微孔注射成型PPS及其性能研究

以超临界氮气(SC N2)作为发泡剂,采用注射成型法制备了微孔化聚苯硫醚(PPS)泡沫塑料,研究了模具流道、SC N2含量、PPS熔胶量位置对微孔化PPS泡沫塑料泡孔特性、相对密度、力学性能及介电性能的影响。结果表明,随着模具流道的延长,微孔化PPS泡沫塑料的泡孔孔径逐渐变大,泡孔密度降低;SC N2含量对泡孔孔径、力学性能及介电性能影响不大,但泡孔密度随SC N2含量的增大而增大;随着PPS熔胶量位置的降低,微孔化PPS泡沫塑料的泡孔孔径增大,泡孔密度降低,力学性能及介电常数也相应逐渐降低。     

Effect of pore size distribution on compressive behavior of moderately expanded low‐density polyethylene foams

We investigated the effect of the pore size distribution on the compressive behavior for moderately expanded elastic polymer foams. Unlike well‐expanded foams, moderately expanded foams have heterogeneous cellular structures and their mechanical properties can depend on the heterogeneity of cellular structures. To clarify the effect of the pore size distribution on mechanical properties, we prepared a series of low‐density polyethylene (LDPE) foams with different pore size distributions and relative densities as models of moderately expanded elasitc polymer foams. We performed the microscope observations and the uniaxial compression tests of the moderately expanded LDPE foams. The compressive behavior of a foam was primarily determined by the relative density, but we found that the compressive behavior also depends on the pore size distribution, especially in the collapse region. In the collapse region, the compressive stress–strain curves showed clear dependence on the heterogeneities of cellular structures. The broader cell distribution resulted in the stronger strain dependence of the stress in the collapse region. We show that we can reasonably predict the compressive stress–strain curves from the pore size distributions. POLYM. ENG. SCI., 59:510–518, 2019. © 2018 Society of Plastics Engineers     

Effect of foaming temperature and rubber grades on properties of natural rubber foams

Foaming temperature and grade of dry natural rubber were varied to evaluate their effects on the morphology and mechanical properties of natural rubber (NR) foams. Three different grades of NR were used; namely ENR‐25, SMR‐L, and SMR‐10. NR foams from these grades were produced at three different foaming temperatures, i.e. 140, 150, and 160°C. The study was carried out using formulated compositions containing sodium bicarbonate as the chemical blowing agent and were expanded using conventional compression molding technique via a heat transfer foaming process. The NR foams were characterized with respect to their relative foam density, density of crosslinking, cell size, compression stress, and compression set. Increase in foaming temperature resulted in lower relative density and larger cell size. It was also discovered that the crosslink density slightly decrease with increasing foaming temperature. For mechanical properties, the highest foam density resulted in the highest compression stress. Compression stress at 50% strain increased with increasing foaming temperature and ENR‐25 foam has the highest compression stress among the produced foams. The results showed that the morphology, physical, and mechanical properties of the rubber foams can be controlled closely by the foaming temperature and rubber grades. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

热解炭微观结构对炭/炭复合材料力学性能的影响

以PAN基针刺纤维毡为基体,采用等温化学气相渗透技术,在温度1000℃、压力5.0~20.0 kPa条件下制备了2种具有不同微观结构热解炭的炭/炭复合材料,研究了其力学性能与热解炭微观结构的关系. 结果表明,压力8.0 kPa下得到的具有单一低织构热解炭的炭/炭复合材料的断裂强度较高,为86±3 MPa,热解炭与炭纤维间界面结合紧密,加载过程中二者同时断裂,呈现明显的脆性断裂行为;压力10.0~20.0 kPa下得到的具有中织构-高织构-中织构热解炭的炭/炭复合材料的断裂强度稍低,为82±4 MPa,加载过程中材料内部不同织构热解炭间多层次界面通过改变裂纹扩展路径而延缓其扩展速度,断口形貌呈现锯齿状,表现出假塑性断裂特征.     

蒸馏水含量对三明治结构硬质聚氨酯泡沫性能的影响

采用异氰酸酯、聚酯多元醇、发泡剂（水）等原料通过一体发泡成型技术制备出一种新型的三明治泡沫夹心复合材料。利用热重分析、扫描电子显微镜等对不同水含量（质量分数分别为0、0.5 %和1.0 %）的硬质聚氨酯泡沫材料的泡孔直径、密度、热导率、压缩性能、三点弯曲和热力学性能等做了研究,进而确定提高硬质聚氨酯性能的最佳工艺。结果表明,随着水含量的增加,硬质聚氨酯泡沫材料泡孔直径增大,密度变小,热导率降低,保温性能提高,而压缩性能和三点弯曲却呈下降趋势;综合考虑硬质聚氨酯泡沫材料泡孔结构和良好的保温隔热及弯曲等力学性能,其最佳含水量为0.5 %。     

