Modelling non-linear stress–strain behaviour of rubber toughened plastics

Abstract

An elastic–plastic model has been developed for describing the non-linear, stress–strain curves of rubber toughened plastics. Following a linear elastic response at low strains, it is assumed that the material undergoes plastic deformation which, for dilatational stress states, is enhanced by the generation and growth of cavities within the rubber particles. The model is based on Gurson's theory of plasticity in porous materials and follows the developments proposed by Bucknall and co-workers. Parameters are included that allow for the effect of pressure on the yield stress of the matrix material between the cavities and for the influence of void interactions on matrix shear banding. Account is also taken of the change in matrix composition, and hence the matrix yield stress, during void nucleation. The nucleation is assumed to occur over a critical range of volumetric strain ε_V and to involve the replacement of rubber particles by an equal volume of effective cavities. Two different nucleation functions have been investigated to describe the dependence of the effective void fraction on ε_V.

Equations that govern the elastic, yield and flow behaviour under multiaxial stress states have been solved to determine required material parameters and to predict behaviour in tension and compression from shear hardening data. The predicted and observed behaviour show good agreement, indicating that the model may be applied with some confidence to stress analyses using finite element calculations.     

Biodegradation Behavior of DOC Isolated Mixed Proteins-Based Plastic Sheets

The biodegradability of plastic sheets made of mixed proteins was investigated. Soybean, castor and rapeseed DOC (Deoiled Cake) isolated proteins-based plastic sheets were subjected to microbial degradation using Pseudomonas aeruginosa. Results from the microbial degradation showed that plastic sheets prepared from mixture of soybean, castor and rapeseed proteins could support the growth of P. aeruginosa. Biodegradable plastic sheet with composition (80:10:10 and 60% PEG₄₀₀) degraded much faster than the other four biodegradable plastics sheets under the conditions examined, suggesting that the biodegradability of protein films is associated with the film composition and the extent of covalent cross-linking.     

Bring back the steel? The growth of plastics in automotive applications

The development of plastics has evolved from the use of natural materials to the use of chemically modified natural materials and, finally, to completely man-made molecules. Plastics continue to improve, to afford flexibility, high-impact, and strength. In automotive applications, plastics have increased in utilization to comprise approximately 10% of the total vehicle weight. They offer increased ductility, freedom from corrosion, and increased styling capability. Although plastics have had a remarkable impact on our culture, it is obvious that there is a price to be paid for their use. Plastics are almost too good, as they are durable when processed correctly, but easily damaged when utilized in the incorrect application. Plastics also degrade very slowly, making recycling mandatory. And finally, while plastics consume only 4% of the world’s oil production (petroleum is the raw material that is chemically altered to form commercial plastics), their cost hinges on the cost of petroleum. As petroleum prices increase, so too will the cost of plastic. In 2004, the higher price of plastic forced many plastic manufacturers out of business, and forced many automotive suppliers to look into alternative replacements. With publications such as USA Today reporting that current oil reserves will only last 40 years, scientists continue to seek cheaper alternatives to plastic. This article summarizes the history of commercial plastic development, with a focus on utilization of the materials in automotive applications. Damage criteria of plastic components, namely scratch, oxidative degradation, and impact, are discussed in relation to coatings and processing robustness. Environmental regulations, particularly in relation to recycling mandates, are explained. And finally, trends in alternative material development, including bioplastics, films, ceramic coatings, and nano-composites; are formulated. Presented at the 83rd Annual Meeting of the Federation of Societies for Coatings Technology, November 6–9, 2005 in Las Vegas, NV.     

Effects of material properties and contact conditions in modelling of plug assisted thermoforming

Abstract

Thin walled food packaging is commonly manufactured using the plug assisted thermoforming process. In this paper the development of finite element models of the process is described. Work has concentrated on understanding the effects of material properties and contact conditions on the output from these simulations. The results have shown that a viscoelastic model must be used to simulate the deformation behaviour of the plastics. Contact conditions must also be accounted for in the models by including the effects of friction and heat transfer between the sheet and tool surfaces. For improved model accuracy, it is recommended that further experimental work should be carried out to enhance the viscoelastic material models and to provide better understanding of actual contact conditions.     

