A periodical of the Faculty of Natural and Applied Sciences, UMYU, Katsina
ISSN: 2955 – 1145 (print); 2955 – 1153 (online)
ORIGINAL RESEARCH ARTICLE
Oryina Emmanuel Ado1, Ibrahim Hamisu1, Nasir Sallau Lawal1*
1Department of Chemistry, Faculty of Physical Sciences, Ahmadu Bello University, Zaria, Nigeria
*Corresponding Author: Nasir Sallau Lawal 
nslawal@abu.edu.ng
The research focused on the extraction of oil from Neem (Azadirachta indica) and Calabash (Lagenaria siceraria) seeds. The extracted oils were characterized to determine their physicochemical properties, which were assessed according to AOAC and ASTM methods. The percentage yields of Neem oil and Calabash oil were 34.50±0.25% and 31.00±0.20 %, respectively. The acid value of Neem and Calabash oils was 8.91±0.10 mg KOH/g and 3.23±0.15 mg KOH/g, respectively. Regarding percentage Free Fatty Acids (% FFA), Neem oil was determined to be 4.87±0.20 while Calabash oil had a value of 1.73±0.10. As for the saponification value, Neem oil had a value of 137.55±0.25 mg KOH/g, while calabash oil had a value of 238.84±0.30 mg KOH/g. The iodine values of neem and calabash oil were 68.00±0.20 and 66.20±0.15 g/100g, respectively. Also, the density for neem oil was determined to be 0.85±0.10 g/mL, while that of calabash oil was 0.90±0.10 g/mL. Furthermore, the extracted Neem and Calabash oils were used to synthesize biolubricants via esterification and transesterification processes using pentaerythritol and Calcium Oxide (CaO) obtained from eggshells, with yields of 60.80±0.15 % for the Neem biolubricant and 53.00±0.20 % for the Calabash biolubricant. The properties of the synthesized biolubricants were determined and compared with those of a mineral lubricant (ISO VG 46). Additionally, tribology studies showed that the COF for Neem and Calabash biolubricants is 0.041 and 0.054, respectively, at a 10N load. Compared with the COF of 0.086 for ISO VG 46 at 10N load, these biolubricants could provide better friction reduction than ISO VG 46; hence, they are suitable for possible application as hydraulic oil.
Key words: Neem, Calabash, Biolubricant, Pentaerythritol, transesterification, Eggshells, Coefficient of Friction (COF).
Neem and Calabash oils were successfully extracted from their seeds, and a comparative analysis of their physicochemical properties was conducted.
Biolubricants were synthesized from Neem and Calabash oils via esterification and transesterification processes using pentaerythritol and Calcium Oxide (CaO) obtained from eggshells.
CaO obtained from eggshells was characterized and found to be active as a catalyst for esterification and transesterification. This process helped convert waste material into wealth, thereby minimizing the risk of environmental pollution.
The CaO catalyst was subjected to a reusability test to determine its sustainability.
At the global level, petroleum-based products are extensively used as lubricants. These products are non-renewable, and persistent use makes them toxic to the environment when improperly disposed of. With the growing demand for fuel, the depletion of world's reserves is imminent. As such, there is a need to find renewable and sustainable alternatives (Syahir et al., 2017).
Biolubricants are promising candidates for eco-friendly lubricants because of their excellent lubricity, biodegradability, viscosity-temperature characteristics and low volatility. Recently, there has been increased concern about enhancing the use of biodegradable vegetable oils in lubricants, mostly due to environmental, health, and safety issues arising from changes in economic and supply factors (Aji et al., 2015). From an emissions perspective, biolubricants have very low potential to emit pollutants containing sulphur compounds, which can damage the environment and the catalytic converters of automobiles (Dattrao et al., 2018).
