Density modeling of polyurethane box foam

A model based on about a dozen fundamental differential equations is used to evaluate and simulate the urethane reactions and physical processes of urethane box foaming. This work focuses on quantitative modeling of foam density for foams using water and physical blowing agents. The final densities of foams range from 30 to 90% of the density as projected with full utilization of the blowing agent. The primary sources of inefficient use of blowing agent are loss of the physical blowing during open‐air mixing and degassing—basically, physical blowing agents with boiling points between 25 and 80°C will evaporate and experience cell rupture in box foams. This loss of blowing agent would not apply to in‐line mixers used for commercial production and should be taken into account with scaling up box or cup foams commercial processes. POLYM. ENG. SCI., 54:1503–1511, 2014. © 2013 Society of Plastics Engineers     

Mechanical and morphological properties of cellular NR/SBR vulcanizates under thermal and weathering ageing

The effects of addition of two chemical blowing agents in cellular rubber blend of natural rubber (NR) and styrene‐butadiene rubber (SBR) at a fixed blend ratio of 1 : 1 on cure characteristics, and mechanical and morphological properties were invesigated. The chemical blowing agents used in this work were Oxybis (benzene sulfonyl) hydrazide (OBSH) and Azo dicarbonamide (ADC). Three different fillers, fly ash (FA) particles, precipitated silica, carbon black (CB) at their optimum concentrations of 40 phr were used, the FA and silica particles being chemically treated by bis‐(3‐triethoxysilylpropyl) tetrasulphide. The results suggested that the overall cure time decreased with OBSH and ADC contents. The OBSH was more effective in cure‐acceleration of the NR/SBR blend than the ADC. The NR/SBR vulcanized foams produced by OBSH and ADC agents had closed‐cell structures. The specific density and mechanical properties of the blend tended to decrease with increasing blowing agent content. The CB gave NR/SBR foams with smaller cell size, better cell dispersion, and higher mechanical properties than the precipitated silica and FA particles. The heat ageing and weathering resulted in an increase in tensile modulus and hardness, but lowered the tensile strength, ultimate elongation and tear strength. The elastic recovery for cellular NR/SBR vulcanizates with FA was superior to that with CB and silica, the elastic recovery of the blends decreasing with blowing agent content. Resilience property was improved by the presence of gas phases. The optimum concentration of OBSH and ADC to be used for NR/SBR vulcanizates was 4 phr. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of multi‐walled carbon nanotube functionalization on the morphological and mechanical properties of nanocomposite foams based on poly(vinyl chloride)/(wood flour)/ (multi‐walled carbon nanotubes)

Experimental results are presented for nanocomposite foams based on unplasticized poly(vinyl chloride)/(wood flour)/(multi‐wall carbon nanotubes) (PVC/WF/MWCNTs). The nanocomposite samples were prepared in an internal mixer and foamed via a batch processing method using compression molding. Nanoparticles were functionalized by sodium hypochlorite solution, and the functionalization process was monitored by Fourier‐transform infrared spectroscopy. The effects of MWCNTs (both neat and functionalized) and blowing agent concentration on the morphological properties (cell size and cell density) and mechanical properties (tensile and flexural strength) of the foam samples were studied. The results revealed that foam cell sizes decreased and cell densities increased with addition of MWCNTs. The dispersion of nanoparticles in the PVC medium was increased by functionalization, and the morphological properties of the foams containing functionalized nanoparticles were improved. Density of nanocomposite foams decreased more with functionalized MWCNTs as compared to other samples. Chemical blowing agent concentration had no significant effect on sample density. Mechanical properties of the samples were improved by using functionalized MWCNTs in comparison with those of foams without this component. J. VINYL ADDIT. TECHNOL., 18:161–167, 2012. © 2012 Society of Plastics Engineers     

Melt viscoelasticity of polyethylene terephthalate resins for low density extrusion foaming

The rheological properties of conventional polyethylene terephthalate (PET) resins are not particularly suitable for low density extrusion foaming with physical blowing agents; as a result, chemically modified resins through chain extension/branching reactions are often used. Such resins have overall higher melt viscosity and higher melt strength/melt “elasticity” than unmodified materials. In this work, following a review of the prior art on PET chemical modification, an unmodified and a chemically modified resin were selected and characterized for their melt viscoelastic properties including shear and dynamic complex viscosity over a broad shear rate/frequency range, storage and loss modulus, and die swell. Certain rheological models were found to provide better fits of the entire viscosity curve for the unmodified vs. the modified resin. Foamed extrudates having variable densities (from about 1.2 to 0.2 g/cc), were prepared by carbon dioxide injection in monolayer flat sheet extrusion equipment. Foams with increasingly lower density, below 0.5 g/cc, were obtained by increasing gas pressure only in the case of the chemically modified resin. The effects of variables such as concentration of the physical blowing agent, resin rheology, resin thermal properties and choice of process conditions are related to product characteristics including density, cell size and crystallinity.     

