Paper mills rarely change a sizing agent because of one number on a technical data sheet. Sizing sits at the meeting point of wet-end chemistry, size-press formulation, the drying curve, and the moisture-resistance target of the finished sheet — and procurement teams are usually the group that has to hold all four variables inside one purchasing decision. When a mill compares an AKD product, an SAE (styrene-acrylic emulsion) product, and a composite that carries both chemistries, it is not comparing three grades of the same thing. It is comparing three mechanisms with three different process footprints.

This FAQ is written for paper mill procurement, technical, and production staff who need to answer a narrower question: given a documented surface AKD sizing agent, a documented cationic SAE surface sizing agent, and a documented composite that integrates AKD waterproofing chemistry with SAE film-forming behaviour, what actually changes on the machine, what interacts with the retention aid and defoamer programs already in place, and when does replacing two additives with one composite make sense — or fail to.

Why Sizing Selection Has Become a Procurement Decision

The sizing category is large, growing, and geographically concentrated. The global paper sizing agent market was valued at approximately USD 3.8 billion in 2025 (Dataintelo), and the same source projects it reaching USD 5.9 billion by 2033 at a CAGR of 5.8%. Published estimates do not agree precisely: independent 2024 market size estimates range from USD 3.16 billion (Market Research Future) to USD 3.95 billion (SNS Insider), and CAGR projections range from 4.14% to 5.8% depending on scope and forecast window. Buyers are better served by planning against the range than against a single point estimate.

What is not in dispute is the mix. Synthetic sizing agents — the family that includes AKD and ASA — held a 54.5% share of the market in 2024 (SNS Insider), and AKD alone accounts for approximately 48% of synthetic sizing agent volume globally (Dataintelo). Rosin chemistry still holds a substantial revenue position at 32.4% in 2025 (Dataintelo). Asia Pacific accounted for 42.3% of market revenue share as of 2025 (Dataintelo), and China's annual sizing agent consumption is estimated at 650,000 tons in 2025 (Dataintelo).

The practical implication for a procurement team is that sizing has moved from a commodity line item to a process compatibility decision. When more than half of category volume is reactive or film-forming synthetic chemistry, the questions that decide whether a trial succeeds are charge, foam, curing, and dosing — not unit price alone.

The Three Mechanisms in Plain Terms

AKD: reactive sizing that develops after drying

AKD (alkyl ketene dimer) is a reactive sizing chemistry. The lactone ring of the AKD molecule reacts with hydroxyl groups on the cellulose chain, forming an ester linkage that presents a hydrophobic tail at the fibre surface. Because the reaction is chemical rather than purely physical, sizing does not reach its final value at the point of application. The final sizing level is normally measured after the sheet has passed the drying cylinders and has had time to cure. For a surface AKD sizing agent such as JH-200, that means the machine drying curve is part of the sizing specification, not a variable that sits outside it.

Two consequences follow for procurement. First, machine trials need a curing window before Cobb water absorption values are judged. Second, because AKD chemistry is reactive and typically cationic in emulsion form, the wet-end charge environment matters when an internal AKD grade is used, since cationic demand from fines, fillers, and anionic trash competes for the same surface.

SAE: film-forming surface sizing

Styrene-acrylic emulsion (SAE) sizing works differently. Polymer particles in the emulsion coalesce into a continuous film as the sheet dries, creating a physical barrier on the fibre surface. There is no covalent bond to cellulose. The effects that follow are surface-oriented: improved surface strength, better printability and ink holdout, and surface water resistance. Because the mechanism is film formation rather than reaction, SAE sizing tends to develop faster and depends more on film quality than on curing time.

SAE is also where ionic character becomes a purchasing criterion. A cationic SAE product such as JH-600 is designed to be retained on an anionically charged fibre surface and to sit compatibly in a size-press formulation built around starch.

Composite: two mechanisms in one drum

A composite sizing agent carries AKD waterproofing chemistry and SAE film-forming chemistry in a single formulation. JH-WH3364 is documented as a composite surface sizing agent built on weak anionic styrene acrylic plus AKD, supplied in a weakly cationic emulsion form. In process terms, a composite asks the mill to accept one dosing point, one tank, and one fixed ratio between the reactive and film-forming components.

