Nanocellulose Embedded Polymer Composite Foams for Flame Retardancy

Abstract

Chapter I explains an overview of nanocellulose and flame retardant properties. Nanocelluloses are used in various applications to improve the quilty of human life. Although nanocelluloses are venerable to fire, these properies can be modifired by chemical treatement such as silylation. This can be used to flame retradanct materials itself and used to flame retradant filler with polymeric composites. Chapter II provides an fabrication of silylated Nanocrystalline cellulose (NCC) for flame retardant application. Employing proper flame retardant materials is one of the most important fire safety guidelines when constructing buildings. Most flame retardants, however, contain halogen atoms that might become harmful gases to human body during combustion. We designed and fabricated an environmental-friendly flame retardant material with a superior performance for thermal insulation. NCC was prepared using acid hydrolysis method, and its surface was chemically modified through silylation treatment. Various characteristics of the flame retardant material, such as morphology, chemical structure, thermal stability, and thermal conductivity were investigated. When a mass ratio of NCC to methyltrimethoxysilane (MTMS) was 1:5, the limiting oxygen index (LOI) of the silylated NCC increased to 34% and a char yield of 80% was obtained. The silylation led to enhancement in the thermal stability of NCC and generation of the char residue. Chemical structure of the residual materials after combustion was investigated by using Fourier transform infrared spectroscopy (FTIR) and X-ray differential photo spectroscopy (XPS). Chapter III demonstrates fabrication of silylated nanofibrillated cellulose and polyurethane composite with TCPP. Improving flame retardancy is one of the most crucial issues to use polymeric materials for building construction. Most of the flame retardant materials containing halogen atoms delay fire spread, but produce harmful gases during combustion. Hence, we designed and fabricated a composite foam by using a green nanomaterial. Silylated and nanofibrillated cellulose (Si-NFC) was added to polyurethane foam (PUF) containing tris(2-chloropropyl) phosphate (TCPP) in order to reduce the emission of smoke during combustion. Thermal characteristics of the composite foams were investigated through thermogravimetric analysis, LOI, and cone calorimeter tests. The LOI of the Si-NFC embedded composite was increased from 19.3% to 24.6%. In addition, the Si-NFC led to an improvement in the thermal stability of the composites by reducing the peak release of heat and smoke. Chemical structure of the residual char was analyzed by using energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. In Chapter IV, the increment of flame retardant propterties of polyurthane composite with TCEP are explained. Delaying flame propagation in the event of a fire can increase the likelihood of preserving life and alleviate damage to property. Here, a strategy for flame retardant polymer composite foam is proposed, which enables the improved performance, good formability, and reduced environmental burden while burning. The strategy is to incorporate sylilated nanocellulose into a polyurethane matrix containing a conventional flame retardant, Tris(2-chloroethyl) phosphate (TCEP). This strategy leads to the generation of char layer faster during combustion, resulting in a delayed flame propagation. The LOI of the samples increased by 28%, and the production rate of toxic gas emission was considerably reduced. The chemical, thermomechanical, and morphological analyses were carried out to understand the underlying physics.

본 논문에서는 나노셀룰로오스를 이용하여 난연 특성을 가지는 멤브레인과 발포 폴리우레탄에 관한 연구를 수행하였다. 나노크리스탈라인 셀룰로오스를 화학적으로 개질하여 실란화를 달성 하였으며, 셀룰로오스와 실란화에 이용한 물질은 가연성을 보이나, 이를 통해 생성되는 폴리실록세인이 표면에 막을 형성하여 난연성을 증가시킴을 확인하였다. 이러한 셀룰로오스를 이용하여 한계산소농도(LOI)가 매우 높고, 열전도도가 낮은 셀룰로오스를 멤브레인 형태로 제조하였다. 또한 피브릴화된 셀룰로오스와 상용 난연제를 동시에 폴리우레탄 폼에 첨가하여 시너지 효과를 유발시켜, 열방출속도, 연기발생속도 등이 낮고, 한계산소농도가 탁월한 발포 폴리우레탄 복합재료를 제조하였다. 특히, 실란화된 나노셀룰로오스가 발포를 위한 핵으로 작용하여 난연제의 단점인 셀 크기가 증가하는 문제를 해결함으로써 평균 셀 크기를 감소시킴과 동시에 발포가 저하되는 현상을 억제함을 확인하였다. 이러한 발포 고분자 복합재료는 기존의 폴리우레탄 폼보다 더 좋은 난연성을 가짐은 물론 친환경적인 충진제를 사용하였기 때문에, 인체에 유해한 상용 난연제의 사용을 감소시키는 효과를 제시하였다.