Cell Morphology Of Foams Research Articles

The effects of ACR/MAH ionic cross-linking on the cell morphology, mechanical properties, and dimensional stability of PVC foams

This study details a novel approach to enhance the dimensional stability of foamed polyvinyl chloride (PVC) materials through the introduction of a reversible cross-linking network. This is achieved via the carboxylation of acrylate polymers (ACR) utilizing the hydrolysis reaction of maleic anhydride (MAH) during the extrusion of PVC foam sheets. Subsequently, an ionic cross-linking network is formed using calcium-zinc (Ca-Zn) stabilizers. This paper elucidates the process of cell formation and the mechanisms underpinning the ACR/MAH ion network formation. Cell morphology of the foamed PVC was characterized using SEM, and the effects of ionic cross-linking on the plasticizing time, dimensional stability, and mechanical properties were analyzed through cell diameter distribution measurements and rheometry. The longitudinal and transverse dimensional shrinkage of PVC-F/MAH1 was reduced by 28.0 % and 28.9 %, respectively. The construction of the ACR/MAH ion cross-linking network not only augments the mechanical properties but also substantially enhances the dimensional stability of the material. This approach underscores the viability of ion cross-linking networks in advancing the performance parameters of PVC foams, suggesting a promising avenue for future research and development in polymer processing technology, and potentially expanding their application spectrum.

Controlling the crystal morphology of high-hardness TPU through two pre-crystallization processes and its impact on physical foaming behavior

Clarifying the relationship between crystal evolution and the physical foaming behavior of high-hardness thermoplastic polyurethane (HD-TPU) is essential for preparing HD-TPU foams with controllable cellular morphology. In this study, two thermal treatment methods, isothermal annealing and isothermal crystallization, were utilized to control the crystal structure of HD-TPU. The effect of crystals on the physical foaming behavior of HD-TPU foams was examined. The annealing process produced mainly lamellae and Form Ⅰ structure, while isothermal crystallization primarily led to Form Ⅱ spherulites. Foams based on original and pre-treated HD-TPU were prepared by pressure quench foaming. The evolution of foam density and cell morphology was discussed. At low foaming temperatures, crystals induced the heterogeneous nucleation. Realizing a uniform cell structure at high foaming temperatures could be challenging when the spherulite size was large. When the size of the spherulite was small but loosely distributed, larger cells with thinner cell walls could be obtained. However, if the spherulite distribution was dense, the spherulites hindered cell growth, resulting in unevenly distributed and deformed cells.

Optimizing the preparation parameters of eco‐friendly flexible polyurethane foams derived from a corn‐based bio‐polyol

AbstractCorn‐based bio‐polyol is employed as an alternative for petroleum‐based polyol to prepare an eco‐friendly polyurethane (PU) foam via a one‐shot method. By varying ratio of gelling catalyst, blowing catalyst, and surfactant during the preparation process, the compression performance, cell morphology, and thermal stability of the PU foam are analyzed. The results obtained indicate that an increase in surfactant content yielded improved foam stability, whereas increased amounts of blowing and gelling catalysts resulted in enhanced compression performance. An optimized foaming process is determined with an NCO/OH ratio of 1.2, 0.2 parts per hundred polyols (pphp) of gelling catalyst, 0.1 pphp of blowing catalyst, and 0.1 pphp of surfactant. Under these specific conditions, the PU foam exhibits a uniform cell structure, exceptional compression performance, and good thermal stability, comparable to those of a reference foam derived from petroleum‐based polyol.

The Study of Crystallization Behavior, Microcellular Structure and Thermal Properties of Glass-Fiber/Polycarbonate Composites

Polycarbonate (PC) foam is a versatile material with excellent properties, but its low thermal stability limits its application in high-temperature environments. The aim of this study was to improve the thermal stability of PC foam by adding glass fibers (GF) and to investigate the effect of GF on PC crystallization behavior and PC foam cell morphology. This study was motivated by the need to improve the performance of PC foams in various industries, such as construction, automotive, and medical. To achieve this goal, PC/GF composites were prepared by extrusion, and PC/GF composite foams were produced using a batch foaming process with supercritical carbon dioxide (SC-CO2) as the blowing agent. The results showed that the addition of GF accelerated the SC-CO2-induced crystallization stability of PC and significantly increased the cell density to 4.6 cells/cm3. In addition, the thermal stability of PC/GF foam was improved, with a significant increase in the residual carbon rate at 700 °C and a lower weight loss rate than PC matrix. Overall, this study highlights the potential of GF as a PC foam reinforcement and its effect on thermal and structural properties, providing guidance for industrial production and applications.

