고분자 발포체는 기공 구조에 의한 낮은 밀도와 우수한 단열 및 방음 성능, 유연성, 충격완화 성능 등의 특성으로 인하여 가정 용품, 전자 제품, 자동차 소재, 건축용 소재, 항공 우주용 소재에 이르기까지 다양한 분야에 폭넓게 사용되고 있다. 최근에는 층간 소음, NVH (noise, vibration, harshness) 등의 이슈가 대두됨에 따라 ...
고분자 발포체는 기공 구조에 의한 낮은 밀도와 우수한 단열 및 방음 성능, 유연성, 충격완화 성능 등의 특성으로 인하여 가정 용품, 전자 제품, 자동차 소재, 건축용 소재, 항공 우주용 소재에 이르기까지 다양한 분야에 폭넓게 사용되고 있다. 최근에는 층간 소음, NVH (noise, vibration, harshness) 등의 이슈가 대두됨에 따라 흡음 및 방진 성능의 향상과 전자제품 특히 전기자동차 산업의 발전에 따른 전자파 차폐 성능이 구현 가능한 기능성 소재에 대한 요구가 증가하고 있다. 또한 지구온난화에 따른 환경 규제가 심화됨에 따라 온실 가스 배출을 줄이고 석유계 화학 물질을 대체할 수 있는 친환경 소재의 필요성이 증가하고 있다. 본 연구에서는 재생가능 친환경 바이오매스 기반 고분자 발포체를 나노 입자로 강화함으로써 기계적 물성 및 흡음 성능을 향상시키고 전자파 차폐 성능을 구현하였다. 분산 공정으로 초임계 유체를 이용하여 나노 입자가 균일하게 분산된 복합 발포체를 제조하였고, 나노 입자는 표면 에너지 차이에 기인하여 기공 표면에 흡착함으로써 기공 구조를 강화하고 안정한 발포체 구조를 형성하였다. 나노 입자로 강화된 복합 발포체의 기계적 물성, 흡음, 전자파 차폐 성능 및 기공 구조와 물성 간의 상관관계에 관한 연구를 진행하였다. 첫 번째로, 나노 입자로 기공이 강화된 고분자 발포체의 구조와 기계적 물성에 관한 연구를 진행하였다. 초임계 유체 이산화탄소에 의해 균일하게 분산 및 박리된 몬트모릴로나이트 나노 입자는 Gibbs absorption에 의해 기공 표면에 흡착함으로써 기공을 강화하고 안정한 발포체 구조를 형성하였다. 몬트모릴로나이트가 5 wt% 충진된 복합 발포체는 고분자 발포체 대비 압축 강도가 240% 탄성율이 220% 향상되었고, 나노 입자의 핵제 효과에 의해 발포율이 상승함을 확인하였다. 두 번째로, 그래핀이 충진된 바이오매스 기반 고분자 발포체의 흡음 성능과 전자파 차폐 성능에 관한 연구를 진행하였다. 초임계 유체 이산화탄소에 의해 균일하게 분산된 그래핀 나노 입자는 고분자 계면에서의 마찰에 의한 열 에너지 손실을 증가시킴으로써 발포체의 흡음 성능을 향상시키고, 그래핀의 전기적 특성으로 인해 전자파 차폐 성능을 구현하였다. 소재의 두께를 줄이기 위해 그래핀 복합 발포체를 압축시킨 후 구조와 물성 변화를 분석하였고, 80% 압축된 복합 발포체는 1 KHz에서 0.5 이상의 흡음률 값을 가지고 전자파 차폐 성능을 나타내었다. 마지막으로, 목질 폐기물을 재활용한 리그닌 기반 고분자 발포체를 합성하고 기공 구조에 따른 기계적 물성과 흡수 성능을 분석하였다. 리그닌 기반 경질 우레탄 발포체는 리그닌의 단단한 방향족 분자 구조에 의해 폴리우레탄 발포체 대비 압축 강도와 탄성율이 증가하였고, 리그닌 기반 연질 우레탄 발포체는 개방된 소수성 기공 구조에 의해 유출된 기름이나 유기 용매 등의 오염 물질을 흡수하는 것을 확인하였다.
