Shear and elongational flow properties of peroxide-modified wood/low-density polyethylene composite melts

Adding fillers to a polymer melt may result in a strain softening behavior in elongational flow in long-chain branched materials, showing strain-hardening behavior when compared with unfilled one. To improve the strain-hardening properties in wood/LDPE composites, the effect of peroxide concentration on both the molecular architecture and molar mass distribution, and the rheological quantities in shear and elongation is studied. Addition of wood flour increases the viscosity according to a logarithmic mixing rule, as expected from the large particle size and the filler fractions used. The peroxide has multiple effects on the molar architecture of the polymer. First, a gel fraction of cross-linked material is formed, the concentration of gel being dependent of the amount of peroxide used. Second, a higher molar mass component is detected, leading to higher value of Mw and to a broader molar mass distribution. Finally, the degree of long-chain branching unexpectedly decreases with increasing peroxide content. The changes in molecular architecture are hardly influenced by addition of the wood flour. The peroxide treatment leads to an improved strain-hardening behavior, detected by elongational viscosity and melt strength measurements. However, the addition of wood flour decreases the amount of strain hardening.POLYM. COMPOS., 33:20842094, 2012. (C) 2012 Society of Plastics Engineers