Heat-resistant adhesives introduction

The early copolymers of vinyl acetate with dibutyl maleate or acrylate esters offered distinct advantages over the homopolymer in their ability to adhere to a vast number of difficult-to-bond surfaces. However, they also had disadvantages, e.g., poor heat resistance, relatively low strength, rather slow setting speed, and comparatively poor machinability. The introduction of vinyl acetate-ethylene copolymers changed this picture considerably. This class of emulsion had all the benefits of homopolymers in strength, machinability and heat resistance in addition to better adhesion characteristics than those of the ester copolymers. 

The next major improvement in aerospace adhesives occured in the late 1950s with the introduction of adhesives based on epoxy resins. Since these adhesives crosslink via an addition reaction, no volatiles are released during heat cure. This made low pressure bonding possible and the use of nonperforated honeycomb feasible in sandwich structure. Other improvements followed that resulted in more durable bonded structure. These include the development of corrosion inhibiting adhesive primers in 1968, corrosion resistant aluminum honeycomb in 1969, and the phosphoric acid anodizing process for preparing aluminum for bonding in 1974. 

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