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  • 523

    Vijay Kumar Thakur, Manju Kumari Thakur and Michael R. Kessler (eds.), Handbook of Composites from Renewable Materials, Volume 7, (523556) 2017 Scrivener Publishing LLC

    *Corresponding author: nurhidayatullaili@um.edu.my

    17

    Nanocrystalline Cellulose: Green, Multifunctional and Sustainable Nanomaterials

    Samira Bagheri, Nurhidayatullaili Muhd Julkapli* and Negar Mansouri

    Nanotechnology & Catalysis Research Centre (NANOCAT), IPS Building, University Malaya, 50603 Kuala Lumpur, Malaysia

    AbstractThis chapter is divided into three sections: the first section briefly discusses the properties of nanocelluloseand it is followed by a section reviewing the progress to date of functionalized nano-cellulose. The last section discusses the applications of functionalized nanocellulose for specific and high-performance purposes. The resulting functionalized nanocellulose products with nano-sized dimensions and excellent physical properties which, combined with their edo-friendliness and their bio-degradability, make them materials of choice in the promising area of bionanotech-nology, opening up major commercial markets and consistent with the green chemistry trend.

    Keywords: Nanoparticles, grafting, dispersion, homogeneity, renewable bioresources

    17.1 Introduction: Natural Based Products

    During the past decades, massive efforts have been made to improve new materials and replace widely used oil-based products by utilizing biorenewable resources (Fattori et al., 2011; Gmez-Guilln et al., 2009; Olivetti, Gaustad, Field, & Kirchain, 2011: Thakur et al., 2013af). Therefore, there is an increasing demand for products made from renewable, nontoxicity, biodegradability, and renewability in the coming decades, as well as sustainable nonpetroleum-based resources (Fattori et al., 2011; Singha & Thakur, 2010ac). Along with the enhancements in processing plant materials, includ-ing cellulose, lignin, starch, and hemicellulose these let the forecast that more and more everyday products will completely or partially composed of biodegradable and biore-newable sources (Chauhan, Mahajan, & Guleria, 2000; Shaabani, Rahmati, & Badri, 2008; Walther, Timonen, Dez, Laukkanen, & Ikkala, 2011; Thakur & Voicu, 2016). From the aforementioned plant material, particularly the cellulose and hemicellulose have promising features, including high abundance and existing refining factories (Chauhan et al., 2000; Thakur et al. 2014ad)). In addition, utilize of cellulose-based materials do not raise ethical concerns since they cannot be utilized as food, which makes them promising in comparison with starch (Shaabani et al., 2008).

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    17.2 Nanocellulose

    The cellulose is a linear polysaccharide consisting of b-1,4 connected glucopyranose units, along with chains of polymer associated by hydrogen bonds forming fibrils bun-dles that contain highly ordered crystalline as well as disordered amorphous domains (Chauhan et al., 2000). The crystalline domains further isolated in nano-scale with reg-ular rod-like and highly ordered nanocrystals, after acid hydrolysis and removing the amorphous regions, which is called cellulose nanofibers, crystalline nanowhiskers, or nanocellulose (Morn, Alvarez, Cyras, & Vzquez, 2008). Nanocellulose obtained from various sources, including algae, sea animal (tunicate), and plant biomass. It also can be produced by biosynthesis by some bacteria known as bacterial cellulose or microbial cellulose (Gardner, Oporto, Mills, & Samir, 2008).

    As natural nano-scaled material, nanocellulose possesses diverse characteristics different from traditional materials, including special morphology and geometrical dimensions, crystallinity, high specific surface area, rheological properties, liquid crys-talline behavior, alignment and orientation, mechanical reinforcement, barrier prop-erties, surface chemical reactivity, biocompatibility, biodegradability, lack of toxicity, and others (Figure 17.1) (Jin et al., 2011; Korhonen, Kettunen, Ras, & Ikkala, 2011; Lee et al., 2009). Such benefits of nanocellulose are chiefly caused by its high stiffness and strength combined with low weight, as well as its renewability, biocompatibility, and biodegradability (Korhonen, Kettunen, et al., 2011).

    17.2.1 Nanocellulose: Properties

    The nanocellulose can be obtained via two approaches: bottom-up by biosynthesis or top-down by disintegration of plant materials (Table 17.1). On top-down approach, the production of nanocellulose chemically induced via destructing strategy of amorphous region and preservation of highly crystalline structure (Malho, Laaksonen, Walther,

    Source of cellulose Pretreatments

    Nanocellulose synthesisNanocellulose applications

    Alkali treatmentWaste water treatmentBiomedical applicationCatalysis

    Acid hydrolysisMechanical treatment

    Fibrillation

    Chemical processChemical processPhysical processEnzymatic process

    Physical processEnzymatic process

    Agricultural residuesWood, PlantsBacteria, Algae

    Figure 17.1 General sources, properties, and application of nanocellulose.

