Blowing Agents Research Articles

The Impact of Mould Temperature and Blowing Agent Content on Structure and Properties of Injection Moulded Parts

The investigation of the influence of mould temperature and blowing agent percentage on structure, and selected properties (weight, mechanical properties, surface state - gloss and colour) of moulded parts from HDPE was the aim of this work. The structure of moulded parts in cross-section perpendicular and parallel to the direction of polymer flow, and quantitative assessment of porous structure using microscopic image analysis were carried out. It was shown that the content of blowing agent in polymer influences not only the amount of pores in the part core, but also the thickness of solid skin. Lower mould temperature favors the formation of a fine porous structure. The formation of the porous structure influenced slightly the weight and mechanical properties of moulded parts. With the increase in blowing agent content, the gloss of parts decreased and also caused the change in their colour. Parts with higher amount of blowing agent were brighter.

Experimental Research of Foaming Concrete Performance with Different Blowing Agent

Low-density foam concrete is inorganic silicate material replace to traditional organic materials for external wall insulation system. Based on the analysis of structure formation mechanism of foaming foam concrete prepared with chemical method, investigation by a large number of comparative tests and quantitative analysis, quantitative relationship of compressive strength, tensile strength, and blowing agent dosage quantitative of 3d, 7d and 28d foaming concrete are analyzed. The relationship between blowing agent and foam concrete strength and thermal conductivity variation is revealed by the research of doped foaming agent concrete strength, improved workability mechanism. And further, independent sealing pores, high mechanical strength of pore wall, pore structure approximate to sphere and pore diameter with similar and small size were all favorable factors for higher strength of foam concrete.

Physical Properties of Tannin/Furanic Resin Foamed With Different Blowing Agents

Tannin/furanic rigid foam made from raw materials of natural origin could be used to replace polyurethane and phenolic foams in many future applications. In this study, diethyl ether, pentane, and a mixture of the two were used to prepare tannin/furanic foams having different microstructures. It was found that the bulk density of the foam could be significantly extended, up to 180 kg/m3. The cell size of the pentane foam was larger than that of diethyl ether foam with comparable density; however, both presented a sudden increase in cell size when the density decreased. The thermal conductivity and mechanical properties were determined for the two foam types at the same density but different cell size. The minimum thermal conductivity for diethyl ether and pentane foams were presented, along with a suggested method for lowering the thermal conductivity of such foam. Additionally, the results of mechanical tests indicate that cell size does not play a role in compressive strength.

Electric Properties of the Laminate Type PTC(Positive Temperature Coefficient of Resistance) Thermistor According to Polymer Blowing Agent

【The electrical properties of a laminated SMD type PTC thermistor for microcircuit protection were investigated as a function of polymer blowing agent addition. Green ceramics for multilayered $BaTiO_3$ -based PTCRs were formed by doctor blade method of barium titanate powders; we successfully laminated the sintered ceramic chips to obtain 10 layer chip PTCRs with PTC effect. The sintered density increases with increasing sintering temperature. The electrical properties of the sintered samples were strongly dependent on the calcination and addition of a polymer blowing agent. When $BaTiO_3$ powders containing 0.2 mol% of $Y_2O_3$ were calcined at $1000^{\circ}C$ for 2 hrs, the resistivity jump was of 1-2 orders of magnitude. The resistivity at room temperature increases according to the polymer blowing agent addition. Also, the sample using the calcined powder showed a lower resistivity than that of the sample prepared using powders without calcinations. With an increase in the OBSH, the magnitude of the resistivity jumped as a function of the temperature increase. The resistivity of the sintered bodies after the addition of 0.5 wt% polymer blowing agent at $1290^{\circ}C$ for 2 h was shown to be about $8.5{\Omega}{\cdot}cm$ ; the jump order of the sintered bodies was shown to be on the order of $10^2$ .】

Development of Water Blown Bio-Based Thermoplastic Polyurethane Foams

Water blown biobased thermoplastic polyurethane (TPU) foams were prepared using synthetic and biobased chain extender. The concentration of chain extender, blowing agent (BA) and surfactant were varied and their effects on physical, mechanical and morphological properties of foams were investigated. Density, compressive strength and modulus of foams decreases with an increase in BA content and increased with chain extender concentration, but do not change significantly with change in surfactant concentration. The glass-transition temperatures of the foam samples increases with an increase in BA and chain extender concentration. The cell size of the foam sample increases slightly with an increase in BA whereas chain extender concentration has no effect on cell size.

