Integrated pretreatment of poplar biomass employing p-toluenesulfonic acid catalyzed liquid hot water and short-time ball milling for complete conversion to xylooligosaccharides, glucose, and native-like lignin

•A combined pretreatment was introduced for the complete conversion of poplar biomass.•TsOH-catalyzed LHW pretreatment solubilized 98.5% of hemicellulose from poplar.•A xylooligosaccharide yield of 49.8% was obtained from single pretreatment.•Subsequent ball milling enhanced the enzymatic hydrolysis of cellulose to 96.5%.•Integrated pretreatment process protected 55.7/100 Ar of β-O-4 linkages in lignin.