Influence of the black seed oil modified epoxy resin/biscycloaliphatic epoxide monomer weight ratio on thermal properties of photocrosslinked coatings

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The influence of the black seed oil modified epoxy resin (EBSO)/monomer 3,4-epoxycyclohexylmethyl 3,4- epoxycyclohexane carboxylate (BCDE) weight ratio in the coatings based on the compounds and photoinitiator triarylsulfonium hexafluoroantimonate (TAS) on thermal properties of photocrosslinked coatings have been studied. The chemical structure of investigated UV-cured coatings was characterized by IR spectrometric analysis. Their thermogravimetric (TG) and differential scanning calorimetry (DSC) behavior were determined by TG and DSC analysis, respectively.

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Nội dung Text: Influence of the black seed oil modified epoxy resin/biscycloaliphatic epoxide monomer weight ratio on thermal properties of photocrosslinked coatings

Cite this paper: Vietnam J. Chem., 2023, 61(6), 732-740 Research Article DOI: 10.1002/vjch.202200194 Influence of the black seed oil modified epoxy resin/biscycloaliphatic epoxide monomer weight ratio on thermal properties of photocrosslinked coatings Nguyen Tien Dung2, Le Xuan Hien1*, Do Minh Thanh1 1 Institute for Tropical Technology (ITT), Vietnam Academy of Science and Technology (VAST) 18 Hoang Quoc Viet, Cau Giay, Hanoi 10000, Viet Nam 2 Hanoi National University of Education, 136 Xuan Thuy, Cau Giay, Hanoi 10000, Viet Nam Submitted November 3, 2022; Revised March 24, 2023; Accepted June 5, 2023 Abstract The influence of the black seed oil modified epoxy resin (EBSO)/monomer 3,4-epoxycyclohexylmethyl 3,4- epoxycyclohexane carboxylate (BCDE) weight ratio in the coatings based on the compounds and photoinitiator triarylsulfonium hexafluoroantimonate (TAS) on thermal properties of photocrosslinked coatings have been studied. The chemical structure of investigated UV-cured coatings was characterized by IR spectrometric analysis. Their thermogravimetric (TG) and differential scanning calorimetry (DSC) behavior were determined by TG and DSC analysis, respectively. It was shown that the testing atmosphere had almost no effect to the form of TG, DTG curves and little effect on value of weight degradation of investigated coatings. The volatilization of low molecular weight compounds was observed in the range from room temperature to 360oC while the thermal degradation of the coatings occurred in the range from 360 to 455.5 oC. The augmentation of the EBSO/BCDE weight ratio from 20/80 to 80/20 led to an increase of the degradation temperatures in the nitrogen atmosphere; extreme character of weight loss variation as well as the reduction of glass transition temperatures of the coatings from 79.8oC (Tg1) and 83oC (Tg2) to 36.8 (Tg1) and 38.9oC (Tg2), correspondingly. Keywords. UV- cured coatings, thermal properties, epoxy resin modified by black seed oil. 1. INTRODUCTION flexible chains. Aromatic and heterocyclic polymers are more thermostable than the linear and fatty Thermal stability is one of the most important cyclic hydrocarbon ones; the absence of hydrogen properties of polymer materials from both academic atoms in macromolecules reduces thermo- oxidative and practical sides. Based on the tight relation degradation of polymers; polymers having stiff between the thermal stability and composition, ladder figure chains are high thermostable since structure, compatibility of constituents of polymer polymer chains are not degraded while scission of a materials one can deeper understand mechanism of single bond occurred.[1] The increase of crosslinking their formation, structure as well as properly select degree enhances thermal stability of thermosetting their application fields from obtained information polymers. Photocrosslinked polymers often have about their heat resistance.