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Saturday, October 23, 2010

Acrilic Copolymer

The most important compolymers are those acrylonitrile. The acrylonitrile butadiene copolymer has its widest use in the form of the latex, and is used for sticking a variety of absorbent materials, including ceramic will tiles. another use is in making bonded (non-woven) fabrics; here softness, resistance to laundering and dry cleaning, and excellent adhesion to textile fibres including cotton, rayon nylon and polyester are essential properties.

In general, variation of the monomer ratio has a marked effect on the polarity of the copolymer, particularly if one monomer is highly polar such as acrylonitrile, and the other highly non-polar such as butadiene. With polymer derived from monomers of widely different adherends will be influenced by the monomer ratio.

Solution form of acrylonitrile/butadiene copolymers may be made up in wide variety of solvents, ethylene dichloroethylene, for example, reduce fire risks, while acetone and ethyl acetate are less toxic. These solution adhesives are use for gluing materials such as leather, plastic film including polyvinylchloride, natural and synthetic rubbers; they show fair adhesion to metal - not sufficient for them to be considered as metal glues, but adequate for bonding many substances, specially thin flexible materials, to metal. Creep resistance, which is low, can be improved by adding a phenolic resin which should be of a type that is intrinsically solid. This type of cold curing adhesive has a strength that is of a lower order than the hot curing adhesives of similar constitution refered to in the section on two polymer adhesives.

Plasticised acrylonitrile/butadiene copolymer adhesive are used in pressure sensitive adhesive tapes, often with a relatively large percentage of coumarone indene resin. The monomer ratio in acrylonitrile/butadiene copolymer adhesives is generally selected to give a flexible material, this requires the butadiene to be in excess of the acrylonitrile, and it usually comprises at least 65% by weight. Flexibility can also be increased by the addition of certain vinyl chloride/vinyl acetate copolymers. Adhesion and tack can be improved by adding (more conveniently to the solution form) a chlorimetal rubber cement. The acrylonitrile/butadiene copolymer have rather low resistance to heat. They have excellent resistance to mineral oils and to water.