Determination of Urea-Formaldehyde Resin Content in Poplar Fiber Based on Hyperspectral Techniques

In this experiment, poplar fibers containing 0%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 25% and 30% of urea-formaldehyde resin were prepared. A model for the detection of urea-formaldehyde resin content in poplar fibers was established by the hyperspectral near-infrared imaging system combined with relevant algorithms. The spectral images of poplar fibers containing different contents of urea-formaldehyde (UF) resin were measured separately using hyperspectral imager. The results of four preprocessing methods, namely mean centering (MC), multiple scattering correction (MSC), standard normal variables (SNV) and first-order derivative (1-Der) were analyzed, and the optimal preprocessing method was selected as SNV. The band combinations with the highest correlation with the urea-formaldehyde resin content were compared and analyzed with the full-band model to establish the partial least squares regression (PLSR) model. The experimental results show that the hyperspectral imaging system combined with the corresponding algorithm can achieve rapid detection of UF resin content in poplar fibers, and the results of this study provide technical support and theoretical reference for determination of resin content in ultra-thin fiberboard production. The method is an innovative model for the determination of UF resin in wood fibers.

Model construction and microwave preheating experiments using fiberboard

Microwave heating is a new type of pre-heating for fiberboard mats. Compared to conventional heating, microwave heating is faster and the surface and interior are evenly heated, thus avoiding the phenomenon of premature hardening of the surface layer of the fibreboard mats. In this paper, the heat transfer law of microwave preheated fiberboard mats was analyzed, and a thermodynamic model of fiberboard microwave heating was established. Furthermore, a microwave preheating simulation was established through COMSOL software; the temperature distribution of the fiberboard after microwave heating was analyzed and the reliability of the simulation model was verified through experiments. The temperature changes of fibers in the two preheating methods were compared by direct contact preheating experiment and microwave preheating experiment. Microwave preheating is more efficient than direct contact preheating, and more uniform temperature distribution in fiberboard mats. The core layer temperature is higher than the surface layer temperature, which can shorten the preheating time. By comparing the COMSOL model with the test, the model can basically reflect the temperature change law of microwave preheating, and the temperature of each layer of the slab is more uniform in the model simulation process. The heating law of the fiberboard was obtained, which provided a theoretical reference for the industrialized microwave preheating of fiberboard.

The effect of hardener on adhesive and fiberboard properties

Ureaformaldehyde adhesive requires hardener and about 4-6.5 pH to be cured. In this study, boric acid, boron oxide, borax, sodium perborate tetrahydrate, sodium chloride, sodium chlorite and control samples containing ammonium chloride was used as an hardener to investigate cureability of urea formaldehyde adhesive. Chemicals used as an hardener tested to demonstrate the effect on gelation time, swelling properties, MOR and MOE. Ammonium chloride, boric acid and boron oxide improved to properties when used as an hardener in single use or in mixture.

Mechanical and physical properties of medium density fibreboard with calcite additive

In this study, it is investigated that are calcite filler can be used in the production of medium density fiberboard. Chips have been to the process of cooking for 4-5 minutes in Asplund defibrator with the vapor pressure of 7-7.5 bar, and 180ºC temperature. 1.5% paraffin and 1% ammonium sulphate to be pulverized is added to fibers on the output of defibrillator and blowline line. Calcite fillers are prepared in a separate tank in order to use calcite instead of lignocellulosic fibers in the production of 1 m³ MDF. After that, urea formaldehyde glue is prepared as three different solutions which include the calcite, respectively with 3% (20 kg.m-3), 6% (40 kg.m-3), 9% (60 kg.m-3). The fibers are dried to moisture of 8%-12%. This press applies temperature about 185-190°C and pressure about 32-34 kg.m-2 to the mixture material for 270 seconds during pressing time. MDF panels (2100 x 4900 x 18 mm) were produced in the process. Both mechanical and physical experiments are performed on boards which are produced.