Isothermal crystallization of polypropylene/surface modified silica nanocomposites

In the present work, 3-methacryloxypropyltrimethoxy-silane silanized silica（SiO2-WD70） and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide immobilized silica（SiO2-WD70-DOPO） nanoparticles were prepared. Silica, SiO2-WD70 and SiO2-WD70-DOPO were incorporated into polypropylene（PP） by melt compounding. Differential scanning calorimetry（DSC）, X-ray diffraction（XRD） and polarized optical microscopy（POM） were employed to investigate the isothermal crystallization behavior of PP and PP/silica composites. The kinetic constant（kn）, and half crystallization time（t1/2） were calculated by Avrami equation,while the surface free energy of folding was calculated by Lauritzen-Hoffman theory. The increased kn, decreased t1/2 and the surface free energy（σe） in the order of PP, PP/SiO2, PP/SiO2-WD70 and PP/SiO2-WD70-DOPO nanocomposites were attributed to the surface modification of silica. XRD indicated that SiO2-WD70-DOPO addition had no effect on PP crystal structure but accelerated the crystallization rate. POM determined that SiO2-WD70-DOPO addition promoted the nucleation of PP by inducing a higher nucleation density during isothermal conditions. The surface modified nanoparticle SiO2-WD70-DOPO might find possible application as a new type of inorganic nano-sized nucleation agent for PP.