Preparation of amidinourea phytate and its flame retardant effect on wood
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摘要:
植酸(Phytic acid，PA)是一种极具潜力的磷系水性生物基阻燃剂，但其单独处理木材存在PA易流失、燃烧烟释放量大等问题，通过与其他氮、硼系阻燃剂复配，可在一定程度上缓减上述问题。然而，由于PA酸性较强，PA及其复配阻燃剂处理木材时会造成木材降解，进而影响其力学强度。以PA和双氰胺为原料合成了一类新型磷氮阻燃剂−植酸脒基脲(Amidinourea phytate，AUP)。利用FTIR、XRD、XPS及TG等手段对AUP阻燃剂理化特性进行了表征。采用TG、Py-GC/MS、氧指数测定仪、CONE等研究了AUP对杨木热解及燃烧行为的影响，探究了其阻燃机制。结果表明：AUP阻燃材在较低的增重率(8.73wt%)下表现出优异的阻燃及抑烟性能，优于增重率为14.8wt%的PA阻燃材，且抗流失性较好；AUP阻燃材的极限氧指数(LOI)值为34.8%，较未处理材提高了54.0%；总释热量和总生烟量分别降低了57.7%、65.7%，成炭率提高了148%，残炭结构更为密实，具有凝聚相与气相协效阻燃效果。此外，AUP阻燃材冲击强度比未处理材提高了58.5%，而PA阻燃材则下降了29.2%。
Abstract:Phytic acid (PA) is a very promising phosphorus-based aqueous bio-based flame retardant, but its treatment of wood alone has problems such as easy loss of PA and high release of combustion smoke. This challenge can be mitigated to some extent by compounding with other nitrogen and boron flame retardants. However, due to the strong acidity of PA, PA and its complex flame retardants used in wood fire-retardant treatment may cause wood degradation, which in turn affects its mechanical strength. In this study, a new type of phosphorus-nitrogen flame retardant, amidinourea phytate (AUP), was synthesised from PA and dicyandiamide. The physicochemical properties of AUP was characterised using FTIR, XRD, XPS and TG. The effects of AUP on the pyrolysis and combustion behaviours of poplar wood were investigated by TG, Py-GC/MS, limiting oxygen index (LOI) tester and CONE, and the flame retardant mechanism was explored. The results showed that the AUP flame retardant wood showed excellent flame retardant and smoke suppression properties at a lower mass gain rate (8.73wt%) than the PA flame retardant wood with a mass gain rate of 14.8wt%, and the loss resistance was better; The LOI value of the AUP flame retardant wood was 34.8%, which was 54.0% higher than that of the untreated wood; The total heat release and total smoke production were reduced by 57.7% and 65.7% respectively, and the char formation rate was increased by 148%, and the residual char structure was denser, with the effect of cohesive phase and gas phase. In addition, the impact strength of AUP flame retardant wood increased by 58.5% compared with that of untreated wood, while that of PA flame retardant wood decreased by 29.2%.
