To develop formaldehyde-free wood-based composites, plywood-like composites (WV/PPF) were prepared using wood veneer (WV) with polypropylene film (PPF) as a novel formaldehyde-free, water-resistant adhesive. To prepare WV/PPF, the effects of hot-pressing conditions (temperature, 165 to 195 °C; pressure, 0.9 to 1.3 MPa; duration, 40 to 70 s/mm; and adhesive dosage between adjacent WVs, 100 to 200 g/m 2 ) were investigated. Results showed that conditions at 180 °C, 0.9 MPa, 70 s/mm, and 150 g/m 2 gave WV/PPF desirable physical-mechanical properties. Then, WV/PPF was compared with plywood-like composites using, respectively, polyethylene film (PEF), urea-formaldehyde resin (UFR), and phenol-formaldehyde resin (PFR) as adhesives. Results showed that the physical-mechanical properties of WV/PPF were favored over WV/PEF and WV/UFR, and were comparable to those of WV/PFR. Maleic anhydride grafted polypropylene (MAPP) or γ-aminopropyltriethoxysilane (APTES) surface modification of WV was performed to enhance the interface compatibility of WV/PPF. Results showed that the physical-mechanical properties of modified WV/PPF were favored over those of WV/PFR; MAPP modification was better for shear properties, while APTES modification was better for dimensional stability and flexural properties. Overall, the environmental and technological benefits demonstrated the potential of WV/PPF as a novel construction and building material.
To achieve value-added utilizations of plantation timbers, eucalyptus veneer/high-density polyethylene film composites were prepared, with process-factors (PF) (hot-pressing temperature, HT; hot-pressing duration, HD; hot-pressing pressure, HP; HDPE-film content, HC) and composite-properties (CP) (water-resistant bonding-strength, BS; modulus of rupture, MOR; modulus of elasticity, MOE) investigated. According to thermal analyses, 140 to 180 °C was appropriate for HT. Based on statistical analyses, HD was easier to affect CP, while MOE was easier to be affected by PF. Quantitative relationships between PF and CP were determined by the neural-network (ANN) modeling. In ANN simulation surveys, CP displayed Gaussian distributions (R 2 > 0.9) when PF changed in current ranges, with positive correlations between BS and MOR (R 2 ≈ 0.5). Combining ANN and the genetic-algorithm, optimal processes (HT, 160 °C; HD, 50 s/mm; HP, 1.3 MPa; HC, 6 layers) were found, and optimal results (BS, 1.30 MPa; MOR, 86.94 MPa; MOE, 8.33 GPa) were comparable to various reported poplar-plywoods. Microscopic images demonstrated that composite interfaces were formed by the mechanical interlocking. The optimal BS attained Chinese standards for water-resistant plywoods, so proposed composites can serve as waterresistant and formaldehyde-free building materials for furniture and interior design.
To blaze new trails for utilizing forestry processing residue, higher plant content biocomposites were proposed based on a combination of moso bamboo flour/silane KH550/high density polyethylene (HDPE), and the materials were characterized by diffractometry, spectroscopy, microscopy, and calorimetry. During surface modification, reactions between bamboo and silane occurred on the lignin aldehyde group. After 6 wt% KH550 treatment, crystallinity of bamboo was increased by 1.11 %, and melting temperature and enthalpy of the composite rose by 2.37 °C and 5.27 J/g, agreeing with improved interface morphology. Increasing in thickness from 3 to 9 mm, the physical and mechanical properties of composite were improved overall. Bamboo content caused the biggest influence, while thickness swelling exhibited the greatest susceptibility. Increasing the bamboo ratio boosted flexural and tensile properties, but it compromised toughness and water resistance, while silane and moulding parameters featured complicated relationships regarding performances. Combining an artificial neural network (ANN), KH550 3 wt%, moulding temperature of 180 °C, and a time of 8 min endowed 9 mm composites of 70 wt% bamboo with performance comparable to load bearing MDF in GB/T 11718.
New plywood composites for furniture and interior decoration were developed with eucalyptus veneers using polyethylene films as formaldehyde-free adhesives. To enhance the interfacial adhesion, the veneers were modified with an oven treatment (temperature: 100, 120, 140, and 160 °C; time: 0.5, 1.0, 1.5, and 2.0 h) or by soaking in a sodium hydroxide (NaOH) solution (concentration: 3%, 7%, and 11%; time: 12, 24, and 36 h). The effects of these treatments on the mechanical properties (flexural strength, MOR; flexural modulus, MOE; wet shear strength, WSS) of the composites were studied. Both treatments improved the three properties of the composites. The heat treatment was better at improving the shear property, while the alkali treatment was better at improving the flexural properties. For the heat treatment, the highest WSS was 81.1% higher than the untreated group. The optimum conditions for the heat treatment were 140 °C and 1.0 h. For the alkali treatment, the highest MOR and MOE were 267.5% and 173.7% higher than the untreated group, respectively. The optimum conditions for the alkali treatment were 3% and 36 h. The changes to the veneer surfaces were determined by scanning electron microscopy.
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