Density Graded Polyethylene Foams Produced by Compression Moulding Using a Chemical Blowing Agent

Density graded polyethylene foams were produced using a chemical blowing agent and compression moulding. To control the local density inside the foams, the top and bottom plates of a compression moulding set-up were placed at different temperatures and moulding times in order to produce symmetric and asymmetric structural foams. Due to different temperature gradients produced inside the samples, complex density profiles were created. From the samples obtained, a complete morphological analysis was performed to extract cell size and cell density across foam thickness in relation with density profiles. Also, to determine the effect of density profile on the mechanical properties, tensile and flexural characterizations were performed. The results obtained are discussed in relation with optimum properties vs. bulk foam density.

Enhancement of Polymer Foam Quality by Modifying Structural and Decomposition Characteristics of Chemical Blowing Agent

The polymer foam quality was enhanced significantly by modifying the structural and decomposition characteristics of chemical blowing agent (CBA), including the basic particle size, compatibility with the polymer matrix and gas yield. The submicrometer semicarbazide-covalently anchored polystyrene (SCPS) particles were synthesized and utilized as a blowing agent for polystyrene foaming. The results demonstrated the decreased basic particle size, enhanced dispersion and modified decomposition characteristic of SCPS improved significantly the foam quality. The SCPS having homogeneous size distribution and good compatibility with the polymer matrix contributed to the uniform dispersion of CBA and thus confined cell coarsening.

Influences of Modified Chemical Blowing Agents on Foaming of Wood Plastic Composites Prepared from Poly(Vinyl Chloride) and Rice Hull

The influences of the types of chemical blowing agent (CBA) namely endothermic, exothermic and their mixture, on the properties of the foamed poly(vinyl chloride) (PVC) and rice hull wood plastic composites (WPC) were investigated in the current research. Specifically, azodicarbonamide and sodium bicarbonate were selected to represent the exothermic the endothermic CBA respectively. Particles of sodium bicarbonate and azodicarbonamide were modified with 25 wt% citric acid and 20 wt% ZnO respectively, and they were used at 0 to 3.0 wt%. Maximum reduction of density by 45% was achieved when the exothermic CBA was applied at 2.0% by weight. Overall, the flexural properties decreased as the level of the CBA was increased from 0-2.0 wt%, but there was an upturn when the CBA reached 3.0 wt%. The mixture of exo/endothermic CBA illustrated the mechanical properties averaged between their parents.

Honeywell Hikes Blowing-Agent Output

Honeywell Hikes Blowing-Agent Output

Long-term Aging of Closed-Celled Foam Insulation

Many factors influence the thermal efficiency [lambda value or k-factor] one obtains with foams blown with any of the commercial physical blowing agents. Factors affecting a product's thermal efficiency depend on, but are not limited to, the blowing agent itself – such items as the blowing agent's molecular weight, its boiling point, and its solubility in the foam matrix. Other factors depend on formulation parameters such as catalyst levels which affect speed of reaction and fineness of cell structure. Still others depend on the mixing efficiency of the equipment used to process the foams. Finally, a great deal of the contribution depends on the amount of protection the foam receives from its immediate environment - ranging from exposed foam to foam enclosed within impermeable facers. The long-term aging of foams has always been filled with myth and controversy. This has been true for every blowing agent that has been commercialized. We will try to dispel some of the myths with the results of several long-term aging studies, run on ecomate® and other commercial Blowing Agents.

Analysis of the Expansion Behaviour of Rubber Compounds with Chemical Blowing Agents

Cellular elastomeric parts are used in various applications. Their cellular structure offers savings potential with respect to component weight, material consumption and costs. The foam structure is generated using chemical blowing agents, which are added to the rubber mixture before processing. Foaming and vulcanisation occur simultaneously in the curing unit. Both processes are adjusted by modification of the rubber mixture, which is one of the most challenging steps in rubber processing. The use of modified vulcameters for determination of the expansion of rubber mixtures is state of the art. However, this method is subject to several limitations. Therefore, IKV developed a new measurement system, which allows the analysis of the free expansion behaviour. Based on the Archimedean principle, the foaming process of rubber mixtures is recorded. A cell structure is generated, which can be analysed using digital image processing. In first experiments, several components of the rubber mixture are analysed using the measuring device in order to identify and categorise influencing parameters.

