Next Article in Journal
Monitoring Parallel Robotic Cultivations with Online Multivariate Analysis
Next Article in Special Issue
Sustainable Water Responsive Mechanically Adaptive and Self-Healable Polymer Composites Derived from Biomass
Previous Article in Journal
Editorial on Special Issue Electrolysis Processes
Previous Article in Special Issue
Terpene Based Elastomers: Synthesis, Properties, and Applications
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Processes
Volume 8
Issue 5
10.3390/pr8050581
processes-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Synthesis, Characterization of sym-2,4,6-trisubstituted-s-Triazine Derivatives and Their Effects on Flame Retardancy of Polypropylene Composites

by
Ali Aldalbahi
1,*,
Bander Alotaibi
1 and
Ayman El-Faham
1,2,*
1
Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
2
Chemistry Department, Faculty of Science, Alexandria University, P.O. Box 426, Ibrahimia, Alexandria 12321, Egypt
*
Authors to whom correspondence should be addressed.
Processes 2020, 8(5), 581; https://doi.org/10.3390/pr8050581
Submission received: 22 March 2020 / Revised: 5 May 2020 / Accepted: 11 May 2020 / Published: 14 May 2020
(This article belongs to the Special Issue Green Synthesis Processes of Polymers & Composites)
Browse Figures
Versions Notes

Abstract

:
Polypropylene (PP) is flammable material, which brings latent danger to the environment and human society. Therefore, developing new environmentally friendly and effective flame-retardant is one of the most important ways to improve the flame retardancy of PP and improve safety during its lifetime. Herein, we describe the synthesis of five sym-2,4,6-trisubstituted-s-triazine derivatives, namely, N2,N4,N6-triphenyl-1,3,5-triazine-2,4,6-triamine (TAT), N2,N4,N6-tris(4-bromophenyl)-1,3,5-triazine-2,4,6-triamine (TBAT), N2,N4,N6-tris(4-chlorophenyl)-1,3,5-triazine-2,4,6-triamine (TCAT), 4,4′,4″-((1,3,5-triazine-2,4,6-triyl) tris(azanediyl)) triphenol (THAT), and N2,N4,N6-tris(4-methoxyphenyl)-1,3,5-triazine-2,4,6-triamine (TMAT), from the reaction of cyanuric chloride and p-substituted aniline employing conventional heating or microwave irradiation. The prepared compounds characterized by different techniques, such as Fourier-transform infrared (FTIR), Ultra-Violet and Visible (UV-Vis), Nuclear Magnetic Resonance spectroscopy (1H-NMR and 13C-NMR), Thermogravimetric Analysis (TGA), and differential scanning calorimetry (DSC). The effect of substituent on the aniline moiety has great impact on its thermal stability, as observed from the TGA and DSC data. Based on the TGA and DSC results, three triazine derivatives TAT, TBAT, and TMAT were used as charring agents in the presence of different proportions of ammonium polyphosphate (APP) to form an intumescent flame-retardant (IFR) system, to improve the flame retardancy of PP. The flammability property of PP was investigated by a vertical burning test (UL94). The results of UL94 revealed that the TXAT/APP (IFR) system influence the PP and could improve the flame retardancy of PP. Best results were obtained with the mass ratio of APP and TXAT 2:1. When the IFR loading was 25 wt%, it displayed great influence and passed V-0 with TMAT, and V-1 with both TAT and TBAT in the UL94 test.

Graphical Abstract

1. Introduction

As one of the most widely used polymers, polypropylene (PP) plays a significant role in our daily lives, and is extensively used in numerous applications, such as in the electrical and insulation field, building materials, transportation aspects, etc. [1,2,3,4,5]. However, PP is also considered a flammable material, releasing smoke and toxic or corrosive gases, which brings latent danger to the environment and human society, and strongly limits its uses. Therefore, developing a new environmentally friendly and effective flame-retardant (FR) agent is one of the most important methods to improving the flame retardancy of PP, and the safety during its lifetime. In addition, applying FR is needed to achieve excellent flame-retardant properties [1,6,7].
Based on that, and due to the flammability of PP, many researchers conducted intensive studies and came up with great efforts to improve the flame retardancy of PP. They suggested that adding flame-retardant agents into PP is one of the most effect methods to adapt its flammability and improve the safety during its uses [6,7,8].
The most common effective flame retardant agent is the one containing halogen (usually bromine) and antimony trioxide synergistic systems [7,9]. However, applying this type of FR agent is limited, since halogenated FR agent during burning produces large amounts of corrosive gases and smoke, which affects the environment and human life [10,11]. Alternative FR additives are metal oxides, such as magnesium hydroxide and aluminum hydroxide. However, to obtain the same level of halogenated FR, a high loading amount of metal oxide is required, which will destroy PP’s mechanical properties remarkably [7,8,9,12,13].
In recent years, many researchers have focused on developing halogen-free flame-retardant agents, such as intumescent flame retardant (IFR) additives. IFR is considered a class of ecofriendly flame retardant additive with the effectiveness of isolating heat and oxygen transfer, cutting the release of smoke, being nontoxic, and avoiding dripping; it is considered to be one of the greatest capable candidates for its qualities, such as being low loading, protecting polymer matrix properties, being environmentally friendly, etc. [4,7,13].
Generally, IFR has three main constituents: (i) an acid source, such as ammonium polyphosphate (APP); (ii) a carbon source, such as a charring agent to form a charred layer, which acts as a physical barrier to reduce heat and mass transfer between gas and condensed phase over the creation of intumescent char cover. Finally, (iii), a blowing agent, such as nitrogen-containing material to produce abundant incombustible gases [8,14,15,16].
Mainly, APP is used as an acid catalyst and as a blowing agent because of its high contents of nitrogen and phosphorus. The charring agents, which presently used are generally small molecular compounds, such as s-triazine derivatives. These types of derivatives are highly nitrogen-containing compounds; during burning, they make multicellular swollen char on the polymer surface. The swollen char displays good adherence and offers an efficient barrier effect against the spread of the flame. In addition, it forms char, which can expand below the action of the blowing source to offer an intumescent char layer, to decrease heat transfer between the heat source and the polymer surface, and limit fuel transfer between polymer and the flame [4,8].
In recent years, various novel charring agents have been investigated and showed high flame retardant efficiency and stability, such as phenolic resin [17], polyamide [18,19], expandable graphite [20,21], etc. Recently, several s-triazine derivatives have been reported as charring agents due to their high nitrogen containing compounds, which can participate in the formation of a high efficiency, stable, char layer [22,23,24,25,26]. These types of derivatives performed excellent synergistic intumescent flame retardant effects with APP [27,28,29,30,31].
The ingredient cyanuric chloride [32,33,34,35] is the starting material used to prepare s-triazine derivatives via nucleophilic substitution reaction of the active chlorine atoms at the s-triazine ring with different nucleophiles [35,36,37,38]. Therefore, the structure of s-triazine derivatives are designed by controlling the substituent groups attached to the s-triazine ring at different temperatures [39].
By taking into account all of these aspects, the present work represents the synthesis and characterization of five sym-2,4,6-trisubstituted s-triazine derivatives (TXAT) based on the different substituent attached to the s-triazine ring. Theses derivatives containing aniline, p-bromoaniline, p-chloroaniline, p-hydroxyaniline, and p-methoxyaniline. The influence of substituent on their thermal stability were considered. Moreover, the prepared TXAT derivatives with higher limiting oxygen index (LOI) values were used together with APP at different weight ratios to improve the flame retardancy of PP. The UL94 V-0 rating was used to find out the flame retardancy properties of the reported compounds.

