SBA-15形貌对聚乳酸微孔发泡的影响

文章采用水热法合成了球状、棒状与环状三种形貌的SBA-15无机介孔粒子,利用含氟硅烷对粒子进行亲二氧化碳修饰后,用于聚乳酸超临界二氧化碳(scCO2)微孔发泡,探索了粒子形貌对聚乳酸发泡材料的泡孔结构的影响。TG,BET和SEM等分析表明,不同粒子形貌的介孔粒子具有不同的硅烷接枝率,在聚乳酸微孔发泡材料中异相成核作用也不同,就泡孔尺寸和泡孔密度来讲,环状SBA-15粒子对聚乳酸发泡的异相成核作用最好,表明介孔粒子有望成为新型的微孔发泡成核剂。     

无机纳米粒子对聚苯乙烯泡孔结构影响的研究

以活性纳米碳酸钙(CaCO3)和有机化纳米蒙脱(土OMMT)为异相成核剂,制备了聚苯乙(烯PS/)无机纳米粒子发泡材料,并利用透射电镜和扫描电镜研究了纳米粒子种类和含量对PS挤出发泡制品的表观密度和泡孔结构的影响。扫描电镜分析结果表明:采用纳米CaCO3为成核剂时所得发泡制品的表观密度为0.451~0.485g/cm3;而用OMMT作为成核剂所得发泡制品的表观密度为0.514~0.573g/cm3,平均泡孔尺寸较小。透射电镜分析结果表明:OMMT在泡孔壁面的取向分布有利于得到闭孔形式的泡孔结构。     

异相成核剂对聚乙烯醇热塑模压发泡的影响

以水为增塑剂兼物理发泡剂,采用热塑模压发泡方法制备了聚乙烯醇(PVA)泡沫材料,研究了成核剂含量、粒子尺寸对PVA泡沫材料泡孔结构的影响,阐述了成核剂异相成核作用与泡沫材料泡孔结构间的关系。结果表明:小粒径、含量适中的成核剂能够在PVA基体中产生较多的异相成核点,且不影响气泡的生长过程,得到孔径分布良好、发泡倍率较高的泡沫材料。     

超临界CO_2微孔发泡制备聚乳酸/磷酸三钙多孔材料

利用超临界二氧化碳(sc-CO2)微孔发泡方法制备聚乳酸/磷酸钙(PLA/TCP)多孔材料,通过扫描电子显微镜(SEM)观察TCP颗粒分散和泡孔形态。结果表明,TCP质量分数为1 wt%和3 wt%时,微米级TCP颗粒均匀分布在PLA基体中,在发泡过程中起到异相成核的作用,减小泡孔尺寸同时增加泡孔密度。当TCP含量为5 wt%时,TCP颗粒出现团聚,异相成核作用减弱,泡孔密度下降。随着发泡温度升高,泡孔尺寸增大的同时泡孔壁变薄甚至破裂,发泡温度对泡孔密度影响不大。增加发泡压力,泡孔的数量急剧增加,同时泡孔的尺寸减少,泡孔壁变厚。     

PET/SiO2复合材料的发泡温度窗口研究

为研究纳米二氧化硅(SiO₂)对聚对苯二甲酸乙二酯(PET)复合材料发泡温度窗口的影响规律，制备了不同SiO₂含量的PET复合材料，并以二氧化碳为发泡剂，利用釜压发泡制备了PET/SiO₂复合发泡材料。然后，利用扫描电子显微镜研究了在不同温度下制备的PET/SiO₂复合发泡材料的泡孔结构，并统计和计算出泡孔尺寸、泡孔密度和膨胀倍率，再结合泡孔结构和膨胀倍率，界定出不同SiO₂含量的PET复合材料发泡温度的上下限，并得出发泡温度窗口，还研究了PET/SiO₂复合发泡材料的光反射率。结果发现，SiO₂对PET复合材料具有显著的气泡异相成核作用，随着SiO₂添加量的增加，泡孔尺寸减小、泡孔密度增大、膨胀倍率先增大后减小；发泡温度上限先升高后降低、下限升高，使得发泡温度窗口先变宽后变窄，这与SiO₂的气泡异相成核作用、对膨胀倍率的调节作用及对基体黏弹性的影响密切相关。随着SiO₂     

纳米粒子在微孔发泡聚合物中应用的研究进展

微孔发泡聚合物是一种发展迅速的新型发泡材料,因其具有质量轻、环境友好、渗透性好等优点,具有极其广阔的应用领域。同时,纳米粒子对微孔发泡聚合物的气泡成核、气泡生长、气泡定型等影响非常显著。因此,纳米粒子对微孔发泡聚合物泡孔形貌调控机理的相关研究,成为近年来国内外学者研究的热点。介绍了聚合物纳米复合材料的制备方法,包括间歇式釜压发泡、连续挤出发泡和注塑成型发泡;然后分析了纳米粒子在微孔发泡聚合物中的添加方法,包括原位聚合法、插层法、直接混合法;综述了纳米粒子对微孔发泡聚合物体系的影响;最后对微孔发泡聚合物的研究方向和应用前景进行了展望。     

