Polystyrene nanoparticles slurry as an additive for developing insulating and waterproof gypsum composites

•Gypsums composites with improved insulating and waterproof properties are developed.•The addition of a 42 wt% of NPS reduced the thermal conductivity in a 36%•The addition of a 42 wt% of NPS increased the contact angle of the composites a 440%•The NPS are homogenously distributed across all the gypsum composites.•The developed composites comply with the regulation UNE EN 13279–1. Lightweight gypsum composites with improved thermal and waterproof properties were produced by using a concentrated slurry containing polystyrene nanoparticles (NPS) as an additive. The NPS/Hemihydrate mass ratio was varied between 0.00 and 0.42. The density of the composites decreased with the increase of the NPS/Hemihydrate mass ratio, due to the change in the internal structure to a more lamellar one with crystals of larger size that grow also in a less compact distribution. This also caused an increase of the porosity (from 0.47 to 0.51) and a reduction in the thermal conductivity from 0.354 W m-1K−1 (NPS/Hem = 0) to 0.225 W m-1K−1 at 32 °C for the composite manufactured with the maximum NPS amount (NPS/Hem = 0.42). The thermal conductivity decrease allowed to reduce the final temperature at the steady state up to 2.5 °C compared with the unmodified gypsum, when they were exposed to a heat source at 45 °C. In addition, it was observed by SEM and TGA that the NPSs were distributed homogeneously throughout the gypsum composites blocks. Although the maximum compressive and flexural strengths decreased with the increase of NPS amount up to 76 and 61 %, respectively; all the synthesized lightweight gypsum blocks satisfied the European standard regulation EN 13279–1. The waterproof properties were measured by the contact angle, passing from 26.2° to 141.5 ° when changing from 0.0 NPS/Hem ratio to the maximum amount.