2. Materials

Polypropylene resin was provided from SABIC (PP 595A, Riyadh, Saudi Arabia). Ammonium polyphosphate commercial grade (phase ll, the degree of polymerization ≥1000) was purchased from Hubei Jusheng Technology Co. Ltd. (Wuhan, China). Cyanuric chloride (98%), aniline derivatives, and all solvents were purchased from Sigma-Aldrich (Chemie GmbH, Taufkirchen, Germany). Hydrazine hydrate (80%) purchased from Alpha Chemika (Mumbai, India). FTIR (KBr, cm−1) recorded on Shimadzu 8201 PC spectrophotometer (Shimadzu, Ltd., Kyoto, Japan). Nuclear Magnetic Resonance (NMR) spectrum (1H and 13C) recorded on JEOL-NMR (400 MHZ) spectrometer (JEOL, Ltd., Tokyo, Japan). Elemental microanalysis (CHN) measured by using Perkin-Elmer 2400 CHNS/O Series II elemental analyzer (PerkinElmer, Inc., 940 Winter Street, Waltham, MA, USA).

3. Methods

3.1. General Method for the Synthesis of sym-2,4,6-trisubstituted-s-Triazine

For the synthesis of the target compounds, two methods were used, as follows:
Method A: conventional heating
Cyanuric chloride 1 (1.84 g, 10 mmol) in 100 mL acetonitrile was added dropwise to a mixture of aniline derivatives 2a–e (30 mmol), K2CO3 (100 mmol) in acetonitrile (100 mL) at 0 °C. After complete addition, the reaction mixture stirred at 0 °C for 1 h, then at room temperature for another 1 h, and finally refluxed for 16–18 h. The solvent was removed under vacuum and then excess of water was added. The final products were isolated by filtration, washed with ethanol-water, and then dried at room temperature to afford the pure products.
Method B: microwave irradiation
Cyanuric chloride 1 (10 mmol) in 25 mL dioxane was slowly added to a mixture of aniline derivatives 2a–e (30 mmol) and K2CO3 (30 mmol) in 20 dioxane at 0 °C. After complete addition, the reaction mixture was stirred at room temperature for 20 min and then irradiated in a microwave oven at 600 W for 20–25 min using a Galanz microwave oven, connected with a refluxing condenser. The solvent was removed under reduced pressure and the solid obtained was washed with water, dried, and then recrystallized to afford the pure product.

3.1.1. N2,N4,N6-triphenyl-1,3,5-triazine-2,4,6-triamine (TAT); 3a

The product obtained as an off-white solid in 84% yield (A), 95% yield (B), mp 230–232 °C (Lit. [40,41] 29–230 °C (isopropanol); in 93 % yield); λmax (nm) in MeOH: 275; FTIR (cm−1): 3370 (NH), 1500 (C=N), 1620, 1495 (C=C), 1260 (C−N); 1H-NMR (DMSO-d6, δ ppm): 6.8–8.0 (m, 15H, Ar–H), 9.3 (s, 3H, NH).

3.1.2. N2,N4,N6-tris(4-bromophenyl)-1,3,5-triazine-2,4,6-triamine (TBAT); 3b

The product was obtained as a white solid in yield 84% (A), 98% (B); mp 268–270 °C; λmax (nm) in MeOH: 283; FTIR (cm−1): 3380 (N-H), 1550 (C=N), 1600, 1440 (C=C), 1250 (C–N), 620 (C–Br); 1H–NMR (Supplementary Materials, DMSO-d6, δ ppm): 7.45 (d, J = 8.8 Hz, 6H, Ar), 7.76 (d, J = 7.2 Hz, 6H, Ar), 9.47 (s, 3H, NH). 13C–NMR (Supplementary Materials, DMSO-d6, δ ppm): 113.8, 122.2, 131.1, 139.2, 163.9. Anal. Calc. for C21H15Br3N6 (587.89): C, 42.67; H, 2.56; N, 14.22. Found C, 42.88; H, 2.64; N, 14.41.

