Hot water treated and untreated black spruce bark (BSB) and trembling aspen bark (TAB) fibers were combined with high density polyethylene (HDPE) to produce bark thermoplastic composites by extrusion. Bark fibers of three size categories (fine, medium, and coarse) were used at contents of 50% and 60% based on oven dry weight. The effects of hot water treatment of raw bark and the addition of coupling agent (MAPE) and lubricants (OP-100, talc) on the flexural and tensile properties of bark/HDPE composites were investigated. Results showed a significant impact of hot water treatment on tensile properties of composites made with BSB and on tensile and flexural strength of composites made with TAB. The addition of coupling agent and lubricants significantly improved the flexural and tensile strength properties of bark/HDPE composites but reduced toughness and strain.

Black spruce and trembling aspen bark fibers and high density polyethylene were used to process bark– plastic composites by extrusion. Fibers of fine, medium, and coarse size and contents of 50% and 60% based on oven-dry weight were used. The effects of species, fiber content and size on the flexural and tensile properties of the composite were investigated and were found to be highly significant. Black spruce bark composites exhibited higher strength but showed more brittle behavior than aspen bark composites. The effect of content on mechanical properties was more important than size. Compared to wood flour composites, those from bark showed lower strength.

Bark residues are mostly used for thermal energy production. However, a better utilization of that resource could be as raw material for particleboard (PB) manufacturing. Bark is also a source of numerous extractives used in several fields including pharmacology and adhesive production. This study aims at analyzing the effect of hot water extracted bark particle content and size on the physical and mechanical properties of bark PBs including the modulus of elasticity (MOE), modulus of rupture (MOR), internal bond (IB), Janka hardness (HJ), thickness swelling (TS) and linear expansion (LE). Moreover, these properties were compared both to a control (100% wood particles) and to PB made from the same content of unextracted bark. The results showed that, while the mechanical properties of the PB made from extracted black spruce and trembling aspen bark decreased with increasing bark content, LE increased. PB made of fine particles often showed higher IB and lower TS values. Hot water extraction of the bark had a detrimental effect on all the physical and mechanical properties of the PBs produced except for the Janka hardness, where no significant decrease was found. TheMOEandMORof the PBs made from 50 percent black spruce and trembling aspen bark met the requirements of the ANSI standard for commercial (M–1) and underlayment (PBU) grades. In contrast, the dimensional properties (TS and LE) of all the boards did not fulfill the minimum requirements of the ANSI standard.

Bark residues are mostly used for thermal energy production. However, a better utilization of that resource could be as raw material for particleboard manufacturing. The use of bark in wood particleboard manufacturing is currently viewed negatively due to the fact that an excessive bark content in the furnish produces significant adverse effects on strength properties and dimensional stability of the boards. Strategies could be found to improve some properties of particleboard made from bark. The effects of bark particle content and geometry on the physical and mechanical properties of the panels including the modulus of elasticity (MOE), modulus of rupture (MOR), internal bond (IB), Janka hardness (HJ), thickness swelling (TS), and linear expansion (LE) were investigated. The best panels in terms of properties were compared to a control made of 100 percent wood particles. The results showed that, while the mechanical properties of the particleboard made from black spruce and trembling aspen bark decreased with increasing bark content, LE increased and TS increased slightly. The IB of particleboard made from 50 percent bark content decreased with increasing particle size. Particleboard made from 50 percent black spruce bark showed the highest MOE, MOR, and IB and the lowest LE with values 12, 37, and 54 percent lower and 45 percent higher than the control, respectively. The MOE, MOR, IB, and HJ of boards made from 50 percent black spruce and trembling aspen bark met the requirements of the ANSI A208.1 to 1999 standard. Particleboard made from trembling aspen bark showed the lowest TS.

The understanding of the interaction between bark extractives and adhesives is fundamental in the manufacture of bark particleboard for optimum adhesive curing, and mechanical and physical properties of the boards. The effect of hot-water treatment on black spruce and trembling aspen bark was investigated to highlight its impact on the bark particles/phenol-formaldehyde adhesive system, and on the physical and mechanical properties of bark particleboard made from hot-water-treated bark of both species. Bark was soaked in hot water maintained at 100°C for 3 h. The results showed that the hot-water treatment affects the physical and chemical properties of the bark by decreasing hydrophilic characteristics, acidity, and the amount of condensable polyphenols that can react with formaldehyde. The mechanical properties, including static bending and internal bond of particleboard made from untreated black spruce and trembling aspen bark, were higher than those of boards made from hot-water-treated bark of the same species. The thickness swelling of particleboard made from hot-water-treated black spruce and trembling aspen bark was higher than that made from untreated bark. One exception occurred for particleboard made from 100% trembling aspen bark for which no significant difference was found between particleboards made from treated and untreated barks.