A study of the variables affecting bubble stability in poly (vinyl chloride) plastisols

Abstract

AbstractThe formation of stable air bubbles during processing is one of the most critical problems encountered in many PVC plastisol applications (often referred to as the “air release problem”). Stable bubbles can lead to both cosmetic and structural defects in finished products. Analysis of the air release problem has been difficult not only because air release is affected by many variables (some of which are interrelated), but also because no air release test has been universally accepted as being reliable. This paper presents a comparison of some of the more commonly used air release tests of the PVC plastisol industry, i.e., the Huff ring test, air injection by syringe, and air entrapment by stirring. Our investigation indicates that results obtained from these air release tests strongly depend upon test procedure, test environment, plastisol age, and even the amount of plastisol in the test container. Among the test methods which were examined, air entrapment by stirring was found to be the most convenient and reliable. Possible causes for the observed discrepancies among the tests and data scatter within each test are discussed in terms of variables which affect bubble stability, such as bubble size, rheology, film stress distribution, surface tension, and the Marangoni effect.