고분자 발포체는 기공 구조에 의한 낮은 밀도와 우수한 단열 및 방음 성능, 유연성, 충격완화 성능 등의 특성으로 인하여 가정 용품, 전자 제품, 자동차 소재, 건축용 소재, 항공 우주용 소재에 이르기까지 다양한 분야에 폭넓게 사용되고 있다. 최근에는 층간 소음, NVH (noise, vibration, harshness) 등의 이슈가 대두됨에 따라 흡음 및 방진 성능의 향상과 전자제품 특히 전기자동차 산업의 발전에 따른 전자파 차폐 성능이 구현 가능한 기능성 소재에 대한 요구가 증가하고 있다. 또한 지구온난화에 따른 환경 규제가 심화됨에 따라 온실 가스 배출을 줄이고 석유계 화학 물질을 대체할 수 있는 친환경 소재의 필요성이 증가하고 있다. 본 연구에서는 재생가능 친환경 바이오매스 기반 고분자 발포체를 나노 입자로 강화함으로써 기계적 물성 및 흡음 성능을 향상시키고 전자파 차폐 성능을 구현하였다. 분산 공정으로 초임계 유체를 이용하여 나노 입자가 균일하게 분산된 복합 발포체를 제조하였고, 나노 입자는 표면 에너지 차이에 기인하여 기공 표면에 흡착함으로써 기공 구조를 강화하고 안정한 발포체 구조를 형성하였다. 나노 입자로 강화된 복합 발포체의 기계적 물성, 흡음, 전자파 차폐 성능 및 기공 구조와 물성 간의 상관관계에 관한 연구를 진행하였다. 첫 번째로, 나노 입자로 기공이 강화된 고분자 발포체의 구조와 기계적 물성에 관한 연구를 진행하였다. 초임계 유체 이산화탄소에 의해 균일하게 분산 및 박리된 몬트모릴로나이트 나노 입자는 Gibbs absorption에 의해 기공 표면에 흡착함으로써 기공을 강화하고 안정한 발포체 구조를 형성하였다. 몬트모릴로나이트가 5 wt% 충진된 복합 발포체는 고분자 발포체 대비 압축 강도가 240% 탄성율이 220% 향상되었고, 나노 입자의 핵제 효과에 의해 발포율이 상승함을 확인하였다. 두 번째로, 그래핀이 충진된 바이오매스 기반 고분자 발포체의 흡음 성능과 전자파 차폐 성능에 관한 연구를 진행하였다. 초임계 유체 이산화탄소에 의해 균일하게 분산된 그래핀 나노 입자는 고분자 계면에서의 마찰에 의한 열 에너지 손실을 증가시킴으로써 발포체의 흡음 성능을 향상시키고, 그래핀의 전기적 특성으로 인해 전자파 차폐 성능을 구현하였다. 소재의 두께를 줄이기 위해 그래핀 복합 발포체를 압축시킨 후 구조와 물성 변화를 분석하였고, 80% 압축된 복합 발포체는 1 KHz에서 0.5 이상의 흡음률 값을 가지고 전자파 차폐 성능을 나타내었다. 마지막으로, 목질 폐기물을 재활용한 리그닌 기반 고분자 발포체를 합성하고 기공 구조에 따른 기계적 물성과 흡수 성능을 분석하였다. 리그닌 기반 경질 우레탄 발포체는 리그닌의 단단한 방향족 분자 구조에 의해 폴리우레탄 발포체 대비 압축 강도와 탄성율이 증가하였고, 리그닌 기반 연질 우레탄 발포체는 개방된 소수성 기공 구조에 의해 유출된 기름이나 유기 용매 등의 오염 물질을 흡수하는 것을 확인하였다.
Now days, polymer foams were used in various end-use industries such as packaging, construction, architecture, electronic devices, automotive, footwear, and sports because of their light weight, excellent strength/weight ratio, thermal and acoustic insulating capabilities, energy absorption performa...
