Haksoo Han

Yonsei University, Sŏul, Seoul, South Korea

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Publications (116)260.14 Total impact

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    ABSTRACT: Light-colored polyimide hybrids with a quaternary alkylammonium modified montmorillonite, Cloisite® 20A (C20A) were successfully synthesized via a solution intercalation method. The structural and morphological features of the PI/C20A hybrids were characterized by Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXD), field emission scanning electron microscopy (FE-SEM), and spherical aberration correction scanning transmission electron microscope (STEM). The dimensional stabilities were strongly dependent upon the chemical and morphological structures which were influenced by the Cloisite® 20A loading content. A critical Cloisite® 20A concentration was obtained for the evolution of both the structural and physical properties of the PI/C20A hybrids. The dynamic stress behaviors were investigated in situ by using the wafer bending method during thermal imidization of the softbaked PI/C20A hybrid precursor and thermally cured hybrid films using a thin film stress analyzer. The PI/C20A hybrid films exhibited stability at 510 oC, high glass transition and relatively low coefficient of thermal expansion, and an improved solvent resistance capacity.
    No preview · Article · Jan 2016 · Macromolecular Research
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    ABSTRACT: To enhance the thermal stability and barrier properties of pure poly(vinyl alcohol) (PVA), five different cross-linked poly(vinyl alcohol)/boric acid (PVA/BA) hybrid films were prepared via a solution blending method, and their properties including barrier properties, thermal stability, transparency, and mechanical properties were investigated as a function of the BA content. The physical properties of the PVA/BA hybrid films were strongly dependent upon the chemical structure and morphology of the films originating from the amount of BA and change in degree of cross-linking. With increasing BA content, the size and amount of PVA crystallites decreased, whereas the cross-linking density increased, resulting in more compact packing of the molecules and lower free volume in the amorphous regions. The glass transition temperature and thermal stability were highly enhanced with increasing BA content. The oxygen transmission rate (OTR) of pure PVA decreased from 5.96 to 0.15 cc/m2 day with increasing BA content and were greatly suppressed by 22.8% for 1% BA, 7.7% for 3% BA, and 2.5% for 3% BA, respectively, relative to pure PVA film. With increasing BA content, their water-resistant pressure and tensile strength increased with BA loading. All the hybrid films showed good transparency. These properties of the cross-linked PVA/BA hybrid films make them potential candidates for versatile applications as coatings, films, and packaging materials.
    No preview · Article · Aug 2015 · Progress in Organic Coatings
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    ABSTRACT: Polyurethane acrylate/surface-modified colloidal calcium carbonate (PUA/SCaCO3) nanocomposite coatings were successfully prepared via a UV-curing technology. The structural and morphological features of the PUA/SCaCO3 nanocomposites were characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM), atomic force microscopy (AFM), and wide angle X-ray diffraction (XRD). The physical properties were strongly dependent upon chemical and morphological structures that originated from differences in SCaCO3 loading. A critical SCaCO3 concentration was observed for the evolution of both the structure and physical properties of the PUA/SCaCO3 nanocomposites as a function of SCaCO3 content. The thermal stability was measured by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively, and displayed some enhancement with the incorporation of SCaCO3 into PUA. Although the nanomechanical properties increased up to 3 wt% SCaCO3 content, they decreased due to lack of interfacial interaction with high SCaCO3 loading. Most importantly, the water uptake and water vapor transmission rate (WVTR) varied from 5.51 to 1.78 wt% and 28.9 to 19.9 g/m2 day, respectively, exhibiting significant enhancement in water resistance. The results clearly reveal that the performance of UV-curable PUA/SCaCO3 nanocomposites is strongly dependent on organically-modified colloidal SCaCO3 nanoparticles.