Literature reports on the use of Neem and calabash seeds as biolubricants were presented elsewhere (Amit et al., 2015; Owuna et al., 2018). So far, the use of pentaerythritol in the transesterification reaction of Neem and Calabash oil extracts to their respective biolubricants are scarce, presented herein, includes a comparative study of the physicochemical properties of Calabash and Neem seed oils and the synthesis of biolubricants from these oils using pentaerythritol and a calcium oxide catalyst obtained from egg shells. The physicochemical properties of the synthesized biolubricants were analyzed and compared with those of a commercial standard (ISO VG-46) for possible use as hydraulic fluids.
Calabash seeds were obtained from the Samaru Market, authenticated at the Herbarium, Department of Botany, Faculty of Life Sciences, Ahmadu Bello University, Zaria, and assigned the vouch number ABU014147. The seeds were de-hulled, dried, ground and sieved to obtain a homogenous powder. The powdered calabash seed weighed 500 g and was then preserved for oil extraction. Neem seeds were obtained from the ABU Zaria main campus, treated the same as calabash seeds, and assigned vouch number ABU090016; the weight of powdered neem seed was determined to be 950 g.
Neem and Calabash oils (Extracted as stated below), Methanol, n-hexane, Pentaerythritol, Potassium hydroxide, Sodium hydroxide and Ethanol were all purchased from BDH and were all analytical grade. Calcium Oxide was obtained from egg shells via calcination in an oven.
A Soxhlet extractor was employed for the extraction of oil from calabash and neem seeds using n-hexane as the extracting solvent in a 500 cm3 round-bottom flask. 50 g of powdered calabash seed was placed in a thimble, while the n-hexane was gently heated. A reflux condenser was fitted (to cool the n-hexane), and the mixture was heated at 65 oC for 2 hours while the condensed hot solvent soaked the thimble. The solvent siphoned into the flask when it reached the top of the siphon tube. The oil was separated from the solvent using a rotary evaporator. The same treatment as above was given to the neem seeds. The percentage yield of the oil was calculated using the equation below (Owuna et al., 2018; Terefa et al., 2018; Awasthi et al., 2019). The procedure was repeated three times with a fresh seed sample, and the percentage yield was recorded.
\[\%\ yield = \ \frac{Weight\ of\ Oil\ (g)}{Weight\ of\ the\ sample\ }\ X\ 100\]
Fig. 1: The extracted Neem (dark) and Calabash (orange) oils
The physico-chemical properties of the extracted oils, such as Acid Value, Saponification Value, Percentage Free Fatty Acids (%FFA), Iodine Value, Density, and Specific gravity, were determined according to AOAC and ASTM methods, respectively.
Calcium Oxide catalyst was prepared from waste eggshells by the calcination method. Egg shells were collected from food vendors at Community Market A.B.U Zaria, then washed using distilled water and sun-dried. Furthermore, the egg shells were crushed and calcined in the furnace at 800 oC for 1 hour. After cooling, the resultant solid product was ground, sieved and kept in air-tight sample bottles. The sample bottles were kept in the desiccator to prevent air from contacting them. The catalyst was activated by impregnating a known quantity of the powdered sample with phosphoric acid (H3PO4). An impregnation ratio of 15 g of H3PO4 to 5 g of the calcined egg shells was used. The use of phosphoric acid in acid impregnation enhances the surface properties, catalytic activity, and stability of the catalyst. The phosphoric acid increases the surface area, thereby allowing for effective activation of the CaO catalyst (Erchamo et al., 2021; Saleem, 2022).
The mixture was stirred for 30 minutes until a paste formed, then allowed to stand for 24 hours. The activated substrate was filtered using filter paper. The mixture was washed by gradually pouring distilled water over the filter paper containing the sample, which was placed over a conical flask. The pH of the filtrate was checked regularly with a pH meter until it was within 6–8. The activated substrate was then dried in an oven at 105 oC for 10 minutes (Olufemi et al., 2020; Correira et al., 2014). The equation of reaction is shown below:
CaCO₃(s) --Δ⟶ CaO(s) + CO₂(g)
The vegetable oils extracted from Calabash and Neem seeds were each filtered to remove any solid precipitates, then dried by heating at 100 0C for 30 min to remove moisture. The experimental procedures reported below were carried out separately for Calabash and Neem oils. The esterification and transesterification reactions are shown in Scheme 1.
