The Application of Oak Bark Powder as a Filler for Melamine-Urea-Formaldehyde Adhesive in Plywood Manufacturing

Abstract

The woodworking industry generates a great amount of bark which has not yet found a wider industrial application. None of the previously conducted research has considered oak bark application (which is one of the most often processed wood species in Poland) as a filler for wood adhesives. Moreover, no studies have determined the properties of bark containing melamine-urea-formaldehyde resin (MUF), which increasingly replaces pure urea-formaldehyde adhesives. Thus, the aim of the study was to determine the possibility of grinded oak bark application as a filler for MUF adhesive in plywood manufacturing. The chemical composition of oak bark was evaluated. Properties of liquid resins, such as viscosity, gel time, pH, and solid content, were determined. Chemical interaction between the filler and resin was assessed with using Fourier-transform infrared (FTIR) spectroscopy. Plywood panels manufactured using MUF adhesive filled with different bark concentrations (10%, 15%, 20%, 25%) were tested in terms of such properties as formaldehyde release and bonding quality. Studies have shown an improvement in liquid resin properties. The course of FTIR spectra did not explain the chemical interaction between the polymer and the filler. The addition of oak bark at a concentration of 15% made it possible to produce plywood panels characterized by reduced formaldehyde release and improved bonding quality.

Utilization of Birch Bark as an Eco-Friendly Filler in Urea-Formaldehyde Adhesives for Plywood Manufacturing

“…It was also pointed out that the addition of extra 10% of WF in Ref20 compared to Ref10 sample led to slight increase of formaldehyde release (3%). The specific chemical composition of BB in the UF adhesive mixture apparently affected the mechanical properties of plywood to a minimal extent which is also supported by other research works [19,20,31].…”

“…Results showed that use of 20% BB leads to a 17% decrease in formaldehyde release. The same authors [31] used oak bark powder as filler for MUF adhesive in plywood manufacturing. The formaldehyde emissions, measured initially and after 8 weeks, experienced a 9% and 31% decrease in comparison with the reference variant, As seen in Figure 2, a significantly greater decrease in formaldehyde emission of plywood samples, comprising BB as a filler was measured after four weeks, compared to the tested WF reference samples.…”

“…For BB flour (10% and 15% addition levels), an exothermic peak corresponded to a continuing exothermic reaction with increase in temperature and it was also visible in the DSC scan. Higher BB content and the overall more viscous mixture results in a slightly earlier start of adhesive mixture curing, while the gluing of the veneers is sufficient [31]. The isothermal section was without a visible peak at the temperature of 105 • C. The determined curing temperatures were equal or lower compared with the pure UF resin [5,108].…”

“…The type and the amount of filler in the adhesive mixture significantly affect the adhesive performance. The choice of filler depends on the resin and targeted application, making fillers one of the most important components of adhesive systems used in the production of plywood [ 15 , 18 , 19 , 31 , 32 ].…”

Eco-Friendly, High-Density Fiberboards Bonded with Urea-Formaldehyde and Ammonium Lignosulfonate

“…Since then, the formaldehyde limit values have steadily been lowered, which has led to the development of less toxic, low-emission, eco-friendly, wood-based panels, where conventional synthetic resins have been partially or completely replaced by sustainable, bio-based adhesives [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ] or by adding formaldehyde scavengers to adhesive formulations, such as urea [ 48 ], sodium metabisulfite (Na 2 S 2 O 5 ), ammonium bisulfite ((NH 4 )HSO 3 ), other ammonium-containing agents [ 49 , 50 ], Al 2 O 3 nanoparticles [ 51 ], etc. Various natural compounds, such as wood bark flours [ 32 , 52 , 53 , 54 ] and tannins [ 55 , 56 , 57 ], have also been successfully used to reduce the free formaldehyde content of wood panels.…”