We investigated the effects of fiber variability, size and content on the fusion characteristics of wood particle-reinforced high-density polyethylene (HDPE). Five types of wood sawdust were used: eastern white cedar, with sapwood, and heartwood treated separately; jack pine divided into wood and bark; and black spruce. Three different fiber length classes were also used. Composite pellets containing wood particles at 25, 35, and 45% by weight with HDPE were made using a co-rotating twin-screw extruder. The pellets were melted and mixed during 7 min in a torque rheometer at 180°C. We also investigated the polymer variation using HDPE, polypropylen (PP), polyvinyl chloride (PVC), and a blend of (80% HDPE+ 20% PP) where wood fiber proportion and length were kept constant. We varied the mixing temperature to reach the melting temperature range of each polymer. Mixing and melting times, maximum torque and stabilized torque were obtained. Adding wood fibers to the HDPE increased processing time and torque energy. At constant fiber length and proportion, torque properties varied with fiber origin. Higher fiber length and proportion increased torque energy and time of stabilization. Thus, using wood fibers with different properties will lead to significant variations in processing, such as in extrusion or injection. The fusion characteristics of wood polymer composite vary among polymers. The PVC showed the highest steady-state torque. The formulation containing a polymer blend of HDPE and PP showed the highest torque energy. This higher torque energy is explained by the interaction of the incompatible polymeric chains of the two thermoplastic polymers. © 2018 Society of Plastics Engineers.

Recent studies have demonstrated the potential of primary sludge (PS) as reinforcing fibers and secondary sludge (SS) as binder or co-binder in wood–plastic composites (WPC). A comparative study was conducted using paper mill sludge produced by three different pulping processes at two SS to PS ratios. The objectives were to determine the impact of PS and SS on the development of high density polyethylene (HDPE) WPC properties. Sludge produced by thermomechanical pulping (TMP), chemithermomechanical pulping (CTMP), and Kraft pulping were used at three different proportions (20%, 30%, and 40%) for composite manufacturing. The use of mixed sludge containing 30% SS resulted in lower tensile, flexural, and impact performance of the WPC compared to mixed sludge containing only 10% SS for the three pulping processes. Sludge type had a significant impact on the WPC physical and mechanical properties. Kraft sludge produced the best WPC properties, followed by CTMP and TMP sludge. Increasing the sludge proportion produced increasingly negative impacts on water absorption and thickness swelling, but improved the flexural and tensile properties.

This study investigated the potential of secondary sludge (SS) as urea–formaldehyde (UF) co-adhesive for particleboard manufacturing. Three proportions of SS from three conventional pulping processes were added in the formulation of particleboard manufacturing. A 33 factorial design was used. All panels were tested for thickness swell (TS), linear expansion (LE), internal bond strength (IB), flexural modulus of elasticity (MOE), flexural modulus of rupture (MOR) and formaldehyde emission. Results indicated that particleboards made with SS from thermomechanical pulp (TMP) and kraft pulp (Kraft) met the ANSI standards for LE, IB, MOE, and MOR (with 7 and 9 % UF). However, the TS of panels made with SS was higher than that of control panels and adding SS to the formulation affected negatively this property. Most of the properties studied in the particleboards made with SS from chemical–thermomechanical pulping (CTMP) process failed to meet the ANSI standards. The main advantage of using SS as co-adhesive is the reduction of formaldehyde emission, in the best case here, about 50 %, with CTMP sludge added, of the particleboards.

Pulp and paper sludge can be recycled in the manufacture of medium-density fiberboard (MDF) because it contains wood fibers. A comparative study was conducted to evaluate the properties of MDF made from virgin fibers mixed with different pulp and paper sludge sources. A factorial design was used in which factors were mill pulping processes, thermal–mechanical pulping (TMP), chemical–thermal–mechanical pulping (CTMP), and kraft pulping, and percentage of sludge mixed with virgin fibers (0, 25, 50, and 75%). Virgin fibers were obtained from paper birch wood, an underutilized species. Chemical composition, physical characteristics, pH, and buffer capacity of sludge were measured. MDF properties decreased mostly linearly with sludge content. Panel properties negatively correlated with the proportion of nonfibrous material such as ash and extractives. TMP and CTMP sludge sources produced panels of similar quality, and kraft sludge produced the lowest quality. It was concluded that the amount of sludge that can be incorporated into MDF without excessive decrease in panel quality depends on the pulping process. At 25% sludge content, all panels met ANSI quality requirements for MDF used for interior applications.

Variability in the chemical composition of surface properties of various wood fibers (eastern white cedar, jack pine, black spruce, and bark) was investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray photoelectron spectroscopy (XPS). Both DRIFTS and XPS showed high variability in fiber surface composition between species and between fiber types (sapwood, heartwood, and bark). Fiber surface was modified by esterification reaction using a maleic anhydride polyethylene (MAPE) treatment. DRIFTS failed to assess surface modification, whereas XPS results showed that MAPE treatment increased the surface hydrocarbon concentration of jack pine wood fiber, indicated by a decrease in oxygen–carbon ratio and an increase in relative intensity of the C1 component in the C1s signal. Lignin concentration variability on the fiber surface was determined as the major factor that prevents esterification from taking place.