Thermal degradation, flame retardancy and mechanical properties of DOPO derivatives/poly(lactic acid) composites
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摘要: 研究9, 10-二氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO)、10-(2, 5-二羟基苯基)-10-氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO-HQ)、6H-二苯并[c, e][1, 2]氧代磷酸甘油酯, 6, 6’-(1, 2-苯乙基)双-, 66’-二氧化物(DiDOPO)三种衍生物的热分解行为,并考察了它们对聚乳酸(PLA)材料热降解、阻燃及力学性能的影响。热重分析结果表明,DOPO阻燃剂初始分解温度(T5%)仅为154℃,DOPO-HQ的T5%提高到342℃,DiDOPO的T5%达到363℃,明显高于DOPO与DOPO-HQ。对比DOPO衍生物/PLA复合材料的T5%发现,T5%(DOPO/PLA,273.5℃)< T5%(DOPO-HQ/PLA,321.5℃)< T5%(DiDOPO/PLA,333.8℃),呈现出与阻燃剂热稳定性相一致的递增趋势。另外,热降解动力学结果表明复合材料的热降解活化能提高。通过热重-红外光谱分析(TG-IR)、裂解-气相色谱/质谱联用(PY-GC/MS)探究DOPO衍生物/PLA复合材料的热降解行为,结果表明三种阻燃剂主要通过产生磷氧自由基实现气相阻燃作用,DOPO-HQ和DiDOPO的特征基团可能在凝聚相中发挥作用。在垂直燃烧测试中三种体系均达到V-0级,其中DOPO/PLA熔滴最严重,DiDOPO/PLA体系熔滴得以抑制。此外,力学测试结果表明,DOPO/PLA拉伸强度比纯PLA下降83.1%,而DOPO-HQ/PLA和DiDOPO/PLA仅分别下降14.2%和15.6%。Abstract: The thermal decomposition behaviors of three kinds of derivatives, including 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO), 10-(2, 5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO-HQ), 6H-dibenz[c, e][1, 2]oxaphosphorin, 6’6-(1, 2-phenethyl)bis-, 6’6-dioxide (DiDOPO), were studied. And effects of these DOPO derivatives on the thermal degradation behavior, flame retardancy and mechanical properties of poly(lactic acid) (PLA) were comparatively studied. TG results show that the initial decomposition temperature (T5%) of DOPO is 154℃, and an increased T5% of DOPO-HQ of 342℃ is displayed. In addition, T5% of DiDOPO reaches to as high as 363℃, which is higher than that of DOPO and DOPO-HQ. As for PLA composites, T5% reveals an increase trend as follow: T5%(DOPO/PLA, 273.5℃) <T5%(DOPO-HQ/PLA, 321.5℃) <T5%(DiDOPO/PLA, 333.8℃). T5% shows an progressively increase trend with the increased thermal stability of flame retardants. Furthermore, the thermal degradation kinetics results indicate that the thermal degradation activation energy of the composites material is improved. The thermal degradation of DOPO derivatives/PLA composites was investigated by thermogravimetric-infrared spectroscopy analysis (TG-IR) and pyrolysis-gas chromatography/mass spectrometry (PY-GC/MS). It shows that the three flame retardants mainly exert their gas phase flame retardant effect by generating phosphorus oxygen free radicals, and the characteristic groups of DOPO-HQ and DiDOPO may play a role in the condensation phase. All the three systems have attained the V-0 rating (UL-94), what’s more DOPO/PLA dripping is the most serious, on the contrary the dripping of DiDOPO/PLA is suppressed. Furthermore, the mechanical test results indicate that the tensile strength of DOPO/PLA decreases by 83.1% compared with pure PLA, while DOPO-HQ/PLA and DiDOPO/PLA only drops by 14.2% and 15.6%, respectively.
