Acidic and alkaline deep eutectic solvents pre-treatment to produce high aspect ratio microfibrillated cellulose

[Display omitted] •Deep eutectic solvents (DES) pre-treatment enhances the microfibrillation process.•Microfibrillated cellulose with high aspect ratio.•Produced microfibrillated cellulose exhibit good mechanical properties.•Reduced energy consumption during the microfibrillation process.•DES are considered as green pre-treatment for cellulose microfibrils production. This study highlights the microfibrillation potential of three deep eutectic solvents (DES) composed of betaine hydrochloride-urea, choline chloride-urea and choline chloride-monoethanolamine. Cellulose fibres (eucalyptus and cotton) were first treated in DES (100 °C for 4 h) and then ground with an ultra-fine grinder to produce microfibrillated cellulose (MFC). DES pre-treatment especially betaine hydrochloride-urea system has significantly improved the microfibrillation process with reduced energy consumption comparable to that of enzymatic treatment (reference pre-treatment). Long and thin microfibril bundles (widths around 50 nm) and individualised microfibrils (widths between 5 and 10 nm) were obtained. MFC gels and nanopapers were characterised using several techniques. Nanopapers produced from DES treated MFC showed good mechanical properties with Young’s modulus higher than 10 GPa. In addition, they exhibited higher quality index (between 73 and 76) than those produced from enzymatic hydrolysis (quality index around 68). DES pre-treatment is a promising way to produce MFC with high aspect ratio.