Preparation And Properties Of Biomass-based Intumescent Flame Retardant Polypropylene Composites

Polypropylene（PP）,as a typical semi-crystalline thermoplastic,has high chemical resistance,electrical insulation,impact resistance and wear resistance,is widely used in machinery,construction,textile,packaging and other fields.However,the limited oxygen index（LOI）of PP material is only about 17.5%,and its heat resistance is poor,combustion heat is high and accompanied by"melting drop"phenomenon,which seriously hinders its practical application.Therefore,it is of great significance to solve the fire risk problem of PP.Expansion type flame retardant（IFR）is a kind of environmental protection flame retardant with high efficiency and low toxicity.The system itself has synergistic effect of acid source,carbon source and gas source.When burning,stable expansion carbon layer will be generated on the surface of the matrix material,which has the effect of heat insulation,oxygen isolation,smoke suppression and drip prevention.However,pentaerythritol（PER）,a common carbon forming agent,is a petroleum based compound,which is easy to absorb moisture,easy to migrate and non-renewable.Therefore,in this paper,silica aerogel coefficent and biomass-based carbonizing agent were prepared to form a new expansive flame retardant system,and expansive flame retardant PP composite materials with different proportions were prepared,and the physical and chemical characterization and performance test of the samples were conducted.The main research contents are as follows:（1）Hydrophobic silica aerogel（SA）was prepared by sol-gel method as a coagent,which together with ammonium polyphosphate（APP）and dipentaerythritol（DPER）formed an expansive flame retardant system.SA/APP/DPER/PP composites were prepared by melt blending method.The effect of SA on flame retardancy and char formation of PP composites was studied by combustion test,thermogravimetric analysis,mechanical property test and smoke density test.The results showed that the LOI of SA@APP/DPER/PP increased from 17.5%to 26.7%,and UL-94 reached V-0grade.The tensile strength,elastic modulus and elongation at break of 2 wt%PP were 23.54 MPa,257.27 MPa and 75.29%respectively.When the smoke density was tested for 600 s,the transmittance of PP reached 28.82%.Raman test shows that the R value of PP is 1.05,which has the best stability of carbon slag.The addition of SA can effectively improve the thermal stability and carbon formation of the composites.（2）In order to further improve the carbon rate of PP,silica coated lignin（Si O₂@AL）was prepared by sol-gel method,FTIR and XRD tests showed that the coating was successful.The combustion test,smoke test and carbon residue analysis of the flame retardant composite were carried out on Si O₂@AL/APP/DPER/PP flame retardant composites.The results show that when PP composite UL-94 with 4 wt%Si O₂@AL reaches V-0 grade,the LOI value reaches 27.6%.Si O₂@AL/IFR/PP has good stability at high temperature.Compared with PP,the thermogravimetric rate is increased by 1.75%,and the residual amount is increased by 0.5 times at 800℃.The smoke density test and carbon SEM analysis showed that the addition of Si O₂@AL made PP form a more stable honeycomb carbon layer,and the total smoke release showed a decreasing trend.（3）In order to achieve a better flame retardant effect,melamine polyphosphic acid（MPP）and modified lignin（Si O₂@AL）were introduced to mix for the expansion flame retardant PP material.The results showed that ul-94 reached V-0 grade when the total amount of flame retardant was 25 wt%（MPP/DPER/Si O₂@AL=6:2:1）.TG results showed that the residual mass reached 14.64%at 800℃.The tensile strength of PP is 12.50 MPa and the elongation at break is 34.43%.In the smoke density test,when the total amount was 25 wt%（MPP/DPER/Si O₂@AL=4:1:1）,the smoke suppression effect was greatly improved,and the D_S10 reached 5.37%.The combination of MPP,DPER and Si O₂@AL shows good synergistic effect and can effectively improve the flame retardant performance of PP.