Chemical Foaming Agent Research Articles

Enzymatic depolymerization of polyester: Foaming as a pretreatment to increase specific surface area

AbstractPoly(ethylene terephthalate) (PET) is widely used for its high strength‐to‐weight ratio, gas barrier properties, and chemical resistance. The growing PET use highlights the demand for a better recycling system. Enzymatic recycling, alongside mechanical and chemical methods, is eco‐friendly and yields properties similar to virgin PET. Substrate properties (Tg, crystallinity, and specific surface area [SSA]) and enzyme stability significantly impact conversion efficiency. Higher SSA and lower crystallinity tend to yield improved depolymerization when employing leaf compost‐cutinase (LCC‐ICCG) enzymes. This study explored melt extrusion and foaming as pretreatment techniques to modify PET structural properties, using a low‐cost chemical foaming agent (CFA). The monomer conversion rate and efficiency during depolymerization were measured and related to the processing, extrudate micro‐ and meso‐structure, and polyester type. Pretreated PET substrates showed reduced Tg, crystallinity, density, and enhanced SSA, resulting in a 90% mass loss for foamed RPET and VPET substrates within 2 days. In contrast, PET with ~30% of cyclohexanedimethanol comonomer exhibited a nearly 50% lower depolymerization rate, with zero BHET production. It indicates that the combination of low crystallinity, low Tg, and high SSA leads to improved monomer conversion. These findings emphasize the significance of amorphization and foaming in enhancing PET enzymatic depolymerization.

Comparative Study of the Foaming Behavior of Ethylene-Vinyl Acetate Copolymer Foams Fabricated Using Chemical and Physical Foaming Processes.

Ethylene-vinyl acetate copolymer (EVA), a crucial elastomeric resin, finds extensive application in the footwear industry. Conventional chemical foaming agents, including azodicarbonamide and 4,4'-oxybis(benzenesulfonyl hydrazide), have been identified as environmentally problematic. Hence, this study explores the potential of physical foaming of EVA using supercritical nitrogen as a sustainable alternative, garnering considerable interest in both academia and industry. The EVA formulations and processing parameters were optimized and EVA foams with densities between 0.15 and 0.25 g/cm3 were produced. Key findings demonstrate that physical foaming not only reduces environmental impact but also enhances product quality by a uniform cell structure with small cell size (50-100 μm), a wide foaming temperature window (120-180 °C), and lower energy consumption. The research further elucidates the mechanisms of cell nucleation and growth within the crosslinked EVA network, highlighting the critical role of blowing agent dispersion and localized crosslinking around nucleated cells in defining the foam's cellular morphology. These findings offer valuable insights for producing EVA foams with a more controllable cellular structure, utilizing physical foaming techniques.

Preparation and properties of PP/SEBS foam materials

In this study, styrene-ethylene-butene-styrene block copolymer (SEBS) is blended with polypropylene (PP) to improve the melt strength of PP. Azodicarbonamide (AC) is used as a chemical foaming agent to prepare PP foaming materials with good mechanical properties by moulding foaming. The melt strength of the material, the content of the nucleating agent and the concentration of the foaming agent will affect the foaming effect of the material. Orthogonal optimization experiments are designed for these three factors to explore the best ratio of foaming materials. The results show that when PP:SEBS = 85:15, the addition amount of nano-SiO2 is 3%, and the content of AC foaming agent is 5%, the cell structure of the foaming material is the best. The cell structure is observed by SEM,the average cell diameter is reduced to 45.73 μm, and the cell density is increased to 4.12 × 106 cells cm−3. The apparent density of the material is measured to be 0.62 g cm−3, which is 32% lower than that of pure PP (0.91 g·cm−3). The tensile strength of PP/SEBS foamed composites is lower than that of pure PP and pure PP foamed materials, but its elongation at break is 124.3% higher than that of pure PP, and 238.8% higher than that of pure PP foamed materials. The bending strength of PP/SEBS foamed material is lower than that of pure PP and pure PP foamed material. The impact strength of PP/SEBS is only 8.4 % lower than that of pure PP, and 60.8 % higher than that of pure PP foamed material.