High-Density Polyethylene/SrAl2O4:Eu2+, Dy3+ Photoluminescent Pigments: Material Design,Melt Processing,and Characterization

High-density polyethylene is a thermoplastic polymer which is extensively involved in the manufacturing of plastic components by injection or blow molding in several industrial domains. Among others, high-density polyethylene is the ideal candidate for the fabrication of indoor and outdoor furniture and general plastic items. In this respect, photoluminescence might be of great relevance as it can replace or support conventional lighting systems in pathway markers and safety signs. In this framework, photoluminescent high-density polyethylene was achieved by the dispersion of SrAl₂O₄:Eu²⁺, Dy³⁺ functional pigments by twin-screw extrusion. The resulting compound was, subsequently, injection molded to form flat substrates. Characterization of the mechanical properties of the photoluminescent plastic substrates was performed by instrumented flat and scratch indentation as well as by dry sliding linear reciprocating tribological tests. Photoluminescence of the substrates was evaluated by digital imaging technique and quantitative measurements of the emission spectra. Experimental findings state that highly performant and enduring photoluminescent plastics can be achieved by compounding high-density polyethylene with SrAl₂O₄:Eu²⁺, Dy³⁺ photoluminescent pigments. Injection molding of the engineered material can lead to plastic items characterized by good mechanical performance and reliable photoluminescent emission over a reasonable time range.     

几种塑料在吐鲁番与广州的户外老化试验

几种塑料试件在我国新疆吐鲁番和广州地区户外老化试验结果,说明塑料在严酷干热气候条件下受户外日光照射后会加速老化;自然环境试验能真实反映塑料制品、制件以及它们的改性材料或产品的光氧老化特征与规律。     

超微多孔塑料成型技术研究

超微多孔塑料 (Supermicrocelularplastic)是一种新型的高分子材料 ,它与传统泡沫塑料相比 ,内部泡孔直径小 (0 1～ 10 μm) ,泡孔密度大 (每立方厘米材料可制泡孔达 10 9～ 10 15) ,泡孔分布均匀。超微多孔塑料的这些独特微观结构 ,使其具有优异的机械性能 ,它具有较高的抗冲击强度和韧性 ,很低的导电系数和导热系数。可以节省原材料达 80 %而不会降低材料的机械性能。由于这些独特的性能 ,超微多孔塑料有很广阔的应用场合 ,可以用在汽车、飞机和建筑等领域。超微多孔塑料是一种很有发展前途的新型材料。超微多孔塑料成型技术目前正吸引着各国研究人员对其进行广泛深入的研究。本文介绍超微多孔塑料成型技术方面的进展和笔者在这方面的前期工作     

Correlation between physical bonding and mechanical properties of wood–plastic composites: part 2: effect of thermodynamic factors on interfacial bonding at wood–polymer interface

Abstract

The main objective of this study was to find out if there is any significant correlation between physical properties and interfacial bonding of interphases in wood–plastic composites. To this end, high-density polyethylene (HDPE), mixture of 3% maleic anhydride grafted polyethylene (MAPE) and HDPE (coded as MHDPE) and polylactic acid (PLA) were separately interacted with veneers to identify factors underlying interfaces. Plastics were first melted at 180?°C and dispensed on wood surfaces so that the contact angle (CA) could be directly measured. Wood sanding moderately decreased the CAs of plastics in order of PLA, MHDPE, and HDPE. The treatment of veneers with MAPE comprehensively improved wetting, as the CA of HDPE was significantly reduced on the wood surface after the treatment. Thereafter, the interfacial shear strengths (IFSS) of the wood–polymer interface were determined using the automated bonding evaluation system. PLA had the highest IFSS both for unsanded and sanded veneers. Comparing both parts of this research finally revealed that applying sanding or/and MAPE treatments resulted in lower surface free energy and higher IFSS at the wood–polymer interface. However, our observations support the idea that, at higher temperatures, wetting of composites is mainly influenced by polymer properties rather than interfacial tension at the wood–polymer interface.     

