Wood-plastic composites (WPCs) are composite material

Composite material

Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...

s made of wood fiber/flour and plastic(s). In addition to wood fiber and plastic, WPCs can also contain other ligno-cellulosic and/or inorganic filler materials. WPCs can also be referred to as natural fiber plastic composites or natural fiber reinforced plastics.

Uses

The most widespread use of WPCs is in outdoor deck

Deck (building)

In architecture, a deck is a flat surface capable of supporting weight, similar to a floor, but typically constructed outdoors, often elevated from the ground, and usually connected to a building...

 floors, but it is also used for railings, fences, landscaping timbers, cladding

Cladding (construction)

Cladding is the application of one material over another to provide a skin or layer intended to control the infiltration of weather elements, or for aesthetic purposes....

 and siding, park bench

Bench (furniture)

A bench is a piece of furniture, on which several people may sit at the same time. Benches are typically made of wood, but may also be made of metal, stone, or synthetic materials. Many benches have arm and back rests; some have no back rest and can be sat on from either side. In public areas,...

es, molding and trim, window

Window

A window is a transparent or translucent opening in a wall or door that allows the passage of light and, if not closed or sealed, air and sound. Windows are usually glazed or covered in some other transparent or translucent material like float glass. Windows are held in place by frames, which...

 and door

Door

A door is a movable structure used to open and close off an entrance, typically consisting of a panel that swings on hinges or that slides or rotates inside of a space....

 frames, and indoor furniture

Furniture

Furniture is the mass noun for the movable objects intended to support various human activities such as seating and sleeping in beds, to hold objects at a convenient height for work using horizontal surfaces above the ground, or to store things...

. Manufacturers claim that wood-plastic composite is more environmentally friendly and requires less maintenance than the alternatives of solid wood treated with preservatives or solid wood of rot-resistant species. These materials can be moulded with or without simulated wood grain details.

Wood-plastic composite is still a very new material relative to the long history of natural lumber as a building material, but can be substituted in most non-structural instances. Although being highly resistant to rot, Wood Plastic Composites still soak up water due to their mixing with organic wood fibers. Some manufacturers have tried to avoid this by loading up their wood fibers with oils or other products that repel water. WPCs add a stage of upstream use to materials previously considered waste lumber. Although these materials continue the lifespan of used and discarded materials, and have their own considerable half life; the polymers and adhesives added make wood-plastic composite difficult to recycle again after use due to the many impurities in such a compound. It can be recycled easily in a new wood-plastic composite.

A major advantage over wood is the ability of the material to be molded to meet almost any desired spatial conditions. It can also be bent and fixed to form strong arching curves. With up to 70 percent cellulose content (although 50/50 is more common), wood-plastic composites behave like wood and can be shaped using conventional woodworking tools. At the same time, they are moisture-resistant and resistant to rot, although they are not as rigid as wood and may slightly deform in extremely hot weather. The material is also sensitive to staining from a variety of agents by virtue of its porosity. A major selling point of these materials is their lack of need for paint as they are manufactured in a variety of colors, but are widely available in grays and earth tones.

Manufacture

Wood-plastic composite lumber is composed of wood from recovered saw dust (and other cellulose

Cellulose

Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....

-based fiber fillers such as pulp fibers, peanut

Peanut

The peanut, or groundnut , is a species in the legume or "bean" family , so it is not a nut. The peanut was probably first cultivated in the valleys of Peru. It is an annual herbaceous plant growing tall...

 hulls, bamboo

Bamboo

Bamboo is a group of perennial evergreens in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae. Giant bamboos are the largest members of the grass family....

, straw

Straw

Straw is an agricultural by-product, the dry stalks of cereal plants, after the grain and chaff have been removed. Straw makes up about half of the yield of cereal crops such as barley, oats, rice, rye and wheat. It has many uses, including fuel, livestock bedding and fodder, thatching and...

, digestate

Digestate

Digestate is solid material remaining after the anaerobic digestion of a biodegradable feedstock. Anaerobic digestion produces two main products: digestate and biogas...

, etc.) and virgin or waste plastics including HDPE, PVC

Polyvinyl chloride

Polyvinyl chloride, commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl groups having one hydrogen replaced by chloride. Polyvinyl chloride is the third most widely produced plastic, after polyethylene and polypropylene. PVC is widely used in...

, PP

Polypropylene

Polypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...

, ABS

Acrylonitrile butadiene styrene

Acrylonitrile butadiene styrene is a common thermoplastic. Its melting point is approximately 105 °C ....

, PS

Polystyrene

Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...

, and PLA

Polylactic acid

Poly or polylactide is a thermoplastic aliphatic polyester derived from renewable resources, such as corn starch , tapioca products or sugarcanes...

. The powder or fibers are mixed to a dough-like consistency and then extruded or moulded to the desired shape. Additives such as colorants, coupling agents, stabilizers, blowing agents, reinforcing agents, foaming agents, lubricants help tailor the end product to the target area of application. The material is formed into both solid and hollow profiles or into injection moulded parts and products.

Wood, resin, regrind, and most of the additives are combined and processed in a pelletizing extruder. The new material pellets are formed in mold and dried. Pre-distribution testing can help determine the optimal combination of chemical agents, design, agitation and other flow aid strategies for the specific material in use.

Fire Hazards

The types of plastics normally used in WPC formulations have higher fire hazard properties than wood alone, as plastic has has a higher chemical heat content and can melt. The inclusion of plastic as a portion of the composite results in the potential for higher fire hazards in WPCs as compared with wood. Some code officials are becoming increasingly concerned with the fire performance of WPCs.