A composite material is made by combining two or more materials – often ones that have very different properties. The two materials work together to give the composite unique properties.
There are two types of composites material.
- Natural composite
Natural composites exist in both animals and plants. Wood is a composite – it is made from long cellulose fibers (a polymer) held together by a much weaker substance called lignin. The bone in your body is also a composite
- Making composites
Most composites are made of just two materials. One is the matrix or binder. It surrounds and binds together fibers or fragments of the other material, which is called the reinforcement Modern examples
- Fiberglass composite
- Wood plastic composites
- Wood plastic composites (WPC)
Wood plastic composites (WPC)
Wood plastic composites (WPC) are composite materials from wood and thermo-plastically process able matrices, which drew increasing attention over the last years. These composites made from blends of thermoplastics and natural fibers have gained popularity in a variety of applications.
By changing the number of carbon in polymer chain the properties of composite material will be change for example polyethylene based WPCs are more thermally stable and ductile in nature and polypropylene based WPCs have higher stiffness and tend to be more brittle in nature.
WPCs provides the mechanical strength and protection called matrix that is the plastic (thermosetting or thermoplastic resin), which ensures the cohesion of the structure and transmission efforts towards the reinforcement while ensuring the cohesion of the material,
Gives it its final form and provides the interface with the mechanical environment and additives (accounting, anti-UV, antioxidants, fire retardants) which give the composite properties particular requirements for durability and performance of these materials for outdoor use.
The production of natural fibers and polymer composites, three general objectives are pursued: achieving a material with recyclable and environmental properties and biological degradation compared to polymers, plastics, wood, wooden plates and similar products;
Achieving special properties, strength and capability of forming more efficient than polymers, MDF and similar products improve mechanical strength, water and oxygen barrier, dimensional stability, thermal; wear resistance, chemical etc.
WPCs thermoplastics are environmentally attractive because sawdust is a waste and thermoplastics are recyclable. The effect of changing the composition of a WPC with recycled poly-propylene (RPP) as a thermoplastic resin, on mechanical and physical properties.
The study evaluated four parameters: particle size of the filler, dose of coupling agent, lubricant content and the mass ratio of the wood and RPP; the results show that the use of small particle sawdust (less than 125 microns) improved tensile and flexural strength, as well as reduced moisture absorption.
Components of WPCs
WPCs are a group of composite materials and products comprised of two primary and distinct phases. One of these phases is the matrix which holds the different components together, binding them and providing load transfer between them. The matrix in WPCs is either a thermoset or more commonly a thermoplastic polymer.
The other primary phase is the wood component. The wood component can be of any shape or size and acts as a filler and/or reinforcement to the composite. Making up a relatively small proportion of the total composite are additives which are added to aid in processing and affect a variety properties of the final product.
They have two components.
- Matrix Component.
- Wood components.
The main advantages of using wood instead of inorganic materials like talcum or glass ﬁbers are the density of the composite, which is considerably lower and therefore of interest for transportation application, as well as the renewability and enhanced recyclability of the WPC.
In production of polymer composite such as polypropylene – wood powder with paddy husk, in order to reduce the price of the product by mixing a substance with low price (wood and paddy husk) and a relatively expensive polymer material, it will be possible to recycle waste materials and to produce a lightweight composite with better abrasion and resistance properties.
The important point is to add wood fiber(solid phase) to polymer matrix which increases the viscosity compared to the polymer raw material. The viscosity increase can be desirable in the process, since it increases the melt strength.
On the other hand, strength and physical- mechanical properties of composites changes with respect to the fiber percentage. Either recycled or virgin plastic materials could be used to produce WPCs.
Today in terms of product variety, market changes and economic and costs fluctuations, there are shortages of raw materials and designs for various projects in the field of wood-plastic composites, which is a need for integration, alignment and more feasibility in the capacities and economic infrastructure potentials.
Fading color and properties change of wood-plastic composites (WPC) during weathering is becoming a great concern both to the manufacturers and consumers.
It must be noted that several works have been conducted on weathering and durability issues of WPCs. Weathering has been reported to cause an increase in surface oxidation (C=O), unsaturation (C=C), while wood lignin content decreased in WPCs . Lignin has been suggested to be a great contributor to WPC color change during weathering.
There is little or inadequate information, however, about the effects of using extractive-free wood and holocellulose (lignin free) fiber as filler/reinforcement on the weathering of high- density polyethylene (HDPE)-based WPCs.
The use of cellulose or holocellulose fiber for WPC production may be a good alternative to minimize the problem of color change during weathering.
The use of pure cellulose fibers over wood fiber in wood plastic composite material offers the benefit of higher thermal stability (up to 270°C) in that thermoplastics (e.g., nylon) can be used to obtain materials for structural applications.
Therefore, cellulose fibers would be a suitable reinforcement for HDPE-based WPCs since they are commonly produced at temperatures below 200°C during pulping.
Background information on the chemistry of wood and plastic behavior during weathering may likely foster research toward production of WPCs with improved weathering performance (color). The determination of crystallinity could provide useful information about the plastic behavior during WPC weathering.