TAILIEUCHUNG - Plastics Technology Handbook 2011 Part 10

Tham khảo tài liệu 'plastics technology handbook 2011 part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 4-50 Plastics Technology Handbook obviates the need for complex jibs and fixtures. The amount of monomer applied should be minimal to obtain a strong joint. Larger amounts only reduce the strength. Notable uses of cyanoacrylates include surgical glue and dental sealants morticians use them to seal eyes and lips. Dimethacrylates such as tetramethylene glycol dimethacrylate are used as anaerobic adhesives. Air inhibition of polymerization of acrylic monomers is used to advantage in this application because the monomers are supplied along with a curing system comprising a peroxide and an amine as part of a one-part pack. When this adhesive is placed between mild steel surfaces air inhibition is prevented since the air is excluded and polymerization can take place. Though the metal on the surface acts as a polymerization promoter it maybe necessary to use a primer such as cobalt naphthenate to expedite the polymerization. The anaerobic adhesives are widely used for sealing nuts and bolts and for miscellaneous engineering purposes. Dimethacrylates form highly cross-linked and therefore brittle polymers. To overcome brittleness manufacturers often blend dimethacrylates with polyurethanes or other polymers such as low-molecular-weight vinyl-terminated butadiene-acrylonitrile copolymers and chlorosulfonated polyethylene. The modified dimethacrylate systems provide tough adhesives with excellent properties. These can be formulated as two-component adhesives the catalyst component being added just prior to use or applied separately to the surface to be bonded. One-component systems also have been formulated which can be conveniently cured by ultraviolet radiation. Vinyl Polymers If the R substituent in an olefin monomer CH2 CHR is either hydrogen alkyl aryl or halogen the corresponding polymer in the present discussion is grouped under polyolefins. If the R is a cyanide group or a carboxylic group or its ester or amide the substance is an acrylic polymer. Vinyl .

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