Processing, structure and properties of plasticized PVC
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.