Composites
In this section we will be looking at the working properties, characteristics, application and advantages/disadvantages of the following composites: MdF, Hardboard, Chipboard, Plywood, OSB, GRP and Carbon Fibre. Wood based composites come in a range of thicknesses and densities offering different properties within the product itself. However, one similarity between them is that they all come in a standard board which is stable and 2440mm long by 1220mm wide. Some boards can be manufactured in bigger sizes at specialist plants.
MDF
Medium Density Fibreboard (MDF) is an engineered wood-based sheet material made by bonding together wood fibres with a synthetic resin adhesive. MDF is extremely versatile and can be machined and finished to a high standard. As a result, MDF has replaced solid timber as a low-cost alternative in a wide range of applications across industry.
The majority of MDF is mainly composed of softwood, although some brands may contain a higher percentage of temperate hardwood if this is locally available to the manufacturer. High levels of hardwood can be found in MDF board from outside the UK and Ireland.
The most common binder for boards intended for dry environments is urea-formaldehyde. Other binders may be used depending on the grade of board and its intended end-use. The exact constituents of an MDF board will vary from product to product.
What are the dangers of working with MDF compared with softwoods, hardwoods or other panel products? The atmosphere created by machining or sanding MDF board contains a mixture of softwood dust and hardwood dust (if it is present). In addition, there will also be free formaldehyde, dust particles onto which formaldehyde is adsorbed and potentially, the resin binder itself and its derivatives. However, the levels of free formaldehyde in boards made within the EU at levels of formaldehyde class E1 are thought to be insignificant.
The majority of MDF is mainly composed of softwood, although some brands may contain a higher percentage of temperate hardwood if this is locally available to the manufacturer. High levels of hardwood can be found in MDF board from outside the UK and Ireland.
The most common binder for boards intended for dry environments is urea-formaldehyde. Other binders may be used depending on the grade of board and its intended end-use. The exact constituents of an MDF board will vary from product to product.
What are the dangers of working with MDF compared with softwoods, hardwoods or other panel products? The atmosphere created by machining or sanding MDF board contains a mixture of softwood dust and hardwood dust (if it is present). In addition, there will also be free formaldehyde, dust particles onto which formaldehyde is adsorbed and potentially, the resin binder itself and its derivatives. However, the levels of free formaldehyde in boards made within the EU at levels of formaldehyde class E1 are thought to be insignificant.
Chipboard
Also sometimes referred to as Particle Board, chipboard is made by mixing small wood particles with epoxy resin, which are pressed together under intense heat and pressure to produce a rigid board, typically with a smooth surface. Chipboard is available in a variety of densities and thicknesses to suit different needs and uses, including low, medium and high-density varieties. The lower densities are fairly soft and pliable, while the higher-density chipboards are more rigid and can be used for more heavy-duty applications. Quite often it is covered with a veneer to protect it and this can be of any colour or pattern.
There are various advantages and disadvantages of chipboard as a sheet material. The main advantages are, of course, the cost-effectiveness and versatility of uses that chipboard provides. The main disadvantage is that untreated chipboard is porous and will therefore soak up any water it comes into contact with. This is true for all grades of chipboard, even the highest densities, so it is important to keep untreated chipboard dry and treated to prevent it from soaking up water and swelling, as this will render the board unusable. Thankfully, it is very easy to treat and cover chipboard with water-resistant veneers, melamine coatings and varnishes to make it more robust.
What is Chipboard Used For? Depending on the density, chipboard is used for all kinds of different interior building and decorating projects. The highest-density grades of chipboard are used for things like:
- Kitchen worktops (coated with melamine)
- Basic structures of kitchen cabinets
- Flooring and flooring insulation/underlay
- Flatpack furniture (usually coated in a veneer)
Plywood
The term “ply,” as it refers to plywood, means the layers manufacturers use to create the boards of various thicknesses. Some projects won’t need a thick board, while others will. Ply achieves the right depth and can also make the boards stronger.
Each layer can also be known as a wood veneer however this term should really be used for he outer layer (refer back to the chipboard with a melamine veneer). A veneer is a thin layer of wood (or other material) that you can glue together to create a different number of plies. Plywood is the finished product when the manufacturer glues the veneers together.
Each layer can also be known as a wood veneer however this term should really be used for he outer layer (refer back to the chipboard with a melamine veneer). A veneer is a thin layer of wood (or other material) that you can glue together to create a different number of plies. Plywood is the finished product when the manufacturer glues the veneers together.
Each ply is placed at 90 degrees to the plies above and below. As a result it is a strong material stable material. There are always an odd number of plies so that the grain runs in the same direction on both outer layers.This alternation of the grain is called cross-graining and has several important benefits: it reduces the tendency of wood to split when nailed at the edges; it reduces expansion and shrinkage, providing improved dimensional stability. It also makes the strength of the panel consistent across all directions. There is usually an odd number of plies, so that the sheet is balanced—this reduces warping and ensures the grain runs in the same on both exterior faces. Because plywood is bonded with grains running against one another and with an odd number of composite parts, it has high stiffness perpendicular to the grain direction of the surface ply.
Smaller, thinner, and lower quality plywoods may only have their plies (layers) arranged at right angles to each other (this is the case for most plywood you wold buy in the UK). Some better quality plywood products will have five plies or more in steps of 45 degrees (0, 45, 90, 135, and 180 degrees), giving strength in multiple axes.
