Gelation and fusion mechanism of PVC plastisols observed by changes of morphology, viscoelastic properties, and ultimate mechanical properties

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Abstract
A PVC plastisol is a suspension of fine particles of poly(viny1chloride) in a plasticizer [1]. The particle size varies typically in the range from 15 to 0.2 um, but it may contain larger and smaller particles also. The sizes in the order of 1 urn and smaller are the primary particles produced by polymerization. The larger ones are agglomerates of the primary particles resulting from the spray-drying and grinding [2]. The applications of plastisols are coatings, films, sheets, foams and rotational castings, where the plastisol is spread on the substrates, and heated to gel and fuse. In the gelation stage the plasticizer diffuses into resin particles and swells the polymer. The “gel point” is defined as a tempera-ture, at which the plastisol film loses tackiness and it is about 75°C. Another definition is the temperature where the film acquires enough cohesiveness to be pulled away from the hot plate without tearing. This occurs at about 80-85°C. However, the material has not attained the intrinsic mechanical strength of the plasticized PVC. The optimum tensile strength is achieved by heating to 175°C or above. This stage is called fusion.