PVC注塑件的密度与收缩

分析了PVC注塑件的密度特征和收缩特征,结果表明:PVC注塑件的密度及其分布与PVC注塑件的收缩相互影响。     

Characterisation and properties of oriented PVC fibres

Drawn PVC fibres were investigated using birefringence, DSC and TMA techniques, and their tenacity was measured. An increase in fibre draw ratio (DR) for heat set samples produced an increase in tenacity, birefringence and X-ray intensity. The linearity of a tenacity/birefringence plot suggested that tenacity was a good indicator of molecular orientation. An ‘undrawn’ filament was substantially amorphous. Drawing without heat setting produced little three dimensional order, and samples relaxed readily on heating. X-ray results for heat set fibres suggested both an increase in the amount of crystallinity, and in crystallite alignment. After heat setting, a minor DSC endotherm was produced; the onset of this endotherm corresponded to the heat setting temperature, as did the onset of shrinkage measured by TMA. For samples with a DR>1.5, maximum shrinkage measured by TMA corresponded to complete elastic recovery.     

Shrinkage behavior of oriented PVC by thermomechanical analysis

This paper describes a novel application of thermomechanical analysis. Observation and measurement of the thermal recovery of stresses induced in oriented PVC by stretching at elevated temperature is achieved by the modification of a commercial TMA instrument. Employment of an electronic signal differentiation system, in combination with this instrument, permits the simultaneous recording of the rate of shrinkage as a function of temperature. Specific examples are given which demonstrate the performance of the instrument and illustrate its application to problems of practical interest, such as effects of stretching and annealing conditions on shrinkage behavior.     

Interfacial instabilities in multimaterial co-injection mouldings: Part 2 - Interfacial mixing in transparent mouldings

Abstract

Previous research in co-injection moulding has produced viscosity ratio guidelines for skin and core components, which must be followed if good core distribution is to be achieved. However, by examining two phase systems of PMMA-PC, which fall within the recommended viscosity range, this work shows that viscosity matching of materials is not a sufficient requirement for interfacial stability. The transparency of the materials allows areas of interfacial mixing to show up as streaks in the mouldings, so that factors affecting stability can be determined. One system is found to be more stable than the others. Explanations for such effects are given by consideration of interfacial mixing, viscosity, tooling geometry, injection speeds, interfacial stresses and shear in multilayered mouldings.     

Determination of frozen-in stresses in thermoplastic injection mouldings

A method and apparatus for providing an overall numerical value of the frozen-in stresses in injection mouldings was developed and compared with existing methods. The developed technique was more rapid and could be employed on either opaque or transparent samples and was more suitable for production quality control purposes. Frozen-in stress values of a number of different thermoplastics moulded under varying conditions of melt temperature and pressure were determined. Some results on the influence of melt flow pattern are also included.     

Structural analysis of an oriented liquid crystalline copolyester

Wide angle X-ray scattering from an aligned sample of a random copolyester is presented, together with an analysis of the derived cylindrical distribution function. High local orientational correlation of chains is observed, although the global orientation is less marked. There is some evidence of lateral biaxiality, which is compared with that predicted for theoretical studies of liquid crystalline structures.     

Structural order in heat treated vinyl chloride polymers

Three vinyl chloride polymers were annealed at temperatures in the range 40–160°C for times varying from 0.5 to 5 h. Structural changes occurring in the polymers were examined by density measurement, differential thermal analysis and X-ray diffraction. It was shown that the three polymers varied in their original crystallinity. Attempts to totally remove this crystallinity, were unsuccessful; further crystallinity could be introduced by annealing above T_g Changes induced by annealing below T_g were not due to crystallization. Methods used to measure crystallinity in poly(vinyl chloride) (PVC) were assessed.     

Modern developments and design criteria for unmodified,modified and oriented PVC pipes

Abstract

Pipe materials technology and market needs have combined to advance developments in material savings while enhancing pipe properties. Progress in increasing PVC pipe material design stresses from 10 to 32 MPa and the corresponding reduction in wall thicknesses and safety factors are described. The concepts of strength and toughness as applied to design criteria for PVC-U, PVC-M and PVC-O pressure pipes are considered. The fulfilment of stringent requirements of modified pipes for the mining industry and other applications is described to illustrate the versatility and durability of PVC pipes.     

