Variation of physical properties of nylon-66/clay nanocompositeswith preparation conditions

채동욱,Jung Ho Lim,Jae Sik Seo,김병철 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.1

Nylon-66 was melt compounded with 5 wt% nanosized organoclay varying the mixing rate and mixing time and their effects on the structure and properties of the nanocomposites were discussed in terms of the dispersion state of nanoclay. For the preparation of the nanocomposites, the total apparent shear (mixing rate mixing time) was fixed to 450 at three different combinations of mixing rate (30, 60, 90rpm) and mixing time (5, 7.5, 15min). While the pristine organoclay showed a (001) peak at 2q = 4.9o in the WAXD patterns, nylon-66/clay nanocomposites gave the disappearance of the peak regardless of mixing conditions, suggesting an exfoliated clay morphology in the nylon 66 matrix. The exfoliation of nanoclay in the nylon-66 matrix was also demonstrated by TEM measurements. On the contrary, rheological measurements revealed that the dispersion state of nanoclay was significantly influenced by the preparation conditions. The dynamic viscosity (h) of nylon-66/clay nanocomposites was increased as mixing rate was increased. For the normalized viscosity (h(t)/h(0)) obtained by time sweep at a given frequency, all the nanocomposites presented a decreased and upturned trend at the measuring time of ca. 500s, while nylon-66 showed an increased one over the entire time range. Nylon-66/clay nanocomposites gave lower value of tand with increasing mixing rate. In the logarithmic plot of storage modulus versus loss modulus, the nanocomposites prepared at higher mixing rate gave smaller slope, indicative of an increased heterogeneity. Nanoclay played a role of nucleating agent for nylon-66 by increasing the crystallization temperature, which was more pronounced at lower mixing rate. The induction time rheologically obtained from time sweep measurement at 1 rad/s at 235oC was shorter for the nanocomposites prepared at lower mixing rate, but at 3 rad/s it was little affected by the preparation conditions.

Effects of Interface Affinity on the Rheological Properties of Zinc Oxide Nanoparticle-Suspended Polymer Solutions

채동욱,김병철 한국고분자학회 2010 Macromolecular Research Vol.18 No.8

The effects of the interface affinity between the nanoparticle and polymer matrix on the rheological properties of nanoparticle suspended-polymer solutions were investigated. Two polymers, polar polyacrylonitrile (PAN) and nonpolar polystyrene (PS), were selected, and the cosolvent was N,N-dimethylacetamide and 0.1~5wt% of polar ZnO nanoparticles in the polymer were used. The inclusion of ZnO notably increased the viscosity (η') of the PAN solutions, even at such a low loading level of 0.1 wt%. A maximum value of η' was observed at a 1 wt% of ZnO content. On the other hand, the η' of the PS solutions decreased with increasing ZnO content. Both the PAN and PS suspension systems exhibited a notable decrease in η' above a critical ZnO content. Although the PAN solutions showed a lower loss tangent (tanδ) at higher ZnO contents, the PS solutions containing > 2 wt% ZnO showed higher tanδ above a frequency of 2 rad/s. On the Cole-Cole plot, the PAN solutions did not give a single master curve depending on the ZnO content. However, the PS solutions showed little scattering from the master curve of a slope of ca. 1. ZnO increased the relaxation time of the PAN solutions but decreased the relaxation time of the PS solutions.

Investigation of phase stability of poly(1-oxotrimethylene)-dissolved aqueous solutions containing ZnCl2/CaCl2/LiCl: Influence of boric acid introduction and aging time

