Study On Application Of Modified Lignin In Intumescent Flame Retardant PBS-based Composites

Polybutylene succinate(PBS)is a polymer with excellent properties and has been widely used in many fields.However,PBS is easy to burn,leading to a high fire safety risk.To expand the application of PBS,it is necessary to improve its flame retardancy.Lignin is a by-product from cellulose industry,having high modulus,excellent char formation performance,and abundant hydroxyl content.Therefore,lignin can be used as a carbonization agent of intumescent flame retardants(IFR)for polymers.In this thesis,lignin was modified to improve the compatibility and synergistic efficiency,and a series of flame-retardant PBS composites were prepared with modified lignin and IFR.The effects of modified lignin on the structure,mechanical properties,flame retardancy of composites were studied.The specific research contents and conclusions are as follows:(1)An esterified lignin was obtained by reacting with butyric anhydride,and esterified lignin/PBS flame-retardant composites were prepared in combination with IFR.The results showed that the hydrophobicity and dispersibility of lignin was enhanced after esterification.The tensile strength of composites prepared with esterified lignin was improved.At the same time,the esterified lignin exhibited a plasticization,which reduced the tensile and flexural modulus of composites.The improvement of dispersibility and the introduction of fatty chains led to the improvement of char-forming ability of lignin.The char layer of composites is complete and dense,and its mass was improved.After adding 19 wt%IFR and 6 wt%esterified lignin,the limiting oxygen index(LOI)of PBS could reach 31.3%,and the peak heat release rate(pHRR)reduced by 54.96%in comparison with PBS.In the UL-94 test,the dripping behavior was suppressed,and the V-0 rate was achieved.(2)A lignin chelate was fabricated with lignin-g-acrylamide and ferric chloride via two-step reaction,and was used as a carbonization agent and catalyst to prepare flame-retardant PBS composites.The results showed that the tensile properties of composites were improved due to the entanglement between PBS and lignin.At the same time,the flexural modulus and strength of composites was enhanced by the high-rigidity of lignin.In addition,the apparent viscosity of composites decreased after introducing lignin chelate,leading to the improvement of processability.A good synergy occured between IFR and lignin chelate.Compared with the specimen using 25 wt%IFR(75P/25I),after adding 1 wt%lignin chelate,the residual content of composites increased by 25.8%,and the number of pore and cracks on the char layer was significantly reduced,meanwhile,the 36.2%of LOI and V-0 rate of UL-94 were achieved.The high-quality char layer delayed combustion process effectively,reducing the pHRR and total heat release(THR)of composites.Moreover,the release of smoke was also suppressed.(3)In order to improve the compatibility of IFR,melamine formaldehyde resin(MF)was used for modification of LAPP,which was obtained by lyophilizing sodium lignosulfonate and ammonium polyphosphate(APP).Then,the properties of MFR/PBS flame-retardant composites were studied.It was found that the thermosetting MF shell improved the compatibility and rigidity of MFR,leading to an improvement of mechanical properties of PBS.With 20 wt%MFR,the tensile strength of composites reached 25.43 MPa and tensile modulus increased by 42.5%,meanwhile,the flexural strength and modulus increased by 18.6%and 40.5%,respectively.The char-forming ability of MFR was improved significantly.The maximum mass of the char reached 18.58%,and the thermal stability of composites was also enhanced.With the addition of 20 wt%MFR,41.6%of the LOI and UL-94 V-0 rate of composites could be achieved,and the LOI was improved by 18.9%in comparison with 75P/25I.