Impact of Silanization on the Structure, Dispersion Properties, and Biodegradability of Nanocellulose as a Nanocomposite Filler

Abstract

For nanocellulose to function effectively as a nanofiller in polymers, its interfacial properties are often modified to enhance the dispersion of nanocellulose in the polymer matrix. However, the effect of different surface modification strategies on the persistence of nanocellulose in the environment is unclear. In this study, we examined the effect of three different hydrophobic silanization reagents on the structure, dispersion properties, and biodegradability of cellulose nanofibrils (CNFs). Specifically, we modified CNFs with hydrophobic alkoxysilanes containing methyl, propyl, or aminopropyl functional groups to form silane-modified CNFs (Si-CNFs). Using a combination of analytical techniques that included ATR-IR, XPS, and solid-state NMR, we demonstrated that silanization coated the CNFs with a nanometer-scale siloxane layer, and the extent of the siloxane coating could be controlled by varying the amount of silane added to the CNFs. The stability of Si-CNFs in chloroform-based casting solutions improved compared to untreated CNFs, and scaled with extent and hydrophobicity of the siloxane coating as quantified via a mass recovery settling test. Improvements in stability in casting solutions translated into improved Si-CNF dispersion in solution-blended polyhydroxyalkanoates composites as determined with optical microscopy and SEM. Conversely, the biodegradability of Si-CNFs, assessed by sample mineralization in a mixed microbial culture from an anaerobic sludge digester, was inversely related to both the degree and hydrophobicity of CNF surface modification. As mineralization of nanocellulose is rapid and complete, tracking biogas production served as a proportional measure of overall biodegradability. In the most extensively silanized samples, no mineralization of Si-CNFs was observed, demonstrating that a <2-nm-thick siloxane coating was sufficiently dense and uniform to prevent microbial access to the easily mineralized nanocellulose substrate. This study highlights the important and contrasting effects that changes to surface chemistry can have on the material and environmentally relevant properties of nanocellulose.

Engineering Lignocellulose Fibers with Higher Thermal Stability through Natural Fiber Welding

“…In contrast to what was observed with untreated CNFs, the fibers modified with MTMS and PTMS, reagents known to deliver superhydrophobic coatings, had systematically lower initial mass losses as more extensive siloxane coatings (see our previous study) were delivered to the CNF surface (see Table ). As considerable effort was taken to anneal, rinse, and dry each Si‐CNF (see Supporting Information), we attribute these mass losses to adsorbed atmospheric water after they had been dried and equilibrated with the atmosphere during open‐air storage.…”

“…A corresponding energy dispersive X‐ray spectroscopy (EDS) map (Figure d) of this 10A‐CNF bundle shows uniform distribution of silicon (from the silane reagent), supporting our conclusion that siloxane polymer uniformly coated the fibrils. Table S1, Supporting Information, presents the EDS‐measured elemental composition of each Si‐CNF; these data indicate that the silane treatment could be controlled to deliver an increasing amount of silicon onto the cellulose surface, as discussed in our previous study …”

“…Many previous studies have investigated silane‐modified materials (including cellulose), primarily focusing on using this functionalization strategy to improve the materials ability to integrate within a larger polymer composite matrix . Some of these studies have also shown that silane modifications can improve biopolymer thermal stability.…”

“…Cellulose nanofibrils (CNFs) were modified with commercially relevant trialkoxysilanes using methods reported in the literature to prepare silane‐modified CNFs (Si‐CNFs) . In a recent study, we evaluated the chemical structure of these Si‐CNFs through X‐ray photoelectron spectroscopy, attenuated total reflectance infrared spectroscopy, and solid state nuclear magnetic resonance spectroscopy. These techniques showed that silanization imparted a siloxane oligomer coating to the CNF surface without damaging the structure of the underlying fibers.…”

Preparation and Properties of Cassava Residue Cellulose Nanofibril/Cassava Starch Composite Films

“…However, CNF is hydrophilic and absorbs moisture when exposed [18]. Therefore, the surface hydrophobicity of CNF can be changed using various chemical modification techniques, thereby improving the compatibility and dispersibility of CNF in specific solvents [19]. Through phosphorylation, carboxymethylation, oxidation and sulfonation reactions, ionic charge can be introduced to the surface of cellulose [20-23]; esterification, silylation, amidation, urethanation, and etherification can make the cellulose surface hydrophobic [24][25][26].…”