Synthetic rubbers (elastomers) are long-chain polymers with special chemical and physical as well as mechanical properties. These materials have chemical stability, high abrasion resistance, strength, and good dimensional stability. Many of these properties are imparted to theoriginal polymer through crosslinking agents and additives. Selected properties of some elastomers are shown in Table 1.
An important property of elastomeric materials is their ability to be stretched at least twice their original length and to return back to nearly their original length when released. Natural rubber is an elastomer constituted of isoprene units. These units are linked in a cis-1,4configuration that gives natural rubber the outstanding properties of high resilience and strength. Natural rubber occurs as a latex (water emulsion) and is obtained from Hevea brasiliens is, a tree that grows in Malaysia, Indonesia, and Brazil.
Charles Goodyear (1839) was the first to discover that the latex could be vulcanized (crosslinked) by heating with sulfur or other agents Vulcanization of rubber is a chemical reaction by which elastomer chains are linked together. The long chain molecules impart elasticity, and the crosslinks give load supporting strength. Vulcanization of rubber has been reviewed by Hertz, Jr.35 Synthetic rubbers include elastomers that could be crosslinked such as polybutadiene, polyisoprene, and ethylene-propylene-diene terepolymer.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
الرجوع الى لوحة التحكم
|