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Wellen R.M.R.,Federal University of Paraiba | Canedo E.L.,Federal University of Campina Grande | Canedo E.L.,Pernambuco Institute of Technology
Journal of Materials Research | Year: 2016

Three classical methods (Pseudo-Avrami, Ozawa, and Mo models) were used to correlate nonisothermal melt and cold crystallization kinetics data of neat poly(3-hydroxybutyrate) (PHB) and PHB/carbon black compounds, measured by differential scanning calorimetry. The applicability of the three models was tested comparing model predictions with experimental data. Results suggest that Pseudo-Avrami model fits the experimental data well. Ozawa model does not fit data well, as verified by the large uncertainties and unphysical values of the fitting parameters. Mo model may be considered adequate if moderately deviations could be tolerated. Datasets of all compositions are included as the Supplementary Information. © 2016 Materials Research Society.

Wellen R.M.R.,Pernambuco Institute of Technology | Rabello M.S.,Federal University of Campina Grande | Fechine G.J.M.,University of Sao Paulo | Canedo E.L.,Pernambuco Institute of Technology
Polymer Testing | Year: 2013

This work is concerned with the melting behaviour and accuracy of differential scanning calorimeter (DSC) analyses of poly(3-hydroxybutyrate) (PHB), a semi-crystalline thermoplastic polymer completely biodegradable and biocompatible, and obtained from renewable resources. Melting parameters of PHB were determined for the first fusion event applying standard experimental procedures for thermal analysis, using heating rates ranging between 1 °C/min and 20 °C/min. The analyses of DSC energy flow scans showed a complex melting peak that may be resolved into three elementary peaks having different intensities at different melting temperatures. Peak temperatures depend on heating rate, while the total crystallinity detected was independent of the rate. A study of 24 DSC runs showed good temperature reproducibility (±0.5 °C), but poor reproducibility of mass crystallinity (±10%). © 2012 Elsevier Ltd. All rights reserved.

Wellen R.M.R.,Pernambuco Institute of Technology | Canedo E.L.,Pernambuco Institute of Technology | Lima C.A.V.,Federal University of Pernambuco | Junior I.C.A.,Federal University of Pernambuco | And 2 more authors.
Materials Research | Year: 2015

Mechanical properties, morphology and nonisothermal crystallization of poly(3-hydroxybutyrate) (PHB) and blends of PHB and polystyrene (PS) were studied by tensile tests, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). A two-phase structure composed by a PHB matrix and nearly spherical particles of PS was clearly noticed in SEM images. The presence of small amounts (0.5% to 3%) of amorphous PS affected the crystallinity of PHB, being more evident when high cooling rates were applied. The kinetics of nonisothermal crystallization was modeled according to Ozawa equation. The dependence of Ozawa parameters on temperature followed the same trend for PHB and PHB/PS blends; model parameters were found to be lower for the blends than for the neat PHB. © 2015.

Costa A.R.M.,Federal University of Campina Grande | Almeida T.G.,Federal University of Campina Grande | Silva S.M.L.,Federal University of Campina Grande | Carvalho L.H.,Federal University of Campina Grande | And 2 more authors.
Polymer Testing | Year: 2015

This contribution is concerned with degradation and chain extension in poly(butylene-adipate-terephthalate), PBAT, compounded in a laboratory internal mixer with an epoxydic chain extender additive. Weight-average mass change during melt processing was estimated from temperature-torque-time data recorded by the equipment. The effect of the additive was found to be strongly dependent on processing temperature, and weakly dependent on concentration. Molar mass more than doubled at 230°C with 2% additive. Long induction times and catastrophic failure to mix, occasionally observed with oligomeric additives processed in internal mixers, are discussed. Possible implementation of the procedure for real-time estimate of chain extension is also discussed. © 2015 Elsevier Ltd.All rights reserved.

Da Silva H.M.,Federal University of Pernambuco | Da Silva H.M.,Pernambuco Institute of Technology | Vilela O.C.,Federal University of Pernambuco | Fraidenraich N.,Federal University of Pernambuco | Veissid N.,National Institute for Space Research
30th ISES Biennial Solar World Congress 2011, SWC 2011 | Year: 2011

It is evaluated the performance of a CPV multijunction (MJ) cell (InGaP/InGaAs/Ge) of 1.0 cm2 area, for concentration rates varying from 1 up to 122X. The parameters which characterize the cell are extracted from experimental characteristic curves using the one diode model. Special attention is given to the series resistance, which affects significantly the cell performance. Results obtained show that the procedure adopted is considerably consistent, enabling to obtain a general picture of solar cell behavior in spite of large temperature and irradiance experimental variations. A large value of series resistance (3.8 Ω) is observed for low concentration values. This resistance decays rapidly, attaining a stable value for high concentrations (0.024 Ω). Average conversion efficiencies of 35% have been measured when converted to temperatures of 47°C. Series resistance obtained for high concentrations (0.024 Ω) limit the concentration rate corresponding to maximum efficiency to values between 243 and 278. Higher efficiencies with higher concentrations, probably, require further reduction of series resistance.

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