Byung Suk Jin

Structure development and biodegradability of uniaxially stretched poly(l-lactide)

Abstract The effects of uniaxial drawing conditions on the orientation of various poly( l -lactide) (PLLA) samples were investigated using Fourier transform infrared dichroism and thermal analysis. The results showed that the orientation in uniaxially stretched PLLA was determined by the drawing rate, drawing temperature, and draw ratio. For the amorphous sample, a higher orientation was obtained at a lower drawing temperature due to the slower chain relaxation. On the other hand, a higher orientation was achieved for the precrystallized samples at a higher drawing temperature due to the larger deformation of spherulites. The hydrolysis tests of PLLA films showed that the rate of hydrolysis was dependent on the degree of orientation as well as the percent crystallinity. After preferential hydrolysis of the amorphous regions, the surface of oriented PLLA samples might be covered by a layer of relatively inactive crystal lamellae, causing a reduction in the rate of hydrolysis.

Structure and properties of biodegradable gluten/aliphatic polyester blends

Abstract Aliphatic polyesters have excellent mechanical properties and biodegradability and are well suited to disposable applications. A drawback is that they currently have a high cost. In an effort to reduce their cost, we have prepared blends of an aliphatic polyester with wheat gluten, an inexpensive biodegradable protein. Plasticizers such as low molecular weight polyols were used in formulations to enhance the processability of the gluten. The resulting biodegradable gluten-based plastics demonstrate good physical and thermal properties. For the gluten granules-based blends, a droplet-like structure was obtained as observed in filler–polymer systems. On the other hand, due to the rheological characteristics of the plasticized gluten, a deformed fine morphology was observed in the plasticized gluten-based blends.

Thermal degradation kinetics of antimicrobial agent, poly(hexamethylene guanidine) phosphate

The thermal degradation of poly(hexamethylene guanidine) phosphate (PHMG) was studied by dynamic thermogravimetric analysis (TGA) and pyrolysis-GC/MS (p-GC). Thermal degradation of PHMG occurs in three different processes, such as dephosphorylation, sublimation/vaporization of amine compounds and decomposition/ recombination of hydrocarbon residues. The kinetic parameters of each stage were calculated from the Kissinger, Friedman and Flynn-Wall-Ozawa methods. The Chang method was also used for comparison study. To investigate the degradation mechanisms of the three different stages, the Coats-Redfern and the Phadnis-Deshpande methods were employed. The probable degradation mechanism for the first stage was a nucleation and growth mechanism, An type. However, a power law and a diffusion mechanism, Dn type, were operated for the second degradation stage, whereas a nucleation and growth mechanism, An type, were operated again for the third degradation stage of PHMG. The theoretical weight loss against temperature curves, calculated by the estimated kinetic parameters, well fit the experimental data, thereby confirming the validity of the analysis method used in this work. The life-time predicted from the kinetic equation is a valuable guide for the thermal processing of PHMG.

SALS study on transcrystallization and fiber orientation in glass fiber/polypropylene composites

This report presents a new technical approach for evaluating the fiber orientation of composites using small-angle light scattering (SALS). Glass fiber (GF)/polypropylene (PP) composites with different fiber orientations were prepared by drawing compression-molded specimens. The drawn samples were remelted and then annealed at 150 °C in order to induce a crystalline structure on the fiber surface, and then underwent SALS analysis. The samples showed a combination of circular and streak patterns. The model calculations demonstrated that the number of nuclei on the fiber surface and the thickness of the transcrystalline layer affected the sharpness and intensity of the streak pattern. In addition, the azimuthal angle of the streak pattern was found to be dependent on the direction of the transcrystalline layer, which correlated with the fiber direction. This correlation suggests that the fiber orientation in the composites can be easily evaluated using SALS.

