Phenol/formaldehyde curing agent

Phenolic Resins. Phenohc resins (qv) are formed by the reaction of phenol [108-95-2] C H O, and formaldehyde [50-00-0] CH2O. If basic conditions and an excess of formaldehyde are used, the result is a resole phenohc resin, which will cure by itself Hberating water. If an acid catalyst and an excess of phenol are used, the result is a novolac phenohc resin, which is not self-curing. Novolac phenohc resins are typically formulated to contain a curing agent which is most often a material known as hexamethylenetetraamine [100-97-0] C H22N4. Phenohc resin adhesives are found in film or solution... 

The most common crosslinking agent for novolac resins is HMTA which provides a source of formaldehyde. Novolac resins prepared from a phenol-formaldehyde (F/P) ratio of 1/0.8 can be cured with 8-15 wt % HMTA, although it has been reported that 9-10 wt % results in networks with the best overall performance.3... 

Coreactants, in microencapsulation, 16 444 Coreactive curing agents, 10 388-389, 392-411, 418. See also Curing agents amine functional, 10 392 401 carboxylic functional polyester and anhydride, 10 401—406 cyanate ester, 10 411 cyclic amidine, 10 410 isocyanate, 10 410 melamine-, urea-, and phenol-formaldehyde resins,... 

Chlorinated rubber is also an effective bonding agent. It can be used for bonding neoprene, nitrile and natural rubbers to metals. Phenol formaldehyde resins have been used alone or in conjunction with chlorinated rubbers, but curing time is lengthy. 

TG-MS is an ideal technique for identifying residual volatiles in polymers. The detection of residual volatiles (and of other impurities) can often yield clues as to manufacturing processes. In many cases, such as in the determination of highly volatile materials, of residual solvents or plasticisers, use of TG-MS is requested. Specifically, there are reports on the entrapment of curing volatiles in bismaleimide laminates [145] and elastomers [48], on the detection of a curing agent (dicumylperoxide) in EPDM rubbers and of bromine flame retardants in electronic waste [50], of plasticisers such as bambuterol hydrochloride [142] or TPP and diethylterephthalate in cellulose acetate [143], on solvent extraction and formaldehyde loss in phenolic resins [164], and on the evolution of toxic compounds from PVC and polyurethane foams [146]. 

Polysulfone A number of adhesives have been found useful for joining polysufone to itself or to other materials. These include 3M Company s EC 880 solvent-base adhesive, EC 2216 room-temperaturecuring epoxy two-part paste, Bloomingdale Division, American Cyana-mid Company BR-92 modified epoxy with DICY curing agent, or curing agent "Z" (both spreadable pastes), vinyl-phenolics, epoxy-nylons, epoxies, polyimide, rubber-based adhesives, styrene polyesters, resorcinol-formaldehyde, polyurethanes, and cyanoacrylates. The EC 880, EC 2216, and the two BR-92 adhesives are recommended by the polysulfone manufacturer. Union Carbide (16) (17). 

Phenolic resins continue to be an important material at both the commercial and the research levels. These complex systems are fascinating not only because of their current usefulness, but also because of their potential to become even more useful materials of the future. The classical phenol-formaldehyde system is deceptively simple and lends itself to much variation depending on factors such as pH, molar ratio of reactants, preparation/cure temperature, and curing agents. The desire to enhance the properties of phenolic resins and expand the processing options has led to considerable work on modified-classical and nonclassi-cal phenolic resins. 

These resins (Resole or Novolac) are used as curing agents or hardeners for epoxy molding compounds for electronics applications such as computer components. 0-cresol-formaldehyde resins have heen also used to modify phenol-formaldehyde resins, and in laminates. 

The novolac resins are prepared by using acidic catalysts and a deficiency of formaldehyde. Because this type of resin is less reactive, cross-linking is accomplished by the addition of a curing agent or catalyst. The most common is hexamethylenetetramine or "hexa." The curing agent serves as a latent source of formaldehyde. As in the case of the resoles, volatiles are emitted during the cure. The chemistry of the phenolic resin is old but complex and well documented in the literature (10). 

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