Documented Product Behaviours Behind This FAQ

Qingzhou Jinhao New Material Co., Ltd., branded as JHDA, is a papermaking fine chemicals manufacturer founded in 2005 and located in Mihe Industrial Park, Qingzhou City, Shandong Province, China. The company covers R&D, production, technical after-sales, and export sales of papermaking chemicals, reports an annual output of 100,000 tons, and operates an overseas supporting production entity, CRM Chemical Technology Co., Ltd., in Long An Province, Vietnam. Its portfolio includes AKD sizing emulsion, cationic styrene-acrylic surface sizing agents, dry strength agents, wet strength resins, defoamers, dryer release agents, and food-grade barrier coatings for packaging paper.

Three products carry the behaviours this article is built around.

For buyers evaluating supply capability alongside chemistry, JHDA's documented commercial terms are an MOQ of 1MT with free trial samples, a monthly capacity of 8000MT, and a production lead time of 4 work days. Customization runs across formulation development, OEM and label production, and specification and packaging customization. Quality documentation includes ISO 9001 certification (certificate number 10423Q01592R1S), ISO 14001 certification (certificate number 10423E01032R2S), a HALAL certificate (number 6637250000) covering paper-making industry additives for Indonesia and global Halal-compliant markets, and SGS product compliance test reports. The company exports to Asia, Africa, and South America.

Process Interactions Every Buyer Should Ask About

Retention aids

Surface sizing agents and retention aids usually meet indirectly rather than directly. Retention aids such as cationic polyacrylamide (CPAM) programmes — the basis of products like JH-8501, a strength retention emulsion with 38.0 ± 1.0% solids, pH 3.0 – 6.0, and cationic character — are dosed in the wet end, while surface sizing is applied at the size press after sheet formation. The interaction is therefore a circulation interaction: broke repulping, white water recirculation, and the return of coated broke to the pulper can carry surface-sizing chemistry back into the wet end, where it adds to cationic or anionic demand and can shift retention performance.

For internal AKD grades, the interaction is direct. An internal AKD emulsion is cationic and competes for fibre surface and fines with the retention system. Mills that run high anionic trash loads from recycled OCC furnish typically see this first as unstable retention and second as inconsistent sizing.

Defoamers

Foam is a film-quality problem before it is a pumping problem. Entrained air in the size-press circuit produces pinholes and skips in the sizing film, which appear downstream as localized Cobb variation and print mottling. This is why the low-foaming behaviour documented for a cationic SAE product such as JH-600 matters during evaluation: a sizing agent that contributes less foam reduces the defoamer demand the mill has to manage.

The reverse risk is also real. Defoamer over-dosing, or a defoamer selected without regard to the size-press emulsion, can destabilize the sizing formulation and impair film formation. JHDA's product portfolio includes a high temperature and alkali resistant paper defoamer, which means the defoamer and the sizing agent can be evaluated as a matched pair rather than as two independent purchases.

Starch and the size-press formulation

Most surface sizing is delivered from a starch-based size-press liquor, so ionic compatibility between the sizing agent and the starch system is a practical constraint. Cationic SAE grades are generally the compatible default in a cationic starch liquor. Anionic surface sizing agents, such as the anionic styrene-acrylic JH-325, are described in JHDA's documentation as starch compatible for cultural paper applications, which indicates the compatibility question is answered per system rather than per category.

JH-WH3364 is documented as a weak cationic composite built from weak anionic styrene acrylic and AKD. That ionic description is worth reading literally during evaluation: it tells a mill that the composite carries an anionic polymer component inside a formulation engineered to behave as a weak cationic product in the size press.

Drying and curing

AKD-containing products place a real demand on the drying section. If the sheet leaves the drying cylinders under-dried, the reaction between AKD and cellulose is incomplete, sizing develops slowly, and the sheet can show unstable water resistance during storage, particularly in humid conditions. Composite products inherit this characteristic because they contain AKD. Any evaluation of JH-200 or JH-WH3364 should therefore include the drying profile as a controlled variable, not as a fixed background condition.

Application Fit: Where Each Route Sits

JHDA's additives are documented as applicable to kraft linerboard, corrugated medium paper, printing and writing paper, household tissue paper, and food-grade cardboard. Within that range, the sizing route splits along the moisture-resistance requirement rather than along the paper grade alone.