채동욱,장한별,김병철 한국유변학회 2018 Korea-Australia rheology journal Vol.30 No.1

Poly(1-oxotrimethylene) (POTM) was dissolved in aqueous solutions containing ZnCl2, CaCl2, and LiCl, and the effects of boric acid introduction on the phase stability of the POTM solutions over various aging times were investigated. In the absence of boric acid, aging at 70°C for 8 h notably reduced the loss tangent (tanδ) for the 7.0 wt.% POTM solutions. Addition of boric acid into unaged solutions had little effect on tanδ over the frequency range measured, regardless of its content, whereas addition of 0.3-1.0 wt.% of boric acid into aged solutions increased tanδ. The dynamic viscosity of the POTM solutions with 1.0 wt.% boric acid was affected little by aging time. Conversely, the POTM solutions without boric acid exhibited increased dynamic viscosity in the low-frequency range with aging time. In addition, the slope of the solutions in the Cole-Cole plot decreased with increasing aging time in the absence of boric acid, whereas aging time had little effect in the presence of 1.0 wt.% boric acid. For dilute POTM solutions (i.e., 0.5 g/dL), the reduced viscosity decreased with increasing aging time in the absence of boric acid, while it was affected little in solutions with the addition of 1.0 wt.% boric acid. In the UV-Vis spectra, the aging-time-dependent increase of the absorbance peak at 390 nm was associated with the generation of a chromophoric complex in the POTM solutions. Conversely, the disappearance of the peak due to the addition of boric acid indicated suppression of complex formation.

Temperature dependence of the rheological properties of poly(vinylidene fluoride)/dimethyl acetamide solutions and their electrospinning

채동욱,Min Hyung Kim,김병철 한국유변학회 2010 Korea-Australia rheology journal Vol.22 No.3

The effects of measuring temperature on the rheological properties of poly(vinylidene fluoride) (PVDF) solutions in dimethyl acetamide (DMAc) were investigated at three different concentrations. Ubbelohde viscometer and rotational rheometer were employed for dilute and concentrated solution regimes, respectively. In the dilute concentration regime, intrinsic viscosity was decreased with increasing temperature over the range of 30 to 70oC but Huggins constant was increased from 0.301 to 0.345. In the high concentration regime, however, dynamic viscosity (h') was increased with increasing measuring temperature. PVDF solutions exhibited almost Newtonian flow behavior at 30oC but a notable dependence of h' on frequency was observed at 50 and 70oC. In temperature sweep measurement, the critical temperature where h' was abruptly increased was reduced with increasing PVDF concentration. Increasing measuring temperature from 30 to 70oC decreased the value of loss tangent (tan d). The Cole-Cole plot at 30oC revealed that PVDF solutions gave a single master curve of constant slope irrespective of PVDF concentration. On the other hand, the slope varied with polymer concentration at 50 and 70oC. As the electrospinning temperature was increased the average diameter of nanofibers in the electrospun web was decreased and the fiber surface got rougher and coarser.

Effects of molecular architecture on the rheological and physical properties of polycaprolactone

채동욱,남윤규,안성국,조창기,이은정,김병철 한국유변학회 2017 Korea-Australia rheology journal Vol.29 No.2

The molecular modification of polycaprolactone (PCL) is of great importance for producing optimum physical properties for a given application. Linear polycaprolactone (L-PCL) and 4-arm star polycaprolactone (4-PCL) with similar molecular weights were prepared, and their rheological, thermal, and morphological properties were investigated in relation to their molecular architecture. In dilute solutions, L-PCL exhibited a higher intrinsic viscosity than 4-PCL. In the molten state, the former displayed a higher viscosity and greater temperature dependence of molecular relaxation time than the latter. DSC thermograms showed that molecular architecture had little effect on the melting/crystallization temperature and crystallinity. Thermogravimetric analysis indicated that the introduction of a branched structure deteriorated the thermal stability of PCL, which might be associated with the increased number of hydroxyl end groups in the polymer chains. In isothermal crystallization under shear at two different temperatures, 4-PCL exhibited longer crystallization times than L-PCL. A more notable difference in dynamic crystallization behavior caused by the chemical architecture was observed at 40°C than at 45°C. Examination with a wide angle X-ray diffractometer revealed that shear and temperature applied during isothermal crystallization, as well as chemical architecture, had little effect on the crystal structure.

