Structure Design And Controlled Fabrication Of Nanocellulose-based Aerogels For Personal Thermal Management

Lightweight,elastic,waterproof,energy-saving personal thermal management（PTM）materials with adjustable heating have gained attention due to the popularization of outdoor sports,the expansion of human exploration,and the increasing awareness of energy conservation.Textile materials,as the interface between the human body and the external environment,are the research focus in the field of personal thermal management.Traditional insulation materials,such as wool,batting,and down,are unable to meet the complex and changeable outdoor environment due to their bulky and heavy nature,drastic reduction in insulation performance under wet conditions.Aerogel,with its three-dimensional porous nano-cell structure,has a low thermal conductivity and density compared to traditional textile materials,making it an excellent choice for PTM in extremely cold climates.Among them,cellulose nanofiber（CNF）aerogel not only inherits the characteristics of nanocellulose,such as high aspect ratio,high specific surface area,ease of modification,and biodegradability,but also has advantages such as light weight,porosity,and adjustable structure.However,in practical applications,CNF aerogel has issues such as poor structural stability,moisture absorption,and limited insulation.Therefore,this study aims to develop a lightweight and high-elasticity CNF-based aerogel with ordered structure,waterproof properties,and adjustable heating mode to achieve technological breakthroughs in lightweight,structured science,and rational functionality of advanced textile materials for PTM.This study focuses on enhancing the thermal management performance of CNF-based aerogels by structural design,interface regulation,and functional optimization.Firstly,using CNF fibers as building units,the influence of ice crystal nucleation and growth on the pore structure of CNF aerogels during ice-guided self-assembly was studied,achieving the controllable and precise construction of a three-dimensional structure.Secondly,the introduction of chitosan（CS）reinforcement and glutaraldehyde crosslinking was used to construct a dual network"interlocking"structure and combined with directional freezing technology to enhance mechanical stability.Thirdly,through UV-induced in-situ grafting of polydimethylsiloxane（PDMS）low surface energy polymer,a"micro-nano"rough structure and"soft-hard synergistic"reinforcement interface were constructed,achieving the synergistic optimization of hydrophobic and wear-resistant functions with a lightweight and porous structure.Finally,by carbonization treatment and silver nanowire（Ag NWs）coating,a multi-mode adjustable Ag NWs/carbon aerogel was prepared,and an environment-adaptive PTM system was constructed.The specific research summary is as follows:（1）Using 2,2,6,6-Tetramethylpiperidinyl-1-oxyl（TEMPO）oxidize CNF as the building unit,we explored the impact of various parameters such as wetting properties,freezing temperature,precursor concentration,additives,freeze-thaw cycles,and temperature gradients on the ice nucleation and growth during the CNF self-assembly process via ice-templating technique.The study aimed to elucidate the mechanism of pore structure regulation for CNF aerogels and achieve in-situ and precise construction of the CNF aerogel three-dimensional network.Results showed that the CNF aerogel possessed a hierarchical pore structure including macro-,meso-,and micro-pores with adjustable pore sizes ranging from 0 nm to 500μm.Furthermore,the direction of the temperature gradient can be adjusted to control the random,unidirectional,and bidirectional three-dimensional structure.（2）Concerning the issue of poor structural stability of CNF aerogel,we introduced CS as a reinforcement and glutaraldehyde as cross-linking agent to construct a dynamic network through Schiff base reaction,and combined with directional freezing process to further prepare anisotropic CNF/CS（G-CNS）"interlocked"double-network aerogel.The impact of cross-linking concentration on the pore structure and flexibility of G-CNS aerogel was studied,and the reinforcement mechanism of dynamic network and anisotropic structure on G-CNS aerogel was explored.The results showed that the cross-linking network could effectively prevent the slippage of CNF under external pressure.At the same time,the three-dimensional ordered structure dispersed the stress,showing compression resilience（no loss after 100 cycles of 60%stress）and toughness（4 times higher than CNF aerogel）in the transverse and longitudinal directions respectively.The G-CNS aerogel had a thermal conductivity of 28m Wm^-1K^-1 in the radial direction and 36 m Wm^-1K^-1 in the axial direction,making it possible to design adjustable structures according to the needs of thermal insulation and heat dissipation in different parts of the human body.（3）To address the issue of the moisture absorption and structural collapse of CNF-based aerogels in humid environments,a UV-induced rapid curing method was adopted to graft low surface energy PDMS onto the G-CNS aerogel matrix,constructing a PDMS/CS-CNF（P-CNS）aerogel with a"soft-hard synergy"interface and"micro-nano rough"structure.The influence of PDMS grafting amount on the interface strength and hydrophobic surface was studied,achieving synergistic optimization of hydrophobic and wear-resistant properties as well as three-dimensional porous structure.Results show that the"micro-nano rough"structure endows the P-CNS hybrid aerogel with super-hydrophobic properties（contact angle of approximately168.0°）.At an ambient humidity of 90%,the thermal conductivity of the P-CNS aerogel is as low as 25.7 m W·m^-1·K^-1,much lower than that of other currently used insulation materials.Compared with traditional thermosetting processes,the UV-induced curing process generates no stress,avoiding the destruction of the aerogel’s porous network structure.The P-CNS aerogel has a density of 9.42 mg/cm³ and a porosity of 99.29%.Moreover,the point-to-point grafting ensures the uniformity and bonding strength of the PDMS coating.The P-CNS hybrid aerogel can recover completely from an 80%deformation radially and has a tensile strength of4.66 MPa axially,withstanding more than 1000 compressive cycles at a 50%deformation.（4）In order to tackle the problem of a single heating mode and limited adaptability to changing outdoor environments in CNF-based aerogels,Ag NWs/carbon aerogels were prepared through G-CNS aerogel carbonization and Ag NWs deposition,while achieving high resilience,super-hydrophobicity,and thermal insulation.The porous structure of Ag NWs/carbon aerogels was further densified,resulting in an increased porosity（99.13%）and specific surface area（503.2 m²/g）.The axial thermal conductivity of Ag NWs/carbon aerogel was 18.2 m W·m^-1·K^-1and the radial thermal conductivity was 91.5 m W·m^-1·K^-1,providing higher guarantee for the transmission efficiency and energy storage capacity of aerogel.The infrared emissivity of Ag NWs/carbon aerogel was only 17%at 7–14μm,the solar absorption rate was approximately91.97%.Under low voltage（5 V）,the temperature can rise by 44.5℃within 3 mins.Ag NWs/carbon aerogels can achieve PTM in different environmental climates through various heating modes,including thermal insulation,self-heating,solar heating,and Joule heating.The temperature can reach 155.7℃under full mode.An environment temperature adaptive multi-mode heating mechanism was explored,providing an effective solution for PTM under extreme climates.