Polymer Recyclers trialling retread compound containing 35% rubber crumb

Tamworth-based Polymer Recyclers Ltd (PRL) is putting together a case for a retread compound with recycled tyre crumb as a major ingredient. The company says it is currently retreading and trialling retread compound containing 35 per cent rubber crumb. It calculates that this method could yield a material saving of 25 per cent.

Bob Kind, technical director at Polymer Recyclers, took Tyres & Accessories through the thinking behind this initiative at the TRA Recycling Day 2015. When truck tyres are retreaded, remaining tread rubber is removed by rasping and the resultant shred is ground to powder. Kind states that the rubber crumb produced in this way has been shown to be very uniform and sells at about 10 per cent of the original compound cost. This material can currently be added back into retread compound at levels of up to 40 per cent, he says.

Charting the particle size distribution of 40 mesh truck tyre crumb, 10 samples were taken through an 800kg load, during which uniformity was shown to be good, except for the content of material held on the 100 micron sieve. PRL looked at the effect of particle size on rubber compound properties and found, surprisingly, improvement in abrasion loss and tear strength as the particle size increased.

Kind suggests that significant cost savings can be made by adding various additions of rubber crumb: “Even a 10 per cent addition gives material savings of 8.75 per cent,” though he qualifies this estimate as “somewhat ambitious as the rubber formulation has to be modified to optimise the rubber properties.”