[1] high thermal properties due to their high It was shown that the thermal stability of crosslinking density, especially the systems polymer materials is affected by the content, containing bis-phenol A structure.[2] structure and compatibility of their constituents, Photocrosslinked tridimensional polymer method of their synthesis and processing, bond networks containing bis-phenol A structure can be energy of polymer structure, type of the bonds obtained by radical photopolymerization of systems (covalent or noncovalent), degree of unsaturation, based on epoxy diacrylate resins or by cationic functional groups, molecular weight, branch degree, photopolymerization of systems containing bis- crosslinking and crystalline degree.[1-11] The phenol A epoxy resins. It was reported that the following relationship between structure of polymers introduction of rubber, vegetable or their derivatives and their thermal stability was reported: into the systems not only favors the Macromolecules with stiff chains are more photopolymerization process but also improves thermostable than the ones of the same class with some properties of photocrosslinked networks like 732 Wiley Online Library © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH
25728288, 2023, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202200194 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Le Xuan Hien et al. flexibility and stiffness.[5,6] Following the direction, UV-cured coatings containing bis-phenol A structure and vegetable residue were prepared by photopolymerization of systems based on epoxy resin modified by various vegetable oils. It was found that cationic UV- curing of the coatings based BCDE on epoxy resin modified by vegetable oil (EVO), TAS monomer 3,4-epoxycyclohexylmethyl 3,4- epoxycyclohexane carboxylate (BCDE), photoinitiator triarylsulfonium hexafluoroantimonate (TAS) occurred very fast under UV-exposure Propylene carbonate leading to the formation of high performance UV– cured coatings.[12,13] The advantage of the black seed 2.2. Preparation of UV-curable formulations oil modified epoxy resin (EBSO) over the other EVO is attributed to the feature of black seed oil UV-curable formulations were obtained by carefully (BSO) - a triglyceride oil with 80% of cis-12,13- mixing EBSO, BCDE and TAS with constituent epoxy-cis-9-octadecenoic acid (C18H32O3) having weight ratio EBSO/BCDE 20/80, 40/60,50/50, one double bond and one epoxy group in the acid 60/40, 80/20; TAS 5% of the total weight of EBSO chain.[12,13] and BCDE (table 1). So, TAS content was the same The work focused on the study of the influence (2.7810-2 mole/kg) in the formulations of of the weight ratio EBSO/BCDE on the thermal investigated coatings. properties of UV- cured coatings based on EBSO, BCDE and TAS. Table 1: Formulations of investigated coatings Total 2. MATERIALS AND METHODS Formulations of investigated epoxy No coatings (weight part) content 2.1. Materials EBSO/BCDE/TAS (mole/kg) 1 20/80/5 6.22 BCDE with commercial name Cyracure 6105, the 2 40/60/5 5.24 boiling point of 355.49oC; TAS mixed in 50% weight of propylene carbonate, with commercial 3 50/50/5 4.74 name Cyracure UVI 6974 and boiling point over 4 60/40/5 4.25 220oC were provided by Aldrich, USA. 5 80/20/5 3.27 Epoxy resin modified by BSO having oil content residue of 39% and epoxy content of 2.51 mole/kg Coatings of the formulations were applied on was prepared at Laboratory for Rubber and Natural glass plates for reflectance IR analysis and Resin Materials, ITT, VAST according to the determination of relative harness. The coating reported procedure.