Structural Construction And Rheological Behavior Of PA1012/EPDM Ionomer Blends With Balanced Strength And Toughness

Polyamides（PA）,one of the most promising and attractive engineering plastics,havebeen widely used in many fields due to their excellent strength and stiffness,low friction and corrosion resistance.However,the intrinsic notch-sensitivity and poor toughness of PAs greatly limit their applications in many fields.Incorporating elastomer is an efficient strategy to achieve desirable toughness for PA.Unfortunately,the strength and stiffness of PA matrix will unavoidably decrease dramatically due to the addition of elastomer.Incorporating sacrifice bonds（hydrogen bonding,metal-ligand coordination complexation,and ion-dipole interaction）into PA/rubber blends to build hybrid network structure is a new way to achieve balanced strength and toughness.In this project,three novel ethylene propylene diene monomer（EPDM）ionomers neutralized by different metal ions were prepared by melt grafting,and used as toughener to obtain PA1012/EPDM ionomer blends.The effect of neutralization levels,content and neutralization ion of ionomers on mechanical properties,rheological properties,crystallization behaviors and morphologies of the blends were systematically investigated.Exploring the corresponding relationship between the characteristic viscoelastic parameters and the key mechanical parameters of PA1012/EPDM ionomer blends,and the optimal components of the blends could be determined by simple and rapid rheology test.The main results are as follows:（1）Three kinds of EPDM ionomers neutralized by Li⁺,Zn²⁺and La³⁺were successfully prepared,and the EPDM ionomer neutralized by lanthanum ion（EMG-La）showed the highest cross-linking density.The crosslinking network constructed by metal ion-COOH sacrificial bond has synergistic toughening and strengthening effect on EPDM rubber.Compared with pure EPDM,the tensile strength and fracture toughness of EMG-La with 1.5 neutralization levels are increased by 76%and 93%,respectively.（2）The PA1012/EMG-Li-X blends show obvious gelation behavior,and have the minimum gel point of 12.3wt%at X=0.5.The tensile strength of the blend corresponding to the“gel point”is 52.8 MPa,which is 1.3 times as high as that of the unneutralized blend.The notched Izod impact strength reaches the maximum value of93.8 k J/m²,which is 14.2 times as high as that of PA1012.The balanced strength and toughness of PA1012/EMG-Li blends are mainly attributed to the effect of Li⁺-COOH coordination on EPDM,the improvement of interfacial compatibility caused by Li⁺-acylamino coordination and the increasement of crystallinity of PA1012.There is a corresponding relationship between the key mechanical parameters and the characteristic rheological parameters of the blends.（3）The PA1012/EMG-Zn-X blends exhibit obvious gelation behavior,and reach the minimum gel point of 13.1wt%at X=0.5.The notched Izod impact strength of the blend corresponding to the“gel point”reaches the maximum value of 101.6 k J/m²,which is 16 times as high as that of PA1012,and the retention rate of tensile strength is 88%.There is a corresponding relationship between“gel points”and“super toughness points”.The balanced strength and toughness of PA1012/EMG-Zn blends are mainly attributed to the effect of Zn²⁺-COOH coordination on EPDM and the improvement of interfacial compatibility caused by Zn²⁺-acylamino coordination.When the content of Li Cl is 1.5wt%,compared with PA1012/EPDM-g-MAH blends,the tensile strength and bending strength of PA1012/EMG-Zn-0.5/Li Cl composite are increased by 27%and 24%,respectively,but their toughness still keeps the same level.（4）The PA1012/EMG-La-X blends show obvious gelation behavior,and reach the minimum gel point of 8.5wt%at X=0.75.The notched Izod impact strength of the blend corresponding to the“gel point”has the maximum value of 98.2 k J/m²,and its mechanical properties are correlated with rheological behavior.The notched Izod impact strength of PA1012/EMG-La-0.75 blend with 5wt%EPDM ionomer is 13.2times as high as that of PA1012（87.3 k J/m²）,and tensile strength retention rate is 94%.The balanced strength and toughness of PA1012/EMG-La blends are mainly attributed to the effect of La³⁺-COOH coordination on EPDM,the improvement of interfacial compatibility caused by La³⁺-acylamino coordination and the increasement of crystallinity of PA1012.（5）The compatibility of three kinds of EPDM ionomers with PA1012 is EMG-La>EMG-Zn>EMG-Li.Strong interfacial interaction endows PA1012/EMG-La blends to achieve balanced strength and toughness at lower ionomer content.The PA1012/EPDM ionomer blends corresponding to the“gel point”exhibit a special double-network structure,and the super toughness of the blends at the“gel points”origins from the deformation cavitation of rubber particles,the shear yield of the matrix and the pull out of PA1012-g-EPDM copolymer.