间乙炔基苯偶氮线性酚醛泡沫的结构与性能研究

采用高温化学发泡法制备了一种间乙炔基苯偶氮酚醛树脂泡沫(EPANF).采用傅里叶红外光谱(FTIR)、凝胶渗透色谱(GPC)、光学显微镜、扫描电子显微镜(SEM)、导热系数分析仪、临界氧指数分析仪和热重分析(TG)等表征了间乙炔基苯偶氮酚醛树脂(EPAN)结构和EPANF的泡孔结构、压缩强度、隔热性能、阻燃性能和热性能.研究结果表明,当所用发泡剂含量为18%,泡沫体的表观密度为0.179 g/cm~3时,EPANF泡孔均匀微细,闭孔率高,泡孔平均粒径为350μm左右.随着表观密度增加,泡沫体压缩强度增大,热导率系数增大,隔热性能略有下降,但其临界氧指数变大,阻燃性能提高.当表观密度为0.363 g/cm~3时,EPANF的压缩强度达到最大为5.63 MPa.EPANF的5%和10%热失重温度分别为333、381℃,其700℃的残炭率和1000℃的残炭率分别为65.8%和58.2%,耐热性和耐烧蚀性较普通线性酚醛树脂有明显提高.EPANF作为热结构材料和烧蚀材料有望在航天航空等领域应用.     

水发泡淀粉挤出泡沫的结构与性能

以水为发泡剂,普通玉米淀粉为原料,采用双螺杆挤出机制备淀粉泡沫材料,研究了发泡剂用量及聚乙烯醇的加入量对泡沫材料结构与性能的影响。 用扫描电子显微镜观察了泡沫材料截面的形态,用万能材料试验机测试了泡沫材料的力学性能。 结果表明,水的质量分数为8%时淀粉泡沫径向膨胀率和发泡倍率最高,分别为22倍和17.6倍,压缩模量最高（4.07 MPa）。 加入质量分数10%的聚乙烯醇(PVA)使淀粉泡沫的孔径变大至1.29 mm,壁厚增加至82.43 μm,同时压缩模量增加至9.70 MPa。     

THIEC改性三聚氰胺甲醛树脂泡沫的制备及其性能表征

首先,采用三-(2-羟乙基)异氰酸脲酯(THIEC)作为增韧剂对三聚氰胺甲醛树脂(蜜胺树脂)进行化学改性,以提高树脂的韧性。然后,将改性蜜胺树脂与表面活性剂、发泡剂、固化剂、成核剂等充分混合搅拌,采用普通热发泡法制得三聚氰胺甲醛树脂泡沫(蜜胺泡沫)。用扫描电子显微镜(SEM)、氧指数仪、万能电子试验机、导热系数仪对蜜胺泡沫的形态结构、阻燃性能、力学性能及热绝缘性能进行了测试和分析。探究了发泡剂、固化剂用量对蜜胺泡沫表观密度及形态的影响。结果表明:当THIEC、发泡剂、固化剂、成核剂的用量依次为蜜胺树脂质量的15%、10%、6%、2%,发泡温度为80℃时,蜜胺泡沫的压缩强度达到150kPa、极限氧指数为34、导热系数为0.027W/(m·K),综合性能良好。     

发泡聚乳酸/热塑性聚氨酯/二氧化硅纳米复合材料的泡孔结构

以超临界二氧化碳作为物理发泡剂,通过快速降压法制备聚乳酸(PLA)/热塑性聚氨酯(TPU)/二氧化硅(SiO2)纳米复合材料发泡样品。发泡样品的泡孔结构使用扫面电子显微镜进行观察。在低频区,SiO2增加PLA/TPU共混物的储能模量和复数黏度。SiO2的加入使PLA/TPU共混物发泡样品的泡孔直径减小、泡孔密度增大。SiO2对PLA/TPU共混物发泡样品泡孔结构的改善归因于SiO2的异相成核作用和对共混物流变性能的改善作用。     

双峰泡孔结构聚苯乙烯材料的制备

以超临界二氧化碳(Sc-CO2)为物理发泡剂,在高压釜中采用两种温度设定方式和降压对聚苯乙烯(PS)进行发泡,测试、分析发泡样品的泡孔结构、泡体密度和断面润湿性能.结果表明,仅通过降压只获得单峰的泡孔结构,而升温与降压协同作用可获得双峰的泡孔结构,大、小泡孔分别在升温和降压阶段成核形成;在发泡温度100℃、饱和温度30~70℃下制备的发泡样品中,大、小泡孔的平均直径分别为50~216和10~15μm.大泡孔的直径较大和密度较高都有利于降低样品的泡体密度,最低达0.15 g/cm3.单峰泡孔结构能在一定程度上提高样品断面的疏水性,使静态接触角(CA)从PS的本征值(87.1°)增大至138.8°;双峰泡孔结构可赋予样品断面更高的CA(155.1°),呈现超疏水特性.     

