**2. Industrial upgrading of xylans**

Cellulose and starch are the main plant-based polysaccharides for industrial use. Hemicelluloses in general, xylans in particular, although they currently represent a modest volume of exploitation, are nevertheless receiving increasing attention [22]. Their original physico-chemical properties bring them closer to hydrocolloids. The latter denote polysaccharides of natural origin or their derivatives, which dissolve or disperse in water to form viscous solutions or suspensions. Hydrocolloids, which have a great affinity for water, affect the texture of the medium to which they are added and modify the consumer's perception of a product, hence their use in particular in the food, cosmetic and pharmaceutical sectors, as a thickener, emulsifier or gelling agent [23]. These polymers have in solution a low viscosity under stress and a high viscosity at rest at high concentration. These characteristics are those sought after for commercial naturally occurring thickeners such as xanthan gum and locust bean gum. In addition, their binding properties have been exploited as additives in the preparation of paper pulps. They provide better flexibility to the fibers and improve the mechanical strength of the paper [24]. Finally, their nutritional properties are not negligible. Xylans are in fact used as dietary fibers. They are not degraded by human digestive enzymes and thus accelerate intestinal transit. In addition, their ingestion would significantly decrease the accumulation of lipids in the liver and the blood cholesterol level [25]. Xylans can therefore be used in the native state, on the basis of their physicochemical properties, but the main ways

**317**

*Chemical Modification of Xylan*

to consider new applications.

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

of upgrading these polysaccharides are based either on their hydrolysis to form precursors used in the chemical industry, or on their functionalization which allows

The petrochemical plants of the world consume 270 million tonnes of oil and gas every year in the production of plastics [26]. Fossil fuels provide the energy and raw material needed to transform crude oil into materials such as polystyrene, polyethylene or polypropylene. The progressive scarcity of these organic materials will inevitably be accompanied by a significant increase in their cost. Biotechnologies and organic chemistry can nevertheless provide solutions and literature offers numerous references on this subject [27, 28]. Biotechnologies currently seem to favor three approaches to replace plastics with products derived from plants: the direct production of plastics by micro-organisms, by cultivated plants or the transformation of sugars. It was in 1977 that the American companies Cargill and Dow Chemical joined their efforts to produce, after fermentation sugars of plant origin into lactic acid and polymerization of the latter, a plastic called polylactic acid [26] or PLA. A few years later, Imperial Chemical Industries marketed another plastic obtained after fermentation of sugars of plant origin [29], Biopol, which is a copolymer of the family of poly-3-hydroxyalkanoates (PHA). This bioplastic is however significantly more expensive than its synthetic counterparts derived from fossil fuels. Its only advantage is its biodegradability. Faced with high production costs, scientists have directed their research towards the direct synthesis of plastics by plants. The objective here is to modify the genetic heritage of cultivated plants in order to make them synthesize plastic directly. However, these works face a series of problems linked to: the physiology of the plant: the chloroplasts of the leaves which are the seat of photosynthesis seem to be a privileged place for the production of plastics by the plant. Too much synthesis at this level lowers the yields of photosynthesis and therefore the amount of produced plastic; to the methods of extraction and purification of plastics from the plant: These methods require the use of huge amounts of solvent; to public opinion: the dissemination of genetically modified organisms (GMOs) in our environment is currently causing sometimes violent controversies. The recent statement of the precautionary principle and the tightening of the regulations linked to this type of manipulation undoubtedly constitute a serious obstacle to the development of such technologies since they impose strictly controlled cultivation conditions incompatible with large-scale production. Organic synthesis provides different responses. One strategy is to chemically modify plant polymers. Remember that the first synthetic polymers were obtained by chemical modification of cellulose, such as nitrocellulose or cellulose acetate, used among others as thermoplastics. The esterification of the hydroxyl groups of the cellulosic fibers by aliphatic chains profoundly modifies their properties, and in particular the thermoplasticity and the hydrophobic character, but also the biodegradability, the solubility, the inflammability, etc. The properties of the material obtained then depend on the length of the grafted chain, as well as on the degree of substitution of the esterified polymer or DS;ie, the number of esterified hydroxyl functions per anhydroglucose unit in the case of cellulose. Cellulosic esters with a short carbon chain (less than six carbon atoms) currently represent an important industrial market, used and marketed in fields as varied as textile fibers, films, film substrates and membranes, coatings and varnishes, thermoplastic materials or composite materials. Cellulose esters, such as cellulose acetate (CA) or mixed esters such as cellulose acetate propionate (CAP) and acetate butyrate (CAB), all made from highly purified microcrystalline cellulose, compete with plastics derived from