Release and fate of fluorocarbons in a shredder residue landfill cell: 1. Laboratory experiments

The shredder residues from automobiles, home appliances and other metal-containing products are often disposed in landfills, as recycling technologies for these materials are not common in many countries. Shredder waste contains rigid and soft foams from cushions and insulation panels blown with fluorocarbons. The objective of this study was to use laboratory experiments to estimate fluorocarbon release and attenuation processes in a monofill shredder residue (SR) landfill cell. Waste from the open SR landfill cell at the AV Miljø landfill in Denmark was sampled at three locations. The waste contained 1–3% metal and a relatively low fraction of rigid polyurethane (PUR) foam particles. The PUR waste contained less blowing agent (CFC-11) than predicted from a release model. However, CFC-11 was steadily released in an aerobic bench scale experiment. Anaerobic waste incubation bench tests showed that SRSR produced significant methane (CH 4), but at rates that were in the low end of the range observed for municipal solid waste. Aerobic and anaerobic batch experiments showed that processes in SRSR potentially can attenuate the fluorocarbons released from the SRSR itself: CFC-11 is degraded under anaerobic conditions with the formation of degradation products, which are being degraded under CH 4 oxidation conditions prevailing in the upper layers of the SR.

A Micro-Scale Surface-Structured PCL Scaffold Fabricated by a 3D Plotter and a Chemical Blowing Agent

To study cell responses, polymeric scaffolds with a controllable pore size and porosity have been fabricated using rapid-prototyping methods. However, the scaffolds fabricated by rapid prototyping have very smooth surfaces, which tend to discourage initial cell attachment. Initial cell attachment, migration, differentiation and proliferation are strongly dependent on the chemical and physical characteristics of the scaffold surface. In this study, we propose a three-dimensional (3D) plotting method supplemented with a chemical blowing agent to produce a surface-modified 3D scaffold in which the surface is inscribed with nano- and micro-sized pores. The chemically-blown 3D polymeric scaffold exhibited positive qualities, including the compressive modulus, hydrophilicity and initial cell adhesion. Cell cultures on the scaffolds demonstrated that chondrocytes interacted better with the surface-modified scaffold than with a normal 3D scaffold.

Extrusion Foam Coating of Coaxial Cables using Butane as Physical Blowing Agent

This paper presents an experimental study on manufacture and characterization of an insulating foam coating in the coaxial cables where a physical blowing agent (butane) is used. Coaxial cables with foam insulator are widely used in communication industries. The insulating foam plays a key role in the attenuation properties of the coaxial cables. In this research work, an extrusion setup was prepared to produce foam insulated coaxial cable using butane as the physical foaming agent. The effect of die geometry (die gap and die outlet diameter) on foam morphology and loss-attenuation were investigated using a blend of LDPE (90%)-HDPE (10%) as the main material. The results show that an acceptable low loss-attenuation is achievable via using a polyethylene compound and adjusting processing parameters.

Effect of Loss of Blowing Agents on Thermal Insulation Properties of Polystyrene Foams

This paper presents a numerical study to characterize the effect of loss of blowing agents on the thermal insulation properties of polystyrene foams. In this study, a transient cell-to-cell diffusion model is developed to predict the loss of the blowing agents. The Mie theory is used to quantify the radiative conductivity. A cubic-series-parallel approach in analogy with electric circuits is employed to acquire the thermal conductivity of the gas-polymer matrix. The effects of foam morphology and blowing agent type on the loss of blowing agents and the resulting thermal insulation properties of polystyrene foams are examined.

Mechanical, Morphological and Thermal Properties of Rigid Polyurethane Foam: Effect of Chain Extender, Polyol and Blowing Agent

The properties of rigid polyurethane foams can be modified over a wide range depending on the raw materials used for its synthesis. The polyols, chain extender and blowing agent have major impact on the properties of the PUF. This investigation reports the effect of polyol and its blends, chain extender such as 1, 4-butanediol (1, 4-BD) and blowing agents [chemical as well as physical; such as distilled water and n-pentane (n-C5), hydrochlorofluorocarbon (HCFC)] on the properties of rigid PUF. Addition of the chain extender improves the mechanical properties initially but then it decreases the properties on further addition of the same. The thermal conductivity of the chain extended and that of the physically blown PUF was lower than the water blown PUF. Higher loading of chain extender and blended polyol decreased the glass transition temperature (Tg) of the PUF due to the decrease in cross-link density because of low –OH functionality in the presence of linear diols like hydroxyl terminated polybutadiene (HTPB). It was observed that there is no significant change in degradation temperature of the chain extended, physically blown and blended system except that observed in the case of HTPB filled PUF.