Effects of Stress Level and Temperature on the Time Dependent Morphological and Physical Properties of PVA Fibers

채동욱,김승규,김병철,Chae, Dong Wook,Kim, Seung Gyoo,Kim, Byoung Chul The Korean Fiber Society 2017 한국섬유공학회지 Vol.54 No.2

The effects of the stress level and heat treatment temperature on the morphological and physical properties of poly(vinyl alcohol) (PVA) fibers were investigated with regard to treatment time. The PVA fibers were heat treated at three different temperatures (210, 220, and $230^{\circ}C$) and stress levels (0.05, 0.15, and 0.25 g/d). Increase in shrinkage was observed with an increase in the heat treatment time when treated at 220 and $230^{\circ}C$ beyond 15 min, while a little extension was observed at $210^{\circ}C$. The shrinkage in the PVA fibers heat treated at $230^{\circ}C$ increased with a decrease in stress levels, exhibiting a different dependence of the shrinkage on the heat treatment time. The WAXS patterns of the PVA fibers heat treated at $230^{\circ}C$ at 0.15 g/d showed that the crystalline peaks became sharp with time up to 15 min beyond which they became dull. The degree of crystallinity, determined from the density measurement, was maximum when heat treated for 5 min regardless of the temperature and the stress level. However, the degree of crystallinity when further treated at 220 and $230^{\circ}C$ decreased, while that showed little change when treated at $210^{\circ}C$. In addition, the variation of the degree of crystallinity with heat treatment time was in good agreement with that of the degree of amorphous orientation. In the DSC thermograms, a greater dependence of the melting temperature and the heat of fusion on the heat treatment time was observed at higher heat treatment temperatures and lower stress levels.

Rheology, Crystallization Behavior under Shear, and Resultant Morphologyof PVDF/Multiwalled Carbon Nanotube Composites

채동욱,홍순만 한국고분자학회 2011 Macromolecular Research Vol.19 No.4

Poly(vinylidene fluoride) (PVDF) composites containing multiwalled carbon nanotubes (MWNTs) in the range from 0.1 to 5 wt% were prepared at 220℃ using a melt-mixer. The storage modulus (G') of the PVDF/MWNT composites increased with increasing MWNT content. In particular, there was a significant increase in G' between 1 and 3 wt%. In the Cole-Cole plot, the PVDF composites with up to 1 wt% MWNTs exhibited a single master curve with a slope of 1.25, but the composites containing 3 and 5 wt% MWNTs showed a decreased slope of 1.13 and 1.03, respectively. From the addition of 3 wt% MWNTs, the yield of the PVDF composites was observed in complex viscosity versus complex modulus plot with little dependence on the loss tangent (tan δ) on the frequency was shown. Both the induction time and crystallization time obtained from the G' versus time plot decreased with increasing MWNT content. The promoting effect of the MWNTs on the overall crystallization behavior was more profound at higher crystallization temperatures. Pure PVDF and PVDF with 0.1 wt% MWNTs showed only α phase crystals, but the PVDF composites with high concentrations of MWNTs (1-5 wt%) appeared to contain a mixture of β and γ phases in addition to the α phase.

Structural Characterization and Physical Properties of Poly(ethylene terephthalate) and Poly(trimethylene terephthalate) Blends: Effects of Blending Time and Blend Ratio

채동욱,최경락,김병철,Chae, Dong Wook,Choi, Kyung Rak,Kim, Byoung Chul The Korean Fiber Society 2017 한국섬유공학회지 Vol.54 No.3

