(WPC) is a composite material that has received much attention in recent years due to its unique combination of properties. This material consists of wood fibers or flour combined with thermoplastic polymers, which leads to the creation of a very widely used material that displays the natural beauty of wood along with the durability and efficiency of plastic. The purpose of this article is to provide an overview of wood-plastic composites, including introduction, key properties, types, examples, applications, comparison with thermowood, and finally a summary of the presented content. Keywords: wood plastic composite, WPC, hybrid materials, wood fibers, thermoplastic polymers, applications, thermowood.
Wood plastic composite (WPC) is a relatively new material that has emerged as an environmentally friendly alternative to traditional building materials. The combination of wood fibers and thermoplastic polymers in WPC leads to the production of a material that has the useful properties of both of its main constituents. Due to its exceptional mechanical properties, environmental sustainability, and aesthetic appeal, this unique combination has attracted a lot of attention from various industries, including construction, automotive, furniture, etc.
WPC is usually composed of a mixture of wood fibers or wood flour derived from various sources, including sawdust, wood chips from cutting tree trunks, and agricultural residues. These natural fibers are combined with thermoplastic polymers such as polyethylene, polypropylene, PVC, etc. which act as a matrix material and hold the wood fibers together (Figure 1). Additives such as coupling agents, UV stabilizers, dyes, and lubricants are often added to raw materials during the compounding process to improve the overall performance and longevity of the final product. The methods of preparing wood-plastic polymers can be classified into two general categories: extrusion process and injection molding process. The extrusion process is usually used in applications such as fencing, decking, and outdoor applications, while the injection molding process is usually used to prepare more complex products, such as automobiles, furniture, and other items.
Types of wood-plastic composites can be classified based on the type of wood and the type of polymer used. The most common types are:
These materials usually consist of a combination of fibers or wood flour, which can be prepared from a variety of different wood sources, and polyethylene, which is a thermoplastic and widely used polymer. Wood fibers lead to natural beauty and strengthening of the final product, while polyethylene acts as a binder and gives properties such as strength and durability to the final composite. The production of WPC based on polyethylene includes a combined process in which wood and polyethylene fibers are combined and processed through extrusion or injection molding methods. During the manufacturing process, additives such as coupling agents, UV light stabilizers, and dyes may be added to the raw materials to enhance specific properties and improve the overall performance of the final composite. The production process of WPC includes a compounding stage in which wood fibers and thermoplastic polymers are mixed, and then we have a forming stage in which the mixture is processed through extrusion or injection molding. During these processes, composite materials can be molded into different shapes and dimensions, which makes it suitable for a wide range of applications (Figure 2).
Polyethylene-based WPC exhibits a wide range of desirable properties that make it an excellent alternative to traditional wood and other materials:
Polyethylene-based WPC is highly resistant to environmental factors such as humidity, UV radiation and temperature changes. This feature ensures minimal degradation and excellent dimensional stability, making it ideal for outdoor applications (Figure 3).
The combination of wood fibers and polyethylene creates a composite material that is more durable and long-lasting compared to natural wood. This product is resistant to decay and insect damage and guarantees a long life of the final product.
Polyethylene-based WPC can be easily molded and shaped during the manufacturing process, which allows the creation of complex designs and profiles for various applications.
Unlike plain wood, polyethylene-based WPC requires minimal maintenance. Also, it does not need regular sealing, staining or painting to maintain its good appearance and performance.
By using recycled or renewable wood fibers and a recyclable thermoplastic, polyethylene-based WPC is more environmentally friendly than materials that rely solely on non-renewable resources (Figure 4).
WPC made of polypropylene offers better stiffness and thermal resistance compared to polyethylene-based WPC. Polypropylene-based wood-plastic composite is another type of WPC that uses polypropylene as a thermoplastic polymer component. Like other types of WPC, this category has gained popularity in various industries due to its unique properties and benefits. The combination of polypropylene with fibers or wood flour leads to the creation of a composite material that provides stiffness, heat resistance and other valuable properties and makes it suitable for a wide range of applications. The production process of WPC based on polypropylene is similar to other types of WPC. This process includes a combined process in which wood and polypropylene fibers are combined and processed through extrusion or injection molding methods, respectively. During the manufacturing process, additives may be incorporated to enhance specific properties and improve the overall performance of the composite material (Figure 5).
Polypropylene-based WPC offers a wide range of valuable properties that make it a preferred choice for various applications:
Due to its higher stiffness compared to other thermoplastic polymers used in WPC, polypropylene has created a composite material with higher strength and load bearing capacity.
WPC based on polypropylene shows better heat resistance compared to some other types of WPC, making it suitable for use in hot and sunny weather.
The combination of polypropylene with wood fibers improves dimensional stability and reduces the risk of warping or distortion over time.
WPC based on polypropylene is resistant to various chemicals and solvents and is known for its durability and suitability for outdoor and industrial applications.