The effect of nanoclay filler addition on the foaming and mechanical properties of polypropylene

AbstractIn this study, onium‐ion‐added nanoclay (NC)/microcellular polypropylene (PP) composites were created using a conventional injection molding machine. A chemical foaming agent was utilized to facilitate mixing. The primary focus was to analyze how altering the NC content affects the mechanical characteristics and the properties of the endothermic chemical foaming agent added PP/NC composites. The composites were created using a chemical foaming agent at a weight ratio of 1 wt% and NC at weight ratios of 0 wt%, 2.5 wt% and 5 wt%. The findings indicated that an increase in the NC ratio led to higher cell count and cell density, along with a reduction in cell diameter. Additionally, the outcomes demonstrated that the foaming of PP/NC composites resulted in decreased modulus of elasticity and tensile strength while enhancing impact strength. © 2024 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Tailoring porosity and acoustic properties in bi-layered diatomite-based foams through multiscale structural approach

A tailored multifunctional diatomite-based foam with porosity and density gradients has been developed through a new technology that enables an unprecedented integration of acoustic, mechanical and thermal properties. The production process consists of a custom-made pilot plant for foaming capable of mixing solid phases, such as diatomite, catalyst and silicon chemical blowing agent, with a liquid solution, made of sodium silicate cross-linking agent and vegetable foaming agent. The resulting foam exhibits a coin-like performance, with a side A showing an open cell morphology, high interconnectivity and low density, and a side B characterized by a partially open cells morphology, low interconnectivity and high density. This approach enables morphology and density to be layered along thickness. A transition zone with intermediate density and morphology separates the two sides, thus rendering the structure a gradient meta-material with hierarchical porosity. Macro- and micro-porosity are generated by physical and chemical foaming agents, while diatomite is responsible for the presence of nanoporosity. The gradient structure has a huge influence on functional properties, such as acoustic (α equal to 0.95 at 800 Hz for side A), thermal (thermal conductivity less than 0.061 W/(m·K) for side A and less than 0.12 W/(m·K) for side B) and mechanical properties.

ANALYSIS OF THE RELATIONSHIP BETWEEN DENSITY AND MECHANICAL PROPERTIES IN EXPANDED PVC FILMS WITH THERMOPLASTIC MICROSPHERES

The production of artificial leather is critically important for the manufacture of various goods, such as vehicle interiors. This manufacturing process is typically carried out by "layer addition", and the final product is called "Supported Expanded Vinyl" or SEV. This process uses chemical foaming agents that degrade with heat to generate nitrogen and carbon gases. Due to new environmental regulations, companies are opting for more sustainable measures such as thermoplastic microspheres that expand with heat. For foams expanded with this method, it is crucial to consider the viscoelastic properties at different expansion ratios as the product's performance in its application depends on these. This paper describes the differences in the mechanical properties of the yield limit and rupture resistance of PVC foams expanded with a chemical agent and those expanded with a physical agent. From the statistical analysis of the behavior of these properties at different densities, prediction models were obtained, and the statistical correlation between the factors and their responses was established. Key words: thermoplastic microspheres, viscoelastic properties, mechanical properties.

Impact of Composition Ratio on the Expansion Behavior of Polyurethane Grout.

Different formulations of foaming polyurethane grout offer controlled expansion rates. This is crucial for precision in filling voids without exerting excessive pressure on surrounding structures, which could potentially cause damage. This study focuses on the impact of composition on the expansion performance of tailor-made polyurethane grouting materials. Initially, multiple unknown chemical reaction kinetic parameters were identified by combining free expansion tests, which involved measuring density and temperature changes, with the particle swarm optimization algorithm. A numerical simulation, integrating chemical kinetic models and fluid flow equations, was established to replicate the free expansion process of polyurethane grout in a cup, aligning with our experimental results. Subsequently, we analyzed the polymerization process of polyurethane grout with varying compositions to determine the effect of composition ratios on grout expansion. Our findings reveal that the expansion ratio of foaming polyurethane is predominantly influenced by the concentrations of physical and chemical foaming agents, followed by isocyanate concentration. Polyol, in contrast, exerts a relatively minor influence. Furthermore, the solubility of the physical foaming agent in the grout determines both its maximum allowable concentration and its maximum contribution to volume increase. This study provides valuable insights for the design and selection of polyurethane grout components tailored to diverse applications.

