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

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

the petrochemical industry such as polyethylene, polypropylene, polyethylene terephthalate, polycarbonates, nylons, etc., for which the basic products, ethylene, propylene, xylene or even ethylene glycol are still very economically attractive. In addition, obtaining cellulose esters requires the prior solubilization of the cellulose, which generates the implementation of a heavy and costly methodology, unlike the synthetic polymers derived from polycondensations. Their properties remain original, however, and they continue to satisfy certain markets. The thermomechanical qualities of cellulose esters remain their main handicap. Indeed, due to the fragility of the polysaccharide chains at high temperatures, the glass transition temperature (Tg) and the material decomposition temperature are often very close. The glass transition temperature corresponds to the transition from a glassy state, in which the polymer is hard and brittle, to a rubbery state for which the polymer is soft and flexible. From this temperature, the material is more flexible and easier to work. This is the reason why a plasticizer is often added in order to lower the glass transition temperature and therefore widen the field of application of thermoplastics. Several plasticizers are commonly used, including on an industrial scale. This is the case for triethylcitrate for cellulose acetate and dioctyladipate for CAP. However, the use of plasticizer can sometimes be inconvenient for certain applications. These small molecules tend to evaporate over time, which can change the performance of the material in the short or medium term. Another solution for lowering the Tg of a polymer is to graft long chain substituents, so as to increase the free volume and therefore reduce the interactions between the polymer chains. The presence of bulky and flexible side substituents such as fatty chains, by removing the polysaccharide chains, lowers their Tg and therefore influences the field of use of these thermoplastics. Studies have shown on a series of cellulose esters ranging from acetate to palmitate (C16), that Tg decreases significantly with the increase in the length of the grafted fatty chains [30]. Thus, without adding plasticizer, it is possible to obtain hydrophobic plastics that are more flexible, more deformable, less brittle, which suggests new areas of application, such as packaging or plasticulture and, in particular, agriculture mulch films [31, 32]. All of these works, initiated from a model substrate, cellulose, makes it possible to envisage new ways of upgrading for polysaccharides, and in particular for wood xylans. The objective of this study is the synthesis of new plastic materials by grafting poly (lactic acid) on xylan (4-O-methylglucuronoxylanes) extracted from chestnut sawdust.

### **2.2 Xylan extraction from wood**

The main problem facing the experimenter is that of the chemical richness of the plant cell wall, which is reflected in the great structural diversity of the macromolecules, essentially polysaccharides, which are represented there. The protocols to be used must therefore be sufficiently selective to allow the extraction of a category of macromolecules; they must also be concerned with protecting the integrity of molecular structures by limiting the degradation of the latter. A detailed study of literature in the field of hemicellulose extraction reveals the existence of a large number of protocols. This observation can only be explained by the wide variety of hemicellulosic structures identified within the plant cell wall. The development of a specific extraction protocol for xylans with a view to their commercial exploitation is the subject of numerous studies. The question to be answered by the experimenter is what type of xylans to extract, from which plant material, for what properties, for what applications and using which protocols. The presence of a polyphenolic frame formed by lignin, as well as the existence of chemical bonds between the different hemicelluloses which constitute the wall, and between the hemicelluloses and lignin limits the extraction of xylans. It is

**319**

methods.

**3.1 Xylan extraction**

*Chemical Modification of Xylan*

illustrated in **Figure 1**.

*Separation of wood constituents.*

**Figure 1.**

**3. Preparation of the copolymers**

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

then impossible to extract a type of polysaccharide without breaking these bonds and therefore without modifying the polymer with respect to its state in situ. It is therefore necessary to apply sufficiently strong extraction conditions to allow the rupture of these bonds, without degrading the extracted molecules. In the case of extraction from wood, the xylans are conventionally collected, after delignification in the presence of sodium chlorite, by an alkaline extraction. Beforehand, it is necessary to eliminate the extractables, so that they do not interfere in the analyses later. A schematic representation of the separation of the constituents of wood is

The DMAc/LiCl solution is prepared for 1 hour at a temperature of 80° C with mechanical stirring. In a flask equipped with a condenser, we mixed a quantity of the solution of DMAc/LiCl, L-lactide (2, 4 or 8 equiv./ OH) and DMAP catalyst (0.1, 0.5 or 1 equi/OH) then heated it to 80° C with magnetic stirring at different reaction times (8, 16, 24 h). At the end of the reaction, a quantity of ethanol is added in order to precipitate the xylan-g-PLLA. The product obtained is purified with the solvent dimethyl sulfoxide (DMSO) and precipitated in ethanol. The obtained copolymer is dried at room temperature and is characterized by different

Chestnut wood glucuronoxylans were extracted by this procedure (**Figure 2**). They were obtained from chlorite-delignified sawdust by aqueous KOH extraction. The MGX has been extracted with a yield of 19%. The obtained fraction is characteristic of a classical MGX with more than 99% of xylose and 4-*O*-methylglucuronic acid (typical markers of glucuronoxylans).

