| Radiate pine is one of the fast-growing woods with the porous lignocellulosic skeleton structure,ascribed by the advantages of abundant,cheap,and light weight,it was widely applied in the indoor decoration field,etc.However,the inherent shortages of radiate pine,such as bad mechanical strength,inflammability and poor thermal conductivity,will limit it utilizing in some fields.Up to now,impregnating modification with resin was an efficient method to improve the mechanical strength and abrasive resistance,nevertheless,the inflammability and thermal conductivity also need be serious considered when it was used as floor and decoration materials.Therefore,improve all of above drawbacks at the same time will expand its applications and increase its commercial value.In this thesis,the epoxy resin(EP)with good adhesive strength was used as the filling resin.Firstly,the flame retardant and thermal conductivity of the epoxy resin were improved by modification,and then the modified epoxy resin was impregnated into the wood cell lumen by vacuum-pressure method to fabricate high-performance radiant pine composites.The thesis mainly carries out the following research work:Firstly,the flame retardant of ammonium polyphosphate(APP)and thermal conductive filler of carbon nitride(g-C3N4)with lamellar structure were assembled together to obtain CN-APP modification addition,and then added the modification into the EP to prepare the multi-functional epoxy resin thermosets(EP/CN-APP).The component and morphology of CN-APP were characterized by infrared spectrometer(FTIR),x-ray diffraction(XRD)and scanning electron microscope(SEM),observing that the g-C3N4 was uniformly distributed on the APP surface.When the addition amount of CN-APP(APP/g-C3N4 was 9/1 by mass)was 7 wt%,the thermal conductivity of EP/CN-APP thermosets was 1.09 W m-1 K-1,which was significantly increased 194.6%comparing with that of EP/g-C3N4 thermosets(0.37 W·m-1K-1)with the same g-C3N4 content.The adsorption and assembly of g-C3N4 on the APP surface could effectively improve the dispersion of g-C3N4 in epoxy resin,that is conducive to form more thermal conduction pathways in the composite and improve phonon transmission,result in the thermal conductivity increasing of EP.The flame resistance of EP composite filling materials was studied by limit oxygen index(LOI)test,vertical burning(UL-94)test and cone calorimeter test(CONE).When the addition amount of CN-APP was 7 wt%,the sample reached UL-94 V-0 level and LOI was 30.1%,showing an excellent flame retardant efficiency.CONE tests indicated that,comparing to the pure EP,the heat release rate(HRR),total heat release(THR),total smoke release(TSP),and other flame parameters of EP/CN-APP thermosets(7 wt%)were got significantly decrease,the layer structure of g-C3N4 could form flame retardant barrier and improve melt viscosity of EP when combusting,thus inhibiting the release of combustible gas,contribute to increase the flame retardant efficiency.Then,the prepared EP/CN-APP pre-polymer(CN-EP)was successfully filled into radiate pine by vacuum-pressure method to fabricate wood composite material(wood/CNEP).Compared with original wood,wood/CNEP has better thermal stability and charring performance.The SEM showed that,the cell lumen of radiate pine was completely filled with EP.The thermal conductivity of wood/CNEP was assessed by thermal detector and thermal infrared imager devices,results in that the longitudinal and horizontal thermal conductivity of modified wood were 0.31 W·m-1K-1 and 0.8 W·m-1K-1,they were increased by 158.3%and 566.7%,respectively,comparing with the unmodified wood.This was ascribed by the multifunctional epoxy resin filling wood cell lumen,and formed effective thermal conductivity paths in the wood.EP itself was a hydrophobic material,and the hydroxyl in EP and wood would form hydrogen bond,both of them could improve the hydrophobic property of wood.Multi-walled carbon nanotubes(MWCNTs)with high thermal conductivity have been widely studied,facile aggregation was one of the MWCNTs shortages in practical application.In this thesis,to overcome the aggregation issue,the surface of APP was firstly coated by waterborne epoxy resin,and then polyurethane chain was grafted onto the surface of epoxy coating,at last the MWCNTs were evenly dispersed to the gap between the chain of polyurethane,and composite filler with core-shell-polymer including brush structure(MF-APP)was be successfully prepared.At last,the multifunctional epoxy resin will be fabricated by adding the MF-APP into EP.When the content of MWCNTs was 1.8 wt%,the EP with 9 wt%MF-APP showed a thermal conductivity of 1.02 W·m-1K-1 which increased 30.8%compared with the EP with the same content of APP(0.76 W·m-1K-1).The uniformly dispersing of MWCNTs in the brush gap,effectively inhibited the agglomeration of MWCNTs and made for forming more effective thermal conductivity network in the materials,furthering,improved the thermal conductivity of the composites.The flame retardant evaluation showed that,the sample reached UL-94 V-0 level,and the LOI value reached 30.8%.CONE test showed that the addition of MF-APP reduced THR and HRR of epoxy resin by 32.8%and 63.5%,respectively,compared with EP/APP/MWCNTs thermosets.The MWCNTs increased the melt viscosity during combustion,the thermal decomposition of APP could promote the charring of epoxy resin,they contributed to limit the oxygen and heat release,therefore,improving the flame retardant performance of the material.Then,the prepared EP/MF-APP pre-polymer(M-EP)was added to radiate pine by vacuum-pressure method to fabricate wood composite(Wood/M-EP).The wood cell lumen was filled with EP/MF-APP,and the composite showed a good hydrophobic performance with a WCA of 136.2°.The longitudinal and horizontal thermal conductivity of wood was 0.39 W·m-1K-1 and 0.94 W·m-1K-1,compared with above Wood/CNEP,wood with MWCNTs had a better thermal conductive property,that was dued to the MWCNTs was a better thermal conductive filler and the structure of core-shell-brush would increase thermal conductivity path.The flame retardant property of wood was assessed by open flame ignition test.The original radiate pine was quickly ignited and continuously combusting until it burning out,fortunately,wood/M-EP had an excellent flame retardant performance,after be ignited,it could self-extinguishing within 10 s.That was owing to the flame retardant APP in EP would thermal decomposed in the combustion process,then the degradation products catalyzed the wood to form thermal insulation carbon layer,that resist the burning of wood.The modified wood has excellent flame retardant property,that contributed to the fire safety performance of wood when in practical application.In summary,filling radiate pine with the multifunctional epoxy resin pre-polymer can improve the thermal conductivity,mechanical properties and flame retardant properties at the same time,furthering to increase the added value of wood,this has great significance to expand the application field of radiant pine. |
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