    No preview · Article · Aug 2015 · Progress in Organic Coatings
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    ABSTRACT: The effects of norbornene (NE) crosslinking and diamine bridge linkages (ether, sulfone, and trifluoromethyl) on polyimide films were investigated. The purpose of this study was to study the behavior of the NE endcapped polyimide with different diamine bridge linkage structure at elevated temperatures on residual stress and modulus change. 5-Norbornene-2,3-dicarboxylic acid was introduced as the end-capping agent in order to increase the ratio of crosslinking in the structure through reverse Diels-Alder reaction. Wide angle X-ray diffraction (WAXD) was measured to study the relation of d-spacing and structure change of the bridge linkage of polymers through NE crosslinking. Coefficient of thermal expansion (CTE) and residual stress were measured to confirm the loaded stress between the substrate and polymer film through a thin film stress analyzer (TFSA). Storage (ε′) and loss modulus (ε″) were studied at elevated temperatures to study the relation of bridge linkage mobility of the polyimide at elevated temperature.[Figure not available: see fulltext.] © 2015, The Polymer Society of Korea and Springer Sciene+Business Media Dordrecht.
    No preview · Article · Aug 2015 · Macromolecular Research
  • Kwangwon Seo · Jongchul Seo · Ki‐Ho Nam · Haksoo Han
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    ABSTRACT: In this work, Al–Si was synthesized via a sol–gel process and introduced in poly 2,2′-m-(phenylene)-5,5′-bibenzimidazole (PBI). As a result, a series of five Al–Si/PBI composite (ASPBI) membranes (0, 3, 6, 9, and 12 wt%) were developed and characterized for application in high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). The chemical and morphological structure of ASPBI membranes were analyzed by Fourier transform infrared spectroscopy, X-ray diffractometer, and scanning electron microscopy. According to the doping level test and thermogravimetric analysis, as the concentration of Al–Si increased, the doping level increased up to 475% due to the affinity and interaction between Al and phosphoric acid (PA). Moreover, the proton conductivity, current density at 0.6 V, and maximum power density of ASPBI membranes increased up to 0.31 S cm−1, 0.320 A cm−2, and 0.370 W cm−2, respectively, because the increased concentration of Al–Si allows the membranes to hold more PA. Alternatively, as the amount of Al–Si increased, the tensile strength of PA-doped and -undoped membranes decreased. This was caused by both excess PA and aggregation, which can cause serious degradation of the membrane and induce cracks. Furthermore, the PA-doped and -undoped ASPBI12 had the lowest tensile strength of 11.6 and 77.2 MPa. The improved proton conductivity and single cell performance of ASPBI membranes implies that these membranes are possible candidates for HT-PEMFC applications. However, further studies seeking to enhance the compatibility between PBI and Al–Si and optimize the amount of filler should be performed. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers
    No preview · Article · Jul 2015 · Polymer Composites
  • Taewon Yoo · Kwangin Kim · Wonbong Jang · Haksoo Han
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    ABSTRACT: The features of norbornene (NE) cross-linked polyimide (PI) were investigated as the ratio of the norbornene monomer was varied. The coefficient of thermal expansion and modulus are important parameters of materials used in the microelectronic industry. Therefore, in this study, 5-norbornene-2, 3-dicarboxylic acid (NE) was introduced as a crosslinking agent to increase the thermal stability at elevated temperatures. 4,4′-Benzophenonetetracarboxylic dianhydride was utilized as a dianhydride and 4,4′-diaminodiphenyl ether was introduced as a diamine monomer. By changing the ratio of each monomer, we were able to control the spacing of the chain and ring opening polymerization, which resulted in improved properties. Each sample was thermally cured which led to a ring opening mechanism of the norbornene through the reverse Diels-Alder reaction. Thermal mechanical analysis was utilized to determine the coefficient of thermal expansion and dynamic mechanical analysis was used to determine the storage modulus (ε′) and loss modulus (ε″) of the PI film. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42607.
