An investigation of the potential of polypropylene and its blends for use in recyclable high voltage cable insulation systems

Most modern extruded high voltage cables employ cross-linked polyethylene (XLPE) as the insulation material. XLPE has excellent thermo-mechanical properties, is relatively cheap and has a low dielectric loss, which make it an ideal material for this application. Unfortunately, XLPE is not easily recycled at the end of its lifetime leading to questions concerning its long-term sustainability. A previous investigation in this series considered the potential of a range of ethylene-based systems to provide suitable recyclable alternatives to XLPE. Whilst blending could allow systems having similar thermo-mechanical and electrical properties to XLPE to be designed, it was not possible to obtain better performance than XLPE using these systems. Polypropylene offers, potentially, a route to improved insulation systems by virtue of its higher melting point and excellent dielectric properties. However, traditional isotactic polypropylenes have always had the problem of being too brittle for inclusion into practical cable designs. Recently a broad range of propylene co-polymers having improved ductility have become available, which may prove more suitable. The current study compares traditional isotactic and syndiotactic polypropylenes to a range of commercially available propylene co-polymers and focuses on their morphology, thermal, thermo-mechanical and electrical properties. These parameters were then taken together to identify the most suitable candidate materials for future cable applications. The use of blending as a means to further optimise the various material properties was also explored.     

Electron beam irradiated HDPE/EVA/Mg(OH) composites for flame-retardant electric cables

The mechanical properties and flammability of high-density polyethylene (HDPE)/ethylene vinyl acetate (EVA) mixed with various amounts of magnesium hydroxide (Mg(OH)₂) as the filler in composites, irradiated with electron beam at an irradiation dose of 150 kGy, have been studied. It is found that high-energy electron beam irradiation has significant effects on the mechanical properties of the HDPE/EVA/Mg(OH)₂ composites. The tensile strength and elastic modulus increased greater than in the unirradiated ones. Meanwhile, with increasing the content of Mg(OH)₂ in the composites, the limiting oxygen index (LOI) value increased sharply. The microstructure of the caves of the unirradiated HDPE/EVA/Mg(OH)₂ composites show poor interface of composites compared with the irradiated ones, as observed in SEM micrographs.     

Electron beam irradiated HDPE/EVA/Mg(OH)2 composites for flame-retardant electric cables

The mechanical properties and flammability of high-density polyethylene (HDPE)/ethylene vinyl acetate (EVA) mixed with various amounts of magnesium hydroxide (Mg(OH)₂) as the filler in composites, irradiated with electron beam at an irradiation dose of 150 kGy, have been studied. It is found that high-energy electron beam irradiation has significant effects on the mechanical properties of the HDPE/EVA/Mg(OH)₂ composites. The tensile strength and elastic modulus increased greater than in the unirradiated ones. Meanwhile, with increasing the content of Mg(OH)₂ in the composites, the limiting oxygen index (LOI) value increased sharply. The microstructure of the caves of the unirradiated HDPE/EVA/Mg(OH)₂ composites show poor interface of composites compared with the irradiated ones, as observed in SEM micrographs.     

Thermal conductivity and mechanical properties of high density polyethylene composites filled with silicon carbide whiskers modified by cross-linked poly (vinyl alcohol)

A thin layer of poly (vinyl alcohol) (PVA) was coated on the surface of silicon carbide whiskers (SCWs) and crosslinked by glutaraldehyde, and then these modified whiskers (mSCWs) were incorporated into high density polyethylene (HDPE) to prepare HDPE/mSCW composites with a high thermal conductivity. The thermal conductivity, mechanical properties, heat resistance, thermal stability and morphology of HDPE/mSCW and HDPE/SCW composites were characterized and compared. The results reveal that the thermal conductivity of both HDPE/SCW and HDPE/mSCW composites increases with the increase of filler loading, and reaches a maximum of 1.48 and 1.69?W/(m?K) at 40?wt% filler loading, which is 251.2% and 300.75% higher than that of HDPE, respectively. Significantly, HDPE/mSCW composites have a higher thermal conductivity than their HDPE/SCW counterparts with the same filler loading. In addition, the heat resistance, Young’s modulus and yield strength of both HDPE/SCW and HDPE/mSCW composites are also improved compared with that of HDPE. mSCW can be homogenously dispersed in the HDPE matrix, which contributes to the formation of thermally conductive networks by the inter-connection of mSCWs.     

