Production of lignocellulosic nanomaterials from thermomechanical pulp: A study of feasibility, tunability, and economic viability

Abstract

Lignocellulosic nanofibrils (LCNFs) have gained attention as sustainable nanomaterials due to their unique chemical and physical properties. However, current production methods often rely on costly feedstocks and chemically intensive processes and very few studies investigate ways to adjust the process to achieve tunable properties. In this study, LCNFs were produced from thermomechanical pulp (TMP) using chemical and combined chemical–mechanical treatments. By varying chemical treatment severity and mechanical processing, LCNFs with diverse physical and chemical properties were obtained. A techno-economic analysis (TEA) was also conducted on two treatments that produced LCNFs with similar properties to identify the more suitable approach for future large-scale production. By varying the severity of the chemical treatment through increasing the number of peracetic acid oxidation pretreatments, a wide range of LCNFs were produced with lignin contents ranging from 3.3%-26.6% and fiber diameters from 52-411 nm. Increased severity of chemical treatment resulted in decreased mass yield from 96.8% to as low as 62.8% due to hemicellulose and lignin loss. Using these LCNFs, thin films were made and tested to further explore the optical and physical properties of the materials. Decreased lignin content led to increased visible light transmittance and decreased sun protection factor and haze. Increased severity of the chemical treatment also decreased average fiber diameter of the LCNFs, accompanied by increased homogeneity, viscosity, elastic modulus, and ultimate tensile strength. Interestingly, the effects of increasing chemical treatment severity on surface wettability were opposing, with reduced fiber diameter leading to lower hydrophilicity and reduced lignin content leading to higher hydrophilicity. Increasing severity of the mechanical treatment, specifically by increasing the number of passes through the microfluidizer, reduced fiber diameters and improved homogeneity, viscosity, surface wettability, elastic modulus, and ultimate tensile strength without altering the chemical composition of the LCNFs. Based on the TEA, the low-severity chemical/high-severity mechanical treatment process yielded the lowest minimum product selling price (MPSP) for LCNFs, at $5.57/kg assuming a 0% discount rate. By comparison, the high-severity chemical/low-severity mechanical treatment process exhibited a substantially higher MPSP of $9.47/kg under the same assumptions. These results demonstrate that controlled adjustment of chemical and mechanical treatment severity provides a flexible approach for engineering LCNFs with tailored, application-specific properties, while techno-economic feasibility plays an important role in identifying the most suitable pathway for future large-scale production. Furthermore, the results of this study lay the framework for future studies in LCNF production at commercial scale with other potential feedstocks.