NOVELTY - Fractionation (M1) for producing value-added bioproducts from a lignocellulosic biomass, involves: (a) mechanically refining the lignocellulosic biomass under mild refining conditions to form a refined biomass pulp with enhanced susceptibility to separation of hemicellulose, cellulose and lignin, and enhanced digestibility of carbohydrates in hydrolysis; (b) separating hemicellulose and sulfur-free high-quality lignin from cellulose in the refined biomass; and optionally (c) producing various bioproducts.    USE - For fractionation of lignocellulosic biomass for producing value-added bioproducts comprising flavonoids (claimed), the flavonoids are useful as antioxidants and for treating some diseases; also for producing the other recovered valuable bioproducts and biofuels e.g. ethanol (biofuel), furfural, xylitol, and xylo-oligomers.    ADVANTAGE - The process is a green process to convert lignocellulosic biomass to a highly digestible biomass and multiple bioproducts under mild conditions involving using a low pressure refiner with minimum refining energy, hemicellulose extraction, enzymatic hydrolysis, sugar/lignin separation, fermentation, and few chemicals. The process can be easily retrofitted into existing mechanical pulp mills. The process provides high yields of biofuel and produces multiple products comprising sugar, from the biomass.    DETAILED DESCRIPTION - Fractionation (M1) for producing value-added bioproducts from a lignocellulosic biomass, involves: either (i): (a) mechanically refining the lignocellulosic biomass under mild refining conditions to form a refined biomass pulp with enhanced susceptibility to separation of hemicellulose, cellulose and lignin, and enhanced digestibility of carbohydrates in hydrolysis, (b) separating hemicellulose and sulfur-free high-quality lignin from cellulose in the refined biomass; and optionally (c) producing various bioproducts; or (ii): step (a), (b) extracting a hemicellulose fraction from the refined biomass pulp to leave a residual pulp containing lignin, (c) hydrolyzing carbohydrates in the residual pulp to sugars, (d) separating a lignin fraction from the sugars, (e) fermenting the sugars to form biofuels, and (f) recovering the hemicellulose fraction and the sugar alcohol as value-added products.