Ricardo García-Alamilla

EVALUACIÓN TÉRMICA DEL CURADO DE ADHESIVOS BASE SBR USANDO PERÓXIDO DE DICUMILO

Curing is an important process in adhesive formulation, but scant reports on the study of the kinetics of curing in adhesive are currently available, particularly for formulations including styrene-butadiene copolymers. The focus of the present work was to thermodynamically quantify the curing reaction in pressure-sensitive adhesives (PSA) obtained from styrene-butadiene copolymers, the effect of dicumyl peroxide (DCP) ratio, which acts as a crosslinking agent, and also evaluate the effect of two reactive adhesive resins, sylvalite and piccolyte. Kinetic parameters were determined by differential scanning calorimetry (DSC) in an isothermic and dynamic mode, gel content was determined as was swelling degree, given these characteristics can be associated with the curing reaction. The kinetic study showed the curing reaction was first order, according to the Ozawa and Kissinger equation. Resins have affinity to BR segment, while in the case of sylvalite and piccolyte to the PS segment, varying behavior with dicumyl peroxide in the adhesive mixture. Lower swelling values were associated with an increase in crosslinking, indicative a curing reaction took place, and the gel content test was used to corroborate the results.

Physicochemical Changes of Cocoa Beans during Roasting Process

During cocoa beans roasting, there are physicochemical changes that develop the chocolate quality attributes. Roasting systems have a particular influence on the development of these characteristics, and the effects of operation variables for each system must be evaluated. The objective of this study was to evaluate the effect of roasting time and temperature in a rotatory system on cocoa beans physicochemical parameters of quality as moisture, water activity, pH, total acidity, color , total phenolic content (TPC), and DPPH radical capacity. Cocoa beans were roasted as a function with a central rotatable design with 22 + 5 central points and 4 axial points ( 1.414, 1, 0, +1, and +1,414) and a response surface methodology was applied. Temperature and time levels were 110–170°C and 5–65 minutes, respectively. The effect of the variables was nonlinear and modeled with a second-order response polynomial. Roasting time and temperature presented a significative effect ( ) on the response variables except for both TPC and DPPH radical capacity in aqueous extract.

Synthesis of High cis-1,4-BR with Neodymium for the Manufacture of Tires

The salt of neodymium has been widely used in industrial polymerization of 1,3-butadiene. We used the ternary catalytic system neodymium versatate/diethylaluminum chloride/triisobutylaluminum (NdV3/DEAC/TIBA) with 0.5 mM NdV3/100 g Bd, NdV3 : DEAC = 1 : 9 mol : mol, and TIBA = 25, 50, 100, and 200 mM. The number-average molecular weight (Mn), weight-average molecular weight (Mw), and polydispersity index (PDI) were analyzed by GPC; the rheological properties were analyzed by DMA. The formulations were prepared with carbon black (IRB6) as reinforcing filler and the mechanical properties were compared to behavior of the different elastomeric compounds. The elastomeric compounds were characterized by their rheological properties, tensile strength, abrasion resistance, tear strength, permanent set, resilience, and fatigue properties. The high cis-1,4 polybutadiene (high cis-1,4-BR) was obtained with a percentage of cis-1,4 ≥97%. The weight-average molecular weight (Mw) was from 150 × 103 to 900 × 103 g/mol and polydispersity index (PDI) was from 3.1 to 5.1. This work is based on evaluation of the effect of the catalyst system on the final properties of the synthesized polybutadiene.

Chitosan-Starch Films with Natural Extracts: Physical, Chemical, Morphological and Thermal Properties

The aim of this study is to analyze the properties of a series of polysaccharide composite films, such as apparent density, color, the presence of functional groups, morphology, and thermal stability, as well as the correlation between them and their antimicrobial and optical properties. Natural antioxidants such as anthocyanins (from cranberry; blueberry and pomegranate); betalains (from beetroot and pitaya); resveratrol (from grape); and thymol and carvacrol (from oregano) were added to the films. Few changes in the position and intensity of the FTIR spectra bands were observed despite the low content of extract added to the films. Due to this fact, the antioxidants were extracted and identified by spectroscopic analysis; and they were also quantified using the Folin-Denis method and a gallic acid calibration curve, which confirmed the presence of natural antioxidants in the films. According to the SEM analysis, the presence of natural antioxidants has no influence on the film morphology because the stretch marks and white points that were observed were related to starch presence. On the other hand, the TGA analysis showed that the type of extract influences the total weight loss. The overall interpretation of the results suggests that the use of natural antioxidants as additives for chitosan-starch film preparation has a prominent impact on most of the critical properties that are decisive in making them suitable for food-packing applications.

Lewis–Brønsted induction acidity in SBA-15 modified with Zr and P

Abstract In this work, we present the synthesis of SBA-15 materials modified with 6 and 9 mol.% of Zr and P, respectively. Silanol SBA-15 groups were detected by Fourier transform infrared spectroscopy. X-ray diffractograms revealed that the typical hexagonal arrangement of SBA-15 was preserved after Zr and P introduction, and the structure was confirmed by transmission electron microscopy. After the Zr introduction, the morphology of SBA-15 changed from fibrous particles to a semi-spherical shape according to scanning electron microscopy, while nitrogen physisorption revealed the stability of the textural materials after the P introduction. The infrared spectra of pyridine adsorption indicated that the Zr and P incorporation into SBA-15 generated adequate Lewis and Br⊘nsted acidities to carry out methanol dehydration and direct the selectivity towards dimethyl ether, with medium-strong acid sites being responsible for obtaining up to 99% selectivity towards dimethyl ether.

Effect of the method and impregnation time on the surface acidity of zirconia modified with boron

In this paper, the synthesis and characterization of boron-modified zirconia is reported. The zirconium hydroxide obtained by sol-gel was modified with boric acid, in order to increase the surface acidity of the zirconia. For this purpose, two impregnation methods were used: conventional and ultrasonic, and the impregnation time was set at 1 or 4 h. The synthesized materials were characterized by thermal analyses, X-ray diffraction, infrared spectroscopy, nitrogen physisorption, and scanning electron microscopy. The boron incorporation delayed the crystallization of solids, which were mainly amorphous but with tendency toward the formation of the tetragonal phase. The modified materials were micro-mesoporous and their specific area was improved, while the pure zirconia showed a lower nitrogen adsorption. Units BO3 and BO4 were identified, confirming the boron presence. In general, the solids showed spherical particles; however, the ultrasonic treatment originated elongated particles. In addition, the acidic properties were evaluated by potentiometric titration and ethanol decomposition. The maximum acid strength of the zirconia increased from −28 mV to over 200 mV; consequently, all the boron-modified materials showed strong and very strong acid sites. The influence on the catalytic activity, due to the method and impregnation time, was clearly observed in the ethanol decomposition. The most active catalysts were those obtained by the ultrasonic method and the best was that impregnated during 1 h.Graphical Abstract