Question 1

AKD vs ASA — which internal sizing agent should I choose?

Accepted Answer

Choose AKD for stable neutral/alkaline systems with slower sizing development; choose ASA when fast sizing speed and high-filler furnishes are needed, but ASA requires on-site emulsification. AKD (alkyl ketene dimer) is supplied as a stable pre-emulsified cationic dispersion that can be stored 4–6 weeks and dosed directly at the wet end. It reacts with cellulose over several hours (or during calendering/drying) to form a covalent beta-ketoester bond — meaning HST values continue to develop after reel. AKD works best at neutral to mildly alkaline pH (7–8.5) and is sensitive to high alum or anionic trash. ASA (alkenyl succinic anhydride) must be freshly emulsified on-site with starch or cationic polymer because its hydrolysis half-life is only 20–40 minutes. However, ASA reacts much faster than AKD, achieves full HST at the reel, and tolerates higher filler (PCC/GCC) loadings. ASA is preferred for alkaline fine paper and packaging grades requiring quick out-of-machine dryness.

Question 2

Why does rosin sizing require alum, and what are the limitations?

Accepted Answer

Alum (aluminum sulfate) precipitates rosin soap onto fibers as aluminum rosinate and provides the electrostatic fixation needed at acidic pH. The main limitation is the requirement for acidic conditions (pH 4–5.5), which degrades paper over decades. Traditional rosin sizing works at pH 4.0–5.5: rosin (abietic acid) is saponified to rosin soap, which forms a colloidal dispersion. Alum added downstream hydrolyzes to Al³⁺ species that deposit positively-charged aluminum rosinate particles onto the negatively-charged fiber surface. On drying, the rosin melts and coats the fibers. The critical drawback is that aluminum sulfate at low pH hydrolyzes cellulose over time, producing 'acid-brittle' paper — which is why libraries and archives have moved to alkaline AKD/ASA systems since the 1980s. Fortified (modified) rosin sizes contain maleic anhydride adducts that improve sizing efficiency at slightly higher pH (up to 6.0) and reduce alum demand, extending the useful life of acidic papermaking operations.

Question 3

What is the Hercules Sizing Test (HST) and what values are typical?

Accepted Answer

HST measures the time (in seconds) for a standard dye solution to penetrate through a paper sample — higher seconds = better sizing. Copy paper targets HST > 60 s; packaging grades vary from 5–30 s. The Hercules Sizing Tester (TAPPI T 530 / ISO 11497) uses a 1% formic acid or naphthol green B solution as the penetrant. A paper sheet is clamped in the optical cell; the tester measures reflectance on the top surface as liquid penetrates from below — when reflectance drops to 80% of initial, the timer stops. This endpoint is correlated with resistance to water-based ink feathering and strike-through. AKD-sized writing paper typically targets 60–120 s at 80°C calendering; rosin-sized newsprint runs 5–15 s; high-barrier packaging papers can exceed 300 s. For AKD, HST measured on the reel will be 20–40% lower than HST after 24 h room temperature cure, because the beta-ketoester reaction continues post-drying.

Question 4

What is warp sizing and why is it necessary?

Accepted Answer

Warp sizing coats yarn with a protective film before weaving to increase tensile strength and abrasion resistance, reducing breakage on high-speed looms. During weaving, warp yarns experience cyclical tension (typically 5–20 cN/tex), bending over heddles and reed wires, and abrasion against each other — 2,000–10,000 cycles per meter of cloth produced. Unsized yarns accumulate micro-damage, leading to ends-down (breakages) that stop the loom and require operator intervention. Sizing agents (starch, PVA, polyacrylate, CMC, or blends) are applied in a slasher machine by immersion in hot size liquor followed by squeezing and drying. For cotton yarns, oxidized starch or starch-PVA blends at 8–12% add-on are standard; for polyester, PVA or polyacrylate at 5–8% add-on provides the adhesion and film-forming needed (starch does not adhere to synthetic fibers well). After weaving, the size must be efficiently removed (desizing) before dyeing — which is where amylase enzymes come in.

Question 5

How does carbon fiber sizing affect composite mechanical properties?

Accepted Answer

Sizing improves fiber-matrix interfacial shear strength (IFSS) by 20–50%, preventing delamination under flexural and interlaminar shear loading; it also protects fiber filaments during handling and winding. Carbon fiber surfaces are chemically inert (graphitic basal plane) and require surface treatment plus sizing to bond with epoxy matrices. Electrolytic oxidation introduces oxygen functional groups (–COOH, –OH, C=O) on fiber surfaces; sizing then provides a coupling layer. Epoxy-compatible sizing agents typically consist of a bisphenol-A or bisphenol-F epoxy oligomer emulsified in water with a non-ionic emulsifier, applied at 0.5–1.5% on fiber weight. This forms a compliant interlayer that transfers shear stress from matrix to fiber, typically increasing ILSS (interlaminar shear strength, ASTM D2344) by 20–50 MPa vs unsized fiber in epoxy. Size type must be matched to the matrix: epoxy sizing for epoxy prepreg systems; polyamide-compatible sizing for thermoplastic CFRTP; sizing removal (desizing at 350–400 °C in air) is required before using carbon fiber with bismaleimide or PEEK matrices.

Question 6

What is the difference between surface sizing and internal sizing?

