Flame Retardant Mechanism Investigation of Thermoplastic Polyurethane Composite/Ammonium Polyphosphate/Aluminum Hydroxide Composites Based on Spectroscopy Analysis
PENG Jian-wen1, XIAO Chong1, SONG Qiang1, PENG Zhong-chao1, HUANG Ruo-sen1, YANG Ya-dong3, TANG Gang1, 2, 3*
1. ASAP Technology (Jiangxi) Co., Ltd., Ji’an 343100, China
2. State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei 230026, China
3. School of Architecture and Civil Engineering, Anhui University of Technology, Ma’anshan 243032, China
Abstract：Ammonium polyphosphate (APP) and aluminum hydroxide (ATH) was introduced to prepare a series of ammonium polyphosphate/aluminum hydroxide/thermoplastic polyurethane composites (TPU/APP/ATH) by melting blending technology. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and laser Raman spectroscopy test were applied to investigate micro-morphology, surface structure, elemental composition, bonding state and graphitization degree of the char residue for TPU and flame retardant TPU composites, which combined with flame retardant tests to discover synergistic flame retardant mechanism of APP and ATH. SEM analysis revealed that TPU/APP/ATH char residue had less void structure and higher densification than APP and ATH alone. XPS revealed that the content of the C element in FR-TPU slag decreased compared with pure TPU, while the content of the O element increased. In these samples, the content of C element in TPU/APP10/ATH10 decreased from 88.2% to 69.24%, the content of O element increased from 8.07% to 17.78%. Compared with TPU/APP20 and TPU/ATH20, the content of P and Al element in TPU/APP10/ATH10 were decreased to 3.91% and 3.31%, respectively. Furthermore, peak fitting for bonding state of C element showed that C—C/C—H, C—O/C—N and CO/CN structure in char residue of TPU was 61.05%, 35.65% and 3.30%. In comparison, those in char residue of TPU/APP10/ATH10 were 45.38%, 45.00% and 9.63%, indicating ATH and APP facilitated the formation of ester, ether, carbonyl, the carboxylic acid (salt), ester group, et al. Peak fitting for the binding state of O element showed that O2/H2O，—O— and O structure in char residue of TPU were 28.75%, 44.36% and 26.89%, compared with 44.33%, 32.78% and 22.89% in char residue of TPU/APP10/ATH10, indicating that the addition of APP or/and ATH was conducive to the formation of O2/H2O structure of O elements. Peak fitting for bonding state of N element showed that —NH— and N structure in char residue of TPU was 40.93% and 59.07%, compared with 47.17% and 52.83% in char residue of TPU/APP10/ATH10, implying ATH and APP promoted the formation of —NH— structure. The Raman spectroscopy test showed that the char layers of TPU/APP10/ATH10 were more graphitized and densified than the sample with APP and ATH used alone. Based on the above researches and flame-retardant tests, the flame retardancy mechanism of TPU/APP/ATH composites can be obtained as follows: ATH was thermally decomposed into alumina, which absorbed heat and released large amounts of water vapor, effectively facilitating APP degradation, producing incombustible ammonia and polyphosphoric acid, which diluted the concentration of flammable gas. As the temperature continued to rise, alumina reacts with polyphosphoric acid to form aluminum metaphosphate (Al(PO3)3), which synchronously catalyzes the carbonization of the polyurethane matrix to form a highly graphitized char layer. The graphitized char layer covered the surface of the matrix together with aluminum metaphosphate, effectively inhibiting the transport of substances and energy in the combustion area, thus achieving flame retardation.
[1] Tabuani D, Bellucci F, Terenzi A, et al. Polymer Degradation and Stability, 2012, 97(12): 2594.
[2] Lou F P, Wu K, Wang Q, et al. Polymers, 2019, 11(1): 125.
[3] Zhou K Q, Gui Z, Hu Y, et al. Composites: Part A, 2016, 88: 10.
[4] Wang S G, Gao R, Zhou K Q. Journal of Colloid and Interface Science, 2019, 536: 127.
[5] Wang B B, Sheng H B, Shi Y Q, et al. Journal of Hazardous Materials, 2016, 314: 260.
[6] Jiao C M, Wang H Z, Chen X L. Journal of Thermal Analysis and Calorimetry, 2019, 137(5): 1579.
[7] Chen X L, Jiang Y F, Liu J B, et al. Journal of Thermal Analysis and Calorimetry, 2015, 120(3): 1493.
[8] ZHAO Liang-cheng, LI Bin, WU Si-rui, et al(赵梁成, 李 斌, 武思蕊, 等). Acta Materiae Compositae Sinica(复合材料学报), 2020, 37(2): 242.
[9] Tang G, Liu X L, Zhou L, et al. Advanced Powder Technology, 2020, 31(1): 279.
[10] Ni J, Song L, Hu Y, et al. Polymers for Advanced Technologies, 2009, 20(12): 999.
[11] Huang S C, Deng C, Wang S X, et al. Polymer Degradation and Stability, 2019, 165: 126.
[12] Deng J, Kang F R, Xiao Y, et al. Journal of Applied Polymer Science, 2020, 137(1): 47679.
[13] Liu L, Zhang H K, Sun L, et al. Journal of Thermal Analysis and Calorimetry, 2016, 124: 807.
[14] Liu C, Zong R W, Chen H Y, et al. Journal of Thermoplastic Composite Materials, 2019, 32(10): 1393.
[15] Guo Y, Xue Y, Zuo X, et al. Polymer Degradation and Stability, 2017, 144: 155.
[16] LIU Xiu-yu，ZHANG Bing, ZHANG Hao, et al(刘秀玉，张 冰，张 浩，等). Spectroscopy and Spectral Analysis(光谱学与光谱分析), 2020, 40(5): 1626.
[17] Hu Sheng, Tan Zhiwei, Chen Fei, et al. Fire and Materials, 2020, 44(5): 673.
