Chemical Composition and Surface Properties of Paper Mill Sludge and their Impact on High Density Polyethylene (HDPE) Composites

<div><p>A comparative study was conducted using paper mill sludge from three different pulping processes at two primary sludge (PS) to secondary sludge (SS) ratios to better understand the role of PS and SS in the development of wood/high-density polyethylene (HDPE) composite properties. Sludge samples from a thermomechanical (TMP), chemico-thermomechanical (CTMP), and Kraft pulping process were used at three proportions (20, 30, and 40%) to produce different composites. Pulp and combined sludge samples were characterized by conventional chemical analysis and FTIR spectroscopy. FTIR spectroscopy enabled the characterization of the inorganic content in the sludge. Results showed that the variation in composite properties according to sludge type could be explained by the chemical composition, regardless of pulping process or SS:PS ratio. Ash and cellulose content were the dominant factors in explaining the composite mechanical properties, and nitrogen content, although low, was the dominant factor in explaining composite toughness.</p></div