轻质环氧树脂微孔发泡材料的力学及隔热性能

通过添加不同含量的化学发泡剂,制备了较小密度(0.5 g/cm~3)的环氧树脂基微孔发泡材料,研究了发泡剂含量(0.25%~2%)对环氧复合发泡材料发泡行为的影响,并讨论了材料的力学性能及隔热性能的变化规律。结果表明,随着发泡剂含量的增加,材料的表观密度不断降低,但泡孔尺寸不断增大,泡孔密度则不断降低。力学性能及隔热性能测试表明,随发泡剂含量的增加,材料的压缩屈服强度和压缩弹性模量不断降低,但是材料的隔热性能不断提高。     

Generation of low‐density high‐performance poly(arylene ether sulfone) foams using a benign processing technique

In this study, a benign process was used to successfully produce low density foam from poly(arylene ether sulfone) (PAES). Both carbon dioxide (CO₂) and water as well as nitrogen and water were used as physical blowing agents in a one‐step batch process. A large amount of blowing agents (up to 7.5%) was able to diffuse into the PAES resin in a 2‐h saturation time. Utilizing water and CO₂ as the blowing agents yielded foam with better properties than nitrogen and water because both the water and CO₂ are plasticizers for the PAES resin. PAES foam produced from CO₂ and water had a large reduction in foam density (～80%) and a cell size of ～50 μm, while maintaining a primarily closed cell structure. The small cell size and closed cell structure enhanced the mechanical properties of the foam when compared with the PAES foam produced from nitrogen and water. The tensile, compressive, and notched izod impact properties of the PAES foams were examined, and the compressive properties were compared to commercially available structural foams. With reduced compression strength of 39 MPa and reduced compression modulus of 913 MPa, the PAES foam is comparable to polyetherimide and poly(vinylchloride) structural foams. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Elaboration and Characterization of Advanced Biobased Polyurethane Foams Presenting Anisotropic Behavior

Biobased and open cell polyurethane (PU) foams are produced from a synthesized sorbitol‐based polyester polyol. Different formulations are developed with various blowing agent systems (chemical vs physical blowing). Synthetized foams are fully characterized and compared. The cell morphology is carefully investigated by tomography and scanning electron microscopy. The chemical nature of the primary compounds, foaming kinetics, density, thermal behavior, and conductivity are fully studied, with also the main transition materials temperatures. It is shown that blowing agents especially impact the foaming kinetics. In the case of chemically blowing foams, higher foaming rate and temperatures are obtained. The mechanical behavior is particularly analyzed using quasi‐static compression tests, according two main axes compared to the rise direction. A direct relationship is observed between the formulation, foam structure, foam morphology, and corresponding mechanical properties. Results clearly highlight unexpected properties of biobased PU foams with unveil anisotropic mechanical properties.     

Microstructure and physical properties of open‐cell polyolefin foams

The cellular structure, physical properties, and structure–property relationships of novel open‐cell polyolefin foams produced by compression molding and based on blends of an ethylene/vinyl acetate copolymer and a low‐density polyethylene have been studied and compared with those of closed‐cell polyolefin foams of similar chemical compositions and densities and with those of open‐cell polyurethane foams. Properties such as the elastic modulus, collapse stress, energy absorbed in mechanical tests, thermal expansion, dynamic mechanical response, and acoustic absorption have been measured. The experimental results show that the cellular structure of the analyzed materials has interconnected cells due to the presence of large and small holes in the cell walls, and this structure is clearly different from the typical structure of open‐cell polyurethane foams. The open‐cell polyolefin foams under study, in comparison with closed‐cell foams of similar densities and chemical compositions, are good acoustic absorbers; they have a significant loss factor and lower compressive strength and thermal stability. The physical reasons for this macroscopic behavior are analyzed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

