Study On Preparation And Ageing-resistant Performance Of Epoxy Resin Modified By Lignin

Corn stalk lignin is a biological refining byproduct derived from corn stalk.It has good compatibility with polymer and was suitable for use in polymer preparation and modification for its high purity,insoluble in water and large amounts of reaction sites in its molecular structure.In this paper,corn stalk lignin was used to blend with bisphenol A epoxy resin at 100^oC for 1 hour to improve the properties of the epoxy resin,thus lignin-modified epoxy was obtained.The influence of the lignin amount on the properties of lignin-modified epoxy was investigated.The results show that the viscosity of modified epoxy is increased after pretreatment in high temperature when the lignin amount increased.The bending strength of the cured lignin-modified epoxy initially increases and then decreases,and its impact strength decreases with the increase of lignin content.But the glass transition temperature（T_g）enhances gradually and the thermal stability is improved.And the burning properties of the lignin-modified epoxy were investigated.The results showed that when the thermal radiation power was 50 kW·m^-2,compared with the unmodified cured epoxy resin,it was helpful for epoxy resins to burn into charcoal and shorten the flaming combustion time after the lignin was added,the heat release rate decreased in the early stage of the combustion,and increased in later stage of the combustion,the total heat release increased slightly in the later stage of the combustion,the total emission of smoke did not change significantly,and effective heat of combustion decreased.The speed of thermal decomposition to generated combustibles was reduced after the addition of lignin,which led to the reduction of quality losses.Corn stalk lignin acted as a burning retardant in epoxy resin.The changes of thermal ageing time on the properties of lignin-modified epoxy resin performances were investigated.Under the effect of thermal aging,the bending strength of the modified resin increase first and then decreases with the extension of aging time.The presence of lignin is beneficial for the increase of epoxy resins’bending strength,but has little influence on the impact strength.The damping loss factor decreases gradually,and the glass transition temperature increases firstly and then decreases.The addition of lignin decreases the damping loss factor and increases the glass transition temperature.The thermal stability of the material decreases slightly with the presence of lignin,but its falling range is less than the non-modified epoxy resin.The thermal ageing of epoxy resin on the surface and the internal occurred at the same time.The surface of the lignin modified epoxy resin changed little in comparison with unmodified epoxy resin in the same condition.The changes of lignin-modified epoxy resin properties was studied with the thermal-oxidative ageing.It shows that,with the extension of ageing time,the bending strength of the modified resin increases initially then decreases,especially,the falling extent of the bending strength of lignin-modified epoxy is lower than the non-modified epoxy,thus the addition and modification of lignin keeps the mechanical properties of epoxy resin in a certain extent;it has little effect on the impact strength with or without the addition of lignin after the thermal-oxidative aging;The modulus’change range of the lignin modified epoxy declines compared with non-modified epoxy resin in same condition;the glass transition temperature of non-modified epoxy resin increases initially and then decreases while the glass transition temperature of lignin-modified epoxy resin has a little change;the thermal stability’s changing range of lignin-modified epoxy is less than non-modified epoxy resin’at the same thermal oxidative ageing condition;lignin could be decomposed to delay the main chain’s ageing of epoxy resin under the thermal oxidative ageing,and the effect of thermal oxidative ageing resistant is superior to thermal ageing;the surface damage is more serious in thermal oxidative ageing than thermal ageing.As the humid-thermal ageing time lasts,the bending strength and impact strength decreases,the damping loss factor and glass transition temperature both decreases,and the thermal stability all decreases for both modified and non-modified epoxy.The addition and modification of lignin has little effect to the humid-thermal ageing properties of epoxy resin.