Compressive behavior of rigid polyurethane foams nanostructured with bacterial nanocellulose at low and intermediate strain rates

Nanocellulose reinforced foams are lightweight with improved mechanical properties; however, the strain-rate effect on their mechanical response is not yet fully understood. In this work, rigid polyurethane foams (PUFs) nanostructured with bacterial nanocellulose at 0.2 wt % (BNCF) and without it (PUF) are synthesized and subjected to compression tests at different strain rates. The BNC acts as a nucleation agent, reducing the cell size but maintaining a similar apparent density of 40.4 ± 3.3 kg m⁻³. Both BNCF and PUF exhibit strain-rate effect on yield stress and densification strain. The BNCF exhibits localized progressive crushing and reduced friability, causing a remarkable recovery in the transverse direction. Numerical simulations show that functionally graded foams subjected to impact could be designed using different layers of PUF and BNCF to vary energy absorption and acceleration rate. The results presented herein warrant further research of the mechanical properties of nanostructured foams for impact applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48701.     

Microstructure,thermal conductivity and simulation of elastic modulus of MAX-phase (Ti2AlC) gel-cast foams

MAX-phase (Ti₂AlC) gel-cast foams manufactured using agarose as gelling agent were investigated in terms of their microstructural, mechanical and thermal properties. The microstructural analysis of Ti₂AlC foams made using SEM were compared with those using X-ray micro tomography. The Young’s Modulus of Ti₂AlC foams was determined using the impulse excitation technique. This experimental data was correlated with the Gibson-Ashby, Spriggs and Cross-property relation models. The thermal conductivity measurements were carried out by Laser-Flash analysis correlating to the pore network in the Ti₂AlC foam structure derived from μCT measurement. FEM-simulations of the mechanical behaviour were carried out on real structure models to determine a strut wise stress distribution under load.     

硅橡胶海绵材料孔隙结构对力学性能的影响

采用不同方法制备了两种密度且孔隙率相近、孔隙结构不同的硅橡胶海绵材料,表征了其孔隙结构的差异,研究了两种孔隙结构明显不同的硅橡胶海绵材料力学性能的差异。结果表明。硅橡胶海绵材料的孔隙结构对拉伸强度、拉断伸长率、压缩应力应变及压缩应力松驰等力学性能有较大的影响。     

单体配比对PMI泡沫塑料结构和性能的影响

探讨了四种不同单体配比(甲基丙烯酸/甲基丙烯腈)对PMI泡沫塑料结构和性能的影响.结果发现随着单体配比的增加PMI泡沫塑料的泡孔孔径先增大后减小,在单体配比为50/50时泡孔孔径最小.同时发现PMI的密度与泡孔孔径成反比,孔径越小,密度越大.PM1泡沫塑料的力学性能与耐热性能与其密度成正比,密度越大,其力学性能和耐热性...     

Study on the effect of dispersion phase morphology on porous structure of poly (lactic acid)/poly (ethylene terephthalate glycol-modified) blending foams

A methodology for blending foam of poly (lactic acid) (PLA)/poly (ethylene terephthalate glycol-modified) (PETG) was proposed. PLA/PETG blends were prepared through a melt blending method, using multiple functionality epoxide as reactive compatibilizer. The effects of blending ratio and compatibilizer content on the dispersion morphology, molecular structure, mechanical properties, and rheological behavior of PLA/PETG blends were studied. Then PLA/PETG blends were foamed using supercritical CO₂ as physical blowing agent, and their porous structure, pore size, as well as pore density were investigated. The results showed that the mechanical properties and rheological parameters such as melt strength and melt elasticity, as well as the porous structure of the foams dispersion morphology of PLA/PETG blends were affected strongly. The melt elasticity of PLA/PETG blends increased with increasing compatibilizer content. Dispersion phase morphology of PLA/PETG blends also had a significant effect on the pore density of all the samples. The results indicated that homogeneous and finer porous morphology of PLA/PETG foams with high expansion ratio could be achieved with a proper content of compatibilizer in the blends.     

