超高分子量聚乙烯超临界CO_2间歇发泡研究

应用超临界CO_2间歇发泡方法研究了温度、压力以及不同发泡工艺对超高分子量聚乙烯(UHMWPE)发泡的影响。结果表明:合适的饱和温度可以提高发泡倍率,减小泡孔尺寸,增加泡孔密度;发泡倍率和泡孔密度与饱和压力成正相关;对比不同工艺条件下的发泡结构与尺寸,得出正向发泡的泡孔尺寸小、泡孔密度高,而逆向发泡的泡孔尺寸大,但发泡倍率高。DSC结果表明:正向发泡的结晶度较高,发泡时异相成核数量增加,从而使泡孔尺寸减小、泡孔数量增加。比较正向和逆向发泡相同发泡倍率下的泡沫压缩性能,发现逆向发泡泡沫的弹性模量大于正向发泡泡沫。     

硅橡胶泡沫材料的泡孔结构

中国工程物理研究院的余凤湄等人利用CT技术研究了通过溶析成孔法、化学发泡法及混合发泡法制得的硅橡胶泡沫材料的泡孔结构。结果发现,成孔方法对硅橡胶泡沫材料的泡孔结构有重要影响：溶析成孔法得到的硅橡胶泡沫材料为开孔结构;     

可常温发泡的轻质高强环氧树脂泡沫的制备及性能研究

以环氧树脂E⁃44作为基体树脂、聚甲基氢硅氧烷（PHMS）为发泡剂、N⁃氨乙基哌嗪（N⁃AEP）为固化剂,采用常温发泡工艺,制备具有良好力学性能及泡孔结构的环氧树脂泡沫,研究各配方组分以及发泡方式对泡沫发泡行为以及压缩性能的影响。结果表明,PMHS含量对泡沫发泡行为有重要影响,需要严格控制,含量超过3 %会较大幅度增大泡孔直径,降低泡孔密度,恶化泡孔结构。同时纳米二氧化硅、甜菜碱（CAB⁃35）以及聚硅氧烷⁃聚氧化烯烃共聚物（DH212）等组分对泡沫的泡孔结构和力学强度都有比较大的影响。     

连续挤出发泡聚乳酸泡孔结构的影响因素

介绍了采用超临界CO2作为发泡剂,连续挤出聚乳酸泡沫塑料的方法。在不同的实验条件下,对聚乳酸进行挤出发泡,得到聚乳酸发泡样品。通过对样品的ESM照片的分析研究,得出了不同的发泡条件对挤出聚乳酸泡沫泡孔结构的影响。结果表明螺杆转速的增加使得泡孔数量增加,泡孔形态更加规整均匀。模头温度影响了泡孔形态,较高的温度会使得样品的泡孔形态受到不利的影响。水分的存在不利于聚乳酸发泡成为均匀发泡倍率高的泡沫制品。成核剂促进异相成核,使发泡样品的泡孔结构更加均匀,大大提高了聚乳酸泡沫塑料的泡孔密度。     

水对硬质聚酰亚胺泡沫泡孔结构与性能的影响

采用预聚法制备了1种芳香族聚酰亚胺泡沫,研究了水含量对聚酰亚胺泡沫分子结构﹑泡孔结构﹑发泡密度、发泡程度以及热稳定性的影响规律。结果表明:在所研究的水含量范围内,水含量对聚酰亚胺泡沫的分子结构和热稳定性几乎没有影响;随着水含量增加,大泡孔增多,泡孔尺寸变大,发泡程度更大,泡沫密度更低。     

热硫化硅橡胶泡沫材料的制备技术

介绍了多种适用于热硫化硅橡胶泡沫的模压发泡成型技术,并分别采用该技术制备了具有不同泡孔结构的硅橡胶泡沫,探讨了成型技术对硅橡胶泡沫开孔率的影响.结果表明:成型技术对硅橡胶泡沫的泡孔结构和开孔率有明显的影响;采用化学发泡技术、联合发泡技术、溶析成孔技术制得的硅橡胶泡沫材料的密度分别为0.51、0.50、0.51 g/cm3,开孔率分别为10%、60%、90%.     