Smaller, thinner, and lower quality plywoods may only have their plies (layers) arranged at right angles to each other (this is the case for most plywood you wold buy in the UK). Some better quality plywood products will have five plies or more in steps of 45 degrees (0, 45, 90, 135, and 180 degrees), giving strength in multiple axes.
It is important to note, though, that veneers can also have various thicknesses. Depending on your location, some parts of the home must meet specific standards for the number of plies required for a board of a certain depth, especially with external walls and roofing. For example shuttering ply just needs to be stable for use in pour ing concrete so surface and edge finish are not important. Marine ply for making boats needs to be flexible and resistant to water so appearance and quality of veneers is important. The adhesive can also play a big part; if you use a waterproof adhesive it won't fall apart if it gets damp or wet.
For decorative plywood, (for example on a jewellery box or table top) it has face veneers of a higher grade than the core veneers. The principal function of the core layers is to increase the separation between the outer layers, effectively thickening it up and increasing resistance to bending. In these circumstances the product must be well designed so that the end grain veneers aren't seen. Also, in larger constructions, thicker panels can span greater distances under the same loads.
Although you don't need to know how the veneers are produced see another commercial approach by clicking here. Recommended reading to get a greater understanding of plywood is available by clicking here.
OSB
Oriented strand board (OSB) is a type of engineered wood similar to the above boards, formed by adding adhesives and then compressing layers of wood strands (flakes) in specific orientations. OSB may have a rough and variegated surface with the individual strips of around 2.5 cm × 15 cm lying unevenly across each other and comes in a variety of types and thicknesses.
Although OSB is not on the A level specification it is a material that is often referred to as plywood. Although it has been around for about 50 years ago it is now becoming much more widely available and is being used a lot more as a plywood replacement especially in construction and the increased use of pre-fabricated timber housing panels. It is commonly known as sterling board or smartply.
It has favourable mechanical properties that make it particularly suitable for load-bearing applications in construction and is now more popular than plywood, commanding 66% of the structural panel market. The most common uses are as structural panelling in walls, flooring, and roof decking. The boards come in 4 categories with OSB1 using urea-formaldehyde as a resin but is non-structural and not waterproof. OSB type 2 can use a variety of resins and is structural but water resistant on the face. OSB types 3 and 4 are structural and can be used in damp and outside environments and use phenol formaldehyde resin throughout.
The video clip above shows the process: The layers are created by shredding the wood into strips, which are sifted and then oriented on a belt or wire mesh. The mat is made in a forming line. Wood strips on the external layers are aligned to the panel's strength axis, while internal layers are perpendicular. The mat is placed in a thermal press to compress the flakes and bond them by heat activation and curing of the resin that has been coated on the flakes. Individual panels are then cut from the mats into finished sizes. Most of the world's OSB is made in the United States and Canada in large production facilities. The largest production facilities can make over 93,000 square metres of OSB per day.
Watch the following videos to help you understand the particular advantages and disadvantages of using Ply and OSB.
Watch the following videos to help you understand the particular advantages and disadvantages of using Ply and OSB.
Glass Reinforced Plastic
Fibreglass is an excellent example of a relatively modern composite material (Invented in 1938 by Russel Games). In industry it is often referred to as Glass Reinforced Plastic (GRP).
GRP is composed of strands of glass. Each individual glass fibre is very fine with a small diameter, and they are woven to form a flexible fabric. The fabric is normally placed in a mould, for instance a mould for a canoe and polyester resin is added, followed by a catalyst (to speed up the reaction). The process is repeated so that there are many layers of fibre glass and resin and allowed to dry/cure. The resulting material is strong and light. Glass Reinforced Plastic can be sanded for a smooth finish and painted.
Three samples of different weaves of fibreglass are seen below. The pattern of weave determines the strength and weight of the Glass Reinforced Plastic, after resin has been added. Different weaves have been developed for different practical applications.
GRP is composed of strands of glass. Each individual glass fibre is very fine with a small diameter, and they are woven to form a flexible fabric. The fabric is normally placed in a mould, for instance a mould for a canoe and polyester resin is added, followed by a catalyst (to speed up the reaction). The process is repeated so that there are many layers of fibre glass and resin and allowed to dry/cure. The resulting material is strong and light. Glass Reinforced Plastic can be sanded for a smooth finish and painted.
Three samples of different weaves of fibreglass are seen below. The pattern of weave determines the strength and weight of the Glass Reinforced Plastic, after resin has been added. Different weaves have been developed for different practical applications.
It appears this one below does work but you just need to click on the link.
Carbon fibre
A carbon fibre is a long, thin strand of material about 0.0002-0.0004 in (0.005-0.010 mm) in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in microscopic crystals that are more or less aligned parallel to the long axis of the fibre. The crystal alignment makes the fibre incredibly strong for its size. Several thousand carbon fibres are twisted together to form a yarn, which may be used by itself or woven into a fabric. The yarn or fabric is combined with epoxy and wound or moulded into shape to form various composite materials. Carbon fibre-reinforced composite materials are used to make aircraft and spacecraft parts, racing car bodies, golf club shafts, bicycle frames, fishing rods, automobile springs, sailboat masts, and many other components where light weight and high strength are needed.