Properties of biodegradable poly(butylene adipate-co-terephtalate) and sodium caseinate blends

Sodium caseinate (NaCAS) was blended with commercially available biodegradable polyester, poly(butylene adipate-co-terephtalate) (PBAT) with the aim to obtain environmentally friendly materials for packaging applications with increased oxygen barrier properties. Mechanical properties (tensile strength, elongation, and Young's modulus) of such blends were determined versus ratio of protein to polyester, plasticizer type and content, and relative humidity conditions. Among the two plasticizers tested, glycerol (Gly) and triethanolamine (TEA), Gly was the most efficient for the improvement of mechanical properties (high strains for low stresses) of PBAT/NaCAS blends. The maximum content of protein in blends to keep interesting mechanical properties was about 30% w/w. At this level, the material still exhibits interesting mechanical properties, that is, maximum tensile strength of 20-25 MPa for elongation at break about 25%. Protein-specific water solubility was determined from a 280-nm absorbance method. PBAT/NaCAS materials exhibit good resistance to water, and NaCAS specific solubility was kept under 7 wt % after 48 h immersion in water even for samples containing 30% w/w NaCAS. The PBAT/NaCAS materials also showed an increase of oxygen barrier properties as NaCAS content increased, leading to materials with oxygen permeability lower than 40,000 cm3 mu m m-2 d-1 atm-1, which is half the initial value of PBAT. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012