Wettability, adhesive performance and structural evolution of an environment-friendly modified silicate binder for foundry moulding and coremaking

Abstract

For the manufacturing of sand cores, silicate inorganic binders have emerged as promising green casting binder materials; however, their adhesive performance requires further improvement. In this study, to evaluate the impact of using water-soluble polyols, i.e. polyethylene glycol (PEG) and xylitol, to modify silicate adhesives, the effect of the content and type of water-soluble polyol on the colloidal stability, wettability and adhesive performance of a silicate binder were investigated. The structural evolution of the modified silicate binder and the polysilicate bondswere studied using characterisation techniques including infrared spectroscopy and 29Si nuclear magnetic resonance (NMR) spectroscopy. Results revealed that PEG 400 and PEG 600 increased the size of polysilicate particles in the solution, resulting in flocculation of the silicate binders and easy precipitation or separation in a short period of time. However, PEG 200 and xylitol exerted little effect on the stability of the silicate solution. Moreover, 0.25 wt% PEG 200 reduced the surface tension of the solution from 78.93 to 54.15 mN/m and the equilibrium contact angle from 45.0° to 34.6°. The polyol promoted the dehydration and condensation of silicic acid gel to form a more stable three-dimensional network structure, improving the bonding strength of casting sand cores prepared using the silicate binder and silica sand from 2.42 to 3.02 MPa. This study not only unveils the role of PEG in improving the wettability and bonding behaviour but also provides an example of the rational use of environment-friendly water-soluble polyols to enhance the performance of green inorganic adhesive materials.