3.1.3. N2,N4,N6-tris(4-chlorophenyl)-1,3,5-triazine-2,4,6-triamine (TCAT); 3c

The product was obtained as an off-white solid in yield 82% (A), 96% (B); mp 245–246 °C (Lit. [42], mp 212–214 °C in yield 22%); λmax (nm) in MeOH: 280; FTIR (cm−1): 3390 (NH), 1550 (C=N), 1630, 1420 (C=C), 1240(C–N), 730(C–Cl); 1H–NMR (Supplementary Materials, DMSO-d6, δ ppm): 7.33 (d, J = 8.8 Hz, 6H, Ar), 7.82 (d, J = 6.6 Hz, 6H, Ar), 9.48 (s, 3H, NH); 13C–NMR (Supplementary Materials, DMSO-d6, δ ppm): 121.9, 125.9, 128.2, 138.9, 164.0. Anal. Calc. for C21H15Cl3N6 (457.74): C, 55.10; H, 3.30; N, 18.36. Found C, 55.23; H, 3.42; N, 18.55.

3.1.4. 4,4′,4″-((1,3,5-triazine-2,4,6-triyl) tris(azanediyl)) triphenol (THAT) 3d

The product obtained as a white powder; in yield 89% (A), 97%(B), mp 285–287 °C (Lit. [43,44] yield 89%); λmax (nm) in MeOH: 275; FTIR (cm−1): 3400 (NH), 1500 (C=N), 1630, 1430 (C=C), 1260 (C–N), 1050 (C–O); 1H–NMR (Supplementary Materials, DMSO-d6, δ ppm): 7.50 (d, 6H, J = 6.8 Hz, Ar), 7.88 (d, 6H, J = 6.0 Hz, Ar), 8.71 (s, 3H, NH); 9.03 (s, 3H, OH) ppm; 13C–NMR (Supplementary Materials, DMSO-d6, δ ppm): 115.0, 128.4, 131.6, 133.8, 161.5. Anal Calc for C21H18N6O3: C, 62.68; H, 4.51; N, 20.88. Found C, 62.81; H, 4.65; N, 21.01.

3.1.5. N2,N4,N6-tris(4-methoxyphenyl)-1,3,5-triazine-2,4,6-triamine (TMAT); 3e

The product was obtained as a grey solid in yield 83% (A), 96% (B); mp 215–217 °C (Lit. [42], mp 212–214 °C in yield 22%); λmax (nm) in MeOH: 278; FTIR (cm−1): 3400 (NH), 1500 (C=N), 1640, 1450 (C=C), 1260 (C–N), 1040 (C–O); 1H–NMR (Supplementary Materials, CDCl3, δ ppm): 3.78 (9H, s, OCH3), 6.81 (d, J = 9.6 Hz, 6H, Ar), 7.04 (brs, 3H, NH), 7.38 (d, J = 9.6 Hz, 6H, Ar); 13C–NMR (Supplementary Materials, CDCl3, δ ppm): 55.5, 113.9, 122.8, 131.6, 155.9, 164.5. Anal. Calc. for C24H24N6O3 (444.19): C, 64.85; H, 5.44; N, 18.91. Found C, 65.01; H, 5.68; N, 18.73.

3.2. Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC)

The TGA performed on a TA Q500 thermal analyzer (Waters LLC, New Castle, DE, USA) with flow rate of 60 mL/min, starting from room temperature to 800 °C. Around 6 mg of sample was placed in an alumina crucible and heated from 25 °C to 800 °C with the heating rate of 10 °C/min under N2 atmosphere; data were collected in Table 1.
Differential scanning calorimetry (DSC) was conducted on TA Instruments DSC Q1000 (Waters LLC, New Castle, DE, USA) in the range between 80 °C and 400 °C under nitrogen atmosphere. The 5–8 mg samples were placed in the aluminum pans and measured under N2 at the heating rate of 10 °C/min. Each sample was analyzed three times and readings were averaged.

3.3. Flammability Test UL94

The vertical burning test was investigated according to the UL94 test standard with the sample dimension of 130 × 13 × 3.2 mm. Before mixing PP, all additives were dried in vacuum oven at 70 °C for 24 h. All samples were prepared by mixing PP with different proportions of APP and TXAT using a two-roll mill mixing (Rheomixer XSS-300, Shanghai Ke Chuang, Shanghai, China) at a temperature range of 170 °C–180 °C for 10 min, and the roll speed was maintained 100 rpm. The formulations of prepared composites in the shape of vertical bars are listed in Table 2.

4. Results and Discussion

4.1. Synthesis of sym-2,4,6-trisubstituted-s-triazine Derivatives

The preparation of the target compounds were performed in one step reaction using conventional heating or microwave irradiation, as shown in Scheme 1. First, the reaction was carried out at 0 °C, due to the high reactivity of the first substitution, and then heated gradually to 80–100 °C, or irradiated by microwave at 600 W. Microwave irradiation always afforded the products in shorter reaction times (Section 3.1) with high yields and purities, as observed form their spectral data (Supplementary Materials).