2.5g CaO (1% by wt of oil) was added to 400 mL of methanol and dissolved by vigorous stirring. The mixture was poured into 50 mL of the calabash oil. The reaction mixture was stirred for 90 min at 60 oC. The heater is then switched off. The reaction was quenched by adding ice, then allowed to settle and separate into phases. The top ester layer is poured into another beaker and washed with 400 mL of water three times. After some time, the water phase containing the remaining alcohol and catalyst settled, leaving a clear ester phase on top, which is separated and used for the next reaction (Dattrao et al., 2018). Yields of Fatty Acid Methyl Esters (FAME) are 42.50±0.20 % (Neem) and 50.10±0.20 % (Calabash).
12.5 g of Pentaerythritol was added to 50 mL of Calabash Seed Oil Methyl Ester in a three-neck round-bottom flask fitted with a thermometer. The mixture was heated on a magnetic stirrer to 150 oC with continuous stirring, then 0.5 g of calcium oxide (CaO) catalyst (1% by wt of methyl ester) was added. The vacuum pump was turned on to remove methanol from the reversible reaction. At the end of the reaction, the mixture was cooled, washed with water, dried with anhydrous sodium sulphate and filtered (Dattrao et al., 2018; Orhevba et al., 2016). Yields of biolubricants are 60.80±0.15 % (Neem) and 53.00±0.20 % (Calabash).
Scheme 1: Reaction pathway for the synthesis of the biolubricants
Physico-chemical Properties of Synthesized Biolubricants
The basic properties of biolubricants were analyzed using American Society for Testing and Materials (ASTM) methods. These properties include: Density, Viscosity, Cloud point, Pour point, Specific gravity, and Flash point. These properties were investigated and compared with those of a mineral lubricant (ISO VG 46) to assess the potential application of the synthesized biolubricants as hydraulic oil (Kamarudin et al., 2020; Owuna et al., 2018).
An empty 2 mL syringe was placed on a weighing balance and recorded as W1. The syringe was then filled with neem oil biolubricant and placed on the weighing balance again. The weight was recorded as W2. The density was calculated as shown below:
\[Density = \ \frac{W2 - W1}{2\ mL}\]
A Brookfield viscometer was used to determine the viscosity values of neem and calabash oil biolubricants at 40 oC and 100 oC. Firstly, spindle size 3 was selected, and the neem biolubricant sample was transferred into a 100 mL beaker. The temperature of the biolubricant was raised to the desired value by heating on a mantle with a thermometer inserted into the beaker. The spindle was attached to the upper coupling and immersed in the sample to the midpoint of the indentation in the shaft. The viscometer was then turned on and allowed to run until a constant reading was attained; the reading was recorded as the absolute viscosity of the biolubricant in centipoise (cP). The values of absolute viscosity in centipoise (cP) at 40 oC and 100 oC were then converted to kinematic viscosity in centistoke (cSt) by dividing by the respective densities. The same treatment above was given to the calabash biolubricant (Rukke and Schuller, 2017).
4 g of neem oil biolubricant sample was poured into a glass test tube until the level is marked with a line. The test tube was tightly capped with a cork, placed in a cooling bath, and monitored every 5 mins. The sample was chilled until it became clouded at the bottom of the test tube. The temperature at which this occurred was recorded as the cloud point (Kamarudin et al., 2020). The same procedure was carried out for calabash oil biolubricant.
Pour point was measured using the same procedure as cloud point described above. However, further chilling of the biolubricant sample continued until the biolubricant sample ceased to flow. The sample was then removed and tilted horizontally for 5 seconds; the temperature at which it no longer showed movement was recorded as the pour point (Kamarudin et al., 2020).