[12,13] application was realized by the use of suitable spiral Chemical formulas of the typical triglyceride of applicators (Erichsen), to make wet films about 30 BSO, bis-phenol A epoxy resin used for the µm. The UV-cured coatings were separated from preparation of the EBSO as well as BCDE, TAS and glass for thermogravimetric (TG) and differential propylene carbonate are shown below: scanning calorimetry analysis (DSC). O CH2 O C (CH2)7 CH CH CH2 CH CH (CH2)4 CH3 2.3. UV-Irradiation O O CH O C (CH2)7 CH CH CH2 CH CH (CH2)4 CH3 UV-Irradiation of investigated coatings was O O performed by use of a Fusion UV (model F 300S) CH2 O C (CH2)7 CH CH CH2 CH CH (CH2)4 CH3 equipped with medium pressure mercury lamps of O 250 mW/cm2 light intensity. BSO 2.4. Analysis -The Persoz hardness was determined using a Pendulum damping tester (model 300) according to the standard Persoz (NFT 30-016). The relative Bis-phenol A epoxy resin hardness of a coating (H) is calculated as following: © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 733
25728288, 2023, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202200194 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Influence of the black seed oil modified... H = Coating persoz hardness/425s, where 425s is ml/min). Thermal properties of the samples were Persoz hardness of a standard glass plate. investigated by two repeated heating-cooling cycles Reflectance IR analysis was realized by use of followed one another from -60oC to 150oC and on Nicolet iS10, Thermo Scientific-USA equipped by the contrary with the rate of 10oC/min. Glass OMNIC 5a software. transition temperature (Tg) was determined from both heating curves. 2.5. Thermal analysis 3. RESULTS AND DISCUSSION + Thermogravimetric analyzer TG 209 F1 Libra, NETZSCH S/N: TGA 209F1 D.0271-L, Germany, Study of the influence of the weight ratio 2015 and NETZSCH - Proteus-61 software at ITT EBSO/BCDE on thermal properties of UV- cured were used for thermogravimetric analysis. coatings in the frame of the work consists of Conditions of analysis: Al2O3 sample crucible, investigation of chemical structure of investigated weight of samples from 8.59 to 8.87 mg, applied coatings, the effect of the weight ratio EBSO/BCDE heating rate 10oC/min from room temperature to in the coatings and testing atmosphere (nitrogen, air) 600oC, testing atmosphere: air or nitrogen (nitrogen on their thermal properties. rate 50 ml/min). + Thermal Analysis System DSC 3+, Mettler- 3.1. Study of chemical structure of investigated Toledo, Swiss and Mettler software at Vietnam- coatings Russian center were used for differential scanning calorimetry analysis. Conditions of analysis: Al IR-spectra of investigated coatings before and after sample crucible, weight samples from 7.57 to 7.70 1.2 s of UV exposure are demonstrated in figure 1. mg, testing atmosphere: nitrogen (nitrogen rate 50 1a 1608 748 1730 3450 791 1798 660 1510 913 1390 2994 2861 832 1437 1012 1053 1252 2932 1b 1180 2a 2b Transmittance 3a 3b 4a 4b 5a 5b 3000 2000 1000 Wavenumbers (cm-1) Figure 1: Reflectance IR-spectra of coatings EBSO/BCDE/TAS with TAS = 5% of EBSO, BCDE total weight before (a) and after 1.2 s of UV-exposure (b). Weight ratio EBSO/BCDE: 1. 20/80, 2. 40/60, 3. 50/50, 4. 60/40, 5. 80/20 Before UV exposure, the investigated coatings absorption bands in IR-spectra demonstrated in are liquid having functional groups of EBSO figure 1, table 2.[5,12,13] (glycidyl epoxy, hydroxyl, ether groups and epoxy Figure 1 and table 2 show also that after 1.2 s of groups in the oil chain of BSO), BCDE (epoxy UV exposure, in investigated coatings content of groups in six-membered hydrocarbon cycles), of TAS, glycidyl epoxy and epoxy groups of BCDE both EBSO, BCDE (carbonyl and methylene groups) sharply decreased, BSO epoxy groups diminished; and EBSO, TAS (aromatic rings) with characteristic hydroxyl groups enhanced, ether groups sharply © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 734
