Cellulose Nanocrystals from Office Paper Waste for Green Mortar: Process Optimization Modeling, Characterization, and Mechanical Properties

Concrete engineers are always looking for materials that can be employed to improve the mechanical performance and lower the carbon footprint of construction products. In this regard, cellulose, a biobased material presents a massive opportunity for its application in the construction industry. Office paper waste (OPW) is cellulose-rich feedstock and a low-cost source to produce cellulose nanocrystals (CNCs). In this study, response surface methodology (RSM) was used for the production of CNCs from OPW using acid hydrolysis technique at different hydrolysis conditions; time (30–90 min), temperature (40–50 °C), and OPW/acid ratio (1:15-1:25 w/v). The physicochemical properties of CNCs were analyzed using various techniques. All the investigated responses mainly well-fitted RSM cubic models (R² = 0.9460 to 0.9969) with insignificant lack-of-fit (p-value < 0.05). The highest yield (> 83%) was achieved at the lowest process time, temperature, and high OPW: acid ratio. The increase in process time and deinked OPW: acid ratio from 30 to 90 min and 1:15 to 1:25 resulted in higher crystallinity of CNCs. However, higher process temperature (50 °C) showed a reduction in crystallinity and length of CNCs. The optimization results of CNC production for meeting application of the CNCs as a construction material are time 90 min, temperature 40 °C, and OPW: acid ratio 1:25. The resulting CNC-mortar was tested under mechanical loadings and yielded 37.4 MPa compressive strength and 5.1 MPa of flexure strength. The study revealed that CNCs isolated from OPW has a great potential to use as a green additive for fabricating strong structural concrete.