular foaming through the blending of PP with high‐density polyethylene (HDPE) as a minor component and the incorporation of nano‐calcium carbonate (nano‐CaCO₃) into PP and its blends with HDPE. Three HDPEs were selected to form three blends with a viscosity ratio less than, close to, or greater than unity. Two concentrations of nano‐CaCO₃, 5 and 20 wt %, were used. The blends and nanocomposites were prepared with a twin‐screw extruder. The foaming was carried out by a batch process with supercritical carbon dioxide as a blowing agent. The online shear viscosity during compounding and the dynamic rheological properties of some samples used for foaming were measured. The cell structure of the foams was examined with scanning electron microscopy (SEM), and the morphological parameters of some foams were calculated from SEM micrographs. The rheological properties of samples were used to explain the resulting cell structure. The results showed that the blend with a viscosity ratio close to unity produced a microcellular foam with the minimum mean cell diameter (0.7 μm) and maximum cell density (1.17 × 10¹¹ cells/cm³) among the three blends. A foamed PP/nano‐CaCO₃ composite with 5 wt % nano‐CaCO₃ exhibited the largest cell density (8.4 × 10¹¹ cells/cm³). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007