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United States Department of Agriculture

Agricultural Research Service

2008 Annual Report

1a.Objectives (from AD-416)
Develop improved rubber composites and their applications by using bio-based fillers. The research product of this work will aid in generating new markets for agricultural materials, and alleviate the problem of surplus agricultural commodities. This work will also aid in reducing our dependence on petroleum by substituting bio-based fillers from renewable resources for petroleum-based fillers (carbon black).

1b.Approach (from AD-416)
This proposal seeks to develop various economically viable bio-based fillers for rubber composite applications, and their optimum use and processing technology in rubber applications. The proposed experimental approach will investigate factors that can influence the properties of rubber composites such as filler size, filler structure, filler-filler interactions, and filler-rubber interactions. The result will then be used to identify commercially viable bio-fillers and to optimize the composite properties. The proposed experiments will also investigate the mixing and flow behaviors of bio-filler reinforced rubber composites, and develop a commercially viable processing technology for these composites.

3.Progress Report
The effect of protein-to-carbohydrate ratio on the physical properties of rubber composites was observed previously in soy composites. In this report period, the effect was investigated with wheat protein (gluten) and carbohydrate (starch). The mixtures of gluten and starch at different ratios were hydrolyzed and used as reinforcement fillers in rubber composites. Composites were formed by mixing wheat co-filler dispersions with carboxylated styrene-butadiene (SB) particles in the aqueous phase, followed by freeze-drying and compression-molding. Composite modulus, recovery, and fatigue properties were measured. Compared with un-reinforced SB matrix, the wheat co-filler reinforced composites exhibited a significant increase in their modulus. It was also observed that varying gluten and starch ratio allows the adjustment of composite modulus and recovery properties. This research addresses NP 306, Component 2.

In order to develop a practical process for these bio-based rubber composites, soy/carbon black co-fillers in rubber composites were investigated through collaboration with an industrial company. Initial testing showed an improvement in some rubber properties.

Commercial wheat flour was shown to be an effective, renewable reinforcement filler for styrene-butadiene latex; composites filled with 40% wheat flour by weight increased the oscillatory storage modulus by approximately 200-fold. The two main ingredients in wheat flour that were responsible for the reinforcement were determined to be starch and wheat gluten. Of these two components, starch has a larger reinforcement effect and swelling the starch molecules via aqueous heating was directly proportional to composite reinforcement. Isolated wheat gluten only increased the oscillatory storage modulus by approximately 25-fold.

The rheological properties of natural rubber composites reinforced with defatted soy flour were studied. Defatted soy flour was shown to increase the modulus of composites by up to 20 times compared to unfilled rubber. The viscosity of filled systems was higher than unfilled systems, but the die swell did not increase for defatted soy flour composites. These results show that defatted soy flour is an effective filler in natural rubber, and they aid in the understanding of the processing of filled composites.

Other research topics currently under investigation are bio-based nano-particles (e.g., biofiber) from agricultural wastes or co-products, Distillers Dried Grains (DDG)-based fillers, and waste products from rice processing. The effect of nanoclay on the rheological properties of bio-based filler-reinforced rubber materials is also under investigation. The plate-like structures of nano-scale clay particulates function as gas barrier, fire-retardant, and reinforcement. Currently, an assortment of nanoclay with different treatments is being tested for compatibility with natural rubber. This research addresses NP 306, Component 2.

1. Rubber reinforcement by using the combination of wheat gluten and starch in rubber composites.

In order to ensure the sustainability of materials we use today, development of different economical options is required. In addition to soy fillers that we have investigated, wheat-based renewable fillers provide another economical option for rubber reinforcement. A method of modifying wheat gluten and starch for rubber reinforcement was developed. A method to adjust the properties of rubber composites by changing the ratio of wheat gluten and starch was also developed. The composite modulus was observed to increase significantly compared to un-reinforced rubber matrix. This work will impact the technology of rubber composites and their applications. This research addresses NP 306, Component 2, Problem Area 2a.

2. Composite reinforcement by starch swelling in wheat flour.

In order to investigate the use of wheat flour as a biomaterial filler for rubber composites, the effects of starch swelling and gluten on the final composite modulus were measured. Starch swelling was shown to be a simple method by which to increase composite reinforcement using commercial wheat flour as filler. Relative reinforcement effects of starch and wheat gluten were determined and starch is more significant in terms of reinforcement. This work will impact the technology of biobased composites. This research addresses NP 306, Component 2, Problem Area 2a.

6.Technology Transfer

Number of the New MTAs (providing only)1
Number of Non-Peer Reviewed Presentations and Proceedings1

Review Publications
Jong, L. 2008. Dynamic mechanical properties of styrene-butadiene composites reinforced by defatted soy flour and carbon black co-filler. Journal of Applied Polymer Science. 108:65-75.

Jong, L. 2007. Viscoelastic properties of natural rubber composites reinforced by defatted soy flour and carbon black co-filler. Journal of Applied Polymer Science. 106(5):3444-3453.

Last Modified: 9/1/2015
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