The polypropylene matrix in the composite helps to absorb low water in the resulting composite, and as a result, it is less susceptible to moisture-related issues such as swelling or decay.
PVC-based WPC consists of wood fibers or flour mixed with polyvinyl chloride (PVC), a widely used thermoplastic polymer known for its resistance to harsh weather conditions and excellent chemical resistance. The wood fibers provide natural beauty and reinforcement, while the PVC acts as the matrix material, giving the composite toughness and long-term performance. PVC-based WPC offers a wide range of useful properties that make it a popular choice for indoor and outdoor applications in various industries (Figure 6). The production process of PVC-based WPC is similar to other types of WPC. Fibers or wood flour are mixed with PVC and processed through extrusion or injection molding techniques. Additives such as impact modifiers, UV stabilizers, and lubricants are often used during the compounding process to enhance specific properties and ensure optimal performance of composite materials.
PVC-based WPC shows a set of useful features that make it a suitable choice for various applications, among these properties, the following can be mentioned:
PVC is inherently weather resistant, making PVC-based wood-plastic composites very durable and suitable for outdoor applications. This product can withstand sunlight, rain and harsh environmental conditions without significant degradation.
PVC-based WPC is resistant to a wide range of chemicals, including acids, bases and salt water, making it suitable for marine and industrial applications.
The presence of PVC in the composite helps to absorb low water and shows minimal swelling or decay when exposed to moisture.
WPC preserves the natural appearance and texture of wood and is a beautiful alternative to traditional plastics.
Unlike traditional wood, WPC requires minimal maintenance. It does not need to be painted, stained or sealed to maintain its appearance and performance.
PVC-based WPC is naturally resistant to termite attacks and the resulting decays, and increases the life of the product and reduces the need for frequent maintenance (Figure 7).
PVC-based WPC maintains its color stability over time and does not require frequent repainting, which is a significant advantage over traditional wood.
The versatility of WPC has made it suitable for a wide range of applications (Figure 8), including the following:
WPC is widely used in porches, fences and other cases due to its resistance to environmental conditions and low maintenance requirements (Figure 9).
WPC is used to produce a variety of furniture, including tables, chairs, and cabinets, offering a durable option with good aesthetics.
WPC is used in the interior components of the automobile and helps to reduce weight and increase stability.
WPC is used to create environmentally friendly and lightweight packaging materials, reducing the environmental impact of packaging waste.
WPC is used in outdoor structures such as gazebos, benches, and flower pots, which provides an attractive and durable solution. As mentioned earlier, additives play an important role in making various types of wood-plastic composites. Tables 1 and 2 show some additives used in wood-plastic composites based on polyolefins and PVC.
While both WPC and Thermowood materials offer environmentally friendly alternatives to traditional wood, they differ in composition and properties. In order to clarify the issue, it is better to first have a definition of thermowood and then discuss the uses of this material and its differences with ordinary wood and WPC. Thermowood wood is a kind of modified wood that is produced by placing natural soft wood such as pine or fir in a heat treatment process. This process involves heating the wood at a high temperature (usually between 160°C and 230°C) in the absence of oxygen (a process known as heat treatment or heat treatment). Heat treatment changes the chemical and physical properties of wood, resulting in more stable, durable and rot-resistant materials.
Due to its increased properties, Thermowood is mainly used in outdoor applications (Figure 10) and is suitable for the following:
Thermowood is a good choice for fencing due to its improved stability and resistance to decay, which makes it more durable in outdoor environments than ordinary wood.
Due to its resistance to weather and its appearance, it is usually used as an external coating and facade of buildings.
Thermowood’s stability and resistance to decay make it suitable for making outdoor furniture pieces such as tables, chairs and benches.
It is used in garden structures such as gazebos and terraces due to its resistance to atmospheric factors and decay.
• Material composition: WPC is a composite material made of wood fibers and thermoplastic polymers, while Thermowood is natural wood that has been subjected to a heat treatment process to increase its properties. • Aesthetics: WPC maintains the natural appearance of wood, but its appearance may not resemble traditional wood. As a natural wood, Thermowood maintains its original aesthetics. • Durability: WPC is very durable, resistant to moisture, decay and insect infestation. Thermowood, although more durable than conventional wood, may still be susceptible to rotting if not maintained properly. • Performance: WPC offers better performance compared to Thermowood because it can be easily molded into different shapes during construction.
Wood plastic composite (WPC) is a hybrid material with exceptional properties that combines the natural beauty of wood with the durability and versatility of thermoplastic polymers. Its diverse applications, from construction to automotive industries, have made it an environmentally friendly alternative. While WPC and Thermowood both offer sustainable options, they differ in composition and properties, allowing consumers to choose the most suitable material for their specific needs. As technology and research advances, WPC will likely continue to expand its applications and positively impact various industries worldwide. Figure 11 briefly shows a picture of the production to consumption and recycling of WPC based on different thermoplastic polymers presented above.
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