M.V. Alonso

Modeling of Fiber-reinforced Phenolic Foam

A statistical predictive model is developed that describes the compression properties of phenolic foam reinforced with glass fibers. An analysis of variance is applied to determine the behavior of composite phenolic foam. The material variables used in the study are fiber length, fiber weight fraction and weight percentage of blowing agent. The responses analyzed are density, compressive modulus, and strength. The foam cell size distribution as a function of density is also studied. Comparison of the experimental results with statistical data indicates that the elastic properties of glass—fiber-reinforced phenolic foam do not depend on the fiber lengths used. Also, the results showed that the density and morphology of composite foam exhibit a strong influence on the responses of the model. The statistical approach has utility for predicting the effects of material variables on elastic properties of foams.

Characterization of cellulose regenerated from solutions of pine and eucalyptus woods in 1-allyl-3-methilimidazolium chloride

Cellulose is currently separated from lignocellulosic materials using non-environmentally friendly processes. The development of new methods for treating biomass and separating cellulose remains a challenge and would be very useful in the context of the biorefinery philosophy. In this work, cellulose has been regenerated from solutions of Pinus radiata and Eucalyptus globulus woods in 1-allyl-3-methylimidazolium chloride. Wood dissolution was performed in a microwave oven at 120 °C for 20 min. Cellulose was characterized and compared to the reference material, microcrystalline cellulose (MCC). Regenerated celluloses showed lower crystallinity and thermal stability than MCC, although the ash contents at 400 °C were higher than in MCC. The regenerated celluloses were obtained without lignin and almost free from hemicellulose. Furthermore, cellulose was not significantly degraded in the dissolution process of both woods. The insoluble solids showed higher content of lignin and hemicellulose than the raw materials.

Diffusivity and Climatic Simulation of Hybrid Foams

Hybrid composite phenolic foams reinforced with glass and aramid fibers were prepared and evaluated as potential materials for insulation and cladding applications. In particular, moisture uptake, flammability, and accelerated aging experiments were performed. A statistical approach was employed to model and predict the moisture absorption of the foams. Hybrid foams exhibited much lower diffusivity of water molecules and moisture content compared to unreinforced foam. The properties of hybrid foams were also compared to commercial expanded polystyrene (EPS) foam. The flammability properties of hybrid foams were markedly superior to EPS. Accelerated aging test revealed excellent dimensional stability of hybrid foams even under extreme conditions. Compressive stiffness of hybrid foams was retained even after aging.

Thermal properties and thermal degradation kinetics of phenolic and wood flour-reinforced phenolic foams:

In the present work, the thermal stability, changes in chemical structure during thermal degradation, and the kinetics of thermal degradation of a phenolic foam were studied. An 8.5 wt% of Pinus radiata wood flour reinforcement was added to the phenolic foam. A commercial phenolic resol was used as the matrix for the foam. The wood flour-reinforced foam showed a structure similar to the phenolic foam according to the Fourier transform infrared spectroscopy results. The wood flour increased the thermal stability of the phenolic foam in the first stage of thermal degradation (T 5% ), decreased it in the second step (T 25% ), and negligibly influenced the final stage. The activation energies of the degradation processes of the studied materials were obtained by the Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa model-free kinetic methods and a 2-Gaussian distributed activation energy model. The values of the activation energies obtained by the model-free kinetic methods for the first degradation stage of the phenolic foams were in a range between 110 and 170 kJ mol−1, whereas for the wood flour it was 162 kJ mol−1 for almost all of the conversion range of its main degradation stage. The applied models showed good fits for all the materials, and the activation energies calculated were in agreement with the values found in the literature.

An exponential chemorheological model for viscosity dependence on degree-of-cure of a polyfurfuryl alcohol resin during the post-gel curing stage

In the present study, the chemorheological behavior of a bio-based polyfurfuryl alcohol (PFA) resin has been determined by rheological isothermal tests at different curing temperatures for the post-gel curing stage of the resin, using three different amounts of catalyst (2, 4 and 6 wt %). Instead of modeling the evolution of the complex viscosity using a widely used chemorheological model such as the Arrhenius model for each tested temperature, the change of the complex viscosity as a function of the degree-of-cure was predicted using a new exponential type model. In this model, the logarithm of the normalized degree-of-cure is used to predict the behavior of the logarithm of the normalized complex viscosity. The model shows good quality of fitting with the experimental data for 4 and 6 wt % amounts of catalyst. For the 2 wt % amount of catalyst, scattered data leads to a slightly lower quality of fitting. Altogether, it is demonstrated that the new exponential model is a good alternative to conventional chemorheological models due to its simplicity and suitability.