A Raman spectroscopic study of aqueous solutions of MgSO, as function of concentration and temperature was performed. From the analysis of the band profile of the internal vibrations of the sulphate ion, the spectroscopic ionic association constant was calculated at different temperatures. It was found that the association is solvent separated in the ranges of concentration and temperature studied. The large differences observed between the values obtained for the spectroscopic association constant and those obtained from macroscopic measurements were interpreted on the basis of a four-step solvent-separated dehydration mechanism. It is, assumed that the Raman spectra reflect only the shortdistance force acting on the sulphate anions. The contribution of the long-range forces for the consecutive steps were calculated using the Bjerrum equation. Good agreement between the overall association constant thus calculated and the macroscopic value was found in the concentration and temperature ranges studied.

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The quantitative determination of crystallinities of polyethylene samples from the analysis of vibrational bands due to 6(CH,) twisting and v(CC) stretching in the Raman spectra between 950 and 1500 cm-' was assessed. Several methods based on manual resolution of band envelopes and on computer-derived information using Gaussian and Lorentzian profiles were compared. The major source of error was found to be the estimation of the amorphous and crystalline interphase content, ab . A new method for the determination of sample crystallinity is proposed based on the time-dependent Fourier transform deconvolution of the spectral region between 950 and ls00 cm-', which takes into account the baseline corrections and the influence of vibrational band shoulders in this region to obtain consistent values of a,, ab and a,.

A comprehensive kinetic model of slow pyrolysis of biomass during a Thermogravimetric analysis (TGA) has been developed, including the simulation of variable heating rates, composition estimation and structural analysis of biomass.Biomass was assumed as a matrix of three solid global components (hemicellulose, cellulose and lignin) in which water and oil can be also present.Kinetics were based on an auto-catalytic model because it can simulate the degradation in cellulosic materials, as the cleavage of the biopolymers produce oligomers that accelerate the further depolymerisation. The reaction pathway followed the Waterloo's mechanism, which stablishes that all solid compounds decompose into volatiles and charcoal. This mechanism was completed by the vaporization of water and oil, and assuming that the formed charcoal can break into volatiles by a slow reaction. The set was solved by the 8 th Runge-Kutta's method and validated by the Simplex Nelder-Mead and Broyden-Fletcher-Goldfarb-Shanno's methods. The development of this model has a high interest because it can help to understand how the conversion from biomass to biochemicals takes place.To assess what parameters can affect the thermal degradation of biomass pure polymeric samples of hemicellulose, cellulose and lignin and complex samples (seeds and woody biomass) were studied and fitted. Two types of operations were consideredtoo. An isothermal degradation from 150ºC up to 350ºC with increments of 50ºC, and a non-isothermal decomposition with heating rate of 5ºC/min, 10ºC/min and 20ºC/min up to temperatures around 800ºC, depending on the studied sample. Average absolute deviations lower than 7% were obtained. It was deduced that there are some interactions between the three main biomass compounds. These interactions were observed by the variations in the kinetic parameters between complex and pure 2 samples, also they were perceived between the isothermal and no-isothermal way. On the other hand, an effect of the biomass structure has been reported by the differences between the kinetics of the seeds and of the woody samples. It is remarkable that the developed model could reproduce the cellulose decomposition with a variable heating rate using a unique set of kinetic parameters. This was possible by a no-Arrhenius' dependence with temperature. In the same way, it was used to predict the initial composition of the studied biomass with deviations lower than 7% for lignin and cellulose.

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