Characteristics of Liquid Rubber Modified Epoxy Adhesive"
Introduction and Objective:
The most common of the high-performance structural adhesives are epoxies, especially in automotive and aircraft industry. Their toughness can be improved considerably by including a toughening agent, such as liquid rubber, prior to curing. In the curing stage micro-phase separation occurs with small rubber-rich domains dispersed within the epoxy matrix. The rubber particles essentially act as shock absorbers, absorbing the fracture energy.
The properties of epoxy adhesives are adversely affected by water absorption and exposure to other deleterious environments. Because epoxy adhesives are permeable to water, water diffuses through them and eventually invades the metal substrate underneath in adhesively bonded metal joints. It is the objective of this study to investigate the effect of rubber content on moisture sorption characteristics of rubber-modified epoxy adhesive in aqueous solutions.
The choice of which adhesive to use in an industrial application requires assessment of its behavior in the real service environment. This assessment involves exposure of the adhesive to the simulated environment for a certain period, and evaluation of the exposed adhesive for changes in properties. Water- and fluid-immersion tests have been widely utilized to evaluate changes in the properties of adhesives. Water-immersion tests are performed by immersing specimens in distilled water and fluid-immersion tests are performed by immersing specimens in a fluid to which the adhesive may be exposed to during industrial use. A sodium chloride solution is the most commonly utilized test solution for testing adhesively bonded automotive joints. Both the water- and fluid-immersion tests are effective techniques in evaluating the properties of adhesives such as the absorption rates of solutions in adhesives, the stability of adhesives, swelling of adhesives, color changes in adhesives, and delamination of adhesives from metal adherents.
The emphasis will be placed upon determining the moisture absorption behavior (including diffusivity) of aluminum powder filled epoxy adhesive under complete immersion in distilled water and in NaCl solutions. The water absorption (diffusion) rate of the adhesives will be measured as a function of the filler content, concentration of the sodium chloride solution and exposure time.