Development of High Strength Adhesive for Bonding Metallic Substrates

Abstract

Grafted Polychloroprene adhesives have been available since the 1990’s. However, companies exercise propriety restrictions due to which there is limited information about their formulation. In this research grafting of Methyl Methacrylate (MMA) onto chloroprene rubber using hydrogen peroxide as an initiator is carried out by free radical polymerization. Rubber radicals react with MMA forming graft copolymers. Eighty-two formulations have been carried out during studies. Fourier transforms infrared (FTIR) spectroscopy showed an absorption spectrum of the grafted copolymer at 1730 cm-1 which is characteristic of carbonyl band (>C=O) of PMMA not present in PCP. The grafted copolymer is then mixed with phenolic resins, magnesium oxide, anti-oxidants and solvents to use in adhesive applications. Grafting factors such as grafting time, grafting temperature, monomer and initiator concentration and their effect on the properties of grafted adhesive is investigated. The adhesion strength of adhesively bonded joints is calculated by 180-degree peel testing of aluminum, canvas and leather substrates. Peel strength increases with increasing the monomer and initiator concentration until a certain limit and then it starts to decrease. Also grafting temperature of 70 0C gives the adequate grafting reaction with maximum peel strength. The grafting time is 1 hour at 60 0C and 45 minutes for 70 0C to achieve the desired properties of adhesive. Viscosity, wettability and solid contents are also measured and compared with the commercially available adhesives. The drying time for the adhesive is optimized to the 4 min for canvas and leather while for aluminum the drying time is 7 minutes. The percentage of solids contents are 55% which depicts the presence of high usable adhesive in the set. Peel tests in different environmental conditions show that grafted adhesive has greater weather and thermal stability than non-grafted adhesive. The formulated adhesive is 1.8 times better than the commercially available adhesive.