棉杆木质素抗氧化性能的改性及对PP抗氧化规律的研究

AbstractIn this paper,the effects of different lignin-based modified products on thescavenging capacity,molecular weight and thermogravimetric (TG)of PP as antioxidantadditives were studied.And the effect on the molding process,thermal properties,crystallization properties,oxidation induction time (OIT),mechanical properties andrheological properties before and after PP thermal oxygen aging were also studied.Themain results are as follows:1.The optimal preparation process of sodium lignosulfonate (SL)was determinedby using the hydrothermal method and the orthogonal experiment with OIT as theobjective function:the reaction temperature was 170C,the reaction time was 7h,themass ratio was 2.5:5,the pH was 12,and the OIT was 9.1+1.025min The optimalprocess for the preparation of low molecular weight lignin (DL)by thermal degradationwas determined based on the content of phenolic hydroxyl:the reaction temperature was200C,the time was 75min,the mass ratio was 2:1,and the content of phenolichydroxyl was +0.042mmol/g;The optimal preparation process of hydroxymethylatedlignin (HL)was determined based on hydroxymethyl content:reaction time was 2.5h,reaction temperature was 70'C,pH was 12,m(lignin):m(formaldehyde)was 4:12.Compared with cotton lignin (CL),the scavenging ability of modified ligninswas stronger,indicating that the modified products had better antioxidant properties.Inaddition,compared with the scavenging ability of the three antioxidants,the sequence is:HLSL>DL,indicating that the three antioxidants can significantly increase thescavenging effect of free radicals.They are new synthetic antioxidants with antioxidantproperties,which can effectively delay the oxidation of PP.Modified antioxidants canalso significantly improve the OIT value of PP;The rheological experiments alsoproved that SL/PP,DL/PP and HL/PP samples can improve the heat-resistant oxygenperformance of PP under hot oxygen shear environment.The addition of SL at 0.3%(wt%),DL at 0.5%(wt%),and HL at 0.5%(wt%)had the best antioxidant effect on PP.3.SL,DL and HL have no effect on the melt temperature of PP sample.The resultsof molecular weight and TG analysis showed that the three antioxidants have stablethermal properties,which means they have the potential to become antioxidants of PP.