4.2. Characterization of the Target Products

4.2.1. FTIR Spectroscopy

The FTIR spectrum for compounds 3a–e illustrated in Table 1 and Supplementary Materials showed absorption peaks in the range 3370–3400 cm−1, and were attributed to N-H bond and characteristic peaks in the range 2850–2930 cm−1 related to C-H sp3 and sp2. The absorption peaks at 1569 and 1550 cm−1 were attributed to C=N bond of the s-triazine ring. The absorption peaks at 1642, 1495, and 1430 cm−1 were attributed to C=C of the phenyl ring, while the absorption peaks in the range 1240–1260 cm−1 attributed to C-N bond (Table 1).

4.2.2. UV-Vis Spectra

The UV-Vis spectroscopies of the prepared compounds 3a–e were measured in methanol (Figure 1). The results showed that the prepared compounds have λmax in range at 275–283 nm, depending on the type of substituent attached to the aniline moiety, as shown in Table 1 (Figure 1). The substituent effects had a clear impact on the λmax as shown in Table 1, where the electron-withdrawing substituents, such as chloro (Cl) and bromo (Br), shifts λmax to longer wavelength (Bathochromic shift) than electron-donating substituents, such as hydroxyl (OH) and methoxy (OMe) group. This behavior can be explained by considering that, the p-position favors the extension of p-conjugation and the formation of highly delocalized in the excited state [45].

4.2.3. Thermogravimetric Analysis (TGA)

The thermal parameters of the prepared compounds 3a–e (TAT, TBAT, TCAT, THAT, and TMAT, respectively) were evaluated using the thermogravimetric technique (TGA). Degradation curves of 3a–e are shown in Figure 2 and summarized in Table 2. The results from thermal degradation data of 3a–e showed that all compounds have good thermal stability and started to degrade in range 240–350 °C, which is expected to have good char residue [27].
As shown in Table 2 the compounds (TAT, TBAT, TCAT, THAT, and TMAT) have one main degradation steps in a range of 320–440 °C (TAT), 330–440 °C (TBAT), 240–340 °C (TCAT), 330–450 °C (THAT) and 350–450 °C (TMAT), with mass loss 5% (TAT, THAT & TMAT), 6% (TBAT) and 80% (TCAT).
The results in Table 2 indicated that TMAT and THAT are thermally more stable and have higher char residue (CR) than TAT, TBAT, and TCAT. This attributed to the type of substituent at the aniline ring attached to the s-triazine moiety, where compounds with an electron-donating group, such as methoxy group in TMAT and hydroxy group in THAT showed higher CR at 600 °C and 800 °C (45 and 35, respectively). On the other hand, compounds with a weak electron-withdrawing group, such as bromine in TBAT and chlorine in TCAT showed lower CR, as shown in Table 2. The bromo derivative TBAT showed higher CR at 600 °C and 800 °C (35 and 22, respectively); compared to its analogs of the chloro derivative TCAT at the same temperatures (15 and 6, respectively); this might be due to the difference in the electronegativity property. While, the unsubstituted derivative TAT was in the middle, as shown in Table 2.
The CR could be utilized for the limiting oxygen index (LOI) evaluation. To find out the correlation between the CR and LOI, the van Krevelen equation indicated below was used [46,47].
LOI = 17.5 + 0.4 (CR)
LOI, defined as the minimum concentration of O2, supports the combustion to sustain in a mixture of O2 and N2 [43,44]. Materials displaying LOI values greater than 26 are classified as self-extinguishing material, while compounds with lower LOI than 26 are considered flammable material [47]. The LOI for TAT, TBAT, TCAT, THAT, and TMAT were calculated at 800 °C (Table 2). The results showed that the type of substituent has a clear effect on LOI values, where the chloro derivative TCAT showed the least LOI at 800 °C (19.9) compared to its analogs of the bromo derivative TBAT (26.3). On the other hand, the methoxy TMAT and the hydroxy derivatives showed the highest LOI values, while the unsubstituted was in the middle, as shown in Table 2.

4.2.4. Differential Scanning Calorimetry (DSC)

The thermal transitions of 3a–e was studied using differential scanning calorimetry technique under nitrogen atmosphere. The DSC data were collected from the second run, as all samples were heated first to 100 °C to confirm the removal of any trace of solvent, then cooled down with the same rate to 30 °C. Then the second run was heated from 30 °C to 300 °C at a scan rate of 10 °C/min to determine the glass transition temperatures (Tg).
The results summarized in Table 2 and shown in Figure 3, reveals that the Tg of the tested compounds 3a–e were in the range of 140–145 °C and are slightly similar to each other.

