(413f) Synthesis of Acrylated Thermoplastic Polymers from Crude Lignin Bio-Oil: Effect of Intrinsic Properties of Crude Bio-Oil and Synthesis Conditions
In the present study, renewable thermoplastic polymers were produced from crude lignin bio-oil using a controlled radical polymerization technique. The bio-oil, produced from red oak lignin by pyrolysis, consists of 4% of phenolic monomers and over 95% of aromatic oligomers. The Mw and Mn of the lignin bio-oil were 653 g/mol and 388 g/mol, respectively, and there were 5.6 moles of -OH groups per mole of lignin bio-oil. The bio-oil composed of mostly multi-hydroxyl group compounds was first functionalized using a combination of partial acrylation and acetylation prior to the subsequence Reversible Addition Fragmentation Chain Transfer (RAFT) polymerization in order to control the number of polymerizable site per molecule while eliminating the radical inhibitory effect of the reside phenolic -OHs. In the present study, the effects of experimental parameters on the polymer synthesis were further studied in detail. It was found that the molecular weight of the arylated polymer and its yield both increase as the degree of the acrylation or the AIBN concentration increase. The results also showed that at least 3wt% of AIBN and 1 unit of acrylation (i.e., 1mole vinyl C=C per mole of bio-oil) are required to obtain reasonably high molecule weights and yields of the polymers. In this study, the polymers with yields up to 68% and Mw of 22kg/mol were obtained upon reacting at 90 for 4 hours. Based on the EPR analysis, it was found that AIBN is partly consumed by the intrinsic free radicals in lignin bio-oil through radical termination reactions. It was also found that the presence of a chain transfer agent can help to reduce crosslinking, therefore preventing gelation during the polymer synthesis. In this study, all resulting polymers exhibited the decomposition temperature higher than 215â, and the temperature for maximum decomposition rate at about 350 â. The solid residues of the polymers upon pyrolysis at 1000 â were about 35-36%, showing their high heat tolerance. While Tgs of the polymers could reach up to 130 â, there was a linear relationship between the Mns of the polymers and their corresponding Tgs. The rheological results showed that the polymers synthesized using lower AIBN concentrations and lower degrees of acrylation exhibited overall reduced complex viscosity and improved meltability.