Enhanced photostability of PVC using benzenesulfonamide derivatives

Introduction

Polymers are manufactured annually in vast quantities due to their diverse and significant industrial and medical applications [1][2][3] . The widespread utilization of synthetic polymers is attributed to their facile and cost-effective production via various convenient manufacturing processes. Approximately 10,000 companies in the United States are involved in the production, processing, and fabrication of polymeric materials [4] . Polyvinyl chloride (PVC) is one of the most widely produced and used polymers worldwide [5] , with extensive applications in outdoor environments [6] , particularly in construction [7][8][9] . However, prolonged exposure of PVC to solar radiation and/or high temperatures causes photodegradation [10] , which leads to changes in its physical and mechanical properties [11] . Structural defects and impurities within the PVC polymer backbone constitute the primary cause of dehydrochlorination and/or photo-oxidation reactions, culminating in the formation of unsaturated centers [12][13][14] . Consequently, protecting PVC from harsh environmental conditions is crucial. Photostabilization of PVC can be accomplished through the incorporation of a diverse array of additives, notably including plasticizers [15] , aromatic compounds [16,17] , heterocyclic compounds [18] , Schiff base complexes [19][20][21] , metal complexes, and inorganic salts. Due to their drug-like properties, sulfonamides remain a subject of interest for structural and pharmaceutical chemists. Benzene sulfonamide derivatives represent a significant class of organic chemical compounds, combining a benzene ring with the sulfonamide functional group (SO 2 NH 2 ) [22][23][24][25][26][27] . This combination endows them with unique chemical and physical properties, rendering them of considerable importance in diverse fields, ranging from pharmaceutical and agricultural industries to materials science and analytical chemistry [28][29][30] . Benzene sulfonamide derivatives are widely used as stabilizers in polymers (e.g., PVC, polyurethane, polyolefins) and for protecting biomaterials, dyes, and pharmaceuticals from photodegradation.

Their unique chemical structure, featuring a sulfonamide group (SO₂NHR) linked to aromatic rings and heteroatoms (N, O, S), provides them with unique chemical and physical properties [30] . The electronic conjugation between the sulfonamide group and aromatic rings enhances UV absorption and efficient conversion of absorbed energy into heat, minimizing harmful photochemical reactions. These properties make them promising light stabilizers.

Materials and Methods

Chemicals (solvents and reagents) were used as received from Sigma-Aldrich (UK) without further purification. Polyvinylchloride (PVC) with a K value of 67 and a degree of polymerization of 800 was obtained from Petkim Petrokimya (Turkey).

Procedure Preparation of Polyvinylchloride (PVC) Films

Commercial Polyvinylchloride (PVC) was dissolved in tetrahydrofuran(THF) (5 g/100 mL), reprecipitated with ethanol(EOH), and dried under reduced pressure at 20 (°C) for 24 (h). Organotin complexes (0.5 wt/wt %) were then incorporated into the PVC at 20 (°C). The resulting mixture was cast onto aluminum(Al) plate stands (Q-Panel-Company, Homestead, FL, USA) [31] to produce 40 µm thick films, A digital vernier caliper was used to measure (Kevelaer, Germany).

Accelerated Testing Method

PVC films were irradiated using a QUV tester (Germany) following a standard procedure for 250 hours. The light source provided an intensity of 6.43 × 10 -9 Einstein (dm -3 ) (s -1) at a wavelength of 365 nm.

Measurement of the photodegradation rate constant (kd) of PVC films by UV-vis spectroscopy.

The UV-visible spectral changes of PVC films under light exposure at λmax = 365 (nm) were measured using a Shimadzu UV-VIS 160A Spectrophotometer (Japan). Using equation ( 1), the photodegradation rate constant (kd) for PVC films was determined.

The variable A represents the initial PVC concentration, while x represents the change in concentration at any time t during irradiation. A 0 denotes the PVC absorption intensity at the beginning of the experiment (t 0 ), while A ∞ denotes the absorption intensity at the end of the reaction (t ∞ ). At gives the absorption intensity after an irradiation time of t. Equation ( 3) is derived by substituting the value of Equation (2) into Equation ( 1).

