Updated August 8, 2017:
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Developing High Performance “Green” Tires using Soy Hull based Cellulose Nanofibers – Executive Summary
Long Jiang and Dilpreet Bajwa
Department of Mechanical Engineering, North Dakota State University
The goal of this research is to create a new rubber material (e.g. tires) that uses soy hull-based cellulose nanofibers (CNFs) instead of traditional carbon black as the main reinforcing and functional agent. CNFs are expected to outperform carbon black in reinforcing rubber because of the former’s very high tensile strength/stiffness, large aspect ratio, and strong chemical bonding with the rubber matrix. This research is important to ND soybean farmers mainly because of the following two reasons. First, rubber, as an indispensable product to modern society, represents a huge market - 317.3 million tires were sold in the U.S. alone in 2010. A rubber product contains about 30 wt% carbon black and replacing it with CNFs would create an important new use for soybean and a new income stream for soybean growers and processors. Second, replacing carbon black will have positive environmental impacts. Production of carbon black consumes unsustainable resources (i.e. natural gas and fossil oil) and generates greenhouse gas (GHG) and hazardous air pollutant (HAP) emissions. By replacing it with CNFs, this research can increase the eco-friendliness of rubber goods through conserving nonrenewable natural resources and cut GHG and HAP emissions.
In this project we first designed and assembled a mobile microfluidization unit and used it to break up soy hull into cellulose nanofibers. We further optimized the unit to improve its efficiency and make it more user friendly. Raw soy hull from a local source and commercial purified soy hull dietary fiber were used as the feedstock for nanofiber production. Chemical treatment was applied to the raw soy hull before microfluidization. The produced cellulose nanofibers were studied using electron microscopy and infrared spectroscopy, and were used to prepare polymer nanocomposites. Both nanofibers (i.e. the one derived from the raw soy hull and the one from the commercial dietary fiber) show stronger reinforcing effect than the cellulose nanofibers produced by USDA Forestry Service Laboratory using soft wood pulp, which suggests great potential of the soy-based cellulose nanofibers. To use the nanofibers to reinforce rubber, they were further treated with bifunctional molecules whose one end can react with the nanofiber and the other end can react with the rubber. These molecules serve as chemical linkages to connect the nanofibers and the rubber molecular chains, thus greatly strengthening the rubber. We have tried five bifunctional molecules to modify the nanofibers, and the refinement of the chemicals and reaction conditions is ongoing. The cellulose nanofibers with and without surface modifications were used to reinforce natural rubber or styrene-butadiene rubber (SBR) through an internal blending, two-roll milling and compression molding process. The mechanical testing results of the reinforced rubber samples were used to optimize the modification method of the nanofibers. This part of research is also ongoing and will continue into the second year of the project.