高分子材料加工技术专业英语 Plastics Materials and Additives 09 Elastomers.ppt

Elastomers MFG 355 Elastomeric Materials Highly amorphous Highly random orientation High elongation Elastomeric Materials Elastomeric Materials Elastomeric Materials Elastomer Processing Aliphatic Thermoset Elastomers These are the most common elastomers These have a double bond after polymerization has occurred These are noncrystalline These are highly flexible Natural Rubber Natural Rubber Raw material extracted from trees Natural Rubber Material is processed Natural Rubber Latex is then dried, sorted and smoked Natural Rubber The difficulties with natural rubber Strength Availability Bacterial breakdown Creep Natural Rubber Creep Solved by Goodyear in the 1800s Discovered that the polymer could be crosslinked (cured or vulcanized) by heating with sulphur Synthetic Polyisoprene or Isoprene Rubber Need Supply of natural rubber disrupted during WWI and WWII Used in tires for bicycles and early cars Used the Ziegler-Natta catalyst system to improve properties The trans- or cis- nature of the rubber could be controlled up to 90% in either direction Butadiene Rubber (BR) Butadiene Rubber (BR) No cis or trans isomers Lower mechanical strength because of no of pendant methyl group but also more flexibility Lower cost (all synthetic from cheap monomer) Improvement of low-temp flexibility Compatibility with other polymer materials Styrene Butadiene Rubber (SBR) Oil-Resistant Elastomers NBR—Nitrile Butadiene Rubber Copolymerization of butadiene and acrylonitrile More expensive than SBR or BR CR—Chloroprene rubber (neoprene) Thermal stability Non-flammable Thermoplastic Elastomers (EPM and EPDM) Many of the properties of thermoset elastomers Resiliency Elasticity More easily processed Injection molding, extrusion and other standard thermoplastic processes Highly compatible with polyolefins EPDM is crosslinked very lightly and may not be capable of being melted Thermoplastic Olefin Elastomers (TPO) Block tripolymers (such as SBS) with hard and soft domains Poor compatibilit