The study found that an average of 0.076 fiber kg/plant is extracted from the two types of crops, which is equivalent to 2.6 % of the total weight of the leaves before scrapping and to 1.75 % of the plant’s total weight. The plant from the first crop

produces less fiber quantity than the plant from the second crop (Table 7.2). Plants from the second crop produced 59 % more fiber compared with the plants from the first crop. Projecting these values per crop unit (hectares) shows that an average 6,175 fiber kg/ha (Table 7.2) may be extracted. The inconvenience is, however, that a great amount of the plant is waste material, an average of 361,757 waste kg/ha (98.2 % of the plant weight). Nevertheless, it is important to point out that evalua­tions showed that 89.20 % of the waste material is moisture, which means that 322,687 kg (89.2 %) of waste correspond to water.

The values found for fiber are due to the fact that the central part of the pineapple leaf consists of bundles immersed into parenchymal tissue and the leaf surface is made of epidermal tissue (Bismarck et al., 2005, Moya et al. 2013a, b). Due to this anatomical characteristic of the leaf, a great amount of water is stored in the paren­chymal tissue, thus increasing weight due to moisture, which results in low fiber percentage (D’Eeckenbrugge et al. 2011; Aragon et al 2012).

According to the evaluations of moisture content of both extracted fiber and waste, extracted fiber presented an average moisture content of 74.24 %, whereas waste moisture content amounted to 89.20 %. In the case of fiber, the percentage found coincides with studies carried out by D’Eeckenbrugge et al. (2011), Aragon et al (2012), and Moya and Solano (2012), who reported moisture contents in A. comosus leaves of the variety MD-2 ranging from 70 to 75 %. Regarding ash quantity, the value is 4.75 % for leaf fiber, which is significantly higher than the value of 1.1 % reported by Mukherjee and Satyanarayana (1986) . On the other hand, the ash content of leaf waste was 10.37 %. High ash content, as is the case of the wastes, has a negative effect on some possible uses; if the waste is used as fuel for heating, the resulting ashes have to be constantly eliminated.

With regard to fiber color evaluation, the average values presented by the fiber coming out of the machine or green condition were L* of 56.02, a* of -10.81, and b* of 35.23. This is a combination of white, green, and yellow shades, which results in a greenish clear coloration of the fiber. No differences in color parameters of fiber in green condition were found between plants coming from the first or second crops (Fig. 7.4); therefore, color could be treated without distinction of crop.

Evaluation of the three bleaching treatments (water, hydrogen peroxide 5 %, and chlorine 1 %) for both the bleaching and drying stages showed that parameter L* (luminosity) increased for all treatments (Fig. 7.4a) , which means that the fiber became clearer; however, differences were found among the bleaching treatments. The fiber in green condition bleached with chlorine 1 % showed a significantly higher value for L*, followed by water treatment, and lastly by hydrogen peroxide 5 % (Fig. 7.4a). After the fiber drying, the L* value decreased with chlorine 1 % treatment; the fiber bleached with the latter treatment shows no statistical differences with water treatment. When the fiber is treated with hydrogen peroxide 5 %, the L* value after drying is significantly higher than for the fiber treated with water or chlo­rine 1 % (Fig. 7.4a).

Parameter a* for fiber color increased its value in both the bleaching and drying stages (Fig. 7.4b), which means that the reddish shade of the fiber was intensified. Chlorine 1 % bleaching was the only treatment showing positive a* values

Fig. 7.4 Variations of the L* (a), a* (b), b* (c), and ДЕ* (d) color parameters after the application of the three treatments for fiber bleaching and after the drying process of natural fiber obtained from A. comosus leaves from the first and the second crops

(Fig. 7.4b) unlike hydrogen peroxide 5 % treatment, which showed the lowest increments of a* in both stages (bleaching and drying). Lastly, water treatment also showed an increment in the value of a* (Fig. 7.4b).

Parameter b* decreased significantly with the bleaching and drying process (Fig. 7.4c), which means that the yellow shades of the fiber diminished. Also, differences were found in this parameter between the bleaching and drying process. For bleaching, water treatment showed the highest reduction of parameter b*, fol­lowed by hydrogen peroxide 5 %, and next by chlorine 1 % with the lowest reduc­tion. After fiber drying, the behavior of the parameter varied, since bleaching with water and hydrogen peroxide 5 % showed no differences (in the b* value) between both treatments, although the values were significantly lower than for bleaching with chlorine 1 % (Fig. 7.4c).

With regard to color change (ДЕ*), it varied from 18 to 33. The highest color changes were found in the bleaching process with water and chlorine 1 %, among which there were no differences; these values were significantly higher than for bleaching with hydrogen peroxide 5 %. For dried fiber, chlorine 1 % was the bleaching treatment showing the highest value of ДЕ* and therefore the most effective, followed by hydrogen peroxide 5 %, and lastly by water.