Preparation, characterization, and antibacterial activity of photocured thymol-doped acrylic resins

This article describes the preparation of thymol-doped acrylic resins by photopolymerization of solutions of thymol in tripropylenglycoldiacrylic monomer. This provides an easy, energy-saving, and environmental friendly process to prepare antibacterial plastics (fulfilling most of the “green chemistry” requirements). The results demonstrate that thymol can be included in the resin even at high concentration (up to 28.6%) without affecting the photocuring reaction and losing transparency. The glass transition temperature of the doped resin decreases when the thymol content increases, as it behaves like a plasticizer with respect to the acrylic resin. As indicated by HPLC analysis, thymol can be released in liquid media at a rate that depends on the chemical nature of the liquid. Evaluation by agar diffusion assays showed an antibacterial activity on both Gram-negative and Gram-positive bacteria (Staphylococcus aureus, Listeria monocytogenes, and Escherichia coli). The antibacterial activity can occur just on the plastic surface when the thymol-doped resins is applied as thin coating, while it is evident also in the surrounding agar medium for doped plastic discs, 1.2 mm thick with a concentration of thymol in the resin higher than 16.7%.     

Effects of the accelerated freeze‐thaw cycling on physical and mechanical properties of wood flour‐recycled thermoplastic composites

This study investigated durability performance of wood‐plastic composites (WPCs) that were exposed to accelerated cycling of water immersion followed by freeze thaw (FT). The WPCs used in this study were made of high‐density polyethylene (HDPE) or polypropylene (PP) with radiata pine (Pinus radiata) wood flour using hot‐press molding. These two types of plastics included both recycled and virgin forms in the formulation. In the experiments, surface color, flexural properties, and dimensional stability properties (water absorption and thickness swelling) were measured for the FT cycled composites and the control samples. Interface microstructures and thermal properties of the composites were also investigated. The results show that the water absorption and the thickness swelling of the composites increased with the FT weathering. In the meantime, the flexural strength and stiffness decreased. Scanning electron microscopy (SEM) images of the fractured surfaces confirmed a loss of interface bonding between the wood flour and the polymer matrix. Differential scanning calorimetry (DSC) showed a decrease in crystallization enthalpy and crystallinity of the wood flour‐plastic composites as compared with the neat PP and HDPE samples. The crystallinity of the FT cycled composites using the virgin plastics (vPP and vHDPE) increased; however, the composites with the recycled plastics decreased in comparison with corresponding control samples. In general, the properties of the composites were degraded significantly after the accelerated FT cycling. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

工程塑料在轴承中的应用

阐述了塑料轴承的选材，设计以及几种工程塑料轴承的研究与开发状况。表明了无油润滑塑料轴承是一种很有发展前途和应用价值的产品，应加快研究与开发。     

Separation of PVC and Rubber from Covering Plastics in Communication Cable Scrap by Tribo-Charging

Abstract

Triboelectrostatic separation of PVC and rubber from covering plastics in communication cable scrap has been performed. In this work, particles charged as positive (+) and negative (?) according to the difference of work function of each material after tribo-charging can be separated through an opposite electric field. In charger material selection tests using a vertical-reciprocation charger, PVC and rubber particles in the covering plastics were charged with the opposite polarity in the charger material made of PP, HDPE, or PET. The difference of charge density (charge to mass ratio, nC/g) of the PVC and rubber was higher in the tribo-charger made of HDPE. Furthermore, in lab-scale triboelectrostatic experiments for separating the PVC and rubber, the charging efficiency of the mixed PVC and rubber increased when the air velocity was adjusted to over 8.2 m/s. The charge density, the electrode potential, and splitter position needed for the separation of the PVC were determined to be 25 nC/g, 30 kV and +2 cm, respectively. In the optimum conditions, we developed a separation technique that can separate up to 99.8% PVC grade with 95.0% of recovery from the covering plastics.     

再生塑料在混凝土中的应用研究

随着经济的快速发展,各国的塑料制品消费量与日俱增,大量的废弃塑料如PET瓶亟待处理。将废弃塑料回收处理并作为一种环保建材掺入砂浆或混凝土中再利用成为解决废弃塑料的方法之一。介绍了混凝土用塑料骨料的类型及回收处理方法及塑料骨料掺入对混凝土力学性能的影响规律。结果表明:混凝土的力学性能,如抗压强度、劈裂抗弯强度等与塑料骨料的替代度密切相关,为废弃塑料在混凝土中的进一步应用提供了一定的参考依据。     

