Submitted to: Rheology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2017
Publication Date: 8/21/2017
Citation: Xu, J., Selling, G.W. 2017. A comparison of the viscoelastic properties of starch-polyacrylamide graft copolymers produced in dimethyl sulfoxide and water. Rheology. 1(2):1000109.
Interpretive Summary: Starch-based polymers can have similar functional behaviors as synthetic polymers, but have much better environmental properties because of their biodegradability. In order to be suitable for those uses that were historically filled by synthetic polymer, the starch needs to be modified. One way to make starch more suitable is by attaching another polymer to the starch, such as polyacrylamide (PAAm). While there are various methods for attaching PAAm to starch, none of these have addressed the use of solvents other than water to carry out the chemistry. Starch-PAAm compositions were produced in water and in dimethyl sulfoxide (DMSO). The final starch-PAAm powders made in both water and in DMSO can absorb a great deal of water and swell into gels at room temperature. How these gels flow is an important parameter in many markets. We explored how solvent selection affects the flow properties of starch-PAAm materials. The results of our study suggest that the produced starch-PAAm materials may have useful properties in a variety of markets, such as cosmetics, bandages, water treatment, paper production and oil drilling muds. This information will allow producers of these materials to develop optimized formulations through solvent selection that will allow increased use of biobased materials.
Technical Abstract: The rheological properties of starch-polyacrylamide graft copolymers prepared in water and in dimethyl sulfoxide (DMSO) were investigated and compared. Both materials can absorb huge amount of water and form gels. Both water-made and DMSO-made starch-polyacrylamide graft copolymer gels exhibited viscoelastic solid properties. The analysis of modulus, concentration dependence, and stress relaxation measurements indicated that both water-made and DMSO-made starch-polyacrylamide gels were physical gels meaning that the cross-linkers between the molecules were of physical junctions. The linear range rheological property analysis suggested that water-made starch-polyacrylamide graft copolymers should be ‘weak’ gels at lower concentrations (<7%), but be ‘strong’ gels at higher concentrations (equal to or greater than 9%); however, the DMSO-made starch-polyacrylamide graft copolymer should be ‘weak’ gels at all measured concentrations. The non-linear steady shearing rheological properties studies showed that both water-made and DMSO-made starch-polyacrylamide graft copolymer gels exhibited shear thinning behaviour, which can be well fitted with the power law constitutive equation. The function and behaviour of both water-made and DMSO-made starch-polyacrylamide graft copolymer gels imply that these starch-based biomaterials can be potential candidates for applications in cosmetic and wound skin care gels; and the desired material’s behaviour and property can be manipulated by the copolymer’s concentration and preparation method such as in water or in DMSO.