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Sizing — Grokipedia Fact-checked by Grok 2 months ago Sizing Ara Eve Leo Sal 1x Sizing is a process used in papermaking , textile manufacturing , and other fields to apply materials that modify the absorption, strength, and wear characteristics of substrates such as paper , yarns , or canvases. [1] In textiles, it primarily involves applying a protective adhesive coating, known as size , to warp yarns to enhance smoothness, strength, and weaveability during weaving . [2] This coating binds yarn fibers, reducing friction , hairiness, and breakage while increasing elasticity and tensile strength, especially for spun or filament yarns . [3] Sizing is mainly applied to warp yarns to withstand weaving stresses from heddles and reeds, minimizing defects and ensuring fabric quality. [4] Key objectives include improving abrasion resistance, eliminating static in synthetics, and ensuring uniform weight and stretch for stable beams. [2] Sizing agents are natural (e.g., starches, carboxymethyl cellulose , proteins like gelatin , comprising about 75% of use) or synthetic (e.g., polyvinyl alcohol , polyacrylates). [5] They are applied as viscous solutions via immersion, drying on machines like slashers. [3] Modern techniques include hot-melt, foam , electrostatic, and emulsion sizing for efficiency and reduced water use. [2] Environmentally, desizing generates high BOD and uses up to 30% of process water, driving biodegradable agents (e.g., soy protein , avocado seed starch ) and no-desizing methods. [4] [6] Sizing remains vital for high-speed production across materials. Introduction and History Definition and General Applications Sizing refers to the application of substances such as starches, gelatins, or synthetic polymers to materials like paper , textiles, and canvases, either incorporated during formation or applied to the surface, to fill pores, reduce liquid absorption, enhance durability , and improve properties like smoothness and printability. [7] [8] [9] These agents act as protective fillers or glazes that modify surface wettability, increase tensile strength, prevent fraying, and promote better adhesion in subsequent processes such as printing or painting . [10] [4] [11] In papermaking , sizing imparts water resistance to reduce ink bleeding and enhance print quality, while in textiles, it coats warp yarns to protect them from abrasion during weaving and improve overall fabric strength. [10] [12] For artistic applications, sizing seals canvas surfaces to prevent paint from soaking into the fibers, thereby preserving the support's integrity over time. [13] In gilding , specialized sizing adhesives facilitate the adhesion of metal leaf to substrates by creating a tacky bonding layer. [14] Emerging uses include supporting photographic emulsions on paper by controlling absorbency for even coating , and reinforcing fibers in composite materials to improve interfacial adhesion and mechanical performance. [15] [16] A key distinction in sizing methods involves wet-end (internal) application, where agents are added to the fiber slurry before sheet formation to hydrophobize the material internally, versus dry-end (surface) application, which coats the formed sheet to create a protective outer film. [17] [7] This differentiation allows tailored control over material properties depending on the end use. [8] Historical Development The earliest known application of sizing techniques dates back to ancient China , where starch was employed to strengthen paper around A.D. 768, providing a smoother surface suitable for writing and enhancing durability . This innovation marked an initial effort to impart water resistance and improve paper quality in early papermaking processes. In medieval Europe , sizing evolved with the adoption of gelatin and animal glues, primarily for treating parchment and nascent paper production between the 12th and 15th centuries. Gelatin sizing, documented as early as 1276 at the Fabriano mill in Italy , became a standard practice by the 14th century , offering better adhesion and protection against ink bleeding compared to earlier methods. [17] These animal-based agents were applied externally to surfaces, reflecting the era's reliance on natural colloids for material enhancement in manuscripts and early printed works. [18] The industrial era brought significant mechanization and chemical advancements to sizing. In papermaking , Moritz Friedrich Illig introduced rosin-alum sizing in 1807, enabling internal application during acidic production and revolutionizing scalable water repellency. [19] Concurrently, the Fourdrinier machine, patented in 1807, facilitated continuous sheet formation, which necessitated efficient internal sizing for mass production . [20] In textiles, William Radcliffe and Thomas Johnson mechanized warp sizing with their beam warper and dressing machine inventions in 1803–1804, automating the application of starch-based sizes to improve weaving