Pulp extrusions incorporating sludge from the pulp and paper industry
Pulp extrusion at ultra-high consistency (≅30% solids) has been shown to be a viable process for converting recovered paper, wastepaper, and papermill residues into solid sheets and profiles. We have previously shown that extrusion of ultra-high consistency pulps and "model" sludges requires the addition of a water-soluble polymer (WSP) to alter the rheological properties of the pulp such that an homogenous "pulp paste" can be formed and extruded. This paper discusses our attempts to evaluate the viability of extruding a variety of papermill sludges. Several sludges were acquired from various mills and classified by ash content, contaminant level, and biological activity. Various blends of sludge, newsprint (ONP), and WSP were prepared and extruded into continuous sheets. The sheets were then cut into strips for consolidation by press drying. These strips were further cut into coupons for tensile testing. The results showed that a variety of sludges could be successfully extruded with adequate tensile strength. However, the presence of contaminants (e.g., chips, staples, plastics, silica) and interfering chemistries posed some difficulties in processing these residues.