James Deng

Medium-density fiberboard performance as affected by wood fiber acidity, bulk density, and size distribution

The properties of medium-density fiberboard (MDF) panels as affected by wood fiber characteristics were investigated. Wood chips from three softwood and one hardwood species were refined under the same refining conditions to make four different types of fibers. The resulting fibers were characterized by fiber size distribution, bulk density, pH value, and buffering capacity. Using the same resin system and hot-pressing parameters, MDF panels were produced and evaluated for internal bonding (IB), modulus of rupture (MOR), modulus of elasticity (MOE), thickness swelling, and linear expansion. The pH values and alkaline buffering capacities of raw materials were reduced considerably after refining. IB was strongly related to the pH value of fibers. The mechanical properties increased with alkaline buffering capacity. IB, MOR, and MOE increased with the bulk density of fibers. Increased proportions of coarse fibers had negative effects on the panel mechanical properties.

Potential of pulp and paper sludge as a formaldehyde scavenger agent in MDF resins

Abstract Sludge of pulp and paper mills have natural adhesive properties. The primary sludge (PS, contains fibers) and secondary sludge (SS, contains proteins) could also be suitable for manufacturing medium-density fiberboard (MDF). Protein in SS can react with formaldehyde (HCHO), and as an additive in urea-formaldehyde (UF) resins it can reduce formaldehyde emission. Thus, SS was investigated in the present study. PS and SS were collected from two mills and characterized in terms of chemical composition, fiber length distribution, pH, and buffering capacity. MDF samples were processed according to an experimental design, in which UF resin content was reduced from 12% to 8% and replaced by SS in the range of 5%–15%. Gel time measurement showed high SS reactivity with UF resin. The SS reduced HCHO emissions by up to 68% compared to control panels, without compromising internal bond strength. The bonding effect of SS was lower than expected due to the high pH, thus the buffering capacity reduced UF performance. Moreover, sludge reduced bending performance. Dimensional stability was the greatest disadvantage of sludge panels.

Quantification of urea formaldehyde resin in wood fibers using X-ray photoelectron spectroscopy and confocal laser scanning microscopy

The potential merits of X-ray photoelectron spectroscopy (XPS) technique for the quantification of nitrogen on the wood fiber surface before and after resination with UF resin was investigated and the resin content was calculated. The bulk nitrogen content of the fibers obtained by XPS after grinding was compared with those obtained by combustion and Kjeldahl methods. Four different fluorescence staining agents were tested by UV spectroscopy. Their λmax shifted to longer wavelengths when reacted with UF resin. Appropriate analysis conditions were tested for a satisfactory analysis of wood fibers by the confocal laser scanning microscopy (CLSM). The result obtained by CLSM was compared with that obtained by XPS.

Performance of long Canadian natural fibers as reinforcements in polymers

Fiber morphology has a significant effect on the mechanical properties of fiber/polymer composites. The performance of nine types of long wood fibers (initial aspect ratio of >40), two long agricultural fibers (initial aspect ratio of >40), and one short fiber wood flour (initial aspect ratio of = 5—10) are compared. The fibers were compounded in polypropylene in a Brabender mixer and subsequently injection molded. The longer natural fibers (both wood fibers and agricultural fibers) did not provide significant additional reinforcement when compared to the wood flour. The fibers were extracted from the final specimens and measured using a Fiber Quality Analyzer. They were found to be severely degraded by processing, while the wood flour morphology was only slightly modified. The degree of length degradation was found to be dependent on fiber strength.

Effects of thermomechanical refining conditions on the morphology and thermal properties of wheat straw fibre

Abstract Wheat straw fibre is prepared by a thermomechanical (TM) refining system. This study investigated the effects of refining steam pressure (4, 6, 8 and 10 bar) and refiner speed (2500 and 3000 rpm) on the morphology and thermal properties of the resulting fibres. After TM refining, the fibres exhibited more surface irregularities and heterogeneities as well as decreased fibre length. The fine content decreased with increasing steam pressure, but the aspect ratio increased. The findings show that higher steam pressure (8 bar) results in more effective wheat straw refining. Refining lowers the pH. Thermogravimetric analysis showed that TM refining does not influence the thermal properties of wheat straw fibres. Weight loss has to be taken into account upon exposure to temperatures around 170°C. The silica content of the fibres was significantly reduced through refining.

Properties of Commercial Kraft Paper Honeycomb Furniture Stock Panels Conditioned under 65 and 95 Percent Relative Humidity

Abstract Physical and mechanical properties of a range of commercially produced kraft paper honeycomb stock panels were assessed to provide technical information of interest to primary and secondar...

Investigation of mechanical properties of sandwich panels made of paper honeycomb core and wood composite skins by experimental testing and finite element (FE) modelling methods

In this study, lightweight sandwich panels with different Kraft paper honeycomb core structures and wood composite skins were constructed. The influence of structural parameters, including core shape, cell size, core density, core and web thickness, and material properties of the core and skin layers on the mechanical behavior of these lightweight sandwich panels were studied by experimental testing and finite element modeling methods. The panels were subjected to compression and shear loadings. Test and simulation results indicated that core density and core shape mainly affected the panel stiffness under out-of-plane loading conditions (e.g. Ez, Gxz and Gyz). Material properties of the skin layer affected the panel stiffness both under in-plane and out-of-plane loadings if the skin layer was orthotropic.

Mechanical and physical properties of particleboard made from two pulp and paper mill secondary sludges

To investigate environmentally friendly alternatives for sludge disposal, three proportions of secondary sludge (SS) from two pulping processes (Kraft and TMP) were incorporated in the formulation of particleboard manufacturing. A 32 factorial design was used where the factors were Urea-formaldehyde (UF) content (5%, 7%, and 9% dry weight of resin per dry weight of particles) and secondary sludge percentage (75%, 100%, and 125% dry weight of SS per dry weight of resin). For each pulping process, 27 panels with SS and 3 control panels (without SS for each resin content) were made for a total of 63 panels. All panels were tested for thickness swell, linear expansion, internal bond strength (IB), flexural modulus of elasticity (MOE) and flexural modulus of rupture (MOR). Results indicated that particleboards made with SS from both pulping processes met the ANSI standards for linear expansion, IB, MOE and MOR. However, none of the tested panels met the standard for thickness swell and adding SS to the formula...

Modification of Wheat Straws through Steam Explosion and its Effect on Panel Properties

Particleboards bonded with urea formaldehyde (UF) and a combination of UF and methylene diphenyl diisocyanate (MDI) resins were manufactured using wheat straws modified through different steam explosion treatments. The effect of steam explosion treatment, resin system, and mixing ratios of wood and straw materials on the panel properties was investigated. Generally, with steam explosion treatment of straw fibers, panel properties in bending and internal bond (IB) strength increased, thickness swelling (TS) and water absorption (WA) decreased. The bending properties for the panels made from the straws pretreated with 12 h water-soaking were significantly improved at the UF/MDI content level of 5%/1%. The IB strength dramatically increased, while TS and WA decreased with the use of dual resins. With increased weight ratio of wheat straw to wood particles, the bending properties, IB strength, TS and WA deteriorated. Pure wheat straw boards had the lowest properties. Wood particles in substitution for part of straw materials helped improve the panel properties. The results demonstrated that steam explosion modification and/or its combination with UF/MDI dual resin system can be a feasible approach to improve the bonding strength for wheat straw based particleboards.