Jong-Shin Park

Characterization of the polyurethane foam using alginic acid as a polyol

In this study, polyurethane foams (PUF) were prepared using alginic acid, glycerin, and poly(ethylene glycol) (PEG) as polyols, 1,6-hexamethylene diisocyanate (HDI) as a diisocyanate, and water as a foaming agent by one-shot process. Their structura, mechanical, and water-absorbing properties were investigated. The amount of alginic acid was varied up to 30 wt%. Fourier transform infrared (FT-IR) analysis showed that urethane linkage was formed by the reactions between −NCO groups of diisocyanate and −OH groups of all polyols used. Also urea linkage was formed by the reactions between −NCO groups of HDI and water or −COO− groups of alginic acid. The reaction times for cream forming increased with increasing alginic acid but foam structures were not formed when alginic acid content in polyols was above 30 wt%. The optical micrographs showed that the average cell size of PUF slightly increased with increasing alginic acid. However, the density of PUF decreased with alginic acid content. The compressive modulus of PUF decreased with increasing alginic acid content. In the mean time, the water absorbency of PUF increased with increasing alginic acid content.

Structural, thermal, and mechanical properties of polyurethane foams prepared with starch as the main component of polyols

In this study, rigid polyurethane foams were prepared using starch as the main component of polyols and their structural, thermal, and mechanical properties were investigated. The starch content in polyols was 30∼50 wt.%. The prepared polyurethane foams had a cell structure. When the starch content and -NCO/-OH molar ratio (TS4-05, TS3-07, and TS3-05) was low, polyurethane foams were not formed. To confirm the formation of a urethane linkage between -OH of the starch and -NCO of the 2,4-TDI, FT-IR spectroscopic analysis was performed. The thermal properties of polyurethane foams were analyzed by DSC and TGA. DSC thermograms showed two endothermic peaks: a sharp peak at a lower temperature and a broad peak at a higher temperature. Both peaks were shifted to higher temperature with starch content in polyols and -NCO/-OH molar ratio. Thermal degradation of polyurethane foams began at a lower temperature and ended at a higher temperature than that of starch. The impact resistance, compressive stress and modulus of polyurethane foams increased with -NCO/-OH molar ratio and starch content.

Hydrophilic and flexible polyurethane foams using sodium alginate as polyol: Effects of PEG molecular weight and cross-linking agent content on water absorbency

Hydrophilic and flexible polyurethane foams were prepared using sodium alginate as a polyol, and characterized by optical microscopy, FT-IR spectroscopy, density measurements, volume swelling, and water absorbency. Optical microscopy revealed that the resulting cells were closed with round and elongated shapes. FT-IR confirmed that the urethane linkages were formed between the isocyanate and sodium-alginate. As an indirect measurement of porosity, the apparent density indicated an initial decrease followed by an increase with increasing glycerin content. The volume-swelling ratio was initially constant, followed by a gradual decrease with glycerin content. The volume swelling ratio increased with PEG molecular weight. The water absorbency initially increased, followed by a decrease with increasing glycerin content. The correlation-ships between water absorbency, density, and volume-swelling ratio indicated that the absorbency was predominantly influenced by density when the PEG molecular weight was low and was greatly affected by the volume-swelling ratio when the PEG molecular weight was relatively high.

Use of acetylated softwood kraft lignin as filler in synthetic polymers

Partially acetylated softwood kraft lignin (ASKL) is used as filler in synthetic polymers such as LDPE, PP, PS and PET. ASKL/synthetic polymer composites are prepared by melt-blending and compression molding with ASKL content up to 50.0 wt%. The chemical and physical properties of ASKL/synthetic polymer composites are also investigated. TGA results show that ASKL is more thermally stable than SKL up to 200 °C. FTIR spectra demonstrate a formation of free volume by crystallization of LDPE in ASKL/LDPE composite. DSC results show that the glass transition temperature of ASKL decreased by acetylation, and ASKL/synthetic polymer composites (50/50 w/w) have a single glass transition. The AFM images of ASKL/synthetic polymer composites show no significant phase separation. Young’s moduli of ASKL/synthetic polymer composites increased with ASKL content in some extents. Tensile strength and breaking strain of ASKL/PET composite are almost retained in spite of the addition of ASKL as a result of a contraction in free volume or densification.

