Engineering carboxymethyl starch and its nanoparticles: Sustainable synthesis, structure-property relationships, and applications - A review.

Starch-based materials have gained increasing attention as renewable biopolymers amenable to functionalization for advanced applications. Among starch derivatives, carboxymethyl starch (CMS) and its nanoparticles (CMS NPs) offer significant advantages over native starch, particularly improved solubility, colloidal stability, and thermal performance, owing to the introduction of tunable anionic carboxymethyl groups. Precise control over degree of substitution (DS), amylose content, and nanoscale morphology enables CMS-based systems with enhanced absorption capacity, stimuli-responsiveness, and film-forming behavior. Despite extensive research efforts, the existing literature remains fragmented and lacks a unified framework linking synthesis parameters and nanostructure to functional performance. This review integrates current knowledge on CMS and CMS NP production, covering carboxymethylation chemistry, reaction efficiency (RE), and nanosizing strategies such as enzymatic hydrolysis, nanoprecipitation, and ultrasonication. The analysis highlights how variations in DS, particle size, amylose content, crystallinity, and molecular architecture govern the physicochemical properties and technological suitability of CMS-based materials. Practical applications, including drug delivery and controlled release, emulsification, bioplastics, absorption, biocatalyst, and adhesives, are critically evaluated, alongside existing limitations and future research needs. By mapping key structure-property-performance relationships and identifying unresolved challenges, this review provides a strategic roadmap for the rational design of next-generation CMS-based materials, bridging molecular engineering with green and sustainable nanotechnology.