Synthesis and Characterization of Storage Energy Materials Prepared from Nano-crystalline Cellulose/

Chinese Chemical Letters Vol. 17, No.8, pp 1129-1132, 20061129http://www.imm.ac.cn/journal/ccl.htmlSynthesis and Characterization of Storage Energy MaterialsPrepared from Nano-crystalline Cellulose 1Polyethylene GlycolXiao Ping YUAN!2, En Yong DING'*'Key Laboratory of Cellulose and Lignocellulosics Chemistry, Guangzhou Institute of Chemistry,Chinese Academy of Science, Guangzhou 510650Graduate School of the Chinese Academy of Science, Beijing 100039Abstract: This paper gives a brief report of the synthesis of a new kind of solid-solid phase changematerials (SSPCMs), nano-crystalline cellulose/polyethylene glycol (NCC/PEG). These PCMshave very high ability for energy storage, and their enthalpies reach 103.8 J/g. They arecomposed of two parts, PEG as functional branches for energy storage, and NCC as skeleton.The flexible polymer PEG was grafted onto the surface of rigid powder of NCC by covalent bonds.The results of DSC, FT-IR were briefly introduced, and some comments were also given.Keywords: Nano-crystalline cellulose (NCC), polyethylene glycol (PEG), phase change materials(PCM), energy storage, DSC.The development and the application of phase change materials (PCMs) as a new kind ofmaterials have attracted both scientific and industrial interest'. According to thepatterns of phase conversion, commonly PCMs are divided into solid-liquid phasechange materials (SLPCMs) and solid-solid phase change materials (SSPCMs).Especially in recent years much effort has been devoted to the research and the use ofSSPCMsS,6 due to the SSPCMs can keep the same shape in a solid state even when thetemperature of the PCMs is over the transition one. SSPCMs can be directly moldedinto PCM devices.Vigo and his colleagues use PEG to graft onto the surface of natural cellulose fiberto obtain SSPCM', and the enthalpy of this PCM is less than 15 J/g. In view ofnano-crystalline cellulose's (NCC's) the high specific surface area and high chemicalreactivity resulted from a lots of hydroxyl groups on its surface-l, NCC is introduced asskeleton for the synthesis of a new kind of SSPCMs.It can be reasonably anticipatedhat more PEG molecules can be grafted onto the surface of NCC than naturalcellulose'-ln with the same amount of celluloses, so the final NCC/PEG composites willhave very high ability for energy storage.中国煤化工MYHCNMHG"E-mail: Dingey@ gic ac.cn1130Xiao Ping YUAN et al.ExperimentalNCC/PEG energy storage material was synthesized through the following three steps: (a)synthesis of nan-clllulose acrylate2.13; (b) synthesis of polyethylene glycol acrylatel4.1s;(c) copolymerization of nano-crystalline cellulose acrylate and polyethylene glycolacrylate. The synthetic router is outlined in Scheme 1.(a) Nano-crystalline cellulose was dispersed in the N, N-dimethyl formamide (DMF)solution (50 mL) in a flask, under N2, after cooling to 0°C, a suitable amount of acryloylchloride was slowly dropped in the flask under mild stirring. After 2 h the unreactedacryloyl chloride and the HCI produced during the acylation reaction were stripped outby N2. The reaction mixture was used in the next procedure.(b) In a 150 mL four- necked round-bottled flask, the solution of polyethylene glycol(w: 4000, 20 g, [OH]=0.01 mol) in 50 mL toluene was added. Under N2, 2 mL ofacryloyl chloride was dropped in the flask at 0°C. After 2 h the reaction was over, themixture was used in the next procedure.(c) The solution of nano-crystalline cellulose acrylate was added to the solution ofpolyethylene glycol acrylate and stirred for 2 h at room temperature. After addition ofsuitable benzophenone as initiator of radical polymerization, the polyethylene glycol wasgrafted on the surface of nano-crystalline cellulose by use of UV radiation. Theresulting product was washed with distilled water and dried at room temperature.Scheme 1- CH2OH-CH2O- - C- -CH=CH20-C(aHoCH2=CH -C-cL“tHO-VOOHO() HO+CH,CH2OHhH+ CH,=CH+ -C-cL “CH,=CH-C-o+CH.CH2O+.R一CH2O-CH=CH2(C) CH2=CH-C- o+CH2CH2O+,R+ THOORJnnet- structure or comb-structure products R=H or CH2= CH-a) 0"C and N2b)benzophenone; UV(250 W) radiation for 30 minResults and DiscussionFigure 1 shows the framework vibration FT-IR spectra for nano-cryatalline cellulose (a),nano-crystalline cellulose grafted by polyethylen中国煤化工lene glycol4000 (c). It can be seen that the absorption band.YHCN M H G8 viratonof the ether group are detected at about 1100cm- 1uu心1 心, 4wwict pulase changematerials.Synthesis and Characterization of Storage Energy Materials.1131Figure 1 FTIR spectra of nano-crystalline cellulose(a) nano-crystalline cellulose grafted bypolyethylene glycol 4000b) and polyethylene glycol 4000(c)了|ach3000Wavenumber (cm-I)18001200600 4000 3000 2000Wavenumber (cm-)1000400Figure 2 The DSC curve of PEG (a) and new solid-solid phase change material (b)WH = 8.880 mgWH=5.630mg;Delta H = 186.2 J/gDelta H = 103.8 JIgPeak= 61.0°CPeak =47.2°COnset: 53.9 °COnset: 40.1 °C40507(204(t/°C .t/°CThe thermal behaviors of energy storage materials prepared from NCC/PEG weremeasured by DSC at the heating and cooling rate of 5"C /min in nitrogen atmosphere.From Figure 2, the enthalpy of polyethylene glycol 4000 is 186. 2J/g, and the enthalpy ofNCC/PEG energy storage materials is 103.8 J/g, which is much higher than those of thesimilar solid-solid phase change materials. The enthalpy of the NCC/PEG energystorage materials is less than that of pure polyethylene glycol, due to the followingreasons: 1. when the pure polyethylene glycol was grafted the surface of nano-crystallinecellulose, some segments of polyethylene glycol can not form crystals due to sterichindrance, and result in the decrease of crystallinity of polyethylene glycol chains; 2. thefree movement of polyethylene glycol chains is restricted in a smaller area and its crystallattice can not regularly arrange because PEG chains are fixed on the skeleton of NCC.From Figure 2, we can also find the phase trmwitiem中国煤化工ppture)shifts from 61.0°C to 47.2°C. The reason for ths: The endgroups of PEG chains are fixed by chemical boMYHCNMHGcc,sothenearby segments cannot crystallize well, due to the steric and the drag effects decrease1132Xiao Ping YUAN et al.the number of segments which can really crystallize.With the decreasing of PEGmolecular weight, physical transition temperature of the composite decreased. Thecrystalline regions turn to smaller, in the result the transition temperature fall down incertain degree.In conclusion, a new kind of SSPCMs for energy storage was prepared fromNCC/PEG.The polyethylene glycol acrylate and nano-crystalline cellulose acrylatecould be substantially polymerized by UV radiation in the presence of photo-initiator.The obtained composite has very high ability for energy storage, which is more than sixtimes of the similar one, and can be used in many fields.References1. G. Hormansdorfer, U. S. P5085790, 1992.2. M. H. Hartmann, U. S. P6689466 B2, 2004.Y. Jiang, E. Y. Ding, Polymer, 2002, 43, 117.4. E. Y. 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