Poly(ethylene terephthalate) (PET) and poly(trimethylene terephthalate) (PTT) were melt blended at $280^{\circ}C$ at varying blending time and ratio. The resulting physical properties were examined in relation to ester exchange reactions. The PET/PTT 50/50 blends (by weight percentage) exhibited double melting peaks ($T_m$) up to 30 min blending time beyond which they were merged to one broader peak. The melting peak had a nearly linear relationship with blending time and displayed a much steeper decrease for ET units than for TT units. Two new peaks for asymmetric aromatic carbons were detected in $^{13}C$-NMR spectra and their intensity increased notably from 40 min blending time which was consistent with thermal analysis. The dissolution of copolyesters occurred even after 10 min blending time and its degree increased with blending time. FESEM images of chloroform etched fracture surfaces displayed coarse and continuous phase properties from 40 min blending time while losing the spherical shape of each component. In the DSC measurement of the PET/PTT blends prepared at various ratios at a given blending time of 20 min, all the blends exhibited a single glass transition temperature ($T_g$) more consistent with the Gordon-Taylor equation than the Fox equation. In addition, a single $T_m$ peak was observed in each sample, except for 50/50 composition, which shows the coexistence of $T_m$ for each component. All blends except for 50/50 exhibited a similar WAXD patterns to their rich component. This was evidenced by solubility test results showing the highest solubility for 50/50 blends. This phenomenon was also confirmed in FESEM measurement of chloroform etched fracture surfaces where the blends composed of an equal amount of the component exhibited coarse and dumbbell-like domains.

Rheological and Physical Properties of Sulfonated Polystyrene Ionomer Solutions and the Membranes

채동욱,최경락,김병철,Chae, Dong Wook,Choi, Kyung Rak,Kim, Byoung Chul The Korean Fiber Society 2018 한국섬유공학회지 Vol.55 No.1

The rheological properties of sulfonated polystyrene (SPS) ionomer solutions were found to be significantly affected by solvent polarity, counterion, sulfonation level, and temperature. In the dilute concentration regime, the reduced viscosity (${\eta}_{red}$) of SPS solutions in the dimethyl sulfoxide (DMSO), which is a polar solvent, increased with decreasing concentration, whereas opposite effects were observed in low-polarity solvent tetrahydrofuran (THF). H-SPS solutions in THF showed typical shear-thinning behavior over all the measured frequencies, while solutions in DMSO showed shear-thickening behavior at low shear rates, followed by shear-thinning behavior at higher shear rates. These different behaviors might result from differences in polymer-solvent interactions and the chain conformation. SPS solutions in DMSO containing monovalent ions ($Na^+$) exhibited higher dynamic viscosity values than those with divalent ions ($Ca^{2+}$, $Mg^{2+}$) because of the different degrees of chain expansion. In DMSO, the dynamic viscosity increased with temperature, regardless of the sulfonation level and counterion. Both the proton conductivity and methanol permeability of the SPS membranes increased with increasing sulfonation level and exhibited an abrupt increase between 10 and 15 mol%, indicative of a percolation threshold.

Rheological Properties of PAN/DMF Spinning Solutions and Physical Properties of Conducting Carbon Nanofibers Prepared by Electrospinning and Carbonization

채동욱,권오주,이은정,김병철,Chae, Dong Wook,Kwon, Oh Joo,Lee, Eun Jeoung,Kim, Byoung Chul The Korean Fiber Society 2016 한국섬유공학회지 Vol.53 No.5

Dynamic rheological properties of polyacrylonitrile (PAN)/dimethylformamide (DMF) solutions were measured at several different temperatures ($25-55^{\circ}C$), and their electrospinning was conducted at corresponding temperatures to prepare PAN precursor fibers. The electrospun fibers were subsequently converted to carbon nanofibers through a carbonization process and their physical properties such as electrical conductivity, morphology and crystal structure were examined with regard to the electrospinning temperature. The dynamic viscosity of PAN/DMF solutions decreased with increasing temperature, exhibiting a lower Newtonian flow region followed by shear thinning. In the Cole-Cole plot, the initial slope decreased with decreasing temperature but a single master curve of constant slope above the inflection point was observed regardless of the temperature. FESEM images showed that the diameter of the PAN precursor fibers and resulting carbon nanofibers decreased as the electrospinning temperature increased. The diffraction peak of carbon nanofiber in the WAXD pattern was shifted from 22 to $24^{\circ}$. Further, Raman spectroscopy showed that the graphitic carbon peak at $1600cm^{-1}$ increased with increasing electrospinning temperature. In addition, the electrical conductivity of the carbon nanofiber increased considerably from 2.95 to 6.15 S/cm with increasing electrospinning temperature from 25 to $55^{\circ}C$.