Mechanical denaturation of high polymers in solutions, 34. Nucleation and growth of poly(vinyl alcohol) crystals from flowing solution

Abstract

AbstractThe nucleation and growth of the crystals of poly(vinyl alcohol) (PVA) from its solution keeping in contact with air under steady‐state flow were investigated. The nucleation was considered to occur close to the solution surface because of the adsorption of PVA molecules to the solution surface. It was ascertained by the following results. The initial fibrillar crystal appeared under the solution surface after a few seconds of stirring. From the measurement of the surface tension of PVA solutions, PVA molecules were recognized to be adsorbed to the solution surface in a very short time. The random coil of PVA molecule cannot be extended and oriented in a solution stirred under steady‐state flow with a shear rate below 5.103 s−1 applied in this experiment. This was concluded from an evaluation of the chain extension in a velocity gradient in shearing flow using the dumbbell model. The propagation of the precipitate is accelerated by turbulent flow induced by the flow of the solution itself, foams and precipitates.