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Biopolymer blends from hardwood lignin and bio-polyamides: Compatibility and miscibility

Muthuraj, R., Hajee, M., Horrocks, A.R., Kandola, B.K.
International journal of biological macromolecules 2019 v.132 pp. 439-450
Fourier transform infrared spectroscopy, Gibbs free energy, biopolymers, glass transition, hardwood lignin, lignin content, melting, polyamides, thermal degradation, thermogravimetry, viscosity
The compatibility of hardwood lignin (TcA)/bio-polyamide (PA) blends, prepared by melt compounding TcA with three different biobased polyamides, PA 1012, PA 1010 and PA 11 in a twin screw extruder has been studied. FTIR studies indicated the existence of physicochemical interactions between the TcA and polyamide. The melting temperatures of the blends were significantly reduced compared to the respective neat polyamides, which was attributed to the enhanced compatibility between the two components. The compatibility was also attributed to the increased glass transition (Tg) of the polyamide. Thermogravimetric studies, while not indicating any interaction during the processing stage, suggested that there was some during the thermal degradation stage, which assisted formation of carbonaceous residue. The addition of each polyamide to TcA considerably reduced its viscosity and enhanced its processability even at high lignin contents. Morphological analysis showed that heterogeneity for all the blends was quite uniform, although TcA domain sizes were considerably smaller (~0.5 μm) in the PA11 matrix compared to those in PA1010 and PA1012, suggesting better compatibility in the TcA/PA11 blends. This observation was consistent with the thermodynamic Gibbs' free energy values of the respective blends. Overall, the order of blend compatibility was TcA/PA11 > TcA/PA1010 > TcA/PA1012.