Methods of Decreasing Edge Internal Stresses in Adhesive-Bonded Joints

4 Methods of decreasing edge internal stresses in adhesive-bonded joints 

The methods of controlling the edge stresses are based on adding substances that produce different mechanisms of adhesive cure in the bulk and at the interface with air. This results in alteration of the physical-mechanicsd properties of the adhesive depending on the distance to the edge—i.e., decrease of the adhesive modulus of elasticity at the edge and increase of the rate of relaxation of the internal stresses. 

Let us consider methods of decreasing the edge stresses of a system based on imsaturated compoimds. For this purpose the capacity of oxygen to inhihit the process of radical polymerization of unsaturated compoimds is exploited. In addition to other factors, the location of the layer under study determines the oxygen concentration in the system. 

At the stage of inhibition of radical polymerization by the oxygen, the following reactions occur [200]  

Given that, for example, for MMA k /ki = 3 x 10 , practically all the polymer radicals react with oxygen but not with a monomer, although the concentration of the latter is 10 times higher than the oxygen concentration (oxygen solubility in MMA is 10 mol/1 when saturated with air). As the reactivity of RO2 relative to monomer is far less than that of R, the conversion of R into RO2 is similar to chain termination. The monomer that has not reacted volatilizes from the adhesive layer. 

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