Blowing agent.pptVIP

Blowing Agents Outline Introduction Polymer Foaming Blowing agent Physical blowing agent Chemical blowing agent Selection criteria for blowing agent Introduction Polymeric foam Introduction Definition The substance that produces a cellular structure in a polymer mass is defined as a blowing agent. Function The blowing agents play a very important role in both the manufactoring and performance of polymer foam Effect of blowing agent on performance of polymer foam Density Cellular microstructure Morphology of the foam Insulation Introduction During manufactoring, the choice of blowing agent and the choice of processing condition/steps are inter-linked, i.e. each drives the other. Physical foaming process The blowing agent modifies melt viscosity and thermal history, and thus rheology during foaming. Chemical foaming process Foaming and shape all happens in one step, sometime, the release of blowing agent is also involved. Physical blowing agent Physical blowing agents(PBA) provide gas for the expansion of polymers by undergoing a change in physical state. The change may involve volatilisition of a liquid, or the release of compressed gas to atmospheric pressure. Common liquid physical blowing agents are low boiling liquid and include short chain aliphatic hydrocarbons and halogenated short chain hydrocarbons. Physical blowing agent Selection criteria for blowing agent The choice of blowing agents is dependent upon the performance, cost-effectivenese and competetiviness of the finished product in a particular application. The ideal blowing agents for making insulation foam have some additional, specific requirements: low thermal conductivity and low diffusion coefficient through the foam. Halogenate hydrocarbons Halogenate hydrocarbons are one of the earlest blowing agent used to make foam. Large scale use of polymer foam was greatly accelerated by discovery and use of chlorofluorocarbons(CFC) Among Halogenate hydrocarbons, trichl