Ten years ago, the idea of rubber scrap as an advanced engineering material was considered ludicrous. Today, according to speakers at a recent recycling conference, it's a reality. ``We're not just a recycler, but an advanced materials producer,'' said Bernard Bauman, president of Composite Particles Inc., at ``Rubber Recycling '98: The North American Experience.''
``The challenge is how to reuse rubber,'' Bauman said. ``You can't melt it down, because rubber is a thermoset.''
One way to approach the problem is to change the surface of the rubber. Some in the recycling industry previously have done this by coating the rubber with polymers.
``Our approach is entirely different,'' Bauman said. ``We chemically modify the surface, changing the backbone in a permanent way.''
The controlled oxidation system Composite Particles developed changes rubber to very polar from non-polar, ``to the point it's actually water-wettable,'' he said.
The major result of this treatment is a dramatic improvement in the bonding capabilities of rubber, according to Bauman. ``The material would tear before the bond would break,'' he said.
Bonding polyurethane with rubber in an 85-15 ratio optimizes the chemistry of the bond.
``For all important engineering properties, the mixture of 85-percent polyurethane with 15-percent rubber was essentially the same as unfilled polyurethane,'' Bauman said. ``There was a little loss of tensile strength, but nobody uses polyurethane at 300-percent elongation anyway.''
Composite Particles also has had success in mixing treated scrap rubber with epoxy, acrylic paints and industrial coatings, according to Bauman.
The company's scrap rubber blends could allow the manufacture of advanced-material parts at a lower cost with improved critical physical properties, he said.
``It could even displace some traditional materials, such as polyurethane foam,'' he said.
Meanwhile, the British firm Watson Brown (HSM) Ltd. has developed a new high-shear mixer that has the potential to recycle vulcanized scrap rubber to give it the same properties as virgin material, according to David Brown of Watson Brown.
Inventor W.F. Watson had the idea for the high-shear mixer as early as the 1950s, Brown said. ``Our question was, is this another cold fusion, or could this be scaled up to benefit the industry?'' he said.
Initial results from company trials performed last year were promising, according to Brown.
``The physical properties were down, but we feel that is strongly influenced by particle size,'' he said.
Soon the company expects to produce batch sizes of up to 440 pounds, Brown said.