4.2.5. Flammability of PP and Its Composites UL-94

Based on the CR and LOI data, three derivatives TAT 3a, TBAT 3b, and TMAT 3e were selected and mixed with APP in different weight ratios to afford several IFRs. These mixtures were used in PP to yield PP/IFRs composites. The UL94 test was used to evaluate the flame retardant performance of neat PP, PP/3a, PP/3b, or PP/3e and PP/IFRs to provide a qualitative classification of the samples used in this work (Table 3). Pure PP is highly combustible, and cannot pass the UL94 test. When the weight ratio was 25 wt% of the TAT 3a, TBAT 3b or TMAT 3e and 75 wt% PP, the composite (PPx, PPy, and PPz, respectively, Table 3) did not pass the UL94 rating. However, there was a remarkable enhancement of UL-4 rating of IFR-PP composite when APP was added to the TXAT/PP composite. When the weight ratio of APP to TAT was 1:1 and the IFR loading was 25 wt % (PPa), the UL94 rating was V-2. The same rating was noticed with the same ratio of TBAT/APP (PPb) and TMAT/APP (PPc), as shown in Table 3. For further increase of the weight ratio of TXAT: APP (1:2) and using loading 25 wt% with 75 wt% PP, the UL94 rating remarkably improved and the char layer formed during combing could be observed obviously, which is unlike from that in neat PP and other PP composites. When the weight ratio of APP to TAT was 2:1 and when the IFR loading was 25 wt% (PP1), the UL94 rating improved and reached the V-1 rating of the UL94 tests, which is better than pure TXAT/PP with the same ratio (PP, PPx and PPa, Table 3). As for APP with TBAT (PP2) with the same weight ratio of 2:1, the UL94 rating also improved and reached the V-1 rating of the UL94 test, which is better than pure PP, TBAT/PP (PPy) and TBAT/APP (1:1)/PP (PPb). As for APP with TMAT (PP3) with the same weight ratio of 2:1, the UL94 rating also improved and reached the V-0 rating of the UL94 test, which is better than pure PP, TMAT/PP (PPz) and TMAP/APP (1:1)/PP (PPc).
Moreover, PP3 sample even reaches UL94 V-0 rating without dripping, while other flame retardant samples reach UL94 V-1 rating. This showed that PPc composite is highly efficient in improving the flame retardancy of PP among all PP composites.
These results demonstrated that the combination of TXAT and APP would cause huge enhancement of flame retardant performance of PP, especially with TMAT derivative. These results agreed with the results obtained in Table 2.
Photographs of PP1, PP2, and PP3 specimens after UL94 tests are shown in Figure 4, it shows that neat PP is in a melted form without obvious char residues; however, char residues were observed for PP1, PP2, and PP3 specimens.

5. Conclusions

The sym-2,4,6-trisubstituted triazine derivatives 3a–e were prepared, characterized, and used as charring agents along with ammonium polyphosphate (as acid source) to construct intumescent flame-retardant systems, which could enhance the flame retardant performance of polypropylene.
The char residue (CR) and limiting oxygen index (LOI) values were calculated from the thermogravimetric analysis (TGA) data. The results showed that TMAT (3e) and THAT (3d) have CR 31.5% and 31.9%, respectively, at 800 °C with LOI (35 and 36, respectively); while the unsubstituted aniline TAT and the halogenated derivatives TBAT, and TCAT showed CR (20%, 22%, 6%, respectively) with LOI (25.5%, 26.3%, 19.9%, respectively). Accordingly, the three derivatives with highest LOI values (TAT, TBAT, and TMAT) were selected and mixed with ammonium polyphosphate (APP) in different weight ratio to construct the IFR system. Combustion behavior showed that PP/IFR blends could acquire significant LOI values, and pass the UL94 V-0 rating. The PP/IFR blends achieve the UL94 V-0, indicating the flame-retardant efficiency is improved. When the components mass ratio of APP: TXAT in the IFR system was (2:1, respectively), the IFR offered the most effective flame retardancy in PP. When the mass ratio of APP and TXAT is 1: 1, the PP/IFR has a UL94 V-2 rating with high dripping. This has satisfactorily proved that IFR is very effective in PP.
Finally, the electron-donating group on the aniline residue attached to the s-triazine ring has a great effect on the thermal stability and intumescent flame retardant behaviors, as observed from TGA data and UL94 V-0.
Efforts on the synthesis and characterization of different generation of sym-trisubstituted s-triazine derivatives are in progress in our lab, which might have special interest as flame retardant agents in the industrial field.

Supplementary Materials

The following are available online at https://www.mdpi.com/2227-9717/8/5/581/s1, Figure S1: FTIR for TXAT derivatives, and Figures S2–S5: 1H-NMR and 13C-NMR of 3b–3e.

Author Contributions

Chemistry and analysis were carried out by B.A.; the series was designed and supervised by A.E.-F. and A.A. All authors contributed to the first and final draft of the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

Deanship of Scientific Research at King Saud University, Saudi Arabia, research group No. (RGP-1441-234).

