Conference highlights quality problems, solutions for WPC decking

The success of wood plastic composites (WPC) in North America risks being undermined by lawsuits relating to a variety of avoidable product failures.

This was the message for attendees at the 11^th International Conference on Biocomposites from Dr. Anatole Klyosov of Boston, Mass.-based consulting firm MIR International Inc.

“From 2004 through to 2010, no less than five WPC manufacturers and suppliers have faced lawsuits and class action lawsuits, and the outcomes of four of these are still pending,” Klyosov told the audience.

Klyosov highlighted five primary problems – all of which have been considered in courts of law over the past few years – as well as technical solutions for each.

The first problem is excessive moisture content in WPC materials, he said. “WPC tends to have a porosity of between 16 and 21 per cent, resulting in buckling, microbial stains and degradation,” he noted. The solution, he continued, is to minimize porosity by controlling the moisture content in the cellulosic component of the WPC, and not exceeding the necessary temperature of the manufacturing or the necessary manufacturing speed.

Second, a too-low amount of antioxidants causes stress, oxidation and crumbling in WPC boards. “The solution is simple: add a right amount of antioxidant to WPC materials,” he said. “A readout for the ‘right amount’ is the oxidation induction number for the product, which is measured using a differential scanning calorimeter instrument.”

A third hazard is post-manufacturing shrinkage of WPC materials, a production problem plaguing fast-cooling hollow boards in particular. “Simple solutions include allowing enough time for WPC boards to relax, cool and shrink at the manufacturing site, and also not running WPC boards with a high speed when it’s not necessary,” Klyosov explained.

A fourth common problem is color fade from having too much regrind and too little of a pigment. “Processors can minimize this problem by minimizing the use of regrind,” he explained. “Also, be sure and add the necessary amount of inorganic pigment, typically from iron oxide.”

Finally, the slippery surfaces of many WPC decks are a most dangerous problem. “WPC is more slippery than wood when wet, and slippery also even when dry,” Klyosov said. Manufacturers can help avoid problems down the road by wire-brushing the board surface, changing the plastic to that which provides better traction, and using coatings available from specialized companies, he noted.

The 11^th International Conference on Biocomposites is being held in Toronto from May 2-4.