Influence of thermal and oil aging on weldline strength of NR/EPDM and NR/NBR blends

Weldline is one of the typical molding defects and appears at the meeting points of multiple melt flows. The presence of weldlines in rubber products is regarded as one of the most undesirable phenomena, since it may result in poor mechanical properties as well as surface appearances. Compression moldings of large or complicated products are usually prepared by multiple charges, which produce weldlines once the melt fronts are joined by impingement flow. In the present study, ethylene propylene diene monomer and acrylonitrile butadiene rubber were blended into natural rubber (NR) in order to enhance the aging properties with respect to the heat, oil and ultraviolet resistances of an NR specimen containing a weldline.