**1. Introduction**

Xylan is a natural biodegradable polymer, a major component of hemicellulose which is one of the most abundant polysaccharides in nature after cellulose and starch. Hemicellulose can be extracted by alkaline solution from plants, including agricultural and forestry products [1, 2]. Xylan is a major component of the hemicellulose of straw, grasses and agricultural residues. It has a skeleton consisting of β (1 → 4) xylopyranose units, and generally has individual arabinose units attached to some of the C3 positions of the xylan skeleton as the main substituent, and small amounts of 4-O-methylglucuronic acid residues essentially linked to C2 position [3]. The solubility of xylan is favored by the presence of charged substituents such as uronic acids, which increase the hydrophily of the polymer and the intermolecular electrostatic repulsions. Its original physico-chemical properties bring it closer to hydrocolloids. It is used in particular in the food, cosmetic and pharmaceutical sectors, as a thickener, emulsifier or gelling agent. In addition, its binding properties have been exploited as additives in the preparation of paper pulps. They provide better flexibility to fibers and improve the mechanical resistance of paper. In recent years, increasing attention has been paid to poly (lactic acid) due to increasing environmental concerns and the decrease in fossil resources [4–7]. In addition, this polymer comes from renewable plant resources and has excellent properties such as biodegradability, mechanical strength, transparency and biocompatibility. It has considerable market potential in the fields of packaging, agriculture and biomedical and it is considered as a substitute for polymers of

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].
