Empirical correlations between test methods of measuring formaldehyde emission of plywood, particleboard and medium density fiberboard

Since different test methods of measuring the formaldehyde emission (FE) from wood-based composite panels have been used for different countries and regions, this study attempted to establish empirical correlations between three test methods (i.e., 24-hour desiccator, 1 m³ chamber, and perforator) for plywood (PLW), particleboard (PB), and medium density fiberboard (MDF), particularly emphasizing on correlations between the 24-hour desiccator and the 1 m³ chamber method. The desiccator method found statistically high correlations with other two methods, resulting in regression coefficient values ranging from 0.96 to 0.88 for PLW, PB, and MDF samples. In particular, the desiccator method had an empirically high correlation with the 1 m³ chamber method that had been adopted as the reference method of comparing regionally different test methods of measuring the FE of wood-based composite panels by the ISO/TC89.     

Short term flexural creep behavior of wood-fiber/polypropylene composites

Short term flexural creep tests were conducted to investigate the creep behavior of wood-fiber polypropylene composites. Three experimental parameters were selected: the addition of a wetting agent, temperature, and wood-fiber concentration. All creep curves are presented in terms of relative creep as a percentage of instantaneous (initial) strain. The creep power law model was used to accurately fit the creep data. The addition of a wetting agent greatly reduced the creep at high stress, but had little effect at a lower stress level. The extent of relative creep increased with increasing temperature. It was found that the slope of the power law model was directly proportional to the temperature. The addition of wood-fibers into pure polymer greatly improved the creep resistance of the matrix polymer. The relative creep of the composites decreased with an increase in wood-fiber concentration. However, the composite showed relatively large creep compared with that of solid wood. It was found that both the time exponent and slope of the power law model were inversely related to wood-fiber concentration. The flexural modulus of the composites also had an inverse relationship with the time exponent.     

A comparison of compounding processes for wood-fiber/thermoplastic composites

This study was carried out to investigate the feasibility of developing a continuous compounding process for wood-fiber/thermoplastic composites using the Szego mill, a unique, high speed planetary ring-roller grinding mill. Prior to compounding, air-dried sawdust was ground to evaluate the grinding effect in the mill. As the feed rate and the mill speed increased, the particle size increased and decreased, respectively. Sawdust particles were successfully compounded in linear low-density polyethylene using the Szego mill without any major heat application. A Gelimat mixer, used for the compounding of wood fiber through a high-shear thermokinetic mixing process, was also employed for comparison. Composites with 30 wt% wood fiber were prepared by both compounding processes, and their mechanical properties were evaluated. The use of a compatibilizer in compounding improved the mechanical properties of the composites regardless of the compounding process. The composites prepared by Szego mill compounding showed comparable strength properties with their counterparts from the Gelimat mixer. Power consumption during mill compounding was in the range of twin-screw extruder processing.     

Effects of formaldehyde/urea mole ratio and melamine content on the hydrolytic stability of cured urea-melamine-formaldehyde resin

The influence of formaldehyde/urea (F/U) mole ratio and melamine content on the hydrolytic stability of urea-melamine-formaldehyde (UMF) resin was investigated. The hydrolytic stability of cured UMF resin was determined by measuring the mass loss and the liberated formaldehyde concentration after acid hydrolysis. A higher F/U mole ratio and greater melamine content of UMF resins resulted in lower hydrolytic stability. These results indicated that higher F/U mole ratio and greater melamine content resulted in more branched network structure, which subsequently increases the susceptibility of cured UMF resin toward acid hydrolysis.     

Adhesion interaction of one-component polyurethane in cross-laminating southern pine wood treated with micronized copper azole—type C (MCA-C)

European Journal of Wood and Wood Products - Compatibility between preservative and resin plays an important role in determining the adhesive performance of preservative-treated engineered wood...     

