Pultrusion is a highly efficient composite manufacturing process. To accurately describe pultrusion, an appropriate model of resin cure kinetics is required. In this study, we investigated cure kinetics modeling of a vinyl ester pultrusion resin (Atlac 430) in the presence of aluminum hydroxide (Al(OH)3) and zinc stearate (Zn(C18H35O2)2) as processing additives. Herein, four different resin compositions were studied: neat resin composition, composition with Al(OH)3, composition comprising Zn(C18H35O2)2, and composition containing both Al(OH)3 and Zn(C18H35O2)2. To analyze each composition, we performed differential scanning calorimetry at the heating rates of 5, 7.5, and 10 K/min. To characterize the cure kinetics of Atlac 430, 16 kinetic models were tested, and their performances were compared. The model based on the [Formula: see text]th-order autocatalytic reaction demonstrated the best results, with a 4.5% mean squared error (MSE) between the experimental and predicted data. This study proposes a method to reduce the MSE resulting from the simultaneous melting of Zn(C18H35O2)2. We were able to reduce the MSE by approximately 34%. Numerical simulations conducted at different temperatures and pulling speeds demonstrated a significant influence of resin composition on the pultrusion of a flat laminate profile. Simulation results obtained for the 600 mm long die block at different die temperatures (115, 120, 125, and 130 °C) showed that for a resin with a final degree of cure exceeding 95% at the die exit, the maximum difference between the predicted values of pulling speed for a specified set of compositions may exceed 1.7 times.
A method for the synthesis of an amine-containing epoxy resin curing agent by dissolving hexakis-[(4-formyl)phenoxy]cyclotriphosphazene in an excess of isophoronediamine was developed. The curing agent was characterized via NMR and IR spectroscopy and MALDI-TOF mass spectrometry, and its rheological characteristics were studied. Compositions based on DER-354 epoxy resin and the synthesized curing agent with different amounts of phosphazene content were obtained. The rheological characteristics of these compositions were studied, followed by their curing. An improvement in several thermal (DSC), mechanical (compression, tension, and adhesion), and physicochemical (water absorption and water solubility) characteristics, as well as the fire resistance of the obtained materials modified with phosphazene, was observed, compared with unmodified samples. In particular, there was an improvement in adhesive characteristics and fire resistance. Thus, compositions based on a curing agent containing a 30% modifier were shown to fulfill the V-1 fire resistance category. The developed compositions can be processed by contact molding, winding, and resin transfer molding (RTM), and the resulting material is suitable for use in aircraft, automotive products, design applications, and home repairs.
The influence of epoxy active diluents, 1,4-butanediol diglycidyl ether (BD) and furfuryl glycidyl ether (FUR), in the mixtures with benzoxazine monomer based on bisphenol A, formaldehyde and m-toluidine (BA-mt), on the properties of a matrix was disclosed in this work. Resins were modified to achieve good tackiness at room temperature and reduced viscosity. The influence of mono- and difunctional modifiers on the process of curing was studied by way of differential scanning calorimetry and oscillatory rheology. The addition of BD and FUR shifted the curing peak to higher temperatures and significantly reduced viscosity. Preferable tackiness at ambient temperature was achieved with 10 phr of epoxy components in mixtures. However, cured blends with difunctional epoxy BD had an advantage over monofunctional FUR in enhanced tensile strength with remaining glass transition temperature at the level of neat benzoxazine (217 °C).
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