High Strength Composites from Wastewater Sludge, Plant Oils, and Fossil Fuel By-Product Elemental Sulfur

Abstract

Herein high-strength composites are prepared from elemental sulfur, sunflower oil, and wastewater sludge. Fats extracted from dissolved air flotation (DAF) solids were reacted with elemental sulfur to yield composite DAFS (10 wt% DAF fats and 90 wt% sulfur). Additional composites were prepared from DAF fat, sunflower oil and sulfur to give SunDAF_x (x = wt% sulfur, varied from 85–90%). The composites were characterized by spectroscopic, thermal, and mechanical methods. FT-IR spectra revealed a notable peak at 798 cm^–1 indicating a C–S stretch in DAFS, SunDAF₉₀, and SunDAF₈₅ indicating successful crosslinking of polymeric sulfur with olefin units. SEM/EDX analysis revealed homogenous distribution of carbon, oxygen, and sulfur in SunDAF₉₀ and SunDAF₈₅. The percent crystallinity exhibited by DAFS (37%), SunDAF₉₀ (39%), and SunDAF₈₅ (45%) was observed to be slightly lower than that of previous composites prepared from elemental sulfur and fats and oils. DAFS and SunDAF_x displayed compressive strengths (26.4–38.7 MPa) of up to 227% above that required (17 MPa) of ordinary Portland cement for residential building foundations. The composite decomposition temperatures ranged from 211 to 219 °C, with glass transition temperatures of − 37 °C to − 39 °C. These composites thus provide a potential route to reclaim wastewater organics for use in value-added structural materials having mechanical properties competitive with those of commercial products.