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Polyaniline (PANI) was chemically synthesized by oxidizing aniline with ammonium persulfate (APS) with and without HCl, to produce granular (G-PANI) and nanorod (NRPANI) forms, respectively. NR-PANI and G-PANI were dedoped with ammonium hydroxide to yield NR-PANIdd and G-PANIdd. SEM images revealed a typical granular morphology for G-PANI and G-PANIdd, while NR-PANI, formed using a 'falling pH method', and NRPANIdd, consisted of micro/nanorods and flakes. The samples were characterized using FTIR and the level of oxidation was determined by XPS. The surface area of the samples was measured by the BET method. The free radical scavenging activity, using the DPPH assay, showed the following ranking: NR-PANI > G-PANI -- NR-PANIdd > G-PANIdd. The radical scavenging activity of the PANIs did not correlate with conductivity or surface area measurements, but was critically dependent upon the level of oxidation, and higher activity was obtained with the more reduced PANI samples. The PANI samples were examined before and after dedoping (dd) using thermogravimetric analysis (TGA), which showed small mass losses in the 200 to 300 °C temperature range, and greater mass losses due to oxidative degradation at higher temperatures. Furthermore, samples were treated thermally at 100, 125, 150, 175, 200, 250 and 300 °C for 30 min in air. SEM images did not show any pronounced effect on the morphologies of the samples from thermal treatment up to 300 °C. The ratios of the intensities (Q/B) of the predominantly quinoid (Q) and benzenoid peaks (B) from FTIR spectroscopic analysis revealed that NR-PANI and NR-PANIdd underwent cross-linking upon thermal treatment up to 175 °C and were oxidized after treatment above 175 °C. G PANI and G-PANIdd also underwent the same chemical changes with oxidation occurring above 200 °C. The free radical scavenging capacity of the samples was evaluated using the DPPH assay, and was found to be independent of the spin concentrations of the samples. All samples exhibited a rapid decline in free radical scavenging capacity when exposed to temperatures above 200 °C, indicating that any polymer processing should be undertaken at temperatures less than this value to achieve high antioxidant activity. NR-PANI/ PET blends were prepared by dispersion in a melt of PET at 265 °C. Blends with 1, 2 and 3 wt% NR-PANI loading were prepared. Optical microscopy revealed an even distribution of NR-PANI particles within the PET matrix. The blends were characterized using FTIR, XPS, DSC and DMTA. Melt flow index (MFI) values suggested hydrolysis of PET chains to lower molecular weight units when NR-PANI was blended. Some PET hydrolysis was also evident from the increasing O/C ratios with an increased NRPANI content in the composites. While the PET glass transition temperature remained relatively unaffected, the degree of PET crystallinity was increased with the addition of NRPANI. The electrical conductivity as well as the free radical scavenging capacity of PET increased with greater NR-PANI loading in the matrix. The mechanical properties of PET, however, declined with NR-PANI loading suggesting a lack of adequate interfacial adhesion between the NR-PANI particles and the PET matrix. NR-PANI/ LLDPE were prepared by dispersing NR-PANI in the melt of LLDPE at 150 °C. The composites had 5, 10, 15 and 20 wt% loading of NR-PANI. ESEM images revealed an even dispersion of NR-PANI in the LLDPE matix. Coalescence of NR-PANI particles and an increase in electrical conductivity was observed at higher loading of NRPANI. The composites were characterized further using FTIR, XPS, ESR, XRD and DSC. The composites exhibited characteristic vibrational bands due to both LLDPE and NR-PANI, but did not show any chemical interaction between the components. With an increased loading of NR-PANI in the composites, the amount of NR-PANI present on the surface of the samples increased, and the crystallinity of LLDPE decreased. The tensile strength and elongation at break of LLDPE also declined suggesting a lack of interfacial adhesion between the NR-PANI particles and the LLDPE matrix. The Young's modulus, however, increased with higher loading of NR-PANI. The composites also demonstrated very good free radical scavenging activity, dependent upon the amount of NR-PANI included in the composites. The NR-PANI/ LLDPE composites were further evaluated for active packaging applications. The oxygen permeability decreased as the amount of NR-PANI in the composites increased. The composite films also exhibited antimicrobial and antioxidant capabilities. The oxidation of fish oil was delayed in the presence of the NR-PANI/ LLDPE composites, and there was a negative correlation between oxidation and the NR-PANI content in the films. Moreover, the composites films were biocompatible to mammalian cells, meaning that NR-PANI/ LLDPE films can potentially be utilized for a range of active packaging applications. |
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