    No preview · Article · Jul 2015 · Journal of Applied Polymer Science
  • Kwangin Kim · Taewon Yoo · Jinyoung Kim · Hyemin Ha · Haksoo Han
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    ABSTRACT: To determine the thermal characteristics of linear and crosslinked polyimides (PIs), BTDA, ODPA, and 6FDA were used to synthesize polyimides. Thermal degradation temperature and glass transition temperature of the resulting PIs were measured using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). To measure the change in modulus and coefficient of thermal expansion (CTE) depending on dianhydride structure, a dynamic mechanical analyzer (DMA) and thermo-mechanical analyzer (TMA) were used. The thermal degradation and glass transition temperature properties of linear PIs varied according to whether the linear chain adopted a bulky or flexible structure. Dynamic modulus and thermal expansion values of linear polyimides also showed good agreement with the TGA and DSC results. As we expected, linear polyimide with bulky 6FDA groups showed better thermal behavior than the flexible polyimides. Crosslinked polyimide nadic end-capped (norbornene) with a bulky dianhydride group had a lower thermal degradation temperature and higher CTE than flexible BTDA and ODPA polyimides. Our results indicate that the mobility of the dianhydride group affects the thermal behaviors of linear and crosslinked polyimides in different ways. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41412.
    No preview · Article · Feb 2015 · Journal of Applied Polymer Science
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    ABSTRACT: A series of low density polyethylene/paraffin wax (LDPE/PW) composite films were fabricated via a twin-screw extruder, and their morphologies, thermal properties, gas and vapor permeations, and surface properties were interpreted as functions of the PW contents. The PW was well dispersed into the LDPE matrix at low PW contents, whereas phase separation and an increase in surface roughness occurred with increasing PW content. The parameter results of surface properties such as contact angle, surface free energy, and solubility showed that the hydrophobicity of the LDPE/PW composite films also increased, and their phase changes and permeation properties were significantly dependent on the PW contents in the LDPE matrix. With increasing PW contents, both the oxygen transmittance rate (OTR) and water vapor transmittance rate (WVTR) of the LDPE/PW composite films decreased at a relatively low measuring temperature (23 °C), and increased at a relatively high temperature (48 °C). These results relate to the morphological structure (including tortuous paths and crystallinity) of the composite films via the incorporation of PW.
    No preview · Article · Feb 2015 · Journal of Polymer Research
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    ABSTRACT: Poly(propylene carbonate)/íµí»½-cyclodextrin (PPC-BCD) nanocomposites were developed as effective extractor for a specific extraction and separation of cadmium(II) by use of inductively coupled plasma-optical emission spectrometry. The selectivity of nanocomposites with different wt% of BCD (PPC-BCD 0.5, PPC-BCD 1, PPC-BCD 3, PPC-BCD 5, or PPC-BCD 10) was investigated toward Cd(II). Based on selectivity and pH studies, Cd(II) was the most quantitatively adsorbed on PPC-BCD 5 phase at pH 6, indicating that PPC-BCD 5 was the most selective toward Cd(II) among other nanocomposites. On the basis of adsorption isotherm study, the superior adsorption capacity of PPC-BCD 5 phase for Cd(II) was found to be 149.25 mg⋅g −1 , following the Langmuir adsorption isotherm model. The kinetic of adsorption for Cd(II) has been examined by pseudo-first-and second-order models. The kinetic exploration suggested a pseudo-second-order kinetic model for the adsorption of Cd(II) on the PPC-BCD 5. Additionally, results of thermodynamic investigation demonstrated favorable spontaneous process for the adsorption mechanism of PPC-BCD 5 toward Cd(II).
    Full-text · Article · Jan 2015 · Journal of Nanomaterials
  • Ki-Ho Nam · Dowan Kim · Jongchul Seo · Kwangwon Seo · Haksoo Han
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    ABSTRACT: Tetrapod zinc oxide whiskers (TZnO-Ws) were successfully prepared by a thermal oxidation method and confirmed using scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD). A series of polyimide (PI)/TZnO-W composite films containing the as-prepared various TZnO-W contents were prepared and their physical properties were investigated to understand their potential use in flexible displays. The morphology, physical, and moisture barrier properties of the PI/TZnO-W composite films were interpreted as a function of the TZnO-W content. The PI/TZnO-W composite films exhibited an optical transparency greater than 80% at 550 nm (a parts per thousand currency sign0.5 wt% TZnO-W content), a low coefficient of thermal expansion (CTE), and enhanced glass transition temperature. However, the thermal decomposition temperature decreased as the TZnO-W content increased. Although the mechanical strength increased up to 0.3 wt% TZnO-W content, it decreased due to poor interfacial interaction with high TZnO-W loading. The water vapor transmission rate (WVTR) and water uptake of the composite films, which were strongly dependent upon their morphological and chemical structure, varied from 508.3 to 325.2 g/m(2)/day and 3.7 to 1.3 wt%, respectively, greatly decreased as the TZnO-W content increased. The water resistance capacity of PI was greatly enhanced and moisture diffusion in the pure PI was retarded by incorporating the TZnO-W.