Preparing low-Density microcellular polystyrene foam by in-Situ fibrillated PTFE and supramolecular nucleator TMC-300 in the presence of sc-CO2

A method using in-situ fibrillated polytetrafluoroethylene (PTFE) and octamethylenedicarboxylicdibenzoylhydrazide (TMC-300) supramolecular nucleator was presented to prepare low density polystyrene foams. This study used a torque rheometer in the molten compound preparation of PS/fibrillated-PTFE/TMC-300 composites. Scanning electron microscopy showed in-situ fibrillated polytetrafluoroethylene in Polystyrene melt and a nanofiber network with high aspect ratio. The formation of nanometer-sized fiber networks improved the melt viscoelasticity of matrices which promoted cell nucleation. As the results demonstrated, low-density foams with 11 μm average cell size were obtained using Polystyrene. The self-assembly nucleating agent TMC-300 was then introduced to the composite materials. TMC-300 and polytetrafluoroethylene as a composite cell nucleating agent were used in Polystyrene foams. Meanwhile, their nucleating efficiency was investigated. TMC-300 completed self-assembly in Polystyrene and served as composite nucleating agent in combination with polytetrafluoroethylene. Compared with the sample PS/PTFE-0.5, the average cell size of the sample PS/PTFE-0.5/TMC-2 had a reduction rate of 28.16% from 12.18 μm to 8.75 μm. The cell density increased by an order of magnitude. The composite nucleating agent was successful in controlling Polystyrene foam cell morphology, thus leading to the preparation of low-density Polystyrene microporous foams.

Enhanced foaming ability of thermoplastic polyurethane by crystallization during mold-opening foam injection molding with supercritical N2 as blowing agents

This study provides an insight into the foaming of thermoplastic polyurethane (TPU), which was improved by the crystallization of hard segment domains. This study investigated the effects of packing time in the mold-opening foam injection molding (MOFIM) technology on the crystallization behavior of hard segments in TPU and the cell morphology of TPU foams. It was observed that the prolongation of the packing time, corresponding to a longer crystallization time before foaming, induced an increased crystallinity in the injection-molded TPU solids and foams due to the crystals becoming more close-packed. The enhancement of the foamability of TPU was attributed not only to the increased crystallinity of hard segments, but also to the broader distribution of crystals at the same crystallinity. Furthermore, TPU foams with greater hardness have smaller cell size, higher cell density, and narrower distribution in cell size owing to their higher viscosity and storage modulus than those with lower hardness prepared under the same conditions.

Rational Design of a Polyurethane Foam.

Polyurethane (PU) foams are exceptionally versatile due to the nature of PU bond formation and the large variety of polymeric backbones and formulation components such as catalysts and surfactants. This versatility introduces a challenge, namely a near unlimited number of variables for formulating foams. In addition to this, PU foam development requires expert knowledge, not only in polyurethane chemistry but also in the art of evaluating the resulting foams. In this work, we demonstrate that a rational experimental design framework in conjunction with a design of experiments (DoE) approach reduces both the number of experiments required to understand the formulation space and reduces the need for tacit knowledge from a PU expert. We focus on an in-depth example where a catalyst and two surfactants of a known formulation are set as factors and foam physical properties are set as responses. An iterative DoE approach is used to generate a set of foams with substantially different cell morphology and hydrodynamic behaviour. We demonstrate that with 23 screening formulations and 16 final formulations, foam physical properties can be modelled from catalyst and surfactant loadings. This approach also allows for the exploration of relationships between the cell morphology of PU foam and its hydrodynamic behaviour.

