Han-Do Kim

Preparation and properties of segmented thermoplastic polyurethane elastomers with two different soft segments

Thermoplastic polyurethane elastomers were prepared from 4,4-diphenylmethane diisocyanate (MDI)/1,4-butanediol (BD)/poly(propylene glycol) (PPG) and MDI/BD/poly(oxytetramethylene glycol) (PTMG). The MDI/BD-based hard-segment content of polyurethane prepared in this study was of 39–65 wt %. These polyurethane elastomers had a constant soft-segment molecular weight (Mn, 2000), but a variable hard-segment block length (n, 3.0–10.1; Mn, 1020–3434). The effects of the hard-segment content on the thermal properties and elastic behavior were investigated. These properties of the PPG-based MPP samples and the PTMG-based MPT samples were compared. The polyurethane prepared in this study had a hard-segment crystalline melting temperature in the range of 185.5–236.5°C. With increasing hard-segment content, the dynamic storage modulus and glass transition temperature increased in both the MPP and MPT samples. The permanent set (%) increased with increasing hard-segment content and successive maximum elongation. The permanent set (%) of the MPP samples was higher than that of MPT samples at the same hard-segment content. The value of K (area of the hydrogen-bonded carbonyl group/area of the free carbonyl group) increased with increasing hard-segment content in both the MPP and MPT samples, and the K value of the MPT samples was higher than that of the MPP samples at the same hard-segment content.

Role of intracellular calcium as a priming signal for the induction of nitric oxide synthesis in murine peritoneal macrophages

Because the role of intracellular Ca2+ in the two‐signal process for the induction of nitric oxide (NO) synthesis is controversial, this study was undertaken to examine the role of Ca2+ in the transcriptional regulation of inducible NO synthase (iNOS) in murine peritoneal macrophages. Treatment of the cells with thapsigargin (TG) or 2,5‐di‐(t‐butyl)‐1,4‐benzodihydroquinone (tBuBHQ), which are the specific and potent Ca2+‐ATPase inhibitors of endoplasmic reticulum (ER), showed modest effects on tumoricidal function, whereas TG or tBuBHQ in combination with interferon‐γ (IFN‐γ) or lipopolysaccharide (LPS) showed marked effects on tumoricidal function of the cells. The tumoricidal effects of the activated macrophages were correlated with the amount of NO synthesis, and totally abrogated by the use of NOS inhibitor, N G‐monomethyl‐l‐arginine (NGMMA). The increases in NO synthesis was reflected as increased amounts of iNOS mRNA by Northern blotting. To confirm that iNOS induction was due to the changes in the intracellular Ca2+ level, the acetoxymethyl ester of 1,2‐bis(2‐aminophenoxy)ethane‐N,N,N′,N′‐tetraacetic acid (BAPTA‐AM), an intracellular Ca2+ chelator, was used. Blocking the increase of cytosolic free Ca2+ significantly decreased the induction of NO synthesis. To demonstrate that intracellular Ca2+ acts as a ‘priming’ signal rather than a ‘triggering’ signal on the induction of NO synthesis by murine peritoneal macrophages, we designed several experiments. When the cells were treated with TG 6 hr after the treatment with IFN‐γ, there was no increase in NO synthesis. In addition, when the cells were treated with TG or LPS 6 hr after treatment with tBuBHQ, a synergistic increase on NO synthesis was shown only in the case of LPS. When phorbol 12‐myristate 13‐acetate (PMA), a protein kinase C (PKC) activator, was added to the cells 6 hr after the treatment with TG, there was a marked co‐operative induction of NO synthesis, even though PMA alone has no effect. Based on the results obtained in this study, we suggest that cytosolic Ca2+ might be enough for the expression of iNOS gene as a priming signal and PKC might be involved in the induction of NO synthesis as a triggering signal by post‐transcriptional modification of iNOS mRNA or iNOS itself in the activated murine peritoneal macrophages.

Characterization of waterborne polyurethane adhesives containing different soft segments

Waterborne polyurethane (WBPU) adhesives were prepared by the pre-polymer process using different polyester polyols (M n = 2000), namely poly(tetramethylene adipate glycol) (PTAd) and poly(caprolactone glycol) (PCL), and polyether polyols (M n = 2000), namely poly(tetramethylene oxide glycol) (PTMG) and poly(propylene glycol) (PPG), as soft segments. This study focused on the effect of various soft segments on the physical, mechanical and thermal properties, as well as adhesive strength of WBPUs. All of the WBPU dispersions showed small particle size and high viscosity. PTAd-based WBPU shows higher thermal stability, mechanical properties and adhesive strength than PCL-R, PTMG- and PPG-based WBPUs. During preparation of adhesive-bonded samples the optimum pressing temperature and pressure, which were the same for all samples, were found to be 100°C and 15 kg/cm2, respectively. However, it was found that only PTAd-based WBPU had good adhesive strength under moderately high temperature (100°C) compared to all other polyol (PCL/PTMG/PPG)-based WBPUs.

