Grafting amount and structural characteristics of microcrystalline cellulose functionalized with different aminosilane contents

Cellulose - Microcrystalline cellulose (MCC) has unique properties and its use as reinforcement for polymer composites has been increasing. However, the intrinsic incompatibility with most polymers...     

Effect of the epoxycyclohexyl polyhedral oligomeric silsesquioxane content on the dynamic fragility of an epoxy resin

This study aims to evaluate the performance of epoxy/epoxycyclohexyl polyhedral oligomeric silsesquioxane nanocomposites focusing on differential scanning calorimetry and dynamic mechanical analysis. Nanocomposites with distinct nanoreinforcement contents (1, 2 and 5 wt.%) were studied. Using differential scanning calorimetry and dynamic mechanical analyses it was possible to assess some properties based on well-established concepts and correlate them with the structure formed. It was observed that the glass transition temperature decreases following the incorporation of epoxycyclohexyl polyhedral oligomeric silsesquioxane, indicating, in principle, that there is more mobility in the new system formed. However, other calculated parameters (cooperative rearrangement region, Angell fragility and Kauzmann temperature) showed no trend as a result of epoxycyclohexyl polyhedral oligomeric silsesquioxane incorporation.     

Correlation of the thermal stability and the decomposition kinetics of six different vegetal fibers

The thermal degradation behavior of six different vegetal fibers was studied using thermogravimetry under nitrogen atmosphere at four different heating rates (5, 10, 20 and 40 °C min^?1). The degradation models Kissinger, Friedman and Flynn–Wall–Ozawa methods were used to determine the apparent activation energy and the frequency factor of these fibers. Furthermore, the solid state degradation mechanisms were determined using Criado’s method. Additionally, X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy were analyzed to corroborate the obtained results. The results indicated that the apparent calculated activation energies can be more closely related to the exponential dependence of the rate of heterogeneous reactions than to the, necessary “energy”, which is commonly used. The Criado’s master curves indicated two different degradation mechanisms for the fibers: diffusion followed by random nucleation. The results also indicated that the crystallinity index as calculated by X-ray diffraction and determinated by FTIR does not necessarily represent higher thermal stability as noted by the thermogravimetric analysis curves. The thermal behavior and the degradation mechanism did not show to be influenced by the lignocellulosic components of the fibers, exception for buriti and sisal. This behavior was attributed to higher extractive content.     

Thermal behavior and the compensation effect of vegetal fibers

The thermal degradation behavior and the Arrhenius parameter of curaua, kenaf, and jute vegetal fibers were studied using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and thermogravimetry analysis. XRD showed that the crystallite sizes in the (200) plane were in the order: curaua < jute < kenaf, and similar results were obtained for basal spacing. FTIR spectroscopy corroborated the XRD results. The thermal behavior of the fibers was analyzed by identifying the cellulose and hemicellulose content using independent parallel first-order models. The results were not very consistent with the kinetic degradation models of Kissinger, Friedman, and Flynn–Wall–Ozawa (taking into account the standard errors), which were used to determine the apparent activation energy of the fibers. In addition, the frequency factor (pre-exponential parameter) was observed to be independent of the heating rate. The fibers exhibited a compensation effect; i.e., higher apparent activation energies led to higher frequency factors. Finally, the solid-state degradation mechanism of all fibers was found to comprise diffusion and random nucleation followed by instantaneous growth of nuclei.