Flame retardancy and smoke suppression of poly (lactic acid) composites modified by polyphosphate
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摘要: 由于聚乳酸(PLA)极易燃烧,并伴有严重的熔滴现象,严重阻碍了在包装、汽车、电气和电子工业等诸多领域的应用,为解决此问题,以PLA为基体,聚苯氧基磷酸-2-10-氢-9-氧杂-磷杂菲基对苯二酚酯(POPP)为阻燃剂,采用熔融共混热压法制备了不同含量的阻燃PLA复合材料。通过极限氧指数(LOI)、垂直燃烧(UL-94)测试、热重分析(TG)和锥形量热等方法研究了PLA复合材料的阻燃性和抑烟性能。结果表明:当POPP的添加量为4wt%时,PLA复合材料的垂直燃烧可达到V-0级,极限氧指数为34.8%。与纯PLA相比,POPP/PLA-4的烟雾释放速率和总烟释放量分别下降了85.83%和77.65%,极大地改善了PLA材料的抑烟性能。此外,对锥形量热测试后的残炭微观结构和热降解行为分析表明,POPP在PLA燃烧过程中的阻燃机制以气相为主、凝聚相为辅。POPP热降解释放出•PO和•PO2自由基,与•H和•OH结合终止气相燃烧循环;在凝聚相中,POPP促进PLA分子间交联成炭,表面形成连续且致密的炭层,提高基材的阻燃性能。Abstract: Due to poly (lactic acid) (PLA) was easy to burn and accompanied by serious droplet phenomenon, its application in many fields such as packaging, automotive, electrical and electronic industries were seriously limited. And in order to solve this problem, PLA was used as matrix and poly (2-10-hydrogen-9-oxa-phosphaphenanthrene hydroquinone phenyl phosphate) (POPP) was used as flame retardant. PLA composites with different contents were prepared via melting blending and hot-compression method. The flame retardant properties and smoke suppression of PLA composites were investigated by means of limited oxygen index (LOI), vertical burning test (UL-94), thermogravimetric analysis (TG) and cone calorimetric test etc. The results show that the LOI of PLA composite with 4wt% POPP is 34.8%, and it reaches a UL-94 V-0 rating. Comparing with pure PLA, the smoke production rate and total smoke production of POPP/PLA-4 are respectively reduced by 85.83% and 77.65%, which dramatically improve the smoke suppression performance of PLA materials. Moreover, the results of microstructure of char residues after cone calorimeter and thermal degradation behavior analysis reveal that the excellent flame-retardant performance of PLA composites are followed a flame-retardant mechanism of gaseous phase at superiority. This is attributed to •PO and •PO2 decomposed by POPP quenching •H and •OH. Otherwise, by promoting the intermolecular crosslinking of PLA, a continuous and dense carbon layer on the surface is formed, which improve flame retardancy of PLA composites.
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Key words:
- poly (lactic acid) /
- polyphosphate /
- modification /
- thermal degradation /
- smoke suppression
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图 2 PLA复合材料在50 kW/m2下的锥形量热测试结果:(a) 热释放速率(HRR);(b) 总释放热(THR);(c) 烟雾释放速率(SPR);(d) 总烟释放量(TSP)
Figure 2. Cone calorimetric results of PLA composites at an external heat flux of 50 kW/m2 as a function of burning duration: (a) Heat release rate (HRR); (b) Total heat release (THR); (c) Smoke production rate (SPR); (d) Total smoke production (TSP)
表 1 聚乳酸(PLA)复合材料的配方及P含量
Table 1. Formulation and P contents of poly(lactic acid) (PLA) composites
Samples PLA/wt% POPP/wt% P/wt% PLA-0 100 0 0.00 POPP/PLA-1 99.5 0.5 0.07 POPP/PLA-2 99 1 0.13 POPP/PLA-3 98 2 0.27 POPP/PLA-4 97 3 0.40 POPP/PLA-5 96 4 0.54 Note: POPP—Poly(2-10-hydrogen-9-oxa-phosphaphenanthrene hydroquinone phenyl phosphate). 表 2 PLA复合材料的阻燃测试结果
Table 2. Results of flame retardant performances for PLA composites
Samples Limiting oxygen index/% Dripping Cotton ignited UL-94 rating PLA-0 16.3 Heavy dripping Yes No rating POPP/PLA-1 24.0 Heavy dripping Yes V-2 POPP/PLA-2 25.2 Heavy dripping Yes V-2 POPP/PLA-3 26.2 Dripping No V-0 POPP/PLA-4 29.8 Dripping No V-0 POPP/PLA-5 34.8 Dripping No V-0 表 3 纯PLA和PLA复合材料的锥形量热数据
Table 3. Cone calorimetry data for pure PLA and PLA composites
SamplesTTI/s Pk-HRR/
(kW·m−2)THR/
(MJ·m−2)SPR/
(m2·s−1)TSP/
(m2·m−2)Av-COY/
(kg·kg−1)Av-EHC/
(MJ·kg−1)FPI/
(s·m2·kW−1)Residue/% PLA-0 43 580.7 115.3 0.120 51.0 0.023 14.1 0.074 0.7 POPP/PLA-3 35 571.9 109.9 0.079 26.5 0.032 14.3 0.061 0.4 POPP/PLA-4 31 518.3 89.0 0.017 11.4 0.046 12.0 0.060 15.5 Notes: TTI—Time to ignition; Pk-HRR—Peak of heat release rate; Av-COY—Average of CO yield; Av-EHC—Average of effective heat of combustion; FPI—Fire performance index. 表 4 氮气氛围下PLA复合材料的TG和DTG结果
Table 4. TG and DTG results under nitrogen atmosphere for PLA composites
Samples T5%/℃ T10%/℃ T50%/℃ Tmax/℃ R600/% PLA-0 338 358 383 385 0.00 POPP 350 389 537 493, 551 32.90 POPP/PLA-1 339 360 385 387 0.75 POPP/PLA-2 334 358 384 386 0.66 POPP/PLA-3 321 353 381 384 0.51 POPP/PLA-4 322 352 383 386 0.71 POPP/PLA-5 319 347 382 387 0.56 Notes: Tx%—Temperature corresponding to mass loss xwt% of material; Tmax—Temperature corresponding to maximum thermal degradation rate; R600—Residue at 600℃. 表 5 纯PLA及复合材料的力学性能结果
Table 5. Test results of mechanical properties of pure PLA and its composites
Samples Impact strength/(kJ·m−2) Elongation at break/% Tensile strength/MPa PLA-0 14.66$ \pm $0.50 7.22$ \pm $0.40 31.81$ \pm $0.50 POPP/PLA-1 11.10$ \pm $0.30 4.08$ \pm $0.30 14.49$ \pm $0.40 POPP/PLA-2 14.41$ \pm $0.20 5.31$ \pm $0.50 16.57$ \pm $0.30 POPP/PLA-3 12.56$ \pm $0.40 3.80$ \pm $0.30 16.16$ \pm $0.30 POPP/PLA-4 12.72$ \pm $0.30 5.13$ \pm $0.20 22.08$ \pm $0.20 POPP/PLA-5 8.41$ \pm $0.30 6.24$ \pm $0.50 23.53$ \pm $0.40 -
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