25728288, 2023, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202200194 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Le Xuan Hien et al. increased while -CH2-, C=O groups and aromatic super acid. The initiation of polymerization process rings remained unchanged. occurred through protonation of epoxy groups by The above presented IR analysis data are in good protons of the formed superacid leading to formation agreement with the reported mechanism of cationic of hydroxyl groups and carbocations. The chain photoinitiated polymerization of epoxy compounds growth by reaction of the carbocations with epoxy in presence of a triarylsulfonium groups and chain transfer by reaction of the photoinitiator.[2,5,6,12,13] Under UV exposure in carbocations and hydroxyl groups resulted in presence of a hydrocarbon compound, TAS formation of ether groups. molecules were subjected to photolysis producing a Table 2: Characteristic IR absorption maxima of constituents, investigated coatings and their intensity variation after 1.2 s of UV exposure Characteristic IR absorption maxima Investigated coatings Wave Intensity Vibration (BCDE + EBSO + TAS) number BCDE EBSO TAS variation Before UV After UV (cm-1) exposure exposure 3450 OH stretching - * - * * Increased 2932, Saturated CH * * - * * Unchanged 2861 stretching Stretching of aromatic 1798 - - * * * Sharply decreased rings in TAS 1730 C=O stretching * * - * * Unchanged Stretching of aromatic 1510 - * * * * Unchanged double bonds Assymetric 1053 - * - * * Sharply increased C–O–C stretching Bending of the rings 913 of epoxy groups in * * - * - Sharply decreased EBSO and BCDE Assymetric 851, stretching, “peak 12 - * - * - Decreased 825 µcm” of epoxy groups in BSO chains Half ring stretching of 791, 748 epoxy groups in * - - * - Sharply decreased BCDE (*): Absorption maxima, (-): No absorption maxima. Unlike ether groups formed in both chain growth Increasing the weight ratio EBSO/BCDE and chain transfer process, hydroxyl groups can be enhances the content of atoms, functional groups formed only in the initiation stage and consumed in only existed in EBSO and diminishes the ones only the chain transfer reaction. So, depending on the presented in BCDE. The content of the groups in concurrence between initiation and chain transfer UV- cured coatings varied in accordance with the reactions, the content of hydroxyl groups in a reaction mechanism compared with initial coatings. coating may have extreme value during UV exposure. 3.2. Influence of the weight ratio EBSO/BCDE on After 1.2 s of UV-exposure the investigated thermal stability of investigated coatings coatings were transformed from viscous liquid to hard, solid coatings with relative hardness shown in In order to determine the influence of the weight table 3. The UV- cured coatings contain methylene, ratio EBSO/BCDE on the thermal stability of hydroxyl, ether groups, double bonds in the BSO investigated coatings, the TG analysis of coating chains, bisphenol A residue in their chemical constituents (BCDE, EBSO, Cyracure UVI 6974) network as well as a definite amount of propylene and UV-cured coatings in nitrogen atmosphere have carbonate, TAS and its photolysis products. been performed. The obtained TG and DTG curves © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 735
25728288, 2023, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202200194 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Influence of the black seed oil modified... properties and relative hardness[13] of UV-cured coatings are shown in table 3. 4 5 1 2 3 3b 2b 1b 3a 2a 1a Figure 2: TG (a) and DTG (b) curves of BCDE (1), EBSO (2), Cyracure UVI 6974 (3). Testing Figure 3: TG curves of EBSO/BCDE/TAS coatings atmosphere: nitrogen having various EBSO/BCDE weight ratios after 1.2 s of UV- exposure. EBSO/BCDE weight ratio: of the constituents and coatings are demonstrated in 1. 20/80, 2. 40/60, 3. 50/50, 4.60/40, 5. 