TRIBOLOGICAL EVALUATION OF LUBRICANTS DEVELOPED FROM SELECTED VEGETABLE BASED OILS FOR INDUSTRIAL APPLICATIONS

ABSTRACT

Mineral oil based lubricants are non-renewable, harmful to health and prone to price fluctuations. Thus, vegetable oils are considered as suitable alternatives to mineral oils for lubricant production. Research on the use of non-edible vegetable oils for lubricant development has become necessary. The tribological evaluation of lubricant developed from non-edible vegetable (jatropha and castor) oils for industrial applications have been carried out in this study. The oils were characterized, modified for suitability and used to develop lubricants for industrial applications. Commercially available mineral oil based lubricant SAE 20/W50 was used as a control. The effect of additives on the tribological performance of jatropha and castor oil based biolubricants developed were also studied. Whereas modification of jatropha oil improved its viscosity but reduced its viscosity index, modification of castor oil greatly reduced its viscosity but improved its  viscosity  index.  Jatropha  and  castor  oils  unlike  other  vegetable  oils,  possess excellent cold flow properties and modification of the oils further enhanced their cold flow properties. The developed jatropha and castor oil based bioluricants had alkaline pH, high viscosity index, appreciable viscosity,  excellent cold flow and corrosion inhibition properties and highly biodegradable with a biodegradability exceeding 80 %, while the mineral oil based lubricant SAE 20/W50 had a poor biodegradability of 35.2 %. The extreme pressure additive cetyl chloride had the most significant effect on the coefficient of friction and anti-wear additive Tricysl Phosphate had the most influential effect on the viscosity index of the jatropha and castor oil based biolubricants. The jatropha and castor oils performed better in friction reduction and wear prevention than the SAE 20W/50 which had 0.114 coeficient of friction and 0.0067 mm3N-1m-1  wear rate. The castor oil had 0.082 coefficient of friction and 0.007 mm3N-1m-1wear rate. The developed jatropha oil biolubricant had coefficient of friction of 0.075 and wear rate of 0.00699 mm3N-1m-1 and was better in friction performance but had similar wear performance with SAE 20W/50. The developed castor oil based biolubricant had 0.067 coefficient  of  friction  and  0.00511  mm3N-1m-1   wear  rate  and  exceeded  the  SAE 20W/50 in friction and wear performance. Thus, modified and unmodified jatropha and castor oils have been found to be suitable for industrial applications in systems exposed to low temperatures.  The developed jatropha and castor oil biolubricants have been found to be suitable environmentally friendly substitutes to mineral oil base lubricant SAE 20/W50 for application in two stroke engines, metal cutting and lubrication of gears in food processing industry.

CHAPTER ONE

1.0       INTRODUCTION

1.1       Background to the Study

Tribology is the science and technology of bodies touching each other while moving; it includes the study of friction, wear and lubrication (Nosonovsky, 2010). Friction and wear  come  from  complicated  and  multi-complex  communication  among  bodies moving while touching each other. Every moving, observable, and shape aspects of the communicating bodies and their neighbourhood influence the surface communication and consequently the tribological behaviour of the entire arrangement.

Also, it can be seen from the systems aspect of friction and wear that the modelling of friction and wear is very difficult. There is dearth of good models that describes comprehensively the friction and wear process; thus, the interpretation of friction and wear data becomes complicated. Additionally, there is no correlation between friction and  wear  for  example  low  friction  does  not  automatically  mean  low  wear  rate (Menezes et al., 2013).

Wear is the continual removal of material from the surface in sliding or rolling contact against a counter surface. Based on the mechanism of material removal we have the following types of wear; adhesive wear, abrasive wear, wear caused by surface fatigue and wear due to tribochemical reactions. Over a longer sliding distance, either one mechanism alone or a combination of several of these wear mechanisms, causes a continual removal of material from the mating surfaces. Continuous steady-state wear and friction conditions may be quantified in terms of wear rate, which is mass or volume of material removed per sliding distance or time. Wear is the main cause of material wastage and loss of mechanical performance therefore; any reduction in wear can give rise to considerable savings (Stachowiak and Batchelor, 2000). The major cause of wear and energy dissipation is friction.

Friction  is  the  opposition  experienced  when  two  bodies  touching  each  other  are moving simultaneously, and it results to energy dissipation at the sliding interface. The dimensionless material property calculated as ratio of tangential force to normal load is called coefficient of friction. Normal load and frictional force are directly proportional to each other; therefore, friction coefficient is constant. It is assumed about 33.33% of the global energy resources is wasted to overcome friction in one form or the other. Reasonable amount of money can be saved via improved friction control and oiling or use of grease, which is an effective means of achieving wear and friction reduction (Bhushan, 2013a).

