Acylation of Lignin with Different Acylating Agents by Mechanical Activation-Assisted Solid Phase Synthesis: Preparation and Properties
Acylated lignins with the substituents of different length of carbon chain were prepared by a mechanical activation-assisted solid phase synthesis (MASPS) technology with a customized stirring ball mill as reactor. The structure and properties were analyzed by UV/Vis, FTIR, NMR, SEM, DSC, and TG. The results showed that either non-cyclic or cyclic anhydrides as acylating agents, the acylated lignins had been successfully prepared. Both aliphatic hydroxyl and phenolic hydroxyl groups participated in the reaction during acylation of lignin with non-cyclic anhydride, and different reactivity of acylating agents resulted in different relative content of phenolic and aliphatic substituents in the products. The reactivity of cyclic anhydrides was weaker than that of non-cyclic anhydrides, and the reactivity of acylating agents decreased with increasing carbon chain length and unsaturated bond of acyl groups. All the acylated lignins except maleated lignin had smaller glass transition temperature (T g) than original lignin. The acylated lignins prepared with non-cyclic anhydrides had better thermal stability than original lignin, and thermal stability increased but T g decreased with increasing chain length of acyl groups. The acylated lignins prepared with cyclic anhydrides had higher T g than those with non-cyclic anhydrides with the same carbon number, and the thermal stability was not improved obviously.
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