Effective Lignin-Based Binders for Particle Boards

In this work, bio-based composites were prepared by transesterification of different types of lignin with tung oil followed by co-polymerization with divinylbenzene in the presence of pine wood particles. The results obtained reveal that regardless of the source of lignin used, the preparation of the composites was successful, with less than 20 wt % of unreacted material recovered after Soxhlet extraction and no residual curing detected via Differential Scanning Calorimetry (DSC). Thermogravimetric Analysis (TGA) of the composites showed that the addition of pine wood particles to the co-polymer decreased the overall thermal stability of the materials due to the faster degradation rate of cellulose and hemicelluloses in wood, in comparison to lignin. Dynamic Mechanical Analysis (DMA) showed that the glass transition temperature and the storage modulus (E’) of the materials are dependent on the source of lignin employed. The latter, when measured at room temperature, increased with the addition of wood particles, demonstrating their reinforcing effect. Commercial alkali lignin exhibited a 3.5-fold increase in E’ after the addition of wood particles smaller than 150 μm. Finally, water absorption experiments and Scanning Electron Microscopy (SEM) images suggest a good interaction between modified lignin and pine wood particles. Overall, the strategy employed for the preparation of lignin-based composites was successful for the different sources of lignin used with final properties being heavily dependent on the specific source employed.