The Development of Silicone Sponge by using a Non-Toxic Blowing Agent

Abstract

Silicone sponges are silicone rubber with cell structure and are produced by adding a chemical blowing agent to the formulation. The main blowing agents used are 2,2-azobisisobutyronitrile, azodicarbomide (ADCA) and dinitrosopentamethylenetetramine (DPT) but all are producing toxic by-products. The silicone industry is looking for non-toxic blowing agent. Primasil has already a formulation to produce sponges but the properties of their sponges and the consistence of its cell structure are limited by different factors such as the conditions of the cure and the type of blowing agent which is baking powder. Primasil sponges have a high density, small shape, and open-cells and non-uniform structure. The aim of this project was to develop and to implement a suitable process for the manufacture of closed-cell sponge formed silicone rubber through the identification and validation of a suitable non-toxic blowing agent; to establish a curing process compatible with the chosen blowing agent; to define a formulation for a range of grades of silicone rubber and finally to apply the formulation, blowing agent and curing process to the production for commercial sales. A literature research and some observations were done on the Primasil formulation, on the suppliers of sponges and on the current blowing agents sold. The elimination of blowing agents and methods of processing before conducting some trials was based on several parameters: safety of operators, protection of the environment and properties of blowing agent. From there, different blowing agents were tried with two established methods (c.f. part 9) in order to produce some silicone sponges by utilising a non-toxic chemical. First, efforts were focused on acquiring a new formulation and a suitable process for it. When formulations and process were defined, the work was concentrated on the properties of the product such as density, cell structure, compression set, elongation, tear and strength. From this project, more investigation will be suggested in order to achieve the goals requested at the beginning of this TCS program.