Thermal tools in the evaluation of decayed and weathered wood polymer composites prepared by in situ polymerization

This study aims to apply thermal tools in the evaluation of decayed and weathered wood polymer composites prepared by in situ polymerization with and without cross-linkers. Pinewood samples were impregnated with methyl methacrylate using glycidyl methacrylate and methacrylic acid as cross-linkers by vacuum/pressure. The polymerization was carried out in an oven at 90 °C for 10 h using benzoyl peroxide as catalyst. All samples were exposed to decay and artificial weathering tests. The characterization was performed by mass loss, color changes, optical images, wettability, thermogravimetric analysis (by means of DTG) and differential scanning calorimetry analyzes. The mass loss was higher in untreated wood in comparison with the composites, ~2.5–10 times. Cross-linked composites showed the highest resistance to fungal biodeterioration. The reduction in L*, chroma and b* confirmed loss of original yellow tones and increase in dark and dull tones of samples. The wettability was very affected by irregularities of the samples’ surface. Only DTG showed a shifting in the temperature of thermal events related to polysaccharides and lignin after exposure to decay and weathering. DTG was the best thermal technique for evaluation of decaying and weathering of wood composites.     

CeCl3-mediated addition of acetylenic bis-lithium salts to aldehydes and ketones: An efficient route to bis-substituted alkyne diols

An efficient, chemoselective protocol to access propargylic diols via a CeCl₃-mediated addition reaction is reported. Propargylic alcohols were transformed into the corresponding acetylenic bis-lithium salt intermediates, which react with aldehydes and ketones in the presence of dry CeCl₃ to furnish the corresponding bis-substituted alkyne diols. This protocol does not involve protection-deprotection or transmetallation steps, and allows the use of poorly reactive or highly enolizable substrates.     

Characterization,thermal properties and phase transitions of amazonian vegetable oils

Thermal profiles of buriti pulp oil (Mauritia flexuosa Mart.), tucumã pulp and kernel oils (Astrocarium vulgare Mart.), rubber seed oil (Hevea brasiliensis), passion fruit oil (Passiflora edulis) and ucuúba butter (Virola surinamensis) were analyzed by thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC). Gas chromatography and calculated iodine values were performed to determine the fatty acid profile and to measure the degree of unsaturation in these oils, respectively. The TG curves showed three steps of mass loss, which can be attributed to the degradation of polyunsaturated, monounsaturated and saturated fatty acids. The DSC crystallization and melting curves are reported and depended on the fatty acid composition. Usually, oil samples with a high degree of saturation showed crystallization and melting profiles at higher temperatures than the oils with a high degree of unsaturation. The data obtained by physicochemical analysis of oil samples were analyzed by principal component analysis and hierarchical cluster analysis to increase understanding of the data set, examining the presence or absence of natural groupings between samples.     

Correction to: Comparative thermostability of whey protein and alginate hydrospheres complexed with divalent cations

Journal of Thermal Analysis and Calorimetry -     

Determination of furanic aldehydes in sugarcane bagasse by high‐performance liquid chromatography with pulsed amperometric detection using a modified electrode with nickel nanoparticles

A glassy carbon electrode chemically modified with nickel nanoparticles coupled with reversed‐phase chromatography with pulsed amperometric detection was used for the quantitative analysis of furanic aldehydes in a real sample of sugarcane bagasse hydrolysate. Chromatographic separation was carried out in isocratic conditions (acetonitrile/water, 1:9) with a flow rate of 1.0 mL/min, a detection potential of – 50 mV vs. Pd, and the process was completed within 4 min. The analytical curves presented limits of detection of 4.0 × 10^?7 mol/L and 4.3 × 10^?7 mol/L, limits of quantification of 1.3 × 10^?6 and 1.4 × 10^?6 mol/L, amperometric sensitivities of 2.2 × 10⁶ nA mol/L and 2.7 × 10⁶ nA mol/L for furfural and 5‐hydroxymethylfurfural, respectively. The values obtained in this sample by the standard addition method were 1.54 ± 0.02 g/kg for 5‐hydroxymethylfurfural and 11.5 ± 0.2 g/kg for furfural. The results demonstrate that this new proposed method can be used for the quick detection of furanic aldehydes without the interference of other electroactive species, besides having other remarkable merits that include excellent peak resolution, analytical repeatability, sensitivity, and accuracy.     

Monitoring electrochemical reactions in situ using steady-state free precession C NMR spectroscopy

All attempts to use in situ¹³C NMR in spectroelectrochemical studies, using static cells and unlabeled substrates, have failed due to the very long average time (several hours). In this paper, we demonstrated that steady-state free precession (SSFP) pulse sequence can enhance signal to noise ratio and reduces the average time of ¹³C NMR signals by more than one order of magnitude. The results showed that each ¹³C NMR spectrum during the electrochemical reduction of 9-chloroanthracene, in a static cell, can be acquired in eleven minutes. This short averaging time allowed the analysis of the reaction every 30 min during 3 h. The phase and truncation anomalies present in SSFP spectra were minimized using Traff apodization function and Krylov basis diagonalization method (KBDM).     

Modeling the Kinetics of Complex Systems: Enzymatic Hydrolysis of Lignocellulosic Substrates

Lignocellulosic biomass is mainly composed of cellulose, hemicellulose, and lignin. Fuzzy logic, in turn, is a branch of many-valued logic based on the paradigm of inference under vagueness. This paper presents a methodology, based on computational intelligence, for modeling the kinetics of a complex reactional system. The design of a fuzzy interpolator to model cellulose hydrolysis is reported, within the perspective of applying kinetic models in bioreactor engineering. Experimental data for various types of lignocellulosic materials were used to develop the interpolator. New experimental data from the enzymatic hydrolysis of a synthetic substrate, on the other hand, were used to validate the methodology. The accuracy of the results indicates that this is a promising approach to extend the application of models fitted for specific situations to different cases, thus enhancing their generality.     

Reaction of 3-Alkenols with Thallium Trinitrate: An Unexpected and Useful Ring Contraction

The first thallium trinitrate (TTN) mediated ring contraction of cyclic homoallylic alcohols, using a 1:1 mixture of AcOH and H₂O as solvent, is described. The reaction of two of these alcohols with excess of TTN in pentane gave α-spirocyclopentyl-γ-butirolactones in reasonable yields.