Author
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Lawton Jr, John |
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Submitted to: Satake Centre for Grain Process Engineering
Publication Type: Proceedings Publication Acceptance Date: 6/7/1996 Publication Date: N/A Citation: N/A Interpretive Summary: Starch can be used alone and in combination with other biodegradable polymers to make many useful articles. Starch absorbs water rapidly when it comes into direct contact with it. By absorbing water, the physical properties of the starch-based articles are changed. By coating the starch-based articles with water resistant biodegradable polymers such as poly(lactic acid), poly(hydroxybuterate-co-valerate) and polycaprolacton, the starch-based articles do not absorb water as fast as uncoated articles. The coated articles' physical properties do not change as much as uncoated ones after direct contact with water. The coatings used in this study do not adhere well enough to the starch-based articles for commercial use. Polymer coatings for starch-based articles show great promise in alleviating some of the water sensitivity associated with these types of products. Unfortunately, better adhesion between the polymers and starch is needed for this goal to be realized. This information will be useful in the formulation and maufacture of starch- based products. Technical Abstract: Thermoplastic starch used alone and in combination with other biodegradable polymers can be processed into many useful articles. Starch is a hygroscopic polymer and will gain or lose water to achieve equilibrium with ambient air. Since water is a good plasticizer for starch, tensile properties of materials made with starch will change with relative humidity. Water can be a solvent for thermoplastic starch. Items that contain starch and come into direct contact with water can be severely altered or destroyed. To help alleviate the problems associated with starch's sensitivity to water, biodegradable water repellent coatings for starch have been evaluated. Hydrophobic polymers such as poly(hydroxybutyrate-co-valerate) which are coated onto starch foam do a good job in protecting the foam from water. Because of their hydrophobic nature, these types of materials do not adhere well to starch. Peel tests done with starch foams and hydrophobic polymers indicate that peel strength is related to the surface energy of the coating. Peel strength of coatings onto starch foam show that poly(hydroxybutyrate-co-valerate) is less than polycaprolacton and polycaprolacton is less than poly(lactic acid). Adhesion strength of coatings to substrate can be predicted from their interfacial tension. These predictions can be helpful in finding new coatings or possible compounds that can be used to lower the interfacial tension between starch and the hydrophobic coatings. |
