In the present work, 3-methacryloxypropyltrimethoxy-silane silanized silica(SiO_2-WD70) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide immobilized silica(SiO_2-WD70-DOPO) nanoparticles were prepared. Silica, SiO_2-WD70 and SiO_2-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/SiO_2, PP/SiO_2-WD70 and PP/SiO_2-WD70-DOPO nanocomposites were attributed to the surface modification of silica. XRD indicated that SiO_2-WD70-DOPO addition had no effect on PP crystal structure but accelerated the crystallization rate. POM determined that SiO_2-WD70-DOPO addition promoted the nucleation of PP by inducing a higher nucleation density during isothermal conditions. The surface modified nanoparticle SiO_2-WD70-DOPO might find possible application as a new type of inorganic nano-sized nucleation agent for PP.
Hanying TangQuanxiao DongPeng LiuYanfen DingFeng WangChong GaoShimin ZhangMingshu Yang
Surface modified rutile-type titanium dioxide(CST) nanorods were used as a UV absorber in polypropylene(PP) thick bars in combination with the hindered amine light stabilizer(HALS) Chimassorb? 944(C944). For all of the tested samples, the photodegradation was mainly limited in the region near the exposed surface, as proved by the carbonyl index and molecular weight. Compared with the typical HALS photostabilization system containing organic hindered phenol UV absorber Tinuvin? 328(T328), the thickness of photodegradation region for PP/C944/CST was only a quarter to that for PP/C944 and PP/C944/T328, while the rates of reduction in molecular weight and increase in carbonyl index were much lower. Optical microscopic observation showed that the evolution of surface micro-cracks in PP/C944/CST was quite different from that in the other samples, while scanning electronic micrographs revealed that the depth of the micro-cracks in PP/C944/CST was much shorter than that in the others. It is therefore concluded that the protection of CST on PP thick bars is mainly attributed to the outstanding UV-shielding and cracks-blocking abilities.
Lin QiYan-fen DingQuan-xiao DongBin WenPeng LiuFeng WangShi-min Zhang阳明书
