Byeong-Uk Nam

High molecular weight bio furan-based co-polyesters for food packaging applications: synthesis, characterization and solid-state polymerization

The goal of this study was to develop ecofriendly bioplastics, which could be applicable in beverage packaging, by synthesizing furan-based co-polyesters and incorporating them into bottles. The furan-based co-polyesters were synthesized by a two-step melt polycondensation reaction using ethylene glycol (EG), 1,4-cyclohexanedimethanol (CHDM), and dimethyl furan dicarboxylate (DM-FDCA). The incorporation of CHDM into the main chain of polymers has been found to increase the chain mobility due to its ring-conformational transition, and it also affects the co-polyesters. The co-polyesters show not only high elongations at break, but also improved Izod impact strengths compared to that of pure poly(ethylene furanoate) (PEF). Despite these characteristics, however, the molecular weights of the co-polyesters were not sufficient for manufacturing purposes. Thus, some samples were further reacted in the solid state by solid state polymerization (SSP) to generate higher-molecular-weight polymers. The crystallization kinetics of the co-polyesters prepared were analyzed to determine the reaction parameters, and the sample whose intrinsic viscosity was greater than 1.0 dL g−1 was successfully processed into bottles. The bottles prepared had higher O2-barrier properties and lower acetaldehyde contents than those of commercially available PET bottles. The results obtained so far show that furan-based co-polyesters can be used for food-packaging applications.

Eco-friendly plasticized poly(vinyl chloride)–acetyl tributyl citrate gels for varifocal lens

We fabricated an eco-friendly, electroactive, reconfigurable, and varifocal PVC–ATBC (ePVC) gel lens. The ePVC gel lens, composed of PVC and environmentally-benign ATBC plasticizer, was reconfigured in response to applied voltage. The proposed ePVC gel lens, whose shape is hemispherical plano-convex, changes its curvature according to various input voltages, and the variation of its focal length was consequently observed. In addition, after removal of the electric field, the proposed electroactive and eco-plasticized ePVC gel lens showed rapid restoration to its initial configuration. Therefore, the focal length of the proposed ePVC gel lens could be considerably changed in real-time under an applied electric field. This is attributed to the electric-field-induced deformation of the eco-friendly plasticized non-ionic ePVC gel lens towards the anode under applied voltages, which changes the meniscus of the ePVC gel lens within a concentric annular anode electrode. As a result, the focal length of the ePVC gel lens in our system increased from 5 mm up to 15 mm with increasing applied voltages from 0 V to 500 V.

Liquid crystal alignment behavior on transparent cellulose films

The liquid crystal (LC) alignment properties of LC cells fabricated with plant-based cellulose films were investigated. These carefully prepared polymer films exhibited good optical transparency in the visible light region (400–700 nm). For example, the transmittance value (91%) of the cellulose film on the glass substrate at 550 nm is better than that (89%) of the polyimide film, the most commonly used LC alignment layer. The LC cells made from rubbed cellulose films showed homogeneous planar LC alignment in the parallel direction with respect to the rubbing direction. The electro-optical characteristics of the LC cells fabricated with the cellulose films such as applied voltage and response time were as good as those fabricated from rubbed polyimide films. We also found that the thermal stability of the LC cell made from the cellulose film is better than that of the polyimide film.

Study on the influence of pretreatment and chain length of substituents on cellulose mixed esters

AbstractIn this work, homogeneous esterification of the cellulose mixed esters was accomplished with water-activated α-cellulose, various saturated fatty acids, and acetic anhydride in lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) medium to study the influence of activation and fatty acyl chain length on the cellulose mixed esters (CME). α-Cellulose was activated for 2 h at 50 °C in deionized water prior to esterification. CME was obtained after esterification for 5 h at 120 °C. The purified products were characterized in various ways. The morphology, structure, total degree of substitution, crystallization characteristics, thermal properties, contact angle, and film properties of CME were examined by FE-SEM, 1H NMR, FTIR, XRD, DMA, TGA, and CAA. These analyses revealed that the water activation pretreatment of α-cellulose was the critical factor affecting the esterification efficiency which is related to the overall properties of the cellulose esters. It is also confirmed that the glass transition behavior of the cellulose esters changes depending on the chain length of the substituents.

Preparation and Characterization of Elastomeric Ethylene Terpolymer Reinforced Poly(Ethylene-Co-Isosorbide Terephthalate)/Multi-Walled Carbon Nanotube Composites

Poly(ethylene-co-isosorbideterephthalate)(PEIT)/multi-walled carbon nanotube (MWCNT)/ethylene terpolymer composites were prepared by a melt mixing process. The effects of MWCNT and the ethylene terpolymer of nanocomposites on the mechanical, thermal and electrical properties were investigated. MWCNT and ethylene terpolymer from 1 to 5 phr and 5 wt.% and 10 wt.% were added to the PEIT matrix, respectively. The thermal properties were evaluated by DSC and TGA. The morphology, mechanical properties and electrical characteristics were assessed by FE-SEM, a notched Izod impact strength tester and a surface resistance meter. As a result, we found that the PEIT/MWCNT/ethylene terpolymer composites have higher conductivity and better mechanical properties than neat PEIT resin.