    No preview · Article · Dec 2014 · Macromolecular Research
  • Ki-Ho Nam · Jongchul Seo · Wonbong Jang · Haksoo Han
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    ABSTRACT: Cross-linked polyimides (PIs) were synthesized by reacting 4,4'-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA) and 2,2'-bis(trifluoromethyl)benzidine (TFDB) with various ratios of the cross-linkable, end-capping agent cis-1,2,3,6-tetrahydrophthalic anhydride (CDBA) via ring-opening metathesis polymerization. Residual stress behaviors were investigated in-situ during thermal imidization of the cross-linked PI precursors using a thin film stress analyzer (TFSA) by wafer bending method. The thermal properties were investigated via differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and thermogravimetric analysis (TGA). The optical properties were measured by ultraviolet-visible spectrophotometer (UV-vis) and spectrophotometiy. All properties were interpreted with respect to their morphology of cross-linked networks: With increasing the amounts of the end-capping agent, the residual stress decreased from 27.9 to -1.3 MPa, exhibited ultra-low stress and high thermal properties. The minimized residual stress and enhanced thermal properties of the cross-linked PI makes them potential candidates for versatile high-density multi-layer structure applications.
    No preview · Article · Nov 2014 · Polymer Korea
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    ABSTRACT: A novel high-performance material, carbon black (CB) polyimide (PI), was obtained by the chemical synthesis of CB (carbon black N326) with PI. Following its synthesis, several analyses were carried out to investigate the thermal and mechanical properties of the newly synthesized CB-PI. The thermal decomposition temperature of CB-PI compared to PI increased by 76°C from 508 to 584°C. The glass transition temperature of CB-PI as evaluated by differential scanning calorimetry increased by 204°C from 379 to 583°C compared to that of PI. Moreover, the mechanical strength of CB-PI increased by 16% compared to that of PI. In addition, the analyses confirm that CB and PI in the synthesized CB-PI were chemically crosslinked, which was shown to be responsible for the superior thermal and mechanical properties of the CB-PI. POLYM. COMPOS., 2014. © 2014 Society of Plastics Engineers
    No preview · Article · Nov 2014 · Polymer Composites
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    ABSTRACT: Polyimide is a major polymer material in the electronics industry, and we conducted a study to cure polyimide at low temperatures in order to improve its thermal and mechanical properties. In this study, polyimide/clay nanocomposites were prepared by the reaction of 4,4’-(hexafluoro isopropylidene) diphthalic anhydride (6FDA) and 4,4’-oxydianiline (ODA) with the addition of 1,4-dizabicyclo[2.2.2]octane (DABCO) as a low-temperature catalyst and nanoclay (Cloisite 20A). The synthesis of polyimide at low temperatures and the dispersion of a nanoclay in the polymer matrix was confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), respectively. Thermal stabilities of the nanocomposites were confirmed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The mechanical properties were measured by an universal testing machine. We demonstrated that when polyimide was cured at low temperatures and short curing times, it was possible to improve the thermal and mechanical properties via the addition of a catalyst and inorganic material. Polyimide with DABCO and 0.25 wt% nanoclay showed a 5 °C higher degradation temperature, 560.88 °C; a 6 °C higher glass transition temperature, 293.62 °C; and a 20 MPa greater tensile strength, 136.94 MPa. Therefore, the polyimide curing process was demonstrated to be successful at low temperatures.
