Low‐Density Nanocellular Foams Produced by High‐Pressure Carbon Dioxide

A new type of nanocellular polymeric material based on PMMA and a MAM triblock copolymer is presented. The production avoids the use of physical additives and leads to completely homogeneous nanostructured polymers with a large number of CO₂ nucleation sites. The foamed materials show average cell sizes <200 nm and relative foam densities of 0.4, presenting a homogeneous cell structure. A physical effect not measured before in nanocellular materials is demonstrated, which leads to an increase of the glass transition temperature due to the confining effect of PMMA chains in the cell walls of the nanocellular foam. The effects of changing saturation pressure and MAM content in the cellular structure are described, together with three‐point bending Young's modulus measured using DMA.

     

Expansion of core–shell PS/PMMA particles

Structured micrometric polystyrene/poly(methyl methacrylate) particles were obtained by suspension polymerization and their expansion behavior was investigated using n‐pentane as blowing agent. The expanded particles presented two distinct microstructures with an outer region (PMMA‐rich shell) composed by cells of about 10 µm while the center of the particle (PS‐rich core) had much larger cells (50–100 μm). The core–shell particles did not expand at 100°C meaning that the PMMA shell hindered the expansion of the particles. Maximum expansion was dependent on the PMMA concentration and also on the heating temperature and the increase in the PMMA molar mass led to a delay in the onset of the process. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4521–4527, 2013     

CO2‐Induced Mechanical Reinforcement of Polyolefin‐Based Nanocellular Foams

The effect of CO₂‐induced crystallization on the mechanical properties, in particular the yield and the ultimate stresses, of polyolefins is studied. PP and SEBS copolymer blends are used as examples and foamed after sorption of CO₂ at temperatures below T_m. CO₂ sorption thickens the crystalline lamellae and consequently increases T_m from 160 to 178 °C for both pure PP and PP/SEBS blend systems. Foams with an average cell size smaller than 250 nm retain the ultimate stress at the level of the polymer before foaming, even without the effect of CO₂‐induced crystallization. Including CO₂‐induced crystallization, the yield and the ultimate stresses of the foam can be improved by 30 and 50% over solid PP and by 22 and 40%, for solid PP/SEBS blends, respectively.

     

Electromagnetic Interference (EMI) Shielding Effectiveness of PP/PS Polymer Blends Containing High Structure Carbon Black

The morphological, electrical resistivity (ER), and electromagnetic interference (EMI) shielding effectiveness (SE) properties of poly(propylene) (PP), polystyrene (PS), PP/PS, and PP/PS/styrene–butadiene–styrene (SBS) blends filled with 10 vol.‐% high structure carbon black (CB) were studied. For the CB/PP/PS blends, TEM and SEM observations indicated that CB is preferentially localized in the PS phase. ER and EMI SE of the CB/PP/PS and CB/PP/PS/SBS blends were bounded between those of the PS composite (lower bound) and the PP composite (upper bound). In the PP/PS volume ratio ranging from (75/25) to (25/75), ER and EMI SE of the CB‐filled blends were independent of the PP/PS volume ratio. The EMI SE obtained by the 2 mm thick plates made of 10 vol.‐% CB‐filled (100/0)–(10/90) PP/PS blends are adequate for computers shielding applications.

     

聚合物纳孔发泡材料制备方法研究进展

综述了近年来聚合物纳孔发泡材料的制备方法,重点对嵌段共聚物和纳米级分散相聚合物共混物发泡法的原理及研究成果进行了介绍和总结,并对其研究方向进行了展望。     

Polypropylene‐dispersed domain as potential nucleating agent in PS and PMMA solid‐state foaming

The potential of using dispersive domains in a polymer blend as a bubble nucleating agent was investigated by exploiting its high dispersibility in a matrix polymer in the molten state and its immiscibility in the solid state. In this experiments, polypropylene (PP) was used as the nucleating agent in polystyrene (PS) and poly(methyl methacrylate) (PMMA) foams at the weight fraction of 10, 20, and 30 wt %. PP creates highly dispersed domains in PS and PMMA matrices during the extrusion processing. The high diffusivity of the physical foaming agent, i.e., CO₂ in PP, and the high interfacial tension of PP with PS and PMMA could be beneficial for providing preferential bubble nucleation sites. The experimental results of the pressure quench solid‐state foaming of PS/PP and PMMA/PP blends verified that the dispersed PP could successfully increase the cell density over 10⁶ cells/cm³ for PS/PP and 10⁷ cells/cm³ for PMMA/PP blend and reduce the cell size to 24 μm for PS/PP and 9 μm for PMMA/PP blends foams. The higher interfacial tension between PP and the matrix polymer created a unique cell morphology where dispersed PP particles were trapped inside cells in the foam. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

