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The Thermosetting Plastics Engineering Essay

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Plastic is classified into thermoplastic and thermosetting. Thermoset materials once formed into permanent shape and cured by a chemical reaction cannot be remelted or reformed into another shape but degrade or de compose upon being heated to too high temperature. Thus, thermosets cannot be recycled. This plastic cure at room temperature by chemical reaction. During curing, they form three-dimensional molecular chains. So, it consists of a network of carbon atoms covalently bonded which reduces the flexibility of the molecules and form rigid solid. Sometimes nitrogen, oxygen, sulfur or other atoms are also covalently bonded into a thermoset network structure [1].

Generally thermosets have good dimensional stability, thermal stability, chemical resistance and electrical properties. Although thermosets is brittle, it has excellent tensile strength. The usage of thermosets has increased markedly. Thermosets are find widespread use in several application such as adhesives, primary and secondary structural members in aerospace, countertops and floors manufacturing facilities and homes, printed circuit boards, conductive polymer elements, encapsulation for electronic materials and recreational products such as tennis racquets [2].

Most famous types of thermosetting plastics are epoxies, phenolics and polyester. Each type of thermosets has own unique set of properties. The table below 1.1 shows trade names, major application characteristics and typical application of three types of thermosets :

Polyester can be a thermosetting plastic or a thermoplastic plastic. Polyester resin is thermosetting. Polyester are low-cost resin systems and offer excellent corrosion resistance [4]. The operating service temperature for polyester is lower than epoxies [4]. Moreover, polyester resins are highly preferred in the market for their high strength, light weight, easy handling and installation and longer functioning life.

Polyester resin are used in electrical components, sheet moulding compound, bulk moulding compound, pipes, tanks, ducts and pultrusion.

Polyester resin are unsaturated resin are formed by the reaction of unsaturated difunctional organic acids with difunctional alcohol. The typical acids are maleic, fumaric, phthalic, and terephthalic. The typical alcohols are ethyelene glycol, propylene glycol and halogenated glycol. One percent catalysts added for curing or crosslinking process.

Fillers is one of the additive. Filler materials are mostly added to polymers to improve polymers by increasing bulk, tensile strength, abrasion resistance, thermal properties and other properties. Their major contribution was in lowering cost of final product by replace some volume of the more expensive polymer. Moreover, cost reduced by faster molding cycles as result of increased thermal conductivity.

Materials used as particulate filler include wood flour, sand, silica flour, glass, fly ash, clay and even some synthetic polymers [6]. Each filler type has different properties and these in turn are influenced by the particle size, shape and surface chemistry [7]. Particle size range all the way from 10 nm to macroscopic dimensions [6].

In developing reinforcing fillers, the aims of process or material modifications are increase the aspect ratio of particles and to improve their compatibility and interfacial adhesion with the chemically dissimilar polymer [7]. Moreover, much kind of treatments researches on fillers are going. This kind of modification enhances the mechanical and thermal properties of final product.

Fly ash

Coal as fueled in power plant produce more half of electricity we consume today. These plants produce a material that is the fast becoming good filler for improving the performance of some product. The material called as fly ash.

Fly ash is best coal ash particles. The name of fly ash exists because it is transported from combustion chamber by exhaust gas. Fly ash is a byproduct from burning pulverized coal in power plant. During combustion, mineral impurities in the coal (clay, feldspar, quartz, and shale) fuse in the suspension and float out of the combustion chamber with the exhaust gases [8]. The fused material will rise and it cools. Upon cooling the fused material transform from vapor state to liquid and to slid state. End of the process spherical particles are formed which called as fly ash. The fly ash collected by using electrostatic precipitators, baghouses or a combination of both.

In past fly ash was generally released into the air, buried in landfill or illegally dumped into our oceans. In recent years the fly ash recycled by using as filler, supplement and other additives. It's really helped to reduce the pollution.

Fly ash is the fine powder formed from mineral matter in coal, consisting of noncombustible matter in coal plus a small amount of carbon that remains from incomplete combustion [9]. Fly ash generally gray in colour and consists mostly of silt-sized and clay-sized glassy spheres. Photo 1.1 shows fly ash which collected from Manjung Power Plant, Perak.

 fly ash.JPG

Photo 1.1: Fly Ash

Fly ashes are particularly rich in SiO2, Al2O3 and Fe2O3, and also contain other

oxides such as CaO, MgO, MnO, TiO2, Na2O, K2O, SO3, etc [10].

Fly ashes divided into two categories, according to origin ASTM, which are class C fly ash and class F fly ash. The chief difference between these classes is the amount of calcium , silica, alumina, and iron content in the ash [11]. The chemical properties of the fly ash are largely influenced by the chemical content of the coal burned which are anthracite, bituminous, subbituminous and lignite. The table 1.2 shows the difference between class C fly ash and class F fly ash.

