Increasing the outdoor durability of urea formaldehide particle board with new generation water-born

2.2. Coating Systems

The commercial water-based impregnation product, having active ingredients of 1.20% propiconazol, and 0.30% iodopropynyl butylcarbamat, was used as a primer for the protection of the samples against biological deterioration, including soft rot and blue stain. The primer was applied to the samples at a spread of 120 g/m² using a brush. Tinuvin 5333 DW as UV absorbers were used in this study. Commercially produced finishing, having acrylic resins, three copolymer dispersion was used as a topcoat for the specimens. A small amount of defoamer and 2,2,4trimethyl-1,3-pentandiolemonoisobutyrate, a coalescending agent was added in the topcoat 160

formulation to reduce the effect of other additives on the photostabilization performance. The characteristic features of wood coating materials in the study are given in Table 1. These formulation products were supplied from BASF Company for the wood coatings (Table 2). Three layers of topcoats were also applied to each sample at a spread rate of 100 g/m² by brush. Later, the specimens were sanded with a 240 grit size of sandpaper and kept at room temperature for two days before applying the second layer of topcoat. Table 1. Acrylic resin types for wood coating systems. Pruducts Acronal Eco 6270 Joncryl 8226 Tinuvin 5333 DW

Table 2. The formulations of wood coating systems. Formulation products X AX Y AY Acronal Eco 6270 73.7 50 23.7 Joncryl 8226 23.7 73.7 50 Tinuvin 5333 DW 6.0 6.0 6.0 6.0 Film-forming agents 0.67 0.67 0.67 0.67 Defoamers 1.0 1.0 1.0 1.0 Dispersing agent 0.6 0.6 0.6 0.6 Rheology modifier 1.3 1.3 1.3 1.3 Distiled water 16.73 16.73 16.73 16.73 The viscosity of the four different coatings applied in this study was determined by using DIN cup/4mm/20 0C. Table 3. The physical characteristics of the four different coatings Coating Systems X AX Y AY

2.3. Artificial Weathering Test

Artificial weathering was performed in a QUV/spray accelerated weathering tester (Q-Panel Lab Products, Cleveland, OH, USA) equipped with 313 nm fluorescent UV (UVB) lamps; the temperature in the chamber was approximately 60 0C (ASTM G 154-12a).The weathering experiment was carried out in cycles of UV-light irradiation for 4h followed by condensation temperature of 50 0C for 4h in an accelerated weathering test cycle chamber over 12 days (288 h). Eight replicate samples for each coating system were prepared for each artificial weathering test condition.

2.4. Surface roughness test

A Mitutoya SurfTest SJ-301 instrument was employed for surface roughness measurements. The Ra and Rb roughness parameters were measured to evaluate the surface roughness of the surfaces of unweathered and weathered coated particle board and uncoated particle board samples 161

Ö. Özgenç, G. Nemli / Sigma J Eng & Nat Sci 11 (2), 159-166, 2020

according to DIN 4768. Ra is the arithmetic mean of the absolute values of the profile departures within the reference length, and Rz is the arithmetic mean of the 4-point height of irregularities [16]. The cut-off length was 2.5 mm, the sampling length was 12.5 mm, and the detector tip radius was 10 μm in the surface roughness measurements.

2.5. Physical and mechanical tests

Panels were kept in a conditioned room with a relative humidity of 65% and a temperature of 20 °C until they reached equilibrium moisture content. They were then cut into test samples based on EN standards and determined the densities of the test samples [17], [18]. Modulus of elasticity (MOE) and modulus of rupture (MOR) from static bending, internal bond strength (IB) and thickness swelling (TS) after 24 h immersion of the samples were determined. Ten samples were cut from test panels to measure physical and mechanical properties [19], [20], [21]. Mechanical tests were performed on a Universal Introns testing machine.

