EFFECTS OF FIBER LOADING ON SOME MECHANICAL AND PHYSICAL PROPERTIES OF SAW DUST REINFORCED HIGH-DENSUTY POLYETHYLENE COMPOSITE

 

Materials made from two or more substances constitutes materials with significantly different physical and chemical properties which remain separate and distinct at the microscopic or macroscopic scale within the finished structure. Natural fiber composites combine plant-derived fiber with a plastic binder. The nature of the fiber component may be wood, sisal, hemp, coconut coir, luffa flax, banana, leaf fiber, bamboo, Okoro, palm-kernel etc. and the binder is high density polyethylene. Advantage of natural fiber composites include light weight low-energy production and sequestration of carbon dioxide reducing the Greenhouse effect. In most cases, the reinforcement is harder, stronger, and stiffer than matrix. The reinforcement usually fiber particulate composites dimension that are approximately equal in all direction. They may be spherical, platelets or any other regular or irregular geometry. Particulate composite tends to be much weaker and less stiff than continuous fiber composites, but they are usually much less expensive. composites are heterogeneous in nature, create by the assembly of two or more components with filler or reinforcing fire and a compatible matrix (Haythan A. A., et al 2018). A composites material can provide superior and unique mechanical and physical properties because it combines the most desirable properties of its constituents while suppressing their least desirable properties. In recent year, there is increasing environmental concerns, greater attentions are being paid towards the use of plants fiber. Taking the advantage of their abundance and availability as renewable resource in the environment, and economical for their cost effectiveness. However, the use of plant fiber as reinforcement in composites materials required extra care regarding fiber/matrix adhesion particularly when the matrix is hydrophobic in nature. This is consequence of the fact that strongly polarized cellulose fiber [hydrophilic] are inherently incompatible with hydrophobic polymers. The main chemical bond theory alone is sufficient to elucidate the complex adhesion issue in composites materials, and consideration of acid -base reaction at the interface. Composites gained so much recognition because of their strength, density, impact, stiffness, elastic modulus etc., also increasing the price of raw -materials in engineering education, along with a continuous threat to our environment from processing has led to the use of natural renewable materials for development and fabrication of polymer composites. There has been research on making composites with synthetic fiber in the past. However, utilize natural fiber reinforcement as a substitution has gained increased attention in various applications. Polymer composites are used for a wide application. However, they do not undergo biodegrading resulting in the generation of solid waste which causes environmental pollution. Researchers are focusing their attention in producing biodegradable composites with natural fiber which are termed as green composites such as water absorption, mechanical properties e.g., Flexural strength test, tensile strength, percentage elongation impact Strength test were studied.

A composites material can be defined as a combination of two or more materials that result in better properties than those of individual components used alone. Composites can also be defined as material that consist of two or more chemically and physically different phases separated by distinct interface. Each phase has its own identity and maintain it physical and chemical properties after it has been integrated into composites. In general, composite contains two (2) components which are polymer and non - polymer. The polymer act as a matrix while non polymer act as a filler. Composites are hybrid material made of a polymer resin reinforced by fiber, combining the high mechanical and physical performance of the fiber and the appearance bonding physical properties of polymer. The short and discontinuous fiber composites are responsible for the biggest share of successful applications, whether measured by number of parts or quantity of materials used. The differences between blends and composites are that the two main constituents in the composites remain recognizable while these may not be recognizable in blends. The predominant useful material used in our day-to-day life are wood, concrete ceramic and so on. The most important polymeric composites found in nature and these are known as natural composites. The composites material are materials composed of two or more distinct phase [ matrix phases and dispersed phase] and having bulk properties significantly different from those of any of the constituent. Matrix phase is primary phase having a continuous character. Matrix is usually more ductile and less hard phase. It holds the dispersed phase and share a load with it. Dispersed (reinforcing phase) is secondary phase it is usually stronger than the matrix, therefore, it is sometimes called reinforcing phase. Composites of polyethylene from source fossil and some lignocellulosic filler from agriculture, among them sponge- gourds, have been reported. 

It comprises of two major components and a bounding zone. These components are; Matrix reinforcement matrix material cover the range from polymer to metal to ceramic. The matrix is a substance that is capable of holding the reinforcing material together by surface materials, a matrix is also defined as a material that give body and grips or holds the reinforcement of the composite together and is usually of lower strength than the reinforcing material. (Hammajam A.A., et al 2020)

Polymers make ideal material as they can be possessed easily, possesses light weight and desirable mechanical properties. Two main kinds of polymers are thermosets and thermoplastics. Thermosets have cross linked polymer structure during the curing process helping them form more stable bond. They can be retained in a partially cured condition too over prolonged period of time imparting thermosets high flexibility. Hence, they get high preference as matrix bases for advanced conditions fiber reinforced composites. Thermoplastics have one- or two-dimensional molecular structure and they tend to act as elevated temperature and display exaggerated melting point. Another advantage is that the process of soften at elevated temperature can be reversed so that composites regain their properties during cooling, aiding applications of conventional compress techniques to mold and compound.