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。     

无机纳米填料影响聚合物微孔发泡材料发泡行为研究进展

从纳米填料影响聚合物微孔发泡材料发泡行为的泡孔成核、泡孔生长、发泡剂气体扩散三个方面综述了近年来无机纳米填料影响聚合物微孔发泡行为的研究进展。并对众多研究结果进行了总结,提出了未来一段时间聚合物纳米复合材料发泡行为研究领域有待于进一步深入的研究方向。     

OMMT对HIPS发泡工艺的影响

研究了注射温度对高冲击强度聚苯乙烯(HIPS)及其与纳米有机蒙脱土(Nano-OMMT)复合发泡材料的泡孔直径、密度和尺寸的影响。结果表明:与纯HIPS发泡材料相比,HIPS/Nano-OMMT复合发泡材料的泡孔平均直径更小、密度更大、尺寸分布更均匀;HIPS/Nano-OMMT复合材料比纯HIPS具有稳定和更宽的加工温度,在170~185℃都能获得高质量的发泡材料。     

振动力场对含有成核剂的微孔塑料泡孔结构的影响

在微孔塑料成型加工过程中,成核剂的加入可以增加泡孔成核点数量,从而增加泡孔密度,改善泡孔的结构,但如果纳米级成核剂在发泡过程中分散性不好,会使泡孔分布不均匀,影响泡孔质量。在实验中,对含有成核剂(纳米碳酸钙)的发泡材料(聚苯乙烯)施加振动场,通过比较发现,施加振动后,纳米级成核剂的分散效果明显改善,颗粒分布变得更均匀,从而使得泡孔分布更均匀,改善了泡孔的结构,提高了微孔塑料泡孔结构质量。     

Preparation and characterization of microcellular thin polycarbonate sheets

A new method was developed for the microcellular processing of polycarbonate (PC) thin sheets by compression molding above PC's glass‐transition temperature and below its melting temperature within a few minutes. The effects of the foaming time, foaming pressure, foaming temperature, and foaming agent active ratio on the cell size, cell density, and relative density were studied. The structures of the microcellular PC foam were controlled in the foaming process by carefully choosing the foaming parameters. In addition, the thermal, dynamic mechanical thermal, and electrical properties of the microcellular PC foam were investigated. A differential scanning calorimetry analysis showed that the microcellularly processed PC may have a plastication effect. The variation of the storage modulus, loss modulus, and tan δ under dynamic mechanical thermal analysis was in accord with the calorimetry analysis. The measurement of the electrical property demonstrated that the insulation ability of the microcellular PC thin sheet was obviously enhanced and the dielectric strength of the microcellular PC foam was decreased compared to the unfoamed PC. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1760–1766, 2006     

Foam processing and cellular structure of polylactide-based nanocomposites

Via a batch process in an autoclave, the foam processing of neat polylactide (PLA) and two different types of PLA-based nanocomposites (PLACNs) has been conducted using supercritical carbon dioxide (CO₂) as a foaming agent. The cellular structures obtained from various ranges of foaming temperature-CO₂ pressure were investigated by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The incorporation with nano-clay induced heterogeneous nucleation because of a lower activation energy barrier compared with homogeneous nucleation as revealed by the characterization of the interfacial tension between bubble and matrix. The grown cells having diameter of ∼200 nm were localized along the dispersed nano-clay particles in the cell wall. The dispersed nano-clay particles acted as nucleating sites for cell formation and the cell growth occurs on the surfaces of the clays. The PLACNs provided excellent nanocomposite foams having high cell density from microcellular to nanocellular.     

改性剂和增塑剂对PVC微孔泡沫塑料形态影响

以超临界CO2为发泡剂,用自制的动态模拟发泡装置研究了聚氯乙烯(PVC)配方中改性剂丙烯酸酯类高分子聚合物(ACR)含量和增塑剂邻苯二甲酸二辛酯(DOP)含量对PVC微孔塑料泡孔形态的影响.结果表明,在其他工艺条件和配方相同的情况下,ACR为4份时得到的PVC微孔泡沫塑料泡孔密度最大,泡孔粒径最小,DOP为2～6份时比较适合PVC微孔发泡,并且振动力场的引入有利于得到细小均匀的微孔结构.     