Accepted Answer

Internal sizing adds chemical agents to the wet-end furnish so they become permanently bonded in the fiber network; surface sizing applies a film at the size press to improve surface strength and printability without penetrating the sheet core. Internal sizing (AKD, ASA, rosin) is added at the headbox or mixing chest; sizing agents react with hydroxyl groups on cellulose and become part of the fiber-fiber bonding network, providing bulk hydrophobicity throughout the sheet cross-section. Surface sizing (oxidized starch, CMC, PVA, synthetic film-formers) is applied after the paper is already formed and partially dried, using a puddle or film press. It does not react covalently with the fibers but forms a film over the surface, improving Scott bond, surface strength (IGT pick test), and resistance to ink feathering. Most commercial printing papers use both: internal sizing sets the baseline HST, while surface sizing optimizes printability and reduces surface linting. Starch concentration at the size press typically runs 5–12% solids at 60–80 °C, with add-on controlled by nip pressure.

Question 7

What is the minimum order quantity (MOQ)?

Accepted Answer

Starter orders from 25 kg (solid AKD wax) or 200 L IBC (liquid emulsions); standard commercial orders are 1,000 kg or 1 MT; FCL is 16–20 MT depending on product density. AKD wax (solid flake) is available from 25 kg woven bags; AKD emulsion and ASA emulsion are supplied in 200 L IBC drums or 1,000 L flexi-tanks for sea freight. Rosin size emulsion and oxidized starch ship in 25 kg bags (starch) or 200 L drums (emulsion). Carbon fiber sizing agent is supplied in 5–25 kg jerry cans (concentrate, dilute on-site to 0.5–2% bath). Textile warp sizing agents are available in 50–200 kg drums. For FCL quantities, ASA requires temperature-controlled (10–25 °C) reefer container as it hydrolyzes above 30 °C during transit. Contact us with your annual volume estimate for freight and lead-time options.

Question 8

What documents are available — COA, MSDS, TDS?

Accepted Answer

Yes — COA, SDS/MSDS, and TDS are provided standard with every order and available on request for samples. COA for AKD includes: active content (%), particle size (D50, D90), cationic charge density (mEq/g), pH, and viscosity. COA for ASA covers: purity (GC %), anhydride content, color (Gardner), and free acid content. Starch COA includes: viscosity (Brabender or RVA), moisture, ash, pH, and substitution degree (DS). SDS is prepared to GHS Rev. 7 / EU CLP format in English and Chinese. For REACH compliance, all products are either registered or fall under the polymers/natural substance exemption — full REACH declaration letters available on request. Carbon fiber sizing COA includes: solid content, emulsion stability (24 h settling test), and sizing uniformity (CV% on fiber).

Paper / Substrate	Sizing Target	Recommended Chemistry	Key Grade
Woodfree writing / copy paper	HST > 60 s, neutral pH	Internal: AKD emulsion	ake-sizing-agent
Uncoated board / packaging paper	Fast sizing, alkaline furnish	Internal: ASA emulsion	asa-sizing-agent
Newsprint / acidic system	Low cost, moderate sizing	Internal: Rosin size + alum	rosin-size-emulsion
Corrugated medium / liner	Surface strength + sizing	Surface: Oxidized starch	oxidized-starch
Release liner / specialty paper	High water hold-out	Surface: Hydrophobic agent	hydrophobic-surface-sizing
Cotton / blended warp yarn	Coat and stiffening	Textile: Cotton sizing agent	sizing-agent-cotton
Polyester / synthetic warp yarn	Adhesion + film-forming	Textile: Polyester sizing agent	sizing-agent-polyester
Carbon fiber tow / prepreg	Fiber-matrix interface	CF: Carbon fiber sizing	carbon-fiber-sizing

Imported Brand Grade	China Equivalent	Major Chinese Producers
Hercules / Solenis AKD wax (C16/C18)	AKD wax + emulsion, C16/C18 mixed chain	星东 (Xingdong), 杭华 (Hanghua), 奥克 (Aoke)
Kemira AKD 2000 series	AKD sizing emulsion (cationic, 15% active)	星东, 江苏华邦 (Huabang), 聚鼎 (Juding)
Buckman ASA emulsifier system	ASA + cationic starch pre-emulsification kit	苏源化工 (Suyuan), 星东, 杭华
Sappi / Mondi rosin size	Modified rosin emulsion (fortified type)	天津格润 (Gelun), 南京嘉隆 (Jialong)
Solenis CATO oxidized starch	Oxidized corn/tapioca starch (DS 0.02–0.06)	天津工发淀粉 (Gongfa), 西王 (Xiwang), 修正 (Xiuzheng)
Toray / Hexcel CF epoxy sizing	Epoxy-emulsion CF sizing agent (1–2% on fiber)	威格林 (Winglin), 哈尔滨天顺 (Tianshun), 精工 (Jinggong)
Novo Nordisk Termamyl (amylase)	High-temp alpha-amylase (80–95 °C, pH 6–7)	诺维信代工厂 / 青岛蔚蓝 (Qingdao WL), 东莞苏纳（Suna）
CHT Bezaktiv warp size (acrylate)	Polyacrylate warp sizing agent (low-foam, fast dry)	蒙马特科技 (Montmartre), 汇达高新 (Huida)

Sizing Agents for Paper, Textile & Fiber Composites

Quick-Pick by System

All Grades (by chemistry class)

Paper Internal Sizing(3)

AKD Sizing Agent (Alkyl Ketene Dimer)

ASA Sizing Agent (Alkenyl Succinic Anhydride)

Rosin Size Emulsion

Paper Surface Sizing(2)

Oxidized Starch (Surface Sizing Grade)

Hydrophobic Surface Sizing Agent

Textile Warp Sizing(3)

Sizing Agent for Cotton Weaving

Sizing Agent for Polyester Weaving

Acrylate Sizing Agent

Carbon Fiber Sizing(1)

Carbon Fiber Sizing Agent

Desizing Auxiliaries(2)

Desizing Enzyme (Alpha-Amylase)

Amylase Desizing Enzyme

Imported Brand → China Equivalent

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