Mechanical properties of extrusion‐foamed rigid PVC/wood‐flour composites

This study was conducted to characterize the mechanical properties of extrusion‐foamed neat rigid PVC and rigid PVC/wood‐flour composites by using endothermic and exothermic chemical foaming agents (CFAs). The specific elongation at break (ductility) of the samples was improved by foaming, while the opposite trend was observed for the tensile strength and modulus of the samples, regardless of the chemical foaming agent type. In addition, experimental results indicated that foaming reduced the Izod impact resistance of both neat rigid PVC and rigid PVC/wood‐flour composites but that this reduction was not statistically significant for the composites. A comparison between batch microcellular processing and extrusion foam processing was made, which demonstrated that foams with very fine cells (microcellular processed) exhibit better impact strength than foams with larger cells (extrusion processed with CFAs).     

PVC/wood‐flour composites compatibilized with chlorinated polyethylene

Chlorinated polyethylene has been demonstrated to be an effective compatibilizer for dissimilar materials in various mixed‐polymer or recycled‐polymer systems. In this paper the use of chlorinated polyethylene to compatibilize polymer/natural‐fiber composites is discussed. Examples of applications in PVC/wood‐flour composites are given.     

Microcellular foaming of impact‐modified rigid PVC/wood‐flour composites

Solid state microcellular foaming technology was employed to investigate the influence of impact modification on the foamability of neat rigid PVC and rigid PVC/wood‐flour composite samples. The effects of impact modifier types (crosslinked versus uncrosslinked) and concentrations on the void fraction of foamed samples were examined. The influence of impact modification on the sorption behavior of CO₂ in the samples was also studied. The experimental results indicate that impact modification accelerates the rate of gas loss during the foaming process, which impedes the growth of nucleated cells, independent of modifier type. Because of this accelerated gas loss, impact modification inhibits the potential of producing foamed samples with void fractions similar to those achieved in unmodified samples.     

Foaming of rigid PVC/wood‐flour composites through a continuous extrusion process

The effects of chemical foaming agent (CFA) types (endothermic versus exothermic) and concentrations as well as the influence of all‐acrylic processing aid on the density and cell morphology of extrusion‐foamed neat rigid PVC and rigid PVC/wood‐flour composites were studied. Regardless of the CFA type, the density reduction of foamed rigid PVC/wood‐flour composites was not influenced by the CFA content. The cell size, however, was affected by the CFA type, independent of CFA content. Exothermic foaming agent produced foamed samples with smaller average cell sizes compared to those of endothermic counterparts. The experimental results indicate that the addition of an all‐acrylic processing aid in the formulation of rigid PVC/wood‐flour composite foams provides not only the ability to achieve density comparable to that achieved in the neat rigid PVC foams, but also the potential of producing rigid PVC/wood‐flour composite foams without using any chemical foaming agents.     

Effects of impact modifiers on the properties of rigid PVC/wood‐fiber composites

This study examined the effects of impact modifier types and addition levels on the mechanical properties of rigid PVC/wood‐fiber composites. The impact resistance of rigid PVC/wood‐fiber composites depends strongly on the type and content of impact modifier. With the proper choice of modifier type and concentration, the impact strength of rigid PVC/wood‐fiber composites can be significantly improved without degrading the tensile properties. Methacrylate‐butadiene‐styrene and all‐acrylic modifiers performed in a similar manner and were more effective and efficient in improving the impact resistance of rigid PVC/wood‐fiber composites than the chlorinated polyethylene modifier.     

Wood‐flour‐reinforced polyethylene: Viscoelastic behavior and threaded fasteners

The tensile stress relaxation and flexural creep properties of wood‐fiber‐reinforced low‐density polyethylene (WFRP) were measured at various temperatures and stress levels. Power law relations were used to correlate the data, and time‐temperature superposition was applied to tensile stress relaxation results. Stress relaxation in WFRP was similar to that of LDPE and greater than that in spruce. The clamping force and torque characteristics of self‐threading screws and internally threaded inserts were measured in WFRP, and the viscoelastic model was extended to predict the relaxation in screw clamping force as a function of time. Both screw pullout force and the amount of clamping force relaxation were greater in WFRP than in spruce.     

Manufacture of rigid PVC/wood‐flour composite foams using moisture contained in wood as foaming agent

Relatioships between the density of foamed rigid PVC/wood‐flour composites and the moisture content of the wood flour, the chemical foaming agent (CFA) content, the content of all‐acrylic foam modifier, and the extruder die temperature were determined by using a response surface model based on a four‐factor central composite design. The experimental results indicated that there is no synergistic effect between teh CFA content and the moisture content of the wood flour. Wood flour moisture could be used effectively as foaming agent in the production of rigid PVC/wood‐flour composite foams. Foam density as low as 0.4 g/cm³ was produced without the use of chemical foaming agents. However, successful foaming of rigid PVC/wood‐flour composite with moisture contained in wood flour strongly depends upon the presence of all‐acrylic foam modifier in the formulation and the extrusion die temperature. The lowest densities were achieved when the all‐acrylic foam modifier concentration was between 7 phr and 10 phr and extruder die temperature was as low as 170°C.     