Spherulitic Morphologies of Poly(ethylene terephthalate), Poly(ethylene 2,6-naphthalate), and Their Blend

The supermolecular structures of poly(ethylene terephthalate) (PET), poly(ethylene 2,6-naphthalate) (PEN), and their blend were investigated with optical microscopy and small angle light scattering. With increasing the crystallization temperature, incomplete spherulitic texture was developed for the PET samples. At a high crystallization temperature of 220°C, the light scattering pattern represented a random collection of uncorrelated lamellae. The general morphological appearances for the PEN samples were similar to that of the PET. A notable feature was that the spherulites of the PEN formed at 200°C showed regular concentric bands arising from a regular twist in the radiating lamellae. The spherulitic morphology of the PET/PEN blend was largely influenced by the changes of the sequence distribution in polymer chains determined by the level of transesterification. The increased sequential irregularity in the polymer chains via transesterification caused a morphological transition from a regular folded crystallite to a tilted lamellar crystallite.

Smad‐induced alterations of matrix metabolism by a myristoyl tetra peptide

Regulation of extracellular matrix (ECM) components is essential for tissue homeostasis and function. We screened a small peptide that induces ECM protein synthesis for its usefulness in protecting keratinocytes. In this report, we demonstrate that myristoyl tetrapeptide Ala‐Ala‐Pro‐Val (mAAPV) stimulates the expression of ECM proteins and inhibits the expression of metalloproteinases (MMPs) that degrade ECM proteins in Hs68 human fibroblast cells. In order to elucidate the underlying molecular mechanisms for the effects of mAAVP, we investigated the changes in gene expression in the presence of mAAPV using a cDNA microarray. Treatment with mAAPV resulted in decreased expression of MMP‐related genes such as MMP1, MMP3, TIMP1 and TIMP3 and increased expression of collagen genes, including COL1A1, COL1A2, COL3A1, COL5A1 and COL6A3. The pattern of gene expression regulated by mAAPV was very similar to that of gene expression induced by transforming growth factor (TGF)‐β, indicating that the TGF‐β signaling pathway is crucial for simultaneous activation of several ECM‐related genes by mAAPV. We examined whether the activation of SMAD, a downstream protein of TGF‐β receptor, is involved in the signal transduction pathway induced by mAAPV. The results demonstrate that mAAVP directly activates SMAD2 and induces SMAD3 to bind to DNA. In conclusion, our results demonstrate that mAAPV both enhances the expression of collagen and inhibits its degradation via production of protease inhibitors that prevent enzymatic breakdown of the ECM. The results suggest that mAAPV would be a useful ECM‐protecting agent. Copyright

Inhibition of UV‐induced matrix metabolism by a myristoyl tetrapeptide

Regulation of extracellular matrix (ECM) composition is important in tissue homeostasis and function. We screened small peptides for their ability to inhibit ultraviolet (UV)‐induced cell metabolism in epidermal fibroblasts. We found that UV irradiation increased matrix metalloproteinase (MMP) expression and inflammatory gene expression in human Hs68 fibroblast cells. We also demonstrated that a myristoyl tetrapeptide with the amino acid sequence Gly‐Leu‐Phe‐Trp (mGLFW) suppressed the UV‐induced expression of MMPs and inflammatory genes. Moreover, mGLFW stimulated the expression of ECM proteins in Hs68 fibroblasts. In order to provide the mechanism of action for mGLFW, we investigated UV‐induced signaling changes in the presence of mGLFW using a cDNA microarray. UV exposure increased the expression of MMP genes, such as MMP1, MMP3, and MMP14, and inflammation‐related genes, including interleukin 1 receptor and peroxisome proliferator‐activated receptor gamma (PPARγ). Treatment with mGLFW abrogated the UV‐induced expression of MMP‐related genes and inflammatory genes. In addition, mGLFW increased the expression of collagen genes, including COL1A1, COL1A2, and COL5A1. We examined whether the activation of AP‐1, a UV‐activated transcription factor, is suppressed by mGLFW. The results demonstrated that AP‐1 expression increased upon UV exposure and that this expression was inhibited by mGLFW. In conclusion, our results demonstrate that mGLFW reversed the effects of UV exposure by enhancing the expression of collagen proteins and suppressing the expression of MMPs, which degrade the ECM.