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Natural and Synthetic Rubber :, Heating, Cross linking, Optimum state of…
Natural and Synthetic Rubber
:
1. Introduction
1.3 Thermoset Elastomer
Crosslinked Rubber
Hard & non-sticky Undergo vulcanization to become permanently insoluble and infisble
1.4 Thermoplastic Elastomer
Do not required cross-linking
2, Rubbery materials that combine the chractheristics of rubber with the recycleability and processing advantages of plastics
1.2 Rubber
The original name given to latex
Rubber is originated from 'rub away'
1.1 Elastomer
Derived from elastic polymer
Displays elestic properties
Rubbery materials
2. Natural rubber and latex
Natural rubber is an elastic hydrocarbon polymer that naturally occurs as milky colloidol suspension (latex) in the sap of the rubber tree (hevea brasilensis)
2.1 Natural Rubber (NR) Latex
Located in latex vessels to be founded in various parts of the tree
Colloid system having the rubber particles dispersed in water
Contains small amounts of proteins, resinous matters (ins, lipids), hydrocarbos and materials substances
2,2 NR Latex
The latex modified for these reasons to have higher dry rubber content, DRC Values (60-65% of rubber)
Modification methods: centrifugation, sedimentation, water evaporation thickening and electrodecantation
Example: foam rubber, gloves, condoms, glues (produced directly from latex)
2.3 Recovering rubber from latex
Involves coagulation, coagulation takes about 12 hours
The coagulum (soft solid slabs) then squeezed through a series of rolls which drive out most of water and thickness to about days
the sheets are then draped over wooden frames and dried in smokehouses for several days
3. Natural Rubber Harvesting And Processing (Vulcanisation Process)
3.1 Definition
Aprocess of coverting natural rubber to more strong and elastic form
it was discovered by Charles Goodyear,a U.S. inventor in the 19th century, which is in 1839
The process involves chemical procedure wherein rubber is blended with activators, accelerator and sulphur (S) at 250 F -400F
3.2 Steps in vulcanisation process
Preparation
Heating
Cross linking
Optimum state of curve
Shaping