3.1. Change in mechanical and physical properties

The single most important factor contributing to the weather conditions of particle boards is the change in moisture content. It appears that UV radiation and chemical changes do not have a significant effect on the effect of weather conditions. Continuous changes in moisture content create shrinkage and swelling stresses in the glue line between adjacent particles in the particle board content, as well as in the particles themselves. It is the absorption and desorption of liquid water that causes excessive thick swelling of the sheet, surface roughness and deterioration. Thickness swelling occurs due to the normal swelling of wood particles and their swelling due to release of the compressible set [6]. The single most important factor contributing to the weather conditions of particle boards is the change in moisture content. It appears that UV radiation and chemical changes do not have a significant effect on the effect of weather conditions. Continuous changes in moisture content create shrinkage and swelling stresses in the glue line between adjacent particles in the particle board content, as well as in the particles themselves. It is the absorption and desorption of liquid water that causes excessive thick swelling of the sheet, surface roughness and deterioration. Thickness swelling occurs due to the normal swelling of wood particles and their swelling due to release of the compressible set [6]. Some of the mechanical and physical properties of the test and control panels before and after the artificial weathering test are given in Table 4. This table generally shows that coating application increases the outdoor durability of UF control panels. From the observations given in Table 4, it is seen that after the weathering test, UF control panels swell by 13.35-29.1% of their original thickness while standing and this process is irreversible. This increase in volume is clearly reflected in the strength properties of the plates. The tear modulus decreased by 40-45% due to the weathering test. While the density was 5.00 g / cm3 in the UF control panels before the weathering exposure, the higher internal bond strength and rupture modulus values of the panels whose density decreased to 4.14 g / cm3 after weathering exposure also decreased. The positive effect of panel density on mechanical properties was mentioned in a similar study. However, the increase in board’s density resulted in poor thickness swelling properties similar to the results of a previous study. Acrylic coating application has significantly improved the rupture modulus and thickness swelling values in weathering conditions. This is due to the reduction of moisture absorption of the sheet surface in weathering conditions with coating application. Thus, the amount of decrease in the internal bond strength values of test plates applied with coating when exposed to weathering conditions is much lower than the UF control panel and is close to MF control panel [10]. 162

Table 4. Mechanical and physical properties of experimental panels.

3.2. Change in surface roughness parameters

Table 5 shows the surface roughness index values and Ra and Rz roughness parameters before and after the artificial weathering test of the control and test panels. After the weathering test, the lowest change index of the Ra roughness parameter was in the Y variation, and the index values of AX variation and MF control panels were also determined to be close index values. The index values of the AY and X variations were also found to be close. After the weathering test, the change index in the Rz roughness parameter is at the lowest AY variation, and the change index in the Y and AX variations is also close values. After weathering testing, the highest Rz change index values were found in UF and MF control panels.

Table 5. Changes in surface roughness parameters of experimental panels after weathering Coating Code

In fact, a coating film can delay and prevent excessive moisture ingress into the panel at best, but cannot stop it. Before coating, the gaps between the particles are closed and the effectiveness of the paints increases if the surface is smoothed. A normal acrylic coating has a limited external life of about two years in particle boards. Therefore, a regular maintenance coat is required to extend the service life of such structures. While smooth surfaces are preferred in the end-use applications of chipboard panels, the thickness of the panels should also be at acceptable levels. Surface roughness and bursting of wood particles have also been serious problems due to weather conditions of particle boards. It allows rainwater to stay on the surface of the board for a long time, thus increasing the risk of more water entering the board. These defects can only be eliminated by using microchips on the surface and making the surface of the card waterproof. Although particle boards have large dimensions, their applications in buildings require many joints [6], [8]. In this study, the durability of UF panels in semi-open outdoor conditions was improved with 4 different waterborne acrylic coating systems. After exposure to the artificial weathering test, the percentage of decrease in the physical and mechanical properties of UF control panels applied the waterborne acrylic coatings is close with MF control panels. The coating systems applied in the study positively affected the durability of the UF control panel in semi-open weathering conditions. In addition, the fact that waterborne acrylic coatings are renewable preservatives can make a significant contribution to the particle board industry. In semi-open outdoor conditions, the durability time of UF control panel is increased with the application of waterborne acrylic coating system, and it has reached a durability close to MF control panel. It is suggested that this study be evaluated in the industry by performing a cost analysis of the application of waterborne acrylic coating on the surface of UF particle board and MF particle board production.