80/20. figures 2 and 3, respectively. Their thermal Testing atmosphere: nitrogen Table 3: Thermal properties of constituents, UV-cured coatings and coating relative hardness Thermal properties of constituents and UV-cured coatings Coating constituents Relative DSC TG analysis No and their weight ratio hardness analysis [10] (Testing atmosphere) T1 T2 T3 Tonset Tmax Tend Ash content Tg1 Tg2 (WL) (WL) (WL) (WL) (WL) (WL) (%) (oC) (oC) 1 BCDE 164 338.7 372 390.6 460 0.80 - - (Nitrogen) (1.96) (47.3) (79.3) (82) (99.2) 2 EBSO 89.1 400.8 437.7 456.6 6.00 - - (Nitrogen) (1.1) (22.3) (62) (94) 3 Cyracure UVI 6974 68.2 257.7 458.9 485.9 500.5 11.50 - - (Nitrogen) (0.95) (51.4) (59.7) (75) (88.5) 4 EBSO/BCDE/TAS = 74.5 195.9 305.8 372.7 398.1 428.1 20/80/5 0.84 6.58 79.8 83.0 (1.38) (7.1) (17.3) (30.3) (51.8) (93.4) (Nitrogen) 5 EBSO/BCDE/TAS = 76.4 196.3 309.9 380.5 401.6 432.7 20/80/5 0.84 4.90 - - (1.41) (6.0) (17.2) (32.6) (54.1) (95.1) (Air) 6 EBSO/BCDE/TAS = 69.8 170.5 301 383.8 406.1 444.7 40/60/5 0.86 5.87 - - (1.15) (7.3) (12.4) (25.2) (46) (94.1) (Nitrogen) 7 EBSO/BCDE/TAS = 55.5 162.2 304 378.8 408.5 447 70.6 50/50/5 0.76 7.57 51.9 (0.79) (6.6) (12.5) (19.2) (45.6) (81.7) (Nitrogen) 8 EBSO/BCDE/TAS = 57.6 159.1 295.2 382.7 410.6 448.3 60/40/5 0.62 9.43 - - (0.52) (3.28) (7.67) (20.7) (47.1) (90.6) (Nitrogen) 9 EBSO/BCDE/TAS = 88.1 166.6 306.7 388.9 424.9 455.5 80/20/5 0.16 9.22 - - (0.47) (3.09) (6.2) (19) (54.5) (90.8) (Nitrogen) 10 EBSO/BCDE/TAS = 83.3 170.3 299.3 391.7 425.3 455.1 80/20/5 0.16 8.66 36.8 38.9 (0.24) (2.9) (6.71) (20.7) (53.5) (91.3) (Air) T1, T2, T3: Temperature of maximal volatilization rate of low molecular weight compounds (oC), Tonset, Tmax, Tend: Temperature of beginning; temperature of maximal rate and temperature of the end of degradation of investigated coatings (oC), respectively; Tg1, Tg2: Glass transition temperature determined by first and second heating - cooling temperature cycle, respectively (oC), (WL): Weight loss (%); (-): No measurement. © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 736
25728288, 2023, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202200194 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Le Xuan Hien et al. The results of the thermal analysis presented in moisture, low molecular weight compounds as well figures 2, 3 and table 3 show that in the range from as weight loss values at the temperatures. The room temperature to 360oC, in a nitrogen increase of weight ratio EBSO/BCDE decreases the atmosphere, all of the coating constituents and tightness of crosslinking in the cured coatings investigated coatings had weight loss due to (expressed by diminution of the relative hardness)[13] volatilization of low molecular weight compounds. and thereby diminishes temperature of moisture and It can be seen from figure 2 and table 3 that low molecular weight compounds volatilization. On temperatures of maximal volatilization rate of the other hand, an increase in the weight ratio BCDE sample were 164oC (weight loss 1.96%) and EBSO/BCDE augments high molecular weight 338.7oC (weight loss 47.3%). It is possible, at 164oC constituent EBSO in the coatings preventing evaporated mixture of BCDE, moisture and other moisture and low molecular weight compounds low molecular weight compounds, at 338.7oC volatilization leading to their higher volatilization evaporated mainly BCDE. Moisture and other low temperature and lower loss. The concurrence molecular weight compounds of EBSO and between the two tendencies is the reason for the Cyracure UVI 6974 samples evaporated with the extreme character of the EBSO/BCDE weight ratio – maximal rate at 89.1oC (weight loss 1.1%) and temperature of maximal volatilization rate and 68.2oC (weight loss 0.95%), respectively. At EBSO/BCDE weight ratio – weight loss value of 257.7oC (weight loss 51.4%) mainly propylene moisture and low molecular weight compounds carbonate (boiling point 242oC) evaporated with relationship. maximal rate from Cyracure UVI 6974 sample. In the range from 360 to 500.5oC various Since EBSO and most of TAS, BCDE chemical reactions could occur leading to participated in the photopolymerization process, crosslinking, degradation, volatilization of [12,13] only a small amount of TAS and BCDE could decomposition products and finally to weight loss of remain unconverted in UV cured coatings. So, investigated samples. Together with volatilization of propylene