Browsing by Author "Tyan, HL"

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Effect of montmorillonite on thermal and moisture absorption properties of polyimide of different chemical structures
(2001-08-15)
Tyan, HL
;
Wu, CY
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The thermal properties and the moisture absorption of three types of polyimide/montmorillonite nanocomposite were investigated: 3,3 ' ,4,4 ' -biphenyl tetracarboxylic dianhydride-4,4 ' -oxydianiline (BPDA-ODA); pyromellitic dianhydride-ODA (PMDA-ODA); and 3,3 ' ,4,' -benzophenone tetracarboxylic dianhydride-ODA (BTDA-ODA). The inhibition effect on in-plane coefficients of thermal expansion (CTE) and moisture absorption of these polyimide nanocomposites by layered silicates from montmorillonite was found to decrease with the crystallinity in the pristine polyimides. The largest reduction, 30% in in-plane CTE occurred in the case of amorphous BTDA-ODA containing 5 wt % montmorillonite as compared with that of pure BTDA-ODA, while the reduction in in-plane CTE was 20% for the case of semicrystalline BPDA-ODA. The maximum reduction in moisture absorption, 43%, also took place for the case of 3/97 ODA-Mont/BTDA-ODA as compared with that of pure BTDA-ODA, whereas the semicrystalline 1/99 PPD-Mont/BPDA-ODA showed a 30% reduction as compared with that of pure BPDA-ODA. (C) 2001 John Wiley & Sons, Inc.
Effect of reactivity of organics-modified montmorillonite on the thermal and mechanical properties of montmorillonite/polyimide nanocomposites
(2001-01-01)
Tyan, HL
;
Leu, CM
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Montmorillonite/polyimide (3,3',4,4'-benzophenone tetracarboxylic dianhydride-4,4'-oxydianiline, BTDA-ODA) nanocomposites displaying different morphological, thermal, and mechanical characteristics were synthesized by involving mono-, di-, and trifunctional group swelling-agent-modified montmorillonite and poly(amic acid). It was found that the dispersion of silicate layers in BTDA-ODA shifted from intercalated to exfoliated structures when the number of functional groups of the swelling agent increased to three as evidenced from X-ray diffraction and transmission electron microscopy studies. The improved morphology of the nanocomposites resulted in their enhanced mechanical and thermal properties. In particular, a 70% increase in Young's modulus, a 50% increase in the maximum stress, and a 30% reduction in the coefficients of thermal expansion for the case of BTDA-ODA nanocomposites containing 5 wt % trifunctional group swelling-agent-modified montmorillonite as compared to that of pure BTDA-ODA.
Enhancement of imidization of poly(amic acid) through forming poly(amic acid)/organoclay nanocomposites
(1999-08-01)
Tyan, HL
;
Liu, YC
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The imidization kinetics of nanocomposites of poly(amic acid) and organoclay were analyzed with in situ Fourier Transform Infrared spectra at several temperatures. The poly(amic acid) studied consisted of pyromellitic dianhydride and 4,4'-oxydianiline. It was found that by dispersing a small amount of organoclay in nanometer scale in the poly(amic acid), both the imidization temperature and the imidization time of the poly(amic acid) can be reduced dramatically. In specific, when two parts of exfoliated silicate layers of organoclay was dispersed in the poly(amic acid), the imidization temperature was lowered by 50 degrees C (250 degrees C versus 300 degrees C) for achieving a complete imidization. Additionally, the imidization time of the poly(amic acid) at 250 degrees C can be reduced to 15 min when the amount of organoclay increased to seven parts. Using a first-order reaction to model the imidization kinetics of poly(amic acid)/organoclay, a 20% drop in the activation energy for imidization of PMDA-ODA/organoclay (7 phr) was obtained as compared to that for imidization of neat PMDA-ODA. (C) 1999 Elsevier Science Ltd. All rights reserved.
Mechanical properties of clay-polyimide (BTDA-ODA) nanocomposites via ODA-modified organoclay
(2000-11-15)
Tyan, HL
;
Wei, KH
;
Hsieh, TE
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Clay-polyimide [3,3', 4,4'-benzophenone tetracarboxylic dianhydride-4,4'-oxydianiline (BTDA-ODA)] nanocomposites were synthesized from ODA-modified montmorillonite (organoclay) and poly(amic acid). The layered silicates of organoclay were intercalated by polyimide (BTDA-ODA), as confirmed by X-ray diffraction and by transmission electron microscopy, and the tensile mechanical properties of the nanocomposites were measured. It was found that the modulus and the maximum stress of these organoclay/BTDA-ODA nanocomposites were much higher than those of pure BTDA-ODA: a twofold increase in the modulus and a one-half-fold increase in the maximum stress in the case of 7/93 organoclay-BTDA-ODA. In addition, the elongation-for-break of organoclay/BTDA-ODA nanocomposites is even slightly higher than that of pure BTDA-ODA, which is a sharp contrast to that of conventional inorganics-filled polymer composites. (C) 2000 John Wiley & Sons, Inc.
