Study On Modification Of Polylactic Acid With Lysine Based Biological Flame Retardant And Its Mechanism

Polylactic acid(PLA),as one of the excellent bio-based plastics,has attracted much attention.However,the high flammability and poor toughness of PLA limit its further application.In addition,the hydrolysis degradation of pure PLA in natural environments(such as water or soil)is slow,and how to improve its hydrolysis degradation rate is also an urgent problem to be solved.Based on the above issues,this paper designs bio-based flame retardant systems with different structures to modify PLA from the perspectives of flame retardancy,toughening,and environmental protection,and studies their impact mechanisms on the degradation behavior of PLA,Specifically reflected in:Firstly,in order to solve the above problems,the bio-based flame retardant DL was designed and prepared in water phase without any organic solvent by using lysine(Lys),derived from animals and beans,and diethylenetriamine penta-(methylenephosphonic)acid(DTPMPA),a scale treatment agent,as raw materials.The combination of the flame retardant DL and polyethylene glycol(PEG)endowed PLA with UL94 V-0 rating and limited oxygen index(LOI)value of 29.4%.The crystallinity degree of PLA with 4 wt%PEG and 6 wt%DL were improved to 39.0%,and the elongation at break,notch impact strength,and unnotched impact strength were increased by 8.25%,9%,and 17%,respectively,compared to pure PLA.Moreover,the aqueous degradation of PLA in the purified water at the ambient temperature was accelerated by the addition of DL and PEG,manifested by the 38%decrease in Mw of PLA.Through the analysis of degradation products,the degradation mechanism was further elucidated.Secondly,considering that DL and PEG have a certain reduction effect on the mechanical strength of PLA,such as Young’s modulus and tensile strength,graphite oxide oxide(GO)with enhancement effect is used to further modify PLA.In order to better disperse GO in the PLA matrix,GO was chemically grafted onto PEG to obtain PEG-GO,which was then introduced into the PLA/4PEG/6DL system.The data shows that this system has a good improvement effect on the flame retardancy,mechanical properties,and UV protection performance of PLA.PLA/4PEG-0.08GO/6DL reached UL-94 V-0,with LOI value increased from 24.7%of pure PLA to 29.7%.The impact strength increased by 27.5%compared to pure PLA,and the Young’s modulus also increased from 3401 MPa to 3439 MPa.In addition,its UPF value is as high as 2000,while pure PLA is only 1.34.Finally,considering the lack of charring agent in the bio based flame retardant DL system,it is difficult to form a continuous protective carbon layer in the PLA combustion process,resulting in a large amount of smoke release,so the DL flame retardant was modified by solid phase condensation method using the reaction activity between the groups in the molecular structure of DL and charring agent Tannic acid(TA),and the intumescent flame retardant TA-DL-200 with "three sources" was prepared.The data shows that the Tonset of PLA/TA-DL-200 system is higher than the corresponding PLA/DL system,achieving better thermal stability improvement.And the Rmax of PLA/10TA-DL-200 system(38.84%/min)is 42.9%lower than that of pure PLA.The TSR of PLA/5TA-DL-200 was reduced by 33.0%compared to that of PLA/5DL,achieving better smoke suppression effects.In addition,compared with DL,TA-DL-200 to a certain extent inhibits the degradation effect of flame retardants on PLA matrix,achieving better mechanical properties.The elongation at break of PLA/5TA-DL-200 is 15.5%higher than that of PLA/5DL,and the impact strength is 39.1%higher.Similarly,the UPF value of PLA/10TA-DL-200 is 2000,achieving extremely strong UV protection performance.