Chitin and chitosan biopolymers: I. A review of historical milestones, sourcing, chemistry, and production processes

Chitin and chitosan, the second most abundant natural biopolymers after cellulose, have emerged as versatile and sustainable materials with immense potential across diverse fields. This comprehensive review, the first part of a series, provides a detailed examination of the foundational aspects of these polymers. We begin by tracing their historical discovery and the evolution of their nomenclature, from Henri Braconnot's initial identification of "fungine" in 1811 to the coining of the term "chitosan" in the late 19th century. The review then details the extensive natural sources of chitin, including the predominant crustacean shell waste as well as promising alternative sources like fungi and insects, discussing the specific advantages and challenges associated with each. A central focus is placed on the industrial production processes, providing a critical analysis of traditional chemical methods, demineralization, deproteinization, and deacetylation, alongside emerging biological and fermentation approaches. We compare these pathways in terms of their environmental impact, economic viability, and the quality of the final product. Furthermore, the review delves into the fundamental chemistry, structural polymorphism (α, β, and γ forms), and key properties such as degree of deacetylation and molecular weight, which govern their solubility and application potential. By consolidating this critical information, this review serves as a foundational resource for understanding the journey of chitin and chitosan from raw materials to industrially relevant biopolymers.