La pataca como materia prima para la producción de bioetanol

absorption measurement, acrylic acid treated flax fiber I showed the best performance in tensile and flexural properties and water resistance of its biocomposites. The chemical and thermal properties of fiber I, as well as the thermal properties of fiber I-HDPE biocomposites were then analyzed and the results are given as follows:

Chemical composition of untreated and acrylic acid treated flax fiber I

The chemical composition of flax fiber I before and after acrylic acid treatment is listed on Table 4.2. Acrylic acid treatment could increase the cellulose content and decrease the hemicellulose and lignin contents of the fiber.

Table 4.2Chemical composition of treated and untreated flax fibers.

Flax Fiber Cellulose

(%)

Hemicellulose (%)

Lignin (%)

Untreated flax fiber I 83.77 5.79 1.16

Acrylic acid treated flax fiber I

86.88 5.23 0.68

Rong and co-workers (2001) also found that chemical treatment (alkali treatment) removed hemicellulose and lignin in sisal fiber. Cox and co-workers (1999) emphasized that hemicelluloses are readily hydrolyzed by acids and even soluble in water at high temperature. Thus, removal of hemicellulose can decrease the water absorption in the final product. Cellulose with high crystallinity and

cohesive density is insoluble in water and is more resistant to dilute acids; however, they can swell and dissolve in strong acid, strong alkali, or concentrated salt solution (Cox et al. 1999).

Characteristic temperatures of untreated and acrylic acid treated flax fiber I

The thermal characteristics of flax fiber I and acrylic acid-treated flax fiber I were determined using the DSC. The resulting DSC thermograms are shown in Figures 4.14 and 4.15.

Figure 4.14 DSC thermogram of untreated flax fiber I (fiber purity: 98-99%).

In the DSC thermogram of untreated and treated flax fibers (Figure 4.14), a broad endothermic curve after temperature of 100°C was observed, indicating the

presence of water (Aziz and Ansell 2004). Aziz and Ansell (2004) observed an endotherm in the temperature range of 50-175°C on hemp fiber.

Figure 4.14 shows that above 169ºC, there is a first slight exothermic peak at 202.53ºC, indicating the first decomposition temperature of untreated flax fiber, and this may be due to the degradation of lignin. The decomposition temperature of lignin was normally around 200ºC (Aziz and Ansell 2004). But it was also reported that the degradation of lignin took place in a broad range of temperature from 200 to 500ºC (Manfredi et al. 2006). The first decomposition temperature of acrylic acid treated flax fiber I was observed at 209.39ºC as given in Figure 4.15. This result shows that chemical treatment improved the heat stability of flax fiber.

Figure 4.15 DSC thermogram of acrylic acid-treated flax fiber I (fiber purity: 98- 99%).

The other polysaccharides such as cellulose and hemicellulose degrade at higher temperature. Manfredi and co-workers (2006) concluded that the degradation of natural fibers may involve two main steps: the first one is the thermal depolymerization of the hemicellulose and the cleavage of glycosidic linkages of cellulose; the second one is related to the decomposition of the α-cellulose. There

are two peaks observed in both curves at temperature above 300ºC, indicating the decomposition temperatures of hemicellulose and cellulose. Manfredi and co- researchers (2006) reported that the sisal fiber started to degrade at 215ºC; hemicellulose and α-cellulose decomposition temperatures of sisal fiber were 290ºC

and 340ºC, respectively. They also investigated the thermal degradation of flax fiber and found that the decomposition temperatures of hemicellulose and α-cellulose in

flax fiber were 285ºC and 345ºC, respectively.

The complete degradation temperatures of flax fibers are not low, but the gradual exothermic reaction in the DSC thermograms indicate that the fiber start to decompose above approximately 200ºC. Therefore, the processing temperature of fiber should be controlled below certain temperature (e.g. 200ºC) to avoid weight loss and discoloration of biocomposites due to excessive heating.

Characteristic temperatures of flax fiber I-HDPE biocomposites

Figure 4.16 shows the DSC thermogram of untreated flax fiber I-HDPE and acrylic acid treated flax fiber I-HDPE biocomposites. The decrease of heat flow in DSC thermograms indicates the melting point of biocomposite.

It was found that the melting temperature of biocomposite (with 10% fiber content) decreased if the fiber were chemically treated. The melting point of untreated flax fiber I-HDPE biocomposite was 138.8°C, while that of acrylic acid treated fiber I-HDPE biocomposite was 137.4°C. No exothermic or endothermic peaks were observed in the DSC thermogram in the range of 160 to 220°C, indicating the steady state of biocomposites. This range of temperatures could be used as processing temperatures of flax fiber-HDPE biocomposites.

-35 -25 -15 -5 5 15 25 0 100 200 300 400 500 Sample temperature (°C) H ea t flo w (mW ) Fiber-HDPE biocomposite without chemcial treatment Fiber-HDPE biocomposite with A treatment 138.8°C 137.4°C

Figure 4.16 DSC thermogram of untreated flax fiber I-HDPE biocomposite and acrylic acid-treated flax fiber I-HDPE biocoposite.

Compared with the HDPE melting temerpature of 139.34°C (Figure 4.8), it was found that the addition of flax fiber into HDPE decreased the melting temperature. Acrylic acid treatment also decreased the melting temperature of the biocomposite in comparison with untreated fiber biocomposite. But all these

changes were in a very small range. Manfredi and co-workers (2006) reported the presence of moisture on their sisal or flax fiber-polyester composites, but this was not observed in our studies.