Chemical methods to increase the reactivity of lignin : In the context of green chemistry and education for sustainable development
The research concerning lignin in high value applications has increased during the last years due to its renewability and availability in the black liquor from pulp mills. Today the major part of kraft lignin found in the black liquor is used as fuel to gain energy in the recovery boiler. Lignin functions as natural glue in plants so that the function of kraft lignin as a phenol replacement in wood adhesives has been researched. Due to lignin's low reactivity the molecule must be modified prior to use. Demethylation is a method to increase the phenolic content in lignin to produce more reactive sites. Thiol mediated and iodine mediated demethylation was performed. Demethylated lignin was characterized by changes in phenolic and hydroxylic groups, molecular mass, elemental composition and other properties using methods including UV, SEC and 31 P NMR.
The results showed a decrease in the phenolic content contrary to the increase that was expected. Really low yields were also gained which makes the results non-representative. Size evaluation showed that the percentage of high molecular content in the demethylated lignin sample had increased, which point towards the loss of low molecular mass fractions. Due to demethylation lignin may have been more hydrophilic and soluble in DMF and water. In addition to this bond cleavage may have produced smaller fragments which also increase the solubility. The results point towards the loss of smaller fragments in the DMF and water phases.
The applied demethylation methods were evaluated in context of green chemistry. Production, waste, involving chemicals and efficiency were discussed and analyzed. The applied demethylation methods use DMF as solvent which is not a green alternative, greener solvents such as water or other energy adding methods could be used to make the process greener. The use ofNaOMe produces methanol as a byproduct which could be eliminated by using NaOH, future studies on the efficiency of the bases in the needs to be done.
Nature science has a reputation of being hard and firm. By bringing in social issues in science education new ways of looking at science opens up. A social problem and at the same time an environmental problem in today's society is the large plastic mountain in the Pacific Ocean. An educational material of the "Samhallsfragor med Naturvetenskapligt Innehiill",SNI, (Societal issues with scientific content) principle has been evaluated with respect to the abilities that can developed together with whether students increase their science knowledge through this. The study showed that students can develop almost all abilities described in the curriculum and their knowledge in science by this type of material.
Keywords Biomaterial, lignin reactivity, thiol mediated demethylation, iodine mediated demethylation, green chemistry, SNl-fall.
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