ABS/PMMA合金组成与性能的研究

对ABS和PMMA合金的组成与性能进行了较详细的研究。内容包括:ABS和PMMA共混物的塑化行为的研究;并对ABS和PMMA合金的组成及各项力学性能之间的关系进行了一系列的研究,研究结果表明:不同ABS、PMMA及ABS与PMMA的配比对ABS/PMMA合金的各项性能有较大的影响。当PMMA含量达到40%时,ABS2/PMMA2合金的表面光洁度由82%提高到3%;ABS1/PM MA2合金的拉伸强度由44 8MPa提高到55 3MPa,但冲击强度由118J/m降到57J/m。     

PS/PMMA共混物中超声波传播特性研究

利用自行设计的装置,采用改变入射角的方法将超声波纵波和横波导入不相容的聚苯乙烯/聚甲基丙烯酸甲酯(PS/PMMA)共混物体系中。研究了两种波的声速和声衰减随共混体系共混比变化的情况,并结合扫描电子显微镜(SEM)检测得到的相畴尺寸进行了分析。结果表明:共混物中的相畴尺寸与其散射衰减之间存在对应关系;由于横波波长更为接近共混体系中的相畴尺寸,横波的散射衰减明显大于纵波。     

Opening Pores and Extending the Application Window: Open-Cell Nanocellular Foams

The production of open-cell (OC) nanostructures in polymer foams without non-foamed solid skins by gas dissolution foaming has been developed in this work. First, several grades of MAM block copolymer (methyl methacrylate-b-butyl acrylate-b-methyl methacrylate) at high content are employed as heterogeneous phase in poly(methyl methacrylate) for producing OC structures. Atomic force microscopy and extensional rheology are used as methods to understand the main features to obtain OC nanocellular structures. Second, the gas diffusion barrier approach is employed for the first time in polymer blends to avoid the appearance of the solid skins in the borders, which typically appears when the cellular polymer is produced by gas dissolution foaming. The influence of the poly(vinyl alcohol) gas diffusion barrier is analyzed, together with the effect of heterogeneous nucleation provided by MAM copolymer, on the solid skins’ formation. The synergy between both approaches allows obtaining porous nanocellular polymeric films with an OC structure non-constrained by the presence of outer solid skins.     

Effect of composition on the linear viscoelastic behavior and morphology of PMMA/PS and PMMA/PP blends

Here, the effect of concentration on the morphology and dynamic behavior of polymethylmethacrylate/polystyrene (PMMA/PS), for PS with two different molecular weight, and polymethylmethacrylate/polypropylene (PMMA/PP) blends was studied. The blends concentrations ranged from 5% to 30% of the dispersed phase (PS or PP). The dynamic data were analyzed to study the possibility of inferring the interfacial tension between the components of the blend from their rheological behavior using Palierne [Palierne JF. Rheol Acta 1990;29:204-14] [1] and Bousmina [Bousmina M. Acta 1999;38:73-83] [2] emulsion models. The relaxation spectrum of the blends was also studied. The dynamic behavior of 85/15 PS/PMMA blend were studied as a function of temperature. It was possible to fit both Palierne and Bousmina's emulsion models to the dynamic data of PMMA/PS blends, to obtain the interfacial tension of the blend. This was not the case for PMMA/PP. The relaxation spectrum of both blends was used to obtain the interfacial tension between the components of the blends. The values of interfacial tension calculated were shown to decrease when the concentration of the blends increased. It was shown using morphological analysis that this phenomenon can be attributed to the coalescence of the dispersed phase during dynamic measurements that occurs for large dispersed phase concentration. When the ‘coalesced’ morphology is taken into account in the calculations the interfacial tension inferred from rheological measurement did not depend on the concentration of the blend used. The values of interfacial tension found analyzing the dynamic behavior of one of the PMMA/PS blend were shown to decrease with temperature.     

Conductive Ceramic Foams from Preceramic Polymers

Ceramic foams in the system Si-O-C, possessing different bulk densities and morphologies, were obtained from preceramic polymers using two different direct foaming approaches. The electric properties of the foams were varied by adding suitable fillers to the precursor mixtures in amounts up to 80 wt%. The electrical conductivity of the foams was varied by several orders of magnitude. The effects of the type of filler and preceramic polymer (methylsiloxane or methylphenylsiloxane resins), as well as the used filler precursor, on the properties of the ceramic foams were investigated.     

