WATER SORPTION AND DIFFUSION IN STARCH POLYOLEFIN BLENDS/

The kinetics of water sorption by starch filled polyolefins has been i nvestigated using blends of a commercial starch masterbatch with low d ensity polyethylene (LDPE), high density PE (HDPE), and copolymers of ethylene with methyl acrylate (EMA), ethyl acrylate (EEA), and n-butyl acrylate (EEA). Transient state diffusion coefficients (D) of water i n the blends were determined using Fickian analysis of the initial sta ges of the sorption isotherms. Measured D values were several orders o f magnitude lower than values reported for either pure starch or LDPE by various investigators. Resin effects on D were in the order D-HDPE < D-LDPE much less than D-EBA < D-EBA < D-EMA. The resin effects dimin ished as the starch content increased. The lower magnitude of D in the blends relative to pure LDPE was attributed to the sorption of water by the dry starch particles, in a manner similar to dual-mode sorption in glassy polymers. Copolymer effects were consistent with reduction in crystallinity caused by the comonomers. The dependence of the diffu sion coefficient on starch content was not described by mixing models of heterogeneous systems or percolation theory.