Wood flour

Abstract

The term “wood flour” is somewhat ambiguous. Reineke states that the term wood flour “is applied somewhat loosely to wood reduced to finely divided particles approximating those of cereal flours in size, appearance, and texture”. Though its definition is imprecise, the term wood flour is in common use. Practically speaking, wood flour usually refers to wood particles that are small enough to pass through a screen with 850-micron openings (20 US standard mesh). Wood flour has been produced commercially since 1906 and has been used in many and varied products including soil amendments, extenders for glues, and absorbents for explosives. One of its earliest uses in plastics was in a phenol-formaldehyde and wood flour composite called Bakelite. Its first commercial product was reportedly a gearshift knob for Rolls Royce in 1916. Though once quite prevalent as a filler for thermosets, its use has diminished. In contrast to its use in thermosets, large-scale use of wood flour in thermoplastics has only occurred within the last few decades. Recent growth has been great: use of wood-plastic composites has grown from less than 50,000 tonnes in 1995 to nearly 600,000 tonnes in 2002. Most of this has been due to the rapid growth in the manufacture of exterior building products such as railings, window and door profiles, and especially decking. Due to its low thermal stability, wood flour is usually used as a filler only in plastics that are processed at temperatures lower than about 200 °C. The great majority of wood-plastic composites use polyethylene as the matrix. This is due, in part, to the fact that many of the early wood-plastic composites were developed as an outlet for recycled film. Some manufacturers also use combinations of thermoplastics and thermosets as the matrix material.

Citation

Clemons, Craig M.; Caufield, Daniel F. 2005. Wood flour. Functional fillers for plastics. Weinheim : Wiley-VCH, 2005: pages [249]-270