Preparation of polypyrrole and polypropylene-grafted-polypyrrole by using ultrasonic irradiation

Abstract

Ultrasonic irradiation has been used to polymerize the nanosized polypyrrole (PPy) at frequency of 20 kHz, reaction temperature of 5 oC and reaction time of 30 minutes. The intensities of ultrasonic irradiation were varied from 20% to 100%. Effects of the intensities variations on the functional group, thermal transitions and degradation behaviours, morphologies and conductivity properties were investigated. Fourier transform infrared spectroscopy (FTIR) showed broad peaks of N-H, C-H and C=C aromatic with increasing the ultrasonic intensity. The glass transition temperature, Tg, appeared at 107.93 oC for PPy polymerized under 20% intensity and kept increased until 118.07 oC under 100% intensity, as indicated by the differential scanning calorimetry (DSC) graph. Meanwhile, the PPy samples were not fully decomposed even at higher temperature of 900 oC as shown by the thermogravimetric analysis (TGA) plots. The maximum temperature and final residue was increased as the ultrasonic intensity increased from 20% to 100%. Field emission scanning electron microscopy (FESEM) micrographs showed no significant changes in size of PPy particles at various ultrasonic intensities. The conductivities of the samples were also unaffected with increasing ultrasonic intensities. Subsequently, polypropylene-grafted polypyrrole (PP-g-PPy) was prepared by using ultrasonic assisted extrusion. It was to investigate the effects of PPy composition on the functional group, rheological, tensile, morphological, electrical conductivity and thermal properties of PP-g-PPy blends. The sample of PPy polymerized under 100% ultrasonic intensity was chosen to graft with PP. The sample formulation of PP/PPy in weight % were consist of 100/0, 95/5, 90/10, 85/15 and 80/20. 1% of dicumyl peroxide was used as the initiator. Frequency of 20 kHz with temperature of 170 ± 5 oC were applied during the process of PP-g-PPy. The FTIR plots confirmed the appearance of PP-g-PPy peaks by shifting the NH stretching of PPy from 3395 cm-1 to 3379 cm-1. TGA plots showed the thermal stability of PP significantly improved by grafting with PPy, and increased with the increment of PPy content. From DSC graph, the melting temperature, crystallization temperature and degree of crystallinity of the blends were lower than the pure PP, and decreased as the PPy content increased in PP-g-PPy. The dynamic mechanical analysis plots showed the storage modulus, loss modulus and tan ? of PP-g-PPy were higher than the pure PP and increased with PPy content increased, over the whole temperature range. The tensile strength and the elongation at break were decreased while the Young’s modulus was increased as the amount of PPy increased. FESEM micrographs showed the tensile fractured surface of 5 wt% PPy content exhibit the most clear of fibrous structure, and getting lower and flat fracture surfaces were formed as the increment of PPy content. The conductivities of samples increased as the compositions of PPy were increased. All the blends and pure PP demonstrated pseudoplastic flow and shear thinning behaviour where the viscosity decreased with the increasing shear rate, as shown in rheology plots. The viscosity increased when PPy content was introduced into PP matrix, and increased with the PPy content. Based on the study conducted, the intensity of ultrasonic irradiation can effects the functional group, thermal transitions and degradation behaviours of prepared PPy and also PPy composition can influence the properties of PP-g-PPy blends.