## 1 Introduction  
In the context of the non-sustainable supply of fossil fuels, lignocellulosicoses have emerged as one potentially suitable option to theoretically swamp the existing petroleum-based fuels [1]. These lignocellulosic substrates are highly likely to shape the future of the bioeconomy given their sustainable supply, relative abundance and readily collectible nature [2]. These biomasses, in their typical native conformation, are composed of sugar polymers of glucose and xylose and are surrounded by a protective sheath of lignin [3]. This renewable feedstock is a rich source for the production of fuels, commodity chemicals and even biomaterials [4]. However, in their native form, certain features associated with their structural integrity make them unresponsive to any external attacks [5]. For example, the complexity of the cell wall structure, degree of polymerization, cellulose crystallinity, extent of lignification and compositional heterogeneity even within one species of biomass, etc. [6, 7] are such major factors. Therefore, pretreatment, to make biomass available for subsequent processing, has been envisaged as an unavoidable step in biomass refining processes [8]. This fractionation step, in principle, disrupts the biomass native structure, exposes the sugar polymers for the subsequent enzymatic process and makes lignin available for easy extraction [9]. There have been a fair deal of studies involving a variety of pretreatment strategies including acids, alkaline reagents, hydrothermal pretreatment, organosolv pretreatment, ionic liquids, steam explosion and even biological pretreatments [10]. These pretreatments have their pros and cons [11]. For example, acidic pretreatments, along with steam explosion and hydrothermal ones, dissolve mostly the xylose portion and keep lignin within a biomass web [12]. On the other hand, ionic liquids also have significant effects on biomass fractionation, but their burdensome cost prohibits their commercial-scale applications [13]. Moreover, biological treatments are associated with prolonged processing times, making them unfavorable for biorefining processes [14]. Organosolv treatments, as compared with other pretreatment schemes, cause considerable alterations in the structural features of biomass [15]. These treatments disrupt the biomass by creating internal slits for enhanced bioconversion efficiency. Moreover, from these solvent pulping strategies, lignin can be recovered with significant characteristic features [16]. This isolated lignin, with adequate purity having low polysaccharides, is highly desired for making lignin-based compounds with tailored properties. Recently, gamma-valerolactone (GVL) has emerged as one such sustainable green solvent for biomass fractionation [17]. This organic solvent is a self-sustained non-toxic product formed within a lignocellulosic biorefinery and is capable enough to extract lignin at near-neutral solvent conditions [18]. Typically, GVL/acid/water has been mostly applied for an enhanced delignification rate with improved cellulose digestion [19]. As it is miscible with water, it induces better hydrolytic effects for biomass to dissolve out the lignin portion [20]. This reagent has also been applied with synergetic effects of metal salts, microwaves and acids [21; 22]. Therefore, in this study, we adapted a GVL assisted fractionation of pinewood biomass to study its effects on the lignin isolation and its characteristic features along with the enzymatic digestion of corresponding carbohydrate fractions. Formally, 80% aqueous GVL was employed along with ball-milled pinewood into stainless steel reactors and was treated for time intervals of 2-4 h with a temperature range of 140-180 \({}^{\circ}\)C.