Influence of polypropylene residues on the physico-mechanical and water-resistance properties of gypsum plasters

Abstract

The main objective of the present research is to determine the feasibility of using polypropylene (PP) waste to produce eco-friendly gypsum-based composites. Four different replacement levels of plastic waste were selected for analysis - 2.5%, 5%, 7.5% and 10% by weight of gypsum. The first stage of the experimental campaign consisted of analysing the resulting composites based on density, mechanical performance (flexural and compressive strength) and surface hardness (Shore C). In the second stage, samples were evaluated based on their water absorption by capillary action or exposing them to continuous moisture in a wet chamber, and water resistance by subjecting them to several wetting-drying cycles. After that, scanning electron microscopy (SEM) analyses were carried out to evaluate the quality of the cohesion at the interfacial transition zone (ITZ) between the PP waste particles and the gypsum matrix. The results showed equivalent compressive strength and even a slight improvement (up to ∼9% when using 2.5% of PP waste when compared to the control material) most likely due to the greater compactness from the improved particle size distribution. In addition, a considerable reduction in water absorption and retention capacity was observed, due to the increasing incorporation of recycled PP into the gypsum matrix. The new PP-containing composites subjected to water absorption by capillary action and continuous moisture tests presented lower water absorption and adsorption capacity, wherein specimens with 10% of PP waste showed a decline of up to ∼37% when compared to the reference material. It was generally observed that the waste material can be considered as a viable partial substitute to the current commercial gypsum for the production of gypsum plasterboards.