成核剂对聚丙烯釜压发泡的影响

用超临界二氧化碳（CO2）釜压发泡的方法,研究了成核剂类型、成核剂粒径以及成核剂添加量对聚丙烯（PP）发泡材料泡孔结构的影响。结果表明,用碳酸钙（CaCO3）作成核剂时PP泡沫的泡孔完整性高,泡孔尺寸分布均匀,且发泡倍率比添加蒙脱土及滑石粉时的要大;成核剂粒子粒径越小,体系的成核点越多,发泡时产生的气泡核越多,所得到的PP泡沫的泡孔密度越大,但是由于纳米碳酸钙（nano-CaCO3）更容易出现团聚现象,直接导致最终发泡制品产生泡孔破裂以及发泡倍率的降低;成核剂CaCO3的添加量为3份时,与添加1份和5份相比,可得到发泡倍率更高,泡孔密度更大的PP泡沫。     

高熔体强度聚丙烯的发泡性能研究

通过反应挤出法对聚丙烯(PP)进行硅烷接枝交联改性获得高熔体强度PP(HMSPP),并对HMSPP的发泡性能及影响因素进行了研究。结果表明,HMSPP具有良好的发泡性能,可以制备出高质量泡沫材料;随着HMSPP的熔体流动速率的降低,泡沫材料的密度和泡孔平均直径降低;随着HMSPP用量减少,HMSPP/PP泡沫材料的泡孔平均直径和密度增大,泡孔尺寸及分布的不均匀程度增加;发泡条件对泡沫结构具有一定的影响,最佳的发泡温度为185~190℃,螺杆转速为40~100r/min;随着口模厚度的增加,泡孔平均直径增加,材料密度下降,而材料内外层泡孔直径不均匀性增加。     

聚醚酰亚胺均相成核发泡行为研究

以超临界CO₂为发泡剂,采用间歇式发泡技术制备了聚醚酰亚胺（PEI）微孔泡沫。通过改变发泡温度、发泡压力与样品浸泡时间等工艺条件,研究了PEI的均相成核发泡行为。实验还通过二次降压法制备了具有复合泡孔结构的PEI微孔泡沫材料。结果表明,复合泡孔结构提高了PEI微孔泡沫的发泡倍率,第一次压力降ΔP₁与第二次保压时间Δt₂是影响复合泡孔结构参数的重要影响因素。     

泡沫炭的制备机理及性质概述

泡沫炭是一种由孔泡和相互连接的孔泡壁组成的具有三维网状结构的轻质多孔材料,不同的发泡前驱体和发泡工艺所制得泡沫炭的性能有所不同。泡沫炭最大的特点是泡孔结构的多样性和可设计性,其主要特性在于其各向同性的高的热传导性。本文以不同发泡前躯体为分类规则,综述了泡沫炭的成核机理及制备工艺,以期为泡沫炭将来的制备工作提供理论参考。     

Effect of processing parameters on cell morphology of polycarbonate foam

Abstract

The purpose of this research is to investigate the effect of processing parameters on the cell morphology of polycarbonate (PC) foam. In this study, foamed PC was prepared using a dynamic simulation foaming set-up. The cell morphology was compared at different temperatures, pressures, gas saturation times, pressure drop rates and shear rates. The cell morphology of foamed samples was characterised using SEM. It was found that foamed samples with better morphology could be obtained by varying mechanical properties, such as pressure, pressure drop rate and gas saturation time. Optimum temperature and shear rate for microcellular foaming of PC are presented.     

