The Use of Additives in Foamable Compositions

摘要

The foaming process, which distributes a gas into a polymer, is truly dynamic. A low viscosity solution of a gas in a polymer goes to rigid or flexible foam with closed or open cell structure in a few seconds. Temperature, pressure, solubility, viscosity, melt elastacticicety, melt extensibility, and density all change in a controlled fashion to give the foam products of modem commerce. Blowing agents provide the gas that expands to form the foam cells while nucleating agents help control that cell structure. Temperature and pressure govern the blowing expansion amount and rate. The type of gas controls much of the process because of condensability, solvent properties, and heat capacity. Some of the details relating to these processes are reviewed with emphasis on the close ties between the chemical additives and the mechanical processing conditions. The second foam making process by removal of a solid from a polymer while not as common as the process of adding a gas does have several interesting applications ranging from electronic insulation to household sponges.