Cellulose nanofibers and the film-formation dilemma: Drying temperature and tunable optical, mechanical and wetting properties of nanocomposite films composed of waterborne sulfopolyesters

Soo-Ah Jin; Emily G Facchine; Orlando J Rojas; Saad A Khan; Richard J Spontak

doi:10.1016/j.jcis.2021.04.032

Cellulose nanofibers and the film-formation dilemma: Drying temperature and tunable optical, mechanical and wetting properties of nanocomposite films composed of waterborne sulfopolyesters

J Colloid Interface Sci. 2021 Sep 15:598:369-378. doi: 10.1016/j.jcis.2021.04.032. Epub 2021 Apr 25.

Authors

Soo-Ah Jin¹, Emily G Facchine¹, Orlando J Rojas², Saad A Khan³, Richard J Spontak⁴

Affiliations

¹ Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, USA.
² Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, USA; Department of Bioproducts and Biosystems, Aalto University, Espoo 02150, Finland; Departments of Chemical & Biological Engineering, Chemistry and Wood Science, University of British Columbia, Vancouver V6T 1Z3, Canada.
³ Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, USA. Electronic address: khan@eos.ncsu.edu.
⁴ Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, USA; Department of Materials Science & Engineering, North Carolina State University, Raleigh, NC 27695, USA. Electronic address: rich_spontak@ncsu.edu.

PMID: 33910071
DOI: 10.1016/j.jcis.2021.04.032

Abstract

Hypothesis: Waterborne sulfopolyesters have gained considerable interest as coating materials due to their excellent film-forming and optical properties. Their commercial use has been limited, however, due to their fragile nature. Incorporating cellulose nanofiber (CNF), a sustainable biopolymer, into the polymer matrix is expected to enhance the mechanical integrity of the nanocomposite as these two components synergistically interact.

Experiments: In this study, we have investigated the suspension and film characteristics of three sulfopolyesters varying in charge density, glass transition temperature and molecular weight, as well as their mixtures with CNF. We have performed steady-shear rheology on mixtures with different CNF loading levels, and resulting films have been subjected to quasistatic uniaxial tensile and water contact-angle tests to elucidate the effects of CNF on mechanical and surface properties.

Findings: Addition of CNF to waterborne polyester promotes shear-thinning behavior that remains unaffected by the CNF content. Solid films cast from these suspensions possess enhanced mechanical properties, as well as tailorable surface hydrophilicity, depending on composition and film-drying temperature. Tensile tests reveal that films containing 10 wt% CNF display the greatest mechanical improvements, suggesting the existence of a previously unidentified Goldilocks composition window.

Keywords: Cellulose nanofiber; Nanocellulose; Sulfonated Polyester; Sulfopolyester; Waterborne coating.