Preparation And Properties Of Cellulose - Based Solid - Solid Phase Change Materials

Cellulose is the most abundant natural renewable polymer in the world, and it is non-toxic, no-pollution, biodegradable, biocompatible and thermal stable. The macromolecule of cellulose is constituted of D-glucose units linked by β (1,4)-glycosidic linkage. There are lots of active hydroxyl in cellulose macromolecule, which induces strong intra-molecular and inter-molecular hydrogen bonding. The hydrogen bonding interactions result in many shortcomings, such as insoluble in common organic solvents and melting temperature higher than the decomposition temperature, which also causes difficulties in derivatization and processing.When polyoxyethylene (2) hexadecyl ether (E2C16) was applied as the phase change material directly, liquid leakage occurs frequently. In this paper, cellulose-based solid-solid phase change materials were prepared by chemical grafting method using toluene 2,4-diisocyanate (TDI) as coupling agent, cellulose as skeleton material, polyoxyethylene (2) hexadecyl ether as phase change material and 1-allyl-3-methylimidazolium chloride as solvent. The effects of the reaction temperature, reaction time, amount of catalyst, feed ratio and short-chain fatty acyl on the structure and properties of cellulose based solid-solid phase change material were investigated in detail. It was found that: The optimal conditions for the prepolymerization reaction were 25 ℃ and 75 min without catalyst. It was found that the factors affecting graft reaction range in the order of reaction temperature> catalyst> reaction time. The optimal conditions for grafting reaction were 90 ℃,6 h and 0.1% DBTDL A series of cellulose-based solid-solid phase change materials with different DS were fabricated through changing the feeding amount of E2C16and glucose unit (AGU) under the optimum prepolymerization conditions. It was showed that the DS value of E2C16 increased firstly and then decreased. When the molar ratio of E;C16/AGU was 4:1, the DS of E2C16 was up to the maximum 1.01. Simultaneously the enthalpy of the solid-solid phase change material achieved the maximum values, melting enthalpy and crystallization enthalpy were 33 J/g and 30 J/g respectively. The corresponding melting peak temperature and crystallization peak temperature were 28.6 ℃ and 14.9 ℃. Fixing the feeding molar ratio of E2C16/AGU at 4:1, cellulose was pre-modified using short-chain fatty acid anhydride (acetic anhydride, propionic anhydride and butyric anhydride), followed by grafting of E2C16. With the anhydride/AGU ratio increasing, the DS value of EaC16 also showed a similar trend as Cellulose-g-E2C16, that is DS value increasing firstly and then decreasing. With the carbon chain length increasing, the DS value of E2C16 showed a trend of increasing continously. The phase transition temperature and enthalpy of the copolymers increased with the increasing of DS value of E2C16. When the ratio of butyric anhydride/AGU was 1.5:1, the DS of E2C16 was up to the maximum value of 1.02, the corresponding melting enthalpy and crystallization enthalpy were 32 J/g and 30 J/g respectively.The heat resistant temperature of cellulose-based solid-solid phase change materials is all higher than 270 ℃. After grafting reaction, crystallinity of E2C16 decreased, but the crystal type is still hexagonal.