Wet-end control delivers substantial payoffs
for specialty paper and tissue makers

Common production challenges in specialty paper and tissue manufacture can be cost-effectively controlled or eliminated through application of the latest online measurement techniques using closed loop control.

In specialty paper and tissue production, the deployment of online measurement using closed looped control used to be mostly ruled out, simply because frequent grade changes, an often-complex process chemistry, small production volumes and slow-running machines made it hard to achieve acceptable payback on investments in measuring technology.

Thankfully for today’s growing number of tissue and specialty producers, that situation has changed. The advent of affordable, highly accurate lab zeta potential analyzers delivering fast and direct measurement is increasing the scope for more controlled, strategic addition of additives, while providing a much better understanding of wet end chemical reactions.

With market demand spurring the use of more cost-intensive additives that deliver faster payback through process optimization, advanced online measuring techniques that provide for automatic control of chemical additives and accurate monitoring of wet end dynamics can eliminate many common production problems while saving money on unnecessary chemicals. The following examples highlight the benefits of applying closed loop control in the wet end.

Application 1: Kitchen towel and bathroom tissue

A mill producing kitchen towel and bathroom tissue was experiencing problems with formation, deposits and stable wet strength in the sheet. The mill uses 100 % virgin pulp, and was dosing with carboxymethylcellulose (CMC) to boost the anionic charge of the fibre to increase adsorption of cationic wet strength resin (WSR).

This strategy is not only costly, it’s often ineffective. Additive costs are high, deposits can occur – and even if wet strength levels in the sheet can be increased, process variability has not been diminished. One reason for this is that anionic CMC dosed during the process remains in the system during the water phase.

This can be clearly shown through cationic demand measurement directly after the pulper, following CMC dosage. After cationic WSR is dosed, it reacts with the anionic CMC. To achieve the desired wet strength, it is essential that these CMC-WSR complexes are retained in the sheet. If not, they will lead to deposits and increased COD and AOX values. Using retention aid to retain theses complexes and to stabilize fines content in the white water is a common practice – but for best results, closed loop retention aid control is vital.

Accurate monitoring of wet end dynamics helps eliminate
many common production problems while delivering substantial
savings on unnecessary chemical additives.


Figure 1:
Charge as an important parameter in evaluating chemical performance.

In wet strength resin-containing grades, process charge can sometimes swing between anionic and cationic. A cationic process indicates free WSR in the water which has not been retained in the sheet. Generally, when a process is too close to point of zero charge, uncontrolled flocculation of chemicals and fibres occurs. This in turn causes formation problems and the tendency to accrue deposits. Accurate online charge control provides mills with the security to run a process close to neutral without the disadvantage of uncontrolled flocculation at the point of zero charge. The payoff: maximum efficiency of the dosed WSR.

Application 2: Tissue with high DIP content


Figure 2:
Typical installation points for wet end control solutions

Tissue products with a large DIP component provide another good example of the benefits of closed loop control in the wet end. Because excess WSR is often dosed to achieve the desired strength properties, deposits and foam are daily production problems.

While many tissue producers are starting to employ cationic fixing agents to improve the stability of the incoming DIP furnish, this must be handled very carefully. Too much fixing agent will reduce the bonding sites on the fibre necessary for WSR adsorption. That means additives should only be used in times of higher anionic trash loads from the DIP plant.

To maintain optimum charge level in the DIP line, the fixing agent must be dosed according to continuous cationic demand measurement of the filtrate in the thick stock.

To optimize polymers in the flotation processes and maximize the efficiency of wet strength resin, defoamer chemicals should be controlled online to the lowest possible level.

Application 3: Multi-grade consumer tissue produced from mixed furnish

In mills using mixed furnish to produce many different grades of consumer tissue, felt deposit problems are a daily occurrence. To determine the origin of stickies, mills usually invest a lot of manpower over time. But applying online charge control in the white water provides ready access to critical information about the driving parameters of the process. Improved, timely process knowledge results in substantially reduced deposits – with the added benefit of often reducing the need for wet end chemicals.

The chemistry of different grades is reflected in the varying charge levels in the white water. This is driven by furnish ratios and by the different amounts of WSR and dyes needed for the production of specific grades.

Online charge control provides key insights as to what’s
really happening during the production process –
helping mills resolve problems faster, and more effectively.


Figure 3:
The impact of online fixative control, reflected by drastically reduced variation in the charge level of white water and machine chest.

A continuous cationic demand signal allows the operator to adjust the process quickly to new parameters, as well as allowing for the establishment of a database over time that provides valuable guidelines for operators for each different grade.

Because cationic demand variations within one grade reflect the quality variation of the incoming furnish, accurate measurement allows for the purely on-demand use of fixing agents – cutting costs and streamlining production. Label paper production with extreme variation in broke quality is a typical example of this type of application.

Accurate analysis = fast ROI

In most paper manufacturing processes, wet end chemicals are added in fixed dosages which are usually optimized for a single process condition, regardless of variations originating from the changing qualities of incoming raw materials and broke lines – even though such variations dramatically affect both the need for and dosage level of wet end additives.

Process stability and paper quality are both significantly improved by accurate closed loop control of chemicals – for fewer production headaches, and significantly reduced production costs.