General information about wood-plastic composites

Introduction

Engineers are always looking for better quality. In mathematics and computer science, it is the process of choosing or finding the best member in the sets of available options. Every process has the potential to be optimized and complex problems can be modeled as optimization problems in the fields of engineering, economic and business sciences. The goal of modeling optimization problems is to minimize time, cost, and risk, or to maximize profit, quality, and robust design effectiveness. Some optimization problems are complex and it is difficult to obtain optimal solutions in a reasonable time with exact solution methods such as dynamic programming and branch-and-bound methods. Therefore, it is economically more economical to develop methods for solving these types of problems that can obtain optimal or near-optimal solutions in a reasonable time. In recent decades, various methods have been developed to solve optimization problems. The engineering methodology aims to optimize the conditions of the process and the product, so that the product and the process have the least sensitivity to the changing factors, and as a result, it will bring high quality products. One of the important tools for robust design is Taguchi parameter design. In parameter design by Taguchi method, it is assumed that there are medium quality materials and components in the product, or that the process uses machines that are not very accurate. This will create some tolerance due to the presence of disturbance factors. Therefore, the sensitivity to disturbance factors and quality changes, which are often caused by environmental conditions, should be minimized.

A basic activity of quality engineering is to design and conduct experiments to collect the necessary data for analysis. Taguchi defines an experiment as making a change in a process to study its effects. He considers the most effective way of conducting experiments to be the method of several factors at any time.

As we know, most of the tools and parts used in our lives are plastic parts. By reviewing the studies conducted in recent years, it can be seen that the use of composites, especially wood-plastic polymer composites, has grown rapidly. The main reason for the development of composites is their optimal properties compared to the constituent components, which is mainly done by substituting composites instead of common materials, especially metals[1]. Composite materials are made from the combination of two or more materials to create optimal properties. Of course, the above statement is a general definition and can include all metal alloys, plastic polymers, minerals, wood, etc. [1].

Due to the quantitative limitation of wood and plastic resources, and the growing demand for industrial and construction uses for raw materials with higher quality and longer life, as well as attention to the aspects of product innovation and environmental effects, WPC1 wood-plastic composite materials can be called as a progressive and developable technology. According to the definition of composite materials, wood-plastic composites are obtained from the physical combination of polymers (mostly thermoplastics) with wood particles, which leads to new properties that are different from the properties of wood and the properties of the primary polymer. The word WPC, meaning a combination of wood and plastic, includes a wide range of composite materials. This range includes for plastic materials, from polyolefins to polyvinyl chloride [1] and for filling materials from wood powder to linen fibers. This new composite has expanded the concept of wood composite from its common meaning, which was referred to materials such as chipboard [2] and MDF [3], to a new space and more importantly to a new material with high performance [2]. This means that today the term WPC does not only refer to wood and plastic composite, but instead of wood, other materials such as rice paddy, bamboo, straw, etc. may be used. should also be used [3].

Many researches have been done in the field of producing high quality parts and using waste materials and producing composite materials. The first generation of wood-plastic composite was a combination of wood powder and polymer materials that did not have high physical and mechanical properties. Currently, by adding different materials, such as various lubricants [4] and compatibilizers [5], very good mechanical properties have been obtained for this composite.The processes carried out on this composite to produce different products are similar to the common processes for polymer materials [2]. .

Most of the parts produced from this composite currently have a wood content between 40% and 80%. Most plastic wood products, such as plastic materials, are obtained from extrusions, which no longer require the costly processes used, for example, to shape wood. Of course, to improve the quality of the appearance of the piece, simultaneous extrusion [6] or coating [7] of the products can also be used [5]. In 2004, Mr. Yaembunying and Prachayawarakorn investigated the effect of recycling polypropylene filled with 40% rice bran on the properties of wood-plastic composite produced in the injection process[6]. Plastic wood was used in the Rolls-Royce factory to make the gear head [8]. This issue happened less than a decade after the registration of the first completely synthetic resin [7]. Since 1950, the use of structural and non-structural wood composites instead of pure wood has increased in North America [8]. In 1983, the American Woodstock company [9], using Italian extrusion technology, produced sheets of wood-plastic composite with a polypropylene base [10] and approximately 50% wood [9].

In 1991, the first international wood-plastic composite conference was held in Madison, Wisconsin [11].  In 1993, Anderson Company [12] started the production of this composite with PVC base. In 1996, many American companies began to produce this composite in granular form for use in other companies and factories. From this time on, the activities in the field of wood-plastic grew strongly[9].

1-3-Properties, advantages and applications of wood-plastic composite

This composite has a wide variety of advantages, the most important of which are the following [2]:

Manufactured products do not need additional treatment.

Manufactured products resist water and weather changes much better than wood.

It is more resistant to the growth of fungi and insect attacks than wood.

With an increase in the percentage of wood, its sound and thermal insulation capabilities increase.

low-cost and waste materials can be used in its production.

Recycling the products produced from this composite, after the end of their useful life, is easily possible.

Wood-plastic composites have lower strength, stiffness and creep resistance than wood of the same size. But compared to wood, they absorb less moisture and are more resistant to rotting and destruction.