Measuring cylinder, volumetric flask, conical flask, sieve, oven, magnetic Stirrer, digital Viscometer, locally fabricated mould with cavities and pH meter were used in this work.

Sulphur, mecapto benzyl thiazol disulphide (M.B.T.S), paraffin oil, n-Hexane, di-ethyl ether, stearic acid, zinc oxide, calcium carbonate and cashew Nut shell Liquid (technical CNSL) were used in this experiment.

Raw Smoked Rubber was purchased from Rubber Research Institute, Benin, South South, Nigeria and taken to the laboratory for further treatment. Cashew seed was purchased from cashew farmers in Egdeda, Kabba, Kogi State and taken to the laboratory for further treatment.

The purchased cashew nut samples were washed thoroughly with detergent, rinsed with distilled water to ensure high degree of purity of the product and dried under the sun for one month for easy shelling. The Shell was removed using knife (plier-like) while wearing hand gloves.

Two procedures are followed for cyclic heating; the first step involves the blending of raw rubber with only paraffin oil while the second step involves blending of 50 % solution of CNSL in paraffin with the raw rubber prior to heating.

Step 1: Typically, 4.00 g of raw rubber was weighed into a beaker, 16.00 mL of di-ethyl ether and 0.10 mL of paraffin was added to soften the rubber chains. After blending, the blend was allowed to dry for 12 hrs. The dried blend was placed in a 500 mL beaker and transferred into pre-heated oven at 60°C for an hr earlier. 1.00 g of this sample was taken at the end of every four hrs of heating. A total of four samples were taken over a period of 15 hours of cyclic heating, representing samples that were heated for 3, 6, 9, 12 and15 hrs respectively. The experiment was also done at 80 and 100°C.

Step 2: Typically, 4.00 g of raw rubber was weighed into a beaker, 16.00 mL of di-ethyl ether and 0.10 mL of 25 % of CNSL was added in paraffin oil to soften the rubber chains. After blending, the blend was allowed to dry for 12 hrs. The dried blend was placed in a 500 mL beaker and transferred into pre-heated oven at 60°C for an hr earlier. 1.00 g of this sample was taken at the end of every four hrs of heating. A total of four samples will be taken over a period of 15 hrs of cyclic heating, representing samples that are heated for 3, 6, 9, 12 and15 hrs respectively. The experiment was also done at 80 and 100°C.

There are two steps involved in this stage: rubber compounding and vulcanization of the compounded rubber.

Step 1: A 50.00 g of rubber was weighed into a container to which 200 mL di-ethyl ether added and container covered up to reduce solvent vaporization. After a period of 12 hr, 50.00 g of calcium carbonate was added and churned which followed by the addition of 2.00 g Zinc oxide and 4.00 g stearic acid which has been previously sieved and, after churning to blend, 1.00 g of M.B.T.S was added. After mixing with the rubber solution, 2.50ml of 50 % solution of CNSL in paraffin was added and blended. Finally, 1.00 g of sieved sulphur was added and blended.

The above procedure was repeated for untreated raw rubber that had been heated in a cycle of 3, 6, 9, 12 and 15 hrs respectively.

Step 2: A6.54 g of compounded dried rubber was weighed into each of cavities in an aluminium mould and the mould and its contents were introduced into oven which had been pre-set at 150°C over a period of 1 hr. The mould and its content was left for a period of 1 hr and 30 minutes in the oven, removed, cooled and opened to remove the cast product.

The second step was repeated for rubber samples that had been heated for 3, 6, 9, and 12 hrs which had equally been compounded as given above.

A 1.25 g of cyclically heated rubber samples compounded with lipid only and dissolved in 80 mL n-hexane was made up to 100 mL in a volumetric flask. 80 mL of this was transferred into a beaker and taken to for viscometric measurement. The viscosity of the solution is then taken from the instrument in centipoises (cp) as shown in table....

The CNSL in this study was obtained by roasting the shell (Thomas et al. 2017). This technical CNSL was done at the temperature between 180 to 200°C. This method recovers 85 – 90 % of the liquid. A dark-brown liquid was obtained which research have has different percentage of components as shown in table 1 (Klimisch, 1997). The characteristics properties of the technical CNSL have been determined according to methods reported in a research work (Chaudhari et al. 2012) using standard equipment/ apparatus following standard methods and the results are represented in tables 2 and 3 for physical and chemical properties respectively. The viscosities study of the CNSL treated and untreated natural rubber as represented in Figs. 5, 6 and 7 show that the treated samples have higher viscosity values than the untreated ones. Fig. 6 show that at 60°C for 15 hrs of heating, the treated samples were stable to thermal treatment while the untreated samples were relatively stable at the same temperature for up to 9 hrs but there were a drop in viscosity after the 9th hr.

This suggests that the treated with CNSL has more resistance to thermal degradation compared to the untreated one. Similar results were also obtained when the temperature was increased from 60 to 80°C with only a point drop in the viscosity values of the treated samples while the results as represented in Fig. 6 show that there was a further drop in the viscosity values for the untreated samples. Fig. 7 also show that as the temperature was further increased to 100°C, there were sharp drops in the viscosity values for the untreated samples while the treated ones remained relatively stable. Generally, viscosity decrease with increase in temperature which can be seen from the results obtained in this research work. This is because at higher temperature, particles have greater thermal energy and can easily overcome the attractive forces binding molecules together (cohesive forces between molecules decreases as temperature increases). This means that as temperature increases, there is an increase in the molecular interchange as molecules move faster at higher temperatures. Therefore, the results obtained above show that the use or incorporation of CNSL as a stabilizing agent helps in the resistance of natural rubber against thermal degradation. Analysis of CNSL show that it contains high content of unsaturated long chain phenol which suggests that its chemical structure form a cross link during vulcanization of rubber to prevent molecular flow when exposed to thermal treatment. Cardanol which is the main constituent of CNSL also has an antioxidant property due to its structure and it prevents aging in rubber materials as phenolic substances have the ability to retard oxygen adsorption. Also, larger molecules have stronger intermolecular forces such as London forces which connect them to one another with greater power to inhibit molecular flow resulting in higher viscosity. This is because viscosity depends on strength of attractive forces between molecules as a result of composition, size and shape. Therefore, CNSL, in addition to molecular structure, also increases the molecular size and shape of natural rubber to resist molecular flow as a result of thermal treatment resulting in stability of natural rubber.