Civil Engineering Reference
In-Depth Information
11.1
Introduction
Nanotechnology is now recognized as one of the most promising areas for techno-
logical development in the 21st century. In line with the development of nanotech-
nology and recent concern about environmental issues [1], more attention have been
paid to utilize biobased materials. In this regard, natural i bers have been gaining
much more interest because of their promising characteristics such as biodegradable
nature, renewability and lower price [2]. Among these natural i bers, cellulose as the
most plentiful biopolymer which exists in a wide variety of natural i bers such as
kenaf [3] , cotton [4] , banana [5] , wood [6] , l ax [7], oil plam [8], bamboo [9] and ani-
mal species like tunicates [10], etc., have been the subject of much research in nano-
technology. Cellulose is a linear biopolymer, having β-D-glucopyranose repeating
units [11] in both crystalline and amorphous region [12]. In the case of application
of cellulose in nanotechnology, two general types of nanocelluloses are recognized,
namely cellulose nanocrystal and cellulose nanoi ber. h ese two nanocelluloses can
be distinguished by their dif erent production processes and structures. Cellulose
nanoi ber, having a high aspect ratio in both amorphous and crystalline regions, can
be produce using some techniques such as electrospinning, rei ning [13] , homogeni-
zation, grinding, cryocrushing [14] , ultrasonication [15] and steam explosion [16] .
While cellulose nanocrystal is the whisker form of nanocellulose, its amorphous part
can be completely removed by acid hydrolysis either H
2
SO
4
or HCL [17].
h ese nanocellulose structures have attracted attention as a potential material in
reinforced nanocomposites. By inserting these nanoscale compounds into polymers
even in small quantities, the properties of polymers improve; however, it depends
on the type of nanocellulose used in the applications [18]. In order to utilize nano-
cellulose as reinforcement in nanocomposites, the strong hydrogen bonds between
nanocellulose, which make it hydrophilic, must be broken down for good dispersion
in the polymers with hydrophobic nature. Surface modii cation is the most common
way to make the surface of nanocellulose hydrophobic and to incorporate it homog-
enously in dif erent polymers, including by grat ing, silylation, acetylation, etc. [19].
Apart from the modii cation processes, drying of nanocellulose is another important
issue which should be considered for adding nanocellulose in polymers. h is is due to
the change of size of these nanomaterials at er drying, which may af ect their unique
properties.
In this chapter, i rst we will discuss the cellulose and nanocellulose structures. Later,
isolation and characterization of cellulose nanoi ber and nanocrystal will be addressed.
Drying and modii cation will also be presented in the chapter. At the end, nanocom-
posite production from nanocellulose with thermoplastic and thermoset polymers will
be discussed.
11.2
Cellulose and Nanocellulose
Cellulose is the most abundant renewable natural biopolymer on earth. It is present in a
wide variety of living species including plants, animals, and some bacteria [20].
