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The extensive use of Poly(vinyl chloride) (PVC) is partly due to the modification of properties which is possible by the addition of plasticizer. Although plasticized PVC is used at temperatures well above Tg, the properties are favourable and the material has a rubberlike behaviour. This is generally considered to be due to the presence of a physical network consisting of small crystallites. However, its service range is limited by its thermoplastic nature. At temperatures above 100 C it has a tendency to flow and to have a reduced mechanical strength. One way to increase the maximum temperature of plasticized PVC is to introduce a permanent chemical network. The reaction of plasticized PVC with [N-(2-amino ethyl)-3-aminopropyl trimethoxy silane] yielded si lane-grafted PVC that was crosslinked by a hydrolitic mechanism. The grafting of the aminosilane was carried out during processing in both a roll mill followed by compression moulding and in a single screw extruder. A controlled reaction was observed when a tin stabilizer was selected. It was found that other thermal stabilizers accelerate the grafting reaction, but destabilize the polymer. The crosslinking of the grafted PVC has been studied in water at different temperatures. The crosslinking occurred faster at high temperatures and was diffusion controlled.....

Plasticised polyvinyl chloride (PPVC) compounds were biaxially stretched, annealed in the drawn state and subsequently exposed to electron beam irradiation. During sample irradiation the crosslinking reaction was promoted by a radiation sensitising monomer, trimethylolpropanetrimethacrylate (TMPTMA), included in the PVC compound formulations. The influence of stabiliser type and level, TMPTMA level and irradiation dose on the network structure produced was investigated. A tin stabiliser, Stanclere TL, was selected for this study as it promoted the crosslinking reaction and it showed no interfering peaks in the wide angle x-ray diffraction (WAXD) traces which were used to follow the development of structural order. The appearance of gel, the material insoluble in THF, in irradiated oriented samples proved that a crosslinked structure was created. The gel formation increased with TMPTMA level and irradiation dose. The gel content was found to affect mechanical properties at elevated temperatures and produced an increase in the area shrinkage temperature. Sample thickness and the plasticiser content were found to have a major effect upon gel formation. The thicker the sample was, the smaller the quantity of gel that was formed. Samples containing 46.5phr plasticiser showed greater gel content than samples containing 25phr plasticiser as a result of the higher molecular mobility in the more plasticised samples. It was also found that the orientation of the film decreased the efficiency of network formation in PVC formulations with a 46.5phr plasticiser content but no significant change in gel content could be detected in those containing 25phr plasticiser. Tensile properties and impact strength at room temperature were slightly improved in irradiated samples. The modified structure resulted in an improvement in tensile strength and penetration resistance at higher temperatures and an increased area shrinkage temperature. Crosslinking did not affect room temperature recovery or crystalline orientation; however irradiation crosslinking reduced crystallinity.

The fusion and rheologica1 behaviour of PVC compounds play a dominant role in the processing operations and in the development of physical properties in the processed material. These phenomena are governed by the complex morphological structure of PVC resin, compound composition and processing-conditions which in turn affect the physical properties of the final product. The fusion process of flexible PVC compounds was investigated by a combination of several techniques. Samples with varying states of fusion were prepared using shear-and temperature as the processing variables in extrusion, Brabender Plastograph and compression moulding. The degree of fusion of processed compounds was characterized by rheology, thermal analysis, acetone test, optical microscopy, tensile strength and extrudate appearance. The formulation of a PVC compound has a strong influence on the rheological properties of the melt. Hence several plasticizers were chosen from a wide activity range and compounded at three plasticizer concentrations of 30, 50 and 70 phr. These compounds were processed at five different temperatures (150-20QOC) in a Banbury mixer. They were further processed in an extruder or on a two-roll mill followed by compression moulding. In assessing the state of fusion a universal method was found which could define the fusion state adequately for a given PVC sample wbich had undergone any processing condition. Rheometer studies were found useful in assessing state of fusion of samples from specific formulation and processing conditions with processing temperature as the variable. Differential scanning calorimetry results showed that more understanding was needed to interpret the results. However, it proved to be a versatile method in determining the maximum temperature a sample would have reached, irrespective of its formulation or processing history. Higher speed mixing data proved to be useful commercially since increased plasticizer concentration gave decreased blending times. Davenport extrusion pressure, tensile properties, morphology and extrudate surface texture showed significant differences between' plasticizers. An identical trend for ease of smooth extrudate formation and its glossy texture was observed.