Electron beam modification of thermoplastic elastomeric blends made from polyolefins

Thermoplastic elastomeric films have been prepared from blends of ethylene vinylacetate copolymer (EVA) with low-density polyethylene (LDPE), high-density polyethylene (HDPE) and polypropylene (PP) by electron beam modification in presence of radiation sensitizer. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) have been used to evaluate the structural changes of these blends. Scanning electron microscopy (SEM) indicates the morphological features of the blends. Significant improvements of mechanical, dynamic mechanical and set properties have been obtained by electron beam modification of the blends of EVA with LDPE and HDPE. However, in the case of EVA/PP, degradation of the PP phase has been observed. The effects of ditrimethylol propane tetraacrylate (DTMPTA) as radiation sensitizer have also been evaluated from the mechanical and dynamic mechanical properties.     

EVA增容PVC／PE共混体系的研究

采用乙烯－醋酸乙烯酯共聚物（ＥＶＡ）作为聚氯乙烯（ＰＶＣ）／高密度聚乙烯（ＨＤＰＥ）共混物的增容剂，通过冲击实验、拉伸实验、动态力学分析和扫描电镜（ＳＥＭ），系统地研究了共混体系的性能与其形态结构之间的关系。结果表明，ＥＶＡ是ＰＶＣ／ＨＤＰＥ良好的增容剂，在一定范围内，ＥＶＡ与ＰＥ对ＰＶＣ有协同增韧效应     

导电炭黑改性PE-RT抗静电复合材料的形貌与性能

以耐热聚乙烯(PE-RT)管材料为基体,以乙烯-醋酸乙烯共聚物(EVA)载体导电炭黑母粒(记作CBE)为导电介质,配以3.86wt%的聚乙烯-辛烯共聚弹性体(POE),采用双螺杆挤出工艺制备了具有导电网状结构形貌的PE-RT抗静电管材料,降低了复合体系的逾渗阈值,并将其与添加导电炭黑(记作CB)的体系进行对比,研究了CB/PE-RT和CBE/POE/PE-RT复合体系的导电性能、微观形貌、流变性能、力学性能及热稳定性能。结果表明:POE和EVA可以产生协同作用,POE的加入改变了PE-RT与EVA的黏弹性差异,EVA在基体中达到逾渗而形成连续的网络结构。CB优先分散在黏度低、极性较高的EVA相中,且POE能够抑制CB由EVA相向PERT相的迁移,CB在EVA相中容易达到逾渗,最终由于双逾渗作用而形成导电网络结构。CB能够提高PE-RT的结晶性能及CBE/POE/PE-RT复合体系的热稳定性能,且CB对CBE/POE/PE-RT复合体系的力学性能影响较小,在一定程度上解决了目前填充型导电体系中导电性能与力学性能之间的矛盾,并且POE对复合体系起到了增塑作用,保持了PE-RT管材可弯曲的优点,拓展了塑料管材的应用范围。     

LDPE / LLDPE / EVA 三元共混膜的力学性能和摩擦性能研究

以低密度聚乙烯(LDPE)和线性低密度聚乙烯(LLDPE)作为基础物质,添加乙烯-醋酸乙烯酯共聚物(EVA),吹制保鲜膜,研究了保鲜膜的力学性能和摩擦性能。研究表明,复合膜的拉伸强度、伸长率、耐戳穿强度和撕裂强度随着EVA含量的增加,总体呈下降趋势,摩擦系数则逐渐上升。     

Polyethylene organo-clay nanocomposites: the role of the interface chemistry on the extent of clay intercalation/exfoliation

