Nitrile Rubber and Phenolic Resin

With nitrile rubbers, the phenolic resin component is more critical and compatibility more of a problem than with the polyvinyl acetal. Since resins having a high pH value tend to less compatible, ammonia and hexamethylene tetramine are preferred to sodium hydroxide as curing catalysts.

Although a wide range of nitrile rubbers, having different but related molecular system is a copolymer of butadiene and acrylonitrile, and is refered to simply as nitrile rubber or more particularly as high nitrile rubber. In spite of this name the monomer ratio is such that butadiene is in excess of acrilonitrile and comprises 60 - 70% of the weight of the copolymer.

Nitrile Rubber/Phenolic Resin Adhesives

Rubber Adhesive Made

It will be clear that rubbers and phenol formaldehyde resin differ in most respect. And because they widely, a variety of properties can be obtained by blending them, adhesives, for example, can be made with certain desirable features in which individually the resin and rubber are deficient. Briefly, the resin reduces extensibility of the rubber whilst increasing its cohesive strength.

The first reference to the use of a combined resin and rubber adhesive was probably the patent that granted over thirty years ago describing bonding to metal, porcelain and glass with a rubber or rubberlike substance mized with a synthetic resin. Since the publication of this patent many rubber and rubberlike substances have no doubt been examined as adhesives in association with a thermosetting resin, especially a phenolic resin. Experience has shown that the most important rubber is nitrile rubber, and its behavior in a two polymer adhesive is in a number of ways rather like that of the polyvinyl acetals discussed previously, some of the comments made in the previous section therefore apply here.

Chemical Reaction Between The Components

Ever since the introduction of the polyvinyl acetal/phenolic resin adhesives there has been considerable interest in the part played by a possible chemical reaction. Since alcoholic hydroxyl groups are present in the acetal there is a possibility of reaction by combination with methylol groups of the phenolic reisn.

The feasibility of a chemical reaction has been considered with respect to polyvinyl formal and also polyvinyl butyral. In the work reported on polyvinyl formal. It is considered that under the influence of phosphoric acid and at a temperature of 150 ^oC for 30 minutes, hydroxyl group of the polyvinyl formal apparently crosslink by co-condensations. It is noteworthy that these conditions also favor homo-condensations of the formal. In the work reported on polyvinyl butyral. It is claimed that reaction occurs with phenolic resins. If the temperature exceeds 170 ^oC, and no mention is made of acidic conditions.