Novel injection molding foaming approaches using gas‐laden pellets with N2, CO2, and N2 + CO2 as the blowing agents

A novel method of producing injection molded parts with a foamed structure has been developed. It has been named supercritical fluid‐laden pellet injection molding foaming technology (SIFT). Compared with conventional microcellular foaming technologies, it lowers equipment costs without sacrificing the production rate, making it a good candidate for mass producing foamed injection molded parts. Both N₂ and CO₂ can be suitably used in this process as the physical blowing agent. However, due to their distinct physical properties, it is necessary to understand the influence of their differences over the process and the outcomes. Comparisons were made in this study between using CO₂ and N₂ as the blowing agents in terms of the part morphologies, as well as the shelf life and gas desorption process of the gas‐laden pellets. After gaining a good understanding of the SIFT process and the gas‐laden pellets, a novel foam injection molding approach combining the SIFT process with microcellular injection molding was proposed in this study. Both N₂ and CO₂ can be introduced into the same foaming process as the coblowing agents in a two‐step manner. Using an optimal content ratio for the blowing agents, as well as the proper sequence of introducing the gases, foamed parts with a much better morphology can be produced by taking advantage of the benefits of both blowing agents. In this study, the theoretical background is discussed and experimental results show that this combined approach leads to significant improvements in foam cell morphology for low density polyethylene, polypropylene, and high impact polystyrene using two different mold geometries. POLYM. ENG. SCI., 54:899–913, 2014. © 2013 Society of Plastics Engineers     

Challenge to fortyfold expansion of biodegradable polyester foams by using carbon dioxide as a blowing agent

This paper presents a new foaming technology using supercritical carbon dioxide as a blowing agent to obtain large volume expansions of biodegradable polyester foams of over fortyfold. The basic approach for the promotion of a large volume expansion ratio with carbon dioxide was to prevent cell coalescence by using a branched material, to dissolve carbon dioxide completely in the melt by promoting convective diffusion under a high processing pressure, to reduce the diffusivity of gas by lowering the melt temperature, and to optimize the processing conditions in the die to maximize volume expansion. The desirable composition of the materials includes dehydrated branched biodegradable polyester (polybutylene succinate), CO₂ (blowing agent), and tale (nucleating agent). A single‐screw extrusion system was used for foam processing. A large volume expansion ratio of up to forty‐fivefold was achieved from the biodegradable polyester foams. The morphologies and volume expansion ratios of biodegradable polyester foams at various processing temperatures and pressures were studied.     

Simulation of liquid physical blowing agents for forming rigid urethane foams

A computer‐based simulation for rigid polyurethane foam‐forming reactions was compared with experimental data for six blowing agents including methyl formate and C5‐C6 hydrocarbons. Evaporation of blowing agent was modeled as an overall mass transfer coefficient times the difference in activity of the blowing agent in the gas foam cells versus the resin walls of the cells. Successful modeling hinged upon use of a mass transfer coefficient that decreased to near zero as the foam resin approached its gel point. Modeling on density agreed with experimental measurements. The fitted parameters allowed for interpretations of the final disposition of the blowing agent, especially, if the blowing agent successfully led to larger foam cells versus being entrapped in the resin. The only component‐specific fitted parameters used in the modeling was the activity coefficient that was lower for methyl formate than the value used for hydrocarbons. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42454.     

Chemical and physical blowing agents in structural polyurethane foams: Simulation and characterization

Physical blowing agents such as n‐pentane and methyl formate and, for comparison, chemical blowing agents such as water were used to prepare structural polyurethane rigid foams of different densities by reaction injection molding. Experimental runs were carried out with formulations based on oligomeric isocyanate and a mixture of polyether polyols. The constitutive equations for the vaporization rate of the two blowing agents and the polymerization kinetics data are reported. Experimental results were compared with the prediction of a simplified theoretical model, and they showed a satisfactory agreement in terms of temperatures and density profile. All the specimens were characterized by physical‐mechanical properties such as hardness, impact strength, flexural strength and elastic modulus and the results were reported in function of the densities. The best mechanical performance were obtained with the physical blowing agents, due to a better density distribution profile and a thicker skin layer.     

