|Title:||Studies on the supramolecular shape memory polyurethane containing pyridine moieties|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Shape memory effect
|Department:||Institute of Textiles and Clothing|
|Pages:||iv, 271 leaves : ill. ; 30 cm.|
|Abstract:||Fabricating smart materials with supramolecular switch is an attractive research topic. In this study, supramolecular polyurethane networks containing pyridine moieties (PUPys) were synthesized from N,N-bis(2-hydroxylethyl)isonicotinamide (BINA), hexamethylene diisocyanate (HDI), 4, 4-diphenylmethane diisocyanate (MDI) and 1, 4-butanediol (BDO). Thereafter, a series of studies were carried out to investigate the supramolecular structure, morphology and shape memory properties. Results show that hydrogen-bonded supramolecular structure and phase separation morphology are formed in the PUPys. The glass transition temperature (Tg) of soft phase is controlled by the pyridine ring via hydrogen bonding. However, the hard phase grows up from amorphous phase to crystalline phase as the BINA content increases. The addition of MDI-BDO promotes the formation of amorphous hard phase. Therefore, the PUPys have much higher glass modulus and much higher maximum tanδ. The rubber modulus increases with the decrease of BINA content as well as the increase of MDI-BDO content. The tanδ decreases with the decrease of BINA content. As for the thermal induced shape memory effect (SME), PUPys have high shape fIxity and high shape recovery with the recovery temperature of 45 °C-55 °C. The pyridine ring is the key element to determine the shape recovery. To achieve satisfying shape recovery, 30wt% BINA contents are required in the PUPys. Additionally, the recovery force increases with the decrease of BINA contents. The addition of MDI-BDO improves the shape recovery force of PUPys. Moreover, recovery temperature increases as the increase of deformation temperature. Finally, it is proposed that hydrogen bonding present in the pyridine ring serves as the molecular switch whereas the hydrogen bonding present in the urethane groups provides PUPys an elastic polymer networks acting as the physically netpoints for the thermal-induced SME. As for the moisture-sensitive SME PUPys have high moisture absorption which increases with the increase of temperature and relative humidity. Thus, the strain recovery start time, strain recovery time and strain recovery end time all increase with the decrease of relative humidity and temperature. The recovery speed is also quicker in the higher relative humidity and higher temperature. In addition, moisture absorption of PUPy increases with the increase of BINA content as well as the decrease of MDI-BDO content. The final shape recovery decreases with the decrease of BINA content significantly and the strain recovery start time, strain recovery time, strain recovery end time and the time length are also short in the higher BINA content PUPys. Moreover, it is found that the low critical value of BINA unit for PUPys having moisture-sensitive SME is still 30wt%. The addition of MDI-BDO improves the moisture-sensitive shape recovery. Finally, it is proposed that the hydrogen bonding present in the pyridine ring serves as moisture-sensitive “switch whereas the formed hard phase via hydrogen bonding present in the urethane groups acts as the physical netpoints for the moisture-sensitive SME. Finally, potential applications of PUPys like smart windows and reshape applications and the future study are suggested in the end of this thesis.|
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