Modification, Characterisation, and Application of Coconut Wastes as Fillers in Rubber Compounding
Chapter One
Research Objectives of the Study
- This research work seeks to broaden the horizon for rubber product development through the reinforcement of composites from renewable agricultural
- This also sorts the use of carbonization as an appropriate modification method for morphological re-orientation of coconut palm waste to alleviate certain inherent weaknesses as stated in the
- The health implication of the use of non-renewable mineral fillers likecarbon black for rubber reinforcements was a major driving force for this research
- This work seek to utilised modern and high-tech analytical laboratory equipment to analyse and evaluate the possible extent of modification attained through carbonisation using standard measurement test.
CHAPTER TWO
LITERATURE REVIEW
Previous Works
The tensile and flexural properties of composites made from coconut shell filler particles and epoxy resin have been studied by Sapuan et al., 2003. They performed several characterisation studies on composites prepared from coconut shell filler particles at three different filler contents of 5%, 10% and 15% by weight. Their experimental results showed that tensile and flexural properties of the composites increased with the increase in the filler particle content. The composite materials demonstrated somewhat linear behaviour and sharp fracture for tensile and slight non- linear behaviour and sharp fracture for flexural testing.
Jacob et al., (2014), worked on the evaluation of mechanical properties of coconut shell fibres as reinforcement material in epoxy matrix. The morphology and mechanical properties of coconut shell reinforced with epoxy resin composite was evaluated to establish the possibility of using it as a new material for engineering applications.
Satyanarayana et al., (1982), reported the structure property studies of fibres from various parts of the coconut tree. Fibres from different structural parts of the coconut palm tree (Cocos nucifera, linn) was examined for properties such as size, density, electrical resistivity, ultimate tensile strength, initial modulus and percentage elongation. The stress-strain diagrams fracture made microfibrillar angle as well as cellulose and lignin contents of these fibres were determined. They conclude that the physical and mechanical properties exhibited by the different fibres from coconut tree can be sued for various applications, especially as composites. Husseinsyah and Mostapha (2011), worked on the effect of filler content on properties of coconut shell filled polyester composites and found out that the tensile strength, Young‟s modulus and water absorption of polyester/CS composites increased with increasing CS content but elongation at break decreased. Morphological study indicates that the tendency of filler-matrix interaction improved with the increasing filler in polyester matrix.
Onyeagoro (2012a, b) carried out a research on cure characteristics and physico- mechanical properties of carbonised bamboo fibre filled natural rubber vulcanisates. The cure characteristics and physico-mechanical properties of carbonised bamboo fibre filled natural rubber vulcanisates were studied as a function of filler loading, filler particle size and compatibiliser. The scorch time, t2 and cure time, t90 of carbonised bamboo fibre filled natural rubber vulcanisates decreased with increased in filler loading and the presence of compatibiliser.
Osman et al., (2010) studied the effect of maleic anhydride-grafted polypropylene (MAPP) on the properties of recycled newspaper (RNP) filled polypropylene (PP)/ natural rubber (NR) composites. The authors found that the incorporation of MAPP reduced the water uptakes of the composites.
In another study by Ansarifer et al., (2005), on the properties of natural rubber reinforced with synthetic precipitated amorphous white silica nano-filler, it was reported that compression set, tensile strength and hardness were improved on addition of filler into the rubber, while elongation at break, tear strength and cyclic fatigue were adversely affected. Yang et al., (2006) studied the influence of graphite particle size, and shape on the properties of acrylonitrile butadiene rubber (NBR) and found that graphite with the smallest particle size possessed the best reinforcing ability, while the largest graphite particles exhibited the lowest function coefficient of the composites among four fillers investigated.
The reinforcing effects of coal shale based fillers on natural rubber on the basis of filler particle size have been investigated by Zhao and Xiang in 2004. The authors reported that the ultra-micro coal-shale powder exhibited excellent filler properties.
Egwaikhide et al., 2007 studied the effect of coconut fibre on the cure characteristics, physico-mechanical and swelling properties of natural rubber vulcanisates. The results showed that coconut fibre could be potential reinforcing filler for natural rubber compounds. The study indicates that the potential of coconut fibre and other agricultural by-products can be exploited further by controlling particle size and particle distribution, improving filler dispersion and also its surface functionality.