Properties of Waterborne Polyurethane Adhesives: Effect of Chain Extender and Polyol Content

A series of waterborne polyurethane (WBPU) adhesives were prepared with various ratios of polyol, poly(tetramethylene oxide glycol) (PTMG), and chain extender, ethylene diamine (EDA), at a fixed content of diisocyanate, 4,4-dicyclohexylmethane diisocyanate (H12MDI) and hydrophilic agent, 2,2-dimethylol propionic acid (DMPA). WBPU adhesives were characterized by IR and 1H-NMR spectroscopies, X-ray diffraction (XRD) and gel permeation chromatography (GPC). It was found that the extent of hydrogen bonds between hard–hard segment (i.e., hydrogen bonds between the NH and carbonyl groups) increased with increasing chain extender content (decreasing polyol content). Moreover, the disordered hydrogen bond of carbonyl group (hydrogen bond of urethane groups in the interfacial region) increased with increasing chain extender content (decreasing polyol content). The cyclic urea and allophanate group, which are attributed to the side reaction and cross-linking reaction, respectively, were found above a molar ratio 0.17 of chain extender to diisocyanate. The adhesive strength was maximum with 0.95 wt% and 63.10 wt% chain extender and soft segment (PTMG), respectively (H2 sample) at room temperature for the WBPU adhesive. However, with increasing application temperature the adhesive strength decreased for all samples.

Colorimetric Assay and Antibacterial Activity of Cotton, Silk, and Wool Fabrics Dyed with Peony, Pomegranate, Clove, Coptis chinenis and Gallnut Extracts

To investigate the antibacterial functionality of natural colorant extracts, five kinds of natural dying aqueous solutions were obtained by extraction from peony, pomegranate, clove, Coptis chinensis and gallnut using water at 90 °C for 90 min with a liquor ratio (solid natural colorant material/water, weight ratio) of 1:10. The colorimetric assay and antibacterial activity of cotton, silk, and wool fabrics dyed with these natural colorant extracts were examined. It was found that these properties were significantly dependent on the structure of colorant and the kind of fabrics. The hues (H) of all fabrics dyed with these natural colorants were in the range of 6.05YR -1.95Y. The order of value (V) was wool, silk and cotton. The chroma (C) of all samples was found to be at very low levels indicating the natural tone. All the fabrics dyed with the five natural colorants (peony, pomegranate, clove, Coptis chinensis and gallnut) extracts displayed excellent antibacterial activity (reduction rate: 96.8 - 99.9%) against Staphylococcus aureus. However, in the case of Klebsiella pneumoniae, the antibacterial activity was found to depend on the kind of natural colorant extract used.

Dyeing properties and colour fastness of cotton and silk fabrics dyed withCassia tora L. extract

A natural colorant was extracted fromCassia tora L. using buffer solutions (pH: 2–11) as extractants. The dyeing solution (Cassia tora L. extract) extracted using pH 9 buffer solution was found to give the highest K/S values of dyed fabrics. Cotton and silk fabrics were dyed withCassia tora L. extract at 60°C for 60 min with pre-treatment of various metal salts as mordants. It was found thatCassia tora L. extract was polygenetic dyestuffs and its major components were anthraquinones. Studies have been made on the effects of the kind of mordant on dyeing properties and colour fastnesses of cotton and silk fabrics. The K/S of cotton fabrics increased in the order of the dyeing using FeSO4>CuSO4>ZnSO4>MnSO4≅Al2(SO4)3>NiSO4>none, however, the K/S of silk fabrics increased in the order of the dyeing using FeSO4>CuSO4>ZnSO4≅Al2(SO4)3>MnSO4≅NiSO4>none. It was found that the K/S values of dyed fabrics were largely affected by the colour difference (ΔE) between mordanted fabric and control fabric. However, they were not depended on the content of mordanted metal ion of the fabrics. Mordants FeSO4 and CuSO4 for cotton fabric, FeSO4, CuSO4, and Al2(SO4)3 for silk fabric were found to give good light fastness (rating 4).