Specific Gravity is the ratio of the density of a biolubricant sample to the density of equal volume of distilled water. This is usually determined by using an instrument called hydrometer (Kamarudin et al., 2020).
1.0 g of neem oil biolubricant was weighed into a conical flask and heated, with the electrode of a thermocouple inserted into the flask. The heating continued in a fume cupboard until the oil was observed to have vaporized. A burning splint was taken close to the mouth of the conical flask. The temperature at which the oil vapour ignited was then recorded as the flash point. The same procedure was carried out for the calabash oil biolubricant to determine its flash point.
The biolubricants synthesized from Neem and Calabash seed oils were analyzed for functional groups using an FTIR instrument (Agilent Technologies) with a wave number range of 4000-650 cm-1 at the Multi-User Science Research Laboratory, Department of Chemistry, A. B. U. Zaria.
The reusability of the CaO catalyst was evaluated over three consecutive reaction cycles under identical operating conditions. After each cycle, the catalyst was separated by filtration, washed with n-hexane and methanol to remove residual organic species, dried at 105 °C, and reactivated by calcination at 800 °C for 3 h. The recovered catalyst was reused without modification of reaction parameters. Catalyst performance was assessed based on ester yield and physicochemical properties of the biolubricant (Tavizón-Pozos et al., 2025). The percentage FAME and biolubricant yield were calculated using the formula below:
\[The\ \%\ FAME\ yield = \frac{\rho(biodiesel)x\ Vol.\ (biodiesel)}{Mass\ (biodiesel)}\ X\ 100\]
\[The\ \%\ Biolubricant\ yield = \frac{\rho(biolub)x\ Vol.\ (biolub)}{Mass\ (biolub)}\ X\ 100\]
The oil yield of Neem seed was 34.50 %, while that of Calabash seed was 31.00 % (Table 1). The result agrees with the work of Abul Kalam et al. (2018), which indicated that the percentage yield of neem oil from seed kernels varies from 25–45 %. The acid value for neem oil was determined to be 8.91 mg KOH/g, while that of calabash oil was 3.23 mg KOH/g. Acid value is the amount of KOH (mg) required to neutralize the free fatty acids in 1 g of oil sample; it indicates the amount of free fatty acids present in an oil and is a good indicator of oil degradation caused by hydrolysis (Tesfaye and Tefera 2017). Low acid values are desirable for oils because they indicate good cleansing properties and stability, while high acid values indicate deterioration (Awasthi and Shikha 2019).
Table 1: Physico-chemical properties of Neem and Calabash oils
| Parameter | Neem Seed Oil | Calabash Seed Oil |
|---|---|---|
| Colour | Dark-brown | Light orange |
| Percentage yield (%) | 34.50 ± 0.25 | 31.00 ± 0.20 |
| Acid value (mg KOH/g) | 8.91 ± 0.10 | 3.23 ± 0.15 |
| % Free Fatty Acids | 4.87 ± 0.20 | 1.73 ± 0.10 |
| Saponification value (mg KOH/g) | 137.55 ± 0.25 | 238.84 ± 0.30 |
| Iodine value (g/100 g) | 68.00 ± 0.20 | 66.20 ± 0.15 |
| Density (g/mL) | 0.85 ± 0.10 | 0.90 ± 0.15 |
| Specific gravity | 0.85 ± 0.10 | 0.90 ± 0.15 |
The Percentage Free Fatty Acid (% FFA) of Neem oil was determined to be 4.87±0.20%, while that of Calabash oil was 1.73±0.20%. % FFA means the percentage by weight of specified fatty acids in oil. The determination of free fatty acid (FFA) content is important for evaluating the quality of the oil raw material and its degradation during storage. Low % FFA values are desirable because they indicate oil stability during storage, whereas high % FFA values indicate instability (Vicentini-Polette et al., 2021).