Carbon composites are composite materials consisting of carbon matrix reinforced by carbon fiber. They may be manufactured with different orientation of the reinforcing phase i.e., carbon fiber. They may be manufactured with different orientation of the reinforcing phase i.e., directional structure, multidirectional. they possess excellent thermal shock resistance, high modulus of elasticity, high thermal conductivity and have excellent heat resistance in non-oxidizing atmosphere.

Composites in which metallic matrix are combined with ceramic or metallic dispersed phase in metal matrix composites. Most metals are alloys make good matrices. The low density of the light materials proves to be more advantage and renders the metal responsive. Aluminum, titanium, and magnesium are the popular matrix metals currently in trend which are particularly useful for air craft applications. Metallic matrix applications required high modulus reinforcement to offer high strength to weight ratios than most alloys.

Composites in which ceramic matrix is combined with ceramic dispersed phase owing to the main advantage observed in conventional ceramic i.e., brittleness, ceramic matrix composites are designed with improved toughness. Because of high melting points, good corrosion resistance, stability at elevated temperatures and high compressive strength, ceramic-based matrix materials become a clear favorite for applications requiring a structural material that withstand temperature above 1500C.Naturally, ceramic matrices are first choice for high temperature applications.

Reinforcement can simply be defined as a substance in a composite material that increases the mechanical properties of the neat resin structure. For proper handling, fillers and reinforcement are used to lower materials cost by reducing the volume of matrix required.

Fiber reinforced composites (discontinuous -short or continuous-aligned), particulate composites (dispersion strengthened or large particles), structural composites (laminates structure).

A composite whose reinforcement is a particle with all the dimensions roughly equal are called particulate reinforced composites. particulate fillers are employed to improve high temperature performance, reduce friction, increase wear resistance and reduce shrinkage (Jaquelin A. D et al 2016). The particles will also share the load with the matrix, but to a lesser extent than a fiber. The particles are either metallic or non-metallic, which are of two types

a) large particle composite.

b) dispersion strengthened composite.

Fiber reinforced composite material consists of fiber of high strength and modulus embedded in or bonded to a matrix with distinct interface between them. Fiber reinforced composites are composed of reinforcing fibers which were characterized as a long fine filament with an aspect ratio of >10(Jaquelin A. D et al 2016) Glass ,carbon, aramid ,boron, and cellulose fiber were widely used as reinforcement in composite material, they were especially useful composite because they contain a reinforcing phase in which high tensile strength were realized when they processed to fine filament, wire or fiber constitute an important class of reinforcing materials. the use of fiber as reinforcing material is due to; The small diameter of fiber with respect to other micro-structural units. A high degree of flexibility permits the use of a variety of techniques for the formation of composite using fiber.

Composite materials consist of two phases. It consists of one or more discontinuous phases embedded in a continuous phase. The discontinuous phase is usually harder and stronger than the continuous phase and is called the reinforcement or reinforcing material, whereas the continuous phase termed as the matrix. The matrix is usually more ductile and less hard. It holds the dispersed phase and shares a lot with it. Matrix is composed of any of the three basic material types i.e., Polymer, metal or ceramics. The matrix forms the bulk from or part or product. The secondary phase embedded in the matrix is a discontinuous phase .it is usually harder and stronger than continuous phase. It serves to strengthen the composites and improves the overall mechanical properties of the matrix. Properties of composites are strongly dependent on the properties.

A laminate is fabricated by stacking a number of laminates in the thickness direction. Generally, three layers are arranged alternatively for better bonding between reinforcement and the polymer matrix for example plywood and paper. A hybrid laminate can also be fabricated by the use of different constituent materials or the same materials with different reinforcing pattern. In most of the applications of laminate composites, man-made fiber is used due to their good combination of physical, mechanical and thermal behavior. According to the end use of the composites this laminate can have unidirectional or bi- directional orientation of the fiber reinforcement.

To investigate some mechanical and physical properties of sawdust fiber reinforced HDPE composites and optimize the sawdust particle size for improving the mechanical properties of HDPE composites.

1. To conduct flexural strength tests, impact strength tests and hardness on the HDPE composites and analyze the results.

2. To conduct density and water absorption tests on the HDPE composites and analyze the results.