Toughening And Strengthening Of Polylactic Acid Based On Blending Core-shell Polyacrylate And MXene

Polylactic acid(PLA)has the advantages of biodegradability and excellent mechanical properties,but the poor toughness of PLA limits its application.The core-shell acrylate polymer(ACR),as toughening agent,was synthesized by semi-continuous seed emulsion polymerization to toughen PLA.However,the rigidity of PLA would reduce after being toughened.Therefore,two-dimensional Ti₃C₂T_x MXene nanosheets were further introduced as the reinforcing agent through in-situ etching.GMA(glycidyl methacrylate)-ACR/MXene hybrid(GACR/MXene)with uniform dispersion and mutual combination were prepared by binary colloidal liquid phase mixing approach.It was further melt-blended with PLA,so as to achieve a reinforced polymer nanocomposite with effect of strong synergy and balanced stiffness-toughness.(1)ACR and ACR modified by interfacial capacitive monomer methacrylic acid(MAA)and glycidyl methacrylate(GMA)(defined as MACR and GACR)were prepared by semi-continuous emulsion polymerization and were characterized by particle size test,infrared analysis,transmission electron microscopy,differential scanning calorimetry and dynamic mechanical analysis.Ti₃Al C₂ MAX phase was in-situ etched by hydrofluoric acid to be translated into two sizes of Ti₃C₂T_x MXene nanosheet(less than 10?m and greater than 50?m).And they were characterized by X-ray diffraction,infrared analysis and scanning electron microscopy.(2)The effects of ACR particle size,core-shell ratio and addition amount on PLA/ACR composites were investigated.With increasing of ACR particle size,the tensile toughness and impact toughness of PLA composites showed a trend of firstly increasing and then decreasing.The best toughening effect was achieved when the particle size of ACR was 81.05 nm,in which the elongation at break(47.10%)and impact strength(39.56 k J/m²)were 7.19 and6.67 times of that of pure PLA respectively.With increasing of ACR core layer ratio,the tensile toughness of PLA composites decreased from 11.31%of core-shell ratio(3/2)to 6.80%of core-shell ratio(3/1),and the impact toughness was remained at 10.30±0.4 k J/m².With increasing of ACR content,the tensile toughness of PLA composites firstly increased to 18.54%of 15%content and then decreased,while the impact toughness increased to 13.20 k J/m² of30%content.(3)The influence of MACR and GACR on PLA/MACR and PLA/GACR composites was investigated.It was found that the more carboxyl groups on the surface of MACR,the lower the tensile toughness of PLA composites,but the impact toughness maintained a higher level overall.When MAA accounted for 1.5%of the total mass of the main monomer,the impact strength reached the maximum value(22.21 k J/m²),which was 3.75 times of that of pure PLA and 2.08 times of that of the PLA/ACR without adding MAA.The results show that the structural similarity of MAA is very obvious for the increasing of impact strength.The more epoxy groups on the surface of GACR,the higher the tensile toughness of PLA composites,while the impact toughness firstly increased and then decreased.When GMA accounted for 3.0%of the total mass of the main monomer,the elongation at break was the highest(146.05%),which was 20.17 times of that of pure PLA and 17.24 times of that of the PLA/ACR without adding GMA.The results show that the reactive interfacial compatibilization of GMA could significantly enhance the elongation at break.(4)GACR/MXene mixtures were prepared,which were uniformly dispersed and combined with each other in PLA composites.The effects of addition amount and size of MXene on PLA/GACR/MXene composites were investigated.With increasing of MXene content,the tensile strength,bending modulus,tensile toughness,impact toughness,crystallinity and compatibility of PLA composites firstly increased and then decreased.When the content of MXene was 0.4 wt%,the maximum tensile strength(54.57 MPa)was achieved,which improved by 12.10%over that of PLA/GACR.When the content of MXene was 1.0wt%,the impact strength(8.25 k J/m²)and elongation at break(27.06%)got the largest,which were 2.38 and 3.74 times of that of pure PLA respectively.The tensile strength and bending modulus increased by 9.12%and 6.86%over PLA/GACR respectively,.In addition,the tensile strength,bending modulus,impact toughness,crystallinity and compatibility of PLA composites with big size MXene(more than 50?m)were inferior to those of PLA composites with small size MXene(less than 10?m),except the tensile toughness.The mechanism of stiffness-toughness balance was discussed.The toughening mechanism were contained with the silver streaks-shear band and cavitation of GACR,the reactivity of interface between PLA and GACR,crack deflection and crystallization toughening of MXene.Strengthening mechanisms were contained with bridging effect of MXene,crystallization strengthening lead by heterophase nucleation and hydrogen bonding effect between PLA,GACR and MXene.