Process Of NCC/APP/SiO₂ By Layer By Layer Self-assembly And Its Flame Retardancy In WPC

This paper was aimed to evaluate process of NCC/APP/SiO₂ with layer by layer self-assembly,which was used nanocrystalline cellulose?NCC?modified ammonium polyphosphate?APP?as anionic polyelectrolyte,and cationic polyethyleneimine?PEI?modified nano-SiO₂ as cationic polyelectrolyte.The flame retardant system was built due to the reaction of NCC/APP anionic polyelectrolyte and PEI/SiO₂ cationic polyelectrolyte.NCC/APP and PEI/SiO₂ were then assemblied on the surface of wood powder and HDPE composites.It was systematically studied the microstructure,chemical structure and thermal properties of flame retardant system,and explored the mechanism of flame retardant system with layer by layers self-assembly method,as well as the flame retardant performance and mechanical properties of the flame retardant wood plastic composites?WPC?.The conclusions were summarized as follows:?1?Nanocrystalline cellulose?NCC?were isolated successfully using 64wt%acid hydrolysis combined with 500 bar homogenization process.After NCC modified APP in NCC/APP system,NCC was dispersed uniformly in the water phase,and APP was embedded between NCC.And after adding NaCl,NaCl-NCC/APP presented low apparent density clew under the meta-microscale.Using cationic PEI modified nano-SiO₂,polyethyleneimine was covalent grafted on the nano-SiO₂.The dispersion of nano-SiO₂ is improved.Nano-SiO₂ was adsorbed closely because of the absorption of the positive and negative charges and the reaction of hydrogen bond.In terms of thermal characteristics,APP after dealing with the NCC modification,thermal degradation temperature moved to the lower temperature,the thermal degradation of NCC/APP was taken place in advance.When the addition of NCC was 1%,T5% of NCC1/APP was up to 303?,Tpeak was also respectively moved forward from 631?to 574?.The residual rate of NCC1/APP under 700? was 74.1%,it was increased by 54.4% compared with the pure APP.T5% of nano-SiO₂ after modified with polyethyleneimine was in advance to 54?,the residue rate was decreased from92.9% to 42.8% under 700?.It was due to that polyethyleneimine decompose a large amount of ammonia in the process of pyrolysis and dilute the combustible gas.?2?In the process of preparing NCC/APP/SiO₂ by layer by layer self-assembly method,firstly the wood powder/HDPE mixtures were impregnated into the NCC/APP colloid,then the NCC/APP/wood powder/HDPE mixtures were drying up.Nano-SiO₂ dispersion was then spraying into the NCC/APP processed woodpowder/HDPE mixtures,then drying,molding.Finally,the flame retardant wood plastic composites were prepared.In terms of thermal characteristics,T5% of WPC/NCC1/APP is decreased by 7?,the residual rate of WPC/NCC1/APP under700? is 25.5%.It is increased by 14.3% compared with WPC/APP.The residual rate of wood plastics composites self-assemblied by NCC1/APP and PEI/SiO₂ under the700 ? is 27.1%.In the flame retardant performance,when the addition of NCC is 1%,the heat release rate?HRR?,total heat release?THR?of WPC/NCC1/APP are all falling,the LOI value is 26.6%.NCC1/APP and PEI/SiO₂ self-assembled on the surface of the wood plastic composites,when the amount of PEI was added to 50%,the flame retardant performance is best,HRR is 152.8kW/m2,Peak HRR is352.2kW/m2,THR is 108.5kW/m2,the LOI value is 27.5%.In terms of mechanical properties,compared with the untreated of WPC,the tensile strength,elongation at break,bending strength and impact strength of wood plastic composites which were self-assemblied layer by layer of NCC1/APP and PEI/SiO₂ were increased.When the content of PEI was 25%,mechanical performance is the best.