**4. Conclusions**

Through this study, it was possible to develop a sustainable polyurethane resin artificial stone (ASPU), using as matrix, for the first time, a polymer resin from renewable and biodegradable source, and as raw material, granite waste. The ASPU represents an innovative novel material, considering that so far, the artificial stones developed used only petroleum-derived resins as matrix.

Furthermore, the manufacturing process was an important factor to produce a technically viable material, with properties enabling its use as a coating in civil construction.

The values of density (2.24 g/cm<sup>3</sup> ), water absorption (0.13%) and apparent porosity (0.31%) presented the possibility of using ASPU in humid environments and denoted the material homogeneity and good load/matrix adhesion.

The bending strength value of 17.31 MPa ranked ASPU as a higher-strength coating material. The SEM micrographs displayed an adequate interaction between granite particles and PU and the little presence of voids, confirming the physical indices and mechanical strength results.

Through the test results, it can be concluded that, owing to ASPU's mechanical and physical properties, the novel artificial stone can be used as a wall covering, on bathroom's and kitchen's countertops and its use in floors must be avoided, specially for high traffic places such as airports and supermarkets.

For ASPU's maintenance, the most aggressive reagents were HCl and KOH, causing the greatest weight loss, therefore, it should be avoided cleaning the stone with cleaning materials that contain these reagents in the components.

From this study, further research can be carried out aiming to evaluate the behavior of ASPU in cold weather countries through a bending test after freezing and thawing cycles. Besides, the changeability of the material can be studied by performing other tests like dilatometry, salt spray and UV rays exposure.

In addition, the PU from castor oil feasibility to be used as matrix resin in artificial stone allows further studies aimed at the development of other types of artificial stones varying the aggregates, wastes, matriz/load proportions and processing parameters.

**Author Contributions:** Conceptualization, C.M.F.V.; methodology, M.L.P.M.G. and E.A.S.C.; formal analysis, M.L.P.M.G.; investigation, R.J.S.R.; resources, C.M.F.V. and M.L.P.M.G.; data curation, G.N.S.B.; writing—original draft preparation, M.L.P.M.G.; writing—review and editing, G.N.S.B.; visualization, E.A.S.C.; supervision, R.J.S.R. and S.N.M.; project administration, E.A.S.C.; funding acquisition, M.L.P.M.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Rio de Janeiro State Research Foundation—FAPERJ (E-26/ 200.139/2022).

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors thank the support of the Brazilian agencies: FAPERJ (E-26/200.847/ 2021), CNPQ (301634/2018-1) and UENF.

**Conflicts of Interest:** The authors declare no conflict of interest.
