Towards greener stone shot and stone wool materials: binder systems based on gelatine modified with tannin or transglutaminase

Abstract

In the pursuit of greener stone wool and related materials, the development, study and discussion of strong binder systems for such materials based on gelatine modified with tannin or transglutaminase are presented. The first systematic studies and direct comparisons of gelatines with four different gel strengths modified with 3–50% chestnut tree tannin or transglutaminase are presented and discussed. The development of these non-toxic, biopolymer-based binder systems was achieved using composite bars comprising stone shots with submillimeter diameters as a versatile model for stone wool. Contrary to conventional binder systems, the gelatine-based binder systems were able to cure at ambient temperature, and increased unaged and aged mechanical strengths combined with decreased binder solubility were generally observed as a function of increased gel strength and viscosity of the gelatine component. Several of the compositions resulted in mechanical strengths before and after ageing treatments that were within the range of conventional binder systems. Intriguingly, the gelatine-based binder compositions generally appeared less sensitive towards ageing treatment than conventional binders and in several cases even displayed mechanical strengths after ageing treatments that were at a similar level or better than the corresponding unaged strengths. The developed binder systems thus displayed unprecedented “self-healing” properties. The first DMA studies of cross-sections of the composite bars showed that these binder systems could withstand temperatures well above those required and/or commonly encountered in for example the production and general use of stone wool products. The first SEM studies of the composite bars revealed that the binders created a honeycomb-like structure around the stone shots with several thinner bridging points between adjacent stone shots. The development of this highly promising new generation of bio-inspired binder technologies is expected to enable the manufacture of greener stone wool and related materials through the use of non-toxic and natural components that enable an environmentally improved route to these materials via the reduction of adverse environmental effects such as high energy consumption and emissions during the curing process.