TAILIEUCHUNG - Handbook of Plastics Technologies Part 5

Tham khảo tài liệu 'handbook of plastics technologies part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | THERMOSETS THERMOSETS Q Ọ II II_ . HOC CH2CH CHCH2 m CH2 j H nCOH Carboxyl-Terminated Nitrile Rubber CN HS CH2CH2OCH2OCH2CH2SS nCH2CH2OCH2OCH2CH2SH Mercaptan-Terminated Polysulfide Rubber Oligomer FIGURE Flexible curing agents for epoxy resins. TABLE Pot Life of Epoxy Curing Agent Systems Aliphatic amines 1 hr Amine-terminated polyamides 3 hr Aromatic amines 18 hr Acid anhydrides 84 hr Lewis acids 6 mo Other Formulating Ingredients. A number of classes of additives are often used by individual formulators to modify or introduce new properties into the epoxy system. Diluents. When epoxy resins are too viscous or too exothermic for a particular process they can be modified by addition of low-molecular-weight aliphatic epoxides. Diepoxides can copolymerize directly into the curing process without reducing cross-linking. Monoepoxides can also copolymerize but do reduce the degree of crosslinking and thus soften properties. The literature also mentions nonreactive diluents such as plasticizers but these would raise serious questions about degradation of properties. Polymer Blends. A number of polymers are mentioned as modifiers for epoxy resins. Coal tar phenol-formaldehyde and polyurethane combine readily to produce intermediate properties. Silicones can add more unique properties. Polyesters and melamine-formaldehyde are also mentioned in the literature. Flame Retardants. Flame retardance can be built into the epoxy resin by use of tetrabromobisphenol A or anhydride curing agents containing phosphorus or halogen. It can also be helped by nonreactive additives such as alumina trihydrate or organo-halogens antimony oxide. Functional Fillers. A variety of fillers can be used to add specific properties. Metals and beryllium and aluminum oxides can be added to increase thermal conductivity Table . Metals can be added to increase electrical conductivity Table . Graphite increases lubricity and .

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