Alkali synergetic two-step mechanical refining pretreatment of pondcypress for the fiber with intact 3D structure and ultrahigh cellulose accessibility fabrication

•Combined chemical impregnation and two-step mechanical refining was successfully used to break biomass recalcitrance.•Prepared fibers exhibited high cellulose accessibility, surface active hydroxyl content and specific surface area.•Fiber with intact spatial structure was promising for cellulose-based composite materials.•The synergistic effects between chemical impregnation and two-step mechanical refining could enhance fiber performances. Although lignocellulosic biomass has promising applications in biodegradable cellulose-based composite materials due to its high specific surface area and high rigid intensity, lignocellulosic fiber with multiple surface reactive sites and intact spatial structure is still a great challenge as a versatile carrier for composite materials. Herein, a feasible strategy that combined alkaline hydrogen peroxide (AHP) impregnation and two-step mechanical refining was presented to treat the pondcypress (taxodium ascendens) for enhancing cellulose accessibility and specific surface area. Additionally, the prepared pondcypress fiber kept the intact spatial structure. First, the destruction of molecular structure barrier was synergistically realized by the NaOH and H2O2, that improved the efficiency of 2nd mechanical refining. Subsequently, the fibers exhibited an excellent dissociated result under the effect of shear stress and friction at low energy consumption (1637 kW h/t). As a result, the fibers achieved ultrahigh cellulose accessibility of 77.07 % and high surface active hydroxyl content of 2.164 × 10−3 mol/g due to the exposure of S2 cell wall at the 16 % H2O2 and 17.5 % NaOH. Moreover, despite the fibers were fibrillated after treatments, the intact spatial structure of fiber was observed by SEM. These results confirm that AHP impregnation and two-step mechanical refining are an effective method to dissociate the fiber, and this work opens up more avenues to use the lignocellulosic fiber in cellulose-based composite materials.