High density polyethylene (HDPE)/clay nanocomposites have been prepared using three different functionalized polyethylene compatibilizers: an ethylene/vinyl acetate copolymer, a polyethylene grafted with maleic anhydride functions and a (styrene-b-ethylene/butylene-b-styrene) block copolymer. The nanocomposites were prepared via two different routes: (1) the dispersion in HDPE of a masterbatch prepared from the compatibilizer and the clay or (2) the direct melt blending of the three components. For each compatibilizer, essentially intercalated nanocomposites were formed as determined by X-ray diffraction and transmission electron microscopy. With the ethylene/vinyl acetate copolymer, a significant delamination of the intercalated clay in thin stacks was observed. This dispersion of thin intercalated stacks within the polymer matrix allowed increasing significantly the stiffness and the flame resistance of the nanocomposite. A positive effect of shear rate and blending time has also been put into evidence, especially for the process based on the masterbatch preparation, improving both the formation of thin stacks of intercalated clay and the mechanical properties and the flame resistance of the formed nanocomposites.     

Aluminum hydroxide filled ethylene vinyl acetate (EVA) composites: effect of the interfacial compatibilizer and the particle size

Ethylene vinyl acetate (EVA) copolymer was filled with aluminum hydroxide (ATH) with three different sizes of 1.8, 1.2 and 0.8 μm in various volume fractions. The effect of interfacial compatibilizer on the properties of the composites was studied by morphology observation, dynamic mechanical analysis, tensile and flame tests. The results illustrated that the incorporation of functionalized polyethylene combined with dicumyl peroxide (DCP) and the silane coupling agent led to a pronounced improvement in the tensile strength compared to the composites with ATH untreated or treated by silane coupling agent alone. It was found that good dispersion and interfacial adhesion between the ATH particles and the matrix can improve the flame properties of composites. The particle size has a great effect on the flammability of the EVA/ATH composites. ATH with smaller particle size can increase the LOI value and improve the UL-94 flammability of the composites.     

Dimensional stability and mechanical behaviour of wood–plastic composites based on recycled and virgin high-density polyethylene (HDPE)

This paper investigated the stability, mechanical properties, and the microstructure of wood–plastic composites, which were made using either recycled or virgin high-density polyethylene (HDPE) with wood flour (Pinus radiata) as filler. The post-consumer HDPE was collected from plastics recycling plant and sawdust was obtained from a local sawmill. Composite panels were made from recycled HDPE through hot-press moulding exhibited excellent dimensional stability as compared to that made from virgin HDPE. The tensile and flexural properties of the composites based on recycled HDPE were equivalent to those based on virgin HDPE. Adding maleated polypropylene (MAPP) by 3–5 wt% in the composite formulation significantly improved both the stability and mechanical properties. Microstructure analysis of the fractured surfaces of MAPP modified composites confirmed improved interfacial bonding. Dimensional stability and strength properties of the composites can be improved by increasing the polymer content or by addition of coupling agent. This project has shown that the composites treated with coupling agents will be desirable as building materials due to their improved stability and strength properties.     

Dynamic mechanical analysis and non-isothermal kinetics of EVA/PPy carbon black nanocomposites

Pure ethylene-co-vinyl acetate (EVA) and its conductive blend-nanocomposite with polypyrrole (PPy)/carbon black (CB) were prepared using a melt mixing process. Dynamic mechanical analysis and non-isothermal thermal gravimetrical analysis were performed on the samples. The storage modulus, loss modulus, and damping factor of the EVA/PPy/CB nanocomposites were significantly affected by the incorporation of PPy/CB. Two thermal decomposition stages were detected for pure and blended nanocomposite samples. Peak analysis was used to deconvolve the first complex decomposition stage. The Coats-Redfern method was used to determine the kinetic parameters. Improving the thermal and mechanical properties of the EVA co-polymer will enable the three-phase blend/nanocomposites to be used in several industrial applications.     