新型PES微孔材料的制备及性能研究

合成了新型双烯丙基聚醚砜(PES), 采用超临界CO2作为物理发泡试剂制备微孔材料, 研究了不同发泡温度、饱和压力、发泡时间和放气时间等因素对微孔形貌的影响. 结果表明, 发泡温度在110~170 ℃之间, 随着温度的升高, 泡孔直径增加, 泡孔密度在140 ℃达到一个最大值; 随着饱和压力的升高, 泡孔直径减小, 泡孔密度增大; 发泡时间和放气时间对微孔直径和密度影响不大; 研究了在不同辐照剂量下微孔材料的交联性能, 结果表明, 在600 kGy辐照剂量以下, 交联效果不明显, 在800 kGy以上, 随着辐照剂量的增大, 凝胶含量增加, 辐照后的样品在265 ℃热处理10 min, 仍能保持完好的微孔结构.     

双分布聚合物泡沫材料热性能的有限元计算

采用有限元法计算了双分布聚合物泡沫的泡孔分布对材料热性能的影响.研究了不同孔隙率下材料热通量的变化,得到了泡孔分布形式、孔隙率与导热系数之间的关系.结果 表明,孔隙率在30％～ 70％之间时,双分布泡孔结构材料的保温性优于单分布泡孔结构材料.其次,随着孔隙率与大孔径泡孔面积占比的增加,材料保温性能增强.最后,相同孔隙率...     

超临界流体制备微发泡聚合物材料的研究进展

以超临界流体为物理发泡剂制备的微发泡聚合物材料具有小的泡孔尺寸和高的泡孔密度,从而赋予材料优异的性能.本文首先阐述了微发泡聚合物材料的制备原理,以及聚合物微发泡过程中泡孔形成的四个阶段;基于这些认识,针对微发泡聚合物材料泡孔形态的改善,即增加泡孔密度、减小泡孔尺寸以及均化泡孔尺寸分布,从加强泡孔成核、控制泡孔增长的角度综述了近年来的研究进展;最后对如何有效控制泡孔形态提出了建议,并对微发泡聚合物材料的应用前景进行了展望.     

耐高温聚酰亚胺泡沫材料

聚酰亚胺泡沫具有低介电、隔热、吸声、高比强度以及高经济效益等诸多优点,因而近些年来在航空、航天、船舶航舰、能源与环境保护等领域有着广泛的应用。聚酰亚胺泡沫按照泡孔结构分为软质开孔泡沫和硬质闭孔泡沫两大类,其通常是由芳香族二酐与芳香族二胺通过缩聚反应制备得到分子量可控的聚酯铵盐,再将其作为前驱体经过热发泡制备得到最终的聚酰亚胺泡沫。前驱体的化学结构对最终的聚酰亚胺泡沫的机械性能和热性能都有非常显著的影响,同时前驱体的分子量也会对泡沫的密度、机械性能和热性能有非常显著的影响。聚酰亚胺泡沫的研究进展,特别是其化学结构、性能和应用都会在本文中逐一阐述。     

PP/HDPE 共混物及其纳米复合材料超临界流体微孔发泡

通过间歇法制备了聚丙烯(PP)/高密度聚乙烯(HDPE)共混物及其纳米复合材料的微孔塑料.用扫描电镜对发泡样品的泡孔结构进行表征,研究了纳米粒子的类型和含量对泡孔结构的影响.结果表明:在PP中加入25%的HDPE可改善泡孔结构;在 PP/HDPE 共混物中加入纳米粒子可使泡孔的直径减小、密度增加、泡孔分布更均匀;泡孔直径随着纳米粒子含量的增加会出现先减小后增加的趋势.     

Towards novel super‐elastic foams based on isoperene rubber: Preparation and characterization

A novel and conventional closed cell polyisoprene rubber (IR) foams were produced by a single step limited‐expansion and two step unlimited‐expansion foaming process, respectively. The effect of 3 to 12 part per hundred rubber (phr) of azodicarbonamide (ADC) foaming agent on their structure and properties of developed novel foams were studied. In developed novel foams, the density was strangely independent of ADC content; however, the cell sizes conversely related to ADC content and it decreased by 60% (555‐330 μm) and the internal cell pressure build up from 1 to 3.7 atm, which was related to pressure‐free foaming method. The both reasons of compressed gas trapped inside cells and constant density not only caused unique enhancement in novel foams mechanical properties as hardness and modulus but also improved their dynamic properties as hysteresis and elasticity. Results of conventional IR foams showed that, their foam density as well as dynamic and mechanical properties sharply decreased with increasing ADC content from 3 to 12 phr. For clear expression, in samples with 12 phr of ADC, novel developed foams have more foam density (180%), more hardness (240%), more modulus (290%), and smaller cell size (75%) than conventional foams. Finally, novel developed foams were super‐elastic material with no hysteresis and no plastic deformation while conventional foams had 40% hysteresis and 10% plastic deformation under the same compression conditions.     