Now days, polymer foams were used in various end-use industries such as packaging, construction, architecture, electronic devices, automotive, footwear, and sports because of their light weight, excellent strength/weight ratio, thermal and acoustic insulating capabilities, energy absorption performance. Due to the rapid development of the application fields of polymer foams, polymer composite foams which have such properties as light-weight, high-performance, and multi-functionality were developed with various strategies as incorporating nanoplatelet and biomass-based fillers. In this dissertation, we developed biomass-based polymer composite foams reinforced by nanoplatelets to investigate tunable mechanical, electromagnetic, and sound wave absorption properties based on structure-property relationship of composite foams. We categorized three research topics: chapter 2 nanoplatelet reinforced polymer composite foams, chapter 3 biomass-based polymer foams reinforced by graphene for wave-absorption, and chapter 4 biomass-based rigid and flexible polymer foams. In chapter 2, we have investigated nanoplatelet reinforcement of cell walls in polymer foams using carbon dioxide supercritical fluid. In chapter 3 and 4, we synthesized biomass-based polymer foams and reinforced by nanoplatelet using supercritical CO2 technique in the mixing process. Biomass-based polymer foams reinforced by nanoplatelets had improved mechanical properties and wave-absorption properties. Firstly, nanoplatelet reinforced poly(ethylene-vinyl acetate) copolymer (EVA) foams were prepared by using CO2 supercritical fluid (CO2 SCF) technique. Reinforcing the cavity cell walls of polymer foams using nanoparticles could offer a new era for the property-structure-processing field in the development of functionalized ultra-light components and devices manufactured from foam. When the nanoparticles were exfoliated in polymers, the viscosity substantially increases and thus mixing or foaming usually became almost impossible. We used CO2 SCF for the mixing and foaming of EVA with montmorillonite (MMT) nanoplatelets. The in-situ evaporation of CO2 induced robust cavity cells of the EVA/MMT nanocomposite foam in a stable form of spherical shapes, which were seldom achieved by other methods. The exfoliated MMT nanoparticles were aligned at the cell walls by the Gibbs adsorption principle to minimize the surface energy at the gas-liquid interface and increase the rupture strength of the cavity walls. It was demonstrated that the developed methodology could be successfully used for foaming EVA containing high vinyl acetate (VA) content (>40 %). Since EVA is too soft to construct cell walls of foam using conventional methods, the applicability of the developed methodology is extensively broadened for superior adhesion and compatibility with other materials. Secondly, we developed graphene-incorporated polyurethane (PU) nanocomposite foams and its metastable form stabilized in the compressed state possessing capabilities of both sound damping and electromagnetic interference (EMI) shielding. Sound absorption and electromagnetic-wave shielding constitute one of the major requirements for human comfort and safety, especially in automobile, airplane, and various manufacturing environments. The CO2 SCF was used for dispersing the graphene sheets in the high-viscosity reactants and the graphene nanoplatelets were successfully aligned on the cell walls in the in-plane direction due to the localized rearrangement of graphene nanoplatelets by the Gibbs-Marangoni flow during the bubble stabilization. Compared with the pristine PU foam, the incorporated graphene substantially increased sound absorption coefficients and compressive strengths by 170% and 55%, respectively. The graphene nanoplatelets desirably reinforced the cavity strength of the foam, and subsequently allowed a compressed metastable state of the foam structures downsized to 1/5 of the pristine volume. This metastable foam provided the sound absorption coefficient as 0.65 (0.1 wt% graphene) and EMI shielding effectiveness as 12.5 dB (1.0 wt% graphene). The developed methodology allowed to impose energy damping capabilities in both sound absorption and EMI shielding effectiveness to foams particularly decreasing the occupation volume. Lastly, we synthesized biomass-based rigid and flexible PU foams. Global warming induced by greenhouse gases from immoderate use of fossil fuel in petrochemical industry was the most critical environmental issue. Consequently, the demand of carbon-neutral biomass for alternative of petroleum-based materials was increased. Lignin-based PU was synthesized by urethane reaction between lignin and isocyanate. Lignin-based rigid PU foams had a low density of 0.118 g/cm3. The diameter of closed-cells was 471 μm and compressive strength and modulus of lignin-based PU foams were increased comparing to the pristine PU foam attributed to the rigidity of lignin aromatic structure. Especially, lignin-based flexible PU foam exhibited open-cell structure and provided an absorption capacity for oil and organic solvents.
