Pulverised Flexible Polyurethane Foam Particles as a Filler in Natural Rubber Vulcanisates

Polyester polyurethane foam was densified and comminuted using an intermeshing disc impact mill. Resultant particles were investigated as a potential filler in natural rubber at concentrations from 0-75 parts per hundred rubber by monitoring tensile properties, elongation set. cure times and fracture surface characteristics.It was found that a filler concentration of 25 parts per hundred rubber produced essentially similar tensile properties, elongation set and cure time to the natural rubber vulcanisate suggesting that the filler was a satisfactory extender for natural rubber.Increasing filler content to 30 parts per hundred rubber significantly increased modulus at 100% and 200% strain and the ultimate tensile stress but worsened breaking strain and elongation set. Therefore in a critical concentration range between 25 and 30 parts per hundred rubber the particles could be regarded as a reinforcing filler extender whereas higher concentrations produced progressively poorer properties but cheapened the product cost.Scanning electron micrographs of fracture surfaces, obtained at 21°C and after immersion in liquid nitrogen, tended to indicate that reinforcement was likely to be a function of relatively weak intermolecular forces at the interface of the elastomer and the particle, molecular entanglements and a possible further contribution due to the aspect ratio of the particles which may act as short fibre reinforcement.