Civil Engineering Reference
In-Depth Information
Figure 11.8
Scanning electron microscopy (SEM) images of (a) PMMA and PMMA reinforced with
various CNC loading, (b) 5%, (c) 9%, (d) 17%, (e) 23%, (f ) 33% and (g) 41% [45].
polymers for electrospinning is to improve the mechanical properties of materials and
to give new functionality to these kinds of electrospun nanoi bers [110] .
11.3.4
Acid Hydrolysis
h e main chemical process to produce nanocrystalline cellulose is acid hydrolysis by
either sulphuric acid (H
2
SO
4
) [111] , hydrochloric acid (HCL) [112] or a combination
of these two acids [113] at various concentrations. In the case of CNC from H
2
SO
4
hydrolysis, the surface of the material becomes negatively charged with sulfonate ester
groups, causing the easy dispersion of CNC in aqueous solvents, whereas those pro-
duced using HCL have weaker charge density and show a higher tendency of l occula-
tion in organic solvents [114]. Native cellulose consists of crystalline and amorphous
regions, and when cellulosic i bers were subjected to insensitive acid treatment, the
amorphous parts break up and just the individual crystallites remain. So, the charac-
terization of CNC is dependent on various parameters, such as reaction time, cellulose
sources, type of acid and reaction temperature [115]. h e pathway of acid hydrolysis
with H
2
SO
4
on cotton linter can be seen in Figure 11.9[116].
In 1951, a process to degrade cellulosic i bers with H
2
SO
4
was introduced
by
Ränby for the i rst time [111]. Since then a series of attempts have been taken to
prepare CNC from various cellulosic i bers such as curaua i bers [117] , coconut husk
[118] , cotton and tunicates [119] , sugarcane bagasse [120] , and wood [121] . In the acid
hydrolysis process a suspension with specii c acid concentration for a particular time
and temperature based on various sources of i bers is mechanically stirred. h en the
reaction is quenched with cold water. Subsequently, the washing process is conducted