Class C

Class F

Fly ash normally produced by burning lignite or sub-bituminous coal which meets the requirements applicable to this class. In addition to pozzolanic properties, Class C fly ash also possesses some cementitious properties. Some Class C fly ashes may have lime contents in excess of 10 %.

Fly ash normally produced by burning anthracite or bituminous coal which meets the requirements applicable to this class. Class F fly ash has pozzolanic properties

Table 1.2: Difference between Class C and Class Fly ash [10]

APPLICATION OF FLY ASH

First for most, large scale use fly ash as filler material applied in recent years. Fly ash is placed in thin lifts and compacted is called structural fillers. Structural fly ash fillers are relatively incompressible are suitable for construct building and other structures [12]. Non structural fly ash can be used for development of parks, parking lots, playgrounds and other similar lightly loaded facilities [12].Fly ash relatively increase the strength of the composite. Fly as posses self hardening properties which can develop the shear strength. Significant increase in shear strength can be realized in relatively short period of the time and it can be very useful in the design of embankments [12].

In addition, fly ash can be used in portland cement concrete to increase the performance of the concrete. Portland cement manufactured with calcium oxide, some which released in free state during hydration. 10 to 20 percent of lime released during hydration of the cement. This lime reacts with fly ash silicates to form strong and durable cementing compounds which can enhance many of the properties of the concrete. The benefits are increased ultimate strength, increased durability, improved workability, increase resistance of sulfate attack, increased resistance to alkali-silica reactivity and reduced shrinkage [12]. By utilize fly ash in concrete life of concrete road and structures will improve. Energy use, greenhouse gas and other adverse air emission can be reduced by replace fly ash in manufactured cement.

Moreover, fly ash can be utilized for construction of road and embankment. There are many advantages of using fly ash which are saves the top soil, avoids creation of lying areas, avoids recurring expenditure on excavation of soil from one place for construction and filling up of low lying areas thus created and control the source of the pollution [12].

Finally, research on agricultural uses of fly ash has been going on research institutes for the past few years. Fly ash can be a soil modifier and enhance its moisture retaining capacity and fertility [12]. It improves the plant's water and and nutrient up take, helps in the development of roots soilbinding stores carbohydrates and oils for use when needed protects the plants from soil borne disease and detoxifies contaminated soils [12].

Drawbacks of fly ash utilization

There is few factors influence to low the fly ash utilization which is listed below:

Poor understanding of chemical composition and bonding of fly ash and its derivatives for proper application.

Fly ash products has no standards and specifications

Lack of reliable and awareness for public on fly ash products

Problem in dry fly ash collecting

Coordination between thermal plants and ash users are weak.

Composites

A composite material is made by combining two or more materials. The combination of materials with the objective of getting a more desirable combination of properties. The composite definition more general and can include metal alloys, plastic co-polymers, minerals, and wood. The major concept of a composite is that it contains matrix material. As a example, composite material is formed by reinforcing fly ash in a polyester resin. Many composite material composed of just two phase which are matrix and dispersed phase. The reinforcement or dispersed phase can be fibers, particulates and the matrix material can be metal, plastic or ceramic. The properties of composites are function of the properties of the consistent phase, their relative amounts and the geometry of dispersed phase [6]. Shape of particle, particle size, distribution and orientation influence the composite. Most of the composite been expected to improve in mechanical characteristics such as impact strength, hardness, tensile strength, and tribology characteristics such as wear, friction. Figure 1.2 shows one simple scheme of classification of composite.

Draw the composite classification

Particle - Reinforced Composite

Particle - Reinforced composite has two sub classifications which are large particle and dispersion - strengthened composite. The difference between two classifications is based on reinforcement or strengthening mechanism. The improvement of composite properties depends on strong bonding at the matrix - particle interface.

Large particle

Large particle defined as particle and matrix interaction cannot be treated on the atomic or molecular level; rather continuum mechanics is used. The large particle phase is harder, stiffer and stronger than matrix. These particles tend to restrain movement of matrix phase in vicinity of each particle. When the load applied on the composite, the matrix transfers some of the applied stress to particles which bear a fraction of the load.

Dispersion-strengthened composite

Dispersion-strengthened composite particles are normally smaller with diameters between 10 and 100 nm. These particles-matrix interaction that lead to strengthening occur on the atomic or molecular level. In dispersion - strengthened the matrix bears the major portion of an applied load, the small dispersed particles hinder or impede the motion of dislocation [6]. The plastic deformation is restricted such that yield and tensile strength, as well hardness is improved [6].

Objective

This study seeks to achieve the following objectives:

Study the mechanical characterisations of fly ash reinforced polyester composites

Study the effect of ethanol in fly ash.

Problem Statement

Prepare the composite of fly ash reinforced polyester in different percentage.

Study the mechanical characterisations of the composites.

Treated fly ash with ethanol will effect the bonding?


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