The Saponification value of neem oil was determined to be 137.55±0.25 mg KOH/g, while that of Calabash oil was 238.84±0.30 mg KOH/g. Saponification value means the milligrams (mg) of KOH required to saponify 1 g of fat or oil. The saponification value is a measure of the molecular weight of fatty acids. The saponification value is used to detect oil adulteration. High saponification values indicate a greater proportion of medium-chain fatty acids in the oil and better usability (Ivanova et al., 2022).
In terms of density, Neem and Calabash oils were 0.85±0.10 g/mL and 0.90±0.15 g/mL, respectively. Also, the Iodine values of Neem and Calabash oils are 68.00±0.20 and 66.20±0.15, respectively; Iodine value is a measure of the unsaturation of fats and oils and is expressed in terms of the number of grams of Iodine absorbed per 100 g of oil sample. The iodine values of these oils suggest a moderate level of unsaturation.
In Table 2, the densities of Neem and Calabash biolubricants are 0.87±0.20 g/mL and 0.93±0.15 g/mL, respectively, while that of ISO VG 46 was 0.85 g/mL, which is similar to the Neem biolubricant synthesized. Compared to the density values obtained from the extracted vegetable oils, there is an increase of 0.2-0.4 g/mL. The Kinematic Viscosities of Neem biolubricant at 40 oC and 100 oC were determined to be 45.80±0.15 cSt and 7.80±0.10 cSt, while those of Calabash biolubricant were 44.60±0.10 cSt and 7.58±0.10 cSt, respectively. These values are within the range of the Kinematic Viscosity of ISO VG 46 at 40 0C and 100 0C, which are >41.4 and >4.10, respectively.
Table 2: Physical properties of synthesized biolubricants compared to ISO VG 46
| Parameter | Neem | Calabash | ISO VG 46 |
|---|---|---|---|
| Yield (%) | 60.80 ± 0.15 | 53.00 ± 0.20 | – |
| Density (g/mL) | 0.87 ± 0.20 | 0.93 ± 0.15 | 0.85 |
| Kinematic viscosity at 40 °C (cSt) | 45.80 ± 0.15 | 44.60 ± 0.10 | > 41.4 |
| Kinematic viscosity at 100 °C (cSt) | 7.80 ± 0.10 | 7.58 ± 0.10 | > 4.10 |
| Cloud point (°C) | 20.00 ± 0.20 | 4.00 ± 0.10 | – |
| Pour point (°C) | 4.00 ± 0.10 | –6.00 ± 0.10 | < –10.00 |
| Viscosity index | 130 ± 0.15 | 128 ± 0.10 | 108 |
| Flash point (°C) | 183 ± 0.20 | 179 ± 0.15 | 227 |
The Cloud point values of Neem and Calabash biolubricants were determined to be 20±0.20 oC and 4.0±0.10 oC while that of ISO VG 46 was not available from literature specifications. The Pour point values of Neem and Calabash biolubricants were determined to be 4.0±0.10 oC and –6.0±0.10 oC, respectively, while that of ISO VG 46 was less than –10. This implies that ISO VG 46 has an edge over synthesized biolubricants for cold-temperature applications.
Furthermore, the Viscosity Indices of Neem and Calabash biolubricants vis-à-vis ISO VG 46 are 130±0.15 and 128±0.10, respectively. This shows that the synthesised biolubricants are more suitable for high-temperature applications. Lastly, the Flash point values of Neem and Calabash biolubricants were determined to be 183±0.20 oC and 179±0.15 oC, respectively, while ISO VG 46 was 227 oC. Generally, a high flash point is desirable for lubricants because it is a safety index for their storage and handling. This means ISO VG 46 will be easy to handle during storage.