Sound‐transmission‐class and fire‐resistance ratings for wood‐frame floors

A collaborative government‐industry research programme was carried out at the National Research Council Canada to develop new sound‐transmission classes and fire‐resistance ratings for wood‐frame floor assemblies protected by gypsum‐board ceilings. Forintek Canada Corp., the Canadian Wood Council, and five manufacturers of wood I‐joists participated in the programme on behalf of the wood industry. Fire‐resistance ratings developed through the research programme range from 30 min to 1h: sound‐transmission classes range from 20 to 65. Many of the ratings will be published in the next edition of the National Building Code of Canada. This paper highlights some of those sound‐transmission class and fire‐resistance ratings and describes how they were derived from data obtained through the research programme. Copyright © 2000 John Wiley & Sons, Ltd.     

New generation of high‐performance PVC alloys

Newly developed alloys of flexible poly(vinyl chloride) (PVC) and polyolefin elastomers have been shown to exhibit improved physical properties compared to those of conventional flexible PVC control compounds. In particular, the new alloys display enhanced electrical properties, better high temperature stability, greater low temperature flexibility, and superior gas barrier properties. In addition, this study demonstrated that PVC/polyolefin rubber alloys have potential utility in many applications where conventional flexible vinyl compounds do not meet certain end‐use performance requirements.     

PVC发泡板材的开发与应用

阐述了ＰＶＣ发泡板材的开发与应用。ＰＶＣ发泡板具有密度小,强度高,防水性好,阻燃,不吸湿,耐化学性优良和热导率低等优点,并且易于用常规机械进行二次加工,是一种替代木材,钢材的塑料制品之一,可广泛用于化工建材各领域。     

硬质交联发泡聚氯乙烯板材的研究进展

介绍了硬质交联发泡聚氯乙烯板材的结构性能、国内外发展现状及其发展前景;硬质交联发泡聚氯乙烯板材具有阻燃性能,有望取代现有的三大泡沫塑料,成为新型节能保温材料;国外生产的硬质交联发泡聚氯乙烯板材产品性能优异,而国内其工业化生产属于空白。与现有建筑用发泡塑料对比,硬质交联发泡聚氯乙烯性能更加优越,其应用前景更加广阔。     

硬质聚氯乙烯低发泡板材的生产技术

ＫＮＤ - 1 2 5型硬质ＰＶＣ低发泡挤出生产线采用德国拜耳公司设备 ,引进瑞士ＡＩＲＥＸ公司的专利生产技术 ,可生产 70 0、5 0 0ｋｇ/ｍ3 两种密度、宽 1 2 2 0ｍｍ、厚 1～ 1 9ｍｍ的各种板材。现以 70 0ｋｇ/ｍ3 发泡板为例 ,探讨生产中出现的故障及解决方法。1　生产中常见故障及解决方法1 1　密度太高( 1 )增大冷却辊和模头距离 ,因板会增厚 ,须提高牵引速度 ;( 2 )不改变回收料用量 ,增大主要转速 ,牵引速度和新料用量 ;( 3)不改变新料用量 ,降低回收料用量 ;( 4)把机筒第 3区温度降低 5℃ ;( 5 )对于 2 .3ｍｍ薄板 ,降低冷却辊压力…     

硬质PVC发泡制品的配方设计

阐述了硬质PVC发泡制品配方中PVC树脂和热稳定剂、发泡剂、优泡剂、冲击改性剂、加工改性剂、填充剂、润滑剂及成核剂等助剂的选用原则,介绍了生产优质硬质PVC发泡制品的基础配方。     

Thoughts and observations on fire‐endurance tests of wood‐frame assemblies protected by gypsum board

Forintek Canada Corp. participated in a series of collaborative research projects with the National Research Council Canada and other organizations to determine fire‐resistance ratings for wood‐frame assemblies used in the construction of Canadian housing and small buildings. Over the course of those studies, Forintek's scientists observed a large number of full‐scale fire‐endurance tests on walls lined on both faces with gypsum board and floor assemblies with gypsum‐board ceilings. Those observations have given Forintek's researchers unique insights into the fire performance of wood‐frame assemblies and fire‐endurance testing. Those insights are the subject of this paper. Copyright © 2002 John Wiley & Sons, Ltd.     

影响PVC芯层发泡管发泡质量的因素

从PVC树脂的选用、不同助剂的用量和功效及混料与挤出过程各相关参数的设置等方面,探讨了影响PVC芯层发泡管发泡质量的各种因素。     

PVC压延发泡地板革的生产技术

介绍了PVC压延发泡地板革的生产技术。     

PVC发泡人造革泡孔质量研究

以理论分析和实践经验论述了提高ＰＶＣ发泡人造革泡孔质量的实质。     

硬质PVC泡沫板材密度与性能的关系

采用两步法成型工艺开发了硬质PVC泡沫板材,测定了其密度均匀性和泡孔孔径,考察了板材密度与性能的关系.结果 表明:①所开发的硬质PVC发泡板材密度均匀,泡孔孔径在320 ～440 μm;②随着密度的增大,硬质PVC发泡板材的力学性能呈线性增长的趋势,热变形温度略微增加.     

High‐molecular‐weight flexibilizers in low‐smoke flame‐retardant PVC compounds

Ethylene copolymer resin (ECR) modifiers play an important role in low‐smoke PVC. As high‐molecular‐weight flexibilizers, these resins reduce smoke and add strength and low temperature flexibility. This combination allows compounders to increase the amounts of flame‐retardant additives without compromising strength or flexibility or by adding liquids which increase smoke. This paper demonstrates these attributes versus liquid plasticizers used in PVC compounds.