Utilization of supercritical CO2 for controlling the crystal phase transition and cell morphology of isotactic polybutene-1 foams

Isotactic polybutene-1 (iPB-1) is a semi-crystalline polymer with multiple crystal forms. In this work, we found a novel method to obtain and adjust the expansion ratio and bimodal cellular structures of iPB-1 foams with annealing and foaming using supercritical CO2. The form I′ can be obtained via the supercritical CO2 annealing, and the ratio of form I and I′ can be adjusted by controlling simply the annealing time. The effects of crystal form ratio on the thermal behavior, rheological behavior and cell morphology of foams were analyzed. Energy storage modulus (G′) and complex viscosity (|η*|) decrease with the increased content of form I. Crystal form I′ has a lower foaming temperature window and bubble growth resistance than form I, resulting in larger cell diameter and expansion ratio. The bimodal cell structure can be observed in the samples with 1:1 form I′/form I, where the average large and small cell size are 122 and 40 µm at 109 °C and 10 MPa CO2, respectively. To regulate the cell distribution, various ratios of mixed crystal phases were applied to investigate their effect on the foaming behavior and bimodal cells structure at different temperatures. Even with a similar expansion ratio, significantly different cell distributions of bimodal cell structure can be easily prepared by simply adjusting the content of form I′, which can broaden the application range of iPB-1 foams.

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

AbstractFoam 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.

Solid-state foaming of acrylonitrile butadiene styrene through microcellular 3D printing process

The lightweight products with superior specific strength are in great demand in numerous applications such as automotive, aerospace, biomedical, sports, etc. This work focussed on the manufacturing of lightweight products using the cellular three dimensional (3D) printing process. In this work, the continuous microcellular morphology has been developed in a single foamed filament using 3 D printing of carbon-di-oxide (CO2) saturated acrylonitrile butadiene styrene (ABS) filaments. The microcellular structures with average cell size in the range of 6–1040 µm were developed. The influence of printing parameters; nozzle temperature, feed rate, and flow rate on the foam characteristics and cell morphology at different levels were investigated. The different kinds of observed foamed extrudate irregularities were discussed.

Preparation of bisphenol A polyaryl ether nitrile microporous foam

Different foam structure of bisphenol A polyarylene ether nitrile (BPA-PEN) foams were prepared by supercritical carbon dioxide foaming method. First, BPA-PEN films obtained by solution casting method. The properties of BPA-PEN films and foams were characterized by scanning electron microscope (SEM), infrared spectrometer (FTIR), thermogravimetric analysis (TGA) and tensile test. The cell morphology of BPA-PEN foams with different adsorption pressure and foaming time have been investigated. The foaming temperature and saturation pressure have a great influence on the cell size and cell density of BPA-PEN foams. As the foaming temperature increases, when the foaming temperature is closer to the optimal foaming temperature, the viscosity of the BPA-PEN/CO2 homogeneous system become lower, which promotes the diffusion rate of CO2 in BPA-PEN and promotes the growth of bubbles. At the same time, the plasticizing effect of gas reduces the glass transition temperature of BPA-PEN/CO2. The best foaming temperature of BPA-PEN is 150 °C. When the foaming temperature exceeds the optimal foaming temperature, the cell density decreases, the cell wall becomes thicker, and the cell distribution becomes uneven. The mechanical properties of BPA-PEN changed significantly before and after foaming.

Anisotropic cellular structures from semi‐crystalline polymer templates

AbstractWe report an investigation to determine the effect of an anisotropic semi‐crystalline template on the resulting cell morphology of microcellular polymeric foams generated in these materials. Poly(ethylene terephthalate) (PET)‐polystyrene (PS) composite foams are prepared by using supercritical carbon dioxide (scCO2) not only as a foaming agent but also as a transport medium of styrene and initiator into a biaxially‐oriented PET templating film. The composite foam so obtained demonstrates a highly interpenetrating network verified by a single Tg of 98°C. Substrate orientation is observed not to dictate the cell formation; however highly anisotropic swelling and a shape‐templating phenomenon is observed, with the most significant dimension change in the thickness of the film. Introducing confinement in the direction of maximum dimension change is found to introduce a highly anisotropic lamellar cell architecture.