(3) Analysis of the above correlation yielded a linear relationship, with the slope (kd) indicating first-order decomposition kinetics for PVC [32,33] .

Determination of the degree of photolysis by measuring weight loss:

To measure the stabilization efficiency, the percentage weight loss of the photodegraded PVC films, in both the presence and absence of additives, was calculated using the following equation:

Where W 1 represents the mass of the initial sample (before irradiation), and W 2 refers to the mass of the sample after the irradiation process is complete [34] .

Technology of Scanning Electron Microscopes (SEM)

Scanning electron microscope (SEM) observations were performed using two instruments: a KYKY-EM 3200 microscope operating at an accelerating voltage of 26 kV, and an Inspect S50 (FEI, Czech Republic) operating at an accelerating voltage of 15 kV at Tarbiat Modares University, Tehran, Iran.

Synthesis of Benzene Sulfonamide Derivatives

The preparation of benzene sulfonamide derivatives was carried out by reacting 0.172 (g) of 4aminobenzenesulfonamide with 0.106 (g), 0.14 (g), 0.151 (g), 0.136 (g), and 0.122 (g) of benzaldehyde, 4chlorobenzaldehyde, 4-nitrobenzaldehyde, 4methoxybenzaldehyde, and 4-hydroxybenzaldehyde, respectively. The reaction steps involved using 30 (mL) of absolute ethanol as a solvent and adding a few drops of glacial acetic acid as a catalyst. The reaction mixtures were then refluxed for 3-4 (h) at 80-90 (°C), and all products were recrystallized and dried to obtain pure products, as shown in the reaction scheme 1.

Results and Discussion 1 H-NMR spectroscopy

In the proton nuclear magnetic resonance (¹H-NMR) spectra of the synthesized benzenesulfonamide derivatives 1-5, the characteristic signal of the formyl proton (H-C=O) at 10.01 ppm was observed in all benzaldehyde derivatives, and a new signal attributed to the imine proton (N=C-H) appeared in the range of 8.41-8.76 (ppm). This can be seen in Figure (1-5) and summarized in Table 2. In addition, the signal of the hydroxyl proton (OH) of compound 5 appeared at 9.80 (ppm), and the signal of the three methoxy group protons (O-CH3) of compound 4 appeared at 3.59 (ppm). Table 3 presented the rate constants for the films that were blank and those that had additives. The breakdown rate's sensitivity to the type and presence of benzenesulfonamide Schiff bases is shown by kd values [31] . The kd for PVC (Blank) film, for instance, was high 88×10 -4 (sec -1 ), but it drastically decreased 39 ×10 -3 (sec -1 ) when benzenesulfonamide derivatives were used as additives. When benzenesulfonamide derivatives are present, PVC photostabilization follows this order: 5 4 3 > 2 > 1. Investigation of the impact of UV exposure on weight loss Photo-oxidation of PVC leads to the formation of free radicals, which promote cross-linking and the elimination of hydrogen chloride (HCl), resulting in a decrease in polymer mass. To evaluate the photostabilizing efficacy of benzenesulfonamide derivatives (1-5) in PVC, the weight loss resulting from photo-oxidation and photodegradation processes was measured. The percentage weight loss was calculated using Equation 4, where W 1 and W 2 represent the initial and final PVC masses, respectively, post-irradiation.

Figure 12 shows that the rate of PVC weight loss was rapid during the initial 100 hours of irradiation and continued to increase in the absence of benzenesulfonamide 1-5. This confirms the significant impact of these additives on PVC stabilization. After 250 hours of irradiation, the control (blank) PVC film exhibited a 61% weight loss (measured after 50 hours from the start of the experiment). In contrast, PVC films containing benzenesulfonamide compounds 1-5 showed lower weight losses of 53%, 47%, 38%, 30%, and 26%, respectively. The figure illustrates that benzenesulfonamide 5 demonstrated the highest stabilization efficacy for PVC [35] . The SEM micrographs Scanning electron microscopy (SEM) images of irradiated PVC films (neat PVC, surface of PVC/benzenesulfonamide films) taken at 15.00 kV after 250 hours of irradiation are shown in Figure 13. These light patches are activation areas that contribute to the deterioration of aging. Both clean PVC and PVC/benzenesulfonamide films developed many surface fractures [36] . After the films were exposed to UV light for 300 hours, the dehydro-chlorination and oxidation processes on their surface caused such fissures. The PVC/Schiff basis films' surface cracks, however, are hardly noticeable, but the apparent cracks on those samples' surfaces are more numerous than on blank PVC. An icerock-like structure is created as a result of hydrogen chloride and volatile chemicals cross-linking and evolving [37] . Good compatibility and homogeneous dispersion are two important factors in improving the performance of PVC composites [38] .

