Preparation And Characterization Of Bamboo-based Nanocellulose Aerogel Oil Absorbents

In recent years,the increasingly frequent marine oil spill accidents have caused serious threats to the marine ecological environment and human health.The development of high-performance oil absorbents to achieve rapid removal is considered to be an efficient and convenient method.Cellulose nanofiber(CNF)aerogels represent a new form of porous material with high porosity,low density and high specific area,that can serve as promising candidates as oil absorbents in oil spill treatment.But there still exsit some problem of the reported CNF aerogels absorbents,such as poor mechanical properties,length process and low resuablilty,which limited their practical application.In this study,high-quality CNF was prepared from bamboo parenchyma cells with low energy input.By combing liquid silane modification and directional freezing method,ultralight,hydrophobic,resuable CNF aerogel oil absorbents were successfully prepared,which provide a viable solution for efficient treatment of oil spills.The detailed research contents and results are highlighted as follows:(1)The mature bamboo(Phyllostachys edulis(Carr.)H.De Lehaie)culm was separated into fiber(BF)and parenchyma cells(BP)using a simple water-basd physical separation technique,and they have show significant differences in cell wall morphology,chemical components,crystallinity index,which results in significant energy consumption to prepare CNF.By using ultrasonication process,BP were totally disintegrated into CNF after 20 min of treatments,and form a stable gel;while the BF could not be completely disintergrated into CNF as the suspension still exited some unfractured fiber bundle,therefore precipitation occured after placing for 20 min.By using microfluidzation process,BP need 5 passes through the homogenizer,while BF need at least 15 passes in order to obtain CNF.Furthermore,by combing the TEMPO pretreatment and microfluidization,only 1 pass through the homogenizaer is needed to prepare CNF with average diameter of 20 nm.(2)The compressive and hydrophobic CNF aerogels were prepared by directly freeze-drying the CNF suspension mixed with acid-hydrolyzed methyltrimethoxysilane(MTMS)sols,namely liquid phase modification.Meanwhile,the aerogels became hydrophobic with a water contact of 141°.The structure and properties of CNF aerogels before and after modification were characterized by various methods,and the mechanism of liquid phase modification of MTMS was systematically studied.The introduction of MTMS significantly improved the toughness of CNF aerogels,and the highest recovery radio of 91%was reported when compressed at 50%strain.The disordered microstructure with randomly interconnected CNF sheets generally results in limited oil absorption properties,with a reduction from 116 to22 g/g after modification.(3)To increase the oil absorption properties,CNF suspensions were successfully fabricated into highly compressible,hydrophobic and anisotropic CNF aerogels with aligned lamellar architectures by directionally freeze-casting of CNF suspensions with acid-hydrolyzed MTMS sol.The obtained CNF aerogels exhibited ultralow densities(5.70–10.92 mg/cm~3),good hydrophobicity(water contact angle of 141°),and excellent compressive recovery ability with a high recovery rate of 90%after 100 compression cycles.Directional freezing significantly improved the oil absorption of modified CNF aerogels,showing a high absorption capacity of 130 g/g toward gasoline,pump oil and chloroform with a fast absorption speed of reaching absorption equilibrium within 5–10 min.(4)In order to further improve the mechanical properties of pure CNF aerogel oil absorbents,polyvinyl alcohol(PVA)was added as a reinforcing component.First,MTMS was added to the CNF/PVA mixed sol and stirred uniformly.Then,the directional freeze-drying method was used to prepare hydrophobic CNF/PVA composite aerogels.The addition of PVA significantly improves the compressibility of the aerogel,which ensured the structural integrity of aerogels after 100 cycles at a large compressive strain of 70%.Also,the aligned macroporous structure allowed the aerogel to absorb oils and organic solvents with a oil absorption capacity of 45-99 g/g and good reusability over 35 absorption-squeezing cycles.