Microfibrillated Cellulose from Pineapple Leaves for Synthesizing Novel Thermal Insulation Aerogels

Aerogels from cellulose and its derivatives, especially cellulosic wastes, have been known as an excellent heat insulation material in steam generation, buildings, intelligent food packaging, fire-retardant clothing, and thermal protective equipment because of their lightweight properties, high stability, and extremely low thermal conductivities. Towards the scope of maximizing the bio-based resources utilization in day-to-day life, pineapple leaves (PLs) are converted into microfibrillated cellulose (MFC) fibers. PLs are first pretreated step by step with NaOH and NaOH/H2O2 solution to enrich cellulose content. This was followed by acid hydrolysis (H2SO4 40 wt%) and high-speed homogenization for MFC production. The obtained cellulose microfibers are further exploited to produce cost-effective, eco-friendly, and high-value engineering aerogels cross-linked by a common polyamide amine-epichlorohydrin (PAE) for the first time. The developed procedure is feasibly applied to mass production at a pilot-scale because of its simplicity, cost-effectiveness, and environmental friendliness. The resulting aerogels exhibit ultra-low density (below 30.0 g/cm3) and high porosity (above 98.0 %) along with high elasticity. Morphology analysis reveals that most of the pores within the aerogels are macroporous, and the diameter of fibers is around 2-3 µm. The heat conductivity of as-fabricated aerogels is in the range of 0.035-0.043 W/m?K, which is comparable to some heat insulation products such as glass wool (0.031-0.043 W/m?K), cellular glass (0.038-0.043 W/m?K), and mineral wool (0.034-0.045 W/m?K). The effects of cellulose and PAE contents on the morphology, physical, mechanical, and thermal behaviors of the synthesized aerogels are also investigated. The MFC aerogels from pineapple leaves are considered novel and promising candidates for bio-based heat insulation applications.