茂金属基聚烯烃泡沫塑料

本文介绍一种生产聚烯烃泡沫塑料块料的独特的氮气热压罐工艺。最新的产品开发包括茂金属基催化聚烯烃泡沫塑料。文章对这些材料的性能和可能的用途进行了讨论     

茂金属聚烯烃

介绍了Ｄｏｗ化学公司采用Ｉｎｓｌｉｔｅ技术生产的聚烯烃塑性体（ＰＯＰ）和两种茂金属聚乙烯,即用于薄避包装容器的高密度聚乙烯（ｍＨＤＰＥ）和用于薄膜制品的线型低密度聚乙烯９ｍＬＬＤＰＥ）以及ＲＡＳＤ公司采用单中心催化剂（Ｓｉｎｇｌｅ－ｓｉｔｅＣａｔａｌｙｓｔ）生产的聚丙烯（ｍＰＰ）,并扼要阐述了产主要性能和应用范围。     

茂金属聚烯烃

介绍了国内外金属催化剂和茂金属聚烯烃技术、特点、研究开发和工业化状况,并对我国发展提出了建议。     

茂金属聚烯烃及其应用

综述了茂金属催化剂主要特性和应用及国外茂金属聚烯烃开发情况。介绍了茂金属聚烯烃的高强度、高抗冲击性、高抗穿刺性、低的热粘合温度、与通用聚烯烃可以任意比例混合使用等特性以及茂金属聚烯烃的发展前景。     

茂金属聚烯烃及其应用

对不同类型的茂金属聚烯烃产品从其特点、产品牌号、应用发展前景等方面进行了综述.茂金属聚烯烃产品发展较快,应用几乎渗透到传统聚烯烃的每一个应用领域,而且发展到可替代部分工程塑料.     

茂金属聚烯烃加工工艺研究进展

总结了茂金属聚烯烃的分子结构及其热性能特点,综述了国外茂金属聚烯烃加工工艺及加工工艺改进方面的研究进展。     

茂金属聚烯烃的进展

简要介绍了茂金属催化剂的结构特点及优势、茂金属聚烯烃工业化的进展情况,同时对如何发展我国茂金属聚烯烃工业提出了一些建议。     

茂金属聚烯烃催化剂的设计

回顾了茂金属催化剂聚烯烃工艺、技术和催化剂的发展，根据茂金属催化聚烯烃的机理，探讨了茂金属催化剂结构与催化活性、立构选择性的关系，研究了催化剂设计的原理和方法。     

茂金属催化剂在聚烯烃中的应用

1引言聚烯烃树脂是合成树脂中最通用的品种之一．自1953年发现Ziegler－Natta催化剂，并用于聚乙烯（PE），聚丙烯（PP）的工业化生产以来，聚烯烃技术获得迅速的发展，并开发出节能型气相法工艺技术，目前全世界聚乙烯年产量已达200000kt，占聚烯轻树脂总产量的30～40％。聚丙烯达17870kt．另一方面，1980年汉堡大学Kaminsky教授发现单活性中心的茂金属催化剂，mPE及其它一些聚烯烃随之诞生。由于该催化剂可以精密地控制聚合物分子，能够按照用户要求“定制”无视立构，等现立构或间规立构的任何一种结构的聚合物，并且可以生产用op－N…     

The recovery behavior of crosslinked closed cell polyolefin foams

In this work an experimental study on the short term creep-recovery response of a collection of crosslinked low density polyolefin foams, with closed cell structure and different chemical composition, is presented. The effect of the maximum creep strain and the relationships between the chemical composition, the morphology of the foams, and their recovery response are examined. The experimental results show that the main mechanism that controls the behavior of these materials is the viscoelastic recovery of the cell walls.     

Mechanical characterization of closed‐cell polyolefin foams

Three different experimental techniques [compression experiments at low strain rates, instrumented falling‐weight impact tests, and dynamic mechanical analysis (DMA)] have been used for the mechanical characterization of a collection of crosslinked closed‐cell polyolefin foams of different chemical compositions, densities, and type of cellular structure. The experimental results that it is possible to obtain from each technique are shown, and related to the different applications of these materials. The relationships between the structure and the mechanical properties are also presented. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 156–166, 2000     

Dynamic mechanical properties of polyolefin foams studied by DMA techniques

In this work a preliminary study on the viscoelastic behavior of polyolefinic foam sheets with different chemical (polyethylene and polypropylene) and cellular structure by means of Dynamical Mechanical Analysis (DMA), in the low frequency and low compression ranges, is presented. Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM) are also used to determine the morphological parameters of the samples. A connection between the morphological parameters (apparent degree of crystallinity, type of cellular structure, homogeneity, cell size and shape, cell-wall thickness) and the viscoelastic behavior, a basic key for the development of mechanical and insulating applications, has been established.     

