**4.1 Characterization of copolymers**

One of the properties verified after the grafting reaction is the solubility of the copolymers and some have been found to be soluble in water and others not; which confirms the modification of the properties of xylan. A copolymer is dissolved in water in a petri dish after evaporation of the solvent at 40° C in an oven, a casting plastic film was obtained (**Figure 6**).

The IR analysis of xylan, PLLA and xylan-g-PLLA is presented in the **Figure 7**. All the xylan absorption bands of type (1 → 4) are presented in the **Table 2**. An absorption band of the groups of hydroxyl is observed at 3544 cm−1, another absorption band at 897 cm−1 of glycosidic C-H (β). [36] Other bands at 1096 cm−1 and 1044 cm−1 of the C-O, C-C and C-OH groups of the ring. A strong absorption band at 1784 cm−1 is observed on the chemically modified xylan characteristic of ester functions (C = O) [36, 37]. Other bands that characterize CH and CH3 are seen at 2984 and 2934 cm−1. All of these absorption bands confirm the modification of the xylan structure.

The <sup>1</sup> H NMR spectrum (**Figure 8**) shows intense signals corresponding to the protons of the xylose units of the unsubstituted main chain, as well as less intense signals attributed to the uronic acid units and to the xylose units which carry them in position 2. The intensity of these signals depends on the degree of substitution by uronic acid. The doublets attributed to the anomeric protons of the xylose units, substituted (4.5 ppm) or not (4.6 ppm), are associated with a coupling constant of about 7 Hz, characteristic of an osidic bond. The coupling constant of the doublet corresponding to the anomeric protons of uronic acid, at 5.3 ppm, is in the order of 2 Hz, which characterizes an osidic bond. It is also possible to observe on the different <sup>1</sup> H spectra of xylans, a fine singlet around 3.4 ppm, which is to be associated with the existence of methyl groups carried, given the integration, by the uronic acid. This last remark confirms the presence of 4-O-methylglucuronic acid. This is fixed in position 2 of the xylose, which

**323**

**Table 2.**

**Figure 7.**

units. We can distinguish on the <sup>1</sup>

*Absorption bands characteristic of glucuronoxylans.*

results in a greater deshielding of the H2 compared to the unsubstituted xylose

*Fourier transform infrared spectra of xylan, PLLA, xylan-graft- poly (L-lactide) copolymer.*

1609 e ν(C=O)acid salt, anti-symmetric vibration

1413 f ν(C=O) acid salt, symmetric vibration

984 m ν(C-O), δ(OH), cycle vibrations 896 m δ(CH) glycosidic (β), cycle vibrations *w: wide, m: medium, f: weak, s: strong, e: shoulder;* ν*: valence vibrations;* δ*: deformation vibrations.*

**Absorptions (cm−1) Relative Intensity Type of vibration**

1721 m ν(C=O) uronic acid

1465 f δ(CH2) symmetric

1165–1149 m ν(C-O-C), ν(C-C) 1131–1121 e ν(C-O-C), ν(C-C) 1096 s ν(C-O), cycle, ν(C-C) 1044 s ν(C-O), ν(C-C)

3404 w ν(O-H) 2919 m ν(C-H)

1257 f δ(CH2)

nals between 1 and 2.5 ppm of the protons of the aliphatic chains shows a signal at 5.20 ppm which corresponds to the CH group, another signal at 1.47 ppm of the proton of the internal methyl group CH3 and at 1.27 ppm for the proton of CH3 at the end of the chains of PLLA (Guang-Xin, 2006). These intense signals corresponding to the protons of the xylose units of the main chain and to the protons of the PLLA groups confirm the chemical modification of xylan.

H NMR spectrum of the modified xylan, sig-

*Chemical Modification of Xylan*

*DOI: http://dx.doi.org/10.5772/intechopen.94208*

### *Chemical Modification of Xylan DOI: http://dx.doi.org/10.5772/intechopen.94208*

*Biotechnological Applications of Biomass*

**4.1 Characterization of copolymers**

plastic film was obtained (**Figure 6**).

possible to observe on the different <sup>1</sup>

the xylan structure. The <sup>1</sup>

In addition, it has been proven that DMAP is used as a hyper nucleophilia catalyst which is 104 times more active than pyridine [10], this is more favorable when the reaction time is longer, favoring depolymerization reactions. The maximum condi-

One of the properties verified after the grafting reaction is the solubility of the copolymers and some have been found to be soluble in water and others not; which confirms the modification of the properties of xylan. A copolymer is dissolved in water in a petri dish after evaporation of the solvent at 40° C in an oven, a casting

The IR analysis of xylan, PLLA and xylan-g-PLLA is presented in the **Figure 7**. All the xylan absorption bands of type (1 → 4) are presented in the **Table 2**. An absorption band of the groups of hydroxyl is observed at 3544 cm−1, another absorption band at 897 cm−1 of glycosidic C-H (β). [36] Other bands at 1096 cm−1 and 1044 cm−1 of the C-O, C-C and C-OH groups of the ring. A strong absorption band at 1784 cm−1 is observed on the chemically modified xylan characteristic of ester functions (C = O) [36, 37]. Other bands that characterize CH and CH3 are seen at 2984 and 2934 cm−1. All of these absorption bands confirm the modification of

