Investigation of Milled Wood Lignin Extraction Using Enzymatic Hydrolysis for Application in Hydrophobic Barriers in the Food Packaging Industry

Sammanfattning: The objective of this report is twofold: to optimise the extraction method of lignin from spruce altering a few process parameters and to investigate the use of lignin as a hydrophobic barrier in food applications. The process used was STEX (steam explosion) pretreatment followed by enzymatic hydrolysis and MWL (milled wood lignin) extraction using a mixture of dioxane-water. The lignin was then collected, dissolved in acetone and coated on filter papers using an airbrush. The extraction was examined with and without enzymatic hydrolysis and with STEX pretreatment for 5 or 15 minutes. NREL (National Renewable Energy Laboratory) procedure was used for the determination of lignin and structural carbohydrate content in the raw and pretreated material. HSQC 2D-NMR was used for a semiquantitative and qualitative analysis of the extracted lignin. For the hydrophobicity testing, a Cobb test was performed to assess the water absorption properties, and a drop test was conducted to measure the contact angle. Furthermore, the surface was observed more closely using an optical microscope. The results showed that the lignin yield (g lignin extracted/g lignin in raw material) was approximately 25% for the 15-minute STEX material and 7-8% for the 5-minute STEX material, regardless of the addition of an enzymatic hydrolysis step. Furthermore, the HSQC 2D-NMR analysis revealed a cleavage of β-O-4 bonds and a higher presence of sugars in the 5-minute STEX samples compared to the 15-minute STEX samples. However, regardless of the STEX duration, the drop test showed an average contact angle of 102 to 110° for all samples. The Cobb test resulted in a Cobb value of 17g/m2. In conclusion, the findings suggest that the enzymatic hydrolysis did not significantly affect the yield or performance of the extracted lignin. Additionally, although the 5-minute STEX material had a slightly higher contact angle than the 15-minute STEX material, all samples showed promising hydrophobic properties suitable for hydrophobic barrier applications in the food industry.