An electromagnetic dynamic film blowing technology for mLLDPE

Metallocene linear low‐density polyethylene (mLLDPE) has superior physical and mechanical properties. However, mLLDPE has very poor film blowing processibility. To overcome this shortcoming, an electromagnetic dynamic extruding film blowing system for mLLDPE was developed. A vibration force field was superposed on the entire extruding process through the screw. The die pressure, the screw load, and the power consumption decreased and the melt strength increased as the vibration frequency and amplitude increased, implying that the bubble stability enhanced, which resulted in the improvement of the processibility. In addition, experimental data show that the film strength in the transverse direction greatly increased and the film mechanical properties in machine and transverse directions became more uniform, so the film quality was improved finally. This rule was confirmed by using two additional materials, high‐density polyethylene and low‐density polyethylene. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 83–89, 2006     

Development and processing of flame retardant cellulose acetate compounds for foaming applications

Cellulose acetate (CA) is a bio-based polymeric material suitable to replace foamed polystyrene (PS) boards in applications for building insulation. Foam boards can be produced by extrusion foaming with physical blowing agents. In addition, the high heat deflection temperature and good mechanical properties (e.g., tensile and compression strength) of CA make it suitable for the injection molding of technical parts. In general, flame retardancy of foamed products is often required in building or electronic applications. This article presents the effects of various flame retardant (FR) additives, process settings, and the calibration of the foam board on flammability, foam morphology, and mechanical properties of extruded CA boards. Different formulations of FR additives and foaming agents were investigated regarding density and morphology of the foamed boards. Furthermore, investigations on foam behavior for foam injection molding with physical blowing agents were conducted. The foamed parts were characterized with regard to their flammability. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48863.     

Effects of the properties of blowing agents on the processing and performance of extruded starch acetate

The extrusion of polysaccharide‐based polymers, such as starch acetate, is quite different from that of ordinary synthetic polymers. To understand how the physiochemical properties of blowing agents affect plasticization and expansion processes, starch acetate was extruded with water, ethanol, and ethyl acetate. The studied properties and factors were the evaporation rate, surface tension, boiling point, solubility index, latent heat of vaporization of blowing agents, extrusion temperature, and nucleating‐ and blowing‐agent concentrations. The properties of the blowing agents and operating conditions affected the solubility of the matrix polymer, the nucleation process, and cell growth, which affected the foam density and specific volume. A high temperature increased the cell density and specific volume when water and ethanol were used because a high temperature increased the solubility of starch acetate in water and ethanol and promoted nucleation. Ethyl acetate already had high solvency to starch acetate and a high evaporation rate. A high temperature reduced the melting strength, thereby reducing the cell density and specific volume. Water evaporation was greater, despite a high latent heat of evaporation (hr) and boiling point, than the average volumes of ethanol and ethyl acetate that evaporated. The blowing‐agent efficiency was a function of the solvency, blowing‐agent evaporation rate, and operating conditions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1880–1890, 2005     

Effect of auxiliary blowing agents on properties of rigid polyurethane foams based on liquefied products from peanut shell

The bio‐based rigid polyurethane (PU) foams were successfully prepared based on liquefied products from peanut shell with water as the blowing agent. The influence of reaction parameters on properties of rigid PU foams was investigated. Rigid PU foams showed excellent compressive strength and low shrinkage ratio, whereas their open‐cell ratio and water absorption were higher. Therefore, rigid PU foams were synthesized with petroleum ether, diethyl ether, and acetone as auxiliary blowing agents and their inner temperature, shrinkage performance, density, compressive strength, water absorption, and open‐cell ratio were determined. The results indicated that above rigid PU foams showed lower compressive strength than the original foam but their water absorption and close‐cell ratio were improved. Compared with the original foam, the highest inner temperature of rigid PU foams with petroleum ether, diethyl ether, and acetone as auxiliary blowing agents was reduced by 11, 19, and 23 °C, respectively. Typically, foams with petroleum ether as auxiliary blowing agent displayed better water absorption and swelling ratio in water and exhibited obvious improvement in close‐cell ratio. These foams were preferable for application in thermal insulation materials because of low thermal conductivity and better corrosion resistance. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45582.     

