Practical Selection for OCC, DIP and Mixed Waste Paper Furnish

Recycled fiber brings a more unstable wet-end environment than virgin pulp. OCC, mixed office waste and DIP often contain high anionic trash, dissolved and colloidal substances, residual ink, fines and stickies. These materials consume retention chemicals, disturb charge balance and affect drainage, formation and machine runnability.

A suitable retention program should be selected according to furnish cleanliness, paper grade, machine speed, ash content, white water closure and available dosing points. Chemical cost is important, but wet-end stability is more important.

The Main Wet-End Challenge

Two issues normally decide the retention result in recycled fiber systems.

The first is anionic trash. It consumes cationic chemicals before they can work on fibers, fines and fillers. When the furnish quality fluctuates, cationic demand also changes, making dosage control difficult.

The second is shear. On modern paper machines, the stock passes through the fan pump, pressure screen and other high-shear positions before reaching the headbox. If the retention system cannot rebuild flocs after shear, the effect will be unstable.

For dirty recycled furnish, a fixing agent or anionic trash scavenger, such as polyamine, PAC or polyDADMAC, is often needed before the main retention aid. This helps create a more predictable wet-end condition.

01-Single-Polymer Retention System

A single-polymer system usually uses one high-molecular-weight cationic polymer, such as CPAM.

It is simple and low-cost, but the flocs are usually large, loose and shear-sensitive. After the fan pump or pressure screen, they are easily broken and difficult to rebuild. In high anionic trash systems, CPAM may also be heavily consumed before it performs real retention work.

This system is more suitable for low-speed machines and lower-grade products, such as low-grade corrugating medium or board core layers. It is rarely a stable stand-alone solution for modern high-speed recycled fiber machines.

Practical note: CPAM should be added as late as possible after major shear points. In dirty systems, charge control before CPAM addition is usually necessary.

02-Dual-Polymer Retention System

A dual-polymer system normally combines a cationic polymer and an anionic polymer, such as CPAM and APAM. It improves retention and drainage compared with a single-polymer system by using charge interaction, patching and bridging.

However, it still depends strongly on dosage ratio, mixing condition and charge balance. If the cationic component is consumed by anionic trash, the retention network becomes weak. If the polymer dosage is too high, formation may be damaged.

This system can be used for some medium or lower-demand recycled grades, but it is often limited when the furnish is dirty, ash is high or the water system is highly closed.

Practical note: Add the cationic polymer first, then the anionic polymer. Avoid strong shear after the second addition point.

03-Bentonite Microparticle Retention System

The CPAM + bentonite system is widely used in recycled fiber papermaking, especially for OCC-based packaging grades.

CPAM forms initial flocs first. After these flocs pass through high-shear areas and become smaller, fully hydrated bentonite is added to rebuild compact microflocs. This gives better retention, drainage, shear resistance and formation stability.

Bentonite systems are commonly applied in corrugating medium, testliner, recycled newsprint, white board and other recycled fiber grades. They are often a practical baseline for medium- and high-speed paper machines.

Practical note: The sequence is critical: CPAM first, then high shear, then bentonite after the pressure screen and before the headbox. Bentonite must be fully hydrated and well dispersed.

04-Colloidal Silica Microparticle System

A colloidal silica system is often used with cationic starch or cationic polymer. Cationic starch can support both retention and paper strength, while colloidal silica helps form fine and shear-reversible microflocs.

This system is more suitable for relatively clean recycled furnish, DIP-based printing and writing grades, coating base paper and white board top layers. In dirty recycled systems, anionic trash may consume cationic starch and increase operating cost.

The system also requires good starch cooking, temperature control, microbial control and pipeline cleaning.

Practical note: Colloidal silica should be added after major shear points. Poor starch preparation can create new wet-end problems.

05-Ternary Retention System

A ternary system is used when the furnish is highly contaminated, with high anionic trash, high conductivity, high ash or serious stickies. A typical program includes a fixing agent, a cationic polymer and a microparticle.

The fixing agent controls dissolved and colloidal substances before the main retention system works. This improves chemical efficiency, drainage, deposit control and machine runnability.

However, control is more difficult. Overdosing PAC, alum, polyamine or polyDADMAC may make the system too cationic and affect sizing, dyes, OBA, starch or other wet-end additives.

Practical note: The fixing agent should be added before cationic retention chemicals or strength agents. Charge measurement is strongly recommended.

06-Organic Microparticle System

Organic microparticles can replace inorganic microparticles in some systems. They are non-abrasive, avoid mineral accumulation in broke return and can provide very good formation.

Their cost is usually higher, and control requirements are stricter. In recycled fiber applications, they are more suitable for specialty grades, tissue or products with high formation requirements.

Practical note: Use only after trial confirmation. Compatibility with charge balance, broke return and other wet-end additives should be checked before mill application.

Selection Guide

For low-speed and lower-grade recycled paper machines, a single- or dual-polymer system may still be workable if charge control is acceptable.

For most medium- and high-speed OCC-based paper machines, CPAM + bentonite is often a balanced choice in performance, cost and operation stability.

For relatively clean recycled furnish where strength is also important, colloidal silica with cationic starch may add value.

For dirty furnish, high ash, high conductivity or serious stickies, a ternary system with a fixing stage should be considered.

PMTEC View

There is no universal retention formula for recycled fiber papermaking.

The correct selection depends on furnish condition, machine speed, drainage load, paper grade and wet-end chemistry. A good retention program should not only improve first-pass retention, but also support stable drainage, cleaner operation, fewer deposits, better formation and more consistent paper quality.

PMTEC supports paper mills with recycled fiber system evaluation, wet-end process analysis, retention program selection and paper machine performance improvement.