| As an important organic material,the quality of wood product is seriously affected by decay and mildew every year.Studies show that about 15%of the timber produced each year is lost due to decay,resulting in huge economic losses.Traditional preservatives have attracted the attention of scholars for the high toxicity and environmental pollution.Plant-derived preservatives are highly effective,harmless to humans and animals,and not prone to drug resistance.The development of new plant-derived wood preservatives can extend the range and service life of wood,which is of great significance and value.Neem seed kernel is rich in a variety of antibacterial active ingredients,so it has the potential to become a new type of wood preservative,but its instability and volatility greatly limit its use.The development of new plant-derived wood preservatives can expand the range of wood use,which is of great significance and value.In this paper,the antifungal effect of neem extract with different solvents was studied,and ethanol was selected as the most ideal extraction solvent.On the basis of the extraction process optimization,the azadirachtin extract was microencapsulated to prepare a new plant-derived preservative with excellent thermal stability.The antifungal mechanism,fixation mechanism and anticorrosion mechanism were studied deeply,which provided a new direction for the development of new botanical preservatives.The main results are as follows:(1)Evaluate of the antifungal effect of neem seed extract on five wood fungi and its components.Three solvents(methanol,n-hexane and ethanol)were used to extract the active components of neem seed kernel,and the antifungal test was carried out.Ethanol was selected as the extraction solvent for the subsequent experiments based on its antifungal efficiency,safety and cost.21,11 and 17 compounds were identified from methanol,n-hexane and 50%ethanol,and a variety of sulphides,squalene and other active substances with insecticidal and bacteriostatic effects were identified.Astaxanthinin and bufalin were isolated from azadirachtin seeds for the first time.(2)Optimization of the extraction rate of neem seed and the study on antifungal mechanism.The parameters of neem extraction technology was optimized using response surface method,the optimal processing conditions were as follows:45%ethanol concentration,liquid ratio 10:1(mL·g-1),temperature 45℃,and the extract efficiency was 14.98%.The minimal inhibitory concentration(MIC)of drug-containing medium method was used to determine the antifungal activity,and the fungal growth was determined.Optical microscope(OM)and scanning electron microscope(SEM)was used to make a preliminary study of the antifungal mechanism,found that the morphology of five kinds of fungi are produced significant influence treated with neem extract,characterized by mycelium distort deformation,fracture,soluble logistics out inside the cell,such as mold spores significantly reduced.(3)Preperation of neem seed extract microcapsules and the determination of their properties.Neem extract was microencapsulated via in-situ polymerization,and the types of wall materials,emulsifier types and dosage,acidifier types and other factors involved in the preparation process were optimized.The results showed that the microcapsules prepared with melamine formaldehyde resin,1%SDS,and 10%NH4C1 had good morphology and uniform particle distribution.The relationship between emulsifying speed,curing time and particle size distribution was investigated.It was found that the faster the emulsifying speed was within 2000r/min,the smaller the average particle size was and the more concentrated the distribution was.When the emulsifying speed was faster than 2000r/min,the wider the particle size distribution was and the larger the average particle size was.The emulsifying speed had little effect on the wall thickness of microcapsules.The curing time had little effect on the particle size of the microcapsule,but the longer the curing time was,the thicker the microcapsule wall was.Fourier transform infrared spectrometer(FTIR)was used to analyze the changes of functional groups of neem extract before and after microencapsulation,and it was found that no new functional groups appeared after microencapsulation,and there was no chemical reaction between neem extract and wall material,only simple physical mixing.The thermal stability of the microcapsules was determined.According to the TG/DTG curve,the thermal stability of the three reagents was as following:wall material(AMS)>neem extract microcapsule(MNE)>neem extract(NE).The volatile and unsTab.neem extract can be solved by microencapsulation.In addition,the thermal decomposition of microcapsule was divided into two stages,in the temperature of 285℃ and 350℃,respectively.While the neem extracts was divided into three stages,225℃,375℃ and 475℃,respectively.Wall material is mainly divided into two stages,and thermal decomposition temperature is 375 ℃.The three maximum weight loss rate is 340 ℃,332℃ and 365℃,respectively.(4)The distribution of microcapsules in wood and the antifungal action of treated wood.Scanning electron microscope(SEM)was used to study the distribution law of microcapsules.It can be seen that microcapsules are mainly distributed in wood ducts,with a small amount of attachment in the grain holes and no capsules in wood rays.The results showed that the MNE treated materials had obvious inhibitory effect on three kinds of mould(aspergillus Niger,trichoderma Verde and penicillium orange),and all of them could reach grade 5 anti-mildew effect.At the same time,NE was followed by anti-mildew effect.AMS had a weak inhibitory effect on Aspergillus niger and Penicillium citrinum,but no inhibitory effect on Trichoderma viride.Indoor corrosion resistance test results showed that,for brown-rot treatment,MNE treated wood has obvious corrosion resistance effect,poplar wood weight loss rate is lower than the untreated wood by 31.7%,and NE treated wood corrosion effect is slightly worse,weight loss rate is lower than the untreated wood by 25.3%.Compared with the weight loss rate of white-rot for 12 weeks,MNE and NE treated wood decreased by 13.7%and 8.4%,respectively.The AMS treated wood had no resistance to the two fungi,and the antifungal effect of the MNE treated wood was mainly derived from neem seed kernel extract.(5)Mechanism of microcapsule fixation and the decay resistance of treated wood.Mycelium can get through poplar grain holes,and multiplied in the wood duct.The mycelia in NE and MNE treated wood were significantly less,AMS treated wood had no antifungal material.The mycelia in MNE and NE treated wood became coarser,the surface was not smooth,fracture occurred,and the growth was significantly inhibited.By means of FTIR,XRD and other characterization methods,it was found that brown rot fungi had stronger degradation ability to cellulose and hemicellulose,and white rot fungi had stronger degradation effect on lignin. |
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