The effect of different palm oil‐based bio‐polyols on foaming process and selected properties of porous polyurethanes

Rigid polyurethane foams were successfully prepared by blending up to 70 wt% of two different palm oil‐based bio‐polyols with a petrochemical polyether polyol. The bio‐polyols were synthesized by epoxidation–oxirane ring‐opening process using water (PP102) and diethylene glycol (PP147), respectively. Due to the high viscosity of both bio‐polyols the reactive mixture was heated to start the foaming reaction at about 50 °C. Under these conditions, the gelling reactions speed up as the amount of PP147 increases but slow down to a great extent when PP102 is used. The thermal conductivity of modified foams is higher and the closed cell content lower compared to reference ones, even when the bio‐foams present a lower apparent density. However, all foams exhibit reduced water absorption, excellent dimensional stability and better thermal stability at temperatures up to 400 °C than the control foam. Conversely, their mechanical and dynamic mechanical properties become poorer as the PP147 concentration increases and even more so if PP102 is used instead. PP147 foams containing up to 50% bio‐polyol could be used as a green replacement of petroleum‐based ones in applications where excellent behaviour in compression (the most affected properties) is not fundamental, with the additional advantages of reduced density and increased content of bio‐derived components. © 2017 Society of Chemical Industry     

Production and aging of highly porous 17-4 PH stainless steel

This study describes production of highly porous 17-4 PH stainless steel for biomedical implant applications by space holder-sintering technique. 17-4 PH stainless steel powders were mixed with space holder and then compacted. For designing pore properties, both spherical and irregular shaped carbamide with different particle size ranges were used as space holder and removed by water leaching. Porous 17-4 PH steel specimens were sintered at 1,260?°C for 40?min. Boron was used as a liquid phase sintering additive. In addition, sintered specimens were aged in order to increase mechanical properties. Specimens were austenitized at 1,050?°C and then quenched. Quenched specimens were aged at times of 1?C6?h at temperatures between 450 and 570?°C. The pore size and shape of the 17-4 PH stainless steel foams replicated the initial size and shape of the carbamide particles. This suggests that pore properties can be designed by using proper size, shape and content of space holder.     

不同孔隙结构的硅海绵材料及其力学性能研究

采用不同方法制备了密度和孔隙率相近、孔隙结构不同的2种硅海绵材料,并表征了其孔隙结构的差异,研究了2种孔隙结构明显不同的硅海绵材料在力学性能方面的差异。研究结果表明：硅海绵材料的孔隙结构对断裂强度、断裂伸长率、压缩应力应变及压缩应力松驰等力学性能有较大的影响。     

Silicon carbide particle reinforced mullite composite foams

Silicon carbide particle reinforced mullite composite foams were produced by the polymer replica method using alumina and kaolin to form in situ mullite matrix. Up to 20 wt.% silicon carbide particles (SiCp) were added to aqueous ceramic slurry to explore its effect on the rheological behaviour of ceramic slurries and also properties of as sintered products. By means of solid loading optimisation and sintering enhancement by silicon carbide, mullite based ceramic composite foams of higher strength were obtained. The strength of the as sintered foams was found to depend greatly on the phase composition, relative density of the structures and the amount of SiCp addition. By studying the effect of the additive concentration, on the mechanical properties of the ceramic matrix, it is found that the optimal silicon carbide addition is 20 wt.%.     

Synthesis of bone-like structured foams

Here we present a processing route to produce multi-structured ceramic foams based on the combination of particle-stabilized foams with polymeric sponges to produce positive and negative templating structures. Polyester sponges are infiltrated with freshly produced calcium aluminate–alumina foams and upon sintering either positive templating structures are produced when wetting the sponges, or negative templating foams with a percolating pore network are obtained when completely filling the sponges. Additionally, by combining different layers of these particle-stabilized foam infiltrated sponges, various different structures can be produced, including sandwich structures, pore size gradients, and ceramic bone-like structures applying to different types of bone. The particle-stabilized foams used were in situ self-hardening calcium aluminate cement enriched alumina foams to obtain crack-free samples with pore interconnections and tailorable pore sizes.     

Mechanical strength and damage tolerance of highly porous alumina ceramics produced from sintered particle stabilized foams

Highly porous alumina particle stabilized foams were prepared by combining the concepts of particle stabilized foams and gelcasting, using sulfonate surfactants and poly vinyl alcohol (PVA) as the gelcasting polymer. The ceramic samples sintered at 1500 °C for 2 h had porosities from 65% to 93%, with pore sizes in two categories: “big pore” around 300 μm and “small pore”, around 100–150 μm, depending on the type and amount of surfactant added. The mechanical behaviour of the foams (axial and diametral compression) depended on the overall porosity and pore size. On average, tensile and compressive strengths around 5 and 16 MPa respectively were measured for samples with bigger pore sizes and larger porosities. Samples with smaller pore sizes and lower porosities produced average values of 12 and 57 MPa for tensile and compressive strengths, respectively. The elastic modulus reached a maximum around 3GPa for “small pore” size samples. The effect of increasing amount of PVA in the samples had a strong effect on the green mechanical strength, but it did not significantly affect the mechanical response of the sintered alumina foams. Large and complex shape sintered components produced using this route showed a remarkable damage tolerance, due to crack tip blunting.     

