Selected Topics on Polypropylene/Woof Flour Composites: Thermal, Mechanical and Time Dependent Response

MARÍA M. REBOREDO; M. I. ARANGUREN; NORMA E. MARCOVICH

Polyolefin Composites

Wiley

Lugar: New Jersey - USA; Año: 2007; p. 150 - 177

The performance of wood flour/polypropylene (PP) composites with modified compatibilities was compared.  Wood flour modification was performed by esterification with maleic anhydride  and a non-commercial maleic anhydride-polypropylene copolymer (MAPP) was selected as compatibilizing agent.  The thermogravimetric analysis indicates that the onset of thermal degradation of treated woodflour occurs at lower temperature than that of the untreated one, and the same behavior was found in the corresponding composites.  Differential scanning calorimetry indicated that both wood flours acted as nucleating agents for PP.  Dynamic mechanical studies suggested that composite properties decreased at concentrations higher than 40 wt% of woodflour and that the overall performance of maleic anhydride treated woodflour composites was lower than that of the composites where a compatibilizing agent was added. The tensile and bending moduli increase with the addition of filler.  This increment was more important in the flexural moduli if treated woodflour was used or if MAPP was added to the composite.  Tensile yield stress of samples prepared from chemically modified wood flour was more affected by the incipient thermal degradation of the woodflour during processing and consequently shows lower values. The addition of woodflour to PP initially increased the impact strength of the material, since new deformation mechanisms are active during fracture.  However, as filler concentration is increased the material becomes more rigid and the impact energy dropped. Short-term and long-term creep tests of composites at different temperatures were carried out. The effect of filler content, addition of compatibilizing agent and temperature was discussed. The creep deformation was generally reduced with woodflour addition, except at very high filler concentrations due to filler-wetting and dispersion problems.  Low temperatures and addition of MAPP also reduced the creep deformation. Attempts to use the time temperature superposition principle to predict long-term creep from high temperature results were not successful due to the ageing of the samples during creep at low temperatures.