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Expanded thermoplastic polyurethane (ETPU) foam materials with superelasticity for footwear application were developed and investigated. ETPU foams with different ratios of CO2/N2 as foaming agents and ETPU foams prepared by pure nitrogen foaming with different kinds of foaming additives were prepared by supercritical (Sc) foaming technology, which further made into sheet forms through the steam molding process. TPU foam exhibits better cell structure, crystallization performance, and mechanical strength with the increased CO2 proportion. Further, the foams using 25% CO2–75% N2 and 50% CO2–50% N2, showed a lower density and excellent resilience and cyclic-compression performance. However, an increase of N2 ratio improves the dimensional stability and compression set of the foam. The introduction of foaming aids enhances the interaction between Sc-N2 and TPU. The ETPU foam prepared under the same conditions has a smaller density and a larger expansion ratio. Especially the ETPU foam prepared by Sc-N2 using monofluorodichloroethane as the foaming assistant as a co-blowing agent, the decrease in cell size (from 117.9 to 19.6 μm) and density (from 0.175 to 0.139 g/cm3) has observed. The study revealed the high potential of these materials in footwear applications and offered sound evidence for mass production in the industry.

This study used water as the physical blowing agent as well as microwave heating (MH) and convection heating (CH) to simultaneously foam and cure natural rubber foam (NRF). Various processing methods and parameters, such as single heating and sequential heating using a mix of CH and MH; were investigated. The correlation between these processing methods as well as different water loadings was then evaluated and compared in terms of physical appearance, density, and morphology. The NRF samples produced using sequential MH and CH (SMC) heating exhibited better shape and structure than samples produced using single heating of either CH or MH only as well as sequential CH and MH (SCM) heating at all water loadings. NRF samples with water loadings of 1.5 and 2.0 phr had a density of less than 0.1 g/cm3. The potential heating mechanism of all the heating methods explored in this study was proposed and discussed to further understand the microwave heating process. The findings of this study proved that water could be utilized as a physical blowing agent in the production of NRF products with microwave-assisted foaming.

Temperature, concentrations and mixing techniques are often the small details that make the difference in scientific advances and bridge the gap between a purely scientific approach and a purely practical one. This work first focuses on the thermal behavior of two blowing agents, widely used in the foam industry, namely sodium bicarbonate, citric acid and their mixtures, using a TGA-DSC. The second part of this work consists in preparing blends with low-density polyethylene at different concentrations and in determining the best combinations that will make it possible to prepare new blends based on optimal concentrations and then to study their physico-chemical properties. This study showed that sodium bicarbonate gives off more gas, since an increase in diameter of nearly 60% was obtained with 2 phr of the later, and nearly 30% with 1 phr of citric acid. However, for mixtures based on optimal concentrations, a synergy was obtained for the 60/40 and 50/50 mixture. Mixing the optimal concentrations also resulted in denser cells with finer and more regular sizes.

In this work, polypropylene (PP) was foamed via rotational molding using a chemical blowing agent (CBA) based on azodicarbonamide over a range of concentration (0 to 0.5% wt.). The samples were then analyzed in terms of morphological, thermal and mechanical properties. The morphological analysis showed a continuous increase in the average cell size and cell density with increasing CBA content. Increasing the CBA content also led to lower foam density and thermal conductivity. Similarly, all the mechanical properties (tension, flexion and impact) were found to decrease with increasing CBA content. Finally, the efficiency of the rotomolding process was assessed by producing neat PP samples via compression molding. The results showed negligible differences between the rotomolded and compression molded properties at low deformation and rate of deformation indicating that optimal rotomolding conditions were selected.

In this study, the synthesis of biopolyols derived from castor oil and glycerol was performed by enzymatic glycerolysis in a solvent-free system applying the lipases: Novozym® 435 (N435), from Candida antarctica fraction B, immobilized on macroporous anionic resin, and Eversa® Transform 2.0, a soluble formulation from Thermomyces lanuginosus. The biopolyols presented different conversion into mono- and diacylglycerol (MAG and DAG) owing to regioselectivity of the lipases. The resulting biopolyols were employed for the synthesis of polyurethane foams using different amounts of chemical blowing agent (water). The NCO source employed was polymeric methylene diphenyl diisocyanate (pMDI). The foams were compared, and the results showed that the PU foams obtained by using the biopolyol from lipase N435 presented uniform pore size and more desirable mechanical characteristics. Although this has arisen, the results obtained by using the lipase Eversa® Transform 2.0 showed the possibility of applying a low-cost enzyme to obtain biopolyols and foams, and there may be a possibility of competition with chemical catalysts.

In this study, foamed recycled high density polyethylene (rHDPE) parts were produced by rotational molding using different concentration (0 to 1% wt.) of a chemical blowing agent (CBA) based on azodicarbonamide. From the samples produced, a complete morphological, thermal and mechanical characterization was performed. The morphological analysis showed a gradual increase in the average cell size, while the cell density firstly increased and then decreased with increasing CBA content. As expected, increasing the CBA content decreased the foam density as well as the thermal conductivity. Although increasing the CBA content decreased both tensile and flexural properties, the impact strength showed a similar trend as the cell density with an optimum CBA content around 0.1% wt. Finally, neat rHDPE samples were also produced by compression molding. The results showed negligible differences between the rotomolded and compression molded properties indicating that optimal rotomolding conditions were selected. These results confirm the possibility of using 100% recycled polymers to produce rotomolded foam parts.

