## 2 Materials and Methods  
Activated carbon from coconut shells (ACCS) was purchased from Aquafloow (Krakow, Poland), who mainly provided the water filters. ACCS was characterized by a specific surface area of 1100 m\({}^{2}\)/g, an apparent density of 0.6 g/cm\({}^{3}\), and a dimensional range of 0.43-1.70 mm. To obtain proper homogenization and adjust the mixture to the pneumatic gluing system, only the fractions of 0.7 mm and smaller were collected and used for adhesive modification. The structural analysis of the sample was performed by Fourier transform infrared (FTIR) spectroscopy. For this purpose, a sample of 1 mg was mixed with 200 mg of potassium bromide (Sigma Aldrich, Darmstadt, Germany). The spectrum was recorded using a Nicolet iS5 spectrometer (Thermo Fisher Scientific, Madison, WI, USA) at a range from 4000 to 500 cm\({}^{-1}\), at a resolution of 4 cm\({}^{-1}\), registering 32 scans. The morphology of the activated carbon was evaluated using a Zeiss EVO 10 scanning electron microscope (SEM) (Carl Zeiss Microscopy GmbH, Jena, Germany), operating with an accelerating voltage of 20 kV. Moreover, energy dispersive X-ray spectroscopy (EDS) was used to determine the elemental composition (C, O, Na, Mg, K) of ACCS during the microscopic analyses. Commercially available UF adhesive supplied by Silekol (Kedzierzyn-Kozle, Poland) was used as a binding agent for particleboard manufacturing. The modification of the adhesive was performed by introducing various amounts of ACCS: 0.25, 0.5, 0.75, 1.0, and 1.5%. Pure UF adhesive without activated carbon was used as a reference variant. Each formulation also contained 3% of an aqueous solution of ammonium nitrate (20 wt. %) as a hardener (Chempur, Piekary Slaskie, Poland). The whole mixture was mixed with a CAT-500 homogenizer (Ingenieurburo CAT, M. Zipper GmbH, Ballrechten-Dottingen, Germany) at 1000 rpm for 90 s. To determine the effect of the performed modification on the properties of the adhesive, the parameters used for the industrial quality control of the resins in the production of the particleboards were investigated [33]. Viscosity was measured using a rotary viscometer Brookfield DV-II+Pro (Middleboro, MA, USA) at 100 rpm using spindle no. 4. Furthermore, gel time at 100 \({}^{\circ}\)C was determined according to PN-C-89352-3 [34] as the time needed for the adhesive to lose its fluidity. The pH was measured using a multifunctional Testo 206 pH meter (Pruszkow, Poland). Each parameter was determined in triplicate. Pine wood particles were supplied by the local manufacturer of wood-based materials. The results of the sieve analysis showed that the vast majority of particles fall within the dimensional range between the fractions 1.0 and 2.5 mm. After drying to reach a moisture content of approx. 3%, the particles were glued in a low-speed laboratory gluing machine that was equipped with a pneumatic adhesive spraying system. The following parameters of the boards were assumed: dimensions of 380 mm \(\times\) 670 mm \(\times\) 12 mm, gluing degree of 10%, and targeted density of 600 kg/m\({}^{3}\). Two single-layer particleboards were produced for each variant of the adhesive mixture using the following pressing parameters: pressing temperature of 160 \({}^{\circ}\)C, unit pressure of 2.5 N/mm\({}^{2}\), and pressing time of 20 s/mm of the final board thickness. The manufactured particleboards were conditioned for seven days at a relative humidity of 65 \(\pm\) 2% and a temperature of 21 \(\pm\) 2 \({}^{\circ}\)C. The density of the resultant boards was determined according to EN 323 [35], and the density profile was determined using the density profiler working on the X-ray system GreCon DAX 6000 (Fagus GreCon, Charlotte, NC, USA) with a measurement resolution of 0.02 mm and a measurement rate of 0.05 mm/s. The manufactured particleboards were tested in terms of their mechanical properties such as internal bond (IB), bending strength (MOR), and modulus of elasticity (MOE) according to EN 319 [36] and EN 310 [37], respectively.