溢流法测定超临界CO_2在聚己酸内酯中的溶解

以超临界CO2作为溶剂,采用溢流法研究聚己酸内酯(PCL)在CO2中的溶胀过程和超临界CO2/PCL体系的热力学平衡规律。考察了温度、压力对溶解度的变化趋势,分析加入有机溶剂后对CO2在聚合物中的溶解度的影响,并应用P-T(Patel-Teja)方程作为热力学模型分析和计算溶解规律。结果表明:CO2的溶解度随温度升高而降低,随压力增大而增大,有机溶剂的加入能够进一步提高CO2的溶解度,在相同的温度压力条件下,加入相当于CO2质量的2.26%的二氯甲烷,最多可使溶解度增加28.06%。在温度313.15—353.15 K、压力10—20 MPa范围内,P-T方程能较好地预测CO2在PCL中的溶解度,其相对误差在-12.53%—12.01%。     

Extrusion of microcellular polysulfone using chemical blowing agents

Microporous polysulfone hollow fibers were developed with the help of chemical blowing agents by means of extrusion. Two chemical blowing agents, azodicarbonamide and 5-phenyltetrazol, were selected, and the foam morphology dependent on the concentration of blowing agent was examined by scanning electron micrograph. By means of changing the processing parameters, e.g., temperature and screw speed, the structures of the foam, usable as membrane, can be controlled. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 1753–1760, 1998     

Foam extrusion of LDPE with solid phase CO2 as blowing agent

Physical foaming usually requires special metering equipment to inject the blowing agent at high pressures. In this study, low density polyethylene (LDPE) was foamed in the extrusion process using dry ice as physical blowing agent. The blowing agent was metered in form of pellets over the hopper. To determine relevant process parameters and improve the understanding of the process a melting model is applied. The influence of the formation of a melt film and melt pool on the dissolution of the blowing agent is discussed. The theoretical considerations are validated in a design of experiment study. As a result, the efficiency of the process is especially affected by the throughput rate, granules temperature, and blowing agent concentration. Further varied parameters are the barrel temperature in the melting zone and diameter of the dry ice pellets. Fast melting and pressure build‐up were shown to reduce blowing agent losses. POLYM. ENG. SCI., 55:2821–2828, 2015. © 2015 Society of Plastics Engineers     

New experimental method for determination of effective diffusion coefficient of blowing agents in polyurethane foams

The effective diffusion coefficients of novel, environmentally friendly, hydrofluorocarbon (HFC) blowing agents for polyurethane foam production were measured. The method was based on gas chromatography and infrared spectroscopy measurements. The accuracy and reliability of the procedure developed were confirmed by comparisons of experimental and the predicted thermal aging curves. The slope of the aging curves (i.e., the change in thermal conductivity with time) depended only on the effective diffusion coefficients. The effective diffusion coefficients of the new HFC blowing agents were close to those of conventional hydrochlorofluorocarbon (HCFC) blowing agents, and the aging behavior of foams produced from HFC or HCFC blowing agents were similar. Polym. Eng. Sci. 44:2229–2239, 2004. © 2004 Society of Plastics Engineers.     

Modeling the phase behavior in binary mixtures involving blowing agents and thermoplastic resins

The thermophysical properties of mixtures of thermoplastic resins and blowing agents, together with the knowledge of the solubilities of these components, are the basis for the manufacturing of plastic foams. In this work, the solubilities of blowing agents trichlorofluoromethane, dichlorodifluoromethane, chlorodifluoromehane, and 1,2‐dichloro‐1,1,2,2‐tetrafluoroethane in thermoplastic resins poly(styrene), high density poly(ethylene), low density poly(ethylene), poly(propylene), poly(vinyl chloride), poly(carbonate) and poly(propylene oxide) were modeled by using the Perturbed Chain‐Statistical Associating Fluid Theory (PC‐SAFT) and the Sánchez‐Lacombe equations of state (EoS), fitting a single temperature‐dependent binary interaction parameter. PC‐SAFT is a theoretically based equation of state with three pure component parameters that describe efficiently the thermodynamics of complex systems. Earlier works with this EoS have already predicted the phase coexistence properties of various refrigerants and higher order alkane series compounds, along with their mixtures. The pure component parameters for the blowing agents were obtained by regression of vapor pressure and liquid density data, while the pure component parameters for the thermoplastic resins were obtained by regression of pure liquid PVT data. The parameter estimation was performed by using a modified maximum likelihood method. The solubility results obtained with both EoS have been compared; the results from PC‐SAFT showed a higher accuracy in terms of solubility pressure deviations. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Preparation of low density carbon foams by foaming molten sucrose using an aluminium nitrate blowing agent

