2.2.1. Development of Artificial Stone Plates

Initially, the waste was dried in an oven at 100 ◦C for 24 h to remove moisture. According to the resin manufacturer's guidelines, 1wt.% of component A for each 1.2 wt.% of component B, for 15 wt.% production. The ASPU plates were manufactured in dimensions <sup>1000</sup> <sup>×</sup> <sup>1000</sup> <sup>×</sup> 12 mm<sup>3</sup> .

The mixture was made in an automatic cylindrical mixer and then the mass was placed into a mold that was previously connected to a vacuum system and over a vibrating table, Produtest, Brazil, to better spread the mass in the cavity and facilitate the removal of air bubbles.

After 2 min of vibration time in the mold, still under vacuum, the mass was compressed in a hydraulic press at a 10 tons compaction pressure, at 80 ◦C for 20 min. After pressing, the mold was disconnected from the vacuum system and cooled to room temperature [11] to remove the artificial stone plate.

The artificial stone plates were then subjected to post curing as shown in Table 1 to promote better cross-linking of polymer chains.


**Table 1.** ASPU post cure steps.

The 60 ◦C was adopted as the minimum temperature based on the resin glass transition temperature (Tg). The maximum temperature was 80 ◦C because allophanate and biuret cross-links occur secondarily at high temperatures and are important in the polyurethane post-cure, increasing hardness, tensile strength and elastic modulus. The biuret cross-links are even more important because they occur at 80 ◦C range with the remaining isocyanate groups [20,21].
