Study On High-Presure Crystallization Of Peek And Peek/C60Nanocomposite

Fullerene/polymer composites have recently attracted considerable attention from the materials research community. It has been shown that incorporating fullerene or its derivatives into a polymer matrix could significantly improve its photovoltaic, electromechanical and thermomechanical properties. Physical mixing by utilizing organic solvents, one of the simplest techniques, resulted in the environmental problems due to the difficulty of the completely removal of the used solvents. Although fullerenes functionalized with hydrophilic groups may promote their through dispersion and strong adherence in a polymer matrix, they lost certain precious properties of original fullerenes. Furthermore, he properties of fullerene/polymer composites are closely related to the morphologies of the polymers formed during melt or solution processing. Solid phase forming under high pressure is also known to be an effective route to create desired crystal morphologies with ideal molecular orientation. However, no investigation on fullerene/polymer composites has been performed at high pressure.Herein, we prepared well dispersed fullerene C60/poly (ether ether ketone)(PEEK) composites, and investigated the high-pressure crystallization behaviors of PEEK and C60/PEEK. One reason for choosing PEEK as the research subject is that its fullerene composite has not been successfully fabricated yet, mainly due to its excellent chemical resistance as well as high processing temperatur. Also, to the best of our knowledge, no investigation was performed on PEEK at high pressure. The results are as follows:1. The high-pressure crystallized PEEK samples were prepared with a piston-cylinder apparatus by varying temperature, pressure, crystallization time and molecular weight, and were investigated using wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The applied etching experiments showed that the solvent-proof and anticorrosion performance of the polymer could be significantly improved through the high-pressure treatment. The results also revealed that PEEK spherulites with folded-chain lamellar as substructures and with different characteristics were formed at high pressure. Crystalline elliptical micro-spheres consisted of flake-like lamellae with rugged surfaces were disclosed with SEM, which may diversify niche applications in functional fillers, carriers, adsorbents and so on. Morphological observations suggested that such micro-spheres might possibly be evolved from a novel dendritic crystal. Furthermore, a granular substructure of the lamellae was observed in such single-phase polymer system with rigid molecular backbones, which further confirmed the model developed by Strobl for polymer crystallization.2. The effect of pressure on fullerene/polymer composite was investigated for the first time. C60/PEEK composites with an overall good C60dispersion were prepared by an easy and environmentally friendly approach. Novel spherulitic structures, which morphology and size can be controlled by the variation of temperature and pressure, were induced by C60nano-aggregations with various morphologies at high pressure. Combining the excellent properties of C60and PEEK, some C60-nucleated spherulitic forms, such as the dendritic spherulites, may be used as surface active materials in functional applications. The study presented here suggested that fullerene was a promising material in promoting the formation of new polymeric structures at high pressure.3. Physical mixing of PEEK and C60by utilizing an organic solvent, dichloroacetic acid, resulted in a composite which lost the precious thermal stability of the original starting materials. However, the colorimetric observation showed that the dissolution of PEEK in dichloroacetic acid was hastened by the introduction of C60.4. The high-pressure crystallized PEEK samples were investigated using thermogravimetric analysis (TGA) and SEM. The results showed that the thermal stability of PEEK could be improved through appropriate high-pressure treatment. Although the10wt.-%loss temperature and maximum decomposition temperature of the PEEK samples decreased with the increase of crystallization temperature and crystallization time, the effect of the applied pressure on preventing them from further degradation was obviously observed. The amorphous region of certain PEEK samples was eroded off after high-temperature degradation, which made the details of the spherulitic structures revealed more clearly using traditional etching technique. PEEK spherulites with different characteristics were disclosed with SEM, including those with sheaf-like structures, quench haloes or interpenetrating fibrils. Furthermore, TGA results on the as-prepared C60/PEEK composites showed that the thermal stability of PEEK was decreased by the introduction of C60. Especially, it decreased with the increase of C60loading levels. The study presented here may be instructive to the applications of the polymer under such ultimate environmental conditions as high pressure and high temperature.