Browsing by Author "Tien, YI"

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High-tensile-property layered silicates/polyurethane nanocomposites by using reactive silicates as pseudo chain extenders
(2001-12-18)
Tien, YI
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Tethered layered silicates/polyurethane nanocomposites displaying high tensile strength and high elongation to break were synthesized by using reactive swelling-agent-modified silicates as pseudo chain extenders for a polyurethane prepolymer. The dispersion of layered silicates in polyurethane was found to be transformed from an intercalated to an exfoliated structure when the number of hydroxyl groups of the swelling agent increased as evidenced from the transmission electron microscopy and wide-angle X-ray diffraction analyses. The improved morphology of the nanocomposites resulted in an ultrahigh efficiency in enhancing the mechanical properties of polyurethane, despite variations in the molecular weight and in the extent of hydrogen bonding in the hard segment phase. In particular, a 34% increase in Young's modulus, a 1.7-fold increase in the tensile strength, and a 1.3-fold increase in the elongation to break occurred in the nanocomposite of polyurethane containing only 1 wt % trihydroxyl-group swelling-agent-modified silicates as compared to those of pristine polyurethane.
Hydrogen bonding and mechanical properties in segmented montmorillonite/polyurethane nanocomposites of different hard segment ratios
(2001-03-01)
Tien, YI
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Hydrogen bonding in the hard segments of the synthesized montmorillonite/polyurethane nanocomposites of various hard segment ratios was found to decrease with the increasing amount of montmorillonite regardless of the hard segment ratios, but reached plateau values at 5 wt% montmorillonite concentration. The maximal reductions of the hydrogen bonding in the polyurethane nanocomposites ranged from 20 to 37%, depending on the hard segment ratios as compared to that in the pure polyurethane. The maximal strength and the elongation at break of the polyurethane nanocomposites increased dramatically as compared to that of pristine polyurethane, and the maximal values occurred at 1 wt% montmorillonite concentration. (C) 2001 Elsevier Science Ltd. All rights reserved.
Synthesis and characterization of novel segmented polyurethane clay nanocomposite via poly(epsilon-caprolactone)/clay
(1999-07-01)
Chen, TK
;
Tien, YI
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A novel segmented polyurethane/clay (PU/clay) nanocomposite based on poly(caprolactone), diphenylmethane diisocyanate, butanediol, and poly(caprolactone)/ clay prepolymer was synthesized as evidenced by FTIR and X-ray diffraction studies. Poly(caprolactone)/clay (PCL/clay) prepolymer was first synthesized in a nanocomposite form as confirmed by X-ray diffraction. X-ray diffraction study showed that PU/clay contained crystalline structure due to the presence of PCL/clay. In mechanical properties, about 1.4% PCL/clay in PU/clay resulted in a large increase in the elongation of PU/clay. However, when the amount of PCL/clay was 4.2%, the elongation of PU/clay was reduced drastically. This behavior indicated that PU/clay can be transformed from an elastomer to a thermoplastic material as the amount of PCL/clay in PU/clay increased. Additionally, the lap shear stress of PU/clay was at least three times that of neat PU as a result of the PCL/clay component. (C) 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2225-2233, 1999.
Synthesis and characterization of novel segmented polyurethane/clay nanocomposites
(2000-02-01)
Chen, TK
;
Tien, YI
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A novel segmented polyurethane(Pu)/clay nanocomposite has been synthesized by polyurethane and organoclay. 12 aminolauric acid (12COOH) and benzidine (BZD) were used as swelling agents to treat Na+-montmorillonite and for forming organoclay (12COOH-mont acid BZD-mont) through ion exchange. The nanometer-scale silicate layers of organoclay were completely exfoliated in PU in the cases of 1, 3 and 5% 12COOH-mont/PU and in the cases of 1 and 3% BZD-mont/PU nanocomposites as confirmed by X-ray diffraction pattern and transmission electron microscopy studies. The segmented structures of PU were not interfered by the presence of the silicate layers in these nanocomposites as evidenced by their glass transition and degree of phase separation from differential scanning calorimetry and Fourier transform infrared measurements. A two-fold increase in the tensile strength and a three-fold increase in the elongation were found for 1% BZD-mont/PU as compared to that of pure PU. Additionally, both 1% 12COOH-mont/PU and 1% BZD-mont/PU exhibited lower water absorption properties than that of pure PU. (C) 1999 Elsevier Science Ltd. All rights reserved.
The effect of nano-sized silicate layers from montmorillonite on glass transition, dynamic mechanical, and thermal degradation properties of segmented polyurethane
(2002-11-14)
Tien, YI
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The glass transition temperature of the hard-segment phase and the storage modulus of segmented polyurethane increased substantially in the presence of a small amount of tethered nano-sized layered silicates from montmorillonite compared with their pristine state (by 44degreesC and by 2.8-fold, respectively). Furthermore, the heat resistance and degradation kinetics of these montmorillonite/polyurethane nanocomposites were enhanced, as shown by thermogravimetric analysis. In particular, a 40degreesC increase in the degradation temperature and a 14% increase in the degradation activation energy occurred in polyurethane containing 1 wt % trihydroxyl swelling agent-modified montmorillonite compared to that of the pristine polyurethane. (C) 2002 Wiley Periodicals, Inc.
Thermal transitions of montmorillonite/polyurethane nanocomposites
(2000-12-01)
Tien, YI
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The hard-segment phase thermal transitions and heat-resistance of benzidine-modified-montmorillonite (BZD-Mont)/polyurethane nanocomposites of different hard segment contents were found to be affected by a small amount of BZD-Mont. In particular, the presence of less than 5 wt% layered silicates from BZD-Mont can result in hard segments not only having a more thermally stable long-range order and a higher melting temperature, but also showing a loss of crystallinity of the hard segment in polyurethane. Additionally, the degradation temperature of BZD-Mont/polyurethane nanocomposite was slightly higher than that of pure polyurethane.