Both oxidation and methoxymethylation of the surfaces of a series of MDI (methylene diphenyl isocyanate) and TDI (toluene
diisocyanate) polyether and polyester soft segment 1–4 butanediol polyurethanes result in increased thermal stability as measured
by TG. Explosive loss of mass above the hard segment melting temperature suggests that the diffusion of the dissociated diisocyanate
moiety is hindered at lower temperatures. Thus suppression of the depolycondensation reaction by chemical blockage of the
surface may result in a material with an increased service life at use temperatures as thermal stability of a polyurethane
may depend upon the low diffusivity of its diisocyanate comonomer. The effect of vacuum, oxygen and water vapor on the kinetics
of mass-loss of several of the polyurethanes is presented.
Authors:A. Pétrissans, R. Younsi, M. Chaouch, P. Gérardin, and M. Pétrissans
Torrefaction is a thermal treatment step in a temperature range of 210–240 °C, which aims to improve the dimensional stability and durability of wood. The mass loss kinetics for torrefaction of wood samples was studied using equipment specially conceived to measure mass losses during thermal treatment. Laboratory experiments were performed under nitrogen for heating rates of 0.1, 0.25, 1, and 2 °C min−1. A mathematical model for the kinetics of the thermodegradation process was used and validated. Measurements of temperature distribution and anhydrous mass loss were performed on dry sample of poplar wood during torrefaction in an inert atmosphere for different temperatures. The mathematical formulation describing the simultaneous heat and mass transfers requires coupled nonlinear partial differential equations. These unsteady-state mathematical model equations were solved numerically by the commercial package FEMLAB for the temperature under different treatment conditions. A detailed discussion of the computational model and the solution algorithm is given below. Once the validity of different assumptions of the model had been analyzed, the experimental results were compared with those calculated by the model. Acceptable agreement was achieved.
The thermal stability of a polypropylene copolymer has been examined at several stages during the processing of the material
into its final product in order to obtain information on the influence of processing steps such as grinding and thermal heating
on the expected lifetime of the material. Mass loss kinetics in an inert atmosphere were able to detect differences in thermal
stability, but oxidative differential scanning calorimetry studies proved to be a more sensitive techiique. A comparative
study of a specially prepared series of samples revealed the importance of additives on measured thermal stability and indicated
that both mechanical and thermal processing can cause reduction in measured thermal stability.