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Koubaa, Ahmed

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Koubaa

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Ahmed

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Université Laval

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ncf10552305

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Voici les éléments 1 - 5 sur 5
  • PublicationRestreint
    Densification of wood veneers by compression combined with heat and steam
    (Springer, 2011-02-01) Mariotti, Nicolas; Cloutier, Alain; Fang, Chang-Hua; Koubaa, Ahmed; Blanchet, Pierre
    Wood veneer 700×700 mm2 specimens made with aspen (Populus tremuloides) and hybrid poplar clone 15303 (Populus maximowiczii × Populus balsamifera) were densified using heat, steam, and pressure. Temperatures of 140, 160, 180, 200, and 220°C were applied at a maximum steam pressure of 550 kPa and maximum press hydraulic pressure ranging from 4.5 to 9.0 MPa. After densification, the oven-dry density increased significantly, veneers darkened, and lathe checks that were present on veneers before densification were conglutinated and veneer surface roughness decreased. Densified veneers showed markedly reduced hygroscopicity: the higher the densification temperature, the lower the wood hygroscopicity. The Brinell hardness of densified veneer was about two to three times that of control for both aspen and hybrid poplar. Tensile and bending strength also increased significantly after densification. However, the mechanical properties of densified veneers decreased slightly with increased densification temperature. The modulus of elasticity in tension and bending increased after densification, especially at high temperatures. A very high compression set recovery was found for veneers densified at low temperatures. Recovery decreased dramatically when densification temperature exceeded 180°C. Almost no recovery was found for veneers densified at 220°C.
  • PublicationAccès libre
    Densification of wood veneers combined with oil-heat treatment. Part II : Hygroscopicity and mechanical properties
    (Dept. of Wood and Paper Science College of Natural Resources North Carolina State University, 2012-01-13) Cloutier, Alain; Fang, Chang-Hua; Koubaa, Ahmed; Blanchet, Pierre
    In an effort to achieve high mechanical performance and improved dimensional stability, densification combined with oil-heat treatment (OHT) was performed. In our previous study, OHT was successfully applied to densified veneer, which resulted in improved dimensional stability. In the present study, the impact of OHT on densified wood veneer hygroscopicity and mechanical properties was determined. OHT at 180, 200, and 220ºC for 1, 2, and 3 hours was applied to densified Aspen (Populus tremuloides) veneers. OHT was found to be an efficient treatment to reduce the hygroscopicity of densified aspen veneers, although OHT had a negative impact on Brinell hardness. However, due to the contribution of densification, the hardness of oil-heat treated veneers was still two to three times higher than that of non-densified veneers. Similar results were found for tensile strength. Bending strength increased slightly at low OHT temperature, and then decreased at high temperature. Bending strength of oil-heat treated densified veneer samples was higher than that of non-densified ones. No significant effect of OHT was found on tensile MOE, but bending MOE increased after OHT. Compared to OHT duration, OHT temperature had a larger impact on densified wood hygroscopicity and mechanical properties.
  • PublicationRestreint
    Effects of hot water treatment of raw bark, coupling agent, and lubricants on properties of bark/HDPE composites
    (Elsevier Science Publishers, 2012-06-13) Cloutier, Alain; Soulounganga, Patrice; Stevanovic-Janezic, Tatjana; Koubaa, Ahmed; Ngueho Yemele, Martin Claude; Wolcott, Michael P.
    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.
  • PublicationRestreint
    Effect of bark fiber content and size on the mechanical properties of bark/HDPE composites
    (Elsevier, 2010-01-01) Cloutier, Alain; Soulounganga, Patrice; Koubaa, Ahmed; Ngueho Yemele, Martin Claude; Wolcott, Michael P.
    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.
  • PublicationAccès libre
    Effects of strands geometry on the physical and mechanical properties of oriented strand boards (OSBs) made from black spruce and trembling aspen
    (Raleigh, N.C. : Dept. of Wood and Paper Science College of Natural Resources North Carolina State University, 2022-05-05) Zhuang, Biaorong; Cloutier, Alain; Koubaa, Ahmed
    Black spruce is widely used for lumber production in Eastern Canada, and it has the potential to replace trembling aspen and paper birch for oriented strand board (OSB) manufacturing. This study evaluated the bending modulus of elasticity (MOE) and modulus of rupture (MOR), the internal bond (IB), and the thickness swelling (TS) of OSB panels made from black spruce and trembling aspen strands and how they were affected by strand geometry. All the panels met the CSA O437 (1993) standard for class O-2 properties except for the TS. The strand thickness had a significantly negative effect on the bending properties but a significantly positive effect on the IB and TS properties. The strand length had a significantly positive effect on the parallel bending properties but a significantly negative effect on the perpendicular bending properties and the IB, except for the TS. The OSB panels made from aspen obtained better bending properties, while the IB and TS properties were lower than those of the OSB black spruce panels. The results indicate that black spruce strands obtained from the Eastern Canadian softwood lumber industry are suitable for OSB production, but more work is required to reduce the TS.