4. Processes of nanocrystalline cellulose

Recently, researchers are exploring the potential utilization of agriculture or forest wastes as NCCs'sources. As a consequence, the various local sources are used to investigate the potential of NCC in certain technologies. The isolation of NCC needs intensive hydrolysis chemical treatment. However, according to the degree of processing and raw material, physical, chemical, enzymatic, and ionic pretreatments are performed before nanocrystalline cellulose synthesis. Figure 5 shows the sources, pretreatments, synthesis, and application of nanocrystalline cellulose. It is good to know that appropriate pretreatments of cellulosic fibers promote the accessibility of hydroxyl group, alter crystallinity, increase the inner surface, and break cellulose hydrogen bonds and hence improved the reactivity of the fibers [6, 7, 10]. Several approaches to diminish cellulosic fibers into nanofibers can be divided into several techniques such as acid hydrolysis, alkali treatment, mechanical treatments, and combination of mechanical and chemical treatments. Common methods for isolate NCC are hydrolysis methods which are a chemical method. Figure 6 shows

Figure 5.

Sources, pretreatments, synthesis, and application of nanocrystalline cellulose. Adapted from Refs. [6, 7, 10].

treatment) and a variety of cellulosic fiber sources. Bondeson et al. [55] conducted an experiment on the isolation of NCC and found that the optimized condition is at a concentration of 63.5% H2SO4, which yielded 38 wt.% of NCCs with a width of 10 nm. Another experiment that is conducted by Ilyas et al. [6] found that the optimum yield for isolating sugar palm nanocrystalline cellulose is at a concentration of 60 wt% H2SO4 and duration hydrolysis of 45 min, with length and diameters of 130 30 and 9 1.96 nm, respectively. Table 3 shows the preparation of NCC using various acid hydrolysis processes from different cellulosic sources. Typical procedures for NCC extraction are composed of several steps: strong acid hydroly-

Production, Processes and Modification of Nanocrystalline Cellulose from Agro-Waste: A Review

There are several limitations when using natural fibers as reinforcement filler in

sis, dilution, dialysis, sonification, and drying of NCC.

Figure 7.

Figure 8.

99

Limitation of nanocellulose. Adapted from Refs. [6, 7, 10].

Mechanism of hydrolysis of acid [53].

DOI: http://dx.doi.org/10.5772/intechopen.87001

5. Limitation and modification of nanocrystalline cellulose

the polymer matrix such as single-particle dispersion, barrier properties,

#### Figure 6.

Typical process for the production of nanocrystalline cellulose. Adapted from Refs. [4, 5, 8].

the typical process for the production of nanocrystalline cellulose. Hydrolysis process includes inserting raw plant fibers into a strong acidic environment with the help of mechanical agitation. Concentrated acid and shear forces on solution generate shear rates in the stream and decrease the size of fibers to the nanoscale. Sulfuric acid (H2SO4) is commonly used in the isolation process of NCC besides other chemicals such as HCL [48], HBr [49], and H3PO4 [50]. Hydrolysis process using sulfuric acid solution resulted in a high number of negatively charged sulfate groups on the surface of NCC. This process limits the agglomeration and flocculation of NCC in an aqueous medium [51]. The drawback from this process is that the NCC displays moderate thermostability. Hence to overcome this drawback, the NCC will either undergo dialysis process using distilled water to fully dispose free acid molecules or use sodium hydroxide (NaOH), which functions to neutralize nanoparticles [52]. Figure 7 displays three steps in the mechanism of acid hydrolysis [53]:


There are numerous studies that have been conducted on the effects of concentration of acid, acid-to-fiber ratio, and temperature and time of the hydrolysis process on the dimensions and morphological properties of yielded nanocrystalline cellulose. According to Azizi et al. [29], there is a strong relationship between the hydrolysis time and acid-to-fiber ratio to the length and dimensions of nanocrystalline cellulose, which by increasing the hydrolysis time and acid-to-fiber ratio would reduce the dimension and length of nanocrystalline cellulose.

Besides that, there are large numbers of published studies [51, 54] that describe the dimension, size, and shape of NCC that were affected by the conditions of hydrolysis process (purity of the material, temperature, time, and ultrasound

Production, Processes and Modification of Nanocrystalline Cellulose from Agro-Waste: A Review DOI: http://dx.doi.org/10.5772/intechopen.87001

Figure 7. Mechanism of hydrolysis of acid [53].

the typical process for the production of nanocrystalline cellulose. Hydrolysis process includes inserting raw plant fibers into a strong acidic environment with the help of mechanical agitation. Concentrated acid and shear forces on solution generate shear rates in the stream and decrease the size of fibers to the nanoscale. Sulfuric acid (H2SO4) is commonly used in the isolation process of NCC besides other chemicals such as HCL [48], HBr [49], and H3PO4 [50]. Hydrolysis process using sulfuric acid solution resulted in a high number of negatively charged sulfate groups on the surface of NCC. This process limits the agglomeration and flocculation of NCC in an aqueous medium [51]. The drawback from this process is that the NCC displays moderate thermostability. Hence to overcome this drawback, the NCC will either undergo dialysis process using distilled water to fully dispose free acid molecules or use sodium hydroxide (NaOH), which functions to neutralize nanoparticles

Typical process for the production of nanocrystalline cellulose. Adapted from Refs. [4, 5, 8].

[52]. Figure 7 displays three steps in the mechanism of acid hydrolysis [53]:

3.Release of the proton and free sugar after the addition of water

would reduce the dimension and length of nanocrystalline cellulose.

glycoside acid

Figure 6.

Nanocrystalline Materials

carbonium ions

98

1.Development of conjugated acid by reactions between oxygen protons and

2.Breaking down of C-O bonds and segregation of conjugated acid into cyclic

There are numerous studies that have been conducted on the effects of concen-

Besides that, there are large numbers of published studies [51, 54] that describe

tration of acid, acid-to-fiber ratio, and temperature and time of the hydrolysis process on the dimensions and morphological properties of yielded nanocrystalline cellulose. According to Azizi et al. [29], there is a strong relationship between the hydrolysis time and acid-to-fiber ratio to the length and dimensions of nanocrystalline cellulose, which by increasing the hydrolysis time and acid-to-fiber ratio

the dimension, size, and shape of NCC that were affected by the conditions of hydrolysis process (purity of the material, temperature, time, and ultrasound

treatment) and a variety of cellulosic fiber sources. Bondeson et al. [55] conducted an experiment on the isolation of NCC and found that the optimized condition is at a concentration of 63.5% H2SO4, which yielded 38 wt.% of NCCs with a width of 10 nm. Another experiment that is conducted by Ilyas et al. [6] found that the optimum yield for isolating sugar palm nanocrystalline cellulose is at a concentration of 60 wt% H2SO4 and duration hydrolysis of 45 min, with length and diameters of 130 30 and 9 1.96 nm, respectively. Table 3 shows the preparation of NCC using various acid hydrolysis processes from different cellulosic sources. Typical procedures for NCC extraction are composed of several steps: strong acid hydrolysis, dilution, dialysis, sonification, and drying of NCC.
