Civil Engineering Reference
In-Depth Information
CH
2
OH
CH
CH
CH
2
OH
CH
2
OH
HC
HC
H
3
CO
O
HC
OH
HC
OH
OH
O
CH
HC
CH
2
OH
CH
CH
OH
HC
OH
OCH
3
H
3
CO
H
3
CO
OH
H
3
CO
CH
2
OH
CH
HC
O
C
OCH
3
O
CH
2
OH
HOH
2
C
CH
O
H
O
HC
HC
O
OH
CH
CH
H
2
C
HC
OH
CH
2
OH
HC
CH
2
CH
HC
HO
O
CH
2
OH
OH
H
3
CO
OCH
3
CH
HC
H
3
CO
O
OCH
3
O
HOH
2
C
CH
2
OH
HOH
2
C
HC
O
HC
CO
O
HC
H
3
CO
CH
2
OH
H
3
CO
CH
2
OH
O
CH
HC
HC
O
OH
CO
H
3
CO
OCH
3
OH
OH
Figure 10.2
Structure of lignin.
In plant cell walls, the individual cellulose molecule chains connect with each other
through hydrogen bonding to form larger units known as elementary i brils, which
are packed into larger microi brils and are 5-50 nm in diameter and several microm-
eters in length [23]. h e i brils are of highly ordered regions (i.e., crystalline phases)
alternated with disordered domains (i.e., amorphous phases) [23-25]. In the crystalline
regions, cellulose chains are closely packed together by a strong and highly intricate
intra- and intermolecular hydrogen bond network, while the amorphous domains are
regularly distributed along the i brils. h ese i brils are comprised of dif erent hierarchi-
cal microstructures commonly known as nanosized i brils with high structural strength
and stif ness, the crystalline part named nanowhiskers [25], or nanocellulose crystals
[5, 26]. Cellulose nanowhiskers are dei ned as elongated crystalline rod-like nanopar-
ticles with a diameter ranging from 2 to 20 nm, typically obtained by acid hydrolysis of
cellulose i bers [5, 10, 27], and are extensively studied as a i ller for polymer composites.