Preparation and properties of phosphorus-containing pyrocarbon — part II. Effect of heat-treatment on phosphorus-containing pyrocarbon

Heat-treatment of pyrocarbon samples containing 3·3–4·1 w/o of phosphorus was performed in vacuum, at various HTT ranging from 1220°C to 2035°C. With increasing HTT, apparent density of the samples decreases and preferred orientation is deteriorated, but their phosphorus content remains unchanged, except at the highest HTT. Such a behaviour is caused by a strong vapour pressure of the elementary phosphorus remaining in the closed porosity. The drop in phosphorus concentration occurring at the highest HTT is also followed by an abrupt change of certain properties; in particular, the interlayer spacing which at lower HTT remains larger than that of the pure pyrocarbon, at this HTT approaches to the pure pyrocarbon value. Such a behaviour may be due to phosphorus incorporated in the pyrocarbon lattice by substitution. This remains stable up to 1800°C, but heat-treatment to 2035°C removes it from the lattice.     

Polyurethane‐infiltrated carbon foams: A coupling of thermal and mechanical properties

The thermal and mechanical properties of polyurethane‐infiltrated carbon foam of various densities were investigated. By combining the high thermal conductivity of the carbon foam with the mechanical toughness of the pure polyurethane, a mechanically tough composite (relative to the unfilled foam) that could be used at higher temperatures than the polyurethane's degradation was formed. Both the tensile strength and the modulus increased by an order of magnitude for the composites compared to unfilled foam, while the compressive and shear strengths and moduli of the composites approached values exhibited by pure polyurethane. At both 300 and 400°C, the rectangular blocks of pure polyurethane lost their mechanical integrity due to decomposition in air. Thermogravimetric analysis confirms substantial initial weight loss above 290°C. Filled carbon foam blocks, however, maintain their mechanical integrity at both 300 and 400°C indefinitely, although the bulk of the rectangular block mass is polyurethane. Three different carbon foam densities are examined. As expected, the higher density foams show greater heat transfer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2348–2355, 2003     

Generation and structure–property behavior of novel liquid crystalline foams produced via a gas supersaturation technique

Linear and star-branched polyoxybenzoate–polyoxyphenoxybenzoate copolymers (POB-co-POPB) at a 65/35 molar ratio were synthesized via melt acidolysis using AB-type monomers and branching agents. By controlling the molecular weight and topology of these polymers, both melt processability and solid-state CO₂ gas absorption behavior were enhanced. POB–POPB copolymers with a molar ratio 65/35 showed a glass transition of 143°C and completion of melting at ca. 300°C. POB–POBP copolymers with a systematically increasing branching agent content showed a systematically decreasing peak intensity in wide-angle X-ray diffraction, indicating that increasing branch-point concentration leads to a decrease in liquid-crystal ordering. Star-branched POB–POPB copolymers showed greatly enhanced carbon dioxide gas absorption behavior relative to their linear counterparts. Whereas CO₂ blown foams of linear POB-co-POPB produced by the gas supersaturation technique had a relatively high density and showed highly anisotropic bubble growth, well-defined, nearly isotropic foams of star-branched POB-co-POPB with a mean cell size from 200 to 400 μ were made using the gas supersaturation technique. Structural features were characterized via scanning electron microscopy, and mechanical properties were determined by indentation testing with a 0.25 in. ball indenter. These LCP foams exhibit relative mechanical properties similar to polystyrene and microcellular polycarbonate foams. A strong inverse relationship was noted between cell size and modulus for liquid crystalline foams with a cell size below 400 μm. © 1994 John Wiley & Sons, Inc.     

Mechanical Properties of Porous Materials

Porous materials are commonly found in nature and as industrial materials such as wood, carbon, foams, ceramics and bricks. In order to use them effectively, their mechanical properties must be understood in relation to their micro-structures. This paper studies the mechanical properties of a few common porous materials: carbon rods, ceramics, polymeric foams and bricks. The characterisation of pore structures was performed using a Mercury Porosimeter. Detailed information was obtained on the density, porosity, surface area and pore size distribution. A large number of experiments on either bending or compression were conducted in order to obtain their macro-mechanical properties such as Young's modulus, hardness and strength. Based on the experimental observations, theoretical models were employed to predict the macro-properties from the micromechanics viewpoint. By studying the deformation of pores the global behaviour was calculated. Two simple formulae for the elastic modulus, E, were proposed: for low values of porosity, , E = E⁰(1 – 2) (1 + 4²) where E⁰ is the elastic modulus when the porosity is zero; for high value of porosity such as for foams E = E⁰ (1 – )². The theoretical results agreed well with the experimental ones. The study has provided insights into the mechanical properties of porous materials over a wide range of porosity values.