Synthetic lignin-like and degradable nanocarriers

Abstract

Lignin is a highly abundant biopolymer that is a by-product formed during paper manufacturing. Lignin is degraded by certain lignase-producing fungi and is relatively stable towards hydrolysis, which makes it an attractive material for diverse applications ranging from packaging to agrochemical delivery. However, a major challenge that hinders the large-scale use of lignin is its ill-defined chemical structure as a crosslinked copolymer with a variable comonomer composition, which results in strong batch-to-batch variations. To eradicate such a structural heterogeneity, herein, we synthesized two lignin-like monomers, comprising linkages found in native lignin, i.e., phenylcoumaran and β-O-4-aryl ether, and used them for the preparation of lignin-like nanocarriers by interfacial crosslinking in an inverse miniemulsion. The lignin-like monomers are accessible by a 2- or 4-step synthesis starting from bio-based compounds and can be prepared on a multigram scale. They carry hydroxyl groups, which reacted with toluene diisocyanate to produce lignin-like polyurethane nanocarriers with diameters between 200 and 400 nm. The nanocarriers might be used for the encapsulation of fungicides and for plant protection, as the lignin-like structure allowed the degradation by lignase-producing fungi, which are the cause of many plant diseases. Therefore, the dispersions might be of interest as a degradable drug delivery system, e.g. in advanced plant protection, or as synthetic alternatives to natural lignin.