Surface modification of polymers and improvement of the adhesion between evaporated copper metal film and a polymer. I. Chemical modification of PET

To improve the interfacial adhesion between evaporated copper film and poly(ethylene terephthalate) (PET), the surface of PET films was modified by treating with hydrazine monohydrate. The effect of the treatment time in the range of 5-20 min with 80 wt% hydrazine monohydrate at 60 °C on the number of polar groups created on PET was investigated. The surface topography of and water contact angle on the PET film surface, the mechanical properties of the PET film, and the adhesion strength of evaporated copper metal film to the PET film surface were also investigated. The introduction of polar groups on the modified PET film surface was examined by FT-IR and ESCA analyses. The amount of polar groups increased to the maximum value with increasing treatment time to 10 min, and thereafter it decreased markedly. The surface roughness increased with increasing treatment time up to 10 min and cracks occurred after 20 min. The water contact angle and tensile properties decreased with increasing treatment time. Using the scratch test, the adhesion between Cu film and PET was found to increase with increasing treatment time up to 10 min and thereafter there was a remarkable decrease in adhesion. From these results, it was concluded that the optimum treatment time with hydrazine monohydrate (80 wt%) at 60°C was about 10 min to improve copper-PET adhesion.

Preparation and properties of new regenerated cellulose fibers

New regenerated cellulose fibers are prepared from solution (chemical cellulose con tents, 3, 4.5, 6, and 9 wt%) using N-methylmorpholine-N-oxide (NMMO)/water (87/13 wt%) as a solvent by dry-wet spinning at a winding speed of 20-100 m/min. The chemical cellulose (97% α-cellulose content, 918 DPw, 98% JIS whiteness) used for this study is prepared from ascidian tunicates by a modified pulping process described in our previous work. The effects of cellulose content and spinning speed on the structure and mechanical properties of fibers are investigated. As the cellulose content increases, the birefringence, crystallinity, and initial tensile modulus of the fibers increase significantly. While the tenacity of the fibers increases with increasing cellulose content up to 6 wt%, there is a great decrease in the tenacity at 9 wt%. That decrease is due to fiber defects. Mechanical properties increase with increasing winding speed. The regenerated cellulosic fibers prepared in this study have a higher ratio of wet strength to dry strength compared to regenerated cellulose fibers produced all over the world.

Synthesis and properties of liquid crystalline polyurethane elastomers

Novel type of mesogenic chain extenders used in this study are N,N′-bis(4-hydroxyphenyl)-3,4,3′,4′-biphenyldicarboxyimide (BPDI) and N,N′-bis[4-(6-hydroxyhexyloxy) phenyl]-3,4,3′,4′-biphenyldicarboxyimide (BHDI). BHDI has a flexible spacer of 6-methylene units but BPDI does not. The liquid crystalline polyurethane elastomers were synthesized from BPDI or BHDI as a mesogenic chain extender, 4,4′-diphenylmethane diisocyanate, and poly(oxytetramethylene)glycol (MW 1000) as a soft segment. Polyurethane based on BHDI exhibited two melting transitions. However, any melting behavior was not shown in the BPDI-based polyurethanes because of higher melting temperature than decomposition temperature. The composition of polyurethanes was varied as a means of manipulating liquid crystalline behavior and physical properties. The BHDI-based polyurethanes containing above 50 wt % of hard segment content exhibited nematic liquid crystal behaviors. As the hard segment content of the BHDI-based polyurethanes increased, the glass transition temperature (Tg), strength, modulus, and the amount of hydrogen bonding increased.

Preparation and application of polyurethane-urea microcapsules containing phase change materials

For thermal adaptable fabrics, the polyurethane-urea microcapsules containing phase-change materials (PCMs: hexadecane, octadecane and eicosane) were successfully synthesized by interfacial polycondensation using 2,4-toluene diisocyanate (TDI)/poly(ethylene glycol) (PEG400)/ethylene diamine (EDA) as shell monomers and nonionic surfactant NP-12 in an emulsion system under stirring rates of 3,000∼13,000 rpm. The mean particle size of microcapsule decreased significantly with increasing the stirring rate up to 11,000 rpm, and then leveled off. The mean particle size increased with increasing the content and molecular weight (eicosane > octadecane > hexadecane) of PCMs at the same stirring rate. The mean particle sizes of microcapsules were found to decrease with increasing the NP-12 content up to 1.5 wt%, and thereafter increased a little. It was found that the melting temperature (Tm) and crystallization temperature (Tc) of three kinds of encapsulated PCMs and their enthalpy changes (ΔHm, ΔHc) increased with increasing PCM contents. The encapsulation efficiencies (Ee) of hexadecane microcapsule linearly increased with increasing the content of hexadecane. It was found that the stable microcapsule containing 50 wt% of hexadecane could be obtained in this study. However, Ee of octadecane and eicosane microcapsules increased with increasing PCM’s contents up to 40 wt%, and then decreased a little. By considering the encapsulation efficiency, it was found that the maximum/optimum contents of octadecane and eicosane microcapsules were about 40 wt%. By the dynamic thermal performance test, it was found that the maximum buffering levels of Nylon fabrics coated with hexadecane, octadecane, and eicosane microcapsules were about −2.4/+2.9°C, −3.6/+3.6°C and −4.0/+4.7°C, respectively.