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a Universidade Federal do Rio de Janeiro, Instituto de Macromoléculas Professora Eloisa Mano ‐ IMA P.O. Box 68525, 21945‐970 Rio de Janeiro, Brasil Experimental Introduction Poly(3-hydroxybutyrate), PHB is a biodegradable polymer that has been widely studied. However, PHB possesses unfavorable properties such as high crystallinity, which lead to brittleness, and low resistance to thermal degradation, which cause the material to be easily degradable. The nanofillers are capable of altering and improving the matrix properties, even when added in small proportions. There is growing interest in developing nanocomposites composed of organic polymers and titanium dioxide nanoparticles. Some features include the mechanical, dielectric, thermal properties, favoring the Nanocomposites preparation All nanocomposites were prepared by solution casting using tetrachloroethane (TCE) as solvent. The PHB in TCE was stirred for 24 h. The fillers were dispersed using ultrasonic bath for 30 min at a concentration of 0.5 % (w/w) in total mass of the system (1.2 g), with weight ratios of 2:1, 1:1 and 1:2 for TiO 2 and SiO 2 . PHB and nanofillers solutions were mixed together for a further 24 h, then they were cast onto plates and kept in oven to eliminate the solvent. *E‐mail – [email protected] features include the mechanical, dielectric, thermal properties, favoring the biodegradability, optical properties, bactericidal effect, magnetic characteristics and permeation. Nanosilica has been used as inorganic filler in polymers because of its high surface area and stability. It can be used for reinforcement of polymer matrices to lower shrinkage on curing, decrease thermal expansion coefficients and improve adhesion properties and corrosion resistance. The low field NMR is another technique that can be used together with the others techniques to determine proton spin-lattice relaxation time (T 1 H) parameter, using the traditional inversion-recovery pulse sequence. The values of this parameter allow us to provide detailed information on mobility at the molecular level. According to this context, the aim of this work was to evaluate the XRD Analysis X-ray diffraction (XRD) was used to calculate 00. It was performed using a Rigaku diffractometer with CuKα radiation (λ = 0.154 nm, 40 Kv, 120 mA) at room temperature, sacnning over the 2θ range, from 2° to 40° in 0.05° steps, at a rate of 1°/min. Low Field – NMR AnalysisThe relaxation time was analyzed in a Maran Ultra lowfield NMR spectrometer (Oxford Instruments – UK), using an 18 mm NMR tube, operating at 23 MHz for the hydrogen nucleus. The pulse sequence used to obtain data on spin lattice relaxation time was inversion-recovery (recycle delay – 180° – τ – 90° - acquisition data) and the 90° pulse of 4.5 μs was calibrate automatically by the instrument`s software. The amplitude of the FID was sampled for 40 τ data points, dispersion of TiO 2 and SiO 2 in PHB matrix . The low field NMR technique provide the understanding of structural differences, due to the domain formation, and also detailed information on molecular mobility at the molecular scale. ranging from 0.01 to 20000 ms and 8 scans for each point. The relaxation values and relative intensities were obtained by fitting the exponential data with the aid of the program WinFIT (version 2.4.0.0). Distributed exponential fits by plotting the relaxation time were performed using the software WINDXP. Results e Discussion Table 1: Degree of crystallinity (Xc) for all nanocomposites Sample Xc (%) Sample Xc (%) PHB 47 PHB3S025 42 PHB3T017 54 PHB3S05 41 PHB3T025 42 PHB3S1 65 PHB3T05 45 PHB3TS21 34 PHB3T1 83 PHB3TS11 23 PHB3S017 28 PHB3TS12 33 Fig. 1: X-ray diffractograms of the nanocomposites PHB/TiO 2 Fig. 2: Domains curves for nanocomposites of PHB/TiO 2 Fig. 3: Domains curves for nanocomposites of PHB/SiO 2 Fig. 4: Domains curves for nanocomposites of PHB/TiO 2 /SiO 2 Table 6 - Relaxation times for all nanocomposites Sample T 1 H (ms) Sample T 1 H (ms) PHB 614 PHB3S025 650 PHB3T017 619 PHB3S05 614 PHB3T025 589 PHB3S1 627 PHB3T05 611 PHB3TS21 630 PHB3T1 553 PHB3TS11 618 PHB3S017 605 PHB3TS12 579 Acknowledgments TiO 2 and SiO 2 had influence on proton relaxation indicating that both were dispersed in PHB matrix. Conclusion The results show how useful is the low field NMR technique to investigate systems with two nanofillers.
