Vulkollan

These systems are dominated by the Vulkollan materials, whtch remain of importance because of their excellent load-bearing and, for a polyurethane, excellent heat-resisting characteristics. 

One inherent weakness of Vulkollan-type materials is their susceptibility to hydrolysis. Life in a humid environment may, however, be doubled by the incorporation of 2 pphr (parts per hundred resin) of a carbodiimide. 

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 ... 

However, subsequent polyesters were produced with low carboxyl values and gas evolution occurred by the reaction already mentioned when discussing the Vulkollans, that between isocyanate and water... 

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 ). 

The compression of effervescent mixtures usually results in severe picking and sticking. By means of flat-faced punches with discs of polytetrafluorethylene, the sticking to tablet-punch surfaces is overcome. Other non-adherent materials, such as Vulkollan (a polyethane), Hostalit (polyvinyl chloride), and Resopal (a melamine), have been used. The disc of the plastic material is attached to the recess of the punch surface by glue or adhesive tape. It should be noted that fragments of the polymer can rub off during compression. 

Farbenfabriken Bayer A.G., Leverkusen, Germany, "Vulkollan as an Elastic Gon-struction Material, p. 18, 1960. 

Vulkollan . [Bayer MQes] Water-CTosslinked polyurethane elastomer for punq> dUfihragms, coupling elmnents, solid tires, rollers, pump housings, seals, wipers, bushes and split secdons f[Pg.403]

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... 

A special case was always the Vulkollan elastomer system of Bayer based... 

Fig. 5.5. Manufacturing route for urethane based on unstable prepolymer systems (Vulkollan) (from Wright Gumming, 1969).

There is only one unstable prepolymer system widely used in commercial practice, namely Vulkollan from Bayer, and this will be described as representative of this class of urethane elastomers. 

Vulkollan is the trade name applicable only to polyurethanes made from polyesters, NDI and chain extenders supplied by Bayer. Materials with somewhat similar properties can be made by substituting MDI for the NDI, but they can no longer be described as Vulkollan. The Vulkollan basic system became available in the early 1950s and has since remained essentially unchanged. 

Two polyesters in particular are used in the manufacture of Vulkollan, i.e. Desmophen 2000 and Desmophen 2001 (see Table 5.13). Desmophen 2000 is a linear polyethylene adipate with an approximate molecular weight of 2000 and a low acid number, and can be considered to be the normal polyester to be used. Demophen 2001 is again a linear polyester with a similar low acid number but consists of a mixed glycol polyester. The effect of using this mixed polyester is to reduce the crystallinity and make the final product more suitable for use at lower temperatures. At normal temperatures, however, Desmophen 2001 products have slightly inferior properties to products from Desmophen 2000. 

COMPOSITION OF TYPICAL NDl/POLYESTER GRADES (VULKOLLAN) (FROM WRIGHT GUMMING, 1969)... 

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