影响HDPE/PS/PMMA三元体系核壳形态的因素

通过密炼得到高密度聚乙烯(HDPE)、聚苯乙烯(PS)和聚甲基丙烯酸甲酯(PMMA)三元体系核壳结构。用扫描电镜(SEM)考察了组分配比、增容剂氢化苯乙烯-丁二烯-苯乙烯弹性体(SEBS)和退火对体系核壳形态的影响。结果表明,组分用量最大的HDPE总是形成基体相,而PS形成壳,PMMA形成核;核壳粒子的尺寸和内部结构随组分用量而变化,随着分散相用量(PS+PMMA)增加,核壳粒子间碰撞融合机会增多,因此核壳粒子尺寸变大,同时核壳粒子由一核一壳逐渐转变为多核一壳结构;而随着核壳粒子中PS用量增加,PMMA核的尺寸显著减小;增容剂SEBS的加入,抑制了共混中核壳粒子间的融合,导致核和壳的尺寸减小;200℃下退火处理使分散相向体系自由能更小的一核一壳结构转变。     

PS/SBR-g-PS共混物的力学性能和形态结构

采用种子乳液聚合技术在丁苯胶乳上接枝聚合苯乙烯 ,合成了一系列丁苯橡胶接枝聚苯乙烯共聚物 (SBR-g-PS)。将其与聚苯乙烯 (PS)树脂共混后 ,考察了 SBR-g-PS的组成 (SBR/ PS)对共混物的力学性能和形态结构的影响。结果发现 ,当 SBR/ PS为 6 7/ 33-5 0 / 5 0时 ,PS/ SBR-g-PS共混物表现出良好的综合力学性能 ,在 SBR-g-PS中随着接枝 PS的增多 ,像胶粒子在基体中的分散状况获得改善 ,在大橡胶颗粒中含有大量的 PS次级粒子。在外负载的作用下 ,共混物中的大橡胶颗粒引发了大量的银纹 ,吸收了断裂应变能 ,从而提高了材料的冲击韧性。     

Compatibilizing Effect of SEBS for Electrical Properties of LDPE/PS Blends

Summary: In the previous study, we observed compatibilizing effects of low density polyethylene (LDPE)/polystyrene (PS) with polystyrene‐block‐poly(ethylene‐co‐butylene)‐block‐polystyrene (SEBS), a triblock copolymer. Blends consisting of 70 wt.‐% LDPE and 30 wt.‐% PS were prepared with a SEBS concentration of up to 10 wt.‐%. This study examined the electrical properties such as the electrical breakdown, water tree length, permittivity and tan δ in the blends. The possibility of using these blends as insulating material substitutes for LDPE was investigated. The electrical breakdown strength reached a maximum of 66.67 kV/mm, which is superior to 50.27 kV/mm of the LDPE used as electrical insulators for cables. In addition, the water tree length decreased with increasing SEBS concentration. The water tree lengths of the blends containing SEBS were shorter than that of the LDPE. The permittivity of the blends was 2.28–2.48 F/m, and decreased with increasing SEBS concentration with the exception of S‐0. Tan δ of the blends increased smoothly with increasing SEBS content.

Breakdown strength , water tree length, permittivity and tan δ of the LDPE/PS/SEBS blends and raw materials.     

超临界CO2中的高分子合成研究进展

介绍了超临界二氧化碳的特殊性质，综述了超临界二氧化碳为介质的高分子合成方面的应用进展情况．皿示出超临界二氧化碳是一种对环境无污染且价廉的绿色介质，具有广阔的应用前景。     

超临界二氧化碳在聚合物共混中的应用

概述了超临界二氧化碳(SC-CO2)在聚合物熔体中的溶解度,SC-CO2对熔体黏度和共混物两相间黏度比以及界面张力的影响,介绍了SC-CO2对聚合物共混物微观形态的影响。     

原位增容PS/LLDPE共混物的结构与性能

在熔融状态下,利用大分子之间的Friedel-Crafts烷基化反应就地增容聚苯乙烯(PS)/线型低密度聚乙烯(LL-DPE)共混物。考察了AlCl3用量对高PS含量PS/LLDPE(80/20,质量比,下同)共混物的PS接枝百分比和力学性能的影响,同时研究了增容前后共混物的热性能与微观结构。结果表明,在PS/LLDPE共混物中加入0.4份的AlCl3,PS的接枝百分比较高;与简单共混体系相比,共混物力学性能与热稳定性都有所提高,同时PS也有一定程度的降解。     

聚合物共混物增容剂的研究

相容性聚合物共混物由于其优异的性能已成为新材料的主要研究方向。但许多共混物是互不相容的,因此必须改善它们的相容性。综述了聚合物共混物的相容性及各类增容剂的特点及应用。同时介绍了无机纳米粒子的引入对不相容聚合物共混体系相容性的影响。     

Foam Processing and Cellular Structure of Polycarbonate‐Based Nanocomposites

Summary: Via a batch process in an autoclave, foam processing of intercalated PC/clay nanocomposites, having different amounts of clay, has been conducted using supercritical CO₂ as a foaming agent. The cellular structures obtained from various foaming temperature‐CO₂ pressure ranges were investigated by SEM. The incorporation with nanoclay‐induced heterogeneous nucleation occurs 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 controlled structure of the PCCN foams changed from microcellular (d ? 20 µm and N_c ? 1.0 × 10⁹ cells · cm^?3) to nanocellular (d ? 600 nm and N_c ? 3.0 × 10¹³ cells · cm^?3). The mechanical properties of PCCN foams under compression test were discussed.

TEM micrograph for the structure of the cell wall foamed at 160 °C.