The study assessed the potential of walnut shells as a filler in natural rubber composites. Walnut shells were finely ground, sieved through a 75 μm mesh, and incorporated into natural rubber at different filler loadings: unfilled, 20 parts per hundred rubber (phr), 30 phr, 40 phr, and 50 phr. The physicochemical properties of the walnut shell powder were analyzed, yielding results of 5.30 for pH, 10.10% for moisture content, 2.50% for ash content, 43.70% for loss on ignition, and an iodine adsorption number of 49.70 mg/g. In comparison, carbon black exhibited a pH of 6.30, moisture content of 2.89%, ash content of 6.35%, loss on ignition of 92.90%, and an iodine adsorption number of 79.88 mg/g. The performance of the composites was evaluated based on tensile strength, hardness, abrasion resistance, and compression set. The findings indicated that the walnut shell-filled composites demonstrated significant reinforcement, particularly at filler loadings of 30–40 phr. However, at higher levels, the walnut shell acted primarily as a diluent rather than a reinforcing agent. Overall, walnut shells were categorized as semi-reinforcing fillers, exhibiting an iodine absorption number of 49.70 mg/g, which is approximately half that of carbon black. This suggests that while walnut shells can enhance certain properties of natural rubber composites, their reinforcing effectiveness diminishes beyond a certain filler loading

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1. Ayo MD, Madufor IC, Ekebafe LO, Chukwu MN. Effect of carbonization temperature on the mechanical and swollen behavior of natural rubber filled groundnut shell. J Mater Sci. 2010;41(3):553–542.
2. Imanah JE, Okiemen FE. Studies in the mechanical properties of natural rubber with agricultural by products. JCSN. 2004;317–322.
3. Ekebafe LO, Ayo MD, Eguare KO, Ugbesia SO. Effect of chemical modification of powdered rubber seed shell as filler on the tensile properties of natural rubber compounds. J Polym Sci Technol. 2010;37(2):1113–1119.
4. Asore JE. Introduction to Rubber Technology. Benin City: Joseg Books Publisher; 2000. 20–25.
5. Dhillon INS. Fruit Production in India. Delhi: Narendra Publications House; 2013.
6. Ishak ZAM, Baker AA. Natural rubber blends and properties. Euro Polym J. 1995;31(3):259–269.
7. Sowińska-Baranowska A, Maciejewska M, Duda P. The potential application of starch and walnut shells as biofillers for natural rubber (NR) composites. Int J Mol Sci. 2022;23(14):7968.
8. Chundawat NS, Parmar BS, Perumal P, Jadoun S, Vaidya D, Chauhan NP. Effect of walnut-shell filler as sustainable material with silane to replace carbon black in natural rubber-based tire tread compound. J Rubber Res. 2023;26(5):425–439.
9. Sowińska-Baranowska A, Maciejewska M. Potential utilization of ground eggshells as a biofiller for natural rubber biocomposites. Mater. 2023;16(8):2988.

The study assessed the potential of walnut shells as a filler in natural rubber composites. Walnut shells were finely ground, sieved through a 75 μm mesh, and incorporated into natural rubber at different filler loadings: unfilled, 20 parts per hundred rubber (phr), 30 phr, 40 phr, and 50 phr. The physicochemical properties of the walnut shell powder were analyzed, yielding results of 5.30 for pH, 10.10% for moisture content, 2.50% for ash content, 43.70% for loss on ignition, and an iodine adsorption number of 49.70 mg/g. In comparison, carbon black exhibited a pH of 6.30, moisture content of 2.89%, ash content of 6.35%, loss on ignition of 92.90%, and an iodine adsorption number of 79.88 mg/g. The performance of the composites was evaluated based on tensile strength, hardness, abrasion resistance, and compression set. The findings indicated that the walnut shell-filled composites demonstrated significant reinforcement, particularly at filler loadings of 30–40 phr. However, at higher levels, the walnut shell acted primarily as a diluent rather than a reinforcing agent. Overall, walnut shells were categorized as semi-reinforcing fillers, exhibiting an iodine absorption number of 49.70 mg/g, which is approximately half that of carbon black. This suggests that while walnut shells can enhance certain properties of natural rubber composites, their reinforcing effectiveness diminishes beyond a certain filler loading

🔒 This is a subscription article

Full text is available to subscribers and institutional members. Please choose an option below to access it.

1. Ayo MD, Madufor IC, Ekebafe LO, Chukwu MN. Effect of carbonization temperature on the mechanical and swollen behavior of natural rubber filled groundnut shell. J Mater Sci. 2010;41(3):553–542.
2. Imanah JE, Okiemen FE. Studies in the mechanical properties of natural rubber with agricultural by products. JCSN. 2004;317–322.
3. Ekebafe LO, Ayo MD, Eguare KO, Ugbesia SO. Effect of chemical modification of powdered rubber seed shell as filler on the tensile properties of natural rubber compounds. J Polym Sci Technol. 2010;37(2):1113–1119.
4. Asore JE. Introduction to Rubber Technology. Benin City: Joseg Books Publisher; 2000. 20–25.
5. Dhillon INS. Fruit Production in India. Delhi: Narendra Publications House; 2013.
6. Ishak ZAM, Baker AA. Natural rubber blends and properties. Euro Polym J. 1995;31(3):259–269.
7. Sowińska-Baranowska A, Maciejewska M, Duda P. The potential application of starch and walnut shells as biofillers for natural rubber (NR) composites. Int J Mol Sci. 2022;23(14):7968.
8. Chundawat NS, Parmar BS, Perumal P, Jadoun S, Vaidya D, Chauhan NP. Effect of walnut-shell filler as sustainable material with silane to replace carbon black in natural rubber-based tire tread compound. J Rubber Res. 2023;26(5):425–439.
9. Sowińska-Baranowska A, Maciejewska M. Potential utilization of ground eggshells as a biofiller for natural rubber biocomposites. Mater. 2023;16(8):2988.