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The behavior of some samples of commercial polystyrene, thermally degraded, was investigated by UV-VIS and fluorescence methods. Excited with different wavelengths in the domain 315-365 nm, the spectra show a peak located at 409 nm. The amplitude and the shape of this peak change after thermal degradation. Minor changes appear at 200°C, indicating relatively stability of the samples, but the modifications are more important at 350°C. At that temperature the samples are affected by oxidation. [ABSTRACT FROM AUTHOR]

Thermal degradation of commercial polystyrene was investigated by XRD and FT-IR metods. The samples were heated 30 minutes at temperatures 140°C, 200°C, 250°C, 300°C and 350°C and then brought back to room temperature. XRD investigation denotes structural modification for samples heated above 200°C. This modification is confirmed by FT-IR measurments. Some vibration bands are affected by thermal degradation at temperatures higher than 200°C. Both FT-IR and XRD methods reveal modification of microscopic structure of the polystyrene submitted to thermal degradation. [ABSTRACT FROM AUTHOR]

The recent interest in the field of bioplastics is to obtain packaging material from pure starch without synthetic polymers. The rheological behaviour represents one of the most important feature of such materials. Samples with different ratio of starch, glycerol and water were prepared and investigate regarding their rheological behaviour. After the samples reaches their limit of swelling and were completely decomposed viscosity was measured with a Brookfield DV-III Ultra rheometer at different temperatures and share rates. The data were analyzed with Kaleidagraph software. For a given sample our measurements show that the viscosity is dependent on share rate and switches from a non-Newtonian to a Newtonian behaviour in function of temperature and sample composition. We used the power law model to describe this dependence and for a given set of data there is only one output for the fit parameters. We consider the best fit of the experimental data when the curve traced by the computer passes almost through all experimental points. In the present research work we establish a particular algorithm of mathematical analysis of experimental data which allows a separation of the contribution of each variable to the viscosity. [ABSTRACT FROM AUTHOR]

The starch in native forms or chemically modified is found as the main component of biodegradable packaging materials. Regarding this the water can produce a fast degradation, of the order of days, of such materials. Four types of packaging materials, one witness and three with different starch, glycerol and water ratios were subjected to natural degradation after absorption of distilled water. The degradation process was monitored by various NMR relaxometry methods based on the measurement of CPMG (Carr-Purcell-Meiboom-Gill) decays with a T1 filter to exclude the signal from free water. The analysis of NMR signal decays was performed using a Laplace inversion algorithm and the dynamic components were identified from the T2 transverse relaxation times distributions. We found that the best package with 68/17/15 ratios between starch/glycerol/water is extremely degraded after just one day forming a colloid substance. After that in time we observe a quasisolid precipitation at the bottom of NMR tube. The reduction of dynamics is observed also in the T2-distributions measured for 5 days. The most resistant package (78/19.5/2.5) was that with a large content of starch but which was also reaching the swallow limit in five days and start to be decomposed. [ABSTRACT FROM AUTHOR]

Some physical properties of poly (acrylic acid) gels with embedded gold nanoparticles, (PAA-GNP), as prepared and after neutralization with triethanolamine, (TEA), were investigated by UV-VIS and fluorescence methods. The UV-VIS spectra of the PAA-GNP gels contain the characteristics absorption peaks of both PAA and GNP pure components, with modified intensities and positions. Excitation at 250 nm of pure PAA and pure GNP are followed by characteristic fluorescence transitions. The peaks of pure components appear in the fluorescence spectrum of the PAA-GNP gels with some modifications compared with the pure state. Some modifications of the UV-VIS and florescence spectra were observed after neutralization with TEA. The particularities of these spectra indicate some changes of the conformation of the polymeric matrices after the introduction of GNP and after neutralization. [ABSTRACT FROM AUTHOR]

