An Improved Wire Adhesion Test Method

A new type of wire adhesion test method has been developed and has been compared to the conventional ASTM (D-2229) method on the basis of both accuracy and precision. The extent to which the ASTM slot type method can bias adhesion measurements by concentrating stresses at the leading edge of the wire-rubber interface has been demonstrated and is in agreement with the findings of other investigators. No such limitation was found with the CSRC method. In terms of precision, the ASTM and CSRC methods were found to be comparable, but the CSRC method was found to be more sensitive to differences in adhesion. The new method was used to show that carbon blacks with higher levels of EM surface area, unit form factor, porosity, and volatile content increased wire adhesion in a NR-sulfur compound, unaged and tested at room temperature. The effects of EM surface area and unit form factor became more important when the compounds were aged severely and tested at 212° F. Increased porosity and volatile content improved adhesion unaged at room temperature, but when adhesion was tested hot and aged, the quality of the rubber deteriorated and adhesion was lowered as the levels of these variables increased. Carbon black loading and type are important in a natural rubber recipe in developing good levels of wire adhesion at various test conditions: first, by altering the rate of vulcanization in a direction that favorably affects the competing reactions of the rubber and brass for sulfur and second, by increasing the reinforcement of the rubber, particularly at high temperatures.