Acknowledgments

The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding this work through research group no. (RGP-1441-234, Saudi Arabia).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Laoutid, F.; Bonnaud, L.; Alexandre, M.; Lopez-Cuesta, J.-M.; Dubois, P. New prospects in flame retardant polymer materials: From fundamentals to nanocomposites. Mater. Sci. Eng. R Rep. 2009, 63, 100–125. [Google Scholar] [CrossRef]
  2. Bourbigot, S.; Le Bras, M.; Duquesne, S.; Rochery, M. Recent advances for intumescent polymers. Macromol. Mater. Eng. 2004, 289, 499–511. [Google Scholar] [CrossRef]
  3. Zhang, F.; Wang, Y.; Jin, Y.; Zhang, J. Simulated effects of physical parameters on heat transfer of intumescent fire-retardant polypropylene during burning. J. Macromol. Sci. Phys. B 2011, 50, 1185–1195. [Google Scholar] [CrossRef]
  4. Shao, Z.-B.; Deng, C.; Tan, Y.; Chen, M.-J.; Chen, L.; Wang, Y.-Z. Flame retardation of polypropylene via a novel intumescent flame retardant: Ethylenediamine-modified ammonium polyphosphate. Polym. Degrad. Stab. 2014, 106, 88–96. [Google Scholar] [CrossRef]
  5. Roder, H.; Vogl, O. 17th international Herman F. Mark symposium: Polypropylene—A material of the future. Prog. Polym. Sci. 1999, 24, 1205–1215. [Google Scholar] [CrossRef] [Green Version]
  6. Hu, X.P.; Li, W.Y.; Wang, Y.Z. Synthesis and characterization of a novel nitrogen-containing flame retardant. Appl. Polym. Sci. 2004, 94, 1556–1561. [Google Scholar] [CrossRef]
  7. Wang, W.; Wen, P.; Zhan, J.; Hong, N.; Cai, W.; Gui, Z.; Hu, Y. Synthesis of a novel charring agent containing pentaerythritol and triazine structure and its intumescent flame retardant performance for polypropylene. Polym. Degrad. Stab. 2017, 144, 454–463. [Google Scholar] [CrossRef]
  8. Alongi, J.; Han, Z.D.; Bourbigot, S. Intumescence: Tradition versus novelty. A comprehensive review. Prog. Polym. Sci. 2015, 51, 28–73. [Google Scholar] [CrossRef]
  9. Li, B.; Xu, M. Effect of a novel charring foaming agent on flame retardancy and thermal degradation of intumescent flame retardant polypropylene. Polym. Degrad. Stab. 2006, 91, 1380–1386. [Google Scholar] [CrossRef]
  10. Huo, S.; Wang, J.; Yang, S.; Zhang, B.; Tang, Y. A phosphorus-containing phenolic derivative and its application in benzoxazine resins: Curing behavior, thermal, and flammability properties. J. Appl. Polym. Sci. 2016, 43403, 1–7. [Google Scholar] [CrossRef]
  11. Qi, Z.; Zhang, W.; He, X.; Yang, R. High-efficiency flame retardency of epoxy resin composites with perfect T8 caged phosphorus containing polyhedral oligomeric silsesquioxanes (P-POSSs). Compos. Sci. Technol. 2016, 127, 8–19. [Google Scholar] [CrossRef]
  12. Rothon, R.N.; Hornsby, P.R. Flame retardant effects of magnesium hydroxide. Polym. Degrad. Stab. 1996, 54, 382–387. [Google Scholar] [CrossRef]
  13. Hornsby, P.R. The Application of Magnesium Hydroxide as a Fire Retardant and Smoke-suppressing Additive for Polymers. Fire Mater. 1994, 18, 267–269. [Google Scholar] [CrossRef]
  14. Yang, R.; Ma, B.; Zhao, H.; Li, J. Preparation, thermal degradation and fire behaviors of intumescent flame retardant polypropylene with a charring agent containing pentaerythritol and triazine. Ind. Eng. Chem. Res. 2016, 55, 5298–5305. [Google Scholar] [CrossRef]
  15. Gao, S.; Zhao, X.; Liu, G.S. Synthesis of an integrated intumescent flame retardant and its flame retardancy properties for polypropylene. Polym. Degrad. Stab. 2017, 138, 106–114. [Google Scholar] [CrossRef]
  16. Johanna, P.; Ren, Y.L.; Boris, M.; Huo, T.G. Phosphorylated sodium alginate/APP/DPER intumescent flame retardant used for polypropylene. J. Appl. Polym. Sci. 2019, 136, 47794. [Google Scholar] [CrossRef]
  17. Huang, H.; Shi, Y.; Lv, G.P.; Liu, Y.; Wang, Q. Flame resistance and aging mechanism of flame retardant polycarbonate sheet containing linear phenolic resin charring agent. Polym. Degrad. Stab. 2015, 122, 139–145. [Google Scholar] [CrossRef]
  18. Chen, M.; Tang, M.; Ma, Y.; Chen, X.; Qin, J.; He, W.; Zhang, Z. Influence of polyamide 6 as a charring agent on the flame retardancy, thermal, and mechanical properties of polypropylene composites. Polym. Eng. Sci. 2015, 55, 1355–1360. [Google Scholar] [CrossRef]
  19. Dong, L.P.; Deng, C.; Wang, Y.Z. Influence of small difference in structure of polyamide charring agents on their flame-retardant efficiency in EVA. Polym. Degrad. Stab. 2017, 135, 130–139. [Google Scholar] [CrossRef]
  20. Bai, G.; Guo, C.G.; Li, L.P. Synergistic effect of intumescent flame retardant and expandable graphite on mechanical and flame-retardant properties of wood flour-polypropylene composites. Constr. Build. Mater. 2014, 50, 148–153. [Google Scholar] [CrossRef]
  21. Wang, G.; Bai, S.B. Synergistic effect of expandable graphite and melamine phosphate on flame-retardant polystyrene. J. Appl. Polym. Sci. 2017, 134, 45474. [Google Scholar] [CrossRef]
