Maria Inez Graf de Miranda

A d.s.c. kinetic study on the effect of filler concentration on crosslinking of diglycidylether of bisphenol-A with 4,4′-diaminodiphenylmethane

Abstract The kinetics of formation of epoxy resin composites was studied using an epoxy matrix of diglycidylether of bisphenol-A (DGEBA) and 4,4′-diaminodiphenylmethane (DDM) as curing agent in the presence of quartz flour as filler. The curing reactions of these systems were kinetically followed by differential scanning calorimetry (d.s.c.) at different scanning rates. The activation energies of the curing reactions were obtained using non-isothermal methods: the single scanning rate method of Barrett as well as the multiple scanning rate methods of Kissinger, Osawa and half-width. The crosslinking process is characterized by an average activation energy of 54.2–62.7 kJ mol −1 despite different methods or filler concentrations being used to obtain it. The reaction rate for the systems with filler concentrations higher than 10 wt% showed a considerable decreasing at higher temperatures at conversions higher than 50%.

Cellulose and Nanocellulose from Maize Straw: An Insight on the Crystal Properties

In this work cellulose was extracted from corn/maize straw (Zea mays) by means of an environmental-friendly multistep procedure involving alkaline treatment and a totally chlorine-free bleaching. This multistep procedure efficiently removed lignin and hemicelluloses. The pulp resulting from each step was characterized by attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR). The optimum pulping time (time of alkaline treatment) was determined by means of thermogravimetric analysis. The extracted cellulose is highly crystalline as verified by X-ray diffraction. The partial acid hydrolysis with sulfuric acid led to the isolation of cellulose whiskers in aqueous suspension as confirmed by light scattering and transmission electron microscopy. The depolarization ratio value of these nanocrystals is the same as that determined for cotton whiskers, showing that this ratio does not depend on the cellulose source. The maize whiskers are arranged laterally in bundles with average thickness around five times that of the crystallite.

Analysis and comparison of the Barrett, Freeman-Carrol and the time-temperature-transformation (TTT) superposition methods: The case of a high Tg diamine/epoxy system

Abstract In the present work the curing process of the epoxy system diglycidylether of bisphenol A (DGEBA) with 4,4′-diaminodiphenylmethane (DDM) has been studied by differential scanning calorimetry (DSC) techniques. Dynamic methods (Barrett and Freeman-Carrol) and the isothermal time-temperature-transformation (TTT) superposition method were applied in order to obtain kinetic features of the curing process. The time-temperature evolution of the glass transition temperature (Tg) and the extent of reaction (α) were used as parameters in order to monitor the curing process. Three different reaction ranges have been observed: the initial range of cure (0.05

Application of the half-width kinetic method on the amine-initiated cross-linking of an epoxy resin with cyclic anhydrides

Abstract The utility of a non-isothermal kinetic method—the half-width method—is demonstrated in the determination of the activation energy for amine-initiated cross-linking reactions of the epoxy resin diglycidylether of bisphenol-A with three different cyclic anhydrides: succinic, maleic and cis -1,2-cyclohexanedicarboxylic anhydrides. Triethylamine was employed as an initiator. The cross-linking reactions were kinetically followed by differential scanning calorimetry at various temperature scanning rates. The half-width method furnished values for the energy of activation in the range 60–100 kJ mol −1 . These values are similar to those obtained by applying the well-known non-isothermal multiple-scanning rate methods of Kissinger and Osawa but differ significantly from the ones obtained by applying the single-rate method of Barret.

Reinforcement of hydroxypropylcellulose films by cellulose nanocrystals in the presence of surfactants

Hydroxypropylcellulose (HPC) films were prepared by casting with cellulose nanocrystals in the presence of anionic surfactant sodium dodecylsulphate (SDS) and cationic surfactant hexadecyltrimethyl ammonium bromide (CTAB). The cellulose nanocrystals were isolated from maize straw, a biomass source produced in huge quantities as an agrowaste in Brazil. These bionanocomposite films had good transparency and their surface hydrophilic character was evidenced by static contact angle measurements. Thermogravimetry (TGA) measurement revealed that nanocrystals and surfactants changed the thermal stability of the HPC films. Dynamic mechanical analysis (DMA) showed that the tensile storage and loss moduli of the HPC films increased by increasing the contents of cellulose nanocrystals and surfactants, especially in the case of CTAB. This good reinforcing effect of HPC matrix can be explained as due to electrostatic attractive interactions brought about by the presence of CTAB and the nanocrystals.

Dynamics of cellulose nanocrystals in the presence of hexadecyltrimethylammonium bromide

A dynamic light scattering (DLS) study was performed to investigate the interactions of maize straw cellulose nanocrystals (CNC) with the cationic surfactant hexadecyltrimethylammonium bromide (CTAB). Phase analysis light scattering (which gives access to zeta potential (ζ) and electrical conductance) technique was used with the aim to obtain additional information. Zeta potential behavior demonstrated the colloidal systems are stable. By electrical conductance data, it was verified that the process of formation of micelles is thermodynamically spontaneous. Dynamic light scattering was shown to be very useful to find the optimum hydrolysis time so as to obtain well dispersed and more isolated nanocrystals. In the presence of the cationic surfactant CTAB, the formation of micelles and aggregates CNC/CTAB were well identified by DLS showing that the dynamics of cellulose nanocrystals in aqueous suspensions is strongly affected by the surfactant.