Now days, polymer foams were used in various end-use industries such as packaging, construction, architecture, electronic devices, automotive, footwear, and sports because of their light weight, excellent strength/weight ratio, thermal and acoustic insulating capabilities, energy absorption performance. Due to the rapid development of the application fields of polymer foams, polymer composite foams which have such properties as light-weight, high-performance, and multi-functionality were developed with various strategies as incorporating nanoplatelet and biomass-based fillers. In this dissertation, we developed biomass-based polymer composite foams reinforced by nanoplatelets to investigate tunable mechanical, electromagnetic, and sound wave absorption properties based on structure-property relationship of composite foams. We categorized three research topics: chapter 2 nanoplatelet reinforced polymer composite foams, chapter 3 biomass-based polymer foams reinforced by graphene for wave-absorption, and chapter 4 biomass-based rigid and flexible polymer foams. In chapter 2, we have investigated nanoplatelet reinforcement of cell walls in polymer foams using carbon dioxide supercritical fluid. In chapter 3 and 4, we synthesized biomass-based polymer foams and reinforced by nanoplatelet using supercritical CO2 technique in the mixing process. Biomass-based polymer foams reinforced by nanoplatelets had improved mechanical properties and wave-absorption properties. Firstly, nanoplatelet reinforced poly(ethylene-vinyl acetate) copolymer (EVA) foams were prepared by using CO2 supercritical fluid (CO2 SCF) technique. Reinforcing the cavity cell walls of polymer foams using nanoparticles could offer a new era for the property-structure-processing field in the development of functionalized ultra-light components and devices manufactured from foam. When the nanoparticles were exfoliated in polymers, the viscosity substantially increases and thus mixing or foaming usually became almost impossible. We used CO2 SCF for the mixing and foaming of EVA with montmorillonite (MMT) nanoplatelets. The in-situ evaporation of CO2 induced robust cavity cells of the EVA/MMT nanocomposite foam in a stable form of spherical shapes, which were seldom achieved by other methods. The exfoliated MMT nanoparticles were aligned at the cell walls by the Gibbs adsorption principle to minimize the surface energy at the gas-liquid interface and increase the rupture strength of the cavity walls. It was demonstrated that the developed methodology could be successfully used for foaming EVA containing high vinyl acetate (VA) content (>40 %). Since EVA is too soft to construct cell walls of foam using conventional methods, the applicability of the developed methodology is extensively broadened for superior adhesion and compatibility with other materials. Secondly, we developed graphene-incorporated polyurethane (PU) nanocomposite foams and its metastable form stabilized in the compressed state possessing capabilities of both sound damping and electromagnetic interference (EMI) shielding. Sound absorption and electromagnetic-wave shielding constitute one of the major requirements for human comfort and safety, especially in automobile, airplane, and various manufacturing environments. The CO2 SCF was used for dispersing the graphene sheets in the high-viscosity reactants and the graphene nanoplatelets were successfully aligned on the cell walls in the in-plane direction due to the localized rearrangement of graphene nanoplatelets by the Gibbs-Marangoni flow during the bubble stabilization. Compared with the pristine PU foam, the incorporated graphene substantially increased sound absorption coefficients and compressive strengths by 170% and 55%, respectively. The graphene nanoplatelets desirably reinforced the cavity strength of the foam, and subsequently allowed a compressed metastable state of the foam structures downsized to 1/5 of the pristine volume. This metastable foam provided the sound absorption coefficient as 0.65 (0.1 wt% graphene) and EMI shielding effectiveness as 12.5 dB (1.0 wt% graphene). The developed methodology allowed to impose energy damping capabilities in both sound absorption and EMI shielding effectiveness to foams particularly decreasing the occupation volume. Lastly, we synthesized biomass-based rigid and flexible PU foams. Global warming induced by greenhouse gases from immoderate use of fossil fuel in petrochemical industry was the most critical environmental issue. Consequently, the demand of carbon-neutral biomass for alternative of petroleum-based materials was increased. Lignin-based PU was synthesized by urethane reaction between lignin and isocyanate. Lignin-based rigid PU foams had a low density of 0.118 g/cm3. The diameter of closed-cells was 471 μm and compressive strength and modulus of lignin-based PU foams were increased comparing to the pristine PU foam attributed to the rigidity of lignin aromatic structure. Especially, lignin-based flexible PU foam exhibited open-cell structure and provided an absorption capacity for oil and organic solvents.
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