# Preparation of an Asymmetric Membrane from
## 1 Introduction  
Today, sustainable development is a particular concern, in which the search for renewable sources aims at developing biodegradable materials with interesting mechanical properties. Lignocellulosic biomass is the most abundant natural cellulose source on earth. Within this source, sugarcane bagasse (SB) is widely available in tropical and subtropical areas [1]. Sugarcane bagasse, which is the solid and fibrous fraction remaining from milling sugarcane, contains mainly cellulose (30-50%), hemicellulose and lignin [2]. The conversion of cellulose into economic highly-valued derivative compounds has drawn widespread attention in the field of green and sustainable chemistry, and stimulated the development of environmentally friendly technologies [3; 4]. High-purity cellulose is suitable for the synthesis of cellulose derivatives. Among the cellulose esters, cellulose acetate (CA) is the most important one because of its biodegradability, low cost, non-toxicity, and being a renewable source [5]. Due to these advantages, CA is extensively used in the preparation of membranes, fibers, films, and biomedical utilities [2; 6; 7]. CA is usually synthesized from acetic acid and acetic anhydride in the presence of sulfuric acid as a catalyst and with a degree of substitution depending on experimental conditions [8]. The degree of substitution (DS), which is the average value of the hydroxyl group in thecellulosic units substituted by acetyl groups, is one of the most important parameters to evaluate CA [9]. In addition, DS significantly affects the polymer crystallinity and solubility in different solvents [10]. The solubility of CA in solvents such as acetone, chloroform, dichloromethane, and DMSO depends on the DS values [11], its value can vary from 0 (cellulose) to 3 (cellulose triacetate, CTA). In the case of the formation of cellulose diacetate (CDA), DS values may vary between 2.0-2.5 [12]. DMSO can dissolve diacetate and triacetate cellulose at room temperature. Asymmetric membranes consist of a relatively dense thin layer, responsible for the separation, and a porous layer, often working as the mechanical support. To produce asymmetric membranes, the phase inversion method is often employed. When a substrate is immersed into a coagulation bath, there is an exchange between the solvent in the casting solution film and the non-solvent in the precipitation medium, leading to phase separation [13]. Ultrafiltration (UF) membranes have been widely employed in order to eliminate colloidal materials, suspended solids (SS), oil droplets, bacteria, and macromolecules for water purification [14; 15]. Membranes fabricated from CA have a moderate flux, a high salt rejection, and are non-toxic [4; 16; 17]. Several publications reported the synthesis of CA from SB applied to membrane preparation for desalination, gas separation or drug release [4; 16; 17; 18]. [PERSON] et al. reported that lignin and hemicellulose remaining in extracted cellulose do not negatively affect the properties of the CA and obtained membranes. [PERSON] et al. also reported that the functional groups in the lignin not only increase the porosity but also enhance the hydrophilicity of the cellulose triacetate substructure [19]. Thus, lignin remaining in synthesized cellulose acetate can also improve the porosity and hydrophilicity because of its abundant hydrophilic groups. However, the solvents used for membrane preparation from sugarcane bagasse are mostly toxic to human health and to the environment; typical examples are chloroform and dichloromethane. It is highly desirable to replace traditional toxic solvents such as chloroform, N-dimethylformamide (DMF), dichloromethane and dimethylacetamide (DMAc) by greener solvents for the preparation of polymeric membranes. DMSO, which can be extracted from lignin or synthesized by oxidation of dimethyl sulfide, is an aprotic organic solvent for membrane synthesis [20; 21; 22]. DMSO not only has a relatively low intrinsic toxicity, but also is biodegradable, forming non-toxic products [23].