紫外光交联无卤阻燃聚乙烯醋酸乙烯酯绝缘材料的研制

以聚乙烯醋酸乙烯酯(EVA)为树脂基体,氢氧化镁(MH)为无卤阻燃剂,并分别加入表面改性剂硬脂酸(SA)和十一烯酸(UA),通过紫外光辐照进行交联,通过凝胶含量测试、红外光谱、扫描电镜等测试研究了交联及2种不同的表面改性剂对EVA/MH性能的影响。研究结果表明,在含有UA的EVA/MH体系中交联后材料的拉伸强度达到10 MPa以上,断裂伸长率达到150%以上,同时氧指数达到43以上。通过微观研究表明这主要是由于含乙烯基的UA在交联过程中参与了交联反应形成了交联点,同时提高了氢氧化镁与树脂基体EVA的界面作用。     

纳米TiO2/液体硅橡胶直流电缆附件绝缘复合材料的介电性能

高压直流电缆附件在电力系统运行中,由于复合绝缘电导率不匹配极易导致电场畸变引发绝缘故障。针对这一问题,采用直接共混法制备了不同掺杂浓度的纳米TiO₂/液体硅橡胶（LSR）复合材料,并对其微观形貌和介电性能进行了测试研究。结果表明:纳米TiO₂粒子在LSR基体中分散较均匀,随着TiO₂掺杂含量的增加,纳米TiO₂/LSR复合材料试样的相对介电常数和介质损耗因数增大。当纳米TiO₂粒子添加量为4wt%时,纳米TiO₂/LSR复合材料的电导率与电缆主绝缘交联聚乙烯（XLPE）的电导率近似相等,且随着电场强度的增大,两者的电导率变化趋势也基本一致。电声脉冲法（PEA）测量结果表明,添加4wt% TiO₂的纳米TiO₂/LSR复合材料内积聚的空间电荷最少。纳米TiO₂粒子的掺杂,提高了TiO₂/LSR复合材料电缆附件绝缘电导率对电场强度的响应依赖特性,使其能与XLPE绝缘电导率较好地匹配,同时一定程度地抑制了空间电荷的积累,有助于直流电缆附件内复合绝缘电场的均匀分布。      

Influence of morphology on the dynamic mechanical characteristics of PP-EP/EVA/organoclay nanocomposites

A study on the dynamic mechanical properties of polypropylene copolymer/ethylene–vinyl acetate/organoclay (PP-EP/EVA/C20A) nanocomposites is presented. Nanocomposites were obtained by melt blending. Morphology consisting of intercalated–exfoliated clay nanolayers preferentially located within the EVA phase was observed by transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD). Polar groups of vinyl acetate in the EVA facilitated the polymer–clay interactions. Changes in the glass transition temperature (T_g) were correlated with changes in the clay intercalation–exfoliation levels. The highly reinforced with intercalated–exfoliated clay layers EVA phase was considered as the origin of the improvement on mechanical properties of the ternary nanocomposites and is associated with the increase on viscosity, heat deflection temperature (HDT), and storage modulus.     

Influence of a fine talc on the properties of composites with high density polyethylene and polyethylene/polystyrene blends

Fine talc filled high density polyethylene (HDPE) and HDPE/polystyrene (PS) blends were extruded, injection moulded and characterized. Some of the mechanical properties of the talc filled HDPE and talc filled 75/25 HDPE/PS blend were deduced from stress–strain measurements. A comparison between the effect of the talc on the properties of the filled HDPE and filled 75/25 HDPE/PS blend showed that the mineral filler had the same effect on both systems provided that its array in the organic matrix is almost the same in both cases. In fact, the rheological results proved that the dispersion of talc in the HDPE matrix was not really affected by the presence of PS. The study particularly focused on the effect of talc on the ultimate tensile strength of the filled HDPE and that of the filled blend. It has been noted that the brittle nature of PS neutralizes, to a certain extent, the degrading effect of talc on this property. Furthermore, both PS and talc have a complementary effect on the stiffness and the resilience of HDPE/PS/talc blend composites.     

