The incorporation of paper deinking sludge into fiberboard

A major waste product resulting from the paper recycling process is known as paper deinking sludge (PDS). This study investigated the mechanical and physical properties of medium density fiberboard (MDF) to which was added PDS as an alternative to the current practice of disposal of PDS in landfill facilities. A treatment method was developed to reduce the moisture content (MC) and consistency of the PDS to within a range suitable for the production of MDF (6% to 9.5% MC). Treated material was found to contain approximately 11 percent silicon, 10 percent aluminum, 4 percent calcium, and 2 percent titanium. Thirty-seven percent of the treated material passed a 200 mesh screen (fine content). Panels were produced using virgin MDF fiber (6% phenol-formaldehyde resin), which included additional factors chosen based on PDS composition. These factors (by percent ovendry furnish weight) included fine content (0% to 35%), kaolin coating clay (0% to 20%) and calcium carbonate from (0% to 4%). A response surface regression model equation was then generated for each property. Coating clay was the primary factor affecting mechanical properties, exhibiting linearly negative effects on modulus of elasticity (MOE), modulus of rupture (MOR) and internal bond (IB) strength. MC, change in conditioned weight, and conditioned volume were found to linearly increase along with clay content. By contrast, the equation for conditioned MC was dependent on fine and calcium carbonate content and included quadratic and linear terms. The model equation for the MC at 30 percent relative humidity (RH) in the linear expansion test included a linear calcium carbonate term as well as quadratic terms for both clay and calcium carbonate. Flammability of the model panels was decreased by increasing clay content and was found to have a strong positive correlation with increased fiber content. Decay by the brown-rot fungus G. trabeum increased with clay content and decreased with increased calcium carbonate content. Comparison of actual results with values predicted using the model equations for mechanical properties (MOE, MOR, and IB strength) and the water absorption test of panels containing PDS were close to the experimental results at lower levels of PDS. As PDS content increased, the deviation of actual from predicted increased. It was believed that this deviation was partially caused by the exclusion of greater than 200 mesh degraded fiber from the model. Model equations for the MC at 30 percent RH, and the behavior of the panels under the influence of fire and decay were found to reasonably approximate the actual results.