Preparation of Lignin Nanoparticles with Entrapped Essential Oil as a Bio-Based Biocide Delivery System

Lignin isolated from beech sawdust was used for the preparation of lignin nanoparticles (LNPs) with entrapped essential oil (EO) from cinnamon bark (Cinnamomum zeylanicum Blume), common thyme (Thymus vulgaris L.), and wild thyme (Thymus serpyllum L.) using a fast antisolvent method. Analysis of EO-loaded LNPs by pyrolysis-gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy confirmed molecular interaction between EOs and LNPs. Quantification of EO incorporation into the LNPs and their in vitro release profiles were assessed by reversed phase high-performance liquid chromatography. Utilized EOs were, to different extents, successfully entrapped inside LNPs, which were attributed to extensive π-stacking between aromatic compounds in EOs like cinnamaldehyde, thymol, and carvacrol on one side and aromatic lignin units on the other side. In vitro release of common thyme and wild thyme EOs from EO-loaded LNPs was strongly delayed compared to the use of pure oil, giving a promising outlook for the development of new bio-based biocide delivery systems for wood preservation.