A comparative study of polyurethane foam by substituting LBA using green polyurethane foam CFA‐1

AbstractPolyurethane foams are well‐known optimal thermal‐insulating materials, which have good thermal insulation performance, high strength, and lightweight properties. Here, we describe a chlorine‐free and fluorine‐free polyurethane chemical foaming agent (CFA‐1) that can react with isocyanate to release CO2 gas and foam polyurethane. We systematically studied its application performance in the field of polyurethane spraying by substituting the current most advanced and environment‐friendly physical foaming agent 1‐chloro‐3,3,3‐trifluoroprop‐1‐ene in different proportions. The results show that highly competitive mechanical properties lead to economical, environment‐friendly, and efficient features. The lower thermal conductivity, more compact and smaller bubble structure, and excellent compression strength were achieved by tuning the proportion of CFA‐1 from 20% to 60%. Thus, a promising material system was established for the development of the rigid polyurethane foam industry.

Computational modeling and simulation of temperature field evolution during the chemical foaming of epoxy foams

AbstractThe evolution and control of the temperature field during the chemical foaming of epoxy resin are of paramount importance because the foam structure results from the competition of resin crosslinking and foaming, both of which are highly dependent on temperature distributions. Herein, the epoxy foams, consisting of diglycidyl ether of bisphenol A, glycidyl amine‐type epoxy resin, and 4,4′‐diamino diphenyl sulfone hardener, are prepared using azodicarbonamide and 4,4′‐oxydibenzenesulfonyl hydrazide as a chemical foaming agent (CFA). Kinetic models for heat release and CFA decomposition are established using the auto‐catalytic and n‐th order models, respectively. By integrating the transient flow of resin during the foaming process, numerical simulations of the temperature field evolution within the self‐expanding geometry are conducted to investigate the effects of foaming temperature, heat transfer coefficient, and mold diameter on spatial temperature distributions. A comparison of the kinetic parameters of epoxy curing and CFA decomposition at various foaming temperatures (433, 443, and 453 K) reveals that the acceleration of the curing rate is consistent with that of the decomposition rate as the foaming temperature increases, then the foam structure remains largely unchanged across different foaming temperatures. However, local overheating is unavoidable for the foams at 443 and 453 K. This study offers a method for optimizing the processing parameters in preparing epoxy foams.Highlights Auto‐catalytic model for predicting heat released rate is well established. The decomposition kinetics of the chemical foaming agent is described by n‐th model. Nonisothermal simulation is implemented to study the self‐expanded process of epoxy foam. The foam structure is predicted by comparing the kinetic between the curing and expansion processes.

Microporous Polyelectrolyte Complexes by Hydroplastic Foaming.

Polyelectrolyte complexes (PECs) have emerged as an attractive category of materials for their water processability and some similarities to natural biopolymers. Herein, we employ the intrinsic hydroplasticity of PEC materials to enable the generation of porous structures with the aid of gas foaming. Such foamable materials are fabricated by simply mixing polycation, polyanion, and a UV-initiated chemical foaming agent in an aqueous solution, followed by molding into thin films. The gas foaming of the PEC films can be achieved upon exposure to UV illumination under water, where the films are plasticized and the gaseous products from the photolysis of foaming agents afford the formation, expanding, and merging of numerous bubbles. The porosity and morphology of the resulting porous films can be customized by tuning film composition, foaming conditions, and especially the degree of plasticizing effect, illustrating the high flexibility of this hydroplastic foaming method. Due to the rapid initiation of gas foaming, the present method enables the formation of porous structures via an instant one-step process, much more efficient than those existing strategies for porous PEC materials. More importantly, such a pore-forming mechanism might be extended to other hydroplastic materials (e.g., biopolymers) and help to yield hydroplasticity-based processing strategies.