The FTIR spectrum of Calabash biolubricant is provided in Figure 3; a broad peak at 3436 cm-1 was observed, confirming the presence of a hydroxyl (O-H) stretch. The absorption wave peak of 3011 cm-1 indicated a strong C–H bond. Furthermore, a prominent peak was observed at 2922 cm-1 indicating the presence of methylene (CH2) group while another peak occurred at 2855 cm-1 due to C–H which confirms the presence of a methyl (CH3) group in the structure. The carbonyl bond (C=O) present in the ester functional group (R-C=O-O-R’) was observed to occur at 1740 cm-1. The absorption wave peaks at 1461 cm-1, indicating the presence of carbon chain bonds between C–C, while the absorption wave peaks at 1170 cm-1, indicating the presence of C–O bonds.
Fig. 3: FTIR Spectrum of Calabash biolubricant
In Figure 4, an absorption band with a broad peak at 3436 cm-1 is observed, indicating the presence of a hydroxyl (O–H) bond. Another absorption wave peak of 3008 cm-1 indicated a strong C-H bond. Also, a prominent peak at 2922 cm-1 indicated the presence of a methylene (CH2) group; another peak at 2855 cm-1 was due to C–H stretching, confirming the presence of a methyl (CH3) group in the structure. The carbonyl group (C = O) present in the ester functional group (R-C=O-O-R’) was observed to occur with a prominent peak at 1744 cm-1. The absorption wave peaks at 1465 cm1 indicated the presence of carbon chain (C-C), while the absorption wave peaks at 1115–1174 cm-1 indicated the presence of C-O bonds.
Fig. 4: FTIR Spectrum of Neem biolubricant
The GCMS profile of the neem and calabash biolubricants produced are provided in Table 3 and 4, respectively. Both the calabash and neem biolubricants contain various ester derivatives. A further analysis of the chromatograms of the synthesised biolubricant showed the presence of additional organic byproducts of the reaction (see SI).
Table 3: GC-MS profile of Neem biolubricant
| S/N | F.A.M.E | Molecular Formula | % Composition |
|---|---|---|---|
| 1 | Methyl tridecanoate | C₁₄H₂₈O₂ | 40.36 |
| 2 | Linolelaidic methyl ester | C₁₉H₃₄O₂ | 21.85 |
| 3 | 12-Methyl-2,13-octadecadien-1-ol | C₁₉H₃₆O | 15.12 |
| 4 | Decanoic acid methyl ester | C₁₁H₂₂O₂ | 7.92 |
| 5 | 14-Methylpentadecanoate | C₁₇H₃₄O₂ | 3.60 |
| 6 | 15-Methylhexadecanoate | C₁₈H₃₆O₂ | 1.97 |
| 7 | 11,14-Eicosadienoic acid methyl ester | C₂₁H₃₈O₂ | 1.53 |
| 8 | 2-Methylbutyl ester | C₈H₁₆O₂ | 1.48 |
Table 4: GCMS profile of Calabash biolubricant
| S/N | F.A.M.E | Molecular Formula | % Composition |
|---|---|---|---|
| 1 | 10-Pentadecen-1-ol | C₁₅H₃₀O | 34.54 |
| 2 | 9,12-Octadecadienoic acid methyl ester | C₁₉H₃₄O₂ | 17.96 |
| 3 | 15-Tetracosenoic acid methyl ester | C₂₅H₄₈O₂ | 7.87 |
| 4 | Hexadecanoic acid methyl ester | C₁₇H₃₄O₂ | 7.60 |
| 5 | Tridecanoic acid methyl ester | C₁₆H₃₀O₂ | 5.36 |
| 6 | 5,17-Octadecadien-1-ol | C₂₀H₃₆O₂ | 5.31 |
| 7 | 13,16-Octadecadienoic acid methyl ester | C₁₉H₃₄O₂ | 5.15 |
| 8 | Methyl 10-oxohexadecanoate | C₁₇H₃₂O₃ | 4.95 |
In order to investigate the morphology and structure of the synthesized CaO catalyst derived from egg shells, Scanning Electron Microscopy (SEM) analysis was conducted. The SEM micrograph shown in Figure 5 shows that the synthesized CaO catalyst consists of grains with irregular shape. The SEM image also shows the spaces between particle sizes, suggesting that the particles are porous. The presence of pores in the CaO gives efficient catalytic activity in biolubricant production.
