Accelerator for curing

A new process to develop interface vulcanization is grafting of selective accelerators onto a polymer chain, which in the subsequent process of vulcanization acts as an effective cure accelerator for the second polymer component in the blend. Beniska et al. [6] prepared SERFS blends where the polystyrene phase was grafted with the accelerator for curing SBR. Improved hardness, tensile strength, and abrasion resistance were obtained. Blends containing modified polystyrene and rw-1,4-polybutadiene showed similar characteristics as SBS triblock copolymers. 

Use Corrosion inhibitor, anthelmintic, insecticide, accelerator for curing polychloroprene. 

Accelerator. [Akzo] Cobalt octoate mixtures accelerators for cure of unsat. polyester resins at R.T. and elevated temps. 

Application of diallyl terephthalate as an accelerator for curing fluorinated polymers such as a terpolymer of tetrafluoroethylene, vinylidene fluoride, and perfluoropropylene [123]. 

Humphreys, of the Loctite Corporation, reported on the chemistry of accelerators for curing anaerobic adhesives. He showed that the reaction between N,N-dimethylaniline derivatives and cumene hydroperoxide is relatively slow even at lOO C. He concluded that the accelerated polymerization of anaerobic adhesives of ambient temperatures caused by cure systems containing combinations of tertiary aromatic amines, hydroperoxides, and sulfonimides does not result from the hydroperoxide-amine reaction. 

Chemistry of Accelerators for Curing Anaerobic Adhesives-Reaction of N, N-Dimethylaniline Derivatives with Cumene Hydroperoxide... 

ZImate n. Trade name of the R. T. Vanderbilt Co., for a group of diallyl dithiocarbama-tes, useful as accelerators for curing rubber. 

MBT is used as both a primary (when used alone) and secondary accelerator (in combination with other accelerators) for curing compounds based on general-purpose elastomers. It is a very potent vulcanization accelerator, giving a very fast rate of crosslinking. Unfortunately, its scorch delay is quite poor. For this reason the sulfenamide accelerators, derived from MBT, were developed. 

When the surface conditions are acidic or the ambient humidity is low enough to affect the cure significantly, a surface accelerator may be used to promote the reaction. Available from most manufacturers, these basic solutions may be dip, wipe, or spray appHed. Recentiy, new additive chemistry has been developed that accelerates the cure under adverse conditions without the need for a separate accelerator. 

A unique process for chemical stabili2ation of a ceUular elastomer upon extmsion has been shown for ethylene—propylene mbber the expanded mbber obtained by extmsion is exposed to high energy radiation to cross-link or vulcani2e the mbber and give dimensional stabUity (9). EPDM is also made continuously through extmsion and a combination of hot air and microwaves or radio frequency waves which both activate the blow and accelerate the cure. 

Eor apphcation temperatures below 10°C or for acceleration of cure rates at room temperature, nonredox systems such as ben2oyl peroxide initiated by tertiary amines such as dimethylaruline (DMA) have been appHed widely. Even more efficient cures can be achieved using dimethyl- -toluidine (DMPT), whereas moderated cures can be achieved with diethylaruline (DEA). 

The recovery of sand from foundry molds and cores is much easier when binders made water soluble by use of sodium alumiaate are used ia place of iasoluble resin binders (35,36). Sodium alumiaate acts as a setting accelerator for Portiand cement (qv) (37). In similar appHcation, addition to concrete provides a longer gel time before fully curing (38). 

Other Accelerators. Amine isophthalate and thiazolidine thione, which are used as alternatives to thioureas for cross-linking polychloroprene (Neoprene) and other chlorine-containing polymers, are also used as accelerators. A few free amines are used as accelerators of sulfur vulcanization these have high molecular weight to minimize volatility and workplace exposure. Several amines and amine salts are used to speed up the dimercapto thiadiazole cure of chlorinated polyethylene and polyacrylates. Phosphonium salts are used as accelerators for the bisphenol cure of fluorocarbon mbbers. 

A study of the effect of stearic acid and 2iac oxide on a sulfonamide-accelerated, sulfiir-cured natural mbber compound dramatically showed the need for both 2iac and fatty acid activators (Fig. 7) (21). 

The earliest study describing vulcanised polymers of esters of acryUc acid was carried out in Germany by Rohm (2) before World War I. The first commercial acryUc elastomers were produced in the United States in the 1940s (3—5). They were homopolymers and copolymers of ethyl acrylate and other alkyl acrylates, with a preference for poly(ethyl acrylate) [9003-32-17, due to its superior balance of properties. The main drawback of these products was the vulcanisation. The fully saturated chemical stmcture of the polymeric backbone in fact is inactive toward the classical accelerators and curing systems. As a consequence they requited the use of aggressive and not versatile compounds such as strong bases, eg, sodium metasiUcate pentahydrate. To overcome this limitation, monomers containing a reactive moiety were incorporated in the polymer backbone by copolymerisation with the usual alkyl acrylates. 

More frequently either methyl ethyl ketone peroxide or cyclohexanone peroxide is used for room temperature curing in conjunction with a cobalt compound such as a naphthenate, octoate or other organic solvent-soluble soap. The peroxides (strictly speaking polymerisation initiators) are referred to as catalysts and the cobalt compound as an accelerator . Other curing systems have been devised but are seldom used. 

The Goodyear vulcanization process takes hours or even days to be produced. Accelerators can be added to reduce the vulcanization time. Accelerators are derived from aniline and other amines, and the most efficient are the mercaptoben-zothiazoles, guanidines, dithiocarbamates, and thiurams (Fig. 32). Sulphenamides can also be used as accelerators for rubber vulcanization. A major change in the sulphur vulcanization was the substitution of lead oxide by zinc oxide. Zinc oxide is an activator of the accelerator system, and the amount generally added in rubber formulations is 3 to 5 phr. Fatty acids (mainly stearic acid) are also added to avoid low curing rates. Today, the cross-linking of any unsaturated rubber can be accomplished in minutes by heating rubber with sulphur, zinc oxide, a fatty acid and the appropriate accelerator. 

The unblocking temperature usually refers to the temperature at which the blocked urethane system must be heated for 30 min in order to achieve cure. The reaction can be accelerated by curing at higher temperatures and/or by the addition of catalyst, as shown in Fig. 6 [62]. Common urethane catalysts like dibutyltin dilaurate are known to decrease the unblocking temperature. 

Recently, a two-part cross-catalyzed system has been developed that takes advantage of both the acceleration abilities of resorcinol resin and ester [179], The term cross-catalyzed is applied because the phenolic resin contains an accelerator-crosslinker for the resorcinol resin while the resorcinol resin carries an accelerator for the PF, in addition to itself being capable of improving PF cure speed. In each part, the resin carrier for the accelerator is not susceptible to acceleration by the material contained. It is only when the systems are mixed that the accelerators are activated. This system is faster and lower in cost than most of the resorcinol accelerators and gives better bonds (in wood products) than the ester cure alone [179], Another variant of the resorcinol approach utilizes resorcinol-glutaraldehyde resins [180-182],... 

For most electron-curable adhesives, a dose of 100 kGy is required to cure. Fig. 4 shows the speed of curing various widths of material as a function of accelerator power. A reasonably controllable speed for moving parts through an accelerator would be approximately 10 m per minute. Based on this criterion, the lower wattage limit for an accelerator curing an adhesive strip 5 cm wide would be 5 kW. For curing very large parts a 50 kW accelerator would be more suitable. 

---