The potential for molding with renewably sourced materials is intriguing while seemingly elusive. The conversation usually does not include a compound based 50% on wood waste materials because of the historical focus on wood-plastic composites (WPCs) as an extruded construction material. As a “green’ material, though it is sublime: the plastics generally come from recycling streams, such as waste film, and the wood is a byproduct of other processes. No trees are cut down. No wells are drilled. WPCs compete against treated wood for decking and railing. WPCs are often overlooked because various studies on renewably sourced plastics focus on so-called bioplastics. WPCs are not considered bioplastics because they use wood as a filler. The cellusoic feedstock is not polymerized.
But maybe some of that is changing. German materials powerhouse Evonik Industries says it has developed a WPC that uses polymethyl methacrylate (PMMA), aka acrylic, as a filler rather than waste high-density polyethylene. On the surface, maybe that makes the story a little less “green”. But use of acrylic as the binder creates greater potential for WPC as an injection molding material.
In an announcement posted for an upcoming WPC conference in Europe, Evonik says it has developed a pure acrylic wood composite in cooperation with Reifenhäuser GmbH & Co., a giant in the field of extrusion machinery. “Known for its durability and fiber wetting, PMMA’s properties are brought to best advantage in combination with wood,” says Evonik in the announcement. “Thus the new material will bring WPCs to a whole new level in terms of weather resistance, color stability, dimensional stability and technical strength without any additional surface treatment.”
First application will be a decking with a specially developed surface structure in various, highly brilliant colors. Then Evonik chemists and engineers will develop a special WPC molding compound with acrylic.
PMMA was commercialized in the 1930s under the trade name Plexiglas by Rohm & Haas. It has been in hot demand lately because it is a transparent, engineering thermoplastic that does not contain the chemical bisphenol A (BPA). It fits well in applications requiring transparency and moderate strength. Wood filler obviously would take away the transparency, but the compound could be brightly colored, and pitched as a “very green” alternative to polycarbonate. Potential applications include signs and molded components for office and outdoor furniture. Rohm & Haas is now a subsidiary of Dow, and the rights to Plexiglas in Europe are owned by Evonik.