The mechanism of reinforcement of elastomers by filler was reviewed by Brahma et al., 2005. They considered that the filler increased the number of chains, which shared the load of a broken polymer chain. It is known that in the case of filled vulcanisates, the efficiency of reinforcement depends on a complex interaction of several filler related parameters. These include particle size, particle shape, particle dispersion, surface area, surface reactivity, structure of the filler and the bonding quality between the filler and the rubber matrix.
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Bhaskar and Singh (2013) studied physical and mechanical properties of coconut shell particle reinforced-epoxy composite. Experimental results showed that density, strength, modulus of elasticity and percent elongation decreased with percent weight of shell particles within the range of (20-35) % of reinforcement.
CHAPTER THREE
MATERIALS AND METHODS
Collection, Treatment of Materials and Reagents
The research work commenced with the sourcing of coconut shells and fibres which was in abundance in Auchi and its environs in Edo State, Nigeria. All compounding ingredients such as zinc oxide, stearic acid, plasticiser/processing oil, sulphur, mercaptobenzothaizole disulphide (MBTS), Tetramethylthiuram disulphide (TMTD), and trimethylquinoline (TMQ); were of commercial grades and they were used without further treatment. Natural rubber (Standard African Rubber, SAR) having the properties given in Table 3.1.
CHAPTER FOUR
RESULTS
Characterisation
Table 4.1: Characterisation of Raw Coconut Shell and Fibre; Carbonised Coconut Shel
CHAPTER FIVE
DISCUSSION
Characterisation
The specific filler properties of the raw and treated shell and fibre were clearly identified during the characterisation process and the results are presented in Table 4.1. The results show that the pH value increased from slightly acidic level to alkaline level as the carbonisation temperature increases, because as the residual materials are lost with increasing temperature, alkalinity increases due to a corresponding loss of H3O and the formation of metal oxides (Cazaurang et al., 1991; Ayo et al., 2011; Momoh et al., 2017a).
There was a decrease of moisture content with increase in carbonisation temperature, thereby drastically eliminating bound moisture. Decrease of moisture with temperature leads to firmer adherence of filler to the rubber matrix with the elimination of shrinkages ( Sapuan et al., 2003; Chanap, 2012).
Ash content and loss on ignition increased with increase in carbonisation temperature. Carbonisation was done for 3hrs each and the higher temperature beyond 600oC burns off all residual materials into ash level and therefore leading to degradation in particles reinforcing properties (Chang and An, 2002; Husseinsyah and Mostapha, 2011). The weight loss on ignition was as a result of loss in the lignocelluloses content during combustion. The concentration level of the carbon content due to carbonisation increased with bulk material loss of lignocelluloses. This is a measure of the effectiveness of the filler at interacting with the rubber matrix which is a necessary factor in filler reinforcements. The higher the value, the greater the reinforcement effect of the filler (Choi et al., 2006; Egwaikhide et al., 2007 a, b).
The iodine adsorption number is a measure of the surface reactivity of the filler. The higher the iodine adsorption number, the larger the surface area available for reaction and this subsequently increased reinforcement ability (Ayo et al., 2011). The bulk density decreased with increase in carbonisation temperature. The densities are influenced by the particle size and structure of the shell. The decrease in bulk density created a better filler-matrix interaction. The interpenetrating network between filler and rubber gets stronger with increase in carbonisation temperature leading to a reinforced composite matrix (Chotirat et al., 2007).
Particle dimensions especially for the fibre indicates that length, width and diameter decrease with increase in carbonisation temperature. Smaller particles have the ability to wet rubber surface more and therefore more reinforcement. Particles mobility also increased with increase in the temperature of carbonisation, possibly because of more kinetics created by energy difference (Dick, 2001; De Rosa et al., 2010)
CHAPTER SIX
SUMMARY, CONCLUSION AND RECOMMENDATIONS
Summary
Coconut shell and fibre were collected, washed to remove debris and sand; and then oven dried at 950C for 2h to remove moisture. The shell and fibre were physically treated through carbonisation at varying temperatures of 300, 400, 500, 600 and 7000C. The raw and carbonised shell/fibre was crushed, ground and serially sieved using graded sieves until a 100 particle sizes were obtained. Both raw and carbonised samples were the characterised using the following parameters and standard method: Ash content, loss on ignition, pH of slurry, bulk density, iodine adsorption value, moisture content, oil absorption. Others especially for the fibre are: conductivity, lumen, width, length, diameter, area and volume.
