Optimization of Glass Transition Temperature and Pot Life of Epoxy Blends Using Response Surface Methodology (RSM)

The aim of this work was to improve the processability of triglycidyl-p-aminophenol (TGPAP) epoxy resin. To achieve this improvement, a diluent, the diglycidyl ether of bisphenol F (DGEBF or BPF), was added to TGPAP, and the blended epoxy was then cured with 4, 4′-diaminodiphenyl sulfones (DDS). A response surface methodology (RSM) was used, with the target response being to achieve a blended resin with a high glass transition temperature (Tg) and maximum pot life (or processing window, PW). Characterization through dynamic mechanical thermal analysis (DMTA) and using a rheometer indicated that the optimum formulation was obtained at 55.6 wt.% of BPF and a stoichiometric ratio of 0.60. Both values were predicted to give Tg at 180 °C and a processing window of up to 136.1 min. The predicted values were verified, with the obtained Tg and processing window (PW) being 181.2 ± 0.8 °C and 140 min, respectively, which is close to the values predicted using the RSM.

Modified Epoxy Resins for Perpreg Technology

A curing system has been developed for obtaining high-strength compositions matrix, which is used in the production of composites based on reinforced carbon fiber using prepreg technology with a curing temperature of . A technology has been developed for combining an epoxy oligomer with a curing agent and modifier. The pot life of the prepared prepregs is at least 15 days.

Analysis of the mechanical composite properties of ii-chamber variations in the closed injection pultrusion process

Pultrusion is an established and efficient process for producing continuous fiber-reinforced composites. The resin systems that are currently most frequently used are unsaturated polyesters and vinylesters. These have a long pot life, are well known, and have good processing properties. Highly reactive resins such as polyurethane (PU) and amine hardening epoxy have been in use for a few years. These resin classes are remarkable for their extended range of properties. This opens up new application fields for pultrusion technology but poses challenges for the processing technology. Short pot lives of just a few minutes require a modified process: closed injection pultrusion (CIP). Various approaches about the design and layout of the internal geometry of the injection and impregnation chambers (ii-chamber) are the subject of ongoing research. Numerous parameters influence the impregnation process in the ii-chamber and the quality of the resulting composite. In this study, two innovative, highly reactive resins for use in the pultrusion process were analyzed, both resins based on aliphatic polyurethanes. In phase 1 of the experiments, a commercial aliphatic polyurethane-system for pultrusion applications was used. In Phase 2, the recently developed bio-based aliphatic polyurethane-system for pultrusion applications was used for the study's main experiments. The aim of the study was to analyze the material and processing properties with various modifications of the impregnation setup. Therefore, a newly developed ii-chamber and die were tested. The ii-chamber was designed to enable easy adjustment of some of the main influencing parameters during the pultrusion process. A test strategy was developed to evaluate the properties of the composites. An assessment of the influence of the process- and die-based parameters should enable an evaluation of the optimal processing settings by analysis of the material characteristics. The most significant effect of variations in the pultrusion process was found in the interlaminar shear strength (ILSS). ILSS was analyzed for all process variations for both resin systems.

Curing Behavior of Waterborne Paint Containing Catalyst Encapsulated in Micelle

This research has studied the feasibility of fabricating a catalyst that activates at 80 °C to ensure the curing performance of two-pack isocyanate curable paints, while remaining inactive at 40 °C to ensure storage stability and pot life. The research examined whether the added dibutyl tin dilaurate (DBTL) provided a catalytic function for curing the waterborne paint, which remains almost inactive at 40 °C and activates at 80 °C or higher. It was confirmed that the use of a non-ionic surfactant with a hydrophilic-lipophilic-balance (HLB) of between 13 and 14 resulted in rapid curing at a temperature of 80 °C or higher, thereby demonstrating catalytic properties. The results also show that the viscosity of the paint remained virtually unchanged after exposure for 1 h at 40 °C. This wass presumed to be the result of the DBTL, which was constrained by the micelles up to a temperature of 70 °C, breaking down the micelles at a temperature of 80 °C or higher. It was also confirmed that the catalytic switching properties were not obtained at a lower or higher HLB. It was found that selecting the non-ionic surfactant by HLB can control the activating temperature of the catalytic properties.

Modified gypsum binder for interior systems

As the main component for many interior plaster mixes, a natural gypsum binder or its analogues is used, which are products of processing of local raw materials or by-products of other industries. Under operating conditions, gypsum binder-based plaster coatings have two main features. The first is the ability to regulate room humidity and absorb harmful emissions. The second is the ability to implement the function of barrier protection in the event of a fire. Improving the quality of plastering works and optimizing their cost is associated with the development of modified compositions based on gypsum, justified use of waste and local building materials, which include clay-gypsum binder. Clay gypsum as a natural material of sedimentary origin is widespread both in Russia and in the states formed in the post-Soviet space. In terms of energy intensity and manufacturability, the processing of raw materials into a clay-gypsum binder does not differ from the conditions of traditional processing of natural gypsum. Compared to lime or cement mortars, mortars based on gypsum binder have greater elasticity and plasticity. Such properties associated with the manufacturability of the application, such as workability and thixotropy, as well as the interval for maintaining the pot life of the mixture, are controlled by the introduction of modifying additives, the evaluation of the formulation of which was the purpose of the research, the results of which are presented in the article. The studies carried out have established that varying the recipe parameters make it possible to regulate both the strength and performance characteristics of mixtures based on gypsum plaster, as well as the manufacturability of their application.

TECHNOLOGICAL AND OPERATIONAL CHARACTERISTICS OF THE VSE-62 LOW-VISCOSITY EPOXY RESIN WITH INCREASED POT LIFE AND ITS APPLICATION

The paper considers the main physical and chemical and thermomechanical characteristics of the VSE-62 epoxy resin. The results of rheological tests of the developed resin in dynamic and isothermal modes, as well as the kinetic parameters of the curing process are presented. They help to determine the technological conditions for obtaining defect-free cured samples. The results of mechanical tests show that this resin’s system is characterized by high values of the glass transition temperature and good mechanical properties at test temperature of 120 °C. The absence of solvents in the composition of the VSE-62 epoxy resin and its low viscosity makes it possible to obtain high-strength materials with reduced porosity.

Catalyzed HTPB/HDI-Trimer Curing Reactions and Influence on Pot Life

In this research, rheokinetics is used to study the curing reaction of hydroxyl terminated polybutadiene (HTPB) and trimer of hexamethylene-1,6-diisocyanate (HDI-trimer) with 1,4-diazabicyclo[2.2.2]octane (DABCO) as catalyst under different catalyst mass fraction. The results show that the pot life of the system depends on the catalyst mass fraction in the binder system. Furthermore, with increased catalyst mass fraction, the fitting diagram obtained by plotting ln (viscosity) versus curing time shows a better linear relationship. Therefore, the amount of catalyst required to achieve a certain pot life can be calculated through the formula. It is worth mentioning that the applicable pot life equations are proposed in the paper. From the equations, we find that under isothermal curing conditions at 35 °C, when the mass fraction of DABCO was 0.216 wt.%, the pot life of the HTPB/HDI-trimer binder system reaches 4 h.

Investigation of rheological and physical-mechanical properties of binders with hardener

The amine type hardeners — Etal-M7 and Etal-23X — have been examined in comparison with the hardener of the same type Etal-45M. They are used for cold curing binders based on epoxy resin ED-20. The investigation demonstrated that binders with the hardeners Etal-M7 and Etal-23X had better pot life, tension strength and heat resistance than binders with the hardener Etal-45M.