INVESTIGATION OF MECHANOCHEMICAL MODIFICATION OF LIGNIN THROUGH   ONE-STEP AND SOLVENT-FREE BALL MILLING

Xiaojie Guo

In this research, mechanochemical modification of lignin was carried out through one-step and solvent-free ball milling process. The modified lignin was utilized for preparing thermoplastic blends and thermosetting resins. Dilignol β-O-4 type lignin model compound containing 2 aliphatic hydroxyls was prepared to investigate the degradation and modification of lignin. The lignin model compound was reacted with acylating reagents in both solution reaction and ball milling environments to simulate the esterification reactions of lignin. The mechanochemical modification approach (occurred through solvent-free ball milling at room temperature within a shorter reaction time) is found to make the hydroxyls in lignin model compound more accessible to reagents than the solution reaction approach. Mechanochemical oleation between organosolv lignin (OL) and methyl oleate (MO) was carried out through ball milling process. The transesterification is found to mainly occur on aliphatic hydroxyls in lignin. Then, oleated OL was blended with poly(lactic acid) (PLA) for preparing PLA/lignin blends through melt extrusion. The dynamic mechanical, rheological, tensile properties and phase morphology of the PLA/lignin blends were investigated. Compared with the PLA/milled OL blends, the PLA/oleated OL blends exhibited a finer dispersion of lignin particles in the blends, increased glass transition temperature and higher tensile modulus and strength. Lignin-derived polycarboxylic acid (LPCA) was prepared throuh an esterification reaction between lignin and cyclic anhydrides via ball milling process. Both alcoholic and phenolic hydroxyl groups in lignin were reacted with cyclic anhydrides and accompanied with the formation of free carboxylic hydroxyl groups. The lignin-based epoxy resins were prepared using LPCA as a curing agent for DER353, and nadic methyl anhydride (NMA) as a co-curing agent. Carboxyl terminated butadiene acrylonitrile (CTBN) liquid rubber was added into the lignin-based epoxy resins to improve the toughness. Curing kinetics and dynamic mechanical properties were investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Fracture toughness (KIC) and impact stregnth were determined to measure the toughness. The CTBN-toughened lignin-based epoxy resins exhibited significant enhanced toughness and comparable stiffness than the lignin-based epoxy resins without CTBN.

INVESTIGATION OF MECHANOCHEMICAL MODIFICATION OF LIGNIN THROUGH ONE-STEP AND SOLVENT-FREE BALL MILLING

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