  22. Zhu, C.J.; He, M.S.; Cui, J.G.; Tai, Q.L.; Song, L.; Hu, Y. Synthesis of a novel hyperbranched and phosphorus-containing charring-foaming agent and its application in polypropylene. Polym. Adv. Technol. 2018, 29, 2449–2456. [Google Scholar] [CrossRef]
  23. Xu, B.; Ma, W.; Wu, X.; Qian, L.J.; Jiang, S. Flame retardancy and thermal behavior of intumescent flame-retardant EVA composites with an efficient triazine based charring agent. Mater. Res. Express 2018, 5, 045309. [Google Scholar] [CrossRef]
  24. Wang, X.J.; Wang, Z.B.; Li, J. Effects of a semi-bio-based triazine derivation on intumescent flame-reardant polypropylene. Polym. Adv. Technol. 2019, 30, 1259–1268. [Google Scholar] [CrossRef]
  25. Zhu, C.J.; He, M.S.; Liu, Y.; Cui, J.G.; Tai, Q.L.; Song, L.; Hu, Y. Synthesis and application of a mono-component intumescent flame retardant for polypropylene. Polym. Degrad. Stab. 2018, 151, 144–151. [Google Scholar] [CrossRef]
  26. Yang, K.; Xu, M.J.; Li, B. Synthesis of N-ethyl triazine-piperazine copolymer and flame retardancy and water resistance of intumescent flame retardant polypropylene. Polym. Degrad. Stab. 2013, 98, 1397–1406. [Google Scholar] [CrossRef]
  27. Zheng, Z.H.; Liu, S.F.; Wang, B.N.; Yang, T.; Cui, X.J.; Wang, H.Y. Preparation of a novel phosphorus- and nitrogen-containing flame retardant and its synergistic effect in the intumescent flame-retarding polypropylene system. Polym. Compos. 2015, 36, 1606–1619. [Google Scholar] [CrossRef]
  28. Wen, P.Y.; Feng, X.M.; Kan, Y.C.; Hu, Y.; Yuen, R.K.K. Synthesis of a novel triazine based polymeric flame retardant and its application in polypropylene. Polym. Degrad. Stab. 2016, 134, 202–210. [Google Scholar] [CrossRef]
  29. Xu, L.F.; Tan, X.W.; Xu, R.J.; Xie, J.Y.; Lei, C.H. Influence of functionalized molybdenum disulfide (MoS2) with triazine derivatives on the thermal stability and flame retardancy of intumescent poly(lactic acid) system. Polym. Compos. 2019, 40, 2244–2257. [Google Scholar] [CrossRef]
  30. Tang, S.; Qian, L.J.; Qiu, Y.; Sun, N. The effect of morphology on the flameretardant behaviors of melamine cyanurate in PA6 composites. J. Appl. Polym. Sci. 2014, 131, 40558. [Google Scholar] [CrossRef]
  31. Tang, W.; Qian, L.; Chen, Y.; Qiu, Y.; Xu, B. Intumescent flame retardant behavior of charring agents with different aggregation of piperazine/triazine groups in polypropylene. Polym. Degrad. Stab. 2019, 169, 108982. [Google Scholar] [CrossRef]
  32. Feng, C.M.; Zhang, Y.; Liu, S.W.; Chi, Z.G.; Xu, J.R. Synthesis of novel triazine charring agent and its effect in intumescent flame-retardant polypropylene. J. Appl. Polym. Sci. 2012, 123, 3208–3216. [Google Scholar] [CrossRef]
  33. Sibdas, S.M.; Niranjan, K. s-Triazine containing flame retardant hyperbranched polyamines: Synthesis, characterization and properties evaluation. Polym. Degrad. Stab. 2007, 92, 947–955. [Google Scholar]
  34. Xie, H.L.; Lai, X.J.; Li, H.Q.; Zeng, X.R. Synthesis of a novel macromolecular charring agent with free-radical quenching capability and its synergism in flame retardant polypropylene. Polym. Degrad. Stab. 2016, 130, 68–77. [Google Scholar] [CrossRef]
  35. Su, X.Q.; Yi, Y.W.; Tao, J.; Qi, H.Q.; Li, D.Y. Synergistic effect between a novel triazine charring agent and ammonium polyphosphate on flame retardancy and thermal behavior of polypropylene. Polym.Degrad. Stab. 2014, 105, 12–20. [Google Scholar] [CrossRef]
  36. Kien-Sin, L.; Soo-Tueen, B.; Lee, T.S.; Tiam-Ting, T.; Ratnam, C.T.; David, H.; Rahmat, A.R. A review of application of ammonium polyphosphate as intumescent flame retardant in thermoplastic composites. Compos. B Eng. 2016, 84, 155–174. [Google Scholar]
  37. Chen, J.L.; Wang, J.H.; Ni, A.Q.; Chen, H.D.; Shen, P.L. Synthesis of a novel phosphorous-nitrogen based charring agent and its application in flameretardant HDPE/IFR composites. Polymers 2019, 11, 1062. [Google Scholar] [CrossRef] [Green Version]
  38. Chen, Y.J.; Wang, W.; Liu, Z.Q.; Yao, Y.Y.; Qian, L.J. Synthesis of a novel flame retardant containing phosphazene and trizine groups and its enhanced charring effect in poly(lactic acid) resin. J. Appl. Polym. Sci. 2017, 34, 44660. [Google Scholar] [CrossRef]
  39. Sharma, A.; El-Faham, A.; de la Torre, B.G.; Albericio, F. Exploring the Orthogonal Chemoselectivity of 2,4,6-Trichloro-1,3,5-triazine (TCT) as a Trifunctional Linker with Different Nucleophiles: Rules of the Game. Front. Chem. 2018, 6, 516. [Google Scholar] [CrossRef] [Green Version]
  40. Huo, S.; Wang, J.; Yang, S.; Cai, H.; Zhang, B.; Chen, X.; Wu, Q.; Yang, L. Synergistic effect between a novel triazine-based flame retardant and DOPO/HPCP on epoxy resin. Polym. Adv. Technol. 2018, 29, 2774–2783. [Google Scholar] [CrossRef]
  41. Kolmakov, K.A. An Efficient, “Green” Approach to Aryl Amination of Cyanuric Chloride Using Acetic Acid as Solvent. J. Heterocycl. Chem. 2008, 45, 533–539. [Google Scholar] [CrossRef]