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Key words:
- PLA /
- DOPO derivatives /
- thermal degradation /
- flame retardancy /
- mechanical properties
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图 1 三种阻燃剂的结构:(a) 9, 10-二氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO);(b) 10-(2, 5-二羟基苯基)-10-氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO-HQ);(c) 6H-二苯并[c, e][1, 2]氧代磷酸甘油酯,6, 6’-(1, 2-苯乙基)双-, 66’-二氧化物(DiDOPO)
Figure 1. Structures of three flame retardants: (a) 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO); (b) 10-(2, 5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO-HQ); (c) 6H-dibenz[c, e][1, 2]oxaphosphorin, 6’6-(1, 2-phenethyl)bis-, 6’6-dioxide (DiDOPO)
图 7 氮气氛围下不同升温速率下TG曲线:((a) PLA; (c) DOPO/PLA; (e) DOPO-HQ/PLA; (g) DiDOPO/PLA)以及Ozawa拟合曲线:((b) PLA; (d) DOPO/PLA; (f) DOPO-HQ/PLA; (h) DiDOPO/PLA)
Figure 7. TG curves of PLA composites at different heating rates in N2: ((a) PLA; (c) DOPO/PLA; (e) DOPO-HQ/PLA; (g) DiDOPO/PLA) and Ozawa plots of PLA composites: ((b) PLA; (d) DOPO/PLA; (f) DOPO-HQ/PLA; (h) DiDOPO/PLA)
表 1 DOPO衍生物/PLA复合材料的配方及含P量
Table 1. Formulation and P content of DOPO derivatives/poly (lactic acid) composites
Sample Components/wt% P/wt% PLA DOPO DOPO-HQ DiDOPO DOPO − − − − 14.4 DOPO-HQ − − − − 9.6 DiDOPO − − − − 11.6 DOPO/PLA 90 10 − − 1.44 DOPO-HQ/PLA 90 − 10 − 0.96 DiDOPO/PLA 90 − − 10 1.16 表 2 三种阻燃剂在氮气和空气下的TG、DTG数据
Table 2. TG and DTG date of three flame retardants in N2 atmosphere and air
Sample T5%/℃ Tmax1/℃ Tmax2/℃ Residue at 600℃/% N2 DOPO 263.1 332.5 463.1 3.13 DOPO-HQ 361.8 422.9 535.2 14.82 DiDOPO 394.3 429.4 473.5 4.74 Air DOPO 276.6 337.2 461.3 1.82 DOPO-HQ 358.1 412.6 501.2 17.71 DiDOPO 398.8 431.6 472.3 3.58 Notes:T5%—Temperature corresponding to mass loss 5% of material; Tmax—Temperature corresponding to maximum thermal degradation rate. 表 3 PLA及其复合材料在氮气和空气下的TG、DTG和Ts数据
Table 3. TG, DTG and Ts date of PLA and its composites in N2 and air
Sample T5%/℃ Tmax1/℃ Tmax2/℃ Residue at 600℃/% Ts/℃ N2 PLA 332.2 369.3 − 0 169.8 DOPO/PLA 273.5 267.5 370.9 0.56 158.6 DOPO-HQ/PLA 321.5 371.9 452.7 2.04 167.5 DiDOPO/PLA 333.8 373.0 404.3 0.60 171.5 Air PLA 318.3 358.0 − 0.12 173.2 DOPO/PLA 271.4 266.3 371.4 0.33 158.1 DOPO-HQ/PLA 322.2 371.7 444.9 2.05 167.6 DiDOPO/PLA 336.1 373.0 404.1 0.47 172.2 Notes: Ts—Temperature corresponding to long-term service of the sample. 表 4 根据Kissinger’s法得到的PLA及其复合材料的活化能
Table 4. Activation energy of PLA and its composites according to Kissinger’s method
Slope R2 $ {E}_{{\rm{a}} } $/(kJ·mol−1) PLA −9381.46 0.9700 78.00 DOPO/PLA −18641.69 0.9982 154.99 DOPO-HQ/PLA −17337.76 0.9986 144.15 DiDOPO/PLA −18370.83 0.9858 152.74 Notes: R2—Linear correlation coefficient; $ {E}_{{\rm{a}} } $—Activation energy. 表 5 根据Ozawa’s法得到的PLA及其复合材料的活化能
Table 5. Activation energy of PLA and its composites according to Ozawa’s method
α PLA DOPO/PLA DOPO-HQ/PLA DiDOPO/PLA $ {E}_{{\rm{a}} } $/(kJ·mol−1) R2 $ {E}_{{\rm{a}} } $/(kJ·mol−1) R2 $ {E}_{{\rm{a}} } $/(kJ·mol−1) R2 $ {E}_{{\rm{a}} } $/(kJ·mol−1) R2 0.05 68.59 0.9846 68.22 0.9963 109.48 0.9938 131.19 0.9872 0.1 71.16 0.9889 101.86 0.9899 115.65 0.9977 143.50 0.9862 0.15 72.38 0.9870 145.29 0.9997 118.33 0.9979 148.29 0.9857 0.2 73.72 0.9861 153.49 0.9997 120.82 0.9975 150.90 0.9854 0.3 75.62 0.9827 157.52 0.9998 126.27 0.9972 153.10 0.9853 0.4 77.20 0.9806 157.95 0.9998 131.30 0.9977 153.63 0.9856 0.5 78.54 0.9794 157.01 0.9998 134.92 0.9981 153.29 0.9857 Note: a—Weight-loss ratio. 表 6 PLA及其复合材料的UL-94和LOI数据
Table 6. UL-94 and LOI date of PLA and its composites
Sample Mass fraction of flame retardant/wt% UL-94 (3.2 mm) LOI/% t1/t2 Dripping Rating PLA − BC Drip − 21.6 DOPO/PLA 10 0.21/0.31 Heavy V-0 33.5 DOPO-HQ/PLA 10 9.33/0.51 Light V-0 29.7 DiDOPO/PLA 10 0.40/0.47 No V-0 30.5 Notes:t1/t2—Duration of sample burning; LOI—Limiting oxygen index. -
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