Furthermore, a suitable formulation was designed and twelve (12) formulations were compounded. The formulations include: Raw shell and shell carbonised at (300, 400, 500, 600 and 700)oC. Also raw fibre and fibre carbonised at (300, 400, 500, 600 and 700)oC.
Additives used for compounding were: Natural rubber of TSR 10 grade, zinc oxide, stearic acid, mercaptobenzothaizole disulphide (MBTS), tetramethylthiuram disulphide (TMTD), trimethyl quinoline (TMQ), sulphur, fillers and mineral oil as processing aid.
Homogenisation, dispersive and distributive mixing were done using a laboratory two- roll mill at 70oC with a mill roll speed of 1:1.25 ratio. Compounded sheets were allowed for maturation at 32oC for 24h.
Rheological tests using ODR 2000 model was carried out before press curing. From the ODR curves/charts, a temperature of 150oC, pressure of 150kg/Cm and a cycle time of 15 minutes were used for the curing process. Physico-mechanical evaluations were made according to standard test methods in order to evaluate the level of reinforcement attained during composites built-up. Evaluations carried out include: hardness (Shore A) abrasion resistance index, compressive strength, tensile strength, elongation at break, modulus and flexural strength. The purpose was to evaluate the level of reinforcement in the composites. Sorption analysis/swollen tests were carried out using four (4) major solvents for 72 hours at 32oC. The solvents used were: benzene, toluene, xylene and hexane. The prescribed standard method used is ASTM D3010. This was done to investigate the level of chemical resistance of cross-linked network.
Other qualitative evaluative analysis carried out include: Fourier Transform Infrared Spectroscopy (FTIR) for functional group determination; Scanning Electron Microscopy (SEM) for micro-structural and morphological determination; X ray Diffraction Analysis (XRD) for Determination of Percentage Crystallinity; X-ray Fluorescence (XRF) of elemental oxide determination; Thermal gravimetric Analysis (TGA) for the evaluation of thermal stability and degradation as a result of temperature effect.
Productions of vibration dampeners for motor cycle hubs and industrial oil seals for bambury mixers were carried out using the best formulation achieved from the simulated analysis evaluated. The formulations with 500oC carbonisation temperature for coconut shell and 600oC carbonisation temperature for coconut fibre were used. Four (4) formulations were drawn and were used. Further evaluative field analyses on the moulded products were dynamic flex fatigue, rebound resilience, crack initiation analysis, weathering/ozone resistance. Analysis of variance study using DMRT and LSD evaluated with appropriate hypotheses for test of significance were carried out.
Conclusion
The Properties of composites filled with carbonised fillers were superior to the uncarbonised fillers. In comparison to a standard product filled with carbon, reinforcements were relatively high and product performance in oil seal and vibration dampener were of high performance without suspicious health challenges as the hazardous nitrosamines content of carbon black are absent in the agro-fillers which are also renewable. Carbonisation temperature ranges from (300-700)oC, with the optimum properties achieved at 500oC for coconut shell and 600oC for coconut fibre. pH increased from acidity to alkalinity as the carbonisation temperatures increase. Metal content activity increased leading to the alkalinity as residual materials were being lost. Increase in carbonisation decreased moisture content of the filler and therefore eliminates product shrinkage defects. The surface area of filler increased progressively during modification. Increase in surface area activities resulted in higher modulus at higher strain, abrasion resistance and lower hysteresis.
Bulk density decreased with filler modification. The density was influenced by the particle size and structure of the shell and fibre. The lower the particle size; the lower the density and therefore, the better the interaction between the rubber matrix and the modified fillers. The physico-mechanical properties indicated that the modified fillers exhibited higher hardness, abrasion resistance, tensile strength and modulus as interaction between fillers and matrix increase.
Values of elongation at break decreased with modification. The decrease in elongation at break has to do with adherence of the filler to the polymer phase leading to the stiffening of the polymer chain. Compressive strength results showed a progressive decrease with modification process. The compressive strength was affected by the affinity of the rubber for the filler surface.