This work investigated the effects of a radiation-protective filler, namely bismuth oxide (Bi2O3), and blowing agents, namely azodicarbonamide (ADC) and oxy-bis (benzene sulfonyl) hydrazide (OBSH), on gamma attenuation and the mechanical, physical, and morphological properties of cellular natural rubber (NR) composites for potential use as light-weight and lead-free gamma-shielding materials. The contents of Bi2O3 were varied from 100 to 300 and 500 parts per hundred of rubber by weight (phr) and the contents of ADC or OBSH were varied from 0 to 8 and 16 phr. The results indicated that the addition of Bi2O3 enhanced the overall gamma-shielding ability, density, tensile modulus, and hardness (Shore OO), but lowered the tensile strength and elongation at break. On the other hand, the addition of ADC or OBSH resulted in decreases in the density, linear attenuation coefficient ( μ), and overall tensile properties but an increase in the mass attenuation coefficient ( μm), with ADC producing better mechanical properties than samples with OBSH. In addition, investigations on the properties of the cellular Bi2O3/NR composites under additional 35 kGy and 70 kGy gamma irradiation revealed that the irradiated samples had increased density, tensile modulus, and hardness (Shore OO), but decreased tensile strength, elongation at break, and μm after such ageing. In conclusion, the overall results suggested that the developed cellular Bi2O3/NR composites not only had efficient and promising gamma-shielding and mechanical properties but also offered comfort and light-weight to users, which could potentially reduce discomforts caused by wearing heavier conventional radiation-protective equipment.

Elastomer foams have been widely used in many applications and have shown potential in some advanced fields because of their excellent flexibility. Elastomers foamed with a physical blowing agent s...

In this work, for making rigid polyurethane foams, only water was used to serve as a blowing agent. Vietnam rubber seed oil-based polyol was also used. Following our previous research results, water content was fixed at 4 wt.% and glycerol content at 3 wt.%, as compared to biopolyol. The effect of the NCO/OH ratio, main catalyst (dibutyltin dilaurate), cocatalyst (triethylamine), and surfactant content as well as the surfactants on performances of foams was investigated through compressive strength, density, cell size, and size distribution. A suitable formulation for making foam by using biopolyol made from rubber seed oil was established. In parallel with it, foam based on commercial polyol derived from petroleum was also manufactured. The characteristics of the foaming process were assessed. The mechanical properties, thermal behavior, water absorption, and dimensional stability of foams were evaluated. The cellular morphology study shows that the cells of foam based on biopolyol were closed and rather uniform; however, cell size was 3% bigger and cell walls were also a bit thicker. The results showed that the properties of foam based on biopolyol were similar to those of petrofoams. This result may open a possibility to replace petropolyol with renewable biopolyol in foam fabrication.

CO2 adducts from hydrophobically-modified polyethylenimines (PEIs) in powder form are newly-developed environment-friendly blowing agents for polyurethanes (PUs). However, they are difficult to disperse into foaming systems that usually contain polyether polyols as the PU soft segments. Herein, we employ mixtures of di(propylene glycol) monomethyl ether-grafted polyethylenimines (DPG-PEIs) and poly(propylene glycol) (PPG) polyols to absorb CO2, with in situ formation of the CO2 adduct particles as PU blowing agents. Their CO2 saturation degrees, revealed by thermogravimetry, scatter in the range of 93–98%. The DPG side chains tend to be exposed at the particle–matrix interface to stabilize the particles. In addition, some PPG oligomers in the matrix might entangle with the CO2 adduct macromolecules during the in situ particle formation. The entangled PPG chains could further stabilize the suspending particles. The high grafting rate and high molecular weight of the PEI backbones could result in small particles, which largely thicken the foaming systems. The optimized blowing agents, with grafting rates between 5% and 8% and PEI backbone molecular weights not higher than 10k Da, show particle sizes from several hundreds of nanometers to ∼1 μm. The resultant foams demonstrate densities below 50 kg/m3 and compressive strengths over 200 kPa, comparable to the values from industrial foams. This in situ CO2 adduction has potential as a universal method suitable for PU foaming at an industrial scale.

Climate change makes it imperative to use materials with minimum global warming potential. The fourth-generation blowing agent HCFO-1233zd-E is one of them. The use of HCFO allows the production of polyurethane foam with low thermal conductivity. Thermal conductivity, like other foam properties, depends not only on the density but also on the cellular structure of the foam. The cellular structure, in turn, depends on the technological parameters of foam production. A comparison of pouring and spray foams of the same low density has shown that the cellular structure of spray foam consists of cells with much less sizes than pouring foam. Due to the small size of cells, spray foam has a lower radiative constituent in the foam conductivity and, as a result, a lower overall thermal conductivity than pouring foam. The water absorption of spray foam, due to the fine cellular structure, also is lower than that of pouring foam. Pouring foam with bigger cells has higher compressive strength and modulus of elasticity in the foam rise direction. On the contrary, spray foam with a fine cellular structure has higher strength and modulus in the perpendicular direction. The effect of foam aging on thermal conductivity was also studied.

