1. Introduction and General Information
Due to the decrease in the forest presence in the world and the increase of the environmental consciousness, as well as the need for wood and wood-based materials, the existing forest resources need to be used efficiently.
Therefore, the search for new products in which wood raw materials can be used in the wastes of the processing industries are being developed, and wood-based composite panel products that can be used instead of solid wood are being developed.
Therefore, the studies for the creation of both economic and high strength and very light materials have been intensified. In this way, the composite materials, which are produced by the combinations of the components that make up the material, have gained a great importance.
The materials formed by combining these materials at the macro level are called “Composite Material” in order to bring together the best features of two or more same or different groups of materials or to create a new feature.
In other words, they can be called materials consisting of different kinds of materials or phases, which are combined to obtain superior properties by correcting each other’s weakness (Candan, 2014; Rosato, 1997).
Figure 1 shows the reinforcing and matrix structures forming the disposable materials.
Figure 1. Reinforcing and matrix structures forming composite materials (Aran, 1990)
Table 1 lists the types of materials used in the composite structures and the shapes of the composite structures.
Table 1. Matrix, reinforcement element and composite structure types (Aran, 1990)
From these two groups of materials, the reinforcing material determines the strength and load-bearing properties of the composite material, while the matrix material plays a role in preventing crack propagation in the transition to plastic deformation and delays the breakage of the composite material (Aran, 1990).
The low specific gravity of composite materials gives great advantages in lightweight structures. In addition, corrosion-resistant, heat, sound and electrical insulation of fiber-reinforced composite materials provide a significant advantage for their respective usage areas (Onat, 2015).
The aim of this study is to produce environmentally friendly, sustainable, recycling and recyclable, very low cost, and high performance biocomposite materials.
2. Historical Development of Composite Materials
Although the production of composite materials, which is widely used in every field, has been produced for the last few hundred years, the first examples are based on very old ones. In the early 1940’s that the subject was dealt with as an engineering subject.
The first examples of the multi-component material are the stage in which the interventions to the material. From the earliest times, people have tried to remove this fragility by adding plant or animal fibers in fragile materials. One of the best examples of these issues is adobe material.
In the production of adobe, stalks and fibers such as ivy branches, and straws which are incorporated into clay mud, increase the resistance of the material during both production and use.
On the other hand, it is understood from the findings that it is not very new application of fibers which are commonly used in equipping composite material. For example, the production of glass fibers is dated to ancient Egypt. It was known that the construction of fine glass fibers in Egypt in 1600 BC was known as XVIII dynasty age.
It is understood from the presence of amphoras which are adorned with various dark and colored glass fibers from the dynasty age.
The first record of the use of glass fibers in industry is dated 1877.There are patents issued at the beginning of this century about the method of producing artificial stone plates using hydraulic binders and fiber materials.
Two of the composite materials, which are the most widely used in everyday applications, are composite materials equipped with asbestos fibers and polyester composites with glass fibers.
The cement and asbestos composites which are used in thin plate construction for the first time, are still used today by preserving their importance. On the other hand, synthetic fibers with fibers have been used in the industry since the mid-1950s.
The most well-known group of this material is” glass fiber reinforced polyester resin composite”. In our country, this material is called” fiberglass”.
Since the beginning of 1960, fiberglass is used in areas such as construction of small boats, liquid tanks, roof plates. “Anadol”, the first domestic automobile produced in our country, is produced from this material. It is called “Glass Reinforced Plastic (GRP)” for synthetic resin matrix materials equipped with glass fibers.
It is now used in other thermoset and thermoplastic resins in addition to polyester which is the most widely used material in the production of glass reinforced plastics.
3. Structure of Composite Materials
The composite materials are manufactured to comprise at least one main material and at least one reinforcing phase. The reinforcement and the main material which make up the composite show a physical association depending on the production method and the shape designed during the production of the composite.
The main material and the reinforcing element, which are combined with various methods, maintain their designed forms by forming a connection region, called the interface between them, in order to exhibit their properties completely without losing.
Figure 2. Schematically components of composite material (Kaya, 1995)
Composite materials have three main components.
These;
1. Matrix,
2. Reinforcement,
3. Additives.
3.1. Matrix
The matrix forms the continuous phase as a thermoplastic or thermoset polymer material. Since the particleboard is a wood composite material, the matrix of this composite material is the glue used. In this study, the wood chips are reinforced with thermoset polyester resin.
When thermoset polymers are heated, a continuoussolidification occurs, they can never be reheated and hardened again. During heating, covalent crosslinking occurs. This type of binding prevents bending and rotating movements. Their structures are hard and brittle (Ay, 2008).
There are 2 types of polyester resin used in composite materials. These are; isophthalic polyester which has better properties such as water resistance and orthophthalic.
