Aging of Environmentally Friendly Alkyd Coating Containing Tinuvin 292 under Effect of UV Radiation

. This study presents durability of environmentally friendly alkyd coating containing Tinuvin 292 (a liquid hindered amine light stabilizer) under UV-thermo-humidity condition. Coatings were accelerated under UV-thermo-humidity complex for 100 cycles. FT-IR, TGA and SEM were used to value the changes of before and after accelerated weathering tested coatings. Results showed that gloss loss, adhesion, flexural strength, impact resistance, relative hardness of tested coating were much improved with 1.5 weight percent (wt.%) of Tinuvin 292. FT-IR spectrums of initial and aged coatings without Tinuvin 292 illustrated the significant changes on intensity of CH 2 and C=O (ester) groups. Meanwhile, coating with Tinuvin 292 exhibited that intensity of CH 2 and ester groups had been changed slightly. SEM images indicated that surface morphology of samples changed differently depending on the presence Tinuvin 292. After aging process, surface of aged coating without Tinuvin 292 became worse than that of coating with Tinuvin 292. TGA also showed that 1.5 wt.% of Tinuvin 292 had improved thermo oxidation stability of environmentally friendly coating.


Introduction
Aging or degradation of paint or varnish coatings under weather factors such as UV radiation, humidity, oxygen, high temperature, etc. leads to the blistering, chalking, losing adhesion [1][2][3].To reduce the aging of coatings exposed to UV radiation, many kinds of UV additives have been added in coatings [3][4][5]

Paint preparation
Raw materials were prepared as in Table 2.The process included four stages, ( (3) Preparation: The rest of xylene (another 10%) was added and stirred for an hour.(4) After that, the paint samples for testing were acquired through filtering before proceeding with the canning step.A 100 hole/mm 2 mesh was used to remove any coarse particles or dirt in this stage.
Then, it was followed by the canning step for storing purposes.

Sample preparation
Testing samples were prepared on steel panels (ISO 1514:2016).Paint coatings were deposited on the cleaned panels by using a sprayer (4 kg/cm 2 of pressure).These coatings were dried at temperature of (25±2) o C and humidity of (50±5) % for 7 days before testing.The thickness of dried coatings was (30±3) µm (measured with Minitest 600 Erichen digital meter).

Effect of anti-UV content on gloss and mechanical properties coating
To study effect of anti-UV (Tinuvin 292) content on gloss loss and mechanical properties of before and after tested coatings, samples were prepared with Tinuvin 292 content of 0; 0.5; 1.0; 1.5; 2.0 wt.% named as M0, M1, M2, M3, M4 and tested for 100 UV-thermo-humidity complex cycles.Samples were covered on standard panels (ISO 1514:2016) and kept at room temperature for 7 days before testing.Results were shown in Table 3. strength and relative hardness of coating became much higher, it meant that the coating was more rigid or brittle and lost its adhesion [22].After testing, properties of M3 and M4 were the same, so M3 was chosen for further study.TiO2 worked as an UV-absorber and a photocatalyst [21,22].As can be seen in Figures 1c and 1d, there was a little difference between before and after-aging samples.These showed

Morphology coatings' surface
To investigate effect of UV-thermo-humidity complex cycles on surface of coatings, M0 and M3 were tested with 100 cycles.Paint was covered on standard panels (ISO 1514:2016) and kept at room temperature for 7 days before testing.Results were shown in Figure 2. Results were shown in Table 4 and Figure 3.
Primary grinding: 90% of xylene were added with all other materials and stirred at 20-40 rpm for an hour.The mixture was kept being conditioned for 24 hours.(2) Fine grinding: The mixture was subjected to fine grinding at a speed of 1,300-1,500 rpm to reach the paint fineness of ≤ 30 µm.
-thermo-humidity complex stability was performed in UV/condensation weathering chamber Atlas UVCON UC-327-2 with UVB-313 fluorescent lamps and a cycle including 8 hours of UV irradiation at 60 °C then following by 4 hours of dark water condensation at 50 °C as ASTM D4587-11.Infrared spectroscopy (FT-IR) was conducted on Fourier FTIR-8700 series converter.Morphology of coating was observed by FESEM Hitachi S4800 machine with magnification of 5,000 times and voltage of 5 KV.Gloss of coating was determined in accordance with ISO 2813:2014 with angle of 60 degrees.Impact resistance of coating was determined in accordance with ISO 6272-1:2011, flexural strength of coating was determined in accordance with ISO1519:2011, adhesion of coating was determined in accordance with ISO 2409:2013 and relative hardness of coating was determined in accordance with ISO 1522:2006.Fineness of paints was determined in accordance with ISO 1524: 2020.Thermal oxidation resistance: Thermogravimetric analysis (TGA) was analyzed by NETZSCH TG 209F1 LIBRA in the air with a heating rate of 10 o C/minute from room temperature to 600 o C.

Figure 1b .
Figure 1b.This can be explained that polymer molecular chain had been cut and molecular length was much shorter.At the same time, intensities of ester group peaks (1723.85 of C=O and 1256.15 of C-O) decreased and ester bond was altered to form new bonds such as ketones due to optical oxidation or groups were stretched and rocked [4, 19-21].However, the vibration was small and low intensity, because

Figure 2 Fig. 2 .
Figure 2 showed that there were no cracks, blisters or surface changes on aged M3.In comparison with initial coating surface, tested sample's surface seemed to be unchanged.For M0, in comparison with initial sample, aged

Paint preparation [18] Emulsion Intermediate preparation
[19]amethyl-4-piperidyl) sebacate and Methyl 1, 2, 2, 6, 6-pentamethyl-4-piperidyl sebacate.The efficiency of Tinuvin 292 provides significantly extended lifetime to coatings by minimizing paint defects such as cracking and loss of gloss[19].Because Tinuvin 292 is a liquid so it can be easily distributed in coatings and overcome disadvantages of above anti-UV additives.This paper presents effect of Tinuvin 292 content on degradation of environmentally friendly alkyd coating based on alkyd and polysaccharide under UV-thermo-humidity condition.Surface's morphology, gloss loss, mechanical properties, thermal oxidation resistance of coatings were investigated.In addition, chemical changes of functional groups were identified by FT-IR.

Table 2 .
Composition of paint

Table 3 .
Gloss and mechanical properties of coating before and after 100 cycles testing

Table 4 .
Decomposition temperature and weight loss.

4 Conclusions The
aim of this research was to compare stability of environmentally friendly alkyd coating with and without Tinuvin 292.After 100 UV-thermo-