Based on ready-made powder compositions of PEN-I materials modified with oxidized or thermally expanding graphite, fireresistant epoxy-novolac foams were obtained. By varying the content of the blowing agent, it is possible to control the apparent density of the foams within 100- 300 kg/m 3 . The physical and mechanical characteristics of the resulting foams were studied. A mathematical model for planning an experiment has been developed, which allows to determine the optimal composition. The results of tests to determine the resistance of foam samples to combustion showed that the resulting foams behave as fire-resistant structural materials.

Foaming behavior of the fluorinated ethylene propylene copolymer (FEP) and its composites assisted with supercritical carbon dioxide (scCO2) as the blowing agent were investigated. The batch foaming process was applied at temperature ranging from 250°C to 265°C and pressure ranging between 12 MPa and 24 MPa. The optimal foaming temperature and saturation pressure were obtained for both pure FEP and FEP composites with 1 wt% different-sized BaTiO3 as nucleating agent. The cell diameter of pure FEP foam ranging from 80–140 µm was observed while the cell diameter decreased to 20–40 µm after adding BaTiO3 particles. The cell density of foamed FEP with BaTiO3 increased significantly from 106 to 108 cells/cm3 and the expansion ratio ranged between 4.0 and 5.5. Moreover, a decrease in an abnormal phenomenon that expansion ratio for the pure FEP foam was observed as the saturation pressure increased. This unexpected phenomenon can be explained by the relationship between foaming and crystallization coupling processes.

In this work, cellulose fibres extracted from bamboo culms were used to fabricate two types of cellular materials: rigid foams and fibrous networks. A relatively simple and low-technology fabrication method is presented, using natural binders and blowing agents to manufacture rigid foams, and fibrillation by partial hydrolysis in H2SO4 to manufacture fibrous networks. The compressive response is related to the internal microstructure and processing parameters. In the case of fibrous networks, the achievable relative density range is determined by the length of initial fibres and extent of external fibrillation. The compressive properties are dictated both by the density of the network and strength of the fibrous bridges, showing a linear stiffness-density relationship due to the length of fibres, and an inverse relationship at increased external fibrillation. The rigid foams showed an orthotropic internal microstructure but nearly isotropic compressive response, due to the influence of the interpenetrating void structure on the deformation and fracture mechanisms. The results show the potential of bamboo-fibre porous materials as low cost, lightweight structural materials.

Blowing agents play an important role in the production of cellular polyurethanes. The traditional chemical blowing agent H2O/CO2 did not meet all application requirements. This led to the introduction of physical foaming agents in the 1950–1960s, which were subject to four further modifications due to climatic hazards. The recently introduced new generation of hydrofluoroolefins (HFOs) hydrocarbons is currently in the application assessment and meets the utility and climate requirements for now. Without waiting for a long-term final assessment of this blowing agent group, an attempt was made to introduce carbon dioxide in the form of adducts with aliphatic amines into the foaming process. As example compounds, CO2 adducts with aliphatic hydrocarbons containing also primary, secondary and tertiary nitrogen atoms in the same molecule were used. The synthesis of adducts was carried out by the absorption of carbon dioxide gas in a solution of amines in monoethylene glycol (MEG) and triethanolamine (TELA). The resulting solutions containing 12–16 wt % CO2 were next used in the application-oriented study. Amines regulating the foaming and gelation processes were used for the production of adducts, which allowed the elimination of organometallic gelling additives. Selected adducts were checked during the production of furniture chair seats on an industrial scale, obtaining integral foams in the range of density 190–294 kg/m3 and hardness 22–38 °ShA. In the production process of these foams carried out at PLASTPUR a double-stream foaming machine from Hennecke was used.

A flame-retardant jute/PP composite with excellent flame retarding and mechanical properties was prepared by the surface powder spraying process. The flame-retardant layer used the green and pollution-free β-cyclodextrin as a char agent. To improve the char forming ability of β-cyclodextrin, ammonium polyphosphate (APP) and melamine (MEL) were also used as acid source and a blowing agent, respectively. The results indicated that the char forming ability of β-CD could be improved by the reaction between β-CD and APP. The composite with 20% flame retardants containing β-CD, APP and MEL (1:2:1) showed the better flame-retardant properties. The LOI value of the composite increased to 27.8%, which reached the second fire resistance according to Japan's JISD 1201-77 standard, and the self-extinguishing time reached to 37 s. Compared with pure jute/PP, the PHRR value and Av-EHC value of the composites were reduced by 50% and 21%, respectively. The carbon residual at 700 °C was increased by 10.9%. The tensile strength and bending strength were increased by 5% and 19%. These results revealed that the flame retardancy, thermal stabilities and mechanical properties of composites containing β-CD/APP/MEL system were significantly improved by the surface powder spraying method.

The foaming behavior of poly(e-caprolactone)/poly (lactic-co-glycolic acid) (PCL/PLGA) blends and the effect of composition on porous structure, compression property and biocompatibility are investigated. Various portions of PLGA are added into matrix PCL at dispersion phase by melt blending. A solid-state batch foaming process is used based on supercritical CO2 as a physical blowing agent. With the PLGA content increased from 5 to 30 wt%, storage modulus and complex viscosity of PCL from rheological tests are improved significantly. Foaming tests reveal that incorporation of PLGA facilitates foaming of PCL by increasing viscosity. With an increase of PLGA content, pore size clearly decreases, and the open–cell content first increases and then decreases slightly. The maximum open-cell content value is greater than 86% for foamed 10 wt% PLGA. Moreover, uni-axial compression testing shows that dispersed PLGA improves the compressive stress distinctly. Cell structure evolutions at linear elasticity, plateau, and densification stages in compression tests are also investigated. Cell viability results demonstrate that there are more and denser live HUVECs detected on scaffold with increase of PLGA content. Compression strength of PCL/PLGA scaffold has more contributions to cell viability than that of porosity and open-cell content.

