The Impact of Substituting Chalk with Fly Ash in Formulating a Two-Component Polyurethane Adhesive on Its Physicochemical and Mechanical Properties

TL;DR

This paper explores replacing chalk with fly ash in polyurethane adhesives, finding it maintains performance and meets environmental standards.

Contribution

The study demonstrates fly ash as a viable, environmentally compliant substitute for chalk in polyurethane adhesives.

Findings

Replacing chalk with fly ash maintains adhesive bond strength and interface performance.

Contaminant elution levels remain well below regulatory thresholds.

Adhesive formulations show compatibility with low-emission certification schemes.

Abstract

This study aimed to evaluate the effect of replacing chalk with fly ash in a two-component polyurethane (2C PU) adhesive on its physicochemical, mechanical, and environmental properties, as a practical application of circular economy principles. Six adhesive formulations were prepared, each containing a chalk-to-fly ash ratio as a filler. The study evaluated rheological, mechanical, thermal, and environmental parameters. Mechanical tests confirmed cohesive failure within the bonded material, indicating that the bond strength at the adhesive–substrate interface exceeded the internal strength of the substrate. The highest contaminant elution levels recorded were 0.62 mg/kg for molybdenum and 0.20 mg/kg for selenium, which represent only 6.2% and 40% of the regulatory limits, respectively. Dissolved organic carbon (DOC) and total dissolved solids (TDS) did not exceed 340 mg/kg and 4260 mg/kg, respectively. GC-MS analysis did not reveal the presence of prominent volatile organic compound emissions. Initial screening suggests possible compatibility with low-emission certification schemes (e.g., A+, AgBB, EMICODE®), though confirmation requires further quantitative testing. The results demonstrate that fly ash can be an effective substitute for chalk in polyurethane adhesives, ensuring environmental compliance and maintaining functional performance while supporting the principles of the circular economy.

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