carbonate and photolysis products of TAS low molecular weight compounds, the reactions became the main volatile low molecular compounds contributed to rather high weight loss values of in investigated UV-cured coatings. BCDE, EBSO and Cyracure UVI 6974 which were The moisture evaporated from investigated 99.2, 94, 88.5% at 460, 456.6, 500.5oC, respectively. coatings with maximal rate in the range from 74.5oC There is a clear difference in the decomposition (coating having the weight ratio EBSO/BCDE = temperature of investigated coatings in the range 20/80) to 55.5oC (coating having the weight ratio from 360 to 600oC. In general, enhancement of EBSO/BCDE = 50/50) and weight loss from 1.38% EBSO/BCDE weight ratio in coatings increases their (coating having the weight ratio EBSO/BCDE = Tonset, Tmax and Tend. Meanwhile, the total weight loss 20/80) to 0.47% (coating having the weight ratio at the temperatures decreased when the EBSO/BCDE = 50/50). All of the UV-cured EBSO/BCDE weight ratio changed from 20/80 to coatings had weight loss caused by volatilization of 50/50, then varied insignificantly or enhanced when low molecular weight (mainly photolysis products of EBSO/BCDE weight ratio changed from 50/50 to TAS, propylene carbonate) in coating composition 80/20 corresponding to the variation of ash content. with the maximal rate in the range from 195.9 In the nitrogen atmosphere Tonset, Tmax and Tend of the (coating having the weight ratio EBSO/BCDE = coating with EBSO/BCDE weight ratio = 20/80 20/80) to 159.1oC (coating having the weight ratio were lowest with the values of 372.7, 398.1 and EBSO/BCDE = 60/40) and total weight loss from 428.1oC, respectively; Tonset, Tmax and Tend of the 7.3% (coating having the weight ratio EBSO/BCDE coating with EBSO/BCDE weight ratio = 80/20 = 40/60) to 3.09% (coating having the weight ratio were highest with the corresponding values of 388.9; EBSO/BCDE = 80/20). The volatilization of BCDE 424.9 and 455.5oC. Total weight loss of the coating and other low molecular weight compounds having EBSO/BCDE weight ratio = 50/50 at Tonset, remained in the coatings occurred in the range from Tmax and Tend were lowest with the values of 19.2; 306.7 (coating having the weight ratio EBSO/BCDE 45.6 and 81.7%, respectively. = 80/20) to 295.2oC (coating having the weight ratio EBSO/BCDE = 60/40) and total weight loss from 3.3. TG and DTG of UV-cured coatings in 17.3 (coating having the weight ratio EBSO/BCDE nitrogen and air atmosphere = 20/80) to 6.2% (coating having the weight ratio of EBSO/BCDE = 80/20). TG and DTG curves of investigated coatings having It was shown from the obtained data about the weight ratio EBSO/BCDE 20/80 and 80/20 after temperatures of maximal volatilization rate of 1.2 s upon UV-exposure are demonstrated in Fig. 4. © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 737
25728288, 2023, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202200194 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Influence of the black seed oil modified... It can be seen from figure 4, the testing Thermal stability of polymer materials depends atmosphere had almost no effect to the form of TG, not only on the chemical nature, molecular structure, DTG and little effect on the value of weight content of constituents but also creation and degradation of investigated coatings. In the range processing method.