    No preview · Article · Nov 2014 · Macromolecular Research
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    ABSTRACT: In this contribution, composite membranes (CM-D and CM-S) of 2,5-polybenzimidazole (PBI) were synthesized by adding inorganic heteropoly acids (IHA-D and IHA-S). IHA-D and IHA-S were synthesized by condensation reaction of silicotungstic acid with tetraethyl orthosilicate (TEOS) in the absence and presence of mesoporous silica (SiO2), respectively. The synthesized composites were structurally and morphologically characterized and further investigated the functional relationships between the materials structure and proton conductivity. The proton conductivity as well as thermal stability was found to be higher for composite membranes which suggest that both properties are highly contingent on mesoporous silica. The composite membrane with mesoporous silica shows high thermal properties and proton conductivity. IHA-D shows proton conductivity of almost 1.48×10-1 Scm−1 while IHA-S exhibited 2.06×10-1 Scm−1 in nonhumidity imposing condition (150°C) which is higher than pure PBI. Thus introduction of inorganic heteropoly acid to PBI is functionally preferable as it results in increase of ion conductivity of PBI and can be better candidates for high temperature PEMFC.
    Preview · Article · Oct 2014 · Journal of Nanomaterials
  • Mijin Lim · Dowan Kim · Jongchul Seo · Haksoo Han
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    ABSTRACT: To enhance the thermal stability and barrier properties of pure poly(vinyl alcohol) (PVA), a series of poly(vinyl alcohol)/vinyltrimethoxysilane (PVA/VTMS) hybrid films were prepared via a sol-gel process, and their physical properties were investigated as a function of VTMS content. During the sol-gel process, simultaneous reactions between hydroxyl groups of PVA and silanol groups of hydrolyzed VTMS and self-condensation of VTMS occurred, inducing a cross-linked network structure and greatly enhanced thermal stability and oxygen barrier properties. The glass transition temperature and thermal decomposition temperature (T 5%) of the PVA/VTMS hybrid films increased from 72.6 to 84.3 °C and 273.6 to 342.2 °C, respectively, with increasing VTMS content from 0 to 20%. Oxygen transmission rates of the hybrid films decreased from 6.12 to 0.17 cm3/m2×day, and those of the hybrid films incorporating 5%, 10%, and 20% VTMS were suppressed by 65.7%, 95.6%, and 97.2%, respectively, versus a pure PVA film. These are dependent on the chemical structure and morphology of the films with differing initial amounts of VTMS. The chemical affinity for water, intermolecular packing, and rigidity in polymer chains increased with increasing cross-linking by VTMS, leading to enhanced oxygen barrier properties and thermal stability in the PVA/VTMS hybrid films.
    No preview · Article · Oct 2014 · Macromolecular Research
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    ABSTRACT: Cover: Polyimide-based spherical aerogel microparticles, a novel form of polyimide aerogels, are fabricated. The existing polyimide aerogels, published earlier by other institutions, can only be fabricated in film shapes. The aerogel microparticles proposed in this study have an advantage over film-shaped aerogels because the microparticles can be easily employed for thermal insulation, drug release, and catalyst support. Further details can be found in the article by J. Kwon,* J. Kim, T. Yoo, D. Park, and H. Han* on page 1081.
    No preview · Article · Sep 2014 · Macromolecular Materials and Engineering
  • Ki-Ho Nam · Wansoo Lee · Kwangwon Seo · Haksoo Han
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    ABSTRACT: A series of polyimide (PI) was prepared by reacting 4,4'-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA) as the anhydride and bis(3-aminophenyl) sulfone (APS), bis[4-(3-aminophenoxy)-phenyl] sulfone (BAPS), 2,2-bis(4-aminopheny1)-hexafluoropropane (6FPD), 2,2-bis[4-(4-aminophenoxy)-phenyl]hexafluoropropane (6FBAPP), 2,2'-bis(trifluoromethypbenzidine (TFDB), or 1,4-phenylenediamine (PDA) as the diamine. Residual stress behaviors were detected in-situ during thermal imidization of the polyimide precursors using a thin film stress analyzer (TFSA), and interpreted with respect to their morphology. According to the molecular orientation and packing order, the residual stress varied from 23.1 to 12.5 MPa, decreased with increasing chain rigidity. The thermal properties of the PI films were investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and thermomechanical analysis (TMA). Their optical properties were measured by ultraviolet-visible spectrophotometer (UV-vis), and spectrophotometry. The properties of PI films were found to be strongly dependent upon the morphological structure. However, trade-offs between residual stress and optical properties were identified.
