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-phospha- phenanthrene-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 k,, decreased t1/2 and the surface free energy （ere） in the order ofPP, 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.