## 1 Introduction  
The process of tanning leather involves the chemical modification of collagen, the primary structural protein of animal hide, to transform it into a durable and pliable material. This process can be broadly divided into three distinct phases: (i) Preparation. The raw hide undergoes a series of preparatory steps to remove unwanted components such as fat, hair, and the outer layer of hides (epidermis and subcutaneous tissue). (ii) Tanning. The core of the tanning process entails the stabilization and cross-linking of collagen fibers, rendering the hide resistant to decomposition and imparting desirable characteristics such as strength, flexibility, and water resistance. Various tanning agents, typically derived from plant, mineral, or synthetic sources, are employed to achieve this transformation. (iii) Finishing. The final stage involves the application of specialized chemicals and treatments to enhance the appearance, texture, and performance of the leather. This may include mechanical operations and coatings [1,2]. Leather is regarded as a sustainable material due to its origins as a byproduct of the meat industry. It effectively utilizes a waste product, minimizing environmental impact and resource consumption. Moreover, leather exhibits inherent biodegradability, unlike synthetic alternatives derived from petroleum [3]. Despite its sustainability advantages, the tanning process itself presents environmental concerns. The use of chemical tanning agents, often of mineral or vegetable origin, can generate hazardous byproducts and pose risks to human health and the environment. Ongoing research aims to develop eco-friendly tanning methods that minimize environmental impact [4]. Global leather production stands at an estimated 10 million tons annually, addressing a significant demand for durable and versatile materials. This production contributes significantly to the economy, generating revenue of approximately USD 40 trillion. Moreover, the tanning process generates valuable byproducts, such as gelatin, which are utilized in various industries, including pharmaceutical and food [5]. In conclusion, leather presents a unique balance between sustainability and functionality. Its origins as a byproduct, biodegradability, and versatility make it an attractive material. However, the use of environmentally harmful chemicals in the tanning process necessitates ongoing efforts to develop sustainable alternatives [6]. The incorporation of bio-based alternatives in the leather industry aligns with the broader transition towards sustainable and circular practices [7]. These innovations offer promising solutions for mitigating environmental impacts, promoting resource conservation, and enhancing the overall sustainability of the leather industry [8]. Bio-based alternatives, encompassing polysaccharides, lipids, and proteins derived from animal or plant sources, have gained prominence due to their biodegradability, biocompatibility, and abundance in nature [9]. One option that follows this trend is the use of alginate derivatives. Algin is a carbohydrate that is abundant in the cell wall of brown algae belonging to the phylogenetic class Phaeophyceae. It has many applications in drug delivery, textile printing, and the food industry (as a thickener and emulsifier) [10]. Alginates are natural linear anionic polysaccharides. They are formed by different proportions of \(\beta\)-D-mannuronate (M) and \(\alpha\)-L-galuronate (G) residues linked by C1-C4 bonds, as depicted in Figure 1[11]. In alginate, M and G units are linked through \(1\to 4\) glycosidic bonds. These bonds create linear dimers within the polymer. The polymer contains homodimers (GG and MM) and heterodimers (MG/GM). A limitation of the use of this material in the textile field is its viscosity [12]. An efficient ecological alternative to reduce viscosity and, consequently, the molecular weight of alignates is represented by the use of ultrasound. In 2017, [PERSON] et al.