Grease resistance and mechanical properties of isolated soy protein-coated paper

Crease-resistant paper has been produced by coating paper with isolated soy protein (ISP). Tensile strength (TS) of ISP-coated paper is 28-30 MPa (between the TS of paper and of ISP film). TS of the ISP-coated paper (2.3 kg/ream) was highest (36.0 MPa) among other ISP-coated papers, but elongation (E) of the papers seemed to decrease (though not statistically significantly) as the thickness of the ISP coating increased. ISP-coated papers were highly impermeable to grease penetration for the first 2 h of the test. The percent stained area of two commercially used polyethylene-laminated papers was higher than those of ISP-coated papers. As the amount of plasticizer (a mixture of glycerol and polyethylene glycol) was increased in ISP-coated paper, the TS decreased and the E increased, When tested, the percent stained areas of the paper containing 0.6 and 1.0 g plasticizer/g protein were lower for the first 2 h than those of the papers containing 0.0 and 0.2 g plasticizer/g protein. Also, percent stained area increased with time. Grease resistance of papers coated with ISP at levels higher than 2.0 kg/ream was equal to or lower than that of polyethylene laminates used for quick-service restaurant sandwich packaging.