Structure–property relationships of medium‐density polypropylene foams

This paper is focused on the production and characterization of a collection of polypropylene (PP) foams with relative densities ranging from 0.3 to 0.6. Samples were foamed using the improved compression moulding method. The process allows controlling density and cellular structure independently as well as obtaining PP foams without fillers, crosslinking or using special PP grades. The influence of blowing agent content, density, cellular structure and foaming conditions on the mechanical response measured in compression, tensile, bending and Charpy impact tests was determined. Results show that density, open cell content and blowing agent concentration have a significant influence on the mechanical performance of medium‐density PP foams. © 2013 Society of Chemical Industry     

Mechanical properties of deproteinized natural rubber in comparison with synthetic cis‐1, 4 polyisoprene vulcanizates: Gum and black‐filled vulcanizates

Gum and black‐filled vulcanizates having various crosslink densities were prepared from 2 types of rubber, namely, deproteinized natural rubber (DPNR) and synthetic cis‐1, 4 polyisoprene vulcanizates (IR). Their mechanical properties, such as tensile strength, tear strength, abrasion loss, and heat buildup resistance, at various crosslink densities as well as at similar optimum crosslink density were compared. For both gum and black‐filled systems, IR possessed a higher crosslink density than that of DPNR at a fixed curative content. Tensile and tear strength of all vulcanizates passed through a maximum with increasing crosslink density. For gum vulcanizates, tensile and tear strengths of DPNR and IR below the maximum were not much different. However, IR had a narrower tear strength peak relative to DPNR. At a comparable optimum crosslink density, DPNR exhibited higher tensile strength and crack growth resistance than IR. For black‐filled vulcanizates, tensile and tear strengths, and heat buildup resistance of DPNR and IR at a given crosslink density were similar. The results revealed that the properties of gum samples were more dependent upon crosslink density than the black‐filled ones because the reinforcement by carbon black overshadowed the intrinsic properties of the rubbers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1139–1144, 2005     

Effect of clinoptilolite filler on the physical and mechanical properties of polypropylene

This study aims to investigate the mechanical and physical properties of polypropylene (PP) filled by natural zeolite. For this purpose, a natural zeolite (at 1–6 wt% filler loadings) with two different particle sizes was used. Two different kinds of silane coupling agents (3‐aminopropyltriethoxysilane, GAPTES and 3‐glycidoxypropyltrimethoxysilane, GPTMS) at three different volume ratios were used to improve the zeolite compatibility with PP and to improve the mechanical properties of composites. Fillers and PP were compounded with a twin screw extruder, and the composites were moulded with injection moulding press. The samples were subjected to mechanical tests (i.e., impact and tensile tests) and physical tests (i.e., hardness, density, and melt flow index, MFI). The physical test results showed that the levels of hardness and density of both unmodified and modified zeolite‐filled PP composites were higher compared with neat PP. The MFI values of composites were decreased by increasing zeolite loading level. Composites including GAPTES modified zeolite showed improved yield strength, impact strength and stiffness compared with composites filled with unmodified zeolite particles. POLYM. COMPOS. 34:1396–1403, 2013. © 2013 Society of Plastics Engineers     

Increasing cell homogeneity of semicrystalline,biodegradable polymer foams with a narrow processing window via rapid quenching

Biodegradable polymer foams have the potential to lessen environmental burdens caused by traditional petroleum‐based plastics. One such family of alternatives, poly(hydroxyalkanoates), have tremendous potential in this regard, but have poor foamability owing to a narrow thermal processing window. Of particular interest for this study is poly(hydroxybutyrate‐co‐valerate) (PHBV). Two chemical blowing agents were tested for their ability to create low density, closed‐cell PHBV foams, and it is shown here that sodium bicarbonate decreases the bulk density compared to azodicarbonamide blowing agents but with the loss of a closed‐cell structure. To counter this, PHBV foams were quenched with water, leading to faster crystalline formation in the polymer matrix. As a result of faster solidification, a more uniform, closed‐cell bubble morphology was entrapped in the final foam product, leading to high‐expansion ratio foam. Thus, PHBV, a material with poor melt strength, has enhanced melt properties for foaming applications when crystallization is induced on the same time scale as cell coalescence. POLYM. ENG. SCI., 54:2877–2886, 2014. © 2014 Society of Plastics Engineers     

Synthesis of Polyurethane Foam Considering Mixture Blowing Agents for Application to Cryogenic Environments

