Preparation And Performance Study Of High-performance Flame-retardant Polylactic Acid Composite Materials

Poly（lactic acid）（PLA）is a thermoplastic aliphatic polyester with the advantages of high strength,high modulus,excellent biocompatibility,biodegradability,easy molding and processing.It is a promising new green and friendly material.However,due to its poor toughness and flammability,the wide application of PLA is seriously limited.In response to these issues,this article utilizes the flame retardant mechanisms of phosphorus based flame retardancy,phosphorus nitrogen synergistic flame retardancy,organic inorganic hybrid synergistic flame retardancy,and phosphorus nitrogen boron multiple synergistic flame retardancy.Four green additives were synthesized around phytic acid to toughen and flame retardant PLA.PLA composite materials were prepared by melt blending,and the mechanical properties and flame retardancy of PLA composite materials were tested using a universal material testing machine and an oxygen index meter,It mainly includes the following four aspects:1.The microcrystalline cellulose（MCC-GMA）rich in epoxy groups was obtained by grafting glycidyl methacrylate on the surface of microcrystalline cellulose,and then the phosphorus flame retardant（MCC-GMA-PA）was obtained by the ring-opening esterification reaction with phytic acid.The effect of different additions on the performance of PLA was investigated.It was found that the mechanical properties first increased and then decreased with the increase of the addition amount.Compared with pure PLA,when the addition amount is 4wt%,the elongation at break increases from 3.9%to 7.1%,the tensile strength increases from 61.8 MPa to 77 MPa,and the impact strength increases from 5.08 J/m to 6.3 J/m.MCC-GMA-PA improved the crystallinity and thermal stability of PLA.With the increase of the addition amount,the crystallinity increased from 27.4%to 39.9%,T_c decreased from 107℃to 99.2℃,and T_on increased from322.9℃to 327℃.In terms of flame retardancy,MCC-GMA-PA promoted the carbon formation of PLA,and the LOI reached 21.9%at the addition of 6wt%.2.In order to further improve the flame retardancy,a phosphorus-nitrogen synergistic flame retardant（MCC-GMA-PA-MEL）was obtained by self-assembly of MCC-GMA-PA and melamine,and the effect of different additions on the performance of PLA was studied.It was found that compared with pure PLA,when the addition amount was 4wt%,its mechanical properties were basically maintained,while its thermal properties and thermal stability were significantly improved.The crystallinity increased from 27.4%to41.01%,T_c decreased to 101℃,and T_on increased to 334.7℃.In the aspect of flame retardancy,because MCC-GMA-PA-MEL promotes the carbon formation of PLA,NH₃ generated by thermal decomposition can dilute oxygen,and the surface lamellar structure plays a barrier role in the mass transfer process.When the addition amount is 4wt%,the LOI increases to 25.7%,which can reach the V-0 level in UL-94 test.3.In order to toughen and flame retard effectively,the organic-inorganic hybrid flame retardant zirconium phytate（Zr-IP₆）was synthesized with sodium phytate（IP₆）and zirconium oxychloride octahydrate as raw materials.It was found that the mechanical properties increased first and then decreased with the increase of Zr-IP₆ content.Due to the unique porous network structure of Zr-IP₆,when the content of Zr-IP₆was 4wt%,the elongation at break increased from 3.9%to 6.6%,and the impact strength increased from 5.08J/m to 10.28 J/m.At the same time,the addition of Zr-IP₆ improved the crystallinity,thermal properties and thermal stability of PLA composites,T_c decreased significantly,and crystallinity and T_on increased significantly.In terms of flame retardancy,the combustion time is significantly shortened,and the LOI reaches 24%at the addition of 4wt%.4.In order to effectively flame retardant PLA and improve the melting drop phenomenon,a phosphorus nitrogen boron multiple synergistic flame retardant（BA-PA-MEL）was prepared with phytic acid,boric acid and melamine as raw materials,and the effect of different additions on the performance of PLA was investigated.It was found that the crystallinity was significantly improved while the mechanical properties and thermal stability were basically unchanged.When the addition amount is 4wt%,T_c decreases 6℃and the crystallinity increases from 27.4%to 47.4%.In terms of flame retardancy,BA-PA-MEL promotes the carbon formation of PLA,and NH₃ generated by thermal decomposition can dilute combustible gases.The LOI increased from 19%to 25.7%,and the melting drop phenomenon was improved.When the addition amount was 4wt%,it could reach the V-0 level in UL-94 test.