• Corrugated and carton board Surface AKD routes suit mills targeting moisture resistance and humid-weather stacking performance, where the anti-humidity sizing auxiliary in JHDA's portfolio addresses corrugated carton damp collapse.
• Printing and writing paper SAE surface sizing is the more natural fit where surface strength, printability, and ink holdout carry the specification. Industry analysis notes that SAE surface sizing agents are important for improved printability in digital printing (Dataintelo).
• Food-grade packaging paper Regulatory framing matters more than mechanism here: European food contact materials must comply with Regulation (EC) No 1935/2004, and paper packaging chemicals in the United States must meet FDA 21 CFR standards for food grade safety. JHDA holds SGS food contact safety testing for packaging paper chemicals and supplies water vapour barrier coating and food-grade waterproof coating for direct food-contact packaging paper.
• Tissue and pulp moulding Strength chemistry rather than sizing chemistry leads the specification, handled by the dry strength and wet strength range including JH-1201 PAE wet strength resin and JH-2219 pulp molding strength enhancer.

Market Trends That Are Shaping the Choice

Four documented trends are visible in third-party sizing agent data, and each one has a direct procurement consequence.

Liquid form still dominates, but solid form is closing the logistics gap. Liquid sizing agents held a 57.8% market share in 2024 due to ease of application (SNS Insider), while solid sizing agents are projected to grow at a CAGR of 5.11% through 2032 on logistical efficiency grounds (SNS Insider). For a mill in a humid climate or with limited tank farm space, solid and higher-solids formats are becoming a realistic comparison against liquid drums.

Sustainability metrics are entering purchase specifications. Bio-based sizing agents reached 38% of global consumption in 2024 (Market Reports World). Whether or not a mill is under a formal sustainability target, VOC, APEO/NPEO, and raw material origin disclosures increasingly appear in supplier questionnaires.

Packaging capacity expansion is driving sizing demand. US packaging paper capacity increased by 4.6% in 2024 (American Forest and Paper Association), and China exported USD 36.5 billion in paper goods in 2024 (OEC). Capacity growth of this kind converts sizing from a consumable into a supply-continuity item.

The supplier set is consolidated. Major global competitors in the sizing agent market include Kemira, BASF, and Arakawa Chemical Industries (Mordor Intelligence). Alternative qualified suppliers matter more when global supply chains lengthen, which is the commercial logic behind regional and second-source qualification.

Substitution: When One Composite Replaces Two Additives — and When It Does Not

This is the question mills actually ask. Replacing an AKD surface size and an SAE surface size with a single composite such as JH-WH3364 changes three things at once: the number of dosing points, the ratio flexibility of the mill, and the storage profile of the chemical.

Three limitations deserve to be stated plainly rather than left to a trial to reveal.

Fixed ratio. The most important limitation of any composite is arithmetic. A composite cannot let a mill raise the AKD share for a humid-season carton order and then lower it for a writing paper grade, because the two chemistries are pre-mixed. Mills whose sizing strategy depends on independent ratio control should keep the two-additive route.

Shorter shelf life and lower solids in the composite. JH-WH3364 is documented at 25.0 ± 1.0% solids with a 4-month shelf life, compared with 30 ± 1% solids and 6 months for JH-600, and 20.0 ± 1.0 or 30.0 ± 1.0% solids with 3 months for JH-200. Substituting a single composite for two products changes both the dosing calculation and the storage rotation rule, and neither can be handled by the pump setting alone.

Composite is not a universal replacement. It integrates AKD waterproofing and SAE film-forming, but it does not reproduce every possible ratio of the two. A mill that needs a highly film-dominant surface for printability, or a highly reactive-dominant surface for moisture resistance, is adjusting a variable that a composite holds constant.

Future Outlook

Three directions look likely over the next planning cycle. The first is continued movement of the category toward synthetic reactive and film-forming chemistry, which already holds the majority of volume. The second is regulatory pressure on food-contact paper packaging, where Regulation (EC) No 1935/2004 in Europe and FDA 21 CFR in the United States set documentation expectations that flow down to sizing agent suppliers. The third is the steady rise of multi-function products: a composite that removes a dosing point is a supply-chain simplification product as much as a chemistry product.

