Compression molding Condensation

A large proportion of the amino resin produced is used as compression-molded plastics, with or without carrier materials such as cellulose. Amino resins are less colored and less light sensitive then phenolic resins, but they are more sensitive to humidity and temperature. Urea formaldehyde resins can be employed up to temperatures of 90° C and melamine formaldehyde resins up to 150°C. The urea formaldehyde resins are particularly suitable for rapidsetting compression molding materials. Of course, aniline formaldehyde resins must be used as pre-cross-linked products, since no aromatic nucleus condensation occurs in the absence of acid catalysts and a postcuring with... 

A polycarbonate TPE polyurethane that claims biostability is achieved through its replacement of virtually all ether or ester linkages with carbonate groups. The soft segment is composed of a polycarbonate diol formed by the condensation reaction of 1,6-hexanediol with ethylene carbonate. The polycarbonate diol is converted to a high molecular weight polyurethane by the reaction with 1,4-methylene bisphenyl diisocyanate (MDI) and 1,4-butanediol. It is reported to be resistant to environmental stress cracking as experienced with insulation on pacemaker lead wires. The polymer can be extruded, injection molded or compression-molded, and can be bonded with conventional urethane adhesives and solvents (Tables 4.4, 4.12, 4.13, and 4.14). 

PGA, is another biodegradable polymer with applicability in bionanocomposites [372] and, like PVA and PVAc, PGA is readily soluble in water and can be processed by extrusion, injection, and compression molding similarly to other thermoplastics. Murugan et al. [373] produced bionanocomposites of PGA and clay by polymerizing glycolic acid under vacuum in the presence and absence of nanoday which act as a catalyst to the condensation polymerization of PGA. They found that addition of clay improved flame retardancy. 

Phenolic and other formaldehyde condensation polymers are also important reactive adhesives. Powdered phenolic resin is mixed with abrasive grains and the mixture is compression molded to form grinding wheels. A B-stage phenolic (Chapter XX) in a solvent is used to impregnate tissue paper. The solvent is evaporated, and the dry sheets are placed between layers of wood in a heated press, where the resin first melts and then cures, bonding the wood to form plywood. Similarly, sheets of paper impregnated with a B-stage melamine-formaldehyde resin are laminated and cured to form the familiar Formica counter tops. 

Polyamide-imides (PAIs) are thermoplastic amorphous polymers prepared by the condensation of an aromatic diamine, such as methylene diamine, and an anhydride, such as trimellitic add chloride. PAIs have good mechanical, thermal, chemical resistance, high strength, melt processability, and high heat capacity. They can be processed into a variety of forms, such as injection or compression molded articles, coatings, films, fiber, and adhesives. The typical heat deflection temperature for neat molded PAI is 278°C,but reinforcements are often used to improve mechanical properties. PAIs are generally soluble in strong aprotic solvents such as NMP and DMAc, and thus misdble blends with PBI are feasible. 

A circular disk comprising 75 wt% of BN powder and 25 wt% of the MAB condensate was made by compression molding. 

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