Research On The Rapid Microwave Preparation Of Cellulose Nanomaterials And Their Stability Mechanism In Functional Fluids

With the continuous exploration and development of oil and gas resources in our country,various functional fluids(such as water-based drilling fluids,magnetorheological fluids,water-based fracturing fluids,etc.)used in drilling engineering have received extensive attention.This thesis focuses on the technical problems of rheological regulation and stability control of such functional fluids,and focuses on the mechanism of cellulose nanomaterials with unique network structure on the rheological properties and stability performance of functional fluids.Also,this thesis explored a variety of new methods for rapid preparation of cellulose nanomaterials based on microwave-assisted technology.More importantly,a series of novel and environmentally friendly functional fluids based on cellulose nanomaterials have been developed.The main research contents of this thesis are listed as follows:(1)Cellulose nanofibers(CNFs)were rapidly prepared from waste bagasse by microwave-assisted chemical pretreatment and mechanical treatment,which are used as rheology and filtration modifiers in water-based drilling fluids(WDFs).In particular,the delignification rate of lignin was96.4%after this microwave pretreatment,and the mean diameter of the treated lignocellulose was decreased from 82±24?m to 9±2?m.The as-produced CNF suspension exhibited typical shear thinning behavior and gel-like viscoelastic properties due to its highly entangled network structure.Formulated fluids with the manufactured CNFs showed good rheological and filtration properties,demonstrating their potential applications in the oil service industry.Then,a faster and novel method(microwave-assisted alkali-H₂O₂ pretreatment combined with ultrasonic treatment)was developed to prepare CNFs to figure out the serious sedimentation and redispersibility problems of magnetorheological fluids(MRFs).This pretreatment removed the most lignin(94.3%),and the structural analysis revealed that the cellulose was also oxidized.The as-obtained CNF suspension exhibited the gel-like viscoelastic behavior.CNFs helped suspend magnetic particles in MRFs,leading to improved stability and magnetorheological properties(i.e.,viscosity reversibility rate of 95.57%after 100 cycles).This result was due to the highly entangled network of CNFs and the electrostatic repulsion between CNFs and magnetic particles.These also indicated that a new path for the production of CNFs from waste bagasse and their high-value utilization in MRFs.(2)Since the presence of residual lignin is conducive to the formation of a highly entangled network structure of nanocellulose,a green and sustainable method(microwave-assisted deep eutectic solvent(DES consisting of choline chloride/lactic acid)pretreatment combined with mechanical treatment)was developed to prepare the lignin-containing nanocellulose(LCNFs).Under optimal conditions(110?and 30 min),the lignin content of 13.7%and the yield of 45.2%in LCNFs were obtained,and 88.4%of DES was recycled and reused.Compared with the CNFs suspension,the LCNFs suspension with the same concentration showed a higher viscosity and a more obvious entangled network structure due to the binder role of lignin between nanocelluloses.Therefore,the addition of a small amount of LCNFs(0.1 wt%)can greatly improve the rheological properties and filtration properties of low-solids WDFs,even better than high-solids WDFs,providing a novel WDF that is sustainable and green for drilling applications.In addition,the application of LCNFs in fracturing fluids(FFs)can also suspend proppants well(even at high temperatures after standing for 24 hours),which significantly improved the rheological properties and suspension stability of FFs.This also provides a sustainable and green approach to improve the oil and gas productivity in the fracturing process.(3)A sustainable,environmentally friendly and ultra-fast method(microwave-assisted natural DES(NADES consisting of betaine hydrochloride/glycerol)pretreatment combined with microfluidization treatment)was developed to prepare LCNFs,which were utilized as rheology modifiers and stabilizers for MRFs.The NADES can be isolated from natural plants,and this sustainable pretreatment method only takes 30 seconds that can remove most lignin(77%delignification)and graft cellulose carboxylate groups.The as-obtained LCNFs suspension can suspend the magnetic nanoparticles well,even after standing for one month,which is mainly due to the physical entanglement of the LCNFs network and the electrostatic repulsion between the LCNFs and the magnetic nanoparticles.More importantly,the magnetorheological properties of MRF modified with LCNF(LCNF-MRF)were improved significantly,and the viscosity of LCNF-MRF at different magnetic fields are also tunable,reversible,and stable(viscosity retention rate of98.7%after 100 cycles).In addition,this smart LCNF-MRF provides a sustainable and effective approach for future practical applications.