A. Maaroufi

Morphology, thermal stability and thermal degradation kinetics of cellulose-modified urea-formaldehyde resin

This article reports a study on the structural characterization and evaluation of thermal degradation kinetics of urea–formaldehyde resin modified with cellulose, known as UFC resin. Structural characterization of UFC undertaken by scanning electron microscopy, Fourier transform infrared and X-ray diffraction analyses reveals that the resin is fairly homogenous, and it constitutes of partly crystalline structure including urea–formaldehyde/cellulose interface morphology different from UFC precursors. Measurement of inherent thermal stability, probing reaction complexity and the thermal degradation kinetic analysis of UFC have been carried out by thermogravimetric/differential thermal analyses (TGA/DTA) under non-isothermal conditions. The integral procedure decomposition temperature elucidates significant thermal stability of UFC. TGA/DTA analyses suggest highly complicated reaction profile for thermal degradation of UFC, comprising various parallel/consecutive reactions. Different differential and integral isoconversional methods have been employed to determine the thermal degradation activation energy of UFC. Substantial variation in activation energy with the advancement of reaction verifies multi-step reaction pathway of UFC. A plausible interpretation of the obtained kinetic parameters of UFC thermal degradation with regard to their physical meanings is given and discussed in this study.

Kinetics of the thermal degradation mechanisms in urea-formaldehyde cellulose composites filled with zinc particles

This paper reports a study on the structural characterization, thermal stability, and thermal degradation kinetics of urea-formaldehyde cellulose (UFC) composites filled with zinc particles. Structural characterization of UFC/Zn composites carried out by SEM, XRD and FTIR analyses reveals that the composites are fairly homogenous, and the interactions between UFC and zinc in the composites are physical in nature. Afterwards, measurements of inherent thermal stabilities, probing reaction complexity, and thermal degradation kinetics of UFC/Zn composites have been carried out. The integral procedure decompositions temperature elucidates significantly higher thermal stabilities of UFC/Zn composites. Isoconversional kinetic analysis suggests multi-step reaction pathways of UFC/Zn composites in terms of the substantial variations in their activation energies with the reaction advancement. Advanced reaction model determination methodology with the help of an innovative kinetic function F(α, T) reveals that the thermal degradation of UFC goes to completion by following complicated multi-step nucleation/growth mechanisms. A detailed account of the mechanistic information regarding to the thermal degradation processes taking place in UFC/Zn composites is given and discussed in the present study.

Composites of zinc phosphate glass/metal: New materials for thermoelectricity and solar cell devices

This work reports a study on thermoelectricity in new composites zinc-phosphate glasses/cobalt. The obtained Seebeck coefficient (S) changes a sign from a high positive to negative values below and above the percolation threshold, respectively, showing p-n type conducting phase transition. Thus, the Seebeck coefficient measurements above the percolation threshold as function of temperature showed respectively an original conducting to insulating phase transition at T=420K, linked with a high negative value of S≤-8000μV/K, giving rise to the highest power factor PF=σS2≈8×10-3W.m-1.K-2. The thermal measurements confirm this transition and indicate a dilation of matrix around this temperature. Such materials with high Seebeck coefficient could be used as new materials for thermoelectricity applications. In addition, the p-n transition in these materials my fined useful application in p-n junction devices.