Archive for the ‘synthetic rubber’ Category
Synthetic Polyisoprene Rubbers (IR)
Trade Name : Natsyn (Goodyear Tire and Rubber Co.), Shell Isoprene Rubber (Shell international Chemical Co.)
Chemistry : IR is synthetic natural rubber that is cis-1,4 polyisoprene. It doesn’t contain the nonrubber substances that are present in NR. The different between two basic types of synthetic polyisoprene depend on the polymerization catalyst system used and are commonly referred to as “high” cis and “low” cis types.
The high cis grades contain approximately 97% cis-1,4 polyisoprene. Because of the high degree of stereoregularity, they are able to crystallize on stretching like NR. Consequently, they can be compounded without fillers, giving tensile strength nearly as high as that of unfilled NR vulcanizates.
The low cis grades contain about 93% cis-1,4 polyisoprene. They have limited use because the physical properties of their vulcanizates are inferior to those of high cis types.
Compounding : Synthetic IR can be compounded using the same ingredients used for NR and it can be blended with other diene rubbers such as NR, SBR and BR.
Applications :Synthetic IR can be used alone or in blends with NR in the manufacture of most products where NR is the traditional choice.
Synthetic Rubber (SR)
For over a century, all rubber goods were manufactured from natural crude rubber which is generated in the rubber tree as a milky liquid known as natural latex. The latter is coagulated and the solid material separated washed and dried to obtain a solid natural crude rubber. After that synthetic crude rubbers were developed and became available in commercial quantities. It’s prepare by reacting certain low molecular weight substances called monomers to form long-chain molecules called polymers that usually obtained and a water emulsion known as synthetic latex, which is similarly coagulated and the solid material separated, washed and dried to obtain solid synthetic crude rubbers.
SR is chemically similar to Natural Rubber (NR) in that they contain olefinic double bonds and could be vulcanized by means of sulphur. These material are obtained through homo or copolymerization of conjugated dienes. In addition mono-olefins and other monomers were increasingly used for the synthesis of saturated polymers which can be crosslinked through reactions other than those involving sulphur. These types of SR can be produced by vinyl polymerization by polycondenzation as well as by polyaddition reactions. Rubbers produced from diene monomers are the most important and widely used ones, whereas saturated rubber constitute as a rule specialty products. By now, the number of SR types offered by the chemical industry to the user has grown very large so that it has become useful to classify the different grades of SR.
Depend on the method used for synthesis one distinguishes chain addition polymerization polycondenzation and polyaddition products.
The polymerization of monomers of the same kind results in homopolymers while that of different monomers produces copolymers. Those copolymers obtained from three different monomers are referred to as terpolymers. The so-called diene rubbers are produced by the homo or copolymerization of conjugated diolefins alone or in combination with olefins so that the polymer chain retains unsaturation which allows vulcanization with sulphur analogous to NR.
By polymerizing simple unsaturated monomers (mono-olefins) and by the polycondensation or polyaddition of saturated components, one obtains fully saturated polymers which cannot be crosslinked with sulphur. By far the greatest number of these polymers are plastics. Howerver, using special methods they can also be loosely crosslinked so that treir physical state can be modified similar to that of diene rubbers through sulphur vulcanization. Thus, these polymers can be used as precursors for producing elastomers.
The different types of rubbers are classified according to ISO R1629 or ASTM-D 1418. Some commercially SR such as butadiene rubber (BR), chloroprene rubber (CR), isobutylene isoprene rubber (IIR), isoprene rubber (IR,synthetic), isoprene rubber (NR, natural rubber), styrene butadiene rubber (SBR).