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图 2 PA、DCD、AUP-x的FTIR图像(a)及AUP-x的XRD (b)、XPS C1s (c)/N1s (d)能谱
Figure 2. FTIR spectra (a) of PA, DCD, AUP-x, XRD (b) and C1s (c)/N1s (d) of XPS patterns from AUP-x
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图 4 AUP- x阻燃剂在N2气氛下的热重分析曲线：(a) TG；(b) DTG
Figure 4. Thermogravimetric analysis curves of AUP-x in N2 atmosphere: (a) TG; (b) DTG
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图 5 未处理材及AUP阻燃处理材的SEM图像：((a), (b))未处理材的横截面；((c), (d)) AUP处理材的横截面；(e) AUP处理材的纵切面；(f) 附着在木材内部的AUP阻燃剂分子形貌
Figure 5. SEM images of untreated wood and AUP flame retardant treated wood: ((a), (b)) Cross section of untreated wood; ((c), (d)) Cross section of AUP treated wood; (e) Longitudinal section of AUP treated wood; (f) Molecular morphology of AUP flame retardant attached to wood
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图 6 未处理材及抗流失测试前后的PA阻燃材、AUP阻燃材极限氧指数(LOI)值
Figure 6. Limiting oxygen index (LOI) values of control, PA/wood and AUP/wood before and after loss resistance test
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图 7 未处理材、PA阻燃材、AUP阻燃材在50 kW/m2下的锥形量热测试结果：(a)热释放速率(HRR)；(b)总热释放(THR)；(c)生烟速率(SPR)；(d)总烟释放(TSP)；(e) CO释放速率(COP)；(f)质量损失速率(MLR)
Figure 7. Cone calorimetric test results of of control, PA/wood and AUP/wood under 50 kW/m2: (a) Heat relaase rate (HRR); (b) Total heat release (THR); (c) Smoke release rate (SPR); (d) Total smoke release (TSP); (e) CO production (COP); (f) Mass loss rate (MLR)
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图 8 未处理材、PA阻燃材、AUP阻燃材分别在N2气氛下的TG (a)、DTG (b)及空气气氛下的TG (c)、DTG (d)
Figure 8. Thermogravimetric curves of control, PA/wood, AUP/wood: TG (a) and DTG (b) in N2 atmosphere; TG (c) and DTG (d) in air
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图 9 未处理材、PA阻燃材、AUP阻燃材锥形量热测试后的残炭数码照片及SEM-EDS图像
Figure 9. Digital photographs and SEM-EDS images of residual carbon from control, PA/wood and AUP/wood after cone test
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图 10 未处理材、PA阻燃材、AUP阻燃材的总离子流图(TIC) (a)及各类型气态产物相对含量(b)
Figure 10. Total ion chromatogram (TIC) (a) and relative content of each type of gas product (b) of control, PA/wood and AUP/wood after cone test
表 1 植酸脒基脲(AUP)的合成配方
Table 1 Formulation of amidinourea phytate (AUP)
Ingredients DCD/g PA/mL Molar ratio (PA to DCD) H2O/mL apH AUP-6 12.6 27.6 1∶6 10.4 3.52 AUP-9 18.9 27.6 1∶9 21.4 4.34 AUP-12 25.2 27.6 1∶12 32.1 5.39 Notes: apH value is tested after reaction at 25℃; PA—Phytic acid; DCD—Dicyandiamide. 
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表 2 AUP-x的元素原子比
Table 2 Atomic fractions of AUP-x
Sample C/at% O/at% N/at% P/at% AUP-6 23.91 38.65 30.36 7.08 AUP-9 25.17 37.02 32.48 5.33 AUP-12 25.34 30.78 38.41 5.47
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表 3 抗流失试验相关参数
Table 3 Parameters related to erosion resistance test
Sample ε/% y1 y2 I/% PA/wood −53.94 68.53±3.49 15.73±1.65 22.89±1.35 AUP/wood −1.36 41.65±0.67 35.55±0.52 85.36±1.09 Notes: ε indicates the moisture absorption rate of the flame retardant material; y1, y2 indicate the amount of drug load before and after the anti-erosion test; I indicates the loss resistance of the flame retardant.
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表 4 未处理材、PA阻燃材、AUP阻燃材的力学性能
Table 4 Mechanical properties of control, PA/wood and AUP/wood
Sample Flexural strength/MPa Flexural modulus/GPa Impact strength/(kJ·m−2) Control 122.68±0.16 11.31±0.08 19.92±0.29 PA/wood 91.65±0.21 10.69±0.11 14.10±0.12 AUP/wood 113.18±0.07 10.81±0.07 31.58±0.25
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表 5 未处理材、PA阻燃材、AUP阻燃材的锥形量热测试参数
Table 5 Cone calorimetric test parameters of control, PA/wood and AUP/wood
Sample Pk1-HRR/
(kW·m−2)Pk2-HRR/
(kW·m−2)THR/
(MJ·m−2)Av-EHC/
(MJ·kg−1)TSP/
(m2·m−2)Av-COY/
(MJ·kg−1)TTI/s FPI/
(s·m2·kW−1)Char yield/
%B-W A-W B-W A-W B-W A-W Control 161.9 — 201.7 — 58.2 — 12.4 3.5 0.026 31 0.154 13.5 PA/wood 104.9 139.1 129.2 165.1 39.2 49.9 9.8 3.6 0.035 19 0.147 19.4 AUP/wood 36.3 42.9 82.1 77.1 20.0 21.4 5.7 1.2 0.041 55 0.670 33.5 Notes: B-W refers to before the loss resistance test; A-W refers to after the loss resistance test; Pk-HRR was the peak values of HRR with time; THR was the total heat release; Av-EHC was the average effective heat of combustion; TSP was the total smoke release; Av-COY was the average CO production; TTI was the time from when the cone shutter opened, exposing the sample to the set heat flux, to the moment flaming was established; FPI indicates fire performance index; Char yield was the carbon residue ratio.