4-*O*-methylglucuronic acid contents were 16.6% (molar ratio), which is in agreement with the data obtained by the colorimetric assays (17.4, mass ratio) and the

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

*Biotechnological Applications of Biomass*

the petrochemical industry such as polyethylene, polypropylene, polyethylene terephthalate, polycarbonates, nylons, etc., for which the basic products, ethylene, propylene, xylene or even ethylene glycol are still very economically attractive. In addition, obtaining cellulose esters requires the prior solubilization of the cellulose, which generates the implementation of a heavy and costly methodology, unlike the synthetic polymers derived from polycondensations. Their properties remain original, however, and they continue to satisfy certain markets. The thermomechanical qualities of cellulose esters remain their main handicap. Indeed, due to the fragility of the polysaccharide chains at high temperatures, the glass transition temperature (Tg) and the material decomposition temperature are often very close. The glass transition temperature corresponds to the transition from a glassy state, in which the polymer is hard and brittle, to a rubbery state for which the polymer is soft and flexible. From this temperature, the material is more flexible and easier to work. This is the reason why a plasticizer is often added in order to lower the glass transition temperature and therefore widen the field of application of thermoplastics. Several plasticizers are commonly used, including on an industrial scale. This is the case for triethylcitrate for cellulose acetate and dioctyladipate for CAP. However, the use of plasticizer can sometimes be inconvenient for certain applications. These small molecules tend to evaporate over time, which can change the performance of the material in the short or medium term. Another solution for lowering the Tg of a polymer is to graft long chain substituents, so as to increase the free volume and therefore reduce the interactions between the polymer chains. The presence of bulky and flexible side substituents such as fatty chains, by removing the polysaccharide chains, lowers their Tg and therefore influences the field of use of these thermoplastics. Studies have shown on a series of cellulose esters ranging from acetate to palmitate (C16), that Tg decreases significantly with the increase in the length of the grafted fatty chains [30]. Thus, without adding plasticizer, it is possible to obtain hydrophobic plastics that are more flexible, more deformable, less brittle, which suggests new areas of application, such as packaging or plasticulture and, in particular, agriculture mulch films [31, 32]. All of these works, initiated from a model substrate, cellulose, makes it possible to envisage new ways of upgrading for polysaccharides, and in particular for wood xylans. The objective of this study is the synthesis of new plastic materials by grafting poly (lactic acid) on

xylan (4-O-methylglucuronoxylanes) extracted from chestnut sawdust.

The main problem facing the experimenter is that of the chemical richness of the plant cell wall, which is reflected in the great structural diversity of the macromolecules, essentially polysaccharides, which are represented there. The protocols to be used must therefore be sufficiently selective to allow the extraction of a category of macromolecules; they must also be concerned with protecting the integrity of molecular structures by limiting the degradation of the latter. A detailed study of literature in the field of hemicellulose extraction reveals the existence of a large number of protocols. This observation can only be explained by the wide variety of hemicellulosic structures identified within the plant cell wall. The development of a specific extraction protocol for xylans with a view to their commercial exploitation is the subject of numerous studies. The question to be answered by the experimenter is what type of xylans to extract, from which plant material, for what properties, for what applications and using which protocols. The presence of a polyphenolic frame formed by lignin, as well as the existence of chemical bonds between the different hemicelluloses which constitute the wall, and between the hemicelluloses and lignin limits the extraction of xylans. It is

**2.2 Xylan extraction from wood**

**318**

then impossible to extract a type of polysaccharide without breaking these bonds and therefore without modifying the polymer with respect to its state in situ. It is therefore necessary to apply sufficiently strong extraction conditions to allow the rupture of these bonds, without degrading the extracted molecules. In the case of extraction from wood, the xylans are conventionally collected, after delignification in the presence of sodium chlorite, by an alkaline extraction. Beforehand, it is necessary to eliminate the extractables, so that they do not interfere in the analyses later. A schematic representation of the separation of the constituents of wood is illustrated in **Figure 1**.
