Browsing by Author "Kim, Young-Teck"

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    A New Method to Determine Antioxidant Activities of Biofilms Using a pH Indicator (Resazurin) Model System
    Kim, Young-Teck; Kimmel, Robert; Wang, Xiyu (MDPI, 2023-02-23)
    Biopolymeric films were prepared with gelatin, plasticizer, and three different types of antioxidants (ascorbic acid, phytic acid, and BHA) corresponding to different mechanisms in activity. The antioxidant activity of films was monitored for 14 storage days upon color changes using a pH indicator (resazurin). The instant antioxidant activity of films was measured by a DPPH free radical test. The system using resazurin was composed of an agar, an emulsifier, and soybean oil to simulate a highly oxidative oil-based food system (AES-R). Gelatin-based films (GBF) containing phytic acid showed higher tensile strength and energy to break than all other samples due to the increased intermolecular interactions between phytic acid and gelatin molecules. The oxygen barrier properties of GBF films containing ascorbic acid and phytic acid increased due to the increased polarity, while GBF films containing BHA showed increased oxygen permeability compared to the control. According to “a-value” (redness) of the AES-R system tested with films, films incorporating BHA showed the most retardation of lipid oxidation in the system. This retardation corresponds to 59.8% antioxidation activity at 14 days, compared with the control. Phytic acid-based films did not show antioxidant activity, whereas ascorbic acid-based GBFs accelerated the oxidation process due to its prooxidant activity. The comparison between the DPPH free radical test and the control showed that the ascorbic acid and BHA-based GBFs showed highly effective free radical scavenging behavior (71.7% and 41.7%, respectively). This novel method using a pH indicator system can potentially determine the antioxidation activity of biopolymer films and film-based samples in a food system.
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    Synthesis and Characterization of Poly(Butylene Sebacate-Co-Terephthalate) Copolyesters with Pentaerythritol as Branching Agent
    Jang, Hyunho; Kwon, Sangwoo; Kim, Sun Jong; Kim, Young-Teck; Park, Su-il (MDPI, 2023-12-19)
    Poly(butylene sebacate-co-terephthalate) (PBSeT) copolyesters are prepared by melt polymerization via two-step transesterification and polycondensation using pentaerythritol (PE) as a branching agent. The effects of the incorporated PE on its chemical, thermal, mechanical, and degradation properties, along with the rheological properties of its melt, are investigated. The highest molecular weight and intrinsic viscosity along with the lowest melt flow index were achieved at a PE content of 0.2 mol%, with minimal reduction in the tensile strength and the highest tear strength. The addition of PE did not significantly influence the thermal behavior and stability of the PBSeT copolyesters; however, the elongation at break decreased with increasing PE content. The sample with 0.2 mol% PE exhibited a higher storage modulus and loss modulus as well as a lower loss angle tangent than the other samples, indicating improved melt elasticity. The incorporation of more than 0.2 mol% PE enhanced the enzymatic degradation of copolyesters. In summary, including within 0.2 mol%, PE effectively improved both the processability-related characteristics and degradation properties of PBSeT copolyesters, suggesting their potential suitability for use in agricultural and packaging materials.
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    TEMPO-Oxidized Cellulose Nanofibril Films Incorporating Graphene Oxide Nanofillers
    Kim, Yoojin; Kim, Young-Teck; Wang, Xiyu; Min, Byungjin; Park, Su-il (MDPI, 2023-06-11)
    To design a new system of novel TEMPO-oxidized cellulose nanofibrils (TOCNs)/graphene oxide (GO) composite, 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation was utilized. For the better dispersion of GO into the matrix of nanofibrillated cellulose (NFC), a unique process combining high-intensity homogenization and ultrasonication was adopted with varying degrees of oxidation and GO percent loadings (0.4 to 2.0 wt%). Despite the presence of carboxylate groups and GO, the X-ray diffraction test showed that the crystallinity of the bio-nanocomposite was not altered. In contrast, scanning electron microscopy showed a significant morphological difference in their layers. The thermal stability of the TOCN/GO composite shifted to a lower temperature upon oxidation, and dynamic mechanical analysis signified strong intermolecular interactions with the improvement in Young’s storage modulus and tensile strength. Fourier transform infrared spectroscopy was employed to observe the hydrogen bonds between GO and the cellulosic polymer matrix. The oxygen permeability of the TOCN/GO composite decreased, while the water vapor permeability was not significantly affected by the reinforcement with GO. Still, oxidation enhanced the barrier properties. Ultimately, the newly fabricated TOCN/GO composite through high-intensity homogenization and ultrasonification can be utilized in a wide range of life science applications, such as the biomaterial, food, packaging, and medical industries.