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表 6 未处理材、PA阻燃材和AUP阻燃材的热重特征参数
Table 6 Thermogravimetric parameters of control, PA/wood and AUP/wood
Sample Atmosphere T5wt%/℃ T10wt%/℃ T50wt%/℃ Tmax/℃ W800℃/wt% Control N2 240 300 353 362 10.9 Air 288 293 369 372 0.1 PA/wood N2 72 194 288 288 27.9 Air 183 233 377 298 17.2 AUP/wood N2 200 252 322 294 29.5 Air 213 274 369 306 16.8 Notes: The data in the table are obtained under nitrogen and air atmosphere. T5wt% refers to the temperature at 5wt% mass loss; T10wt% refers to the temperature at 10wt% mass loss; T50wt% refers to the temperature at 50wt% mass loss; Tmax refers to the temperature at which the rate of heat loss is maximized; W800℃ refers to the residual rate of the sample at 800℃.
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其他相关附件
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目的
植酸(PA)是一种环保且高效的磷系水性生物基阻燃剂，而其单独应用于木材阻燃处理时会引起诸如吸湿性增强、燃烧时烟释放量大等问题。因此本研究旨在保证阻燃性能的同时，改善单独应用PA时的负面影响，以PA和双氰胺(DCD)为原料合成了阻燃、抑烟、抗流失性兼备的新型磷氮阻燃剂——植酸脒基脲(AUP)。
方法利用FTIR、XRD、XPS、TG等手段对AUP阻燃剂化学结构、结晶特性、热稳定性等进行了表征，并推测了AUP的合成机理。用15wt% AUP水溶液浸渍杨木得到AUP阻燃材，并利用万能力学试验机、极限氧指数测定仪、锥形量热仪、TG、SEM-EDS、热裂解-气相色谱/质谱联用仪(Py-GC/MS)等测试分析了AUP处理对杨木的力学性能、阻燃性能、热解特性等的影响，探究了其阻燃机理。
结果由FTIR、XPS表征可以推测出AUP的化学结构及其合成机理，即DCD溶于水后，在强酸性环境下，其中的氰基与水发生加成反应异构化为脒基脲，脒基脲进一步与PA发生酸碱反应成盐。AUP阻燃材的抗吸湿率仅为-1.36%，AUP抗流失率为85.36%，说明其对杨木吸湿性影响较小，抗流失性能优异；由SEM图像可以看出AUP颗粒整体形貌较为规整，呈片层堆叠的三维的花球状结构；力学测试表明，AUP阻燃材冲击强度比未处理材则提高了58.5%，弯曲强度降低了7.74%，而PA阻燃材冲击、弯曲强度均有不同程度的降低，这主要是由于AUP酸性较PA小，浸渍处理时木材的酸降解在一定程度上受到抑制，且木材细胞腔及间隙内填充了相对分子量较大的AUP药剂，受力时能起到一定的缓冲，增强了木材纤维骨架的韧性；极限氧指数测试中，经AUP处理后的杨木试样极限氧指数值(LOI)为34.8%，其经抗流失性测试后的LOI值为34.6%，说明AUP阻燃剂的抗流失性较强，浸水后对阻燃材的阻燃效果影响较小；锥形量热测试中，经AUP处理后，木材的总释热量(THR)降低到20.0 MJ·m，该值远低于PA阻燃材(39.2 MJ·m)，经抗流失试验后，AUP阻燃材THR值仅增加了6.9%；AUP阻燃材总生烟量(TSP)下降了65.7%；AUP阻燃材的失重速率较素材大幅降低，残炭率为33.5%，比未处理材提高了148%。