By Kemira’s Vladimir Grigoriev, Head of Application Excellence, Packaging & Hygiene Solutions, Americas, and Jennifer Riser, Principal Scientist, Product Development, Packaging & Hygiene Solutions, Americas
As tissue manufacturers increasingly rely on recycled fibre, the production and operational issues related to degradation of fibre quality and the presence of troublesome hydrophobic contaminants, known as stickies, are increasing. These issues lead to operational inefficiencies, sheet defects, and converting breaks. Traditional chemical approaches to tackle the challenges require multiple component additions. This article explores a novel amphoteric polymer technology that delivers dual functionality – combining superior fines and colloidal retention with effective stickies control in a single solution, boosting productivity and quality outcomes.
Challenges with recycled tissue manufacturing
The tissue industry’s push toward higher recycled content and reduced freshwater consumption brings sustainability benefits but also intensifies operational challenges. Successfully addressing challenges related to furnish quality deterioration and the agglomeration of hydrophobic contaminants, i.e. stickies, is now critical for maintaining both production efficiency and quality.
The degradation of fibre quality leads to a multitude of interconnected problems. The weakened and shortened fibres in recycled furnish lead to poor retention performance and reduced strength properties. Recycled tissue and towel processes often suffer from excessive dust generation, e.g. during converting operations, which can affect product quality and pose operational risks and health and safety hazards.
An even greater challenge facing recycled tissue production is the management of stickies. These accumulated hydrophobic particles, originating from recycled sources, e.g. from the adhesives, coatings, and inks used in the original paper products, create multiple production headaches. Stickies cause machine deposits and sheet defects, damaging operational efficiency and product quality. Converting efficiency can also suffer as stickies-related breaks increase.
Limitations of conventional approaches
Conventional solutions to these challenges typically involve multiple chemical additions, each targeting specific aspects of the problem. For fines retention and dewatering, mills traditionally rely on medium to high molecular weight (MW) polyacrylamides (PAMs): cationic PAMs for tissue grades and anionic PAMs for towel production. Towel processes require anionic PAMs as fibres are highly cationised from using wet strength resins. For bath tissue, positively charged cationic PAM works well. In addition, glyoxylated polyacrylamide (GPAM) is used for strength enhancement and dust control, a fundamental challenge in modern tissue manufacturing. Stickies control requires a specific program involving chemicals for dispersion, passivation, and fixation, typically utilising high charged low MW polymers, such as polyamines.
Conventional retention aids are long-chain, linear polyacrylamides that are either cationically or anionically charged. These polymers operate through a bridging mechanism that requires polymer extension for effective flocculation, making them sensitive to process conditions. Additionally, this approach has another limitation: the risk of overflocculation, which is detrimental for tissue formation and strength.
Novel amphoteric polymer technology
Kemira has developed a novel amphoteric polymer technology that fundamentally changes the approach to recycled tissue and towel production. This innovative chemistry combines positive and negative charges, creating unique interaction capabilities with both anionic and cationic substances and thus addressing multiple process issues simultaneously from fines retention to stickies control.
The novel polymer’s efficiency stems from its ability to form three-dimensional structures under normal papermaking conditions – a mechanism of action that is not driven by polymer extension like in conventional retention polymers. Thus, the amphoteric polymer is capable of effectively interacting with anionic furnish components including fibers, fines, colloidal materials, CMC (carboxymethyl cellulose), and anionic functional promoters, as well as with cationic additives, such as PAE-based (polyamide-epichlorohydrin) wet strength resins, GPAM, and cationic starch.
This dual functionality makes the polymer uniquely suited for delivering superior performance particularly in recycled fibre systems, while the combination of anionic and cationic charges makes it suitable basically for any tissue or towel grade, with or without wet strength. Compared to conventional cationic PAMs, the amphoteric polymer has a substantially lower molecular weight and optimal balance between the MW and charge, which facilitates gentle fibre flocculation without adversely affecting formation, a critical issue for tissue. It improves fines retention, which helps to maintain or increase dry tensile strength while providing positive effects on press dewatering. The polymer can be applied to either thick stock or thin stock.
