The Preparation Of Intercalated-Modified LDHs/Nanocellulose Lightweight Foams

Intercalated-modified LDHs/nanocellulose lightweight foams is a kind of environmental thermal-insulated materials with lightweight,high porosity,high mechanical strength,low thermal conductivity and good thermal-insulated performance.In this paper,the ZnAl-N0₃-LDHs was synthesized by co-precipitation method then modified by ion exchange method to produce ZnAl-PMo₁₂O₄₀-LDHs,ZnAl-PW₁₂O?40?-LDHs and ZnAl-SiW₁₂O₄₀-LDHs.And the micromorphology,composition,structure and properties of hydrotalcite-like compounds were characterized by SEM,ICP,XRD,FT-IR and TG.Finally,we prepared the CNF/ZnAl-N0₃-LDHs/H₃BO₃,CNF/ZnAl-PMo₁₂O₄₀-LDHs/H3B03,CNF/ZnAl-PW₁₂O?40?-LDHs/H₃BO₃ and CNF/ZnAl-SiW₁₂O₄₀-LDHs/H3B03 by vacuum freeze-drying method.And the micromorphology,structure,thermal stability,thermal conductivity,fire resistance and combustion performance of the nanocellulose lightweight thermal-insulated foams were characterized by SEM,FT-IR,TG,back-fire experiment,combustion and thermal conductivity test.?1?ICP analysis showed that the chemical formula of ZnAl-N0₃-LDHs precursor synthesized by co-precipitation method is Zn_0.76Al_0.24?OH?₂?NO₃?0.·0.59H₂O.And the chemical formulas of the three intercalated-modified LDHs obtained by ion exchange method are:Zn_0.75Al_0.25?OH?₂(PMo₁₂O₄₀)_0.013?NO₃?_0.21·0.42H₂O,Zn_0.73Al_0.27?OH?₂(PW₁₂O?40?)_0.037NO₃)_0.16·0.58H₂O,Zn_0.73Al_0.27?OH?₂(SiW₁₂O₄₀)0.037?NO₃?_0.16·0.64H₂O.?2?The results of SEM,XRD and FT-IR confirmed that the micro-morphology of ZnAl-N0₃-LDHs,whose interlayer space is 0.8888nm,with high crystallinity and interlayer regularity,is uniform and the layers are stacked,tightly arranged.And the infrared characteristic absorption peaks of hydrotalcite-like compounds exist in the ZnAl-N0₃-LDHs.The micromorphology of ZnAl-PMo₁₂O₄₀-LDHs,ZnAl-PWi2O40-LDHs and ZnAl-SiW₁₂O₄₀-LDHs maintained the lamellar structure of the ZnAl-N0₃-LDHs,are all flaky particles,with uniform size and good dispersion,but the crystallinity of samples reduces significantly.And the corresponding interlayer space is 0.9749 nm,1.109 nm and 1.144 nm,respectively.Besides,the infrared characteristic absorption peaks of LDHs and[PMo₁₂O₄₀]3-,[PW₁₂O?40?]3-,[SiW₁₂O₄₀]3-existed in the samples.?3?TG results showed that ZnAl-N0₃-LDHs precursor had good thermal stability and its CR800? was 66.26%.However,the pyrolysis rate of ZnAl-PMo₁₂O₄₀-LDHs,ZnAl-PW-2040-LDHs,ZnAl-SiW₁₂O₄₀-LDHs,which performed excellent thermal stability,were significantly slower than those of ZnAl-N0₃-LDHs,and the CR800? increased significantly to 74.54%,79.97%and 82.82%.?4?The micromorphology of CNF/ZnAl-N0₃-LDHs/H₃BO₃ lightweight thermal-insulated foams with 50%ZnAl-N0₃-LDHs showed that ZnAl-N0₃-LDHs has local agglomeration and poor dispersion in CNF.Comparing with pure CNF,the CR800? of CNF/ZnAl-N0₃-LDHs/H₃BO₃ reached 29.08%,higher than 8.26%of pure CNF.The heat-resistant irradiation time was prolonged by 575.24 s at T250? and the V250? slowed down to 0.1412?