J. S. P. Rai

Process modeling, optimization and analysis of esterification reaction of cashew nut shell liquid (CNSL)-derived epoxy resin using response surface methodology.

Concept of five-levels-four-factors central composite rotatable design was utilized for the optimization of reaction conditions of cardanol-based vinyl ester resin production, by employing response surfaces methodology, to establish a relationship between the process variables and the extent of conversion under a wide range of operating conditions which resulted in different extent of conversions. The maximum extent of conversion of cardanol-based epoxidised novolac resin (CNE) and methacrylic acid (MA) catalyzed by triphenylphosphine was found to be 95% at optimum set of conditions of molar ratio (1:0.9) between CNE and MA, catalyst concentration (1.49%), reaction temperature (89.96 °C) and reaction time (17,991s). Geometrical representation of the mathematical models in three-dimensional response surface plots and isoresponse contour plots served as a good aid in understanding the behavior of reaction under different operating conditions by only limited sets of experiments. A statistical model predicted that the highest conversion yield of novolac resin would be greater than 95% at the optimized reaction conditions. The predicted values thus obtained were close to the experimental values indicating suitability of the model.

KINETICS AND MECHANISM OF ESTERIFICATION OF MONOEPOXIES

ABSTRACT The esterification of monoepoxy diluents (phenyl, cresyl, and butyl glycidyl ethers) and acrylic acid in presence of triphenylphosphine as catalyst was performed at 70 ○, 75 ○, 80 ○, 85 ○, and 90 ○C, and it followed first-order kinetics. The reactivity of aromatic monoepoxies was found to be higher than aliphatic, due to the inductive effect of phenyl and butyl groups. The activation energy of the esterification of the monoepoxy increases as Pv < Cv < Bv and varies from 67 to 82 KJ/mole. The specific rate constants were found to obey the Arrhenius expression. The kinetic and thermodynamic parameters viz., activation energy, frequency factor, entropy, enthalpy, and free energy revealed that the reaction was spontaneous and irreversible, resulting in a highly ordered, activated complex. A suitable mechanism is proposed and discussed.

Synthesis of Vinyl Ester Resins in the Presence of Monoepoxies: A Kinetic Study

The synthesis of vinyl ester resins V1, V2, and V3 was carried out using bisphenol-A–based epoxy resin and acrylic acid in presence of phenyl, cresyl, butyl, and glycidyl ethers, respectively, as reactive diluent and triphenylphosphine as catalyst. The reaction was performed at 70°, 75°, 80°, 85°, and 90°C and it followed the first-order kinetics. The specific rate constants, calculated by the regression analysis, were found to obey Arrhenius expression. The kinetic and thermodynamic parameters activation energy, frequency factor, entropy, enthalpy, and free energy revealed that the reaction was spontaneous and irreversible with highly ordered activated complex. The activation energy of the esterification of epoxy resin in presence of monoepoxy diluents increases in this order: V1<V2<V3. The experimental results were explained by proposing a reaction mechanism and deriving the rate equation.

Rheological Behavior of Vinyl Ester Resin

ABSTRACT Vinyl ester resins with varied acid values (11, 22, 32, 38, and 48 mg KOH/g solid) were prepared by reacting epoxy-novolac resin with methacrylic acid. The rheological behavior of these synthesized vinyl ester resin (VER) samples containing styrene as reactive diluent was studied using a Haake Rotovisco RV 20 viscometer. The apparent viscosity was found to be inversely proportional to the square root of the acid value in the temperature range of 25–40°C and at shear rates ranging from 100–800 sec−1. The zero-shear viscosity of these VER samples containing styrene (40% w/w) as reactive diluent decreased linearly with temperature. The activation energies for flow at constant shear stress (25–100 Pa) for a particular sample were found to be constant. The activation energy at constant shear rate decreases with the increase in the shear rate (50–400 sec−1). The activation energy at constant shear rate and shear stress decreased with the increase in the acid value. The viscosity of vinyl ester resin containing styrene as reactive diluent decreased almost 50 times with the increase in the concentration of reactive diluent from 30% to 100% (w/w of the resin).

Synthesis, characterization and curing behaviour of partial esters of cycloaliphatic epoxy resins

Partial esters of cycloaliphatic epoxy resins C1 and C2, containing glycidyl and epoxy cyclohexane groups, respectively, as their reactive units were synthesized using a 1:0.4 stoichiometric ratio of resin and methacrylic acid in the presence of triphenylphosphine. The reaction was performed as a function of temperature to determine various kinetic and thermodynamic parameters of the reaction. The prepared esters of C1 and C2, designated as C1P and C2P, respectively, were characterized for their structure by FT-IR spectroscopy. The degree of esterification and epoxy content in partial esters were determined by their epoxide equivalent weight. The curing behaviour of the CERs and their esters was studied using DSC. Dynamic DSC scans of cycloaliphatic epoxy resins mixed with nadic methyl anhydride (NMA)/methyl tetrahydrophthalic anhydride (MTHPA) showed that curing of C1 starts earlier than that of C2. DSC thermograms for the curing of C1P and C2P with benzoyl peroxide (BPO) and NMA/MTHPA showed two distinct exothermic peak positions, T p and T p′, due to the curing of esterified fraction and epoxy groups, respectively. The hydroxyl groups formed during partial esterification were found to catalyse the epoxy–anhydride reaction.