Our previous results proved that synthesized lignin grafted poly(ε-caprolactone) (lignin-g-PCL) co-polymers possess excellent compatibility and dispersion in various solvents and can be applied to manufacture eco-friendly materials such as biodegradable plastics. Molecular weight is a vital parameter for the synthesis, structure, property, and biodegradability of lignin-g-PCL. However, lignin possesses a heterogeneous structure with broad molecular weight distribution. In this study, kraft lignin, an industrial waste from paper and pulping mill, is fractioned into different molecular weights (&lt;1,000 Da, 1,000-2,500 Da, 2,500-5,000 Da, and &gt;5,000 Da) using sequential solvents fractionation with acetone−methanol cosolvent and dose-increasing hexane. Lignin-g-PCL copolymers with different lignin molecular weight are afterwards synthesized, and structurally characterized by gel permeation chromatography (GPC), Fourier-transform infrared spectroscopy (FTIR), 31P nuclear magnetic resonance (NMR) and 2D heteronuclear single quantum correlation (HSQC) NMR. The thermal properties are analyzed by differential scanning calorimetry (DSC) and thermogravimetry (TG). The surface energy is measured with inverse gas chromatography (iGC). This work is expected to provide a rational structure-properties correlation for lignin-g-PCL polymers to be applied in packaging and biomedical fields.

Effect of lignin molecular weight on structural and thermal properties of synthetic lignin-grafted-poly(ε-caprolactone)

ACS Spring 2022

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