  42. Stagi, L.; Chiriu, D.; Scholz, M.; Carbonaro, C.; Corpino, R.; Porcheddu, A.; Rajamaki, S.; Cappellini, G.; Cardia, R.; Ricci, P. Vibrational and optical characterization of s-triazine derivatives. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2017, 183, 348–355. [Google Scholar] [CrossRef] [PubMed]
  43. Zhou, J.; Wang, J.; Jin, K.; Sun, J.; Fang, Q. s-Triazine-based functional monomers with thermocrosslinkable propargyl units: Synthesis and conversion to the heat-resistant polymers. Polymer 2016, 102, 301–307. [Google Scholar] [CrossRef]
  44. de Hoog, P.; Gamez, P.; Driessen, W.; Reedijk, L.J. New polydentate and polynucleating N-donor ligands from amines and 2,4,6-trichloro-1,3,5-triazine. Tetrahedron Lett. 2002, 43, 6783–6786. [Google Scholar] [CrossRef]
  45. Cao, C.; Fang, Z. Substituent effects on the UV spectra of extended benzylidene anilines p-X-PhCH=NPhCH=CHPh-p-Y. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2013, 111, 62–67. [Google Scholar] [CrossRef] [PubMed]
  46. Liu, Y.L.; Chiu, Y.C.; Chen, T.Y. Phosphorus-containing polyaryloxy diphenylsilanes with high flame retardance arising from a phosphorus–silicon synergistic effect. Polym. Int. 2003, 52, 1256–1261. [Google Scholar] [CrossRef]
  47. van Krevelen, D.W. Some basic aspects of flame resistance of polymeric materials. Polymer 1975, 16, 615–620. [Google Scholar] [CrossRef]
Processes 08 00581 sch001 550
Scheme 1. Synthesis of sym-2,4,6-trisubstituted-s-triazine derivatives.
Scheme 1. Synthesis of sym-2,4,6-trisubstituted-s-triazine derivatives.
Processes 08 00581 sch001
Processes 08 00581 g001 550
Figure 1. UV-Vis spectrum of sym-2,4,6-trisubstituted s-triazine derivatives (TXAT) in methanol.
Figure 1. UV-Vis spectrum of sym-2,4,6-trisubstituted s-triazine derivatives (TXAT) in methanol.
Processes 08 00581 g001
Processes 08 00581 g002 550
Figure 2. Thermogravimetric Analysis (TGA) degradation curves for (a) TCAT, THAT; (b) TBAT (p-Br), TAT (p-H), TMAT (p-MeO) derivatives.
Figure 2. Thermogravimetric Analysis (TGA) degradation curves for (a) TCAT, THAT; (b) TBAT (p-Br), TAT (p-H), TMAT (p-MeO) derivatives.
Processes 08 00581 g002
Processes 08 00581 g003 550
Figure 3. DSC (Differential Scanning Calorimetry) curves for sym-2,4,6-trisubstituted s-triazine derivatives (TXAT).
Figure 3. DSC (Differential Scanning Calorimetry) curves for sym-2,4,6-trisubstituted s-triazine derivatives (TXAT).
Processes 08 00581 g003
Processes 08 00581 g004 550
Figure 4. PP1, PP2, and PP3 specimens after UL94 tests.
Figure 4. PP1, PP2, and PP3 specimens after UL94 tests.
Processes 08 00581 g004
Table
Table 1. FTIR (cm−1) and Ultra-Violet and Visible (UV)-Visible (λmax nm) data for compounds 3a–e.
Table 1. FTIR (cm−1) and Ultra-Violet and Visible (UV)-Visible (λmax nm) data for compounds 3a–e.
CompoundFT-IR (cm−1)λmax (nm)
TAT; 3a3370 (NH), 1500 (C=N), 1620, 1495 (C=C), 1260 (C-N)275
TBAT; 3b3380 (NH), 1550 (C=N), 1600, 1440 (C=C), 1250 (C-N)283
TCAT; 3c3390 (NH), 1550 (C=N), 1630, 1420 (C=C), 1240 (C-N)280
THAT; 3d3400 (NH), 1500 (C=N), 1630, 1430 (C=C), 1260 (C-N)275
TMAT; 3e3400 (NH), 1500 (C=N), 1640, 1450 (C=C), 1260 (C-N)278
Table
Table 2. Thermal degradation parameters for 3a–e.
Table 2. Thermal degradation parameters for 3a–e.
Sample IDTemperature Range (°C)Mass Loss (%)Tg (°C)CR at 600 °CLOI at 600 °CCR at 800 °CLOI at 800 °C
TAT320–440501452929.12025.5
TBAT330–440601403531.52226.3
TCAT240–340801431523.5619.9
THAT330–450501434535.53531.5
TMAT350–450501414535.53631.9
Table
Table 3. Flammability test of the prepared polypropylene (PP) composite.
Table 3. Flammability test of the prepared polypropylene (PP) composite.
Sample IDPP (wt%)APP (wt%)FR (wt%)UL94Drip
PP neat10000N/RYes
PPz75025N/RYes
PPx75025N/RYes
PPy75025N/RYes
PPc7512.512.5V-2 aYes
PPa7512.512.5V-2 aYes
PPb7512.512.5V-2 aYes
PP37516.668.33V-0 bNo
PP17516.668.33V-1 cNo
PP27516.668.33V-1 cNo
a V-2 allows flaming drips; b V-0 rating is the highest flame-retardant rating for materials; c V-1 rating allows non-flaming drips.

Share and Cite

MDPI and ACS Style

Aldalbahi, A.; Alotaibi, B.; El-Faham, A. Synthesis, Characterization of sym-2,4,6-trisubstituted-s-Triazine Derivatives and Their Effects on Flame Retardancy of Polypropylene Composites. Processes 2020, 8, 581. https://doi.org/10.3390/pr8050581

AMA Style

Aldalbahi A, Alotaibi B, El-Faham A. Synthesis, Characterization of sym-2,4,6-trisubstituted-s-Triazine Derivatives and Their Effects on Flame Retardancy of Polypropylene Composites. Processes. 2020; 8(5):581. https://doi.org/10.3390/pr8050581

Chicago/Turabian Style

Aldalbahi, Ali, Bander Alotaibi, and Ayman El-Faham. 2020. "Synthesis, Characterization of sym-2,4,6-trisubstituted-s-Triazine Derivatives and Their Effects on Flame Retardancy of Polypropylene Composites" Processes 8, no. 5: 581. https://doi.org/10.3390/pr8050581

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop