The Crack Propagation And Fracture Behavior For The Composites Of Polypropylene Filled With Inorganic Particles

This work, as a sub-project to analyze the relationship between structure and fracture properties of polymer, granted by National Nature Science Foundation, is an attempt to study the plane-stress fracture performance of CaCO3 particles and coal gangue powder filled PP composites, with and without the modifier incorporated, respectively, using the essential work of fracture (EWF) method.For CaCO3 particles filled PP composites, the validity of EWF evaluation was verified at first. The crack propagation and the character, size and development of the plastic deformation zone ahead of the crack tip were observed and illustrated on line. The influence of CaCO3 and PP-g-MA content on the essential work of fracture, plastic deformation work, crack opening displacement, etc., was analyzed and the edge of plastic zone was measured accurately to seek the interrelation between the plastic work and composition. The distribution of fracture energy in different stages was discussed through a rational method for energy partition. The critical crack opening displacement (COD)C method was employed to predict the specific essential work of fracture. The comparison between the estimated (through (COD)C ) and directly measured (through EWF) values of we provided preference for the physical meaning of (COD)C parameters, thus explained the deformation behavior and fracture properties of the composites through another method. It was found that the plane-stress EWF approach worked well for the pure PP, PP/CaCO3 and PP/CaCO3/PP-g-MA composites, which all behaved in a typical ductile tearing manner as full yielding of ligament and stable propagation of crack. The specific essential work of fracture, we, of PP/CaCO3 composites was appreciably lower than that of pure PP, while the specific plastic work item, βwp, decreased markedly with increasing CaCO3 content as both the values of β and wp decreased. For the composites modified with PP-g-MA in which the mass ratio of PP to CaCO3 was fixed, we increased considerably at first and then decreased with increasing amount of PP-g-MA, while wp increased remarkably. The effect of CaCO3 andPP-g-MA, respectively, on both the fracture toughness and the plastic deformation energy, was mainly achieved through their influence on the properties in necking and tearing procession after yielding. It can also be found Pwp, which presented the total plastic deformation energy dissipated on the crack tip, and the displacement to failure, which measured the ductility; wpand the maximum load per unit ligament area for both PP/CaCO3 and PP/CaCO3/PP-g-MA composites varied in consistent direction, respectively. The estimated and directly measured values of we also varied in completely consistent direction and the numerical discrepancy between them was not apparent, though the absolute identity cannot be achieved. And it was shown that the slope of eb-l curves, ep, which was rarely discussed in the literatures, had similar variation with p.Then, another kind of filler particles—coal gangue powder was filled into polypropylene, and the adhesion on the interface was feinforced using proper surface agent and modifier. The effects of different kind of PP matrix and coal gangue powder contents, as well as the powder treated with different modifiers on the mechanical and processing performance were investigated. The results of conventional tests showed that with increasing content of the coal gangue powder, the tensile elongation at break and impact strength decreased while the tensile yielding strength and MFR changed little; the use of stearic acid in the treatment of the coal gangue powder could improve the elongation at break, impact strength and processability of the composites. The tensile strength and impact strength can be improved with incorporation of PP-g-MA. The results of fracture toughness of the composites showed that the we value decreased remarkably at low content of coal gangue powder while the pwp value was definitely higher than that of pure PP. However, an increase instead of gradual reduction of the we values were observed with the further increase of coal gangue powder content and they were slightly lower than that of pure PP, while the Pwp values decreased gradually with increasing content of coal gangue powder and all of them were lower than that of plane PP. The we values of the ternary composites with PP-g-MA incorporated varied fluctuantly while the Pwp values increased firstly then decreased with increasing amount of PP-g-MA, which showed that PP-g-MA of proper amount can improve the plastic deformation ability of the composites.