The amphoteric nature of the new polymer technology also ensures high performance in environments with elevated conductivity and alkalinity, which is beneficial for colloidal particle retention and stickies fixation in highly closed loop systems. Laboratory studies demonstrate the polymer’s superior ability to manage colloidal materials and fines. While traditional cationic PAMs show only little evidence of binding colloidal particles, the amphoteric polymer facilitates significant agglomeration of colloidal materials, effectively adhering them to long fibre and fines, and simultaneously bridging fines and fibres, illustrated by microphotographs below. The enhanced colloidal management translates to improved machine runnability and increased production efficiency through improved retention and reduced deposition and process water contamination.
Dual functionality: achieving next level in retention and stickies control
The polymer’s resistance to challenging wet-end conditions makes it particularly valuable in recycled systems where conductivity and pH fluctuations among other issues can compromise conventional polymer performance.
Studies show that in recycled towel and napkin furnishes, amphoteric PAM provides improved drainage performance compared to anionic PAM while maintaining retention levels. The technology shows particular promise when combined with either PAE or GPAM wet strength resin and silica. This patent-pending synergistic combination allows mills to further boost drainage and retention and achieve increased process efficiency.
Beyond the retention performance, the amphoteric polymer also excels as a stickies fixative, significantly outperforming traditional polyamine-based fixation agents. Studies indicate substantial improvements across multiple performance criteria.
In filtrate turbidity tests, which assess the overall retention effectiveness, the amphoteric PAM achieved a 70% reduction compared to just 30% with conventional polyamine fixatives, see graph below. For hydrophobic particle reduction, a key indicator for stickies removal efficiency, the amphoteric polymer delivered over a 90% reduction in problematic particles, versus 70% with a traditional polyamine. Similarly, in reducing hydrophobic agglomerates, the amphoteric PAM achieved more than a 90% reduction, while polyamine fixatives managed only around 30% (see graph below). Controlling the hydrophobic agglomerate population is crucial for avoiding deposit build-up, which can lead to production interruptions.
Success story: Improving productivity and converting efficiency in the production of recycled napkin and towel
A North American AfH napkin and towel manufacturer operating a high-speed Fourdrinier machine was facing persistent challenges: sticky contaminants and frequent converting breaks that were limiting production efficiency. Additionally, low retention and drainage performance prevented the mill from reaching optimal machine speeds, constraining overall capacity. The furnish – comprising 80% old corrugated cardboard (OCC) and 20% mixed office waste (MOW) – was typical of high-recycled-content operations but presented significant processing demands.
To address these issues, Kemira introduced a novel amphoteric polymer at a dosage of 1.5 lb/ton. With its dual functionality, the polymer replaced the previously used GPAM dry strength resin, consolidating drainage enhancement and stickies control into a single, more effective solution.
The results were compelling:
- 20%-point increase in first pass retention
• 2.1% increase in machine speed
• 1.6% boost in production rate
• Improved energy efficiency through reduced refining power without compromising strength.
• Reduced dust formation, contributing to better machine cleanliness and improved working conditions for operators.
• Up to 70% reduction in downtime from stickies-related cleaning of forming fabrics and press equipment.
• 19% reduction in converting breaks, directly enhancing converting efficiency.
Conclusions
As the tissue and towel industry increasingly incorporates recycled content, the need for advanced chemistry solutions becomes critical to sustaining operational excellence. Amphoteric polymer technology marks a significant step forward in this space. Its dual affinity for both anionic and cationic substances makes it uniquely effective in the complex environments of recycled furnish systems.
By simultaneously addressing retention and stickies control through a single, targeted chemical addition, amphoteric PAM outperforms traditional retention aids and fixation agents. Case studies highlight its ability to resolve multiple production challenges simultaneously, positioning it as a pivotal enabler in recycled tissue manufacturing.
The benefits are clear: enhanced dewatering, retention and stickies fixation improve machine productivity, while effective stickies control boosts converting efficiency. For mills aiming to optimise recycled grade operations, this technology offers a compelling path to greater efficiency, reliability, and performance.
Acknowledgements
We gratefully acknowledge the contributions of Lucyna Pawlowska and Michael Wallace to data generation, analysis, visualisation, and insightful discussions.
