Thermal Behavior of Hydroxymethylated Resorcinol (HMR)-Treated Maple Veneer

The objective of this research was to study the effect of hydroxymethylated resorcinol (HMR) treatment on the thermal and dynamic mechanical properties of maple veneer. The veneers were soaked in HMR solution for either 1, 15, or 30 min, and subsequently dried for either 1, 12, or 24 h at 20°C and 65% relative humidity. Dynamic mechanical thermal analysis (DMTA) tests were performed at a controlled heating rate of 5°C/min using a 3-point bending mode at an oscillatory frequency of 1Hz and an oscillating dynamic strain of 0.01%. Differential scanning calorimetry (DSC) was performed from -40 to 150°C at a heating rate of 10°C/min. Depending on the amount of drying, the storage moduli of wood can be unaltered or reduced as a response to HMR soaking time. Overall, there was no evidence that HMR treatments reinforce wood.The lignin glass-transition temperature of HMR-treated maple veneer decreased with an increase in treatment time. The lowering of Tg by HMR treatments was confirmed by DSC results. Both DMTA and DSC data showed a glass-transition shift of wood hemicellulose that was subtle or none in responding to HMR treatments. HMR was theoretically determined to have a closer solubility parameter match (better compatibility) with lignin compared to the other wood cell-wall polymers (i.e., cellulose and hemicellulose). Based on these findings, HMR is postulated to act as a lignin plasticizer.This study provides new insights into the interactions of HMR with wood and is expected to stimulate further investigations that lead to a better understanding of the wood bond durability enhancement of HMR treatment

Dimensional Stability Measurements of Thin Wood Veneers Using the Wilhelmy Plate Technique

The objective of this study was to investigate the effect of hydroxymethylated resorcinol (HMR) and a commercially available water repellent (WR) treatment on the dimensional stability and water uptake behavior of maple veneers. The Wilhelmy plate technique was used to assess the effects of the chemical treatments on the veneer by comparing the perimeter of the veneers before and after 24 h water immersion and by monitoring the initial water uptake behavior. The veneers were treated with the HMR and WR by dipping treatment at three different loadings: 5, 15, and 30 min of treatment time.Water uptake into the untreated veneer increased dramatically during the 30 min of immersion time in water, compared with the HMR-treated veneer. Water uptake into the HMR-treated veneer, which was treated at the highest retention level (30 min), was limited during the initial stage of the waterimmersion test.The initial amount of water uptake into the veneer was lowered by 65% to 75% as a result of the HMR treatment, and the initial amount of water uptake into the water repellent-treated veneers was lower than that of the HMR-treated veneers depending on the HMR/WR treatment retention level. The initial amount of water uptake of the water repellent-treated veneers was lowered by 5 to 10%, compared with the HMR-treated veneers at the treatment time of 15 and 30 min.HMR treatment improves the dimensional stability of wood as evidenced by the reduced swelling of the HMR-treated samples compared to the untreated samples in the water-immersion test.The changes of sample perimeters measured by the Wilhelmy plate method were larger than those measured by digital calipers because the Wilhelmy plate method measures the perimeter change on the microscopic (cellular) level. It is hypothesized that the Wilhelmy plate method is a more effective tool than the caliper method for investigating the dimensional stability of small, thin, or nonrectangular samples in aqueous environments

A Periodically Rotating Distributed Forcing of Flow over a Sphere for Drag Reduction

In the present study, we propose a periodically rotating distributed forcing for turbulent flow over a sphere for its drag reduction. The blowing/suction forcing is applied on a finite slot of the sphere surface near the flow separation, and unsteady sinusoidal forcing velocities are azimuthally distributed on the sphere surface. This forcing profile periodically rotates in the azimuthal direction over time with a forcing frequency, satisfying the instantaneous zero net mass flux. The Reynolds number considered is Re=104 and large eddy simulations are conducted to assess the control performance. It is shown that the drag reduction performance varies with the forcing frequency, and the control results are classified into low-frequency ineffective, effective drag reduction, and high-frequency saturation regimes. With forcing frequencies in the effective drag reduction regime, a helical vortex is generated from the forcing on the sphere and evolves in the shear layer, and this vortex is responsible for the separation delay and flow reattachment resulting in the base pressure recovery and drag reduction. The maximum drag reduction is about 44% with the forcing frequency in the effective drag reduction regime, while controls in other regimes do not produce a drag reduction