[1] from room temperature to 360oC both of them had It can be noted that there are many similarities in weight degradation caused by volatilization of low the chemical structure of investigated coatings and molecular weight compounds at three different UV-cured coatings based on epoxy diacrylate resin, temperatures. Their thermal degradation occurred in monomer acrylate: Presence of bisphenol A residue, the range from 372.7 to 455.5oC. When the weight C–C bonds of methylene groups, hydroxyl groups. ratio of EBSO/BCDE = 20/80, weight degradation The similarities in the chemical structure of the caused by volatilization of low molecular weight coatings may be a premise for their agreement in compounds in the air took place at 76.4, 196.3 and thermal behavior: Volatilization of moisture and low 309.9oC, higher than corresponding temperatures molecular weight constituents in the range from 150 74.5; 195.9 and 305.8oC in a nitrogen atmosphere. to 290oC, degradation of the cured polymer network The temperatures of beginning (Tonset), maximal rate from 310 to 450oC, formation of CO2 from remained (Tmax) and end (Tend) of thermal degradation of the thermal degradation parts from 500 to 580oC. coating in the air were 380.5, 401.6 and 432.7oC, Chemical reactions like dehydroxylation, scission of respectively, higher than corresponding temperatures C–C bonds between methylene groups and moisture of 372.7, 398.1, and 428.1oC in a nitrogen volatilization occurred in the range from Tonset to atmosphere. When the weight ratio of EBSO/BCDE 510oC. The processes could take place strongest near = 80/20, weight degradation caused by volatilization 400oC. Over 510oC there were water, methane and of low molecular weight compounds in the air some other alkane, aromatic compounds, CO2, CO in happened in 83.3, 170.3, and 299.3oC, on the whole, the degradation products.[10] lower than corresponding temperatures of 88.1, Investigated UV-cured coatings contain 166.6, and 306.7oC in a nitrogen atmosphere. The bisphenol A residue – a high thermostable structure Tonset, Tmax, Tend of thermal degradation of the part. The content of the part increased while coating in the air were 391.7, 425.3, and 455.1oC, a EBSO/BCDE weight ratio enhanced. This might be little higher or about the same compared with the main reason for the increase of Tonset, Tmax, and corresponding temperatures of 388.9, 424.9, and Tend of investigated coatings while the EBSO/BCDE 455.5oC in nitrogen atmosphere (table 3). weight ratio enhanced. The results of the study of the influence of TG /% DTG /(%/min) EBSO/BCDE weight ratio on UV-curing of coatings 100 based on EBSO, BCDE, TAS with TAS = 5% total 0 weight of EBSO, BCDE showed that after 1.2 s of 2ak 2aN [1] 80 1bk -2 UV exposure the coatings having EBSO/BCDE 1bN -4 weight ratio of 20/80, 40/60, 50/50, 60/40, 80/20 60 -6 contained hydroxyl group content according to the ratio of 1, 2, 2.22, 2, 1.93 and corresponding ether 40 -8 group content to the ratio of 1.42, 3.67, 4.75, 3.5, 20 2bN -10 1.[13] It is possible that the highest content of -12 hydroxyl and ether groups of the coating with 0 2bk 1ak 1aN weight ratio of EBSO/BCDE = 50/50 plays an 100 200 300 400 500 600 Temperature / C important role in the lowest weight loss at Tonset, Tmax and Tend of the coating since C–O bonds are more Figure 4: TG and DTG curves of investigated thermostable than C–C bonds.[9] coatings TG curve of coating with EBSO/BCDE = 20/80 in the 3.4. Influence of the weight ratio EBSO/BCDE on air (1ak) and in nitrogen (1aN). TG curve of coating glass transition temperature of investigated with EBSO/BCDE = 80/20 in the air (2ak) and in coatings nitrogen (2aN). DTG curve of coating with EBSO/BCDE = 20/80 in the air (1bk) and in nitrogen (1bN). DTG curve of coating with EBSO/BCDE = DSC curve of investigated coating with 80/20 in the air (2bk) and in nitrogen (1bN). Symbols: EBSO/BCDE weight ratio of 20/80 after 1.2 s of UV Weight ratio EBSO/BCDE: 20/80 (1), 80/20 (2); TG exposure is shown in figure 5. curves (a), DTG curves (b); testing atmosphere: Glass transition temperatures of investigated nitrogen (N), air (K) coating determined from the first and second © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 738
