Crystalline Curing

Heat of solution, adsorption, or desorption Specific heat, activation energy, polymer crystallinity, curing time... 

These are water-soluble crystalline compounds sold as concentrated aqueous solutions. The methylol groups are highly reactive (118—122) and capable of being cured on the fabric by reaction with ammonia or amino compounds to form durable cross-linked finishes, probably having phosphine oxide stmctures after post-oxidizing. This finishing process, as developed by Albright Wilson, is known as the Proban process. 

Benzil. Ben il [134-81-6] (diphenylethanedione) is a yellow soHd that crystallines from alcohol in hexagonal prisms. Ben nil can be prepared by the oxidation of bennoin [579-44-2] (2-hydroxy-2-phenylacetophenone) (298,299), which is itself prepared by the self-condensation of bennaldehyde (300). Ben nil is commercially produced in Japan and is used as a uv resin curing sensitizer (301). It has also been suggested as a chigger repeUant (302). 

The processing of hides and skins into leather results in a large quantity of waste materials (9). The hide in the salt-cured condition contains salt in a crystalline form, water as salt solution, and as hide Hquid components, flesh, blood, manure, and surface dirt from the animal. 

The pseudocross-links, generated by the hard-segment interactions, are reversed by heating or dissolution. Without the domain crystallinity, thermoplastic polyurethanes would lack elastic character and be more gum-like in nature. In view of the outlined morphology, it is not surprising that many products develop their ultimate properties only on curing at elevated temperature, which allows the soft- and hard-phase segments to separate. 

Properties. The outstanding characteristic of melamine, usually a white crystalline matrial, is its insolubiUty in most organic solvents. This property is also evident in melamine resins after they are cured. On the other hand, melamine is appreciably soluble in water, its solubiUty increasing with increased temperature. The properties of melamine are Hsted in Table 5. 

The prime function of the saturated acid is to space out the double bonds and thus reduce the density of cross-linking. Phthalic anhydride is most commonly used for this purpose because it provides an inflexible link and maintains the rigidity in the cured resin. It has been used in increasing proportions during the past decade since its low price enables cheaper resins to be made. The most detrimental effect of this is to reduce the heat resistance of the laminates but this is frequently unimportant. It is usually produced by catalytic oxidation of o-xylene but sometimes naphthalene and is a crystalline solid melting at 131°C. 

Meta-phenylenediamine, a crystalline solid with a melting point of about 60°C, gives cured resins with a heat distortion temperature of 150°C and very good chemical resistance. It has a pot life of six hours for a 200 g batch at room temperature whilst complete cures require cure times of four to six hours at 150°C. About 14 pts phr are used with the liquid epoxies. The main disadvantages are the need to heat the components in order to mix them, the irritating nature of the amine and persistent yellow staining that can occur on skin and clothing. The hardener finds use in the manufacture of chemical-resistant laminates. 

Crystalline polyesters are highly important as adhesive raw materials. They are normally crystalline waxes and are highly symmetrical in nature, which can aid the crystallization process [26]. Poly(hexamethylene adipate) and poly(caprolactone), shown in Table 2, are only two of the many crystallizable backbones. Poly(ethylene adipate) and poly(letramethylene adipate) are also commonly used in urethane adhesives. The crystalline polyesters are used in curing hot melts, waterborne polyurethanes, thermoplastic polyurethanes, and solvent-borne urethane adhesives. The adipates are available mostly as diols. The poly(caprolactones) are available as diols and triols. 

These adhesives differ from normal hot-melt adhesives, such as the standard ethylene vinyl acetate hot melts. Standard hot-melt adhesives like EVA have no curing mechanism. They are heated above the crystalline melting point and applied as a low-viscosity liquid in the same manner as is the curing hot melt. The bond is closed in the same manner and strength is developed upon crystallization. 

Coran and Patel [33] selected a series of TPEs based on different rubbers and thermoplastics. Three types of rubbers EPDM, ethylene vinyl acetate (EVA), and nitrile (NBR) were selected and the plastics include PP, PS, styrene acrylonitrile (SAN), and PA. It was shown that the ultimate mechanical properties such as stress at break, elongation, and the elastic recovery of these dynamically cured blends increased with the similarity of the rubber and plastic in respect to the critical surface tension for wetting and with the crystallinity of the plastic phase. Critical chain length of the rubber molecule, crystallinity of the hard phase (plastic), and the surface energy are a few of the parameters used in the analysis. Better results are obtained with a crystalline plastic material when the entanglement molecular length of the... 

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