efficiency. [21] The 20th century witnessed a shift from natural agents like starch and rosin to synthetic alternatives for superior performance. Alkyl ketene dimer (AKD) emerged in the late 1950s as a reactive internal sizing agent, forming covalent bonds with cellulose under neutral or alkaline conditions to enhance hydrophobicity without acidity. [22] By the 1980s , alkenyl succinic anhydride (ASA) gained prominence during the widespread adoption of alkaline papermaking , offering rapid reactivity and efficiency in high-speed mills, though requiring careful emulsification to prevent hydrolysis . [23] These developments underscored a broader transition toward more stable, process-compatible sizing for industrial demands. Papermaking Sizing Internal Sizing Internal sizing in papermaking involves the addition of hydrophobic agents to the pulp slurry at the wet end of the process, prior to sheet formation on the paper machine , where these agents react with cellulosic fiber s to create barriers that resist water penetration. [23] This wet-end incorporation ensures uniform distribution throughout the paper structure , enhancing bulk hydrophobicity and influencing properties such as absorbency and strength. [23] Typical addition levels range from 0.05% to 0.25% based on dry fiber weight, with retention promoted by cationic starches or other aids to anchor the agents on fiber surfaces. [23] The primary internal sizing agents include rosin , alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA), each operating through distinct chemical mechanisms tailored to paper pH conditions. Rosin sizing, the earliest method, was developed in 1807 by Moritz Friedrich Illig and requires an acidic environment ( pH 4.5–5.5) along with alum as a mordant to form insoluble calcium or aluminum resinate precipitates that deposit on fibers via ionic interactions. [24] [23] In contrast, AKD and ASA enable neutral to alkaline sizing ( pH 7–8.5), with AKD forming covalent β-keto ester bonds with cellulose hydroxyl groups through a nucleophilic addition reaction, often requiring curing time or heat for full efficacy. [23] ASA, structurally similar but more reactive, undergoes ring-opening hydrolysis to form ester linkages with cellulose , though it hydrolyzes rapidly in water if not quickly retained, necessitating on-site emulsion preparation. [23] The basic reaction for AKD sizing can be represented as follows, where the ketene moiety reacts with a cellulose hydroxyl group: ( R − C H X 2 − C H X 2 ) X 2 C = C = O + C e l l − O H → ( R − C H X 2 − C H X 2 ) X 2 C H − C ( = O ) − O − C e l l + H X 2 O \ce{(R-CH2-CH2)2C=C=O + Cell-OH -> (R-CH2-CH2)2CH-C(=O)-O-Cell + H2O} ( R − CH X 2 ​ − CH X 2 ​ ) X 2 ​ C = C = O + Cell − OH ​ ( R − CH X 2 ​ − CH X 2 ​ ) X 2 ​ CH − C ( = O ) − O − Cell + H X 2 ​ O This β-keto ester linkage provides permanent hydrophobicity by orienting alkyl chains away from the fiber surface. [23] These agents reduce water penetration into the paper matrix, improving dimensional stability during printing or writing by minimizing swelling and cockling, though excessive sizing can lower porosity and complicate recycling by hindering fiber repulping. [23] In modern practice, AKD and ASA dominate internal sizing for neutral and alkaline papermaking , comprising the majority of global applications in the 21st century due to compatibility with calcium carbonate fillers and superior efficiency over rosin . [23] Rosin persists in some acidic systems but represents a declining share as mills shift to neutral processes. [23] Surface Sizing Surface sizing in papermaking involves the application of sizing agents to the exterior of the already formed and partially dried paper sheet, typically at the size press stage, to enhance surface properties such as printability and handling without significantly affecting the bulk characteristics of the paper . This process occurs after the initial web formation and drying , where the paper passes through a size press that meters and applies the sizing solution, followed by further drying to set the film. Common application methods include flooded nip (tub) size presses, metering blade coaters, and calendar-integrated systems, which allow for controlled penetration and uniform coverage. Agents such as modified starches, gelatin , and acrylic emulsions are frequently used, with the solution typically applied at solids concentrations of 5-12% to achieve dry pickup rates of approximately 0.5-2% by weight of the base paper . [25] [26] Key sizing agents in surface sizing include starch derivatives like cationic and oxidized starches, which promote better penetration and film formation due to their altered charge and solubility properties; cationic starches, for instance, improve fiber bonding and retention through electrostatic interactions, while oxidized variants enhance film strength via depolymerization . The typical pH of starch solutions used for paper sizing is slightly acidic, ranging from 5 to 7. Commercial oxid