Activated Gas Plasma Surface Treatment of Polymers for Adhesive Bonding: Part 2
PICATINNY ARSENAL DOVER NJ DOVER United States
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Activated gas treatment of polyethylene and nylon 6 adherend surfaces greatly improves their bondability after such treatment, bond failure often occurs in the polymer rather than at the adhesivepolymer interface. Similar treatment of many other polymers results in increased bondability. The effect of the treatment depends on such parameters as length of treatment, chemical species present in the activated gas, and temperature of the polymer surface during treatment. Each polymer was treated with excited oxygen and excited helium each was treated for several different periods of time. The treatment was followed by tensile testing of lap-shear sandwich specimens bonded with an epoxy adhesive. Plots of bond strength vs treatment time showed maxima for high density polyethylene HOPE treated with helium, cellophane treated with both oxygen and helium, and fluorinated ethylene-propylene copolymer FEP treated with helium and oxygen. The plots for most polymers showed an initial rapid increase in bond strength followed by a slower increase. Bond strengths of a poly-oxymethylene copolymer Celcon treated with helium reached a fairly constant value after about ten minutes. Polypropylene was treated with helium at several temperatures. Low temperature treatment gave very poor results while treatment near the softening point of polypropylene gave an eightfold increase in bond strength.