Microstructure and physical properties of open‐cell polyolefin foams

The cellular structure, physical properties, and structure–property relationships of novel open‐cell polyolefin foams produced by compression molding and based on blends of an ethylene/vinyl acetate copolymer and a low‐density polyethylene have been studied and compared with those of closed‐cell polyolefin foams of similar chemical compositions and densities and with those of open‐cell polyurethane foams. Properties such as the elastic modulus, collapse stress, energy absorbed in mechanical tests, thermal expansion, dynamic mechanical response, and acoustic absorption have been measured. The experimental results show that the cellular structure of the analyzed materials has interconnected cells due to the presence of large and small holes in the cell walls, and this structure is clearly different from the typical structure of open‐cell polyurethane foams. The open‐cell polyolefin foams under study, in comparison with closed‐cell foams of similar densities and chemical compositions, are good acoustic absorbers; they have a significant loss factor and lower compressive strength and thermal stability. The physical reasons for this macroscopic behavior are analyzed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Anomalous thickness increase in crosslinked closed cell polyolefin foams during heat treatments

When crosslinked closed cell polyolefin foams are under a temperature above the melting point of the base polymer, a reduction of their size is expected due to the gas diffusion out of the foam. However, some kinds of crosslinked closed cell polyolefin foams present one direction (thickness direction) in which the foam size increases during the first minutes of the thermal treatment. The thickness of the foams after the thermal treatment can be higher than the thickness of the original foams. An experimental study is presented on the thickness increase, as well as on the changes in the dimensions and the properties of foams with different densities, which were obtained from different foaming processes and made of different base polymers, as a function of the treatment temperature and the treatment time. This investigation sought to discover the physics mechanisms that control the anomalous thickness increase. The experimental results show that the thickness increase of these materials is related to the anisotropic cellular structure of the original foams. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2825–2835, 1999     

Improved adhesion of LDPE films to polyolefin foams for automotive industry using low-pressure plasma

The use of polymer films for technical applications has increased considerably in the last years, since they offer good balanced properties. Polymer films find many applications as individual materials or as laminates with other films, foams, membranes, etc. In these cases it is necessary to improve the low intrinsic surface energy of polymer films to ensure their optimum mechanical performance. In this work, low-pressure glow discharge plasma with different gases is used to improve the adhesive properties of a low-density polyethylene (LDPE) film, to obtain the optimum mechanical response of laminates with polyolefin foam for automotive applications (steering wheels). The results show a remarkable increase in T-peel strength of the adhesive joints. Furthermore, since automotive industry is characterized by high technical requirements, the evaluation of the durability of the adhesive joints (in terms of storage conditions: temperature and relative humidity) shows that the T-peel strength of adhesive joints is subjected to an aging process that slightly decreases their mechanical performance, but does not restrict the use of these laminates in automotive uses.     

Heat-shrinkable films based on polyolefin waste

Polyethylene wastes (low-density polyethylene, high-density polyethylene and their binary blends) were subjected to high-energy radiation, using a ⁶⁰Co gamma radiation source. The crosslinked materials thus obtained were processed to heatshrinkable films. Tensile strength could be sharply improved by increasing the dose up to 20 Mrad, simultaneously increasing the elongation at break of the most degraded PE waste. An increase of the degree of compatibility of LDPE and HDPE waste was also observed. All samples examined exhibit a “memory effect” after drawing at 130°C and cooling under tension followed by further heating under relaxed conditions. The value of shrinkage depended on the degree of degradation of the PE waste and on the irradiation dose.     

Alkali-bonded SiC based foams

Silicon carbide (SiC) foams were developed by using a low temperature process such as chemical consolidation that is suitable to replace the sintering step. An alkali aluminosilicates binder, also known as geopolymer, was used. It was prepared from metakaolin, as aluminosilicatic raw powder, and KOH/K₂SiO₃ aqueous solution. The foaming agent was the metallic silicon present as impurity in SiC powders. Different grades of SiC were used as the main component (90 wt%) of the foams and the micro and macrostructures varied with the morphologies of the SiC raw powders. The surface of SiC grains participates to the geopolymeric process because of the dissolution of the silica layer into the alkaline solution. SiC foams were tested and characterized under oxidative atmospheres up to 1200 °C.     

Effect of the elastomer viscosity on the morphology and impact behavior of injection molded foams based on blends of polypropylene and polyolefin elastomers

The impact resistance of injection-molded polypropylene (PP) parts is severely reduced when they are foamed. It is necessary to implement strategies, such as elastomer toughening, to increase the impact behavior of foamed parts. However, the knowledge on the effect of elastomer addition on the morphology, cellular structure, and impact of injection-molded cellular parts is very limited. In this work, foamed parts based on blends of PP and polyolefin elastomers have been produced and characterized. A high and a low viscosity octene-ethylene copolymer (EOC) and a high viscosity butene-ethylene copolymer (EBC) were employed. The blends have been thermally and rheological characterized. Solids materials and foams (relative density 0.76) were injection-molded. The solid phase and cellular structure morphologies were studied using scanning electron microscopy. The results showed that elastomer toughening has been successful to obtain an improvement of the impact behavior in solid and cellular polymers. In this case, EOC materials provide an appropriate interfacial adhesion and optimized cellular structure which results in high impact resistance. The optimum elastomer to improve the properties is the EOC with a higher viscosity which provides impact resistance with n values below 3 due to the toughening of polymer matrix, thick skin thickness, and low cell size.