/s.Besides,the ignition time was delayed by 2 s and the burning time was shortened by 1 s.The combustion resistance time was prolonged by 17 s.Furthermore,the thermal conductivity of the CNF/ZnAl-N0₃-LDHs/H₃BO₃ is 0.04758 W/?m·K?.The results showed that the addition of ZnAl-N0₃-LDHs is beneficial to the thermal performance of CNF/ZnAl-N0₃-LDHs/H₃BO₃ lightweight thermal-insulated foams,such as thermal stability,fire resistance,combustion and thermal-insulated performance.But the thermal conductivity of CNF/ZnAl-N0₃-LDHs/H₃BO₃ is slightly increased compared with that of pure CNF,thus ZnAl-N0₃-LDHs has no positive effect on the thermal conductivity.?5?The micromorphology of CNF/ZnAl-PMo₁₂O₄₀-LDHs/H₃BO₃ lightweight thermal-insulated foams with 62.5%ZnAl-PMo₁₂O₄₀-LDHs showed that the poles of foams are regular and the dispersion of ZnAl-PMo₁₂O₄₀-LDHs is uniform in the CNF,so the agglomeration has improved.Compared with pure CNF,the Rmax2 of CNF/ZnAl-PMo₁₂O₄₀-LDHs/H₃BO₃5 whose CR800? was 18.03%higher than that of pure CNF,decreased to 0.3063%/?.The heat-resistant irradiation time prolonged by 867.8 s at T250? and the V250? slowed down to 0.1236 ?/s.During the combustion process,the CNF/ZnAl-PMo₁₂O₄₀-LDHs/H₃BO₃ was not ignited for 81 s and the carbon layer was basically intact when leaving the fire.Furthermore,the thermal conductivity of CNF/ZnAl-PMo₁₂O₄₀-LDHS/H₃BO₃ is 0.04404 W/?m·K?.The results showed that ZnAl-PMo₁₂O₄₀-LDHs has better dispersion than ZnAl-N0₃-LDHs,and the thermal performance of CNF/ZnAl-PMo₁₂O₄₀-LDHs/H₃BO₃ lightweight thermal-insulated foams is more significant.?6?The micromorphology of CNF/ZnAl-PW₁₂O?40?-LDHS/H₃BO₃ lightweight thermal-insulated foams with 62.5%ZnAl-PW₁₂O?40?-LDHs showed that the structure and poles of foams are regular and uniform,and there is no agglomeration observed.Compared with pure CNF,the RmaX2 of CNF/ZnAl-PW₁₂O?40?-LDHs/H₃BO₃,whose CR800? was 18.35%higher than that of pure CNF,decreased to 0.3716%/?.The heat-resistant irradiation time prolonged by 1447.68 s at T25?and the v250? slowed down to 0.0961 ?/s.During the combustion process,the CNF/ZnAl-PW₁₂O?40?-LDHs/H₃BO₃ was not ignited for 67 s and the carbon layer was basically intact,when leaving the fire.Furthermore,the thermal conductivity of CNF/ZnAl-PW₁₂O?40?-LDHs/H3B03 was 0.04251 W/?m·K?.The results showed that ZnAl-PW₁₂O?40?-LDHs has better thermal stability and dispersion than ZnAl-N0₃-LDHs,thus CNF/ZnAl-PW₁₂O?40?-LDHs/H3B03 lightweight thermal-insulated foam performs excellent thermal performance.?7?The micromorphology of CNF/ZnAl-SiW₁₂O₄₀-LDHs/H₃BO₃ lightweight thermal-insulated foams with 50%ZnAl-SiW₁₂O₄₀-LDHs showed that the structure and poles of foams is compact and regular.Compared with pure CNF,the Rmax2 of CNF/ZnAl-PW₁₂O?40?-LDHs/H₃BO₃5 whose CR800? was 23.01%higher than that of pure CNF,decreased to 0.3231%/?.The heat-resistant irradiation time prolonged by 1017.64 s at T250? and the V250? slowed down to 0.1151 ?/s.During the combustion test,the CNF/ZnAl-SiW₁₂O₄₀-LDHs/H₃BO₃ was not ignited for 70 s and the carbon layer was basically intact,when leaving the fire.Furthermore,the thermal conductivity of CNF/ZnAl-SiW₁₂O₄₀-LDHs/H₃BO₃ was 0.03799 W/?m·K?.The results showed that ZnAl-SiW₁₂O₄₀-LDHs significantly improves the thermal stability,fire resistance and combustion performance of CNF/ZnAl-SiW₁₂O₄₀-LDHs/H₃BO₃ lightweight thermal-insulated foams,which shows high thermal performance.