发泡工艺对超临界CO2／PP微孔发泡泡孔形态的影响

研究了超临界CO2／PP微孔发泡过程中发泡温度和饱和压力对结晶性聚合物PP泡孔形态的影响。结果表明，温度对泡孔形态影响很大，温度升高，熔体黏度和表面张力降低，泡孔变大，泡孔密度减小。与发泡温度相比，CO2饱和压力对泡孔结构的影响较小。压力太低，CO2的溶解度小，泡孔壁太厚，泡孔分布不均匀。随着压力升高，CO2的溶解度增加，熔体黏度减小，所以泡孔直径和泡孔密度都增加，泡孔壁变薄。     

Preparation Process Orthogonal Optimization and Mechanical Properties of Microcellular Foam Polypropylene

Melt strength, pressure and the amount of gas have significant effects on the foaming of polypropylene (PP). It is convenient to study the influence of these factors on foaming effect by orthogonal test. The experiment result shows that within the set factors and levels, the improvement of melt and the concentration of foaming masterbatch has the greatest influence on the cell size and density of foamed PP, respectively. When the concentration of azodicarbonamide (ADC) is 15 %, PP/ethylene-propylene terpolymer (EPDM) = 90:10, and SiO₂ content is 3%, the foaming effect is the best. At this time, the cell diameter decreases by 42.7%, cell density increases by more than 7.5 times compared with that without optimization. Material density decreases from 0.92 to 0.56 g cm⁻³. It is also found that good closed-cell structure can improve the bending and impact properties of PP in varying degrees, especially the impact strength is 55.7% higher than that of neat PP. Finally, the promoting mechanism of cell structure on mechanical properties of materials is discussed, which is of great significance for the preparation of microfoamed PP materials and the deep research of its cell structure.     

新型多孔聚酯纤维的制备

介绍了一种制备发泡聚酯纤维的方法,并研究了处理工艺与多孔结构的影响。通过光学显微镜结果分析及计算,研究了加压压力、加压时间、发泡温度及发泡时问等参数对纤维中气泡密度的影响。结果表明,在其他工艺条件不变的情况下,发泡聚酯纤维中气泡密度分别随着压力、加压时间、发泡温度和发泡时间的增加而增大。其中发泡时间大于10 s后,时间对气泡密度无明显影响。     

Cell structure and impact properties of foamed polystyrene in constrained conditions using supercritical carbon dioxide

To obtain cellular with small cell diameter, to control cell structure and to improve impact strength of foaming materials, the quick-heating method was applied for foaming polystyrene (PS) using supercritical CO₂ (Sc-CO₂) as physical blowing agent. Then, changes of cell structure and impact strength in microcellular foamed PS materials under constrained conditions were studied. The effects of foaming processing parameters, such as foaming temperature, saturation pressure and foaming time on the cell structure and impact strength of foamed PS in the constrained conditions were studied. The results showed that the Sc-CO₂ solubility and nucleation density in the constrained conditions were not influenced compared with those under free foaming conditions. However, cells in constrained foaming process are mostly circular and independent with thick cell walls; the phenomenon of cell coalescence and collapse was effectively eliminated under constrained conditions. In addition, cell diameters in constrained foaming process decrease with increase in foaming temperature and increase with increase in the foaming time. Compared with that in free foaming conditions, the cell growth was restrained dramatically under constrained conditions which resulted in smaller cell diameter. Moreover, higher impact strength could be obtained for foamed PS as foaming time was prolonged, foaming temperature was increased or saturation pressure was enhanced.     

Foaming behavior of high‐melt strength polypropylene/clay nanocomposites

The foaming behavior of high‐melt strength polypropylene (HMS‐PP) and HMS‐PP/Cloisite 20A nanocomposites (PPNC) was studied in a batch process. PPNCs with 2, 4, 8, and 10 wt% clay were prepared in a twin screw extruder. The morphology of the nanocomposites was studied using XRD and TEM. Subsequently, foaming experiments were conducted using supercritical CO₂ as the blowing agent in a batch process, and foams with cell sizes varying from the sub micrometer to the micro meter range were prepared. The effect of variation in saturation pressure and temperature, foaming temperature, foaming time, and quench temperature was determined experimentally. Dynamic rheological measurements were conducted to relate the influence of nanocomposites morphology with foam cell growth and nucleation. Extensional rheological measurements were also conducted to detect the presence of strain hardening effect at the foaming temperatures used in the experiment. It was found that the nucleation efficiency of clay reduces with increase in clay loading. Also, the optimum amount of filler for generation of fine celled foams was found to be around the percolation threshold of the polymer. The extended strain hardening effect shown by the polymer in presence of clay plays an important role in stabilizing foam cell sizes. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