Poly(acrylic) gels, (PAA), with polymeric concentrations 0.5, 1 and 1.5%, in aqueous state and neutralized with triethanolamine, (TEA), were investigated by UV-VIS and fluorescence methods. Such gels are suitable to obtain biocompatible matrices for some medical drugs. The aqueous gel with 1% PAA concentration shows an important absorption at 214 nm. At 1.5% PAA concentration the absorption increases and the peak shifts slowly to 212 nm. The absorption increases after neutralization and the maximum of absorbance shifts to 200 nm. Excitation of aqueous gels at 250, 270 and 290 nm is followed by two important fluorescence transition centered at 320 and 405 nm. The position of the fluorescence peaks is influenced by the polymeric concentration and by the neutralization. The UV-VIS and fluorescence investigations indicate some conformational changes determined by the neutralization. [ABSTRACT FROM AUTHOR]

The effects of gamma radiation on the local structure of PVA membranes containing TiO were investigated by ESR and XRD methods. An intense ESR signal is observed after irradiation at 16 KGy dose. This signal appears only for irradiated samples and it is associated with the breaking of the polymeric chain, followed by local reorganization of the polymeric segments and the apparition of the unpaired electrons and free radicals. The intensity of the signal decreases with the concentration of TiO, indicating a shielding effect of the dopand. That the modification of local order of the polymeric chains has been modified after irradiation is confirmed by XRD method. [ABSTRACT FROM AUTHOR]

The UV-VIS absorption property and the structural modification of PVA membranes gamma irradiated were investigated by XRD, UV-VIS and Raman spectroscopies. The increase of UV absorbance is observed after irradiation. This behavior is correlated with the scission effect and local ordering of the polymeric chain induced by irradiation. These effects were probed by XRD and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

The effect of air and UV exposure on the tacrolimus was observed by Raman and UV VIS spectroscopy. For moderate time exposure the chemical structure of tacrolimus is not affected. The absorption property of tacrolimus was enhanced by addition of TiO. [ABSTRACT FROM AUTHOR]

The UV-vis absorption properties of polyvinyl alcohol (PVA) membranes containing 0.04 ml silver nanoparticles were investigated by UV-vis spectroscopy. The samples were investigated in initial state and after UV and gamma exposure. Some modification appears in the spectra of samples containing AgNPs after gamma irradiation. This behaviour indicates modifications induced in the local structure of the polymeric membranes. [ABSTRACT FROM AUTHOR]

The effect of UV exposure on PVA membranes doped with TiO2 was observed by UV-vis and Raman spectroscopy. After several hours of moderate UV exposure, the absorption coefficient of non doped membranes is modified. The absorption property of PVA was enhanced by addition of TiO2. [ABSTRACT FROM AUTHOR]

The structural and dynamic changes occurring in high-density polyethylene exposed to gamma-, X-radiation and extreme temperature have been investigated by high-resolution solid state CP/MAS 13C NMR and ¹H NMR relaxometry. The 13C CP/MAS NMR spectra show that the gamma and X-radiation can induce the formation of Y-type branches in HDPE. The Laplace distribution of transverse T2 and longitudinal T1 relaxation times are used first to identify dynamics and morphological components of HDPE samples and then to characterize the degradation effects of these samples subjected to external aging factors. The small amplitude of the fourth component from T2 Laplace spectra confirms the connection of free ends of polymer chains to form Y-branches HDPE subjected to X-radiation. The T1 spectra Laplace show that the cooling at nitrogen temperature will affect mostly the crystallinity of HDPE. [ABSTRACT FROM AUTHOR]

The dispersion of clotrimazole in the polyacrylic acid (PAA) matrix and the possible interaction between the drug and polymeric matrix were investigated by Raman imaging spectroscopy. The optical analysis shows an inhomogeneous distribution of the clotrimazole in the polymeric matrix. An area of 10x10 μm of the sample was scanned and a spectral image map of the most important bands was constructed. The imaging spectral map was constructed observing the intensity of the characteristic band 1045 cm-1 of clotrimazole respectively 1450 cm-1 of PAA, recorded for each point of the scanned area. The spectrum of the clotrimazole in the PAA matrix is essentially identical to the spectrum of pure clotrimazole. This indicates non interaction between polymeric matrix and clotrimazole. [ABSTRACT FROM AUTHOR]