Low density carbon foams have been prepared by thermo-foaming of molten sucrose using aluminium nitrate as a blowing agent to produce solid organic foams followed by dehydration and carbonization. Gas bubbles are generated in the molten sucrose due to water vapour produced by the acid catalysed condensation between sucrose hydroxyl groups and NO_x gases produced by the thermal decomposition of the aluminium nitrate. Higher melt viscosity achieved by cross-linking of the condensation products of sucrose through co-ordination of the aluminium ions with the hydroxyl groups stabilizes the bubbles against coalescence and rupture. The foam volume, foaming time and setting time depend on the aluminium nitrate concentrations. The carbon obtained by the pyrolysis of the solid organic foams has turbostratic graphite structure. The foams produced have an interconnected near-spherical cellular structure. The carbon foams prepared at aluminium nitrate concentrations in the range of 0.5–4 wt.% have a density and average cell size in the ranges of 0.085–0.053 g/cc and 1.55–0.83 mm, respectively. The alumina (～0.17–1.34 wt.%) produced from the aluminium nitrate is concentrated more on the surface of cell walls, ligaments, and struts.     

Extraction of anthocyanins from Arrabidaea chica in fixed bed using CO2 and CO2/ethanol/water mixtures as solvents

Leaves of Arrabidaea chica (Humb. Bonpl.) Verlot are rich in anthocyanins and have been used as a medicinal plant in the Amazon region. In order to obtain different extracts from this plant, a sequential extraction in fixed bed was carried out at 40 °C and 300 bar, using supercritical carbon dioxide (scCO₂) in a first step, and a mixture containing CO₂/ethanol/water at mass ratios of approximately 80/20/0, 80/14/6 and 80/10/10 in a second extraction step. The residue from the second step was extracted with water at 40 °C and atmospheric pressure. Ethanolic, aqueous and hydroalcoholic (70:30, v:v) extracts were also obtained by conventional extraction methods at atmospheric pressure. All extracts were analyzed for global extraction yield, total phenolic content, total flavonoids, and carajurin content. High performance liquid chromatography (HPLC) was used both to quantify carajurin, which is the main anthocyanin component of A. chica, and to monitor qualitatively two other anthocyanin pigments found in that plant. The extraction yield in the first step was only 0.65% using pure scCO₂, but this extraction was highly selective to extract carajurin from the three main anthocyanins. The accumulated global yield of the two steps ranged from 3% when the solvent ratio (80/20/0) was used in the second step to about 50% when 6 or 10% water was used, showing the highest yield when the extraction was done with water. The highest contents of total phenolic compounds (178 mg GAE/g extract) and total flavonoids (373 mg EC/g extract) were found in the process performed with the extraction mixture (80/20/0), and the highest carajurin content was obtained in the ethanolic extracts.     