Miscibility and transesterification in blends of liquid crystalline copolyesters and polyarylate
(1998-08-01)
Tyan, HL
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Blends of poly(oxybenzoate-p-ethylene terephthalate) (POB-PET) and polyarylate were confirmed to be a partially miscible system by differential scanning calorimetry. When 60/40 POB-PET/PAr blend was annealed at high temperature (above 270 degrees C) for several minutes, the ester-ester interchange( transesterification)in the blend took place immediately, as evidenced by Fourier Transformed infrared analyses. The analysis of the blend annealed at 290 degrees C by H-1-C-13 nuclear magnetic resonance disclosed that there were four new diads appearing in 15 min and an additional one produced in 60 min during the heat treatment. The miscibility between POB-PET and polyarylate increased with the mol concentration of these new diads judging from differential scanning calorimetry. The evolution of the concentration of the diad ethylene glycol-isophthalate during the annealing can be described by a second-order reaction. The activation energy of forming the diad ethylene glycol-isophthalate was 26.5 kcal/mol, and the preexponential factor for the transesterification reaction is 3.7 x 10(8) min(-1). (C) 1998 John Wiley & Sons, Inc.
Miscibility in blends of liquid crystalline poly(p-oxybenzoate-co-p-phenyleneisophthalate) and polyarylate
(1998-06-06)
Wei, KH
;
Tyan, HL
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The miscibility of liquid crystalline poly(p-oxybenzoate-co-p-phenyleneisophthalate) (HIQ35) and polyarylate (PAr) coprecipitated from a mixed solvent of phenol/tetrachloroethane was investigated with differential scanning calorimetry. It was found that the amorphous phase of HIQ35 and PAr formed a partially miscible blend at low concentration of HIQ35. No measurable interaction between HIQ35 and PAr occurred when the weight fraction of HIQ35 was close to or less than that of polyarylate, as evidenced by wide-angle X-ray diffraction results. Upon annealing at 315 degrees C for several minutes, the apparent miscibility of HIQ35 with polyarylate appeared as a result of an initial reaction between the polymers. For longer annealing time, the thermal degradation of HIQ35 joined in the reaction. This reaction or degradation in the blend was confirmed by nuclear magnetic resonance analysis and the intrinsic viscosity measurement of the blend. (C) 1998 John Wiley & Sons, Inc.
The mechanical properties of ternary liquid-crystalline polymer blends
(1996-05-01)
Wei, KH
;
Hwang, WJ
;
Tyan, HL
;
交大名義發表
;
材料科學與工程學系
The possibility of improving the compatibility of and the adhesion between liquid-crystalline poly(oxybenzoate-co-oxynaphthoate) (Vectra) and polycarbonate (PC) by adding a stable compatibilizer based upon the transesterification between liquid-crystalline poly(oxybenzoate-co-ethylene terephthalate) (POB/PET) (60/40) and polycarbonate was investigated. The goal was to provide a physical interaction between the matrix polymer and the liquid-crystalline polymer through a third polymer that contained similar chemical structural units to those in both polymers. It was found that at proper compositions the adhesion between Vectra and PC was greatly improved by the presence of the compatibilizer, as indicated by the morphological evidence. These ternary liquid-crystalline polymer blends displayed improved ultimate tensile stress (30% increase as compared to PC) and elongation at break (seven times as compared to binary blend) even under a nominal injection-moulding process. The impact property of the ternary liquid-crystalline polymer blend was also improved as compared to that of the binary liquid-crystalline polymer blends. Copyright (C) 1996 Elsevier Science Ltd.
The role of partial miscibility on the properties of ternary blends of liquid crystalline copolyesters and polyetherimide
(1998-05-01)
Wei, KH
;
Tyan, HL
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Binary blends of liquid crystalline copoly(oxybenzoate-p-ethylene terephthalate) at molar ratio 60/40, POB-PET, and polyetherimide (PEI) were investigated with differential scanning calorimetry and polarised optical microscopy. It was found that POB-PET and PEI were partially miscible when PEI was the major component. Adding a small amount (5 phr) of POB-PET to the originally immiscible blends of liquid crystalline copoly(oxybenzoate-naphthalate) (73/27), Vectra, and PEI resulted in better interfacial adhesions between Vectra and PEI as evidenced by the morphological observations with scanning electron microscopy. The enhancement in the interfacial adhesions caused an increase in the ultimate tensile strength and the impact strength of these ternary blends of Vectra, POB-PET and PEI as compared to that of the corresponding binary blends of Vectra and PEI in an injection molding process. (C) 1998 Elsevier Science Ltd. All rights reserved.
Thermally and mechanically enhanced clay/polyimide nanocomposite via reactive organoclay
(1999-07-01)
Tyan, HL
;
Liu, YC
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
High modulus and thermally stable clay/polyimide (pyromellitic dianhydride-4,4'-oxydianiline, PMDA-ODA) nanocomposites were synthesized from reactive organoclay and poly(amic acid). The reactive organoclay was formed by using p-phenylenediamine as a swelling agent for silicate layers of montmorillonite. The swelling process was first carried out through ion exchange between the onium of one amine end group of p-phenylenediamine and the sodium ion in montmorillonite. The other amine end group of p-phenylenediamine reacted with the dianhydride end group of poly(amic acid), producing an irreversible swelling. This irreversible swelling resulted in a nanostructured material containing intercalated nanometer silicate layers dispersed in PMDA-ODA as confirmed by both X-ray and transmission electron microscopy. The glass transition temperature and the thermal decomposition temperatures of this type of clay/PMDA-ODA are higher than that of pure PMDA-ODA. A 2,5-fold increase in the modulus of clay/PMDA-ODA film was obtained as compared to that of pure PMDA-ODA film. Both the maximum and the elongation-for-break of these clay/PMDA-ODA nanocomposites increased with the amount of organoclay. The maximum reduction in out-of-plane coefficient of thermal expansion of this type clay/PMDA-ODA was 50% as compared to that of pure PMDA-ODA.