加工参数对微孔PC泡孔性能的影响

采用模压法成功制备了薄型微孔聚碳酸酯（PC）片材,研究了加工参数（发泡时间、发泡压力和发泡温度）对泡孔性能的影响,结果表明：泡孔尺寸随发泡时间的延长先减小后增大,随发泡压力的增加而减小,随发泡温度的增加而增大;泡孔密度的变化趋势随与泡孔尺寸的变化趋势相反;相对密度则随加工参数的增加而降低。通过比较各加工参数对泡孔性能的影响,可以发现发泡时间对微孔PC片材泡孔性能影响最大,且最佳的发泡时间约为8min。     

超临界CO_2发泡聚苯乙烯工艺研究

以超临界CO_2为发泡剂,采用釜压法在不同发泡工艺条件下制备了聚苯乙烯(PS)发泡试样,通过扫描电子显微镜对PS发泡试样的泡孔形貌进行了表征,探讨了不同发泡工艺对PS发泡试样发泡性能的影响。结果表明,随发泡温度的升高,PS发泡试样泡孔尺寸增大,泡孔密度下降,而泡沫密度呈现先降低后升高的趋势,发泡倍率与此相反;增大保压时间和保压压力,可提高试样的发泡效果。当发泡温度为136℃,保压压力为20 MPa,保压时间为4 h时,PS发泡试样的发泡效果最好,其泡沫密度为0.043 g/cm~3,发泡倍率为24.4,泡孔尺寸为59.8μm,泡孔密度为6.20×107个/cm~3。     

工艺参数对PC塑料泡孔结构影响

采用自制的微孔发泡模拟机研究了温度和压力以及气体饱和时间对微孔聚碳酸酯（PC）泡孔结构的影响。结果表明，对于微孔PC泡沫塑料的成型存在一个最佳温度值;随着饱和压力升高，泡孔直径变小，泡孔的密度增大；气体饱和时间对PC泡沫塑料泡孔结构的影响不是很明显，在一定的饱和时间范围内，延长PC发泡时间有利于得到更均匀的泡孔结构。     

Effect of die temperature on the morphology of microcellular foams

A study on the extrusion of microcellular polystyrene foams at different foaming temperatures was carried out using CO₂ as the foaming agent. The contraction flow in the extrusion die was simulated with FLUENT computational fluid dynamics code at two temperatures (150°C and 175°C) to predict pressure and temperature profiles in the die. The location of nucleation onset was determined based on the pressure profile and equilibrium solubility. The relative importance of pressure and temperature in determining the nucleation rate was compared using calculations based on classical homogeneous nucleation theory. Experimentally, the effects of die temperature (i.e., the foaming temperature) on the pressure profile in the die, cell size, cell density, and cell morphology were investigated at different screw rotation speeds (10 ～ 30 rpm). Experimental results were compared with simulations to gain insight into the foaming process. Although the foaming temperature was found to be less significant than the pressure drop or the pressure drop rate in deciding the cell size and cell density, it affects the cell morphology dramatically. Open and closed cell structures can be generated by changing the foaming temperature. Microcellular foams of PS (with cell sizes smaller than 10 μm and cell densities greater than 10 cells/cm³) are created experimentally when the die temperature is 160°C, the pressure drop through the die is greater than 16 MPa, and the pressure drop rate is higher than 10⁹ Pa/sec.