There are polyester production companies for general use in Turkey. Advantages of polyester resins; easy to use and very low cost (0.5 – 1 $/kg) (Arıcasoy, 2006).
3.2. Reinforcement
Reinforcement; aramid, carbon, graphite, boron, silicon carbide, alumina, glass and polyethylene materials are used in the form of short or long continuous fibers and the matrix has a function of reinforcing about 60% volume. In the study, the material to be reinforced with polyester resin is the particleboard.
Wood is recyclable, renewable, and biodegradable biomaterial. Approximately 40%-45% of a wood is composed of cellulose, 10%-25% hemicellulose, and 18%-35% lignin. Although the chemical structure of cellulose in different natural fibers is similar, the degree of polymerization varies.
The mechanical properties of a biofiber depends on its degree of polymerization (Mohanty et al. 2005). Softwoods are generally preferred in the production of composite materials. This is because; the fibers obtained from softwood should have a high aspect ratio.
The regular lumen structure can be added to this (Mohanty et al. 2005). In this study, some of the sample groups were supported with jute plant fibers. Jute has good antistatic and insulating properties, low temperature conductivity and reasonable humidity. Fibers are 17-20 microns in diameter, 1-4 meters in length.
Figure 3. Wood chips Figure 4. Jute plant fiber Figure 5. Glass fiber
3.3. Additives
Fillers, chemicals and other additives are added to the matrix in order to improve the properties according to their characteristics (Arıcasoy, 2006).
General additives used in polyester resin are as follows (Cam Elyaf, 2014);
Inhibitors:
The additives in this group are used to slow down the reactivity of the polyester to prevent the polymerization of polyester resins before use. The most commonly used inhibitors are hydroquinine and tertiary butyl carbonate (TBC).
The inhibitor is generally used in milliseconds relative to the resin and must be very carefully balanced so that it does not completely block the hardening of the resin.
Promoters:
These additives react with the catalyst to accelerate the polymerization reaction.While inhibitors give the resin a certain shelf life, promoters accelerate hardening from the addition of catalyst.
The balance between the promoter and the inhibitor is very sensitive and the overpowering of any additive may disrupt the balance. Major promoters are cobalt naphthenate, cobalt octoate, dimethyl aniline (DMA), and diethyl aniline (DEA).
Catalysts:
The catalyst (initiator) is not part of the chemical reaction but provides the energy necessary for the start of the process. By adding the catalyst, the balance between the promoter and the inhibitor is impaired and the control of the reaction order passes to the catalyst.
The catalyst releases oxygen (or forms free-radical molecules) and may be seen as fuel for the polymerization process. The reaction initiated by the addition of catalyst is exothermic. That means when the structure of the network is formed, heat is generated.
4. Material and Production Method
The particleboard panels are to be reinforced with polyester resin. The reinforcement material of the composites is the wood chips. Polyester resin is preferred because it is a suitable polymer for improving the physical, mechanical, and biological properties of the wood chips.
The wood chips that are obtained from various types of wood were reinforced with VRTM by adding polyester resin and composites were produced. As a production method, “Vacuum Assisted Resin Transfer Molding” method was preferred.
It is basically the same as the “Resin Transfer Molding” method. In this method, the system is powered by vacuum. The previously prepared reinforcement materials are placed in the mold and isolated from the external environment by the vacuum bag. Resistance is provided by the help of vacuum.
Figure 6. VRTM production method (Ataş, 2014)
Areas of use today; truck body parts, car body panels, bus panels, spoilers, dashboards, medical devices, storage tanks, vehicle seats, chemical pumps, nautical parts such as small boats, wind energy tribune wings, aircraft parts, bullet bodies, bicycle bodies and doors (Cam Elyaf, 2014).
5. Findings
The results of the tests performed on the experimental plates produced to determine the effect of the composites produced on the physical and mechanical properties of the composites produced are given in Table 2.
Table 2. Averages of test values of the composite groups
6. Conclusion and Recommendations
This study showed that new generation composites with very high-performance mechanical properties, improved physical properties, resistant to water absorption, resistant to biological factors can be produced.
In this way, value-added products will be produced. In addition, these new generation composites can be used in places such as construction which demand high performance and automotive.
These high value-added products can be produced for small or medium sized enterprises in the forest products industry with their order-based boards, composites, wood waste chips, chips, and VRTM production facility for different sectors.
Doç. Dr. / Asst.Prof. Zeki Candan
Istanbul University
Cerrahpaşa Forest Faculty
Forest Industry Engineering Department
Mert Yıldırım
Istanbul University
Cerrahpaşa Forest Faculty
Forest Industry Engineering Department
Eda Silan
Yıldız Technical University
Chemistry Metallurgy Faculty
Chemical Engineering Department
References
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