In this article, poly (lactic acid) (PLA) was foamed via batch foaming using supercritical nitrogen as a physical blowing agent by two methods, conventional foaming process (CFP) and low-temperature foaming process (LTFP). The fabrication processes, cell morphologies, thermal properties, crystallization behavior, and electrical resistance of resulted foams were studied to investigate the effect of foaming on these properties of PLA. It was found that the foams resulted from CFP method have micrometric cell sizes, while LTFP method led to nanometric cell structure and high cell density. Also scanning electron microscopy showed that the PLA foams have a heterogeneous cellular structure. The results showed that the foaming process increased the melting point and degree of crystallinity of PLA, which led to decrease in the electrical resistance of samples.

This paper presents an enhanced gas chromatography–mass spectrometry method for the separation of cell gases in polyurethane foam. The novel method was then tested on several polyurethane foams produced at different mixing times, showing successful results. The measurement of gas content in polyurethane foams has been rarely considered in published literature. This parameter, indeed, plays a critical role in the deterioration of polyurethane foam thermal conductivity. This is because of the diffusion of gases which is the main mechanism of foam aging. Hence, an improved gas chromatography–mass spectrometry method was developed to offer simultaneous separation of several types of gas in only one column, using gas chromatography as its main concept. The composition of a sample gas consisting of N2, O2, CO2, and C5H10 was accurately calculated by measuring the ratio of each peak area on the chromatograms, with argon being used for sampling. This fast and simple method was found to be useful, on one hand for the accurate determination of C5H10 and CO2 cell gases used as blowing agents, and on the other hand for N2 and O2 air gases that diffuse rapidly from the surrounding environment into foam cells. The effect of mixing time on foam kinetics, cellular structure, foam thermal conductivity, and the overall thermal conductivity of cell gas mixture was also investigated. By complex analysis of foam density, the presence of open cells, cell size, and thermal conductivity of cell gas mixture, the lowest measured value of foam thermal conductivity was explained. The major goal of these experiments was to show the importance of foam cell gas analysis, together with foam structure, which is uniquely done to contribute to the understanding of polyurethane foam thermal conductivity. The thermal conductivity of cell gas mixture is considered as an example of the potential applications of this novel gas chromatography–mass spectrometry method.

The presented research concerns the production of foamed thermoplastic composites reinforced with natural fiber in the direction of obtaining lightweight construction materials. The purpose of the work was to obtain solid and porous polypropylene (PP) systems reinforced with cut basalt fiber (WB). As a foaming agent, Expancel MB930 microspheres from AkzoNobel were used, while to improve the adhesion between the fiber and the PP matrix, an additive in the form of polypropylene grafted with maleic anhydride PP-g-MA (Polybond 3200) was used. The production of composites involved mixing the ingredients by extrusion and then molding PP/WB composite in the injection process. In addition, at the injection stage, selected systems were expanded with 1.5% by weight of microspheres. The work evaluated the impact of fiber content (5, 10, 15% by weight) and its preparation as well as the impact of a compatibilizer on the properties of solid PP composites and a comparison of these properties with analogous systems with a porous structure. PP/WB materials were characterized in terms of physical and mechanical properties (density determination, static tensile and bending test); DSC and TGA thermogravimetric analysis. Foamed PP systems with fibers have better mechanical properties compared to pure PP; the addition of a compatibilizer to PP/WB composites increases the strength parameters compared to systems without its participation.

Polyurethane foam insulation based of environmentally friendly chemical components using novel foaming agents was obtained. Physical and mechanical properties of thermal insulation was investigating. The infl uence of foaming agents on insulation properties and production technology of preinsulated pipes, fi ttings and polyurethane shells was studied. It is shown that when using water and dimethoxymethane, polyurethane foam insulation has quite good physical and mechanical properties and can be used in the production of PI pipes, shells and fi ttings.

This paper focuses on the development of polyvinylidene fluoride microfoam by implementing a chemical blowing agent through a continuous process. The objective was to investigate the effects caused by varying concentrations of chemical blowing agent, the use of a master batch as formulation variables, and variation of die temperature on the properties of polyvinylidene fluoride foam produced continuously. By using a 10% master batch formulation (contains 2% chemical blowing agent in final product), the cell density was increased while the cell size and foam density were decreased; the average cell size, cell density, and void fraction were found to be 50 μm, 7.7 × 106 cells/cm3, and 33%, respectively. This is due to the increased cell density primarily due to the increased nucleation sites. At a lower chemical blowing agent, concentration of 1%, the die temperature was varied over a range of 125–145 °C, as this is approximately the melting point of the polyvinylidene fluoride. Decreasing the die temperature from 135 °C to 130 °C caused the cell density to increase and cell size to decrease, while void fraction decreased from 58% to 39%. This is due to the loss of melt strength upon increasing the temperature of the melt PVDF as it exits the die. Keywords: Polyvinylidene fluoride foam, Chemical blowing agents, Continuous process, Die temperature, Master batch