**2.1 A new way of chemical upgrading of plastic xylans of plant origin**

*Biotechnological Applications of Biomass*

non-degradable basic products [8, 9]. In order to improve the specific, thermal and mechanical properties of xylan, modification is one of the ways that best responds to this limitation of properties and that can enhance it. For example, acetylation of xylan increases its hydrophobicity and thermal stability [10, 11]. Indeed, the grafting of poly (L-lactide) is one of the modifications which gives a product derived entirely from nature. The concept of grafting PLLA on polysaccharides is already studied. Recently, a study has shown that PLLA-g-hemicellulose is a good accounting for a mixture between wood hydrolysates and PLA [12]. The blocks or grafted copolymers such as cellulose-graft-PLA, xylans-grafts-PLA, PLA-grafted starch copolymers, having hydrophobic and hydrophilic segments, have been reported to form different types of microstructures and have been applied as biomaterials [13]. Several researchers have studied cellulose graft copolymers such as poly (lactide) grafted cellulose or poly (ε-caprolactone) grafted cellulose, as biodegradable plastics, and have indicated that chains of poly (lactide) or poly (ε-caprolactone) acted as internal plasticizers for the polysaccharide and it was found that the properties of the xylan-g-PLA copolymers strongly depend on the length of the PLA chains grafted on the xylan [14–17]. In fact, the grafting reaction depends on the method used according to the case of the modification of the xylan or of the PLLA [18] and also of several parameters such as: temperature, reaction time, type and quantity of catalysts, etc. Trimethylamine is the catalyst used for grafting PLLA on chitosan with a yield of less than 50%. Other catalysts are used for this type of reaction such as DMAP which can open the lactide cycle [12], carbine [19]. In a study [20], the catalyst used is triazobicyclodecene (TBD) at low temperatures and for short periods of time. This part is concerned with the structural analysis of xylans extracted from chestnut sawdust as well as their transformation into plastic films. After extraction and purification, the structure of these polysaccharides was characterized by IR and NMR. In a second part, the xylans were modified by the grafting of the PLLAs. Finally, a study of the physical and thermomechanical

properties of the synthesized copolymers is carried out [21].

Cellulose and starch are the main plant-based polysaccharides for industrial use. Hemicelluloses in general, xylans in particular, although they currently represent a modest volume of exploitation, are nevertheless receiving increasing attention [22]. Their original physico-chemical properties bring them closer to hydrocolloids. The latter denote polysaccharides of natural origin or their derivatives, which dissolve or disperse in water to form viscous solutions or suspensions. Hydrocolloids, which have a great affinity for water, affect the texture of the medium to which they are added and modify the consumer's perception of a product, hence their use in particular in the food, cosmetic and pharmaceutical sectors, as a thickener, emulsifier or gelling agent [23]. These polymers have in solution a low viscosity under stress and a high viscosity at rest at high concentration. These characteristics are those sought after for commercial naturally occurring thickeners such as xanthan gum and locust bean gum. In addition, their binding properties have been exploited as additives in the preparation of paper pulps. They provide better flexibility to the fibers and improve the mechanical strength of the paper [24]. Finally, their nutritional properties are not negligible. Xylans are in fact used as dietary fibers. They are not degraded by human digestive enzymes and thus accelerate intestinal transit. In addition, their ingestion would significantly decrease the accumulation of lipids in the liver and the blood cholesterol level [25]. Xylans can therefore be used in the native state, on the basis of their physicochemical properties, but the main ways

**2. Industrial upgrading of xylans**

**316**

of upgrading these polysaccharides are based either on their hydrolysis to form precursors used in the chemical industry, or on their functionalization which allows to consider new applications.