25728288, 2023, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202200194 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Le Xuan Hien et al. heating-cooling cycles were 79.8oC (Tg1) and 83oC photopolymerization[5] and thermal curing[8] of the (Tg2) respectively. The determined Tg2 was higher systems based on epoxy diacrylate resin, glycidyl than Tg1 due to the volatilization of low molecular ether of octo – cresol formaldehyde, tung oil weight compounds playing the role of plasticizer in modified epoxy resin without or with vegetable and UV-cured coating like propylene carbonate, TAS their derivatives. It can be noticed also that they photolysis products etc. as well as possible further have the same range of Tg as the UV-cured coatings reactions of unconverted species in the investigated based on vegetable derivatives having various sample at elevated temperature (thermal post curing chemical structures like epoxidized castor oil, effect).[11] phloroglucinol triepoxy and diglycidylether of vanillyl alcohols.[6] 4. CONCLUSION The increase of the EBSO/BCDE weight ratio in the coatings based on EBSO, BCDE and TAS from 20/80 to 80/20 considerably enhances their thermal durability and decreases their Tg. The volatilization of low molecular weight compounds occurred in the range from room temperature to 360oC while the thermal degradation of the coatings happened in the range from 360 to 455.5oC. The multi–sided effect of the enhancement of the bis-phenol A residue, extreme character of the variation of hydroxyl and ether groups and reduction of crosslinking degree in investigated coatings with the augmentation of the Figure 5: DSC curve of investigated coating with EBSO/BCDE weight ratio on the coating mobility EBSO/BCDE weight ratio of 20/80 after 1.2 s of UV might be the main reason of the change of their exposure. Heating curves of the first (1) and second thermal durability and Tg as well as the extreme (2) heating-cooling cycles character of the variation of their weight loss. The results of the determination of Tg are Acknowledgments. The authors are grateful to the demonstrated in table 3. Institute for Tropical Technology, Vietnam Academy It can be seen from table 3 and figure 5 glass of Science and Technology for its financial support transition temperatures of investigated coatings by grant of the 2022 basic subject. decreased from 79.8oC (Tg1) and 83oC (Tg2) when EBSO/BCDE weight ratio of the coating was 20/80 REFERENCES to 36.8 (Tg1) and 38.9oC (Tg2) when EBSO/BCDE weight ratio of the coating was 80/20. 1. D. W. V. Krevelen. Properties of polymers The obtained values of glass transition corelations with chemical structure. Elsevier temperature are the sum of factors contrary to each publising company, Amsterdam-London-New York other affecting in investigated coatings: Increase of 1972, 13. EBSO/BCDE weight ratio in the coatings enhances 2. N P. Cheremisinoff (ed), M. Decker. Handbook of bisphenol A content, a stiff part in coating structure. polymer Science and Technology, New York, 1989, At the same time the increase of the EBSO/BCDE 541. weight ratio diminishes crosslinking degree because 3. N. Mukhin, I. Sokolova, D. Chigirev, L. Rudaja, G. of the reduction of the total epoxy and high Lebedeva, R. Rastro, M. Bolsakov, Marc-Peter crosslinkable BCDE epoxy content (table 1) as well Schmidt, S. Hirsch. Composite ferroelectric coatings based on a heat-resistant polybenzoxazole polymer as augmentation of long, bulky and flexible matrix, Coating, 2020, 10, 286. substitute groups in the cured coatings. It is clear 4. B. Yin, J. Zhang. A novel photocurable modified that factors enhancing mobility in the cured coatings epoxy resin for high heat resistance coatings, Coloid gained the ascendancy when EBSO/BCDE weight Polym Sci., 2020, 298, 1303-1312. ratio of the coatings increased. 5. L. X. Hien, D. T. N. Minh, N. T. V. Trieu, C. Decker. The above mentioned results show that the Influence of some vegetable oils on the investigated coatings are more thermostable than photocrosslinking of coatings based on an 0-crezol those obtained by photoinitiated radical,[7] cationic novolac epoxy resin and a bis-cycloaliphatic © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 739
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