PE废塑料的再生利用

PE（聚乙烯）是产量最大的通用塑料之一,具有很多应用的优点,是制造地膜、包装用膜、电线电缆塑料软管等材料的原材料。也是塑料行业研究领域上的一个大热点。从PE废塑料的生产现状及应用进展出发,介绍了PE废塑料常用再生方式和存在的问题,并提出未来的发展方向。     

不同木粉比例PVC木塑界面的介观模拟以及力学性能预测

研究了DPD(耗散粒子动力学)方法模拟不同木粉比例的PVC木塑中木粉的分布状况,从介观尺度表征了木粉在材料中的聚集状态,通过木粉在木塑材料中的分布情况预测高木粉填充木塑材料的力学性能,并与试验值进行对比,得出当木粉含量达到15%~31.5%可以达到力学性能最优区间。     

含孔片状废旧PET增韧水泥基复合材料的制备及性能评价

废旧塑料高值化利用对促进塑料循环利用具有重要意义。从提高填充材料和基体的啮合强度出发,开发以含孔废旧塑料为增韧材料的增韧水泥基复合材料是废旧塑料高值化利用的有效途径之一。以含孔片状废旧聚对苯二甲酸乙二醇酯(PET)和水泥复合,制备了增韧水泥基复合材料,并考察其抗折强度、冲击性能和拉伸拔脱载荷,分析了其增韧机理。相比未用PET增韧水泥基体,增韧水泥基复合材料的冲击强度由14.6 J/m^2增加到36.7 J/m^2,增加了1.5倍,抗折位移也由0.66 mm陡增至7.4 mm,但抗折强度由7.67 MPa降低到2.85 MPa。上述结果表明,含孔废旧PET塑料片和水泥基体形成的互穿结构起到了传递、分散载荷的作用,使增韧水泥基复合材料由瞬态脆性破坏转变为渐进式韧性破坏,虽然水泥基体的抗折强度降低,但显著延长了水泥基体的弯曲断裂过程,使增韧后的水泥基复合材料具有更强的抵抗碎裂的能力。此外,在研究范围内,水泥基复合材料中废旧PET塑料片材越多,单位塑料片对复合材料的增韧贡献度越大,具有增韧“筷子效应”。     

Unter welchen Voraussetzungen bewähren sich Korrosionsschutzauskleidungen aus Fluorkunststoff-Folien

Under what conditions are anticorrosion liners made from fluorinated plastic film effective ? Equipment lined with fluorinated plastics is nowadays making a major contribution to the solution of difficult materials problems. If such equipment is to be used successfully, it is essential that its manufacturer is familiar with the specific properties of the lining materials and takes them into account in the design and production of the equipment. However, it is just as important for the operator to adjust to the material when operating the plant. On the basis of many years of experience, the most important problems associated with loose liners made from polytetrafluoroethylene (PTFE) – viz. leakproofness and permeability of the liner, flange system, dimensional stability towards vacuum, handling, and installation – are indicated and possible solutions stated.     

Basic study on separate charge of coal and waste plastics in coke oven chamber

Nippon Steel Corporation started to operate a waste plastic recycling process using coke ovens at Nagoya and Kimitsu Works in 2000 and at Yawata and Muroran Works in 2002. Now the total capacity is 120,000 tons per year and the recycling process is operating smoothly. In this process, coals and added plastics are carbonized and changed into coke, tar, oil and coke oven gas in a coke oven chamber. At present, upper limit of the addition rate of waste plastics to blended coals is 1% so that the plastic addition does not affect coke strength. However, the amount of waste plastics in Japan is as much as about 10 million tons per year and there is a real need for increasing the amount of waste plastics treated by the waste plastic recycling process using coke ovens. We investigated a method of increasing the addition rate of waste plastics without affecting coke strength by charging coal and plastic separately in a coke oven chamber. In the case of the same plastic addition rate, charging the plastic in the bottom or the top part of the coke oven chamber can decrease the deterioration of coke strength compared with charging a homogeneous mixture of coal and plastic. Charging the plastic in the bottom decreases the coke strength to a greater extent than charging the plastic in the top. This is because the decomposition of the plastic charged in the bottom decreases the bulk density of the upper coal layer. The results suggest that charging the coal and waste plastics separately increases the amount of waste plastics treated in the waste plastic recycling process using coke ovens. In order to commercialize this method, further studies are necessary concerning the charging method, device and the effect of this method on the coke oven operation.