N/O co-doped porous carbon synthesized by lewis acid salt activation for high rate performance supercapacitor

Cellulose derivatives are widely used as carbon precursors for porous carbon materials because of their high carbon contents and low cost. Herein, N/O co-doped porous carbon materials were synthesized from sodium carboxymethyl cellulose by one-step carbonization and activation with zinc nitrate hexahydrate, a lewis acid salt, as the chemical foaming agent and activation agent and urea as the nitrogen source. The nitrogen content and oxygen content of the optimized sample reached 7.6 at.% and 12.7 at.%, respectively, and the specific surface area reached 1318 m2 g−1. The doping of nitrogen element increased the specific capacitance by nearly two times. In a three-electrode system, the maximum specific capacitance reached 234 F g−1 at 0.1 A g−1 in 6 M KOH electrolyte. The maximum energy density of symmetric supercapacitor was 15.7 Wh kg−1 at the power density of 497.3 W kg−1. The capacitance retention maintained 90.3 % after 10,000 cycles at 20 A g−1. This work provides a novel method for the preparation of porous carbon materials derived from sodium carboxymethyl cellulose and expands its application in energy storage devices.

An application performance study of monoisopropanolamine carbonate in refrigerator insulation materials

Monoisopropanolamine carbonate is a green, safe, and environmentally friendly non-chlorofluorinated polyurethane chemical foaming agent (CFA-1) that can react directly and rapidly with isocyanate to release carbon dioxide for foaming purposes. In this study, we investigated a mixed system of CFA-1, 1,1,1,3,3-pentafluoropropane (HFC-245fa), and cyclopentane (CP) to evaluate its foaming flow performance in refrigerator insulation material applications. We also examined various performance indicators of the resulting foam materials, such as compressive strength, closed cell ratio, and thermal conductivity. The experimental results demonstrated that by adding CFA-1 as a foaming agent, the density and dimensional stability of the foam were comparable to those achieved with the CP + water or CP + HFC-245fa system. In addition, there was a slight improvement in the closed cell ratio and compressive strength, which led to a reduction in the cell diameter within the CP + CFA-1 foaming system compared with those in both CP + water (28.79% decrease) and CP + HFC-245fa (26.11% decrease) systems. This optimized foam material exhibited an enhanced thermal insulation performance, with a 4.20% lower thermal conductivity compared to the CP + water system and 1.88% compared to the CP + HFC-245fa system. Replacing the HFC-245fa physical blowing agent with CFA-1 to prepare low-energy refrigerator insulation materials using rigid polyurethane foam technology offers significant benefits, including eliminating chlorofluorocarbon usage while reducing greenhouse gas emissions.

Properties of chemically foamed polypropylene materials for application to automobile interior door panels

Abstract In recent years, alternative approaches have been implemented in the automotive sector to reduce raw material costs and protect the environment. An increase in weight causes both fuel consumption and CO2 emissions to rise. This study aims to reduce exhaust emissions due to weight reduction by using foamed polypropylene in the door panel production of a subcompact crossover SUV car and saving energy by shortening the injection cycle time. The newly produced 2 % ITP 822 chemical foaming agent added door panel was compared with the current door panel performances. As a result of foam morphology structure, impact, and hardness tests, it was decided that ITP 822 is a suitable chemical foaming agent. In addition, a weight reduction of 5.2 % was achieved. Moreover, the injection cycle time has been reduced by approximately 12 %, reducing the total cycle time from 35 s to 31 s.

Enhanced sensing performance of EVA/LDPE/MWCNT piezoresistive foam sensor for long-term pressure monitoring

Conductive polymer composites (CPCs) with piezoresistive properties are smart detecting systems with high sensitivity, fast response, and low energy consumption. To enhance their sensitivity and cope with their high filler content requirements, solid CPCs are normally transformed into blends and foams, which reduces the elastic modulus, enabling larger deformations, wider detection range, and increased sensitivity. However, providing reversible and durable sensing properties remains challenging as it depends on the phase morphology, foam cell structure, and particle dispersion. To this end, we use multi-walled carbon nanotube (MWCNT) as a conductive filler with a high aspect ratio and develop CNT-filled ethylene vinyl acetate/low-density polyethylene (EVA/LDPE) blend foams. We fix the foam structure using chemical foaming and crosslinking agents in a compression molding process. To optimize the piezoresistive behavior, we follow a step-wise tuning approach, studying the blending morphology, the foaming attributes, the particle dispersion and affinity, thereby selecting the most promising formulations for further investigations. The least mechanical and electrical hysteresis is obtained at minimum foam density, which is obtained at a compromised crystallinity and crosslinking density. The higher affinity of MWCNT to EVA and the faster crosslinking of the EVA phase results in uniformly dispersed small cells at EVA-rich formulations and 4 phr MWCNT content. The final foam sensor demonstrates an impressive response and recovery times of less than 200 ms and remarkable durability thanks to the optimized cell morphology and mechanical properties. These findings expand the application of carbon-filled polyolefin foams in pressure monitoring, particularly in wearable sensors for strain and motion sensing.

