Plasticizer effect on mechanical properties of beta-lactoglobulin films

The mechanical properties (elastic modulus, EM: tensile strength, TS and % elongation, %E) of beta -lactoglobulin (beta -Lg) films plasticized with di fferent plasticizers were determined. Six plasticizer types were studied ov er a range of concentrations. Propyleneglycol-plasticized beta -Lg films we re the most brittle, with mechanical properties independent of plasticizer content. Films with other plasticizers studied (glycerol, Gly, sorbitol, So r; polyethylene glycol, PEG 200 and PEG 400 and sucrose, Suc) exhibited neg ative exponential dependence on plasticizer concentration for EM and TS, wh ile they exhibited linear dependence on plasticizer concentration for %E. T he EM and TS data for each plasticizer were fitted with an exponential mode l, while %E data were fitted with a linear model to quantify the plasticize r effect. The EM0, TS0 and %E-0 of beta -Lg films without plasticizer deter mined from the fitted equations were 1500. 37.28 MPa and 0, respectively. T he k(EM), k(rs) and k(E) values determined from the fitted EM, TS and %E da ta, respectively, reflect the efficiency of plasticizers. The k(EM), k(TS) and k(E) values indicate that plasticizer efficiency generally decreased in the order Gly, PEG 200, PEG 400. Sor and Suc. on the bases of mole plastic izer-oxygen-atom/mole beta -Lg and mass plasticizer/mass beta -Lg. These re sults reflect the effect of plasticizer composition. size and shape. The k( EM), k(TS) and k(E) value order was reversed when the basis was changed to mole plasticizer/mole beta -Lg. The latter results clearly reflect the effe ct of plasticizer number of 0 atoms. (C) 2001 Elsevier Science Ltd. All rig hts reserved.