The Effect of Polyglycols on the Fatigue Crack Growth of Silica-Filled Natural Rubber

Polyglycols are mainly used as plasticizers to enhance the incorporation of polar fillers in non-polar elastomers. Polyglycols can help to prevent the self-agglomeration of the filler particles and thereby improve their dispersion in the rubber matrix. It can also prevent undesired chemical reactions of the polar components in the curing system with the surface of the filler particles. Therefore, it is expected that polyglycols can play a crucial role as plasticizer and coupling agent in a silica-filled rubber compound. In this work, polyethylene glycol (PEG) and polypropylene glycol (PPG) in two different concentrations were applied in a silica-filled natural rubber (NR). Their effects are compared with the influence of the coupling agent bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPT), which is widely used in rubber industry as silica coupling agent. Firstly, the cure characteristics and fundamental mechanical properties have been studied, whereas the ability of polyglycols to improve cure efficiency as well as filler-elastomer interactions has been confirmed. Moreover, polyglycols are improving the fundamental mechanical properties in general, whereas the polyglycols-treated silica-filled NR composites show lower tensile strength and modulus with a higher elongation at break compared to the TESPT-treated silica-filled NR. Finally, the effect of polyglycols on fatigue crack growth (FCG) resistance was investigated using a Tear and Fatigue Analyzer (TFA (c), Coesfeld GmbH & Co. KG, Germany). It has been found that 2 phr of PEG leads to a higher improvement of FCG resistance in comparison with the corresponding content of TESPT. However, 4 phr of polyglycols significantly decreases this property again. Moreover, the application of PPG generally leads to decreasing FCG resistance. As conclusion, it was stated that the polyglycols act as agent leading to significant improvement of fundamental mechanical behaviour in general as well as to improvement of FCG behaviour using specific polyglycol.