Preparation and characterization of polyurethane foam using a PLA/PEG polyol mixture

Polyurethanes are polymers with urethane linkages in their backbone. It is prepared by polyaddition polymerization between isocyanates and polyols, which produce different chemical, physical, and mechanical properties depending on their types and characteristics. Previous reports of polyurethane foams prepared by using PEG polyol indicated prominent features in the elasticity and recovery of the foams. However, it is necessary to improve the mechanical strength of these materials. In this study, polyurethane foams were prepared using a PLA/PEG polyol mixture and 1,6-hexamethylene diisocyanate. PLA polyol was synthesized by the direct condensation polymerization of lactic acid. The polyurethane foams were characterized using FE-SEM analysis, FT-IR spectroscopy, water absorbency measurement, and mechanical property measurement. In FE-SEM analysis, it was shown that the PLA content of polyol mixture significantly affected the porous structure. FT-IR spectra confirmed that urethane linkages formed between the PLA/PEG polyols and the isocyanates. The water absorbency decreased due to the hydrophobicity of PLA. With respect to the mechanical properties, the breaking stress and the Young’s modulus increased with increasing PLA content. When the PLA content of polyols was 60 and 70 percent, the breaking strain was significantly higher than those of other polyurethane foams.

Preparation and Characterization of Thermoplastic Polyurethanes Using Partially Acetylated Kraft Lignin

Thermoplastic polyurethanes were prepared using 90 % acetylated softwood kraft lignin, polyethylene glycol and 4,4-methylene diphenyl diisocyanate. Due to the glass transitions of the compatible soft and hard segment mixtures, the polyurethanes exhibited the first glass transitions at −40 to 10 °C, and the transition temperatures increased with increasing hard segment content. Due to the glass transitions of the microphase separated hard domains, the second glass transitions occurred at 150 °C. The viscous responses during the second transitions decreased as the separated hard domains-induced chemical and physical crosslinks increased. The Young’s modulus and tensile strength increased with increasing hard segment content, whereas the breaking strain decreased. The phase morphology changed from an isolated hard domain structure to an interconnected one as the physical crosslinks increased, which caused drastic changes in the increasing or decreasing tendency of the tensile strength or breaking strain. Because of the phase morphology, the polyurethanes exhibited viscoplasticity or viscoelasticity.

The Mechanical Properties of Polyurethane Foam Wound Dressing Hybridized with Alginate Hydrogel and Jute Fiber

The purpose of this study is to fabricate a smart wound dressing by hybridizing hydrophilic polyurethane foam (PUF) and alginate hydrogel. Hydrophilic PUF is used to maintain damaged tissue in a moist environment. Despite its many strong points as a wound dressing, hydrophilic PUF cannot be loaded with ingredients such as growth factors and cytokines that would enhance wound healing. Therefore, we introduce a pH-sensitive alginate hydrogel with the ability to selectively release drugs within the pH range of wounded skin. Due to the small pore size of PUF and the high viscosity of the alginate solution, the two are not easily penetrable. As such, a vacuum method is used to insert alginate hydrogel into the PUF. The optimum conditions for the vacuum method chosen are to be proposed. However, the mechanical strength of PUF decreased after containing alginate hydrogel. Therefore, Na-alginate powder for PUF, various types of crosslinking agents and jute fiber for alginate hydrogel were introduced to improve the mechanical properties of hydrogel/PUF hybrid wound dressing. Three different types of crosslinking agents are used for the gel formation. The most suitable crosslinking agent and its concentration for alginate hydrogel is also determined by the experiments. The experimental results are discussed with proper schemes and reasonable explanations.

