Extraction de cellulose nanofibrillée à partir de biomasse agricole et étude des applications potentielles
Malladi, Rajini Priya
Cette étude est dédiée à l'extraction de la nanocellulose à partir de fibres naturelles telles que celles de carotte, de lin, de chanvre et d'asclépiade. La biomasse a été purifiée à l'aide d'un procédé à étape unique qui comprend par ailleurs divers traitements avec de nombreux produits chimiques. Les NFC et les NCC ont été extraits des déchets de carottes par un broyage à billes suivi d’une hydrolyse acide. L'effet du temps de broyage à billes sur la fibrillation et la morphologie des NFC a été étudié. Les propriétés mécaniques des NFC issus de la carotte ont également été étudiées. Les films de nanocellulose (NF) ont également été préparés en coulant les suspensions extraites (NFC et NCC). Afin d'améliorer caractère hydrophobe, les films de nanocellulose ont été recouverts d'un revêtement TiO2 par technique sol-gel avec et sans oxydation TEMPO. Les NCF purs et oxydés ont été revêtus de dioxyde de titane (TiO2) via approche sol-gel par revêtement par immersion.Abstract: The production of cellulosic materials is increasing tremendously in need to change towards the renewable raw materials and eco-friendly sustainable material. Cellulose is often considered one of the most important natural resource. With the advent of nanotechnology, the researchers and industries focus in the production of nanocellulose in huge quantities. The trailing purpose behind the growth of research in nanocellulose lies in their promising properties such as low density and high mechanical strength. Cellulose nanofibrils (CNF), otherwise known as nanofibrillated cellulose (NFC), micro fibrillated cellulose (MFC) or cellulose nanofibers and Nanocrystalline cellulose (NCC) are the materials with significant barrier, mechanical and colloidal properties. The above properties make nanocellulose promising for applications in such fields as papermaking, composites, packaging, coatings and biomedicine. Cellulose can be found in different sources like wood, natural fibers (agriculture biomass), marine animal (tunicate), algae and fungi. The composition of this lignocellulosic biomass is different for each source. With the ever-increasing demand in renewable resource, the crop waste is meant to be an appropriate material. The recovery of waste makes it possible to protect the environment and to benefit from low cost reinforcements. Agriculture waste biomass is significant resource for the reason it is environmentally friendly, cost next to nothing, high in strength, readily available and renewable. The crop waste constitutes abundant natural fiber. The agriculture waste can be obtained from cotton stalk, pineapple leaf, rice straw, flax, hemp, milkweed, carrot, soy pods, rice husk etc. These materials can be used in multitude applications like paper and textile industry, composites, building, furniture and medical fields. The NFC market is currently emphasized because of the augmented focus of the governments, industries, funding agencies and Universities. The bio-based economy is rapidly increasing resulting in the higher investments. The industries producing NFC are Paperlogic, University of Maine, Borregaard Norway, American Process, Nippon Paper Japan, Innventia Sweden, CTP/FCBA France, Oji Paper, Japan. This study is dedicated to the extraction of nanocellulose from nat6ural fibers viz carrot, flax, hemp and milkweed. The biomass was purified using single step process which otherwise includes various treatments with many chemicals which is discussed under literature review. The very first step in the extraction of nanocellulose is the purification of biomass to remove any traces of lignin, waxes etc. In a usual study, this includes many stages like acid and alkali treatments, bleaching etc. In this research work, the purification of biomass (flax, hemp and milkweed) was achieved in single step using Hydrogen peroxide. The fiber length remained unaffected during the process. The XRD results showed that the crystallinity of the fibers was not affected when purified. NFC and NCC was extracted from carrot waste by ball milling and acid hydrolysis respectively. The effect of ball grinding time on the fibrillation and morphology of the NFC was studied. The mechanical properties of carrot NFC was also studied. The nanocellulose films (NFs) were also prepared by casting the extracted NFC and NCC suspensions. The structural, functional, crystalline and thermal properties of resulted NFC and NCC was characterized. The results exhibited that length and the diameter of the NCC prepared from carrot was in the range of 54 - 610 nm. Significant improvement in crystallinity was observed for NFC (69 %) and NCC (78 %) compared to that of raw fibers (36 %). The nanocellulosic films prepared by using NFC and NCC, optical and morphological properties were analyzed. The films exhibited the significant improvement in the transparency and homogeneity with increase in the grinding time. Generally, the nanocellulose films has low oxygen permeability and high oil resistant due to their dense web like network. However, these films are not stable at high moisture medium. In order to improve the hydrophobic nature of the films, coated with TiO2 sol-gel coating with and without oxidation of TEMPO. The neat and oxidized NCF were coated with Titanium dioxide sol-gel (TiO2) by dip coating. The TiO2 coated NCF was dried at 65 ºC for two hours and then treated at 95 ºC for one hour to form the TiO2 on the surface of the films. The effect of TiO2 coating on neat and oxidized NCF was characterized to understand the morphological, optical, functional, and barrier properties. The contact angle measurement showed that the hydrophobic nature of the non-oxidized TiO2 coated and oxidized TiO2 coated films were increased drastically from 89° to 41° and 29° respectively. Notably, the barrier and optical properties of the coated films were significantly improved compared to that of the neat NCF films. Importantly, the tensile strength and elasticity of the TiO2 coated NCF films were improved considerably compared to neat NCF.
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