Supercritical CO2 intercalation of polycaprolactone in layered silicates

Supercritical carbon dioxide (scCO₂) intercalation of polycaprolactone (PCL) in layered silicates (clay) is studied. Wide angle X-ray diffraction patterns find that PCL is slightly intercalated in unmodified montmorillonite clay (NaMMT) but considerably intercalated in organic-modified montmorillonite clay (OMMT). The interlayer spacing in OMMT increases considerably from 1.94 nm in OMMT to 3.58 nm in the OMMT/PCL 10/90 sample. PCL8 having molecular weight of 80,000 is harder to intercalate into OMMT than PCL1 having molecular weight of 10,000. Higher scCO₂ pressures at a temperature allow larger intercalations of PCL in OMMT to exhibit larger interlayer spacings in OMMT. The interlayer spacings in OMMT, however, are not clearly found to relate with the CO₂ temperature at a given pressure. TGA data show that OMMT enhances the thermal stability of PCL1, with a higher content of OMMT giving a higher amount of PCL1 residue. DSC data find that the PCL1-intercalated OMMT expedites the melt-crystallization rate of PCL1 from the melt but suppresses the crystallinity of PCL1. Study of Avrami's rate constants k and exponent n finds that the PCL1-intercalated OMMT enhances the isothermal crystallization rate of PCL1 and that the crystal growth dimension is 3 for pure PCL1 but decreases with increasing OMMT content in the blends. Modulus data find that the PCL1-intercalated OMMT is an effective reinforcement for PCL8.     

CO2/N2开关型脒基表面活性剂软模板制备介孔二氧化硅

模板法是制备介孔SiO₂的常用方法之一,而模板法通常需要脱除模板后才能得到介孔结构。以传统表面活性剂为模板合成介孔二氧化硅,除模板方法还有高温焙烧、溶剂萃取等,但这些方法均存在一定的缺点,如导致结构坍塌、消耗大量溶剂等。本文采用开关型表面活性剂N'-十二烷基-N,N-二甲基乙基脒碳酸氢盐为模板剂,以正硅酸四乙酯(TEOS)为硅源在碱性条件下合成SiO₂。与常规除模板法不同,本实验在反应结束后加热并通入N₂使表面活性剂分解失去表面活性,用水和丙酮洗涤后得到了形貌规整、孔道有序、具有较高比表面积和孔容的介孔SiO₂。同时还研究了有机盐乙二胺四乙酸二钠(Na₂EDTA)对介孔有序度、所得介孔材料比表面积、孔容孔径和模板残留量的影响。     

Preparation and characterization of foams from sheet glass and fly ash using carbonates as foaming agents

Glass foams were produced using sheet glass cullet and fly ashes from thermal power plant with added carbonates (commercial dolomite- and calcite-based sludges) as foaming agents. The influence of type and amount of carbonates as well as of the sintering temperature on the apparent density, compressive strength, microstructure and crystalline phases was evaluated. The experimental results showed that homogenous microstructures of large pores could be obtained by adding just 1–2 wt.% carbonates and using low sintering temperature (850 °C), leading to foams presenting apparent density and compressive strength values of about 0.36–0.41 g/cm³ and 2.40–2.80 MPa, respectively. Good correlations between compressive strength, apparent density and microstructure (pore size, struts’ thickness and internal porosity) were observed.     

不同发泡剂及工艺条件对BR／SBR／NR发泡材料相结构及尺寸稳定性的影响

分别采用一段和两段模压法制备了以顺丁橡胶（BR）／丁苯橡胶（SBR）／天然橡胶（NR）为基体的橡胶发泡材料,研究了三种化学发泡剂N,N＇-二甲基戊次甲基四胺（H）、4,4＇-氧代双（苯磺酰肼）（OBSH）以及H／OBSH（质量比1：1）复配对发泡及硫化特性的影-向,以及3种发泡剂和2种成型工艺对收缩率及相结构的影响。结果表明,发泡剂H对硫化性能影响最大,含发泡剂H的混炼胶在分解过程中释放的热量最多;加入3种发泡剂都具有一种较大的泡孔镶嵌在较小的泡孔丛中的泡孔形态;密度和线收缩率均随着时间的增加而增加,经H／OBSH复配的发泡剂更适合该体系成型,材料线收缩率均比单独使用H和OBSH小,两段模压法可以有效地提高发泡材料的尺寸稳定性,收缩率降低至3．88％,同时发泡剂使用率最多可提高31．67％。     

Preparation of carbon foams with enhanced oxidation resistance by foaming molten sucrose using a boric acid blowing agent

