Assessing effects of thermoset polyester resin waste powder on the processing and mechanical properties of natural rubber

Products made of glass fibre reinforced polymers are often disposed of in landfill, incinerated or processed into waste powders at the end of their service life. Waste powders can be recycled as fillers for use in virgin polymers. The effects of up to 50 parts per hundred rubber by weight thermoset polyester resin waste powder on the viscosity, cure and mechanical properties of a sulphur-cured natural rubber compound were studied. The powder had resin polymer particles and glass fibre fragments ranging from approximately a few microns to 700 microns in size. The viscosity remained unchanged and the cure properties deteriorated when the powder was added to the rubber. The hardness, Young’s modulus and tensile modulus increased whereas, the tensile strength, elongation at break, stored energy density at break and tearing energy decreased. There was also evidence of poor adhesion between the powder and rubber. It was concluded that the waste powder could be recycled as an extender filler to replace a portion of the raw rubber in the compound.