Vulkollan rubber

Polyurethanes (PUs) are a family of condensation polymers that include the urethane (-NHCOO-) group in the chemical structure (Figure 5.1). The history of PUs started in 1937 when Dr Otto Bayer of Bayer Germany invented the diisocyanate polyaddition process. The early applications of PUs were mainly on soft foams and nonsegmented semicrystalline fibers. The lack of rubber materials during WWII has led to the intensive development of PU elastomers. In 1950, Bayer launched the first PU elastomer product, Vulkollan rubbers. Since then, PU elastomers have been used extensively, particular in medical, textile, automobile, and architecture industries [1-3]. 

Liquid rubber technology has largely stemmed from the development of the polyurethanes. These materials were first produced in the 1930s in fibre form in an attempt to circumvent the Du Pont patents on the nylons. During World War II this led on to the solid Vulkollan rubbers and subsequently to the rigid and flexible foams. Modern processes can be adapted for such disparate products as car tyres, car body parts and soft, printers rollers. Such technology owes little to the traditional methods of the rubber industry. 

In the case of the Vulkollan rubbers the hardness is adjusted by varying the ratio of two polyesters, one polyethylene adipate and the other a polyethylene/propylene adipate copolymer and/or by varying the amount of diol or by use of some trifunctional hydroxy compound such as trimethylol propane in part replacement of the diol. 

Some typical properties of a Vulkollan-type polyurethane cast rubber and a black-reinforced polyurethane rubber processed by conventional techniques are compared with black-reinforced natural and nitrile rubbers in Table 27.2 ... 

RUBBER (Synthetic). Any of a group of manufactured elastomers that approximate one or more of the properties of natural rubber. Some of these aie sodium polysulfide ( Thiokol ). polychloiopiene (neoprene), butadiene-styrene copolymers (SBR), acrylonitrilebutadiene copolymers (nitril rubber), ethvlenepropylene-diene (EPDM) rubbers, synthetic poly-isoprene ( Coral, Natsyn ), butyl rubber (copolymer of isobutylene and isoprene), polyacrylonitrile ( Hycar ). silicone (polysiloranei. epichlorohy-drin, polyurethane ( Vulkollan ). 

Vulkollan-type rubbers suffer from the disadvantage that the prepolymers are unstable and must be used within a day or two of their production. Moreover, these rubbers cannot be processed with conventional rubber machiners, so the products are usually made by a casting process. Attempts were then made to develop other polyurethane rubbers which could be processed by conventional techniques. 

Polyurethane rubbers, in general, and the Vulkollan-type rubbers, in particular, possess certain outstanding properties. They usually have higher tensile strengths than other rubbers and possess excellent tear and abrasion resistance. The urethane rubbers show excellent resistance to ozone and oxygen (in contrast to diene rubbers) and to aliphatic hydrocarbons. However, they swell in aromatic hydrocarbons and undergo hydrolytic decomposition with acids, alkalis, and prolonged action of water and steam. 

Rubber, Vulkollan (German) a 0 631-1943 Silicone (Polydimethylsilanediol) (Series Of Additives) a e h n 631-2722... 

Rubbers, foams, coatings e.g., Vulkollan, Adiprene C, Chemigum SL, Desmophen A, Moltopren. 

In spite of the processing limitations imposed by the use of unstable prepolymers this group of casting processes, particularly that used for making Vulkollan, remains important because of the good mechanical properties exhibited by the cross-linked rubber. 

In many respects the chemistry of flexible urethane foam manufacture is similar to that of the Vulkollan-type rubbers except that gas evolution reactions are allowed to occur concurrently with chain extension and cross linking (see Figure 1.30). Most flexible foams are made from 80/20 TDl, which refers to the ratio of the isomeric 2,4-tolylendiisocyanate to 2,6-tolylendiisocyanate. Isocyanates for HR foams are about 80% 80/20 TDI and 20% PMDI, and those for semiflexible foams are usually 100% PMDI. 

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