Use of nut shells as fillers in polymer composites

Authors: Sutivisedsak, Nongnuch; Cheng, Huai; Burks, Charles - Chuck; Johnson, Judy; Siegel, Joel; Civerolo, Edwin; Biswas, Atanu

Submitted to: Journal of Polymers and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2012
Publication Date: 5/16/2012
Citation: Sutivisedsak, N., Cheng, H.N., Burks, C.S., Johnson, J.A., Siegel, J.P., Civerolo, E.L., Biswas, A. 2012. Use of nut shells as fillers in polymer composites. Journal of Polymers and the Environment. 20(1):305-314.

Interpretive Summary: Nut shells are renewable lignocellulosic materials that can be obtained as agricultural byproducts. They are often utilized in relatively low-value applications such as composts, mulches, fertilizers and animal feed. In a continuing effort to upgrade their value of nut shells, we are exploring their possible application as fillers in PLA and LDPE polymer composites. In this work we examined the possibility of using these biodegradable materials as fillers in poly(lactic acid) and low density polyethylene. The nuts were ground into powder, blended with the polymer, and then injection molded with final weight varying from 10 to 40 weight %. The mechanical and thermal properties of the composites were then studied. In this work, the nutshells from pistachio, almond, and walnut, which are cost-competitive and naturally renewable, were used as fillers with plastics to make polymer blends. These blends containing nut shell fillers showed promise to promote the biodegradability, lack of toxicity, thereby more environmentally friendly in terms of disposal and decreased risk with respect to handlers and consumers. This work benefits the nut growers of central valley of California.

Technical Abstract: The three nutshell fillers including walnut, almond and pistachio nutshell were added to PLA. All the physical properties of samples deteriorated relative to PLA. When subjected to heat pre-treatment, although the physical properties of PLA-filler samples still deteriorated, the extent of deterioration was much smaller for tensile strength and Young’s modulus. In fact, the Young’s modulus for 10% almond nutshell filler and 10-20% walnut shell filler were roughly comparable to those of PLA itself. The treatment of maleic anhydride and peroxide caused further reduction in tensile strength and elongation at 10 and 20% filler loadings. As for Young’s modulus, this treatment either showed equivalent Young’s modulus, or made the Young’s modulus worse. The nutshell deteriorated all the properties in LDPE material, with walnut nutshell showing the most negative effect. The LDPE and the fillers, when subjected to heat pre-treatment, tensile strength and elongation at break were still reduced, but Young’s modulus was roughly maintained up to 40% filler level. The chemical treatment of maleic anhydride/peroxide in most nut shells at 10 and 20% filler loading either made no difference in Young’s modulus or in a few cases showed a slight improvement. In addition to mechanical properties, thermal properties of all samples were evaluated by differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) of stretch-fractured samples from mechanical tests was also performed.