# Spanish Poplar Biomass as a Precursor for Nanocellulose Extraction
## 1 Introduction  
During the recent decades, increasing environmental awareness incited many governments, institutions, and firms to reduce fossil fuel consumption. Carbon footprint and resource non-renewability are amid the fundamental reasons to lessen dependence on petroleum resources. In the same context, lignocellulosic biomass emerged as a reliable alternative for petroleum based plastics [1]. Lignocellulosic biomass is estimated to be the most widely spread biopolymer on earth. Global annual production of this biopolymer is roughly calculated to be 1.3 \(\times\) 10\({}^{10}\) metric tons [2]. Lignocellulosic biomass encompasses: (1) agriculture wastes (palm residues, empty fruit bunch, straw, bagasse, corncob, and stover), (2) forest wastes (branches, unwanted stems, and withered leaves), (3) food wastes, and (4) industrial wastes (waste paper, and demolished wood) [3]. Ample of lignocellulosic residues and their capacity to act as a \"carbon sink\" promoted their use in more than 200 applications, comprising construction materials, moderate strength composites, adhesives, packaging, coatings, dental fillings, implants, scaffolding, and drug delivery [2, 4, 5]. However, mechanical reinforcement performed by lignocellulosic fibers is the major applicationproven to develop many products [6; 7]. Energy generation can be a direct application to lignocellulosic either through bioethanol production [8] or combustion of biomass through gas turbine [9]. Lignocellulose biomass has advantage over other types of biomass (for instance, poultry wastes and algae) in the terrestrial abundance in large quantities and low content of ash [10; 11]. Lignocellulosic biomass consists of cellulose chains (monomer is glucose) winded with hemicellulose threads, and all wrapped in phenolic aromatic lignin medium [12]; the chemical composition of each of these constituents varies from one plant to another. However, cellulose varies from 35 to 45%, hemicellulose varies from 22 to 30%, and lignin from 12 to 20% [13]. Poplar (polylus sp.) is considered a rich source of lignocellulosic biomass. Around the globe, indigenous and planted poplar tree area surpassed 80-90 million ha [14; 15]. In addition to rapid growth, the poplar cultivation technique can be tailored to serve diverse applications. For instance, construction wood, paper pulp, and biofuel are promising applications to poplar tree; just like other biomass including algae and poultry waste [10; 16], poplar showcased promising results to produce fuel [17; 18]. In addition, poplar ability to grow on waste water promoted its phytoremediation capacity [19]. In Spain, poplar area surpassed 144,000 ha, with 17,000 ha in the Andalusian region only. High planting density in Andalusia (1320 tree/ha) reduces the quality of harvested material, with 13 tons/ha dry waste, which makes it more sensical to develop ways to valorize extracted waste biomass [19; 20]. Amid poplar wastes valorization methodologies, we can mention the development of nanocellulose extraction protocols from poplar. Nanocellulose is a magical particle which has received ever increasing interest during the last two decades. Nanocellulose mechanical properties are a non-negligible asset, the tensile strength of nanocellulose exceeds 10 GPa (10 times of steel), and its tensile modulus averages to 130 GPa despite its low density (1.5-1.6 gm.cm\({}^{3}\)) [21]. Low thermal expansivity and capacity to form translucent films (particle smaller than light wavelength), in addition to vapor and O\({}_{2}\) barrier properties and, most importantly, biocompatibility (or biodegradable) enabled nanocellulose to become a versatile material in a multitude of applications [22; 23; 24]. Polymeric composite reinforcement and paper (board) strengthening are direct applications to high mechanical properties [25; 26]. Barrier properties, in addition to mechanical properties and biodegradability, make nanocellulose a perfect match for packaging solutions [27].