Conclusions

PVC films incorporating benzenesulfonamide-derived Schiff bases showed significantly reduced photodegradation rate constants (kd) compared to the control (Pure) PVC films. Specifically, the kd values of the modified PVC films ranged from 3 × 10 -4 (s -1) to 39 × 10 -4 (s -1 ), compared to 88 × 10-4 (s -1 ) in the control film. Among the derivatives tested, benzenesulfonamide 5 showed the highest light-stabilizing activity. These results clearly demonstrate the lightstabilizing effect of benzenesulfonamide derivatives on PVC films. Weight loss tests of irradiated films confirmed a weight loss of 35% in the presence of benzenesulfonamide compounds (1-5). Scanning electron microscopy (SEM) of additive-treated PVC after irradiation for 250 h revealed an inhomogeneous surface morphology resembling broken rocks, indicating structural changes induced by the irradiation process.

References

1. Huang Z, Ding A, Guo H, Lu G, Huang X. Construction of nontoxic polymeric UV-absorber with great resistance to UV-photoaging. Scientific Reports. 2016 May 3;6(1):25508.
2. Saeki Y, Emura T. Technical progresses for PVC production. Progress in Polymer Science. 2002 Dec 1;27(10):2055-2131.
3. Zhang X, Zhao T, Pi H, Guo S. Mechanochemical preparation of a novel polymeric photostabilizer for poly (Vinyl chloride). Journal of Applied Polymer Science. 2010 Jun 5;116(5):3079-3086.
4. Real LP, Ferraria AM, do Rego AB. Comparison of different photo-oxidation conditions of poly (vinyl chloride) for outdoor applications. Polymer Testing. 2008 Sep 1;27(6):743-751.
5. Starnes Jr WH. Structural and mechanistic aspects of the thermal degradation of poly (Vinyl chloride). Progress in Polymer Science. 2002 Dec 1;27(10):21332170.
6. Yousif E, Hasan A, El-Hiti GA. Spectroscopic, physical and topography of photochemical process of PVC films in the presence of Schiff base metal complexes. Polymers. 2016 May 25;8(6):204.
7. Fahmy MM, Mohamed RR, Mohamed NA. Novel antimicrobial organic thermal stabilizer and costabilizer for rigid PVC. Molecules. 2012 Jul 2;17(7):7927-7940.
8. Iván B, Kennedy JP, Kelen T, Tüdõs F, Nagy TT, Turcsányi B. Degradation of PVCs obtained by controlled chemical dehydrochlorination. Journal of Polymer Science: Polymer Chemistry Edition. 1983 Aug;21(8):2177-2188.
9. Caraculacu AA, Bezdadea EC, Istrate G. Structure of branching in PVC. Journal of Polymer Science Part A-1: Polymer Chemistry. 1970 May;8(5):1239-1246.
10. Yousif E, Haddad R, El-Hiti GA, Yusop RM. Spectroscopic and photochemical stability of polystyrene films in the presence of metal complexes. Journal of Taibah University for Science. 2017 Nov 1;11(6):997-1007.
11. Kameda T, Ono M, Grause G, Mizoguchi T, Yoshioka T. Antibacterial effect of thiocyanate substituted poly (Vinyl chloride). Journal of Polymer Research. 2011 Sep;18:945-947.
12. Balakit AA, Ahmed A, El-Hiti GA, Smith K, Yousif E. Synthesis of new thiophene derivatives and their use as photostabilizers for rigid poly (Vinyl chloride). International Journal of Polymer Science. 2015;2015:510390.
13. Yousif E, El-Hiti GA, Hussain Z, Altaie A. Viscoelastic, spectroscopic and microscopic study of the photo-irradiation effect on the stability of PVC in the presence of sulfamethoxazole Schiff's bases. Polymers. 2015 Nov 2;7(11):2190-2204.