Lubrication  is  defined  as  the process  or technique of using a lubricant  to  reduce friction and/or wear in a contact between two surfaces. Tiny layers of little tearing strength gas, liquid or solid are introduced among two surfaces so as to better the smoothness of movement of one body over another and thereby hindering damage. These thin portions of matter that separate contacting solid objects  are often difficult to observe. Mostly, the width or height of these thin portions of matter are between 1 –100 micro meters, although wider and higher films can be encountered.

The  act  of  making  better  and  or  investigating  useful  influence  of  tiny  films  in hindering damage in solid-solid contacts is commonly termed lubrication (Bhushan, 2013a).  Lubricants  minimize  friction,  prevent wear, provide cooling and  transport debris away from interface. Lubricants can be solids, solid/liquid thick colloid such as grease, liquids, liquid-liquid dispersions or gases. A thin layer of gas is suitable for low body  to  body  force  while  solid  thin  layers  mostly  apply  to  low  velocity  bodies communication.   Detailed   observation   of   fluid   thin   layers   is   usually   called„ hydrodynamic oiling‟ while „solid greasing‟ is the one done by solids. A specialized form of liquid or gas oiling where face to face interaction among the communicating objects and the liquid or gas smoothener is referred to as „elastohydrodynamic smoothening‟ which is of beneficial applications. Smoothening that involves the chemical reactions between the liquid lubricant and the surfaces being lubricated is known as „boundary and extreme pressure lubrication‟. Significant factors that affect lubricant effectiveness include:

1)  rheological properties for example viscosity, viscosity index, pressure-viscosity Index.

2)  Chemical properties for example reactivity with the top layer, boundary film- forming behaviours, abnormally high pressure constituents and shear force of solid lubricant or paintings.

3)  Heat energy behaviours of smootheners for example specific heat, conductivity and diffusivity.

4)  Hotness or coldness properties of oils for example pour-point temperature, cloud-point temperature, smoke point temperature, flame point temperature and resistance to oxidation.

Functionality of lubricants is defined by their chemical structure and their physical properties. The chemistry of hydrocarbon Base Lubricants is derived from organic chemistry. Different categories are given by their chemical composition and structure (Dresel & Mang, 2007).

Failure in machine parts due to absence or wrong choice of lubricants brings enormous cost (Dowson, 1979; Musa & Omisanya, 2021). In a 1986 survey it was revealed that supplying all the worm gear drives in the United States of America (USA) with a lubricant that allows a relative increase of 5% in the mechanical efficiency compared to a conventional mineral oil would result in savings of about US$ 0.6 billion per annum (Pacholke & Marshek, 1986). The total cost of energy waste and material loss resulting from frication and wear is approximately $40 billion a year for the various industries in the USA (Jost, 1981; Stachowik & Batchelor, 2000).

Lubricants are very important consumables in virtually every industry. Within the last decade the annual worldwide consumption of lubricants is over 40 million metric tonnes. According to Ajithkumar (2009), lubricants are made up of over 9 out of 10 parts base oil and lower than 10% package of additive. The base oil used for the formulation of most lubricants is environmentally hostile mineral oil  and 30% of lubricants consumed ends up in the ecosystem (Bartz, 2006; Ajithkumar, 2009).

However, mineral oil reserve is depleting and the environmental concern about the damaging impact of mineral oil is growing. The search for environmentally friendly substitutes to mineral oils as base oils in lubricants has become a frontier area of research in the lubricant industry. Vegetable oils are perceived to be alternatives to mineral oils for lubricant base oils due to certain inherent technical properties and their ability to be biodegradable.

Plant base oils when placed side by side with petroleum oils, has large fire point, elevated temperature rheology stability, high oilness and loss due to evaporation (Adhvaryu & Erhan, 2002, Mercurio, et al., 2004; Souza, et al., 2019). Vegetable oils have been found to be of less hazard to the ecosystem during deliberate or accidental release into the environment compared to mineral oil (Mercurio et al., 2004; Awoyale et al., 2011). Poor hydro-oxidative homogeneity, large hotness or coldness sensitivity of wear and friction behaviour and poor low temperature behaviour are acknowledged to be the hindrance of plant oils application as parent material for smoothness oils used in industries (Erhan & Asadaukas, 2000; Adhvaryu et al., 2005). The present labours to eliminate these problems includes the addition of chemicals, transformations using heat and chemicals (Li & Wang, 2015).  This work aims at developing lubricant from non-edible  vegetable  (jatropha  and  castor)  oils  and  to  evaluate  the  tribological properties  of  the  developed  lubricants.  The  research  also  studied  four  selected additives to determine which of the additives has the most significant effect on the tribological performance of lubricants developed from jatropha and castor oils.