Carbon particulate and controlled-hydrolysis assisted extrusion foaming of semi-crystalline polyethylene terephthalate for the enhanced thermal insulation property

This work presents a facile method to produce low-density PET foams using pristine semi-crystalline resin by moisture-induced controlled-hydrolysis in a tight processing window (moisture content ∼ 0.12 wt.%). We investigated the effect of moisture and moisture containing activated carbon (AC) on the foam expansion ratio, cell morphology, and PET resin degradation and crystallization properties. Controlled-hydrolysis increased the melt-flow rate of PET resin (intrinsic viscosity: 0.52 to 0.54 dL/g) without losing crystallinity, and thus the PET foams possess better tensile properties (∼2 MPa stress and ∼100% strain) and higher thermal stability (>200°C) than chemically modified PET foams. The foam density could be made as low as ∼ 0.15 g/cm3 using a lab scale twin-screw extruder. A strand array die was also designed to produce plate-shaped foam samples. AC allowed easier control of the moisture content and delayed resin degradation in extrusion. Both AC and micrographite (mGr) could stabilize the PET foam morphology in extrusion and serve as good infrared attenuation agents (IAAs) in a simulated housing thermal insulation experiment.

Mechanical and flame‐resistance properties of polyurethane‐imide foams with different‐sized expandable graphite

AbstractPolyurethane‐imide (PUI) composite foams with expandable graphite (EG) of different sizes were prepared by a polyimide prepolymer method. EG particles were treated with a silane coupling agent to improve compatibility with the foam. The effect of EG particle size on cell morphology, thermal degradation, flame‐resistance and mechanical properties of PUI foams was investigated. Results showed that the mean cellular diameter of foams with EG particle was much higher than that of foams with surface‐modified EG particle at the same filler loading. When filler particle diameter increased from 20 to 90 μm, the compressive strength, density and closed‐cell ratio of foams increased, and then decreased when filler particle diameter further increased from 90 to 150 μm. Thermal stability of foams increased with the increasing filler particle diameter from 20 to 50 μm, and decreased with the increasing filler particle diameter from 50 to 90 μm. The limited oxygen index (LOI) value of foams with surface‐modified EG increased from 24.8% to 32.1% when EG particle diameter was below 90 μm. Foams with surface‐modified EG exhibited enhanced mechanical properties, thermal stability and flame resistance than foams with neat EG at the same loading.

Impact response of shear thickening fluid filled polyurethane foam core sandwich composites

Up to date, a considerable experimental work has been performed to reveal the impact behavior of polymer foam core sandwich composites. Though, a few attempts have been made to integrate shear thickening fluids (STF) in closed cell rigid polyurethane foams (PU). STF possess a unique rheological property providing a rapid response to the structure against impact loads. The effects of STF on polymer foam cell morphology, thermal stability, and mechanical performance are investigated with advanced characterization techniques. The drop-weight impact test results of sandwich composites show that STF filled PU foam cores exhibit a higher energy absorption rate compared to its neat counterpart. Specific compressive strength and impact energy absorbing capability of STF filled PU foam cores increase with respect to the higher cell thickness-to-length ratios and higher cell densities achieved with STF inclusion. In addition, STF filled PU foam core sandwich composites are found to respond with lower damage width compared to neat PU foams.

Morphological evaluation of ultralow density microcellular foamed composites developed through CO2-induced solid-state batch foaming technique utilizing water as co-blowing agent

In this work, microcellular acrylonitrile-butadiene-styrene foams were developed with utilization of water as a co-blowing agent and CO2as the primary blowing agent through the solid-state batch foaming process. The effect of saturation parameters with the content of the co-blowing agent has been studied extensively for various foaming attributes. The co-blowing agent enhanced the average cell size and the expansion ratio which are useful for better thermal insulation. The maximum expansion ratio of 29.9 obtained from the effect of saturation temperature and co-blowing agent, 23.6 from the effect of saturation pressure and co-blowing agent, and 22.4 from the effect of saturation time and co-blowing agent. The co-blowing agent significantly affects the cell morphology of polymeric foam with saturation parameters.

Prepare Foam with Injection Molding Method in Acrylonitrile-Butadiene-Styrene (ABS) Matrix Using Chemical Foam Agent

In this study, it is aimed to decrease the weight of the material by using polymer foam materials with lower density instead of commercial polymers which have wide usage area. For this purpose, polymer foam was produced by using an acrylonitrile butadiene styrene (ABS) matrix and an endothermic chemical foam agent using injection molding method. The foam cell morphology, shell layer thickness and mechanical properties of the final part were investigated taking into consideration the weight-changing ratios of the foam agent content (1-1,5-2-2,5-3%).