Study of the fracture behavior of flexible polypropylene foams using the Essential Work of Fracture (EWF)

Two types of commercial low density polypropylene based flexible foams produced by extrusion foaming were characterized in terms of their fracture behaviour using the concept of the Essential Work of Fracture (EWF), focusing on the influence of the foam’s relative density and cellular structure on the values of the fracture parameters. With that in mind, correction procedures based on the expansion ratio of the foams and their cellular structure were proposed, with the objective of taking the complexity of these materials into account in the obtained fracture parameters. Significant differences were found between the fracture parameters of the two foams related to differences in their cellular structure, particularly cell size, cell aspect ratio and preferential cell orientation. Generally speaking, the specific fracture elastic contribution in the two considered extrusion directions increased with increase of the cell aspect ratio, especially in the case of the foams with a marked cell orientation in the direction of the extrusion flow. In any case, the fracture parameters for all foams were considerably lower in the direction perpendicular to the extrusion flow, hence demonstrating the highly anisotropic fracture behaviour of these foams due to the anisotropic cellular structure induced during foaming.     

Physical properties of silicone foams filled with carbon nanotubes and functionalized graphene sheets

Free-rising silicone foams were made with loading fractions of up to 0.25 wt.-% functionalized graphene sheets (FGS) and up to 1.0 wt.-% carbon nanotubes (CNTs) using hydrogen as blowing agent. Scanning electron microscopy of the samples revealed an open cellular structure and a homogeneous dispersion of both types of nanofillers. The incorporation of nanofiller affected the foaming process and thus the final foam density and cellular structure. Transmission electron microscopy revealed the formation of a CNT network throughout the sample, while FGS presented an exfoliated and intercalated dispersion. The thermal stability of the samples was drastically affected by the presence of both nanofillers. Both nanofillers showed a positive effect on the compressive response of the foams. However, the nanocomposite foams were found to decrease the acoustic absorption with nanofiller content probably due to the variable foam structure and improved stiffness.     

Poly(lactic acid)/organoclay nanocomposites: Thermal,rheological properties and foam processing

In this study, polymer nanocomposites based on poly(lactic acid) (PLA) and organically modified layered silicates (organoclay) were prepared by melt mixing in an internal mixer. The exfoliation of organoclay could be attributed to the interaction between the organoclay and PLA molecules and shearing force during mixing. The exfoliated organoclay layers acted as nucleating agents at low content and as the organoclay content increased they became physical hindrance to the chain mobility of PLA. The thermal dynamic mechanical moduli of nanocomposites were also improved by the exfoliation of organoclay; however, the improvement was reduced at high organoclay content. The dynamic rheological studies show that the nanocomposites have higher viscosity and more pronounced elastic properties than pure PLA. Both storage and loss moduli increased with silicate loading at all frequencies and showed nonterminal behavior at low frequencies. The nanocomposites and PLA were then foamed by using the mixture of CO₂ and N₂ as blowing agent in a batch foaming process. Compared with PLA foam, the nanocomposite foams exhibited reduced cell size and increased cell density at very low organoclay content. With the increase of organoclay content, the cell size was decreased and both cell density and foam density were increased. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 689–698, 2005     

Supercritical CO<Subscript>2</Subscript> assisted preparation of open-cell foams of linear low-density polyethylene and linear low-density polyethylene/carbon nanotube composites

The open-cell structure foams of linear low-density polyethylene (LLDPE) and linear low-density polyethylene (LLDPE)/multi-wall carbon nanotubes (MWCNTs) composites are prepared by using supercritical carbon dioxide (sc-CO₂) as a foaming agent. The effects of processing parameters (foaming temperature, saturation pressure, and depressurization rate) and the addition of MWCNTs on the evolution of cell opening are studied systematically. For LLDPE foaming, the foaming temperature and saturation pressure are two key factors for preparing open-cell foams. An increase in temperature and pressure promotes both the cell wall thinning and cell rupture, because a high temperature results in a decrease in the viscosity of the polymer, and a high pressure leads to a larger amount of cell nucleation. Moreover, for the given temperature and pressure, the high pressurization rate results in a high pressure gradient, favoring cell rupture. For LLDPE/MWCNTs foaming, the addition of MWCNTs not only promotes the cell heterogeneous nucleation, but also prevents the cell collapse during cell opening, which is critical to achieve the open-cell structures with small cell size and high cell density.     

