Synthesis And Application Of Cellulose Nanocrvstals Grafted Polyethylene Glycol As Solid Solid Phase Change Material

Energy consumption and resource shortage have seriously affected the development of the whole society.How to effectively use and save energy has gradually become a research hotspot,and energy storage is an effective method to solve this problem.Therefore,efficient energy storage technologies have attracted much attention.Compared with traditional sensible heat storage technology,solid-solid phase change latent heat storage technology has attracted wide attention due to its advantages such as high energy storage density and stable operating temperature.In this study,high-performance nanocellulosic crystals(CNCs)were prepared by using a novel oxidation method using biomass cellulose with abundant natural reserves as raw materials.In this study,high-performance cellulose nanocrystals(CNCs)were prepared by using a novel oxidation method using biomass cellulose,which is rich in natural reserves and renewable raw materials,as a framework material.Research on the influence of reaction time on the microstructure,chemical structure,thermal stability and suspension stability of CNCs framework materials has important guiding significance for the extraction and application of renewable biomass green resources.On this basis,using polyethylene glycol(PEG)as a phase change energy storage unit,a CNCs-g-PEG solid-solid phase change material(PCM)was prepared by a graft copolymerization method.Investigating the solid-solid phase transition behavior and heat storage/release mechanism of composite systems.This kind of green solid-solid phase change composite material is of great significance to improve energy utilization efficiency,fully develop renewable resources,and solve problems such as resource shortage and energy shortage.(Ⅰ)Preparation of carboxylated cellulose nanocrystals by high performance hydrogen peroxide oxidation and their characterization:The CNCs was prepared by hydrolyzing microcrystalline cellulose by an environmentally friendly Fe2+/H2O2 oxidation method,and the by-products of the reaction were water and oxygen.The mechanism of Fe2+/H2O2 oxidation was explored,and the influence of reaction time on the microstructure,chemical properties and suspension stability of CNCs was investigated.Electron spin resonance spectroscopy indicated that the Fe2+/H2O2 system produces highly oxidizing hydroxyl radicals.The obtained CNCs showed a clear rod shape,a uniform and narrow size distribution.The oxidation system had no effect on the glucose ring structure of CNCs.Hydroxyl radicals primarily attack primary hydroxyl groups and introduce carboxyl functional groups.The obtained CNCs had a small size(the length of 94.6 nm,the diameter of 20 nm),high carboxyl content(2.2 mmol/L),and excellent thermal stability(the initial decomposition temperature To of 308.2℃)and good suspension stability(greater than 24h)at 60℃ for 12 h,which provides a prerequisite for CNCs applications in the field of high temperature energy storage.At the same time,Methylene blue(MB)adsorption experiments were performed to verify that the prepared CNCs had a large number of carboxyl groups on the surface,which lays the foundation for the subsequent loading of phase change polymers to synthesize phase change materials.(Ⅱ)Controllable design and preparation of cellulose nanocrystal grafted polyethylene glycol solid-solid phase change composites:In the aqueous solvent,a Fe2+/H2O2 mixed system was used as the initiator,and PEG was used as the phase change unit.The solid-solid phase change composite material with the CNCs grafted PEG side chain was obtained by graft copolymerization.The effects of different reaction times on the thermal stability,phase transition properties,solid phase transformation behavior and shape stability of PCM were investigated.PCM exhibited good solid-solid phase transition behavior due to the limitation of the movement of the PEG side chain by the CNCs framework.Compared with pure PEG,PCM had a lower and suitable phase transition temperature,and the thermal decomposition temperature was higher than 300℃,especially PCM-12h exhibited better thermal cycle stability,ambient temperature responsiveness and shape stability.It could actively absorb storage and release heat to maintain a suitable target temperature range(15-30℃).It provided a novel solid-solid phase change material suitable for human microenvironment heat storage and temperature regulation.It could be used in energy storage areas such as textile/clothing and building insulation materials with intelligent heat storage temperature control.