Microcellular Polycarbonate with Improved Notched Impact Strength Produced by Injection Moulding with Physical Blowing Agent

Polycarbonate has the reputation of having a tough breaking behaviour, but it is often unknown that this applies only to special conditions. The impact strength of polycarbonate depends on the temperature, the thickness (with a tough brittle transition at thickness increases), contribution of notch tip radius, impact speed, physical blowing agent, molecular weight of the polymer and the processing parameters. Research results indicated that microcellular foams produced by injection moulding with physical blowing agent (MuCell™ Technology by Trexel) shows significant higher notched impact strength than compact polycarbonate, if the compact material is brittle under the same test parameters. However, if the compact polycarbonate breaks toughly, the notched impact strength of the foamed material is always lower. Therefore, it is highly important to pay attention to the test parameters and conditions when comparing the toughness of the foamed with the compact material. The toughness of microcellular foams shows similar properties to PC/ABS and PC/PP blend systems, which provides the possibility to combine the higher impact strength with the advantages of microcellular foaming like weight reduction, lower shrinkage, shorter cycle times, lower clamp forces and reduced melt viscosity. In order to use technologies and conditions which are applied in the polymer industry, all materials were produced by an injection moulding process. Special processing technologies like gas counter pressure and precision mould opening were used in order to reach microcellular foam structures with cell diameters around 10 μm. These technologies yield exactly adjustable foam morphologies. Special morphologies are required to improve the notched impact strength of the foamed material. Two different equivalent models were extracted from the analyses, which indicate significant higher notched impact strength than the compact material under the same test conditions. The knowledge of the ideal foam morphologies enables the industry to produce foamed materials with improved mechanical properties.

Effect of Exo- and Endothermic Blowing and Wetting Agents on Morphology, Density and Hardness of Thermoplastic Polyurethanes Foams

Thermoplastic polyurethane (TPU) combines the property characteristics of high quality polyurethane elastomers with the processing efficiency of thermoplastics. Foaming of TPU material inputs for existing applications also leads to improved material properties for new applications. The mixture of exo- and endothermic type of blowing agents is investigated for production of TPU foam technique. Azodicarbonamide (ADC) and sodium bicarbonate are used as exothermic and endothermic blowing agents, respectively. The thermal decomposition and foaming behaviors of blowing agent ADC with kicker and the combination of exo- and endothermic blowing agents are investigated systematically. The ingredients of the mixture of exothermic blowing agent are mixed to suit the processing of TPU. Injection molding of TPU exo- and endothermic blowing agents has been carried out successfully and the morphology is studied using scanning electron microscope. In addition, the effect of wetting agents on the decomposition temperature and processing is also studied. The effectiveness of the use of exo- and endothermic blowing agents is established with the uniform and consistent cell structure with a density reduction of 40% in the foam.

Strategies for Processing Wood Plastic Composites with Chemical Blowing Agents

The production of a cellular structure in wood-flour/plastic composites (WPC) is overwhelmingly dominated by the gaseous emissions/ volatiles released by the wood-flour (WF), which prevents the formation of a uniform and fine-celled structure. By adopting effective processing strategies, the adverse effects of these volatile emissions on the foam morphology of WPC can be largely suppressed. This study discusses these strategies, and presents the results obtained from extrusion processing in cases where the chemical blowing agent (CBA) predominantly controls the density reduction. The effects of CBAs on extrusion processing of WPC are discussed. All the CBAs used, produced uniform and reasonably fine-celled structures.

Foamability of Thermoplastic Vulcanizates Blown with Various Physical Blowing Agents

Thermoplastic vulcanizate (TPV) is a special class of thermoplastic elastomers (TPEs) made of a rubber/plastic polymer mixture in which the rubber phase is highly vulcanized. It is prepared by melt mixing a thermoplastic with an elastomer and by in situ crosslinking of the rubber phase. Currently, TPV is replacing EPDM rubber dramatically because of the impressive advantages for automotive sealing applications. Some of the advantages of TPV compared to that of EPDM rubber are good gloss, recyclability, improved colorability, shorter cycle time, and design flexibility. The development of TPV foaming technology is to fulfill the requirement of achieving lower cost, lighter weight, and better fuel economy. Foaming of TPV has not been investigated extensively. The complete dissolution of the blowing agent in the molten polymer is the most critical step in TPV foaming processing, and this strongly depends on the solubility of the blowing agent, the saturation pressure, the degree of mixing, and residence time. In our study, we attempted to understand the foaming behavior of commercial TPVs in general, with various blowing agents. The effect of blowing agent type and concentration on the expansion behavior, the cell-number density, and the foam structure under the different processing conditions are examined. These experimental results will be used to determine optimized TPV formulations to ensure good foamability, while retaining the properties of TPV.