Low Cationic Starches in Surface Sizing

Low Cationic Starches in Surface Sizing: A Technical Playbook for R&D Teams

Low cationic starches for surface sizing promise cleaner effluents, higher surface strength, and smoother runnability, but the public narrative often stops short of the engineering details R&D needs to validate and scale them mill-wide.

This rewrite identifies the gaps in typical explanations and provides a lab-to-machine checklist tailored for surface sizing with Shalbond-grade low cationic starches.

What the Original Gets Right

• Low cationic grades are engineered for surface sizing (not wet end), carrying fewer cationic moieties to balance cellulose affinity and holdout while reducing effluent load from broke cycles.
• Enzyme-free, ready-to-cook products simplify operations versus on-site hydrolysis of standard surface sizing starches, improving consistency and runnability at the size or film press.
• Commercial claims include stronger surfaces, improved print quality, and lower COD/BOD impact from repulped, surface-sized broke relative to nonionic/oxidized starch baselines.

Gaps R&D Still Needs to Close

• No quantitative charge design space is stated (e.g., cationic DS or charge density) to correlate to holdout vs penetration for different basis weights and porosities.
• Application targets (solids, temperature, pH, Brookfield/Ford viscosity, add-on g/m²) are not specified, which slows lab translation to size/film press trials.
• Depth-of-penetration control methods are not detailed; in practice, cationic PAM co-addition or rheology tuning can shift z-direction distribution and bending stiffness.
• Performance diagnostics and acceptance criteria (Cobb60, IGT pick, z-direction holdout via CLSM, inkjet gamut/density) are not listed with pass/fail thresholds.
• Broke loop integration benefits are asserted, but the test protocol to verify COD/BOD and cationic demand deltas on repulped sized paper is not outlined.

Evidence You Can Build On

• Cationic surface sizing shows better surface holdout than oxidized starch, enabling stiffness, opacity, pick resistance, and print quality improvements while lowering white-water COD and cationic demand in mill and lab studies.
• Penetration can be actively tuned with cationic PAM; confocal laser scanning microscopy (CLSM) confirms higher surface residence and stiffness gains when cationic polymers manage starch mobility at the nip.
• Vendor data for low cationic products report approximately 90% self-retention on broke vs approximately 30% for native starch, 30% lower starch consumption at equivalent viscosity, improved runnability, and measurable reductions in COD/BOD from repulped surface-sized sheets.

Shalbond Technical Guidance for Surface Sizing with Low Cationic Starch

1. Formulation Targets by Grade Family

• Charge density: Select low cationic surface grades designed for size/film press to maximize surface holdout while avoiding wet-end interactions. Treat DS/charge as a design variable to balance pick strength vs flexibility for each furnish and basis weight.
• Rheology: Tune to a press-specific window (e.g., Ford #4 approximately 25–35 seconds or equivalent Brookfield at application temperature) to stabilize film transfer without misting or streaking at target speeds.
• Solids and temperature: Adopt vendor-recommended solids and cook conditions for enzyme-free low cationic starches to reduce variability versus on-site hydrolysis workflows.

2. Penetration and Holdout Control

• Use cationic PAM co-additives (low MW, appropriate charge density) when additional surface holdout is needed for stiffness or ink holdout. CLSM can verify z-distribution shifts versus oxidized starch baselines.
• For porous sheets, bias toward slightly higher viscosity and lower penetration to protect pick strength and print gloss, validated by IGT/IGT Pick and print density measurements.
• For tensile/TEA upgrades, allow controlled penetration while maintaining a thin continuous surface film. Balance via rheology and nip loading studies.

3. Broke Loop and Effluent Testing

• Repulp surface-sized paper at defined add-on levels and measure filtrate COD/BOD and cationic demand. Compare low cationic versus oxidized/native controls to quantify predicted reductions.
• Track white-water load and retention aid demand over multi-day campaigns to capture steady-state benefits from higher self-retention and lower dissolved load.

4. Press and Runnability Playbook

• Film/Size Press: Set nip pressure, pond height, and temperature for targeted add-on. Verify sheet moisture profile and avoid post-nip ribbing at higher machine speeds.
• Runnability: Enzyme-free low cationic products eliminate conversion variability, supporting higher molecular weights without misting or pick-outs at the press.
• Speed Scaling: Step-test in 50–100 m/min increments while monitoring IGT Pick and Cobb60. Lock settings when pick margin meets target and Cobb reduction satisfies grade specifications with minimal starch consumption.

Validation Matrix (R&D Friendly)

• Structure and Residence: CLSM cross-sections (fluorescently tagged starch) for z-direction mapping versus oxidized/native controls.
• Surface Performance: IGT Pick, surface strength/Scott Bond, print density, gloss, and inkjet gamut on treated versus control sheets.
• Liquid Resistance: Cobb60 and dynamic penetration for aqueous fluids appropriate to end use (inkjet, packaging, specialty).
• Runnability: Press current, web breaks, misting, and size/film press defect logs across a speed ladder trial plan.
• Circularity: COD/BOD and cationic demand of filtrates from repulped surface-sized paper together with white-water load trends during extended campaigns.

This matrix connects molecular design (charge, MW, rheology) to z-distribution, surface performance, and environmental KPIs in a way that mill engineering teams can reproduce and scale.

Where Shalbond Adds Value

• Fit-for-purpose low cationic surface sizing grades, supplied enzyme-free, with application windows tailored to size or film press operation and high-speed runnability targets.
• Method templates for CLSM z-mapping, IGT/Cobb/print quality ladders, and broke repulp filtrate testing to document reductions in COD/BOD and chemical demand versus oxidized/native baselines.
• Penetration control packages co-developed with cationic PAM options when stiffness and ink holdout must be maximized on porous bases without compromising press stability.

By executing against these lab and machine protocols, mills can validate reported benefits such as higher surface strength, reduced starch consumption at equal viscosity, and improved broke circularity with quantifiable evidence rather than directional claims.

References R&D Can Use

• Cargill article outlining low cationic surface sizing concept, enzyme-free operations, and benefits to strength, print, and effluent load.
• Vendor technical page with claims for self-retention (~90%), reduced starch consumption (~30%), runnability, filler enablement, and COD/BOD/testing direction on repulped sheets.
• TAPPI proceedings demonstrating cationic surface starch improving holdout, pick, stiffness, print quality, and lowering COD versus oxidized starch, with CLSM evidence of z-distribution.
• BioResources study on using cationic PAM to hold starch at the surface and increase bending stiffness with calorimetry and CLSM confirmation.

Shalbond’s application team can supply grade selection, dosing windows, and a full validation kit so your trials move from pilot to standard work with confidence.Ready to plan a surface sizing trial matrix or request a sample for lab screening? Contact Shalbond’s paper technical team to align charge, rheology, and press settings with your grade targets.