1.2       Statement of the Research Problem

Wear and tear due to friction in moving contacting machines parts is a major problem in most industries. Lubricant has been developed to mitigate this negative effect of friction, commercially available lubricants are made from mineral oil which is harmful to the environment and humans. Besides this, petroleum reserve is depleting globally leading to increase in the cost of mineral oil available for lubricant production. These problems call for attention to search for cheap available alternatives that have no controversy for food security and non-edible vegetable oil has been identified as a viable option.

Several   researches   have   been   carried   out   that   studied   the   development   and performance of bio-based lubricants for industrial applications. However, there are scanty literature on the tribological performance of non-edible vegetable oil based lubricants. Specifically, there are limited publications on the tribological properties of lubricants developed from jatropha and castor oil. Research on the friction and wear performance of lubricants developed from jatropha and castor oils is an area needing attention and this research seeks to address this gap.

The overall tribological performance of a lubricant is a function of the base oil and additives. There are very few existing literatures on the influence of the concentration of additives on the wear and friction performance of jatropha and castor oils. This research will also consider the determination of how the tribological performance of lubricants developed from jatropha and castor oils will be affected by additives.

1.3 Aim and Objectives of the Study

The  aim  of  this  study  is  to  evaluate  the  tribological  performance  of  lubricants developed from selected vegetable based oils for industrial applications.  The aim will be achieved through the following objectives:

1)  Determine and modify the profile of jatropha and castor oils for lubricant production.

2)  Develop lubricant from modified jatropha and castor oils.

3)  Evaluate the tribological properties of lubricant developed from modified and unmodified jatropha and castor oils.

4)  Determine  the  effects  of  additives  on  the  tribological  performance  of  the developed jatropha and castor oil based biolubricants.

1.4       Justification of the Study

Tribological deficiencies which are largely due to inappropriate use of lubricants or the absence of lubricants  produces  enamours  losses (energy and material)  that occurs simultaneously in all mechanical devices in operation. Use of mineral based lubricants is harmful to environment and health of humans involved in the production and use of mineral based lubricants. Therefore, this research seeks to develop environmentally friendly and non-harmful, biodegradable lubricants from two vegetable oils that are produced in Nigeria.

The use of edible vegetable oil for lubricants formulation is challenging as there is competition for its use as food. This work developed industrial lubricant from non- edible vegetable (jatropha and castor) oils. This research is therefore a step further in the right direction to solve the food versus debate on the use of vegetable oil.

This research will encourage rural people to use waste and non- arable lands for non – edible oil production which will reduce poverty and create jobs among the poor.  The reduction  in  energy and  material  losses  that  is  envisaged  to  be  derived  from  the outcome of this research is most significant in this period of global economic down- turn.

Despite the progress in research in the use of vegetable oils for the development of industrial lubricants, literature is scanty on the tribological performance of jatropha and castor oils. Additionally, there is a dearth of knowledge on the tribological evaluation of lubricants developed from modified castor and jatropha oils.

Most of the additives used for the formulation of lubricants contain heavy metals as well as sulphur and phosphorous compounds that are harmful to man, animals and the environment; there is therefore need to search for minimum quantity of additive to be used for vegetable oil based lubricants formulation and this work is a further effort in search of which selected additives most significantly affects the tribological performance of developed lubricants. The knowledge of the most significant additive will aid in reducing the number of additives to be used thereby protecting the environment from harmful chemicals.

1.5       Scope of the Study

This work evaluated the density, flash point, pour point, viscosity, viscosity index, corrosion resistance, oxidative and thermal stability of locally available jatropha and castor oils. Chemical modification of the jatropha and castor oil were carried out followed  by  the  development  of  lubricants  from  the  modified  vegetable  oils. Evaluation of the tribological performance of the lubricants developed from the modified  and  unmodified  vegetable  oils  was  also  carried  out.    The  work  also determined the most significant additive that affects the tribological performance of the developed lubricants using design of experiment through the Taguchi method. Only four selected environmentally friendly additive were used in this study and the tribological performance of the developed lubricant was evaluated using ball-on-disc tribometer only.

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