Caustic study on stress singularities in polypropylene/CaCO3 nanocomposites with nonionic modifier

Local singularities at the crack tip of neat polypropylene (PP) and polypropylene/CaCO3 nanocomposites were studied by the reflective optical caustics method. The caustic spots were recorded by a CCD camera and the corresponding stress intensity factor was calculated. Experimental results showed that the stress intensity factor K1 increased to some extent by adding a certain amount of nonionic modifier into neat PP. However, the addition of CaCO3 nanoparticles considerably negated the desirable effect induced by the nonionic modifier. Mechanisms of such phenomenon are presented and discussed.