有机支架结构对丁苯橡胶/乙烯-醋酸乙烯共聚物复合发泡材料性能的影响

为提高橡胶发泡材料尺寸稳定性及实现其广泛的工业化应用,基于硫磺和过氧化二异丙苯的交联体系,通过机械共混的方式,以具有结晶性的乙烯-醋酸乙烯共聚物(EVA)构筑有机支架结构,制备了高尺寸稳定性的丁苯橡胶(SBR)/EVA复合发泡材料.研究了不同醋酸乙烯(VA)含量的EVA对SBR/EVA复合材料结晶性、相容性、泡孔形貌、...     

HDPE／EVA共混体系的研究

采用ＤＳＣ，ＷＡＸＤ和力学性能测试，研究了ＨＤＰＥ／ＥＶＡ共混体系。结果表明，ＨＤＰＥ／ＥＶＡ共混体系是不相容的，但在共混组成中含有少量（＜１０％）的ＥＶＡ，力学性能下降很少，而加工性能得到改善，具有一定实用价值。     

聚乙二醇改性相变微胶囊制备MicroPCMs-WF/HDPE复合材料物理力学性能

以正十二烷醇（DA）为芯材,密胺树脂（MF）和聚乙二醇改性密胺（PMF）树脂为壁材制备了相变微胶囊（MicroPCMs）,并分别添加到木粉/高密度聚乙烯（WF/HDPE）复合材料中,获得了具有相变蓄热能力的MicroPCMs-WF/HDPE复合材料。采用SEM、FTIR和纳米压痕等方法对MicroPCMs的表面形态、力学性能进行了分析与表征,同时对MicroPCMs-WF/HDPE复合材料的物理力学及热性能进行了测试。结果表明:经聚乙二醇改性后,改性微胶囊（PMF-MicroPCMs）的弹性模量和硬度较未改性微胶囊（MF-MicroPCMs）分别增加了13.9%和30.0%;MicroPCMs-WF/HDPE复合材料的熔融温度区间（22.2~28.7℃）满足人体舒适温度范围,较纯WF/HDPE复合材料温度变化速率明显减缓;相比纯WF/HDPE复合材料,MicroPCMs-WF/HDPE复合材料的吸湿性、冲击强度和表面硬度增加,弯曲和拉伸性能下降;PMF-MicroPCMs-WF/HDPE复合材料的性能均优于MF-MicroPCMs-WF/HDPE复合材料,且达到了木塑装饰板材的力学性能标准要求。      

Cyclodextrin microencapsulated ammonium polyphosphate: Preparation and its performance on the thermal,flame retardancy and mechanical properties of ethylene vinyl acetate copolymer

Cyclodextrin microencapsulated ammonium polyphosphate (MCAPP) was prepared by the reaction between cyclodextrin (CD) and toluene-2,4-diisocyanate (TDI) with the goal of improving the water durability of APP and preparing a novel functional flame retardants. The Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS) results indicated MCAPP were successfully prepared, and the water contact angle (WCA) results indicated that cyclodextrin resulted in the transformation of hydrophilic to hydrophobic of the flame retardant surface. The MCAPP was then incorporated into the ethylene vinyl acetate copolymer (EVA) system and the effects of the MCAPP on the mechanical, combustion, thermal, interfacial adhesion and flame-retardant properties of EVA cable were investigated and compared by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), limiting oxygen index (LOI), mechanical test, cone calorimeter and UL-94 test. The characterization for the various properties of EVA composites demonstrated that cyclodextrin microencapsulation technology could enhance the interfacial adhesion, resulting in the improved mechanical, thermal stability, combustion properties and flame-retardant properties compared with those of EVA/APP/CD system. Furthermore, the water resistance experiments results demonstrate that EVA/MCAPP composites have good water durability due to the hydrophobic property of MCAPP. Above all, the microencapsulation of APP with cyclodextrin developed in this study may be a promising formulation for combining the acid source, the carbonization agent and the blowing agent in one flame retardant, and the MCAPP can solve the water resistance and the compatibility problem of the flame retardant during the industrial application.