Civil Engineering Reference
In-Depth Information
i ller of dif erent chemical nature will be analyzed and reported, taking into account the
required functionality of the device in the proper i nal application. h e combination of
cellulose with dif erent i llers can indeed bring benei ts: these include improving com-
posite properties and delivering unique functions. In other words, the properties of the
i nal materials can be adjusted as a function of the size, shape, particle size distribution
of the nanoi llers and interactions occurring with the cellulose surfaces. h e ef ect of
the second reinforcement will be considered for a wide variety of potential applica-
tions, including network structures for tissue engineering, antimicrobial i lms, elec-
tronics, protective coatings, barrier/i lter membrane systems. Ternary multifunctional
nanocomposites based on polymer (thermoplastic or thermoset) systems with added
cellulose-based nanometric i llers, such as microi brillated cellulose nanoi bers (MFC),
cellulose nanocrystals (NCC), or bacterial cellulose (BC), and additionally i lled with
other types of nanoreinforcements (metallic, ceramic, carbon-based and biological)
have recently attracted signii cant scientii c and industrial interest. h eincreasingintro-
duction of cellulose-based nanometric i llers in the i eld of polymer composites is par-
ticularly owed to their performance improvement over plant i ber composites, which
include cellulose extracted in macroscopic form as reinforcement in a polymer matrix.
h e reason for this interest is that plant i bers, despite being chemically treated to assist
the removal of non-structural matter, show a large presence of defects in their struc-
ture. h ey would therefore eventually of er a mechanical performance which, albeit
sui cient for most current semi-structural uses of composite panels, is very far from
that of micro-crystalline cellulose [1]. In contrast, the exceptional mechanical strength,
together with high aspect ratio and large surface area, enable these nanomaterials to
reinforce a wide variety of polymers even at very low i ller loadings. In general, nano-
composites thus obtained have improved stif ness, strength, toughness, thermal stabil-
ity and barrier properties compared to the pure polymer matrix. Other materials are
widely available throughout the world, which could be used as nanoreinforcements for
polymer matrices such as, for example, layered silicates: however, cellulose nanometric
i llers compare favorably in this regard in view of their renewable nature [2]. Other sig-
nii cant advantages of cellulose nanometric i llers are their low cost and density, their
high surface functionality and reactivity and the wide variety of source materials avail-
able throughout the world.
Over time, a number of possibilities have been explored to produce cellulose-based
nanometric i llers. In particular, microi brillated cellulose (MFC) (Section 6.2.1) is
formed by i brous cellulose structures with the length of several tens of microns and
generally a few tens of nanometers thick, as it consists of aggregates of microi brils,
naturally occurring as an ef ect of the hierarchical structure of cellulose in plants [3]. In
other words, MFC is formed by long, l exible and entangled cellulose nanoi bers, where
both amorphous and crystalline phases are present [4].
As it is generally the case for all cellulose nanometric i llers, microi brillated cellulose
can be obtained from wood, as well as from agricultural by-products and waste, such
as crops aimed at textiles production (such as, e.g., sisal) or aimed at food production
(such as, e.g., fruit crops, like pineapple, and cereal crops, such as wheat, sorghum,
etc.) [5]. MFC can be isolated using dif erent mechanicals, normally involving a high-
pressure homogenization step, whilst in some cases the process has been optimized by
applying chemical [6] and enzymatic pretreatments [7] of the cellulose raw material.
