RUBBER-TO-METAL BONDING: AN INVESTIGATION OF CHEMICAL REACTIONS AND ADHESION AT THE INTERFACE
Adhesion of rubber to steel plays an important role in many areas of technology. However, adhesion of natural rubber (NR) to most metals is poor due to the polarity of the rubber surface. In order to obtain adhesion, the substrates are often plated with brass, which is one of the few metals that NR will adhere to. The goal of this research was to elucidate the chemistry between rubber and brass at the interface and to develop primers that could replace the brass plating. Rubber fracture and model rubber experiments were used to determine the mechanisms responsible for adhesion between rubber and brass. Plasma polymerization was used to develop acetylene primers to replace brass plating. In the rubber fracture experiments, failure surfaces from rubber/brass lap joints and single wire adhesion tests were analyzed using X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). It was concluded that a rubber boundary layer existed, which consisted of high levels of oxidation and silicon that were related to adhesion failure. The composition of this layer depended on cure cycle. Model rubber experiments were used to determine the effects of two vulcanization accelerators, N,N-dicyclohexyl-2-benzothiazole sulfenamide and N-tert-butyl-2-benzothiazole sulfenamide, on the reactions between rubber and brass. Squalene, a low molecular weight hydrocarbon was used in place of NR. The chemical reactions between rubber and brass were characterized by IR, Raman, and XPS analysis. Analysis of the brass substrates after reaction with the model rubber systems showed that stearates, copper oxide, and sulfides formed initially on the surface. This was followed by squalene deposition and polyene formation (crosslinking). The rates at which these reactions occurred depended on the accelerator. Plasma-polymerized acetylene primers were developed using a microwave reactor. It was determined that low levels of fragmentation of acetylene molecules led to good adhesion in the rubber/plasma film/steel system. Fragmentation was controlled by the processing parameters, such as pressure, power and flow ratio used in the deposition process. Rubber/steel lap joints prepared from steel adherends coated with plasma-polymerized acetylene films outperformed joints prepared from brass-plated steel adherends in tests of initial adhesion and durability of adhesion.
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:model rubber systems plasma polymerized acetylene to brass adhesion failure analysis ir raman and xps
Date of Publication:01/01/2001