Cellulose Non Freezing Bound Water and Activation Energy of Desorption by Thermogravimetric Analysis

Understand water-cellulose interaction isa key factor in cellulose processing strategies and to achieve the best propertiesfor each application. The emergence of new advanced materials based on nanocelluloses calls for more precise methods to study these systems. In this work, we described the study of water-cellulose interaction by thermogravimetric analysis (TGA), comparing dynamic and auto stepwise methods. The auto stepwise method was able to identify with precision the different species of water: i) the free water or freezing water, ii) the freezing bound water and iii) the non-freezing bound water. The Ozawa-Flynn-Wall method was used to estimate the activation energy of bound water desorption, Ea average = 50.45 kJ.mol-1 and the cellulose degradation energy, Ea average = 143.18 kJ.mol-1. The results obtained given a new knowledge on the interaction between water and cellulose since other techniques such as DSC are not sensitive to non-freezing bound water increasing the range of water content that can be studied.

Пики термодесорбции водорода: моделирование и интерпретация

Various models of hydrogen thermal desorption peaks are analyzed. The dynamics model of the volume-averaged concentration with a continuum parameter allows integrally taking into account the degree of dominance of the limiting factors (diffusion and recombination of atoms into molecules during desorption). An analytical criterion for peaks symmetry is proposed in the context of comparison with the method of decomposing the component spectrum into the sum of Gaussian. Modifications of the Kissinger method for estimating the activation energy of desorption in experiments with several heating rates and procedures for solving the inverse problem of parametric identification of a unimodal peak using only one heating rate are presented. A comparative with a diffusion model with dynamic boundary conditions is performed. It is shown that the cause of local peaks can be not only capture with different binding energies but also the dynamics of interaction of bulk and surface processes, change in the surface structure during heating.

Wettability Control of Gold Surfaces Modified with Benzenethiol Derivatives: Water Contact Angle and Thermal Stability

The water wettability of Au surfaces has been controlled using various benzenethiol derivatives including 4-methylbenzenethiol, pentafluorobenzenethiol, 4-fluorobenzenethiol, 4-methoxybenzenethiol, 4-nitrobenzenethiol, and 4-hydroxybenzenethiol. The water contact angle of the Au surface modified with the benzenethiol derivative was found to vary in the wide range of 30.9° to 88.3°. The contact angle of the modified Au films annealed was also measured in order to investigate their thermal stability. The change in the contact angle indicated that the modified surface is stable at temperatures below about 400 K. Meanwhile, the activation energy of desorption from the modified surface was estimated from the change in the contact angle. The modified Au surface was also examined using X-ray photoelectron spectroscopy.

Estimation of Activation Energy of Desorption of n-Hexanol from Activated Carbons by the TPD Technique

Activated carbon and five kinds of metal-ion-substituted activated carbons, viz. Ag+-activated carbon, Cu2+-activated carbon, Fe3+-activated carbon, Ba2+-activated carbon and Ca2+-activated carbon, were prepared. A model for estimating the activation energy of desorption was established. Temperature-programmed desorption (TPD) experiments were conducted to measure the TPD curves of n-hexanol and hence estimate the activation energy for n-hexanol desorption from the various activated carbons. The results showed that the activation energies for n-hexanol desorption from the Ag+-activated carbon, the Cu2+-activated carbon and the Fe3+-activated carbon were higher than those from the unsubstituted activated carbon, the Ca2+-activated carbon and the Ba2+-activated carbon.