Study On The Preparation Of Polypropylene Based Cotton Stalk Lignin Composite Materials And Their Anti-oxidation Performance

In order to reduce the aging and degradation phenomenon of food grade polypropylene（PP）caused by thermal oxygen during molding,processing and using,enhance its anti-oxidation performance,and improve the recycling of bio-based resources in Xinjiang,this work used modified cotton stalk lignin（LG）as the filler or antioxidant to prepare three PP based cotton stalk lignin composite materials.The changes of crystallization,mechanical properties and structure of composite materials before and after aging were investigated by indoor thermal oxidation aging test,and then the influence of LG on the anti-oxidant performance of PP was discussed.The main contents are as followed:（1）Four kinds of PP/LG composite materials with different wood-plastic mass ratio were prepared by using Titanate Coupling Agent NDZ-201.Thermal analysis showed that the thermal stability performance of PP/LG composite materials was significantly improved than that of pure PP in different degrees.Crystallization performance research showed that some LG particles in PP/LG composite materials were agglomerated.The crystallization rate was slower than that of pure PP,but the nucleation crystal size was larger,the density was smaller when the addition of LG was low.However,the crystal boundary contour of the materials was not obvious and the number of spherulites decreased after the addition of LG was too high.What’s more,the diffraction peak position and crystallization peak area between PP/LG composite materials with different wood-plastic mass ratio and pure PP were slightly different,but the typical PP diffraction peaks were retained,and the crystallinity of the composite materials decreased to different degrees after thermal oxygen aging.Mechanical properties and static capillary rheological properties of PP/LG composite materials were better retained than pure PP after thermal oxygen aging,and the retention rates of impact strength and elongation at break were the best,reaching 68.1%and 77.3%,respectively,when LG additive amount was 10 wt%.The surface morphology and elemental analysis of composite materials proved that LG could slow down the degradation of PP and improve its service life.（2）Four kinds of PP-g-MAH/LG composite materials with different wood-plastic mass ratio were prepared by the grafting modified PP with MAH and ATA reagent,and the LG pretreated with Zn Cl₂.Through structure analysis,it was confirmed that the graft modification was successful and the coordination bond was formed between ligand ATA and Zn²⁺metal ions.The metal-ligand energy sacrifice bond was successfully combined into the composite materials.Four kinds of PP-g-MAH/LG composite materials were tested for thermal analysis,of which the anti-oxidation performance before and after 20 days thermal oxygen aging was studied.The results showed that the thermal stability performance of PP-g-MAH/LG composite materials was significantly improved than that of pure PP in different degrees.LG had the significant effect on the molding temperature of PP’s T_mand T_c,increasing by about 19℃and 20℃,respectively.Crystallization performance research showed that the crystallinity of composite materials with 10 wt%addition of LG was the highest before and after 20days thermal oxygen aging.After thermal oxygen aging,the impact strength and elongation at break retention rates of the composite materials with 10 wt%LG content were the best,reaching 79.1%and 86.1%,respectively.The composite materials with LG content of 15 wt%had the smoothest surface,no obvious ravine cracks,the maximum static torque at 10 min and the slowest downward trend,all of which were higher than pure PP.（3）Vanillin（VA）was prepared by UV photodegradation method from LG.Structure and thermal analysis showed that the extracted VA and the standard VA were basically consistence.The orthogonal test showed that the optimum reaction conditions were as followed:the temperature of 55℃,the UV lamp wattage of 1000 W,the reaction time of 4 h,the catalyst mass ratio of 15 wt%,the yield of VA was 34.01%.Four kinds of PP/VA materials were prepared with VA as the antioxidant,of which the thermal analysis and the anti-oxidation performance before and after 20 days thermal oxygen aging were studied.The results showed that the addition of VA could improve the thermal performance of PP,had little effect on the T_mand T_cof PP,and played a heterophase nucleation role on PP,helping PP form denser spherulites.Thermal oxygen aging test results showed that VA had good antioxidant influence on PP.When VA content was 0.9 wt%,the retention rates of impact strength and elongation at break after thermal oxygen aging were optimal,reaching 85.3%and 87.3%,respectively,and had the most smooth surface where was not present obvious fold and collapse,the largest static torque at 10 min,all of which were higher than pure PP.The tensile strength of PV-3 blown film materials changed from 13.98 MPa of pure PP to 19.73 MPa,and the elongation at break changed from 652.06%of pure PP to 703.87%,which proved that PP/VA materials still exhibited a good application prospect after blow molding.