PVC专用注射螺杆的结构设计及参数优化

在设定了PVC专用注射螺杆的结构参数及范围后,进而采用正交试验法在Adina流体分析模块中进行了计量段塑化过程的模拟分析,通过观察熔体在计量段的压力场、剪切应力场和速度场,优选了计量段参数,并最终设计了PVC专用注射螺杆;最后对所设计的螺杆进行了三维建模。     

PVC/NE复合材料的结构流变学及力学性能

采用熔融共混法制备了聚氯乙烯/霞石复合材料(PVC/NE),并测试了其形态、结构流变学和力学性能。结果表明,NE用量存在最佳值,用量过多对复合材料介观结构的贡献不大;NE均匀分散在PVC基体中,且用量约为50phr时,复合材料的冲击强度和表面硬度最佳。     

Structural changes of PVC in PVC/LDPE melt‐blends: Effects of LDPE content and number of extrusions

This paper investigates the structural changes of polyvinyl chloride (PVC) in melt‐blends of a low‐density polyethylene (LDPE) and polyvinyl chloride (PVC), and the effects of LDPE content and number of extrusion passes. These effects were examined in terms of changes in weight average molecular weight and number average molecular weight, polyene and carbonyl indices, color changes of the blend, and the variations in glass transition and decomposition temperatures. It was found that loading LDPE into PVC led to the formation of short‐chain LDPE grafted PVC (s‐LDPE‐g‐PVC) copolymers, via a macro‐radical cross‐recombination reaction, which had greater weight average molecular weight with unchanged number average molecular weight, increased decomposition temperature, lower glass transition temperature, as compared to the pure PVC sample. The dehydrochlorination reaction of PVC was suppressed by the macro‐radical cross‐recombination reaction with addition of LDPE, the effect being more pronounced at 13.0 wt% LDPE. For a given LDPE content, the macro‐radical cross‐recombination and dehydrochlorination reactions competed with one another, thus causing the increases in molecular weight average and molecular weight number up to the 4th extrusion pass. At the 5th extrusion pass, the dehydrochlorination reaction was predominant owing to a depletion of LDPE content to be grafted onto PVC molecular chains. The glass transition and decomposition temperature decreased with increasing number of extrusion passes. Polym. Eng. Sci. 44:487–495, 2004. © 2004 Society of Plastics Engineers.     

Structural changes in partially oriented polyester yarns subjected to dry and wet heat

An examination by X-ray, birefringence, and infrared methods was carried out on partially oriented polyester yarns subjected to dry and wet heat under varying tensions that allowed shrinkage and extension processes to occur. The results can be interpreted in terms of a two-phase morphology in which one phase is a network and the other crystalline. On this basis the evidence suggests that the crystalline phase is composed of extended chains and the network of randomly folded chains with cohesion points randomly distributed between them.     

Relaxation patterns in powder injection mouldings made with repeated flow Reversals

Injection moulding suspensions based on both high and low molecular weight organic vehicles and incorporating both spherical and anisotropically shaped particles were prepared. A double end-gated rectangular bar cavity was used for injection moulding. Conventional mouldings were made by injection from one gate followed by static hold pressure. Modulated pressure mouldings were made in the same way but reciprocating flow was induced between the gates during solidification. The mouldings were sectioned, polished and heat treated whereupon a pattern of rings emerged in relief preserving the history of flow reversals as the solid-liquid interface advanced from the mould walls.     

Structural studies of oriented carbon nanotubes in alumina channels using high energy X-ray diffraction

Structural studies of multi-wall carbon nanotubes prepared by template pyrolytic carbon deposition from thermal decomposition of propylene at 800 °C inside channels of an alumina membrane have been performed using X-ray diffraction. The two-dimensional diffraction pattern of the deposited carbon nanotubes, recorded directly within the alumina template using an image plate detector, exhibits two dark arcs corresponding to the (0 0 2) graphitic reflection. The anisotropic scattering distribution indicates alignment of the nanotubes. The diffracted intensity was measured for the powdered samples after removing the alumina membrane using a point detector. A maximum scattering vector of K_max = 20 Å⁻¹ yielded the radial distribution function, providing evidence that the investigated nanotubes form a distorted hexagonal network that implies the presence of five-membered rings.     

Structural order in alkali-degraded PAN as seen in studies of low-temperature thermal conductivity

The thermal conductivity, κ, of polyacrylonitrile (PAN), subjected to varying degrees of degradation, has been measured in the temperature range 2–100 K as a means of studying the structural order of the samples. Although, at higher temperatures, the variation in κ throughout the range of specimens is only ～ 30%, at 2 K there is an order of magnitude increase in conductivity between the undegraded and most highly degraded samples. Such a change is indicative of a pronounced decrease in crystallinity, and this interpretation is supported by estimates of crystallinity as seen through X-ray analysis.     

Structural,Electrical and Optical Properties of PVC/ZnTe Nanocomposite Thin Films

Journal of Inorganic and Organometallic Polymers and Materials - ZnTe nanoparticles (NPs) were synthesized using hydrothermal method and then were dispersed in poly(vinyl-chloride) (PVC) to prepare...