Лако-красочные материалы — производство

Different mechanisms of alkaline catalysis have been suggested according to the alkali used. When caustic soda is used as the catalyst, the type of mechanism which seems the most likely is that which involves the formation of a chelate ring similar to that suggested by Caesar and Sachanen [7]. The chelating mechanism was thought to […]

Consideration must be given to the possibility of direct intervention by the catalyst in the reaction. Hydrochloric acid is the most interesting case of an acid catalyst, as is ammonia of an alkaline catalyst. When the PF reaction is catalyzed by hydrochloric acid, two mechanisms may come into operation. Vorozhtov has proposed a reaction route […]

Phenols condense initially with formaldehyde in the presence of either acid or alkali to form a methylolphenol or phenolic alcohol, and then dimethylolphenol. The initial attack may be at the 2-, 4-, or 6-position. The second stage of the reaction involves methylol groups with other available phenol or methylolphenol, leading first to the formation of […]

A. Pizzi Ecole Nationale Superieure des Technologies et Industries du Bois, Universite de Nancy I, Epinal, France I. INTRODUCTION Phenolic resins are the polycondensation products of the reaction of phenol with formal­dehyde. Phenolic resins were the first true synthetic polymers to be developed commer­cially. Notwithstanding this, even now their structure is far from completely clear, […]

Interfacial aspects and adhesion of polysulfides have been studied extensively and reported by us [3,17]. The epoxy-modified polysulfide has improved adhesion due to chemical reactions that increase electronic attraction forces. Water has been found to be the most potent debonding agent in cured polysulfides. Formation of thiourethane is responsible for excellent adhesion of polysulfide onto […]

Fettes and Gannon were the first to report reactions of liquid polysulfide polymers with epoxy resins [16]. In these adhesives, the epoxy resin is the major component. The polymer LP-3 in which n = 8 has been used most extensively. This polymer has a molecular weight of about 1000 with viscosity in the range 7 […]

Typical examples of physical, rheological, and mechanical characterization of sealants include specific gravity, percent solid, viscosity, flow, application time, working life, tack-free time, standard curing rate, liquid-immersed curing rate, resistance to rupture, low-temperature flexibility, peel strength, resistance to solvents, tensile strength, elongation modulus, chalking, accelerated storage stability, and hydrolytic stability. Usmani has proposed the use […]

The polysulfide sealant must be specifically formulated to meet the desired requirements and to obtain optimum properties. Pot life, working properties, and sealant properties should be properly adjusted. Suitable fillers should be dispersed and suitable additives should be incorporated into the formulation. Curing agent, curing modifier, filler, plasti­cizer, and adhesion additive are discussed briefly below. […]

This polymer does not contain S-S or forrmal linkages, and these are the weak links in conventional polysulfides. The polythioether polymer has excellent resistance to fuel and organic solvents and has better thermal stability than that of conventional polysulfides. Polythioethers can be terminated with mercaptan, hydroxyl, silyl, and nonreactive end groups. The curing chemistry can […]

In the 1960s Diamond Alkali marketed several polymers having a polyether backbone terminated with mercaptan groups [5,6]. Polymers of poly(oxyalkalene)polyol backbone can be esterified with thio-substituted organic acids to produce terminal mercaptan end groups. These polymers were cured similarly to conventional polysulfides, but gave gen­erally poorer properties and were therefore withdrawn from the market. In […]