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United States Department of Agriculture

Agricultural Research Service

Title: Evaluating Renewable Cornstarch/biochar Fillers as Potential Substitutes for Carbon Black in SBR Composites)

item Peterson, Steven - Steve

Submitted to: Meeting Abstract
Publication Type: Abstract only
Publication Acceptance Date: 5/15/2010
Publication Date: 6/30/2010
Citation: Peterson, S.C. 2010. Evaluating Renewable Cornstarch/biochar Fillers as Potential Substitutes for Carbon Black in SBR Composites. Meeting Abstract. Ref #10021277, pg. 17.

Interpretive Summary:

Technical Abstract: The continually growing demand for fossil fuels coupled with the potential risk of relying on foreign sources for these fuels strengthens the need to find renewable substitutes for petroleum products. Carbon black is a petroleum product that dominates the rubber composite filler market. Agricultural starches have been shown to be excellent reinforcing fillers and are renewable; however, they are also needed as a food source. Biochar as a potential filler has the double advantage of being both renewable and inedible; it also is a significant source of elemental carbon, although obviously not as pure as carbon black. In this initial study, the feasibility of a slow pyrolysis corn stover biochar as a filler material for styrene-butadiene rubber (SBR) was explored. The only pre-treatment of the biochar consisted of filtering out large particulates > 710 um followed by 2 hours of (dry) planetary ball milling. Since the aggregate particle size of the milled biochar was still fairly large (number and volume weighted average sizes of 0.89 and 7.72 um, respectively, compared to 0.31 and 0.62 um for carbon black), cornstarch was used as a co-filler. Starch is renewable, and the ability of starch to swell and make large, 3D networks from amylose and amylopectin chains makes it an excellent reinforcing filler. Corn stover biochar was combined in ratios of 1:3, 1:1, and 3:1 with either pure food grade cornstarch or commercial whole grain corn flour. An aqueous dispersion of this filler mixture was then heated, pH adjusted, and homogenized with the appropriate amount of latex to make composites of 10, 20, 30, and 40% filler. The homogenized composites were freeze-dried and compression molded to make solid bars that were tested rheologically. Temperature sweep experiments carried out on a controlled strain rheometer measured the composite modulus of the sample as a function of temperature from -70°C to 140°C. Reinforcement strength was determined by comparing the samples’ composite modulus at a given temperature. Filler reinforcement strength went in the order cornstarch > carbon black > biochar, with relative reinforcement factors of 340, 270, and 43 times stronger than the unfilled SBR. The various co-filled composites ranged in between the values for cornstarch and biochar; the 3:1 cornstarch:biochar composite was essentially the same as the carbon black control. Future work will focus on techniques to improve the reinforcement properties of biochar including ash removal and structure changes via calcination.

Last Modified: 8/24/2016
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