Preparation of starch-based polyurethane films and their mechanical properties

In this study, polyurethane films were prepared using starch as the main polyol component, and the mechanical properties of these films were investigated. The starch content of the polyols was 30–50 wt%. To confirm the formation of a urethane linkage between the −OH of starch and −NCO of toluene 2,4-diisocyanate, Fourier transform infrared (FT-IR) spectroscopic analysis was performed. Differential scanning calorimetry (DSC) thermograms of the polyurethanes resulted in two endothermic peaks, which shifted to higher temperatures with increasing starch content and −NCO/−OH molar ratio. Due to the melting behavior of polyurethane, films could be prepared by hot pressing at an appropriate temperature. Polyurethane films were prepared with various polyol starch content and −NCO/−OH molar ratios. Tensile testing indicated that the breaking stress and elastic modulus increased significantly with starch content and −NCO/−OH molar ratio. In addition, bending tests indicated an increase in breaking stress and bending modulus with starch content and −NCO/−OH molar ratio and decreased breaking strain. The strain rate in both tensile and bending tests had a significant effect on the mechanical properties.

Potential of a bio-disintegrable polymer blend using alkyl-chain-modified lignin

In this study, butylolactone-modified lignin (BLL) and tetrahydrofuran-modified lignin (THFL) were used for alkyl chain modification of lignin in order to mimic the relation of lignin-carbohydrate-complex (LCC) and cellulose. The result of FT-IR and 1H-NMR analysis indicate that lignin was well modified. It is confirmed that Aromatic OH of lignin (ArOH, 9.86 ppm) and Aliphatic OH of lignin (AlOH, 3.88 ppm) were decreased. Tensile properties of THFL/polypropylene (PP) blend are increased better than lignin/PP or acetylated lignin/PP. BLL/polyethylene terephthalate (PET) blend shows typical “rule of mixture” behavior because property of alkyl chain (P4HB) well reflected that used for modification of BLL. The results of thermal and mechanical analyses of modified lignin/matrix blends demonstrate that the characteristics of the alkyl chains used to modify lignin were well reflected in the final blends compared with lignin/matrix. In the case of THFL/ PP blend shows phase separation because of miscibility gap between alkyl chain of THFL and PP. The result of XRD analysis indicate that BLL/PET shows increased crystallinity because of good compatibility and THFL/PP shows opposite behavior. It can be confirmed that type of alky chain and miscibility gap between alkyl chain-matrix affect mechanical properties enormously in the fungi degradable environment.

Effect of alkyl-chain-modified lignin in the PLA matrix

Lignin has enormous potential for use as a raw material in the polymer industry. However, lignin has not been utilized as a raw material despite its many advantages because of its brittleness and difficulty of processing. Chemical modification of lignin is an important area of lignin research. In this study, two types of alkyl-chain-based modification agents were used. In the case of the polymeric materials blend, polymers are blended well so that the polymer solubility parameter (SP) values are close to each other. This is similar to the well-mixed combination of water and alcohol. If the SP value is very different, phase separation occurs, as in the relationship between water and oil. The two alkyl chain derivatives block the hydroxyl groups of lignin and replace them with glycoside. Moreover, they can alter the SP value of the modified lignin to make it similar to that of a synthetic polymer to enable blending. Cellulose is compatible with hemicellulose, which is coupled to lignin by ether, glycoside, and ester bonds in plant fibers. To mimic this structure, in this study, lignin was combined with an alkyl chain with a similar SP value and was used as a matrix polymer to form glycoside bonds. This relationship between lignin and the alkyl chain is similar to that between the cellulose and lignin-carbohydrate-complex (LCC). PLA-modified lignin (PLAL) and tetrahydrofuran-modified lignin (THFL) exhibited remarkable changes in the presence of an alcohol functional group. The results of 1H-NMR analysis confirm those obtained by FT-IR analysis. The results of the DSC analyses indicate that lignin and modified lignin exhibit different thermal properties. The results of the thermal and mechanical analyses of the modified lignin/PLA blends demonstrate that the characteristics of the alkyl chains used to modify lignin were well reflected in the final blends. Alkyl-chain-modified lignin that mimics LCC was observed to enhance the compatibility between the matrix polymers used in this study and modified lignin.