Viscoelastic behavior of degradable polyolefins aged in soil

Samples of polypropylene and a high density polyethylene/polypropylene blen d filled with different biodegradable additives (rice starch/iron oxide mix ture, Bioefect 72000 and Mater-Bi AF05H) have been subjected to an outdoor soil burial test for 21 months. Changes on the morphology of the samples ha ve been studied by differential scanning calorimetry. The degradation proce ss also has been analyzed in terms of the mechanical behavior of the polyme rs. The three characteristic relaxation zones alpha, beta, and gamma (in or der of decreasing temperature) of the dynamic-mechanical relaxation spectra of the samples have been characterized according to the Fuoss-Kirkwood equ ation. When two relaxations were overlapped, a deconvolution method was app lied. It has been observed that the degradation process affects just to a s mall extent the amorphous phase of the polymers. That the beta relaxation i s the most sensitive to the exposure time suggests that degradation starts in the crystalline-amorphous interface. However, the crystalline phase is a lso affected significantly by the degradation process. The mechanical resul ts are in good agreement with the calorimetric measurements, proving that d egradation takes place in two stages with different time scales depending o n the additive used. (C) 2000 John Wiley & Sons, Inc.