Polyurethane foams (PUFs) are a significant group of polymeric foam materials. Thanks to their outstanding mechanical, chemical, and physical properties, they are implemented successfully in a wide range of applications. Conventionally, PUFs are obtained in polyaddition reactions between polyols, diisoycyanate, and water to get a CO foaming agent. The toxicity of isocyanate has attracted considerable attention from both scientists and industry professionals to explore cleaner synthesis routes for polyurethanes excluding the use of isocyanate. The polyaddition of cyclic carbonates (CCs) and polyfunctional amines in the presence of an external blowing agent or by self-blowing appears to be the most promising route to substitute the conventional PUFs process and to produce isocyanate-free polyurethane foams (NIPUFs). Especially for polyhydroxyurethane foams (PHUFs), the use of a blowing agent is essential to regenerate the gas responsible for the creation of the cells that are the basis of the foam. In this review, we report on the use of different blowing agents, such as Poly(methylhydrogensiloxane) (PHMS) and liquid fluorohydrocarbons for the preparation of NIPUFs. Furthermore, the preparation of NIPUFs using the self-blowing technique to produce gas without external blowing agents is assessed. Finally, various biologically derived NIPUFs are presented, including self-blown NIPUFs and NIPUFs with an external blowing agent., This research is part of grant PID2020-119546RJ-I00 funded by MCIN/AEI/10.13039/501100011033.

In the present study, semi-crystalline polypropylene (PP) and amorphous polystyrene (PS) were adopted as matrix materials. After the exothermic foaming agent azodicarbonamide was added, injection molding was implemented to create samples. The mold flow analysis program Moldex3D was then applied to verify the short-shot results. Three process parameters were adopted, namely injection speed, melt temperature, and mold temperature, three levels were set for each factor in the one-factor-at-a-time experimental design. The macroscopic effects of the factors on the weight, specific weight, and expansion ratios of the samples were investigated to determine foaming efficiency, and their microscopic effects on cell density and diameter were examined using a scanning electron microscope. The process parameters for the exothermic foaming agent were optimized accordingly. Finally, the expansion ratios of the two matrix materials in the optimal process parameter settings were compared. After the experimental database was created, the foaming module of the chemical blowing agents was established by Moldex3D Company. The results indicated that semi-crystalline materials foamed less due to their crystallinity. PP exhibits the highest expansion ratio at low injection speed, a high melt temperature, and a low mold temperature, whereas PS exhibits the highest expansion ratio at high injection speed, a moderate melt temperature, and a low mold temperature.

In this work, microcellular acrylonitrile-butadiene-styrene foams were developed with utilization of water as a co-blowing agent and CO2 as 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.

The effects of blowing agent, talc, and injection velocity on properties of polypropylene molded parts were presented. Blowing agent was dosed to plastic in amounts 1–2% and talc 10–20%. The results of selected properties, such as weight, thickness, hardness, impact strength, tensile strength, and gloss, were presented. The article also presents microscopic investigations. The blowing agent and talc content have a large impact on mechanical properties and gloss of parts than addition of blowing agent. The use of the blowing agent in an amount of 2 wt% will allow the reduce injection cycle time by reducing the hold pressure and hold time. Addition of blowing agents lowers of tensile strength, hardness, impact strength, and significantly affected the gloss. Talc filler contributes to a significant increase in the weight of parts, a decrease in hardness, impact strength, and tensile strength. The injection velocity has no significant effect on parts properties.

Currently, the fabrication of microcellular semi-crystalline polymer foams using supercritical CO 2 as a blowing agent had attracted worldwide interest. In this paper, a novel and facile isothermal crystallization induction method was proposed to prepare biodegradable microcellular semi-crystalline poly (butylene succinate) (PBS) foams by supercritical CO 2 . In order to improve melt viscoelasticity and increase cell nucleation number, chain extender (CE) and polyhedral oligomeric silsesquioxane (POSS) were introduced into PBS through melt blending method. Differential scanning calorimetry results showed that with the addition of CE and POSS, the crystallization temperature of various PBS samples increased and their crystallinity kept unchanged almost. Compared with those of pure PBS, the complex viscosity and storage modulus of chain extended PBS (CPBS), PBS/POSS and CPBS/POSS increased. The effect of chain extension, POSS addition and induction time on the foaming performance of various PBS samples was studied systematically. Microcellular CPBS/POSS foam was successfully fabricated at the induction time of 18 min and foaming temperature of 90 °C, in which the cell size and volume expansion ratio could reach 6.80 ± 1.21 μm and 7.48 ± 0.03 times, respectively. Finally, the formation mechanism of various PBS foams by isothermal crystallization induction method was presented and the thermal conductivity of various PBS foams was investigated.

Decreased viscosity due to the influence of blowing agent in thermoplastic polymer melts is a key issue for understanding the process of foam extrusion. In a process for direct foam extrusion, a novel approach for inline viscosity measurement of single-phase systems in single screw extruders is used to experimentally evaluate a viscosity decrease. Two blowing agents (propane and carbon dioxide) are tested for their effect on the viscosity of a polypropylene melt. While mass fractions of blowing agent below [Formula: see text] show little to no effect in regard to viscosity reduction compared to a pure polymer melt, a mass fraction of [Formula: see text] already results in significantly decreased viscosity values. While melt temperature influences the viscosity of the polymer melt, measurements show no significant additional effect in regard to a lowered viscosity of a single-phase system of polymer and fully dissolved blowing agent.