Chemical foaming of polylactic acid/polypropylene and polylactic acid/polyamide 6: Evaluation of changes in their properties

Most of the polymers made from fossil fuels end up as waste material and this environment-damaging situation has revealed the need to take some precautions such as the use of eco-friendly, biodegradable materials obtained from renewable sources as an alternative. Biopolymers are being evaluated as alternatives to traditional polymers especially in the automotive industry due to their better-understood properties such as mechanical and physical behavior through the studies conducted. On the other hand, when the literature studies are evaluated, it can be seen that the production of foam materials, which are focused on lightness and carbon dioxide (CO2) emission limitations that are important and essential for the automotive sector, is an area that is also researched and studied for biopolymers. Several studies are carried out with both physical and chemical foaming agents on this subject in recent years. In this study, it is aimed to develop light, environmentally friendly, high-performance polylactic acid (PLA) based polymeric composite foams that can be used in the automotive industry by using twin screw extruder and compression molding methods. For this purpose, polyamide 6 (PA6) and polypropylene (PP) polymers were used with PLA and by adding 1 wt.%, 1.5 wt.% and 2 wt.% chemical blowing agents to the polymer mixtures, the physical, thermal, mechanical, morphological properties and changes in these properties were investigated. The most suitable chemical blowing agent ratio was found to be 1.5 wt.% for PLA/PP and PLA/PA6 mixtures.

Comparison of Conventional and Microcellular Injection Using New Chemical Agents

ABSTRACT This study is mainly focused to obtain stable dimensions for plastic products used in manufacturing industries. A technique of microcellular foaming injection method was chosen with added chemical blowing agents to decrease the mass, clamping force, and cycle time. Mold flow analysis was run to compare the conventional plastic injection (KP) method with chemical foaming injection molding method using added TecoCell H1 (TH) and CS (TCS). The primary process conditions are considered as temperature of the mold, velocity of injection, pressure and time of holding, and cooling time. The experiments were carried under polymer material as (polypropylene) Moplen EP548P. The new chemical blowing agents TH and TCS, having different reactive material ratios (50% and 25% endothermic) and gas concentration ratios, were utilized at a rate of 1% by weight claiming to be a novel method for producing the parts with high efficiency. The results of both the flow analysis and the injection molding experiments demonstrate that, plastic samples produced by conventional plastic injection could be made approximately 7.5% lesser weight, with 33% lesser force of clamping, and a gain of cycle time nearly 15% by adding chemical blowing agents to the process. Topsis technique is carried for determining the best fabrication method. It was observed that, the injection molding method with Tecocell H1 (TH) chemical foaming agent exhibited better results in terms of less clamping force, reduced cycle time, and weight of the product. The experimental results are validated using the Topsis method and the results are satisfied. Hence, the chemical blowing agent Tecocell H1 (TH) can be applied as a foaming agent for manufacturing the plastic products and increase the efficiency of the production.

A novel foaming technique to develop functional open‐cell polylactic acid scaffolds for bone tissue engineering

AbstractThe aim of this study was to develop a solvent‐free polylactic acid (PLA) open‐cell porous scaffold for bone tissue engineering using compression molding and a new chemical foaming compound, that we named CFCO. The latter is composed of a blend of PLA and azodicarbonamide (ADA) as a chemical foaming agent, with the addition of chitosan‐grafted PLA (CS‐g‐PLA) copolymer at various concentrations. The novelty of this approach is that during the foaming, that is, during the decomposition of the ADA foaming agent, the CS‐g‐PLA copolymer is projected toward the surface of the pores and strongly adhere there, which was confirmed by scanning electron microscopy and confocal microscopy. The results showed that at 6.90 wt% of CS‐g‐PLA copolymer, the immobilization of the latter on the surface of the pores led to a 52% increase in cell proliferation compared to the pure PLA control sample and a 26% increase compared to scaffolds that had 10 wt% of CS‐g‐PLA copolymer dispersed throughout the entire PLA matrix.

