MATS 3011 Lecture Notes - Cross-Link, Modulus Guitars, Supercooling
Document Summary
Long molecular chains are frozen in position as in a glass. Leathery or glass transition region: this region is within a deltat =~ 20 oc of tg. Rubbery plateau: the material is both viscous and elastic (viscoelastic). At a molecular level, chains can move & rotate easily but not quite independent of each other. @ very high t, have viscous liquid: modulus decreases dramatically; chain can rotate and molecules can freely move & independently of each other. Make it more rigid by putting cross links btwn changes (similar effect as decreasing t) Sulfur compounds are added in most vulcanisation process. Chains of sulfur atoms bond with adjacent polymer backbone chain & as a result, they cross link them. Key idea behind vulcanisation: link polymer chains w/ strong covalent bonds. -> as a result, modulus of elasticity goes up. -> also, tensile strength of a material goes up & resistance to degradation also goes up.
