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( Kyung Yun Choi ),( Soo Bok Kim ),( Seokhu Bae ),( Jeong-hwan Yoon ),( Ju-ho Yun ),( Namil Kim ) 한국고무학회 2020 엘라스토머 및 콤포지트 Vol.55 No.2
The effect of a greenhouse-covering material on its indoor environment and on the characteristics of cherry tomatoes grown in it was investigated. The conventional polyethylene (PE) film on the greenhouse roof was replaced by a polycarbonate (PC) sheet, while maintaining the main structural frame intact. Color changes and the formation of water droplets on the PC surface were avoided by applying coextrusion and coating layers. When compared to the PE greenhouse, the PC greenhouse enabled increased light transmittance and thus a higher indoor temperature during both summer and winter. The thermal insulating property of the PC sheet effectively reduced the heating loss by approximately 55% during winter. The cherry tomatoes grown in the PC greenhouse exhibited superior fruit characteristics in terms of size, weight, and sugar content. The total amount of cherry tomatoes produced per unit area (1,000 m<sup>2</sup>) in the PC greenhouse was found to be greater by approximately 19% compared to that in the PE greenhouse.
Improved Mechanical and Durability Properties of PVC Sheet by Designing Three-Layered Structures
( Jun-young Park ),( Woo-sang Kim ),( Hae-cheon Kang ),( Seokhu Bae ),( Jeong-hwan Yoon ),( Juho Yun ),( Eun-kyoung Lee ),( Namil Kim ) 한국고무학회 2019 엘라스토머 및 콤포지트 Vol.54 No.4
A three-layered PVC sheet consisting of polyvinyl chloride (PVC) and woven polyester fabric was prepared by extrusion and calendering. The flexibility and durability of the PVC were tuned by adding plasticizers, additives, and surface coatings. The tensile and tear strengths of the three-layered PVC sheet were higher than those of commercial two-layered sheet, while exhibiting low weight. The concentrations of the total volatile organic compounds (TVOCs) and formaldehyde (HCHO) emitted from the sheet were also lowered. The PVC sheet remained stable after prolonged exposure to UV light, signifying that the PVC sheet is suitable for cargo screen applications.
Performances of Plastic Pulley with High Mechanical Properties and Low Friction
( Namil Kim ),( Jung-seok Lee ),( Byung-kook Hwang ),( Seokhu Bae ),( Jeong-hwan Yoon ),( Juho Yun ) 한국고무학회 2019 엘라스토머 및 콤포지트 Vol.54 No.2
Polyphenylene sulfide (PPS) was filled with glass fiber (GF), aramid fiber (AF), and solid lubricants to improve the mechanical properties and wear resistance. The addition of GF effectively enhanced the tensile strength, flexural modulus, and impact strength of PPS, while solid lubricants such as polytetrafluoroethylene (PTFE), molybdenum disulfide (MoS<sub>2</sub>), and tungsten disulfide (WS<sub>2</sub>) lowered the friction coefficients of the composites to below 0.3. The ball nut and motor pulley of the electric power steering (EPS) were manufactured using the PPS composites, and feasibility was ascertained thereafter by conducting the durability test. The composites filled with GF and AF showed high mechanical strength, but slip occurred at the interface between the pulley and belt while testing above 50°C. When small amounts of lubricants were added, the slip was no longer detected because of the suppression of friction heat. It is realized that the low friction as well as high mechanical properties is important to ensure the reliability of plastic pulleys.