Fig. 5: SEM Micrograph of synthesized CaO catalyst
Fig. 6: EDS spectrum of synthesized CaO catalyst
Lastly, Figure 6 above is the Energy-Dispersive Spectroscopy (EDS) chromatogram, which shows the elemental composition of the synthesised CaO catalyst. The EDS chromatogram clearly indicates that CaO was formed at a high concentration. The percentage atomic compositions were obtained as 58.78, 25.78, 4.73, 4.21, 3.72, 1.57, 1.12 and 0.94 % for calcium (Ca), oxygen (O), magnesium (Mg), aluminum (Al), carbon (C), titanium (Ti), potassium (K) and sodium (Na), respectively. The results confirm that indeed CaO was produced.
To test the reusability of the CaO catalyst obtained from eggshells, three synthetic cycles were conducted, and the results are presented in Table 5. Based on the data obtained, there is a decrease in catalytic activity (biolubricant yield) during the three consecutive uses. This could be attributed to the leaching of calcium from active sites into the methanol phase and to the poisoning of catalyst active sites by the reaction medium, which reduced the contact area between base sites and reactants (Nabilah et al., 2021).
Table 5: The percentage FAME, Neem and Calabash biolubricant product yield after three cycles.
| Neem | Calabash | ||||
| Run/Cycle | FAME Yield (%) | Biolubricant yield (%) | Run/Cycle | FAME Yield (%) | Biolubricant yield (%) |
| 1st | 42.50 | 60.80 | 1st | 50.10 | 53.00 |
| 2nd | 37.40 | 52.25 | 2nd | 42.20 | 47.25 |
| 3rd | 30.80 | 44.80 | 3rd | 33.60 | 39.40 |
The tribological performance of the ISO VG-46, Neem and Calabash biolubricants was investigated using a pin-on-disc tribometer (Anton Paar Model) shown in Figure 7. It can be observed that for the 8N load, the Coefficient of Friction (COF) for mineral lubricant (ISO VG-46) is 0.068. However, the Neem biolubricant showed a lower COF (0.051), while the Calabash biolubricant had a higher COF (0.071). The high COF of the Calabash biolubricant could be attributed to insufficient lubrication between the contacting metal surfaces, compared to ISO VG-46. For the 10 N load, the mineral lubricant (ISO VG-46) had a COF of 0.086. The COFs for Neem and Calabash biolubricants are 0.041 and 0.054, respectively, which means that at a 10N load, these biolubricants could provide better friction reduction than ISO VG-46.
Fig. 7: Tribology test for ISO-VG 46, Neem and Calabash biolubricants at 8 N and 10 N loads
The oils extracted from Neem and Calabash seeds showed good potential as base stock for biolubricant production. Neem and Calabash seeds yielded good oil percentages of 34.50% and 31.00%, respectively; the low Acid and % FFA values of the oils confirmed the stability and quality of the oil raw material. Biolubricants were synthesized from Neem and Calabash seed oils via esterification and transesterification processes, using CaO a catalyst obtained from eggshells. The major lubricating properties of Neem and Calabash biolubricants, compared to ISO VG 46, showed good agreement. The tribology study also showed that the biolubricants reduced the Coefficient of Friction (COF) between contacting surfaces. Hence, the synthesised biolubricants can preferably serve as alternatives to mineral-based lubricants in hydraulic applications. Moreover, the use of a CaO catalyst derived from eggshells, if scaled up, could greatly contribute to the recycling of waste materials in the environment into wealth.
The authors express profound gratitude to the Federal Scholarship Board National Award (FSB–NA) for the disbursement of scholarship funds which contributed in no small measure to the research process.
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