The synthesis and characterization of a DOPO derivative bearing an active terminal epoxy group: e-DOPO and its application in rigid polyurethane foam

DOPO and its derivatives are excellent phosphorus-based flame retardants, which are applied to a series of polymer materials. In this article, a DOPO derivative bearing an active terminal epoxy group was synthesized using a non-solvent method. Fourier transform infrared spectroscopy, nuclear magnetic resonance, mass spectrometry, ultra-performance liquid chromatography, differential scanning calorimetry, thermogravimetric analysis, and viscosity measurements were performed to determine its molecular structure, purity, thermal performance, and fluidity. A possible fragmentation mechanism of the as-prepared DOPO derivative was analyzed using electron ionization mass spectrometer. All the results indicate that the synthesis was successful and the product had satisfactory purity and its initial decomposition temperature (T5%) under nitrogen and air atmosphere was 246°C and 240°C, respectively. Then, as a comparison with dimethyl methyl phosphonate, triethyl phosphate, and DOPO, e-DOPO was applied to a rigid polyurethane foam to investigate its effect on the flame retardancy, thermal stability, and cell morphology of polyurethane foam by limiting oxygen index, cone calorimetry, thermogravimetric analysis, and scanning electron microscopy. The results indicate that e-DOPO has a greater effect than DOPO and can effectively reduce the heat release and smoke release and improve the limiting oxygen index and thermal performance of the polyurethane foam. The cell size of the sample containing e-DOPO was more uniform.

The distinctive nucleation of polystyrene composites with differently shaped carbon‐based nanoparticles as nucleating agent in the supercritical CO2 foaming process

AbstractMicrocellular polystyrene (PS)/carbon‐based nanoparticle (CbN) composites were prepared by a pressure release process using supercritical CO2 as the foaming agent. Nanocomposite foams with different shapes or dimensions but with CbNs with a similar surface structure showed a quite different cell nucleation. The underlying nucleation mechanism was semi‐quantitatively analyzed by classical nucleation theory, which indicated that the energy barrier for heterogeneous nucleation was related to the shapes of the fillers. Below 80 °C and 20 MPa, the nucleation density of the composites with different fillers showed marked differences, among which the nucleation density of PS/fullerene (FE) was the highest, followed by PS/carbon nanotubes (CNTs) and PS/thermally reduced graphene (TRG). However, the difference in nucleation density of PS/CbNs decreased with increase in filler content to 0.3 wt%. With increase in foaming temperature, the PS/TRG composite foams showed the highest cell density and no cellular merging and collapsing at 100 and 120 °C. The results obtained from DSC, rheology and positron annihilation lifetime spectroscopy measurements showed that FE nanoparticles exhibited the strongest plasticization effects on the matrix followed by CNTs and TRG nanoparticles. The distinctive plasticization suggested that the shapes of CbNs have a strong influence on the interaction between the PS matrix and the nanoparticles, which could affect the energy barrier for heterogeneous nucleation. The influence of CO2 on the rheology and thermal properties of the composites was investigated using high pressure DSC and high pressure rheology measurements. The results revealed that at high temperature high viscosity became the key factor to determining the cell morphology of nanocomposite foams by preventing bubble coalescence and collapse. © 2018 Society of Chemical Industry

Morphological, acoustical, and physical properties of free-rising polyurethane foams depending on the flow directions

Polyurethane foam is widely used for automobile compartments as sound absorption materials due to its excellent noise dissipation characteristics. This sound absorption property is strongly dependent on the cavity and pore structures of the foams, and the cell morphology can be modulated by controlling experimental parameters. Two types of gelling catalysts were demonstrated in fabrications of polyurethane foams to control the cell morphology. The cell morphology of the free-rising polyurethane foams was investigated using dibutyltin-dilaurate and triethylenediamnine gelling catalysts, and the cell structures were analyzed from the free-rising samples obtained in various sampling heights and flow directions. The finer cell morphology was obtained with the organotin type catalyst by the faster gelling reactivity, compared with the amine type catalyst. In addition, the spherical small cavities in the samples obtained from horizontal planes of the free-rising foams revealed higher sound absorption coefficient and physical toughness than the elliptical irregular cavities from vertical planes, due to the higher homogeneity of cavity distributions in the horizontal planes.