For procurement teams, the durable implication is that sizing agent selection should be documented the way a machine part is documented — mechanism, application point, curing requirement, ionic compatibility, shelf life, and substitution boundary. Suppliers who can provide that documentation, alongside pre-shipment testing and matched auxiliary chemistry, reduce the number of variables a mill has to discover during a trial.

Technical FAQ

1. What is the mechanism difference between AKD, SAE, and a composite sizing agent?

AKD is a reactive sizing chemistry whose lactone ring reacts with cellulose hydroxyl groups to form an ester bond, giving a hydrophobic fibre surface; final sizing develops after the drying cylinder. SAE is a styrene-acrylic emulsion that forms a continuous film on the fibre surface as the sheet dries, improving surface strength, printability, and surface water resistance without covalent bonding. A composite sizing agent such as JH-WH3364 carries both mechanisms in one formulation, built from weak anionic styrene acrylic plus AKD and supplied as a weakly cationic emulsion.

2. Does a surface AKD sizing agent reach full sizing performance at the size press?

No. Because AKD reacts with cellulose rather than forming a purely physical film, sizing develops progressively and the final sizing level is normally assessed after the drying cylinders and after a curing period. JH-200 is documented as a surface AKD sizing agent that reacts with cellulose, with final sizing developing after the drying cylinder. Under-dried sheets can therefore show slow sizing development and less stable water resistance during storage.

3. Is a cationic SAE surface sizing agent compatible with starch-based size press formulations?

Cationic SAE grades are generally the compatible default in a cationic starch size-press liquor, because their charge character matches the starch system and supports retention on the anionically charged fibre surface. JH-600 is documented as a cationic moisture resistant SAE surface sizing agent with 30 ± 1% solids, pH 2.0 – 5.0, viscosity below 50 cps at 25°C, and water solubility. JHDA also supplies anionic styrene-acrylic grades documented as starch compatible, so compatibility is confirmed per system rather than assumed per category.

4. How does a sizing agent choice interact with a mill's retention aid program?

Interaction depends on where the sizing agent is applied. Surface sizing agents applied at the size press do not contact the retention aid directly during normal operation, but broke repulping and white water recirculation can carry them back to the wet end and add to the charge load. Internal AKD grades interact directly, because a cationic AKD emulsion competes for fibre surface and fines with the cationic retention system, and high anionic trash from recycled furnish can destabilize both retention and sizing consistency.

5. Will switching to a composite sizing agent change the mill's defoamer requirement?

It can reduce it. Foam in the size-press circuit causes pinholes and skips in the sizing film, which show up as local Cobb variation and print mottling, so a sizing agent with lower foam contribution lowers defoamer demand. JH-600 is documented as cationic with low-foaming behaviour. The reverse risk also applies: defoamer over-dosing or a defoamer selected without regard to the size-press emulsion can destabilize the sizing formulation, so the two should be evaluated together.

6. Can a composite sizing agent directly replace both an AKD surface size and an SAE surface size?

It can replace both where the mill's AKD-to-SAE ratio is stable and does not need to be adjusted by grade or season, and where the objective is fewer dosing points, fewer tanks, and simpler incoming inspection. JH-WH3364 integrates AKD waterproofing and SAE film-forming behaviour in one product documented at 25.0 ± 1.0% solids, pH 2.0 – 5.0, viscosity not more than 50 cps at 25°C, and weak cationic character. It does not replace every possible ratio of the two chemistries.

7. What is the main limitation of replacing two sizing additives with one composite?

Fixed ratio. A composite holds the AKD-to-SAE ratio constant, so a mill can no longer raise the reactive share for a moisture-critical carton grade and lower it for a printability-critical grade. Storage is a secondary limitation: JH-WH3364 is documented with a 4-month shelf life, compared with 6 months for JH-600 and 3 months for JH-200, so substitution changes the storage rotation rule as well as the dosing calculation.

8. What should a mill validate before switching sizing routes?

Four things. First, the drying profile, because AKD-containing products need adequate drying for the cellulose reaction to complete. Second, ionic compatibility with the size-press starch liquor and, for internal grades, with the retention aid system. Third, sizing development over time, measured as Cobb value after curing rather than immediately after the size press. Fourth, dosing and storage logistics, since solids, viscosity, and shelf life differ between an AKD grade, an SAE grade, and a composite.