H NMR spectrum (**Figure 8**) shows intense signals corresponding to

H spectra of xylans, a fine singlet around

the protons of the xylose units of the unsubstituted main chain, as well as less intense signals attributed to the uronic acid units and to the xylose units which carry them in position 2. The intensity of these signals depends on the degree of substitution by uronic acid. The doublets attributed to the anomeric protons of the xylose units, substituted (4.5 ppm) or not (4.6 ppm), are associated with a coupling constant of about 7 Hz, characteristic of an osidic bond. The coupling constant of the doublet corresponding to the anomeric protons of uronic acid, at 5.3 ppm, is in the order of 2 Hz, which characterizes an osidic bond. It is also

3.4 ppm, which is to be associated with the existence of methyl groups carried, given the integration, by the uronic acid. This last remark confirms the presence of 4-O-methylglucuronic acid. This is fixed in position 2 of the xylose, which

*Photograph of a xylan-g-PLLA film. Note: Xylan-g-PLLA, xylan-graft-poly(L-lactide).*

tions for having a larger DS and DP are: 16 h, 8 eq/OH, 1 eq/OH.

**322**

**Figure 6.**

**Figure 7.** *Fourier transform infrared spectra of xylan, PLLA, xylan-graft- poly (L-lactide) copolymer.*


#### **Table 2.**

*Absorption bands characteristic of glucuronoxylans.*

results in a greater deshielding of the H2 compared to the unsubstituted xylose units. We can distinguish on the <sup>1</sup> H NMR spectrum of the modified xylan, signals between 1 and 2.5 ppm of the protons of the aliphatic chains shows a signal at 5.20 ppm which corresponds to the CH group, another signal at 1.47 ppm of the proton of the internal methyl group CH3 and at 1.27 ppm for the proton of CH3 at the end of the chains of PLLA (Guang-Xin, 2006). These intense signals corresponding to the protons of the xylose units of the main chain and to the protons of the PLLA groups confirm the chemical modification of xylan.

#### **Figure 8.**

*1 H RMN spectra of xylan-graft-poly (L-lactide) copolymer (DMSO).*

#### **Figure 9.**

*Evaluation of the tangent of the loss angle and the loss modulus E" of xylan-g-PLLA as a function of temperature.*

For medium DP of fixed PLLA, it did not vary a lot (about 2 or 3). It confirms that the chains are very short but long enough to enhance the filmogenic character of materials [21].

#### **4.2 Mechanical properties**

The mechanical properties of PLA have been studied by various researchers [38, 39]. PLA has mechanical properties similar to those of polystyrene [40]. Dynamic mechanical analysis (**Figure 9**) showed that the glass transition temperature of the xylan-g-PLLA film is 147°C. For the new PLLA-g-xylan material, the results of mechanical tests (**Figure 10**) show that the film has a nominal strain ε rupture = 8 ± 2.5%, its Young's modulus E = 1.2 ± 0.1 GPa (1200Mpa) and a nominal stress of about 60 MPa. These mechanical properties are close to those of polypropylene [41].

**325**

*Chemical Modification of Xylan*

**5. Conclusion**

**Figure 10.**

The modification of xylan by grafting the PLLA on the xylan extracted from the sawdust of chestnut was carried out in this work. The synthesis of branched xylang-PLA co-polymers is carried out from L-lactide and xylan using DMA as solvent for the xylan and 4-dimethylaminopyridine (DMAP) as catalyst at a temperature of 80° C. These copolymers are characterized and infrared analysis has shown the appearance of the characteristic band of the esters at 1784 cm−1 and of other bands

the appearance of the PLLA aliphatic protons was observed on the spectrum of the grafted xylan. The xylan copolymers are insoluble in water. The higher the DS, the more difficult the solubility is in water. Dynamic mechanical analysis has shown

H NMR analysis,

of the group CH3 on the xylan-g-PLLA spectrum. Following the <sup>1</sup>

that Tg of the xylan-g-PLLA film is 147°C.

*Elongation at breakaccording to thenominalstrain (5%).*

*DOI: http://dx.doi.org/10.5772/intechopen.94208*

*Biotechnological Applications of Biomass*

*H RMN spectra of xylan-graft-poly (L-lactide) copolymer (DMSO).*

**Figure 8.** *1*

**Figure 9.**

*temperature.*

For medium DP of fixed PLLA, it did not vary a lot (about 2 or 3). It confirms that the chains are very short but long enough to enhance the filmogenic

*Evaluation of the tangent of the loss angle and the loss modulus E" of xylan-g-PLLA as a function of* 

The mechanical properties of PLA have been studied by various researchers [38, 39]. PLA has mechanical properties similar to those of polystyrene [40]. Dynamic mechanical analysis (**Figure 9**) showed that the glass transition temperature of the xylan-g-PLLA film is 147°C. For the new PLLA-g-xylan material, the results of mechanical tests (**Figure 10**) show that the film has a nominal strain ε rupture = 8 ± 2.5%, its Young's modulus E = 1.2 ± 0.1 GPa (1200Mpa) and a nominal stress of about 60 MPa. These mechanical properties are close to those of

**324**

character of materials [21].

**4.2 Mechanical properties**

polypropylene [41].

**Figure 10.** *Elongation at breakaccording to thenominalstrain (5%).*
