Fatigue Crack Growth of Recycled Rubber in Natural Rubber/Butadiene Rubber Blends

Fatigue Crack Growth of Recycled Rubber in Natural Rubber/Butadiene Rubber Blends (2015-2019)

Researcher: Dayang Habibah, Abang Ismawi Hassim

The increasing use of rubber in many applications results in a growing volume of rubber waste. The disposal of waste automotive tyres in particular is an increasing environmental problem worldwide due to the ever-increasing numbers of vehicles on the road. Various methods of handling waste tyres have been reviewed as alternative solutions to the tyre recycling issues. Inclusion of rubber powder made from End of Life Vulcanised Rubber tyres into new rubber products will be of significant environmental and economic benefit, provided it does not considerably affect the quality of the product. To date, most rubber or non-rubber companies are able to produce ground rubber from tyre waste, but the main issue is relatively low quantities being used in the manufacturing of new high performance products or re-used in new tyres.

The method of production of recycled rubber powder (RRP), such as cryogenic or ambient temperature milling of the End of Life Vulcanised Rubber Tyres, affects the morphological structure and size of the particles. The ambient process produces a coarse structure, whereas the cryogenic process results in smooth textures. Smaller particles than 400 μm for ambient ground RRP, are currently only produced in small batches, so not readily commercially available, with the only source being cryogenic ground production. Thus, the emergence of smaller sized RRP produced using cryogenic methods in micronised form certainly appear to have great potential for many applications.

The overall aim of this research is to investigate the mechanical and crack growth behaviour with incorporation of RRP in Natural and Butadiene rubber blends. In this research, two types of RRP, smaller size particles (~ 74 μm) produced by the cryogenic method and common commercial particles sizes (~ 400 μm) from ambient ground production are incorporated in rubber compound as recycled filler. 

For quasi-static tensile tests, the tensile failure of RRP filled materials is dependent on the filler size and type of rubber matrix. The relationship of the interface morphology with tear strength and abrasion resistance were also discussed. Quasi-static tests are relatively useful for comparing the performance of fillers in rubber matrices, but those tests do not reflect the performance under dynamic applications for real world products. Wear loss in tyres or cracking in rubber mountings is usually associated with crack growth due to repeated cyclic stress. Therefore, crack growth resistance is of great importance in determining the strength and durability of rubber products. How does these particle size of RRP influence the crack growth rates of the rubber compound? 

The effect of an artificial sharp cut on the fatigue crack growth (FCG) rate in carbon black filled NR/BR containing CRP400 or MRP074 was investigated in detail. The fracture mechanics approach was used in the crack growth measurement which relates crack growth rate (dc/dN) and strain energy release rate (T, also called tearing energy). Single-edge notched tensile (SENT) specimens were used and crack growth rates were monitored during cyclic deformation with different tearing energies. The dynamic behaviour of RRP in filled rubber compounds was studied in terms of absolute and relative hysteresis loss. 

Results indicated a correlation between absolute/relative hysteresis loss and fatigue crack growth rate under specific dynamic strain amplitudes. Differences in relative hysteresis loss showed that additional energy dissipation, due to multiple new crack surfaces at the crack tip, contributes to the FCG of the RRP compounds. At higher tearing energy, beside other factors affecting the FCG performance of the RRP compounds, both higher absolute and relative hysteresis loss are slightly detrimental to the crack growth rates. Microscopic and macroscopic fracture surfaces after FCG test corresponding to the crack path deviation have also been studied.

Thesis

Dayang Habibah binti Abang Ismawi Hassim, Fatigue crack growth of recycled rubber in natural rubber/butadiene rubber blends, PhD thesis, University of Plymouth, 2019.

Journal publications arising from this research

DH Abang Ismawi Hassim, Frank Abraham, John Summerscales and Paul Brown, Fatigue properties and fracture morphology of micronised rubber powder (MRP) from waste tyres in unfilled elastomers, International Journal of Materials, Mechanics and Manufacturing (IJMMM), 2018, 6(4), 281-285.

DH Abang Ismawi Hassim, F Abraham, J Summerscales and P Brown, The effect of interface morphology in waste tyre rubber powder filled elastomeric matrices on the tear and abrasion resistance, Express Polymer Letters, 2019, 13(3), 248-260.

DH Abang Ismawi Hassim, F Abraham and J Summerscales, Fatigue crack growth and fatigue fracture morphology of recycled rubber powder filled NR/BR blend compound: Rubber Chemistry and Technology, in press (2020)

DH Abang Ismawi Hassim, F Abraham, J Summerscales and P Brown, Fatigue crack growth of natural rubber/butadiene rubber blend containing waste tyre rubber powders, Solid State Phenomena, accepted for publication in 2020.

Conference papers arising from this research

DH Abang Ismawi Hassim, F Abraham and J Summerscales Mechanical, dynamic and morphology properties of natural rubber (NR)/butadiene rubber (BR) blends with recycled rubber powder, 12th Fall Rubber Colloquium/Kautschuk Herbst Kolloquium (KHK), Hannover ~ Germany, 22-24 November 2016, poster.

DH Abang Ismawi Hassim, F Abraham, J Summerscales and P Brown, Fatigue properties and fracture morphology of micronised rubber powder (MRP) from waste tyres in unfilled elastomer, 2nd European Conference on Materials, Mechatronics and Manufacturing (ECMMM 2018), Krakow ~ Poland, 10-12 February 2018 (published in IJMMM, 2018).

DH Abang Ismawi Hassim, F Abraham, J Summerscales and P Brown, The influence of tyre fine waste particles as filler in elastomer matrix, on tear strength, abrasion and interface morphology, RubberCon2018, Istanbul ~ Turkey, 10-11 May 2018.

DH Abang Ismawi Hassim, F Abraham, J Summerscales and P Brown, Abrasion resistance and fatigue crack growth in dependence of recycled tyre filler content and the interface morphology, 13th Fall Rubber Colloquium/Kautschuk Herbst Kolloquium (KHK), Hannover ~ Germany, 6-8 November 2018, poster.

DH Abang Ismawi Hassim, F Abraham, J Summerscales and P Brown, Fatigue crack growth of natural rubber/butadiene rubber blend containing waste tyre rubber powders, 7th International Conference on Solid State Science and Technology (ICSSST 2019), Putrajaya ~ Malaysia, 11-13 November 2019, accepted for publication in SSP.

Presentations without publication

Mechanical and fatigue properties of rubber compounds containing rubber powder made from waste tyres, Postgraduate Society Conference Series, University of Plymouth, 5 December 2016, oral presentation.

Influence of interface morphology on abrasion resistance and fatigue crack growth of waste tyre powders filled rubber compound, Materials and Structures (MAST) Research Group, University of Plymouth School Engineering, 23 January 2019.