Research Of Influence Factors On The Mechanical Properties And Toughening Mechanism Of Sandbag Microstructure-Toughened PA6/EPDM-M/CaCO₃Ternary Composite

In this paper, ethylene propylene diene terpolymer rubber/maleatedethylene propylene diene terpolymer rubber （named: EPDM-M） andcalcium carbonate （CaCO₃） were employed to modified the toughness ofPolyamide6（PA6）. The influence factors of mechanical properties of PA6based ternary composites was analysed by orthogonal design; Effect ofsurface morphology of CaCO₃, tensile rate and ambient tempreture on themorphology structure and mechnical properities of PA6based compositeswere studied. The microstucture morphological evolution of “sandbag”which nano-CaCO₃coated by EPDM-M investgated by Scanning ElectronMicroscope（SEM） in the process of tensile deformation of PA6/EPDM-M/n-ano-CaCO₃. The toughening mechanism of “sandbag” microstructureparticles was further discussed from fracture energy and Crack source areas.The main works and conclusions were listed as follows:The result of Orthogonal design analysis showed that CaCO₃particle size was the key factor on the mechanical behaviors of PA6/EPDM-M/Ca-CO3. When particle sizes of CaCO₃were same, the CaCO₃which surfacecoated by nanometer spherical shaped CaCO₃or needle-like CaCO₃has alarger specific surface area than ground CaCO₃, which lead to a bettertoughening effect on the PA6based ternary composites.Tensile rate and ambient temperature have distinct effect on themechanical performance of PA6and PA6based composite. Under roomtemperature, PA6/CaCO₃composites didn’t emerge yielding phenomenonwith the increasing tensile rate. however, PA6、PA6/EPDM-M, PA6/EPDM-M/nano-CaCO₃（one step） and PA6/EPDM-M/nano-CaCO₃（two-step） sys-tem have taken place into the neck phenomenon, and deformation energy ofnecking process be reduced along with the increasing of the stretching rate.When the tensile rate was50mm/min, the tensile fracture manner of all thePA6and PA6based composites changed from ductile fracture to brittle frac-ture with the increasing temperature. In addition, the select ambiment tem-perature range had no significant effect on the impact fracture surface ofPA6and PA6/CaCO₃, but had significant affect on the others three kinds ofPA6based composites, all of them appeared ductile-brittle transition pheno-menon at15℃.The “sandbag” structure evolved in the process of PA6/EPDM-M/nano-CaCO₃（two-step） tensile deformation was observed by SEM. there wasno obvirous change before the composites generated plastic deformation. From plastic deformation until fracture, the “sandbag” structure generateddeformation along the stretching direction, and a large number of holesgenerated due to interfacial debonding between “sandbag” and matrix. Asthe tensile going on, the microfiber forming inhert the “sandbag” along thestretching direction, leading to the composites fracture, eventually.At single-edge notched tensile test, with tensile rates increasing, allthe PA6/CaCO₃composites generated brittle fracture. However, the casesof PA6, PA6/EPDM-M, PA6/EPDM-M/nano-CaCO₃（one step） andPA6/EPDM-M/nano-CaCO₃（two-step） were not same as PA6/CaCO₃,which fracture energy of them were reduced with the increasing of tensilerates. Studied the impact fracture morphology at room temperture, thefracture surface of PA6and PA6/CaCO₃were smooth, with smaller Cracksource areas. Otherwise, one step system has relatively small Crack sourceareas due to so much agglomeration of CaCO₃inside. However, bothPA6/EPDM-M and two step system have larger crack source areas. The twostep system has the largest capability of dissipation of impact energy by the“sandbag” occuerd deformation when loadding force, through formingmicrofiber inside the sandbag structure, and the matrix generating plasticdeformation at the same time. Therefore, the two step system showed arelatively high impact strength and fracture energy.