Continuous extrusion foaming process of biodegradable nanocomposites based on poly(lactic acid)/carbonaceous nanoparticles with different geometric shapes: An insight into involved physical, chemical and rheological phenomena

AbstractOne‐step extrusion foaming process of biodegradable poly(lactic acid) (PLA)‐based nanocomposites in the presence of chemical foaming agent and chain extender has great complexity to control. In this work, PLA‐based nanocomposites containing different carbonaceous nanoparticles with different geometric shapes were obtained through a co‐rotating twin‐screw extrusion process to get insight into the dominant phenomena, which control the structural and final properties of PLA foams. The reactive extrusion foaming of PLA melt was investigated in the presence of carbon black, carbon nanotubes (CNTs), graphene oxide (GO), and a chain extender additive as well as a chemical foaming agent. Nanoparticles affect the continuous extrusion foaming of PLA melt through several phenomena, including providing bubble heterogeneous nucleation sites, intensifying the chemical decomposition of the foaming agent, improving the PLA structural modification reaction, increasing PLA molecular weight and restricting the dissolved gas removal from the melt. By influencing the involved phenomena in process, the nanoparticles at low levels, especially CNT and GO, increased the void content and cell size of PLA foams. The incorporation of CNT and GO nanofillers at the 0.5 phr level increased the electrical conductivity of PLA foams sharply by 9 and 10 orders of magnitude, resulting in lightweight, biodegradable semi‐conductive foams.

The Facile and Efficient Fabrication of Rice Husk/poly (lactic acid) Foam Composites by Coordinated the Interface Combination and Bubble Hole Structure

The possibility of agricultural-forestry waste (rice husks) and biodegradable plastics (poly(lactic acid)) being used to produce ecologically friendly foam composite was discussed in this work. The effects of different material parameters (the dosage of PLA-g-MAH, type and content of chemical foaming agent) on the microstructure and physical properties of composite were investigated. PLA-g-MAH promoted the chemical grafting between cellulose and PLA, and made the structure denser, thus improving the interface compatibility of the two phases and resulting in good thermal stability, high tensile strength (6.99 MPa) and bending strength (28.85 MPa) of composites. Furthermore, the properties of rice husk/PLA foam composite prepared by two kinds of foaming agents (endothermic and exothermic) were characterized. The addition of fiber limited the growth of pores, which provided better dimensional stability and narrower pore size distribution, made the interface of the composite bond tightly. And the bubble can prevent crack propagation and improve the mechanical properties of the composite. The bending strength and tensile strength of composite were 37.36 MPa and 25.32 MPa, which increased by 28.35 % and 23.27 %, respectively. Therefore, the composite prepared by using agricultural-forestry wastes and poly(lactic acid) possess acceptable mechanical properties, thermal stability and water resistance, expanding the scope of application.

Open-cell mullite ceramic foams derived from porous geopolymer precursors with tailored porosity

Porous geopolymer precursors were firstly prepared by the direct foaming method using bauxite, fly ash (FA), and metakaolin (MK) as raw materials, and porous mullite ceramics were prepared after ammonium ion exchange and then high-temperature sintering. The effects of chemical foaming agent concentration, ion-exchange time, and sintering temperature on porous geopolymer-derived mullite ceramics were studied, and the optimal preparation parameters were found. Studies have shown that the concentration of blowing agent had great influence on open porosity (<i>q</i>) and porosity and cell size distributions of geopolymer samples, which in turn affected their compressive strength (<i>σ</i>). Duration of the ion exchange had no obvious effect on the sintered samples, and the amount of mullite phase increased with the increase in the sintering temperature. Mullite foams, possessing an open-celled porous structure, closely resembling that of the starting porous geopolymers produced by directly foaming, were obtained by firing at high temperatures. Stable mullite (3Al₂O₃·2SiO₂) ceramic foams with total porosity (<i>ε</i>) of 83.52 vol%, high open porosity of 83.23 vol%, and compressive strength of 1.72 MPa were produced after sintering at 1400 ℃ for 2 h in air without adding any sintering additives using commercial MK, bauxite, and FA as raw materials.