Molecular Dynamic (MD) Simulations of Organic Modified Montmorillonite

Abstract

This study complements the knowledge about organobentonites, which are intended to be new binders in foundry technology. In the developed materials, acrylic polymers act as mineral modifying compounds. Modification of montmorillonite in bentonite was carried out in order to obtain a composite containing a polymer as a lustrous carbon precursor. The polymer undergoes thermal degradation during the casting process, which results in the formation of this specific carbon form, ensuring the appropriate quality of the casting surface without negative environmental impact. The present paper reports the results of computational simulation studies (LAMMPS software) aimed at broadening the knowledge of interactions of organic molecules in the form of acrylic acid and acrylate anions (from sodium acrylate) near the montmorillonite surface, which is a simplified model of bentonite/acrylic polymer systems. It has been proven that the –COOH group promotes the adsorption of acrylic acid (AA) to the mineral surface, while acrylate ions tend to be unpredictably scattered, which may be related to the electrostatic repulsion between anions and negatively charged clay surfaces. The simulation results are consistent with the results of structural tests carried out for actual organobentonites. It has been proven that the polymer mainly adsorbs on the mineral surface, although it also partially intercalates into the interlayer spaces of the montmorillonite. This comprehensive research approach is innovative in the engineering of foundry materials. Computer simulation methods have not been used in the production of new binding materials in molding sand technology so far.

Organobentonite Binder for Binding Sand Grains in Foundry Moulding Sands

“…The specific crystalline structure and the highly chemically reactive surface of layered MMT allow its properties to be altered by reacting with selected organic compounds. These reactions can take place through electrostatic forces via ion exchange, the formation of secondary bonds leading to the adsorption of neutral molecules or covalent bonds between the reactive surface groups of the mineral and the organic molecules of the modifier as a result of the grafting process [ 23 ]. Regardless of the mode of interaction, the formation of MMT structures intercalated with macromolecular compounds offers the opportunity to develop a new precursor with the desired structure of shiny carbon as a result of thermodestruction of the organic part of the composite without losing the key binding properties of the casting binder.…”

Thermostability of Organobentonite Modified with Poly(acrylic acid)

“…In this application, it is important for PAA to have the lowest possible average molar mass to increase its ability to be intercalated between MMT packages. At the same time, poly(acrylic acid) is one of the most widely used water-soluble anionic polyelectrolytes, used in the production of hydrogels, superabsorbents and ion-exchange resins, as well as dispersing and binding agent [ 16 , 17 ]. In addition, it is used as a food additive due to its low toxicity [ 18 ].…”

“…The research results in this area conducted for the new binding material under consideration (organobentonite MMT-PAA) have already been largely published. They found that the produced organobentonite meets the requirements for binding materials, and the resulting casting has no surface defects [ 13 , 17 , 24 ]. The only remaining issue is to discuss the research topic related to its thermal stability.…”