Currently, the formation of nanocells and complex cellular structure (CCS) in semi-crystalline polymer using supercritical fluids as blowing agent had become a big and newly developing challenge worldwide. In this paper, a facile methodology of polymer blending and batch foaming was proposed to fabricate CCS with large cells in micro-size and small cells in nano-size in semi-crystalline poly (lactic acid) (PLA) foams. Thermoplastic polyurethane (TPU) was introduced into PLA through melt mixing method to improve the viscoelasticity and foaming behaviors of PLA. Differential scanning calorimetry results showed that with the addition of TPU, the cold crystallization temperature of various PLA samples increased and their crystallinity kept unchanged almost. Compared with those of pure PLA, the complex viscosity, and storage modulus of PLA/TPU blends increased. Interestingly, with the increasing TPU content, the CCS appeared and became distinct in PLA/TPU blending foams as well as the thermal conductivity of various PLA foams decreased, respectively. The formation mechanism of CCS in nanocellular PLA/TPU blending foams was proposed and explained by schematic diagram. With the foaming temperature rising from 135 to 140 °C, a transition from nano-cells to micro-cells was also observed in PLA/TPU 5 blending foam, due to the decreased melt viscosity.

Foamable inks for inkjet-based 3D printing processes, like PolyJet™ printing, open the way to produce light-weight additive manufactured parts in one process step. A new ink formulation, consisting of acrylic components and a modified blowing agent is presented. The goal is to directly produce foam during the printing process in contrast to other methods for 3D printing of foams, which are currently used. The presented characterization of the ink is focused on viscosity, decomposition temperatures of the blowing agents, and UV–polymerization of the ink matrix. More advanced ink characterization includes jetting tests at different inkjet-printheads and foaming of printed layers, as well as microscopic characterization of the foams.

This study is focused on the fabrication and evaluation of polyurethane (PU) foam fabricated using soy-based polyol that can potentially replace conventional petroleum-based PU foam for thermal applications. Rigid soy-based PU foam samples investigated in this study were produced by copolymerization of diisocyanate with soy-based polyol in presence of Xiameter X0193 surfactant, dibutyltin dilaurate (DBTL) as a catalyst, and water as a blowing agent. Different formulations with varying amounts of blowing agent and catalyst were investigated to optimize the mechanical and thermal properties of soy-based PU foam when compared to commercial petroleum-based foam as a control sample. The prepared samples were tested for density, compressive strength, thermal conductivity, tensile strength, dimensional stability, and thermal stability using the ASTM standards. The cellular structure of the fabricated foam samples was investigated using scanning electron microscopy. It was observed that an increase in density leads to a decrease in insulation. Overall, soy-based foams exhibited similar thermal conductivity as compared to petroleum-based foams.

A novel hybrid silicone foam was successfully prepared by mixing shear stiffening gel (STG) with polymethylvinylsiloxane (MVQ) using expandable microsphere as a blowing agent. Storage modulus of STG/MVQ composite foam increased from 0.045 MPa to 0.38 MPa, when the shear frequency shifted from 0.1 Hz to 100 Hz, presenting a remarkable shear stiffening characteristic. The tensile result demonstrated that the elongation at break of the hybrid foam was as high as 814%. Besides, the hybrid foam gained excellent self-healing performance due to the cold-flow feature and viscous state of STG. More importantly, the drop hammer test indicated the safeguarding performance enhanced as the STG contents increased, with the residual peak force decreasing from 36.72 KN to 31.50 KN. In addition, a possible mechanism was proposed that it was the dynamic “B O bonds” that played a significant role in shear stiffening.

Glass fiber (GF) reinforced polycarbonate (PC) is a composite material that is used in the production of mobile phones, automobiles, LCD monitors, and laptops. With an increase in the GF co...

The biodegradability and low cost of natural fibers make them attractive for composite applications. However, the density of natural fibers is higher than that of polymers, which increases the dens...

By proper formula of recycled polyethylene terephthalate (r-PET) and additives (i.e. chain extender, nucleating agent, antioxidant, blowing agent, antistatic agent, processing aid, and impact modifier), a r-PET composite foaming sheet with high crystallization temperature (Tc; 217 °C), good flexural strength (623 Kgf/cm2), great tensile strength (506 Kgf/cm2), high melting temperature (Tm; 245 °C), good flexural modulus (22,881 Kgf/cm2), moderate surface electric resistance (8.6 × 1011 Ω/sq.), low density (0.85 g/cm3), small average cell size (160 μm), and high notched Izod impact strength (155 J/m) has been successfully prepared with thermochemical extrusion foaming process. To evaluate the feasibility for electronic package, furthermore, we have also manufactured the prototype of electronic package and passed the falling examination at 1 m, proving that it is a potential microcellular cushion composite with excellent physical characteristics.

