CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Polyurethanes are special group of polymeric materials which essentially are different from most of the other plastic types. Polyurethanes are polymers that consist of units joined by urethane links (Kugler et al, 1997).They are obtained by polymerizing multifunctional isocyanates and polyol.
Polyurethanes can exist as both rigid and flexible foams, and as a coating or adhesive material. Since polyurethanes come in so many forms and can have a wide variety of properties, it is also used in many different applications. Rigid polyurethanes are used as insulation and flotation, while flexible ones are used for cushioning and packaging (Gharehagh and Ahmadi, 2012). In addition, they are used as adhesives in construction and transportation. Polyurethanes are mostly thermosets, which means they are hard to melt and reprocess and can therefore have the disadvantage of being non-recyclable. Since the polyurethane products specially foams are playing an indispensable rule in our daily life because of wide range of applications in automotive, household, refrigerators, insulations, reducing of the fire risk of such a products are become more vital (Usman et al, 2012).
In flexible polyurethane foams, the fillers promote an increase in density and resistance to compression. In addition, properties such as tensile strength are significantly affected by the introduction of filler. They have been widely applied in biomedical applications, building and construction, automotive, textiles and in several other industries due to their superior properties in terms of hardness, elongation, strength and modulus (Chattopadhyay et al., 2007).
Urethane group is the major repeating unit in polyurethanes, produced from the reaction between alcohol (–OH) and isocyanate (NCO). Polyurethanes also contain other groups such as ethers, esters, urea and some aromatic compounds (Zia et al., 2014). Among the major applications, polyurethane foam is one of the prominent products which are being used globally to a significant amount. Polyurethane foams can be easily tailored to obtain specific products by merely changing the types and quantities of surfactants, catalysts, blowing agents, isocyanate, polyol as well as the extent of intercalation and exfoliation between fillers and matrices to meet the desired purpose (Taheri and Sayyahi, (2016), and Scridaeng et al, (2015)).
Polyurethane exhibit wide application as coatings due to their specific properties such as excellent mechanical strength, toughness, good abrasion, corrosion and chemical resistance and low temperature flexibility (Ismail et al, 2011). One of the important categories of polyurethanes is “polyurethane elastomers” that has been widely incorporated into different engineered products and proven to offer highly impeccable properties (Zia et al, 2013). Initially, most of the polyols used to prepare polyurethanes were obtained from petroleum sources but the high energy demands as well as environmental concerns have increased the necessity for more suitable and environment-friendly substitutes. Mineral calcium carbonate (CaCO3) holds the largest market volume in the plastic sector and is mainly imported. Hence, the need to source for renewable materials, which can serve as alternative fillers to the conventional mineral calcium carbonate (CaCO3) with a view of minimizing the polyurethane foam production cost because the higher the filler content the lesser the polyol used in foam production. In flexible polyurethane foams, the fillers promote an increase in density and resistance to compression. In addition, properties such as tensile strength are significantly affected by the introduction of filler.
Flexible polyether foams are classified as low density, medium density and high density (Ajiwe et al., 2005). The price of foam depends mainly on its density. As a result of the high cost of raw material, there is a need to source for cheaper, a readily available and eco-friendly material that can be used as filler. Filler, as used in plastic and rubber industries is a finely divided solid material which is added to the liquid, semi-liquid or solid composition to modify the physical properties of the composition and to reduce cost.
Accordingly, it is necessary to determine the correct concentration of the filler in the polymer matrix, so as to obtain a product of reliable quality. There are so many fillers used in the production of foam such as goat femur, groundnut husk, calcium carbonate (CaCO3), Clay, snail shell, eggshell, cocoanut husk, and corn cob etc. Predominantly, fillers are used to cheapen end products, in which they are called extenders. Among over twenty most important fillers, calcite (CaCO3) holds the largest market volume and is mainly used in plastic sectors. Other fillers include dolomite (CaMg (CO3)2), kaolin and talc (Hans, 2005). The use of inorganic fillers have several disadvantages including difficulty of preparing and maintaining the dispersion; problems with removal of entrained air; difficulty of mixing and pumping the filler/polyol slurry; loss of the foam physical properties; difficulty of processing on all types of foam machinery, and, due to their abrasive nature, increased wear on machinery components (Bartczak et al., 1999).