以上结果表明，相比未处理材与PA阻燃材，AUP阻燃材的力学性能、阻燃抑烟性能都有所提升。AUP阻燃处理加速了杨木热解，但其促进作用弱于PA，表明AUP阻燃材热稳定性优于PA阻燃材，且阻燃处理对于杨木在空气气氛下的热解行为影响更为显著；AUP阻燃材残炭结构最为致密、而且出现了一定程度的膨胀发泡，表面裂缝少，细胞结构保持较完整、密实，残炭中检测到了P元素，这表明AUP分子结构中的磷酸基团受热分解生成含磷酸性物质，这些酸性物质会催化杨木脱水脱氧反应，形成更为稳定的残炭结构，并且该结构能够进一步隔绝氧气及热量，阻碍杨木内部的氧化热解反应，这也揭示了AUP在凝聚相中催化杨木成炭的阻燃机制；与未处理材相比，AUP阻燃剂的添加显著改变了木材热解气相产物的组成，热解生成了大量的NH、1-四唑-2-基乙酮等含氮化合物，羟甲基糠醛、糠醛等醛酮化合物，小分子的酚类含量均有所降低，而乙酸含量有一定程度增加，由此可知AUP的加入，一方面改变了木材的热解路径，降低了分解产物的可燃性，另一方面，AUP阻燃剂分解产生的水、NH等不可燃气体稀释了可燃性气体及O的浓度，有助于阻断或延滞木材的气相燃烧反应。
结论本研究所制备的AUP阻燃剂具有室温下溶解度低、升温溶解度增加的溶解特性，加入AUP阻燃剂后的杨木冲击性能有所提升，阻燃抑烟性能显著提升，成炭率高，炭层断裂的缝隙变窄、深度变浅，表面致密，内部依然保持较完整的细胞结构。AUP阻燃材在力学性能、阻燃性能等方面均优于PA阻燃材，解决了PA单独用作阻燃剂处理杨木时所造成的易流失、力学性能下降、烟释放量增大的问题。此外，AUP阻燃剂在杨木燃烧过程中表现出凝聚相和气相协效阻燃作用，能够有效抑制基材的燃烧和分解。
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植酸(phytic acid，PA)，主要来源于果实和种子，生物相容性好，磷含量高达28%，是一种极具潜力的水性生物基阻燃剂。但其单独处理木材存在PA易流失，燃烧烟释放量大等问题，通过与其他氮、硼系阻燃剂复配，可在一定程度上缓减上述问题。然而，由于PA较高的酸性，PA及其复配阻燃剂处理木材时会造成木材一定程度降解，从而影响其力学强度。因此，满足阻燃性能的同时，良好的抑烟能力以及合适的酸碱度成为新型植酸基木材阻燃剂的关键所在。本研究利用简单酸碱成盐反应，以PA和双氰胺(DCD)为原料合成了一种新型磷氮阻燃剂----植酸脒基脲(简称为AUP)。综合利用红外光谱、X射线衍射、X射线光电子能谱、热重分析等手段对AUP 阻燃剂理化特性进行了表征，探究了AUP阻燃剂的阻燃机制。在此基础上，用15wt% AUP水溶液浸渍杨木得到的AUP处理材，利用热重分析仪、极限氧指数测定仪、锥形量热仪、万能力学试验机等仪器研究了AUP处理对杨木的热稳定性、阻燃性能、力学性能的影响，探究了其阻燃机制。结果表明：与PA相比，AUP酸碱度与基材相当，抗流失性能优异，对基材力学性能影响小，AUP阻燃材冲击强度比未处理材提高了58.5%，而PA阻燃材则下降了29.2%。另外，AUP富含氮元素，可充分发挥P-N协同效应，提高阻燃及抑烟效率。AUP阻燃材在较低的载药率(8.73%)下表现出优异的阻燃及抑烟性能，优于同等测试条件下载药率为14.8%的PA阻燃材；与未处理材相比，AUP阻燃材的LOI值为34.8%，提高了54.0%；总释热量和总生烟量分别降低了57.7%、成炭率提高了148%，残炭结构更为密实，表现出凝聚相与气相协效阻燃效果。
未处理材、PA阻燃材、AUP阻燃材的总释热量与总生烟量对比
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