Plastics is a group of materials commonly encountered on a daily basis by many people. They have enabled rapid, low-cost manufacturing of products with complicated geometries and have contributed to the weight reduction of heavy components, especially when produced into a foamed structure. Despite the many advantages of plastics, some drawbacks such as the often fossil-based raw-material and the extensive littering of the material in nature, where it is not degraded for a very long time, needs to be dealt with. One way to address at least one of the issues could be to use polymers from nature instead of fossil-based ones. Here, a β-glucan concentrate originating from barley was investigated. The concentrate was processed into a foam by hot-melt extrusion, and the processing window was established. The effect of different blowing agents was also investigated. Water or a combination of water and sodium bicarbonate were used as blowing agents, the latter apparently giving a more uniform pore structure. The porous structure of the foamed materials was characterized mainly by using a combination of confocal laser scanning microscope and image analysis. The density of the samples was estimated and found to be in a similar range as some polyurethane foams. A set of 3D parameters were also quantified on two selected samples using X-ray microtomography in combination with image analysis, where it was indicated that the porous structure had a pre-determined direction, which followed the direction of the extrusion process.

The melting and thermal degradation of porous polylactide have been studied by differential scanning calorimetry and thermogravimetric analysis. The pores are formed from a solution of azobisizobutyronitrile in acetone and ammonium carbonate in a water–acetone mixture and thermostatting of the filled polymer and via exposing the samples to a medium of supercritical carbon dioxide. It has been shown that the blowing agents destroy the crystalline regions of the polymer and decrease the melting point and heat of fusion of the crystallites depending on the plasticizing impact on the polymer matrix, the pore formation method, and the nature of the blowing agent. Pore formation in polylactide leads to a decrease in the initial thermooxidative degradation temperature of the polymer and a change in the process mechanism.

Cellulose nanofibers (CNFs) were modified with 2 bilayers coating composed of polyethlenimine (PEI), melamine and phytic acid using a layer-by-layer self-assembly technique. The (PEI + melamine/phytic acid)2 based coating was successfully deposited on the surface of modified cellulose nanofibers (MCNFs). Herein, the CNF referred to the carbon source and the phytic acid was chosen as the acid source. Polyethylenimine and melamine served as the blowing agents. Then the CNF and MCNF were introduced to the polyvinyl alcohol (PVA) matrix to investigate the thermal decomposition, flammability, light transmittance and mechanical properties of the PVA/CNF and PVA/MCNF composites. The thermal decomposition of PVA-MCNF-6 (with 6 wt% MCNF) was retarded compared with that of pure PVA. Meanwhile, the addition of 6 wt% MCNF obviously reduced the peak heat release rate of PVA, as evidenced by the 37% reduction. The PVA/CNF and PVA/MCNF composites exhibited similar light transmittance compared with the pure PVA film. Moreover, the addition of CNFs in the PVA matrix resulted in higher tensile strength and elongation at break than those of the PVA matrix.

Thermal conductivity (λ) of a rigid polyurethane (PU) foam plays a vital role in determining the performance of thermal insulation. To accurately predict this property for a given recipe in a few seconds is the first step towards striking a balance between compressive strength, λ, and more properties of a foam product in industrial applications during formulation. What experimentally observed from PU closed-cell foams made from PAPI-27 Polymeric Methylene Diphenyl Diisocyanate (PMDI), Voranol 360, and n-pentane were: (1) foam shrinkage and even collapse occurred on both low (typically less than 0.9) and ultra-high (close to 2.0) indexes of isocyanate (IA); (2) to achieve the lowest λ for the best thermal insulation, it was suggested to use the highest IA without any foam shrinkage, the fastest stirring rate under safety, and the least physical blowing agent (PBA) until a sharp turn in the trend of λ; (3) there was a definite link between foam density (ρf), closed cell content (ccc), and λ: (a) a low λ requested a high ρf and ccc (b) a denser foam could be achieved by at least three ways. Increasing the agitation rate had a limit, above which the change in density became insignificant. However, a higher IA and reducing the amount of PBA had always been linear with ρf. (c) ρf was the cornerstone of ccc. In low ρf range, a growth of density gave rise to a distinct improvement of ccc, beyond which ccc reached a plateau for any higher density. The foam thermal conductivity during polymerization was successfully simulated by Matlab with 0.0157 % deviation. λ was initially dominated by the contribution from the resin mixture until the gel reaction time. Then, the dominant was shifted to the contribution by the gas component. The magnitude of thermal radiation was rather low throughout the reaction.

Melamine polyphosphate (MPP) was firstly microencapsulated by toluene diisocyanate cross-linked carboxymethyl chitosan (CMCS), and then was applied to prepare flame retardant (MCMPP) and water resistant thermoplastic polyurethane (TPU) composite. Characterization by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) indicated that the cross-linked carboxymethyl chitosan was microencapsulated on the surface of MPP particles. The increased water contact angle demonstrated that microencapsulation significantly reduced hydrophilic groups in CMCS. The limiting oxygen index value was increased to 29.4%, and UL-94 test rating was reached up to V-0 for the TPU composite sample containing 15 wt% MCMPP. Moreover, the incorporation of MCMPP significantly reduced the peak heat release rate, the total heat release, the total smoke release and carbon monoxide production by 65.9%, 24.1%, 87.3% and 60.6%, respectively. Morphology observation by SEM suggested that flame retardants be well dispersed and can form compact char residue. The TPU/MCMPP composite sample achieved V-0 rating in UL-94 test after immersing in water for 72 h at 70 °C, which is due to the increased compatibility of MCMPP with the matrix provided by the hydrophobic structure of microencapsulated cross-linked carboxymethyl chitosan. It is proposed that microencapsulated MPP simultaneously play roles of acid source, carbonization agent and blowing agent in the formation of intumescent char layers during combustion.

