Fanica Mustata

Cellulose extraction from orange peel using sulfite digestion reagents

Orange peel (OP) was used as raw material for cellulose extraction. Two different pulping reagents were used, sodium sulfite and sodium metabisulfite. The effect of the main process parameters, sulfite agent dosage and reaction duration, on cellulose yield was investigated. A central composite rotatable design involving two variables at five levels and response surface methodology were used for the optimization of cellulose recovery. Other two invariable parameters were reaction temperature and hydromodulus. The optimum yields, referred to the weight of double extracted OP, were 40.4% and 45.2% for sodium sulfite and sodium metabisulfite digestions, respectively. The crude celluloses were bleached with hypochlorite and oxygen. The physicochemical characterization data of these cellulose materials indicate good levels of purity, low crystallinities, good whitenesses, good water retention and moderate molecular weights. According to these specific properties the recovered celluloses could be used as fillers, water absorbents, or as raw materials for cellulose derivatives.

Optimization of isolation of cellulose from orange peel using sodium hydroxide and chelating agents.

Response surface methodology was used to optimize cellulose recovery from orange peel using sodium hydroxide (NaOH) as isolation reagent, and to minimize its ash content using ethylenediaminetetraacetic acid (EDTA) as chelating agent. The independent variables were NaOH charge, EDTA charge and cooking time. Other two constant parameters were cooking temperature (98 °C) and liquid-to-solid ratio (7.5). The dependent variables were cellulose yield and ash content. A second-order polynomial model was used for plotting response surfaces and for determining optimum cooking conditions. The analysis of coefficient values for independent variables in the regression equation showed that NaOH and EDTA charges were major factors influencing the cellulose yield and ash content, respectively. Optimum conditions were defined by: NaOH charge 38.2%, EDTA charge 9.56%, and cooking time 317 min. The predicted cellulose yield was 24.06% and ash content 0.69%. A good agreement between the experimental values and the predicted was observed.

Rheological and thermal behaviour of DGEBA/EA and DGEHQ/EA epoxy systems crosslinked with TETA

Abstract Isothermal variation of the viscosity has been investigated in the temperature range 20–60°C for diglycidyl ether of bisphenol A/epoxy aniline/triethylenetetramine (DGEBA/EA/TETA) and diglycidyl ether of hydroquinone/epoxy aniline triethylenetetramine (DGEHQ/EA/TETA) systems. The variation of the viscosity versus time and temperature has been determined using a ‘Rheotest 2.1’ viscometer equipped with cone and plate geometry (36 mm diameter and 0.3° angle) at a shear rate of 1 s−1. The cure kinetics were studied using the DSC technique. The thermal behaviour of cured products was investigated by thermogravimetric analysis using a MOM Budapest derivatograph. The activation energies for the curing reaction calculated from the gel time have values between 18.78 kJ mol−1 for the DGEBA/EA/TETA and 60.93 kJ mol−1 for the DGEHQ/EA/TETA system. The cured products present good thermal stability, the activation energies of decomposition have values of 96.46 kJ mol−1 for the DGEBA/EA/TETA and 93.70 kJ mol−1 for the DGEHQ/EA/TETA system.

Thermal behavior of epoxy resin cured with aromatic dicarboxylic acids

The curing kinetics and thermal properties of diglycidyl ether of bisphenol A crosslinked with two aromatic diacids were studied using non-isothermal differential scanning calorimetry and simultaneous TG/FTIR/MS analysis. In the crosslinking of the epoxy resins with anhydrides, there is an intermediate stage resulting acids, while the direct use of acids eliminate this phase. The kinetic parameters of the curing reactions were calculated using Kissinger, Flynn–Wall–Ozawa methods and also the multivariate nonlinear regression method included in Netzsch Thermokinetics software. The kinetic parameters and the thermal degradation mechanisms for the crosslinked resins were determined using the same software. The thermal degradation processes occurred in three steps, depending on the chemical structure of the samples. The thermal lifetime of the crosslinked resins was also calculated.

PREPARATION AND PROPERTIES OF POLYHYDROXYETHERESTERIMIDES FROM RESIN ACIDS

New polyhydroxyetheresterimides were synthesized from imidodicarboxylic acid of Diels-Alder adduct of resin acid with maleic anhydride and some epoxy resins at molar ratio 1/1. Imidodicarboxylic acid was obtained from Diels-Alder adduct of resin acids with maleic anhydride and p-aminobenzoic acid. The obtained polymers have low molecular weights and are soluble in high and medium polar solvents. IR, 1 H-NMR and other methods were used to characterize the monomers and polymers. Thermal stability of these polymers was also investigated.

Pressure sensitive adhesives modified with resinic acids

Pressure sensitive adhesives containing resinic acid derivatives in their structure were synthesized. The insertion of resinic acid derivatives as pendant group was carried out to improve the cohesive strength of acrylic polymers. IR, 1 H-NMR spectroscopy and other methods were used to characterize the monomers and polymers. The inherent viscosity of the polymers was found to be in the range 0.16-0.81 dL/g and the energy of thermal decomposition in the range 42-156 kJ/mol.

Formaldehyde resins from p-nonylphenol and resin acids

p-Nonylphenol, resin acids, and paraformaldehyde, in varying molar rations, were condensed under acid catalysis (hydrochloric acid). The resins thus obtained were characterized by spectroscopic methods and used as a starting material in pressure-sensitive formulae. The presence of these resins confers high adhesiveness and acceptable cohesive strength.