In recent time there is growing efforts to develop new classes of bio-inspired composite materials. The main advantage of these types of materials is that they are environmentally friendly and do not contribute to the depletion of energy resources because they are derived from renewable resources (Toro et al, 2007). However, previous studies have proved that snail shell is an agriculture byproduct that has been listed worldwide as one of the worst environmental problems. This research work is therefore, targeted at exploring other source of calcium carbonate particularly the organic substance with special interest in CaCO3 from snail shell.
The effect of filler on the properties of the foam depends on the factors such as surface area, porosity, bulkiness and surface chemistry. Filler makes an impact from the materials that are added to polymer formulation to lower the cost or to improve its properties (Saint-Micheal et al., 2006). In principle, any material can be used as filler. However, some aspects must be considered when selecting the material for this purpose. These include: size, in that the particles must be small and able to easily disperse in the polymer matrix; chemical purity, to avoid undesired reactions; and abrasiveness, which can cause excessive deterioration to the mixing equipment and increase costs (Nunes et al., 2000).
Thus, this study harnessed the use of some organic materials as fillers and their effects on the physio-mechanical properties of flexible polyether polyurethane foam.
1.2 Problem Statement
High cost of raw materials used for the production of polyurethane foam especially polyol and isocyanate, demands sourcing for a cheaper, readily available and eco-friendly material that can be used as filler.
Mineral calcium carbonate (CaCO3) holds the largest market volume in the plastic sector and is mainly imported. Hence, the need to source for renewable materials, which can serve as alternative fillers to the conventional mineral calcium carbonate (CaCO3) with a view of minimizing the polyurethane foam production cost.
And the snail shells disposal poses a significant challenge to these industries in this time of increasing environmental safety which have necessitated the need to utilize these snail shells as fillers by polymer industries.
1.3 Research Justification
Snail shells have been identified to contain up to 90% CaCO3 which make them suitable for used as filler in polyurethane production. In addition, snail shells have been confirmed to be readily available.
The use of snail shell in the foam production if established will provide means of cleansing the environment of pollution problem which the snail shells constitute and also provide alternative use for the snail shells.
It usage will also, provide an alternative to the predominantly used mineral calcium carbonate, hence reduce its importation.
1.4 Aim and Objectives of Study
The aim of this research work is to investigate the effect of snail shell on the mechanical properties of flexible polyether foam. This aim was achieved via the following objectives:
- Minimizing Cost
High cost of raw materials used for the production of polyurethane foam especially polyol and isocyanate, demands sourcing for a cheaper, readily available and eco-friendly material that can be used as filler. Mineral calcium carbonate (CaCO3) holds the largest market volume in the plastic sector and is mainly imported. Hence, the need to source for renewable materials, which can serve as alternative fillers to the conventional mineral calcium carbonate (CaCO3) with a view of minimizing the polyurethane foam production cost.
- Influencing Recycling
The use of snail shell organic filler would help in solving the challenges associated to disposal of wastes from flexible polyether foam industries, as organic fillers are good biodegradable influencer.
- Solving Environmental Pollution Problem
To use snail shell in foam production to establish means of cleansing the environment of pollution problem which the snail shells constitute and also provide alternative use for the snail shells.
1.5 Scope of Study
The scope of this work covers the collection, preparation of filler and production of flexible polyether foam using snail shell as filler at different percentage and comparing the result obtained with those available in the literature, using density, compression set, indentation hardness index, flammability as parameters to characterize the foam and optical microscopy showed the surface morphology of the fillers on the polyurethane matrix.
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