In this work, a new strategy was proposed to improve the foamability of poly(aryl ether ketone) (PAEK) based on novel long-chain branched PAEK (LCB-PAEK). To improve the resin melt strength, the amorphous LCB-PAEK was fabricated via a simple ternary copolymerization of phenolphthalein, 4,4′-difluorobenzophenone, and 1,1,1-tris(4-hydroxyphenyl)ethane. To regulate the extent of reaction and avoid crosslinking, 4-fluorobenzophenone was introduced as the end-capping reagent. The presence of long-chain branches were proved by gel permeation chromatography and rheological characteristics, including storage modulus and tensile viscosity. Afterwards, the prepared LCB-PAEK samples were foamed using supercritical carbon dioxide (ScCO2) as the blowing agent. The influence of branching content on foaming results was investigated in detail, and significant improvement in foamability was observed. By regulating the foaming parameters, the highest expansion ratio of 27.5 was achieved, which was almost ninefold higher than that of linear PAEK. In addition, the good mechanical properties indicated the promising applications of LCB-PAEK foams as high-performance structural foam.

Thermal expansion microcapsules were prepared by using acrylonitrile and methyl methacrylate as polymerization monomer and isooctane as the blowing agent. The structure, composition, appearance, an...

Mold filling plays a crucial role in determining the cells' structural morphology and uniformity in high-pressure foam injection molding. This process affects the formation, deformation, and dissolution of premature cells, which nucleate in the melt/gas mixture during the mold filling. We investigated the mold-filling phenomena and the cell structure development in the high-pressure foam injection molding process with mold opening. Polystyrene was used as the matrix, and carbon dioxide and nitrogen were used as physical blowing agents. We adopted an in-situ visualization technique, which enabled us to monitor and study the formation and evolution of the cells during the mold-filling and melt-packing phases. It was found that both the shape and the size of cells, which had nucleated during the mold filling process inside the melt, were changed by the packing condition selected. Statistical analyses have shown that the packing pressure and its duration were the most influential parameters affecting the size and the shape of cells that had nucleated in the melt before the mold opening. A greater packing pressure and a longer packing time resulted in a smaller cell size with a larger deformation in the melt during mold filling. A proper packing condition eventually removed all of the cells and re-dissolved them back into the melt before mold opening. The effect of the mold-filling parameters on the final cellular structure was also investigated, using carbon dioxide and nitrogen as physical blowing agents. A complete dissolution of the premature cells during the mold-filling and packing phases resulted in a more uniform and finer cellular structure after mold opening. The obtained results and the developed knowledge provide a deeper insight into the fundamental aspects of cellular structure development in foam injection molding process, which can be used to produce highly expanded, ultra-light foams with uniform cell structure.

Although it is known that the extrusion process significantly affects the cell morphology of thermoplastic polyurethane (TPU) foam, its effect on foam shrinkage, which is a critical problem in foam processing, has not yet been studied. Extrusion also significantly influences the thermomechanical properties and foaming behavior of TPUs. In this study, polyether-based TPUs of three different hardness levels were foamed by one-step batch foaming using CO2 as the blowing agent. Although the molecular weight decreased significantly after extrusion, the re-distribution of hard segments in the TPU caused the cell density to increase by 30 to 50 times. In addition, the elongation at break of the TPU solids increased by 40%. The cell size, expansion ratio, cell density, and shrinkage versus saturation temperature (Tsat), and saturation pressure (Psat) were also studied extensively. The results show that Tsat has a significant effect on expansion ratio and Psat has more impact on foam shrinkage, while the extrusion processing has little impact on foam shrinkage. In our case, a TPU foam with more than six times expansion and a fine cell structure with limited shrinkage was successfully prepared.

Poly(ethylene-co-octene) (POE) elastomers with different copolymer compositions and molecular weight exhibit quite distinctive foaming behaviors and dimensional stability using supercritical carbon dioxide (CO2) as a blowing agent. As the octene content decreases from 16.54% to 4.48% with constant melting index of 1, both the melting point and crystallinity of POE increase, due to the increase in fraction of ethylene homo-polymerization segment. the foaming window of POE moves to a narrow higher temperature zone from 20–50 °C to 90–110 °C under 11 Mpa CO2 pressure, and CO2 solubility as well as CO2 desorption rate decrease, so that the average cell diameter becomes larger. POE foams with higher octene content have more serious shrinkage problem due to lower compression modulus, weaker crystal structure and higher CO2 permeability. As POE molecular weight increases at similar octene content, there is little effect on crystallization and CO2 diffusion behavior, the foaming window becomes wider and cell density increases, mainly owing to higher polymer melt strength, the volume shrinkage ratio of their foams is less than 20% because of similar higher polymer modulus. In addition, when the initiate expansion ratio is over 17 times, POE foams with longer and thinner cell wall structures are more prone to shrinkage and recovery during aging process, due to more bending deformation and less compression deformation.