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对杨木的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(8.73%)下表现出优异的阻燃及抑烟性能,优于增重率为14.8%的PA阻燃材,且抗流失性较好;AUP阻燃材的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 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 weight gain rate (8.73%) than the PA flame retardant wood with a weight gain rate of 14.8%, 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 the total amount of smoke production were reduced by 57.7% and 65.7%, respectively, and the charcoal rate was increased by 148%, and the residual charcoal structure was more compact. 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 5 未处理材及AUP阻燃处理材的SEM图像:(a)、(b)为未处理材的横截面;(c)、(d)为AUP处理材的横截面;(e)为AUP处理材的纵切面;(f)为附着在木材内部的AUP阻燃剂分子形貌
Figure 5. SEM images of untreated wood and AUP flame retardant treated wood: (a), (b) are cross section of untreated wood; (c), (d) are cross section of AUP treated wood; (e) are longitudinal section of AUP treated wood; (f) are molecular morphology of AUP flame retardant attached to wood.
表 1 AUP-x的合成配方
Table 1. Formulation of AUP-x
Ingre-dients DCD/g 60%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℃; AUP—Amidinourea phytate; PA—Phytic acid; DCD—Dicyandia-mide. 表 2 AUP-x的元素原子比
Table 2. XPS patterns of AUP-x
Sample AUP-6 AUP-9 AUP-12 C /atom% 23.91 25.17 25.34 O /atom% 38.65 37.02 30.78 N /atom% 30.36 32.48 38.41 P /atom% 7.08 5.33 5.47 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 indicates the amount of drug load before and after the anti-erosion test; I indicates the loss resistance of the flame retardant. 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 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·k−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 39.0 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 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. 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℃/% Control N2 240 300 353 362 10.9 Air 264 293 369 372 0.1 PA/wood N2 72 194 288 264 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 5% weight loss; T10wt% refers to the temperature at 10% weight loss; T50wt% refers to the temperature at 50% weight 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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