Polyurethane foams, which are among the most widely used insulating materials, are generally fabricated by the chemical reaction between isocyanate and polyol‐containing chemical additives and blowing agents. Recently, many kinds of blowing agents have been used for the fabrication process of polyurethane foam, such as hydrochlorofluorocarbons (HCFCs) and chlorofluorocarbons (CFCs). However, issues have continuously arisen regarding the destruction of the ozone layer due to these compounds. In the present study, polyurethane foams are manufactured using a mixture of water blowing agents and hydrofluorocarbons (HFC‐365mfc). These samples are subjected to mechanical tests to investigate the effects of the blowing agents on the mechanical properties of the polyurethane foam within a temperature range of 25 to ?163 °C. In addition, thermal and microstructural investigations are conducted depending on the content of the HFC‐365mfc. From the scanning electron microscopy observations, the sizes of the structure cells and the windows are found to decrease with the increase in HFC‐365mfc content. In addition, from the Fourier transform‐infrared spectroscopy observations, the chemical bonds that affect mechanical performance are found to be more distributed with the increase in HFC‐365mfc content.     

Insulation performance and microstructure in modified polyethylene by MPE

Electrical measurements have shown to be able to provide useful information on physical, chemical, and microstructural properties of dielectric material. In this article, the depolarization characteristics of low‐density polyethylene blended with a small amount of metallocene catalyzed polyethylene were measured by pulsed electro‐acoustic method under various stresses. According to space charge limited current theory, the derivation of quantities such as mean volume density of space charge, apparent trap‐controlled mobility, trap depth distribution, and threshold stress were discussed. The test results showed that low‐density polyethylene blended with 1 wt % metallocene catalyzed polyethylene could effectively decrease deep trap density, increase shallow trap density, and then improve the mobility of charges. We also measured the breakdown voltage and tensile strength of the blends. It was found that low‐density polyethylene blended with a small amount of metallocene catalyzed polyethylene could effectively improve its breakdown voltage and tensile strength but reduce the material tenacity. Finally, mechanical relax and crystalline morphology of blends were studied by dynamic mechanical measurement, wide‐angle X‐ray diffraction, and small‐angle X‐ray scattering experiments. The results showed that the improvement of electrical properties and mechanical strength in the blends were relevant to the crystalline morphology. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Cross-linking and foaming behavior of elastomers with water based blowing agents

Physiologically hazardous chemical blowing agents are state of the art for the foaming of extruded rubber profiles. Water is a potential alternative to these blowing agents and is incorporated into rubber compounds in the form of water-loaded hygroscopic substances such silica or hydrates. To achieve an optimum foaming result, the water desorption and cross-linking reaction has to be coordinated. Studies of the foaming behavior in the salt bath of the Sponge Rubber Analyzer show, that the density of an ethylene propylene diene monomer (EPDM) rubber compound is reduced to about 60% and a nitrile butadiene rubber (NBR) compound to approximately 70%. The low reference densities of chemically foamed EPDM of 30% and NBR of 45% are not achieved. This is attributed to the premature foaming when using water-loaded silica as blowing agent. Due to the low resistance of the rubber matrix, large cells are formed by coalescence, which collapse at low cross-linking densities. Investigations of the cross-linking behavior of EPDM and NBR with water-loaded silica as blowing agent state, that the cross-linking density is reduced to about 65% for EPDM and 50% for NBR when water is present. Furthermore, the incubation time is shortened by inhibition of the CBS retarder in the cross-linking system of the NBR. However, this is not sufficient to fix the foamed cells.     

Microcellular injection molding of in situ modified poly(ethylene terephthalate) with supercritical nitrogen

The microcellular injection molding (commercially known as MuCell) of in situ polymerization‐modified PET (m‐PET) was performed using supercritical nitrogen as the physical blowing agent. Based on the design of experiment matrices, the influence of operating conditions on the mechanical properties of molded samples was studied systematically for two kinds of m‐PETs, namely, n‐m‐PET and m‐m‐PET synthesized using pentaerythritol and pyromellitic dianhydride (PMDA) as modifying monomers, respectively. Optimal conditions for injection molding were obtained by analyzing the signal‐to‐noise (S/N) ratio of the tensile strength of the molded samples. The specific mechanical properties, especially the impact strength, of the microcellular samples under those optimal conditions increased significantly. Scanning electron microscope analyses showed a uniform cell structure in the molded specimens with an average cell size of around 35 µm. The m‐m‐PET modified with PMDA generated a slightly finer cell structure and a higher cell density than the n‐m‐PET. POLYM. ENG. SCI., 54:2739–2745, 2014. © 2013 Society of Plastics Engineers