Fourier transform infra-red spectrum (FTIR) determined the functional groups present and showed how they were optimised/removed during carbonisation. The spectra results indicated the destruction of cellulose, hemicellulose and lignin components of the shell and fibre to ensure compatibility between the filler and the hydrophobic rubber matrix. The scanning electron microscopy (SEM) provided micro-structural evidence of characteristic cellular morphologies of composites as the modification process proceeds. X-ray diffraction (XRD) investigated the level of amorphousness and crystallinity of the modified filler. Modification diminished amorphousness and strengthened crystallinity; thereby giving the filler a penetrating ability into the rubber matrix. X-ray fluorescence (XRF) exposed the entire elemental oxides present in the shell and fibre and showed how they were optimised. Carbonisation increases the K2O and increased the bond strength between filler and matrix through the existing electrovalent bond in potassium oxide.
Thermal gravimetric analysis (TGA) examined the thermal stability of the bulk components of the coconut shell and fibre. Carbonisation brought about modification by burning off lignocelluloses which hinders filler matrix interpenetrating network interactions. Carbonisation improved the surface morphology of the filler and upon the natural rubber matrix. Optimum properties were observed at 500oC treatment for the coconut shell and 600oC treatment for fibre and further evaluative analysis of dynamic flex fatigue, rebound resilience relationship, vulcanisate chemical resistance in organic solvents, weathering and ozone resistance tests confirmed improvement made by modification through carbonisation.
Physical modification actually took place through carbonisation. Increase in carbonisation temperatures attracted corresponding increase in the physico-mechanical, chemical, crystalline, thermal, morphological and elemental properties of the composites. Modification through carbonisation gave a clear indication of reduction of potential surface hindrances of the developed fillers, thereby creating a high interactive surface between filler and rubber matrix of the composites as well as an increase in the carbon content of the fillers.
The experimentally evaluated results of mechanical and chemical sorption properties that gave the optimised formulation for the fibre and shell composites used in the modelled products (vibration dampeners and industrial oil seals) performed very with high significant levels on a theoretical predictive evaluation as mathematically modelled by means of statistical analysis of variance (ANOVA). The predictive results obtained using the new Duncan‟s multiple range test (DMRT) presented a high significance differences between subject factors of mechanical properties and samples (modification temperatures) at 95% probability and deterministic levels. There was a high correlation between experimental values and theoretically predictive values. The formulation and design of other engineering items from the optimised composites is highly encouraged.
Decisions: Since Fcal > Ftab in both hypothesis (A) and hypothesis (B) and in all their variances, we therefore accept H1: The physico-mechanical properties changes and chemical sorption properties leading to product reinforcements as carbonisation treatment at the evaluated varying temperatures were therefore significant. This significance positively supported the experimental results achieved using physico- mechanical properties as parameters for products reinforcements.
Fibre and shell composites from coconut palm waste can be a material of choice not just for automobile parts and oil seals; but also for aerospace construction, building, bridge bearings and electrical appliances for conductivities. Removing them from the environment as wastes will guarantee a safer environment and open an entrepreneurial opportunity for the conversion of waste to wealth. A good knowledge of structural designs, joining mechanisms, composites development and manufacturing techniques would enhance better applications in other areas of engineering.
Recommendations for Further Studies
Future work is needed to further the understanding of a wide range of modification; possibly chemical modification of the coconut palm wastes. Based on the results shown in this thesis, future work will need to be focused on the following aspects:
- Chemicalinfusion and Carbonisation was a physical modification process. Other chemical modification means such as alkylation, benzoylation, mercerisation and dehydroxylation could be encouraged to evaluate chemical grafting on the composites matrix; and possible reinforcements.
- Long-term weathering or accelerated weathering treatment on the producedmodels is needed to simulate the circumstances in real
- Further range of mechanical tests such as creep, load bearing strength andintense mechanical deflections would be required before possible commercialisation can take place using the derived and optimised
Multiple mould cells that will be amenable to multi-moulding techniques capable of giving rise to at least five (5) moulded pieces at a moulding cycle instead of the one-off intermittent moulding technique used to produce the industrial oil seals and motor cycle dampener would be required. A polished mould surface would be a necessity at achieving precision engineering items using the optimised formulations.
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