Hydrolytic stability and crystallinity of cured urea-formaldehyde resin adhesives with different formaldehyde/urea mole ratios

This study investigated the relationship between the hydrolytic stability and the crystalline regions of cured UF resins with different formaldehyde/urea (F/U) mole ratios to better understand the hydrolysis of cured urea-formaldehyde (UF) resin adhesives responsible for its formaldehyde emission in service. As the F/U mole ratio decreased, the hydrolytic stability of cured UF resins improved, but decreased when the particle size of the resin was reduced. To further understand the improved hydrolytic stability of cured UF resin with lower F/U mole ratios, X-ray diffraction (XRD) was extensively used to examine the crystalline part of cured UF resins, depending on F/U mole ratios, cure temperature and time, hardener type and level. Cured UF resins with higher F/U mole ratios (1.6 and 1.4) showed amorphous structure, while those with lower F/U mole ratios (1.2 and 1.0) showed crystalline regions, which could partially explain the improved hydrolytic stability of the cured UF resin. The crystalline part intensity increased as cure temperature, cure time and hardener content increased. But the 2θ angles of these crystalline regions did not change, depending on cure temperature and time, hardener type and level, suggesting that the crystalline regions of the cured UF resin were inherent. This study indicates that the crystalline regions of cured UF resins with lower F/U mole ratio contribute partially to the improved hydrolytic stability of the cured resin.     

Rapid concentration of some bacteriocin-like compounds using an organic solvent

Food Science and Biotechnology - A new solvent extraction method for isolation of bacteriocin-like compounds (BLCs) from bacterial culture broth was developed. Culture supernatant of Pediococcus...     

Effects of formaldehyde/urea mole ratio and melamine content on the hydrolytic stability of cured urea-melamine-formaldehyde resin

The influence of formaldehyde/urea (F/U) mole ratio and melamine content on the hydrolytic stability of urea-melamine-formaldehyde (UMF) resin was investigated. The hydrolytic stability of cured UMF resin was determined by measuring the mass loss and the liberated formaldehyde concentration after acid hydrolysis. A higher F/U mole ratio and greater melamine content of UMF resins resulted in lower hydrolytic stability. These results indicated that higher F/U mole ratio and greater melamine content resulted in more branched network structure, which subsequently increases the susceptibility of cured UMF resin toward acid hydrolysis.     

Cure kinetics of melamine–formaldehyde resin/clay/cellulose nanocomposites

As a part of improving the properties of surface laminates for wood-based panel products, this study attempted to investigate cure kinetics of the melamine–formaldehyde (MF) resin/clay/cellulose nanocomposites. Three different methods (Ozawa, Kissinger, and isoconversion) of differential scanning calorimetry (DSC) were employed to study cure kinetics of the nanocomposites, using three different heating rates (5, 10 and 20 °C/min). Both Ozawa and Kissinger methods showed that the overall activation energy (E_a) of the nanocomposite at the 0.5 wt% nanoclay level reached a maximum and then decreased thereafter. But, the Ozawa method provided greater E_a values than those of the Kissinger method. The isoconversional method provided the change of activation energy (E_α) values as a function of the degree of conversion (α). The E_α values increased as the degree of conversion increased, while the influence of nanoclay levels followed a similar trend to the overall E_a values from the both Ozawa and Kissinger methods. These results indicated that the exfoliation of layered nanoclay particles into MF resin delayed the cure of MF resin/nanoclay/cellulose nanocomposites.     

Effects of weight average molecular mass of phenol-formaldehyde adhesives on medium density fiberboard performance

) of phenol-formaldehyde (PF) adhesives on the performance of medium density fiberboard (MDF). To obtain different PF resins, a series of PF resoles were prepared by blending low (LMW) and high (HMW) resins in different proportions. Six blending ratios of LMW:HMW were chosen: 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100. The prepared resins were characterized with size exclusion chromatography (SEC) for their determination and differential scanning calorimetery (DSC) for thermal cure kinetics. As the proportion of HMW was increased, and hence the viscosity of adhesives increased. The thermal curing kinetics of the blended resins obtained by DSC showed that total thermal energy (ΔH) and activation energy (Ea) of cure decreased with increasing resin as determined by SEC. Test result for a series of fiberboards prepared with the blended resins showed that the LMW:HMW blending ratio of 40:60 gave the highest internal bond (IB) strength. The optimum viscosity of PF resin was approximately 300 mPa.s. The maximum values of MOR and MOE were found at a blending ratio of 80:20 (LMW:HMW). The density profile indicated that MOR and MOE were influenced by the maximum density of the board surfaces while the IB correlated to the minimum density in the core regions of the board.

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