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    Table 17.1 Synthesis route of nanocellulose.

    Synthesis routeFeeding

    materials Properties Applications ReferencesBottom-up

    biosynthesisFermentation of

    low-molecular weight sugars using bac-teria from Acetobacter species

    Termed as bacte-rial cellulose

    Inherently nano-sized ribbon shaped cel-lulose fibrils

    Largest dimension ranging from 25 to 86nm

    Length up to several micrometers

    High critical sur-face energy

    Tissue engineering

    Biomedical engineering

    Advanced fiber composites

    (Malho et al., 2012; Wu et al., 2012)

    Top-down disintegra tion of plant materials

    Treated natural fibers with strong ultra-sound to dis-integrate larger bundles of natural fibers into smaller elementary fibrils whilst retaining the fibrous texture

    Using high-pressure homogenizer to reduce the size of wood fibers down to nanometer scale

    Nanocellulose with organized in extended chain confor-mation with a high degree of long range order

    Diameter of 530 nm, length of 100500 nm or length of 100 nm to several micrometer

    The morphology and dimension assessed as elongated rod-like nanopar-ticles and each rod could be regarded as a rigid cellulosic crystal without apparent defect

    (Aulin et al., 2012; Korhonen, Hiekkataipale, et al., 2011)

    Ikkala, & Linder, 2012; Wu, Saito, Fujisawa, Fukuzumi, & Isogai, 2012). The chemi-cal and/or mechanical destruction applied, which involves acid hydrolysis, enzymatic treatment, high-pressure homogenization, and grinding (Aulin, Salazar-Alvarez, & Lindstrm, 2012; Korhonen, Hiekkataipale, et al., 2011).

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    These synthesis routes of nanocellulose produced three different types of nanocel-lulose (i) cellulose nanocrystals (CNCs) with another designation, including nano-crystalline cellulose, cellulose (nano) whiskers, and rod-like cellulose microcrystal; (ii)cellulose nanofibrils (CNFs), with the synonyms of nanofibrillated cellulose, micro-fibrillated cellulose, cellulose nanofibers; and (iii) bacterial cellulose, also referred to as microbial cellulose (Table 17.2) (Figure 17.2).

    17.2.1.1 Nanocellulose: Mechanical Properties

    One of the main driven for utilizing nanocellulose is the possibility to exploit the stiff-ness and strength of cellulose crystal. In general, the mechanical properties of nano-cellulose characterized by its features in both the ordered crystalline domains and disordered amorphous regions of the nanoparticles (Jonoobi, Harun, Mathew, Hussein, et al., 2010). Cellulosic chains in disordered regions contribute to the plasticity and flexibility of the bulk material, but those in other domains contributing to the stiffness and elasticity of the material. The modulus of different types of nanocellulose expected to result from a mixing rule between the modulus of the crystalline domains and the amorphous fraction (Cervin, Aulin, Larsson, & Wgberg, 2012; Mihranyan, Esmaeili, Razaq, Alexeichik, & Lindstrm, 2012).

    Although it is challenging to determine the true modulus and strength of cellulose crystals, theoretical calculations, and numerical simulations used to estimate the axial modulus of cellulose crystal to be approximately 58180 GPa, which gives specific val-ues similar to Kevlar (60125 GPa) and potentially stronger than steel (200220 GPa) (Table 17.3).

    As for the tensile strength of nanocellulose concerned, theoretical predictions indi-cate that it has a tensile strength in the range 0.322 GPa. The predicted high tensile strength of nanocellulose is due to the extended chain conformation of crystalline cel-lulose, high density of covalent bonds per cross-sectional area, and the large number of inter- and intramolecular hydrogen-bonding sites (W. Hamad, 2006; Xiong, Zhang, Tian, Zhou, & Lu, 2012).

    17.2.1.2 Nanocellulose: Physical Properties

    In general, b-1,4-anhydro-d-glucopyranose units in nanocellulose structure do not lie precisely in the plane but rather assume a chair conformation with sequential glucose residue rotated through the 180 angle. Another important characteristic of nanocel-lulose is that three hydroxyl groups of each glucose unit, which endows nanocellulose a reactive surface covered with numerous OH groups (Bai, Holbery, & Li, 2009; Xiong et al., 2012). The capability of these OH groups to form hydrogen bonds has a key role in the fibrillar formation and semicrystalline packing, which controls the essential physical features of this highly cohesive nanomaterial