Synthesis Of Pyridone/Pyrone Derivatives And Their Effects On The Thermal Stability Of Hemp Fibre

Natural-fibre-based biocomposites present several advantages,such as rich sources,renewable,good biodegradability,low cost,and so on.In recent years,natural fibre has become a research hotspot of composite materials.Hemp fibre with high specific strength and modulus of natural fibre,which have been widely used in textile,automotive,building and biocomposites.Flammability is one of the important properties of hemp fibre/polymer composites,and restricts their application.Therefore,modifications of natural fibre are necessary to improve their fire resistance.Although some studies have shown that nitrogencontaining heterocyclic compounds can be used of natural fibre flame retardancy,the thermal stability effect caused by the change of molecular structure has not been systematically studied.The relationship between structure change and thermal stability provides theoretical guidance for the development and optimization of nitrogen-containing heterocyclic flame retardants.In view of the poor thermal stability of hemp fibre,a variety of heterocyclic compounds with various substituents were synthesized.Hemp fibre was treated with nitrogen-containing heterocyclic compounds by impregnation and blending.The effect of substituent effect on the thermal stability of hemp fibre was investigated.The coupling modification method was used to improve the interfacial property of hemp fibre.Based on the nucleophilicity of nitrogen atoms in the amide structure of ?-ketoamide derivatives,the reaction conditions were regulated to choose the direction of reaction.A series of pyridone derivatives with abundant functional groups were synthesized via Vilsmeier reaction,which have the advantages of easy operation and mild condition.The yield of products was above 80%.Two kinds of pyridinone isomers were demonstrated utilizing malonitrile,under controlled conditions,derived from ?-ketoamide derivatives.The yield of products was above 85%.A series of pyridone derivatives were prepared by self-condensation of ?-ketoamide derivatives.We obtained some of heterocyclics by high atom economy.All the atoms of raw materials are almost retained in the product.The yield of products was above 81%.Based on the nucleophilicity of oxygen atoms in the amide structure of?-ketoamide derivatives,A series of nitrogenous substituted pyranones were direct synthesized from ?-keto amides and ethylcyanoacetate in the presence of sodium ethoxide/ethanol.The reaction process via nucleophilic addition-elimination and tautomerism The substituent effect has little effect on the yield of the product.Whether it is electron withdrawing or electron donating substituent and increasing the number of substituents,the product can be well synthesized.The desired products were formed in good-to-high yields(82%).The structure of the products was characterized by NMR,MS,IR and elemental analysis.The effects of electronic properties of substituents,substituent position and substituent number on the thermal stability of hemp fibre raw materials and fabrics were studied.Electronic properties of substituents,substituent position and substituent number of pyridone/pyrone showed that even simple changes in small molecular structure can lead to large thermal stability effects of hemp fibre materials,that is,substituents position(meta-,ortho-,and para-)and substituents electronic effect can lead to electronic cloud distribution and density changes of structural units,resulting in differences in thermal activation energy,and changes in decomposition temperature and the carbon yield of hemp fibre raw materials and fabrics.The results of TGA analysis showed that the p-substituent structure of the donor electron of pyridone/pyrone derivatives is conductive to the increase of decomposition temperature,which can improve the pyrolysis activation energy of the products,and then improve the thermal stability of hemp fibre raw materials and fabrics.At the same time,increasing the aromaticity of substituents can also improve the thermal stability of hemp fibre raw materials and fabrics.The thermal stability of hemp fabrics was further enhanced by coupling agent modification.The SEM observation showed that the product has obvious adhesion with hemp fabrics.TGA analysis showed that the carbon yield of hemp fabrics increased from 13.5% to 29.6%.LOI analysis showed that the LOI value increased from17.1% to 29.9%.The burning test reached B1 value.