    No preview · Article · Jul 2014 · Polymer Korea
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    Jinuk Kwon · Jinyoung Kim · Dongmyung Park · Haksoo Han
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    ABSTRACT: A novel method for synthesizing a microsponge polyimide (PI) film with excellent thermal stability, chemical resistance, and heat insulation performance was developed. The synthesized microsponge PI film has open cells with sizes between 1 and 10 μm and a porosity of 76%. Furthermore, the film contains several layers overlapping in multiple grid structures, which complicates the heat transfer paths. Thus, the heat transfer coefficient of the microsponge PI film is 67% less than that of existing polyimide film (0.054 vs. 0.16 W/m·K). This reduced heat transfer coefficient results in excellent heat insulation performance of the microsponge PI film. The thermal decomposition (pyrolysis) of the microsponge PI starts at 498 °C and its glass transition temperature is 317 °C, which indicates excellent thermal stability. However, its Young's modulus, an indicator of mechanical strength, is nearly 74% less than that of conventional PI film (26 vs. 100.2 MPa).
    Preview · Article · Jul 2014 · Polymer
  • Dowan Kim · Mijin Lim · Insoo Kim · Jongchul Seo · Haksoo Han
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    ABSTRACT: A series of poly(urethane acrylate)/Cloisite 15A (PUA/C15A) nanocomposite films were successfully prepared via a UV-curing system, and their physical and barrier properties were investigated as a function of clay content. The physical properties were strongly dependent upon the chemical and morphological structures originating from differences in Cloisite 15A content. With high clay content, the PUA/C15A nanocomposite films displayed an intercalation/exfoliation combined structure. However, no strong interfacial interactions occurred between the PUA and clay, possibly leading to poor dispersion with relatively high clay content. The thermal stability displayed some enhancement with the introduction of clay into PUA, while the gas and moisture barrier properties showed significant enhancement. The oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) decreased with increasing contents of Cloisite 15A, and varied within the range of 714.0-71.1 cm(3)/m(2) day and 29.9-13.9 g/m(2) day, respectively. Thus the enhanced gas and moisture barrier properties of PUA/C15A nanocomposite films make them promising candidates for food and pharmaceutical packaging applications. However, further studies will be performed to increase the compatibility and dispersion of clay particles in the PUA polymer matrix.
    No preview · Article · Jun 2014 · Progress in Organic Coatings
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    ABSTRACT: A series of polyimide (PI) nanocomposite films with various surface-modified colloidal calcium carbonate (SCaCO3) contents were prepared and their physical properties were investigated to understand their possible use as polymer substrates. The morphology, thermal stability, residual stress behavior, moisture barrier and optical properties of nanocomposite films were investigated as a function of the SCaCO3 content and were found to be strongly dependent upon the chemical and morphological structures. With the addition of up to 0.5 wt% SCaCO3 in the PI matrix, resultant nanocomposite films exhibit not only enhanced thermal properties, but also minimized residual stress and excellent optical properties, simultaneously. With increasing SCaCO3 content, the water vapor transmission rate (WVTR) is greatly decreased from 630.76 to 484.22 g/m2/day. The residual stress was in the range of 26.0 to 12.1 MPa and is highly dependent on both temperature variation and SCaCO3 content. Although the residual stress becomes lower at 0.5 wt% SCaCO3 content, it increases at relatively high SCaCO3 loadings due to inadequate dispersion of the SCaCO3 and low interfacial interactions between the polymer and filler surfaces. Therefore, further studies are needed to maximize the performance of nanocomposite films by enhancing the compatibility of the polymer matrix and fillers.
    No preview · Article · Jun 2014 · Macromolecular Research