14. Kruger GJ, Gafner G. The crystal structure of sulphathiazole II. Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry. 1971;27(2):326-333.
15. Gelbrich T, Hughes DS, Hursthouse MB, Threlfall TL. Packing similarity in polymorphs of sulfathiazole. CrystEngComm. 2008;10(10):1328-1334.
16. Sanphui P, Sarma B, Nangia A. Polymorphism in secondary benzene sulfonamides. Crystal Growth & Design. 2010 Oct 6;10(10):4550-4564.
17. Basak AK, Chaudhuri S, Mazumdar SK. Structure of 4amino-N-2-pyridylbenzenesuphonamide (Sulphapyridine), C11H11N3O2S. Acta Crystallographica Section C: Crystal Structure Communications. 1984 Nov 15;40(11):1848-1851.
18. Ajibade PA, Kolawole GA, O'Brien P, Helliwell M, Raftery J. Cobalt (II) complexes of the antibiotic sulfadiazine, the X-ray single crystal structure of [Co(C10H9N4O2S)2(CH3OH)2]. Inorganica Chimica Acta. 2006 Jul 1;359(10):3111-3116.
19. Roy S, Nangia A. Kinetic and thermodynamic conformational polymorphs of bis(p-tolyl) ketone ptosylhydrazone: the Curtin-Hammett principle in crystallization. Crystal Growth & Design. 2007 Oct 3;7(10):2047-2058.
20. Dolle RE, Bourdonnec BL, Worm K, Morales GA, Thomas CJ, Zhang W. Comprehensive survey of chemical libraries for drug discovery and chemical biology: 2009. Journal of Combinatorial Chemistry. 2010 Nov 8;12(6):765-806.
21. Yousif E, Ahmed DS, Ahmed AA, Hameed AS, Yusop RM, Redwan A, et al. The effect of high UV radiation exposure environment on the novel PVC polymers. Environmental Science and Pollution Research. 2019 Apr 1;26:9945-9954.
22. Ahmed DS, El-Hiti GA, Hashim H, Noaman R, Hameed AS, Yousif E. Physical and morphological properties of poly (Vinyl chloride) films upon irradiation in the presence of tetra Schiff bases as photostabilizers. Arab Journal of Physics and Chemistry. 2018;5:1-6.
23. Mohamed S, Yousif E, Kadhom M, Bufaroosha M. Enhanced photostability of poly (vinyl chloride) films through antipyrine derivatives: a comprehensive study on UV resistance and degradation inhibition. Macromolecular Research. 2024 Aug 19:1-9.
24. Mohamed SH, Hameed AS, El-Hiti GA, Ahmed DS, Kadhom M, Baashen MA, et al. A process for the synthesis and use of highly aromatic organosilanes as additives for poly (Vinyl chloride) films. Processes. 2021 Jan 4;9(1):91.
25. Mohamed SH, Yousif E, Hameed AS, Ahmed DS, Zainulabdeen K, Saleh HM, et al. Morphology and performance of poly (Vinyl chloride) thin films doped with polyorganosilanes against photodegradation. Silicon. 2023 Jun;15(9):4027-4038.
26. El-Hiti GA, Alotaibi MH, Ahmed AA, Hamad BA, Ahmed DS, Ahmed A, et al. The morphology and performance of poly (Vinyl chloride) containing melamine Schiff bases against ultraviolet light. Molecules. 2019 Feb 22;24(4):803.
27. Yousif E, Ahmed DS, Ahmed AA, Hameed AS, Yusop RM, Redwan A, et al. Experimental relationships between surface roughness, irradiation time and photodecomposition rate constant of PVC films doped by polyphosphates. Science Letters (ScL). 2018;12(2):19-27.
28. Hashim H, El-Hiti GA, Alotaibi MH, Ahmed DS, Yousif E. Fabrication of ordered honeycomb porous poly (Vinyl chloride) thin film doped with a Schiff base and nickel (II) chloride. Heliyon. 2018 Aug 1;4(8):e00718.