Microcellular thin PET sheet foam preparation by compression molding

This study has created a new way of microcellullar processing PET thin sheet foam using a conventional hydraulic press by compression molding and by setting the temperature of press plates differently. Comparing this study with our previous work, the emphasis is on the difference of plate temperature. The nonisothermal condition is used to control the foaming agent decomposition to lead to more uniform cell size microcellular foam. A variety of cell sizes, cell densities, and relative densities are obtained as a consequence of the different foaming temperature, time, pressure, and foaming agent content via isothermal and nonisothermal conditions. The effect of isothermal and nonisothermal foaming on the cell size, cells density, and relative density has been discussed. The electrical properties of the microcellular poly(ethylene terephthalate) (PET) samples prepared in nonisothermal foaming have been investigated. The experimental results show that the microcellular PET foam has lower dielectric constant and dielectric loss and higher electric resistivity than unfoamed PET. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1698–1704, 2004     

Processing and characterization of microcellular foamed high-density polythylene/isotactic polypropylene blends

In this paper, a study on the batch processing and characterization of microcellular foamed high-density polyethylene (HDPE/iPP) blends is reported. A microcellular plastic is a foamed polymer with a cell density greater than 10⁹ cells/cm³ and fully grown cells smaller than 10 µm. Recent studies have shown that the morphology and crystallinity of semicrystalline polymers have a great influence on the solubility and diffusivity of the blowing agent and on the cellular structure of the resulting foam in microcellular batch processing. In this research, blends of HDPE and iPP were used to produce materials with variety of crystalline and phase morphologies to enhance the subsequent microcellular foaming. It was possible to produce much finer and more uniform foams with the blends than with neat HDPE and iPP. Moreover, the mechanical properties and in particular the impact strength of the blends were significantly improved by foaming.     

Cellulose nanofibre–poly(lactic acid) microcellular foams exhibiting high tensile toughness

We report here the morphology and tensile properties of polylactic acid–cellulose nanofibre (PLA–CNF) microcellular nanocomposites. Two types of CNF were used for the nanocomposite preparation, native and surface acetylated CNF (ac-CNF). Samples were foamed in a mould to enable tensile testing. The effect of the mould use on the foam morphology was first assessed by comparison with free foamed samples. We found that the mould affected the cell growth stage of the foaming process in neat PLA foam while its effect was less important in nanocomposites. Stiffening and strengthening effect of CNF was greatly enhanced by foaming when compared to their solid counterparts. The most notable change in tensile properties was however the large increase in strain at break resulting in the high tensile toughness of microcellular PLA–CNF nanocomposites. Strain at break increased up to 7.5 times in neat PLA and up to 31.5 times in the foam containing 3% of CNF. Surface acetylation of CNF significantly affected the properties of foams with 9% of CNF loading: while foams with ac-CNF were stiffer, foams with native CNF exhibited higher strain at break and so higher overall toughness.     

超临界CO2制备NaCl/PS微孔泡沫复合材料

利用超临界流体发泡技术制备了氯化钠(NaCl)颗粒填充聚苯乙烯(PS)的微孔泡沫复合材料。通过扫描电子显微镜(SEM)观察了材料的断面形态,并分析了氯化钠的粒径、含量及超临界CO2的饱和温度对微孔泡沫复合材料的泡孔形态的影响。结果表明:含有NaCl颗粒的微孔PS泡沫与纯PS泡沫在泡孔的形状和泡孔的尺寸等方面有所不同,纯PS微孔泡沫材料的泡孔分布较均匀、形状呈椭圆形,而添加了NaCl的PS微孔泡沫出现了大、小泡孔并存的泡孔结构。     

Microcellular foaming of silicone rubber with supercritical carbon dioxide

In spite of great concern on the industrial application of microcellular silicone rubber foams, such as in electric and medical devices, only a few works can be found about the foaming of silicone rubber. In this study, microcellular silicone rubber foams with a cell size of 12 μm were successfully prepared with curing by heat and foaming by supercritical CO₂ as a green blowing agent. The microcellular silicone rubber foams exhibited a well-defined cell structure and a uniform cell size distribution. The crosslinking and foaming of silicone rubber was carried out separately. After foaming, the silicone rubber foam was cross-linked again to stabilize the foam structure and further improve its mechanical properties. Foaming process of cross-linked silicone rubber should be designed carefully based on the viscoelastic properties because of its elastic volume recovery in the atmosphere. The basic crosslinking condition for small cell size and high cell density was obtained after investigating the rheological behavior during crosslinking.     

Preparation of microcellular poly(ethylene terephthalate) and its properties

Engineering plastics poly(ethylene terephthalate) (PET) is relatively difficult to process microcellularly compared to general thermal plastics because of its low melting viscosity. A new method was developed to microcellularly process PET in this study with a general hydraulic press above PET's crystallization temperature and below its melting temperature within times of a few minutes. A processing window existed in which to prepare microcellular PET under certain foaming time, pressure, temperature, and foaming reagent content scope. The effects of foaming time, temperature, pressure, and foaming reagent content on the thermal, mechanical, and dynamic mechanical thermal properties of microcellular PET foam were investigated. Differential scanning calorimetry (DSC) analysis showed that the transition temperature and crystallinity of microcellular PET had small changes with increasing foaming time. Under some processing conditions used in this study, the tensile strength and breaking extension of microcellular PET foam were both increased at the same time, indicating strengthening and toughening effects. The variation of storage modulus, loss modulus, and tan δ under dynamic mechanical thermal analysis was in accord with DSC analysis and mechanical measurements. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1956–1962, 2003