Supercritical CO_2 Assisted Preparation of Open-cell Foams of Linear Low-density Polyethylene and Linear Low-density Polyethylene/Carbon Nanotube Composites

The open-cell structure foams of linear low-density polyethylene(LLDPE) and linear low-density polyethylene(LLDPE)/multi-wall carbon nanotubes(MWCNTs) composites are prepared by using supercritical carbon dioxide(sc-CO_2)as a foaming agent. The effects of processing parameters(foaming temperature, saturation pressure, and depressurization rate) and the addition of MWCNTs on the evolution of cell opening are studied systematically. For LLDPE foaming, the foaming temperature and saturation pressure are two key factors for preparing open-cell foams. An increase in temperature and pressure promotes both the cell wall thinning and cell rupture, because a high temperature results in a decrease in the viscosity of the polymer, and a high pressure leads to a larger amount of cell nucleation. Moreover, for the given temperature and pressure, the high pressurization rate results in a high pressure gradient, favoring cell rupture. For LLDPE/MWCNTs foaming, the addition of MWCNTs not only promotes the cell heterogeneous nucleation, but also prevents the cell collapse during cell opening, which is critical to achieve the open-cell structures with small cell size and high cell density.     

Effect of Supercritical Carbon Dioxide Conditions on PVDF/PVP Microcellular Foams

Supercritical carbon dioxide (ScCO₂) was used as a physical foaming agent to prepare poly(vinylidene f luoride)/poly(N-vinyl pyrrolidone) (PVDF/PVP) microstructure material. The effects of foaming conditions including saturation pressure, foaming temperature and foaming time on PVDF/PVP foams morphology, thermal and electrical behavior were systematically investigated by scanning electron microscope, differential scanning calorimeter and broadband dielectric spectrometer. Small cell and low cell density were achieved at low pressure of 12 MPa, as increasing saturation pressure, the average cell size increased first, and then decreased. The competition between the cell growth and cell nucleation played an important role in average cell size, which was directly related to ScCO₂ processing conditions. With increasing foaming temperature, cell size was increased and cell density was decreased, in a nearly linear manner. The variation of foaming time was considered to be closely related to the time for cells to grow. Thus, the results revealed that the average cell size enhanced with extending foaming time. The thermal properties of PVDF/PVP composites are slightly inf luenced by foaming parameters, and the dielectric constant of PVDF/PVP composite foams decreased with increasing volume expansion ratio.     

Foaming of trans‐polyisoprene using N2 as the blowing agent

Foaming of trans‐1,4‐polyisoprene (TPI) polymer was carried out through a batch process using nitrogen (N₂) as the blowing agent. TPI vulcanizates having varying crosslink densities were prepared by varying crosslinking agent content and curing time. The vulcanizates were then saturated with N₂ inside a pressure vessel at a pressure of 14 MPa and varying temperatures for 5 hours before effecting the foaming by rapidly quenching the pressure. The effects of varying the crosslinking agent content, silica filler content, and precuring time of the vulcanizates and the effects of varying the gas saturation temperature of foaming on the cell characteristics and physical properties of the foam prepared were investigated. The cells of the TPI foams had a spherical, closed structure. The density, expansion ratio, cell size, cell density, and tensile properties of the foams varied with varying crosslink density of the TPI vulcanizates as well as the saturation temperature of foaming. The important effects of crosslink density and saturation temperature on the N₂ solubility in the TPI matrix and thus on the foam expansion were discussed. The silica filler was found to be acting as a cell nucleating agent and reinforcing filler for the TPI foams.     

应用超临界CO2制备微孔聚丙烯的微孔形貌

研究了应用超临界CO2技术制备微孔聚丙烯时发泡条件和聚丙烯(PP)的熔体强度对微孔形貌的影响。结果表明:在一定的饱和压力下,随着温度的升高,PP的变形能力改善,有利于泡孔的长大。随着饱和压力的增加,PP的熔点降低,升高压力和升高温度具有一定的等同作用。由于CO2在PP内分散的不同,高压低温时得到的泡孔比高温低压时得到的泡孔要规整。降压速率对泡孔形貌的影响因饱和压力的大小而异,饱和压力较高时随着降压速率的提高,孔密度增加,泡孔形貌经历了一个从球体到多面体转变的过程。由于PP熔体强度较低,在发泡温度和PP熔点之间非常接近时,CO2气体容易冲破孔壁而使泡孔呈开孔结构。