Boric acid was used as a blowing agent as well as a boron precursor for the preparation of boron-doped carbon foams from molten sucrose. The H⁺ generated, due to the formation of a complex between sucrose and boric acid, catalyzes the –OH to –OH condensation reaction leading to the polymerization and the foaming of the molten sucrose. The char yield of the solid organic foams increased from 24 to 39 wt.% when the boric acid concentration increased from 0 to 8 wt.%, due to the formation of the B–O–C cross-links between sucrose polymer by B–OH to C–OH condensation. The inductively coupled plasma analysis showed the presence of 0.44–3.4 wt.% boron in the carbon foams. The density and compressive strength decreased and cell size increased with boric acid concentration. The room temperature thermal conductivity of the boron-doped carbon foams was in the range of 0.057–0.043 W m⁻¹ K⁻¹. The weight loss studies by dynamic and isothermal heating showed the increased oxidation resistance with boron concentration.     

A parametric study into the morphology of polystyrene-co-methyl methacrylate foams using supercritical carbon dioxide as a blowing agent

In this study the foaming of poly(styrene-co-methyl methacrylate) (SMMA) using supercritical carbon dioxide is investigated. The effect of different foaming parameters such as temperature and pressure is studied in a quantitative and systematic way, with the aim to control and predict the resulting foam morphology. It is shown that once the polymer properties, such as the glass transition temperature and the solubility of CO₂ are known, full control of the desired foam morphology can be obtained by a proper selection of temperature, pressure and depressurization rate.     

Extrusion of polystyrene nanocomposite foams with supercritical CO2

Intercalated and exfoliated polystyrene/nano‐clay composites were prepared by mechanical blending and in situ polymerization respectively. The composites were then foamed by using CO₂ as the foaming agent in an extrusion foaming process. The resulting foam structure is compared with that of pure polystyrene and polystyrene/talc composite. At a screw rotation speed of 10 rpm and a die temperature of 200°C, the addition of a small amount (i.e., 5 wt%) of intercalated nano‐clay greatly reduces cell size from 25.3 to 11.1 μm and increases cell density from 2.7 × 10⁷ to 2.8 × 10⁸ cells/cm³. Once exfoliated, the nanocomposite exhibits the highest cell density (1.5 × 10⁹ cells/cm³) and smallest cell size (4.9 μm) at the same particle concentration. Compared with polystyrene foams, the nanocomposite foams exhibit higher tensile modulus, improved fire retardance, and better barrier property. Combining nanocomposites and the extrusion foaming process provides a new technique for the design and control of cell structure in microcellular foams.     

二氧化碳在CH4+CO2+N2/C2H6三元系中的结霜温度计算

含CO₂的天然气体系在历经低温工艺时,由于CO₂的三相点温度(216.55 K)较高,容易凝华结霜产生固体CO₂,因而有必要对CO₂在天然气中的结霜温度进行计算。根据气固相平衡原理,分别采用道尔顿分压定律、PR状态方程对CO₂在CH₄-CO₂-N₂和CH₄-CO₂-C₂H₆三元系中的结霜温度进行了计算。此外,还采用HYSYS软件对CO₂的结霜温度做了相应的计算。将3种方法的计算结果和实验结果进行了比较,结果表明3种方法在预测三元系中CO₂的结霜温度时,都具有良好的精度。其中,PR状态方程法和HYSYS法的精度略高于道尔顿分压定律法;道尔顿分压定律法虽精度最低,但计算最简单,且也能获得满意的精度,可做工程快速估算使用。     

RG-CPA方程计算超临界CO2-醇体系汽液相平衡

综合考虑缔合作用和密度涨落的影响,将经重整化群修正的CPA方程（RG-CPA方程）扩展到二元体系汽液相平衡的计算。通过一个温度下的汽液相平衡数据回归得到二元交互作用参数,预测其他温度下的相平衡。采用这种方法计算了超临界CO₂与醇二元体系的汽液相平衡性质和临界曲线。结果表明,RG-CPA方程预测超临界CO₂与醇二元体系的气液相组成和密度具有较高的精度,液相组分平均绝对偏差为0.032,气相组分平均绝对偏差为0.019。与原始CPA方程相比,RG-CPA方程能更好地预测气液临界曲线。