The mainstream paper chemical industry is now concentrated in fewer hands, but the choice of wet-end chemical products is more diverse than ever

by Leslie Webb

Chemical capers at the wet end

The last few years have been busy for suppliers of paper chemicals, not only in developing new products, but also in terms of rationalizing company structures, improving their environmental record and defining their relationship with customers. Re-structuring of the industry is an ongoing process driven by the need to deliver better profit margins and to enhance shareholder value, much like it is in the paper industry. The separation of the specialty chemicals side of many of the established names like ICI and Rhone-Poulenc has spawned brand new names like Zeneca and Rhodia.

Merger and acquisition (M&A) activity is also a prominent feature in the chemical industry, including those companies that produce paper chemicals.

One of the most recent examples is the $2.4 billion deal which saw Hercules take over the BetzDearborn business, which had itself only been formed a couple of years earlier through the merger of Betz and Grace Dearborn.

This deal was hardly surprising as Hercules had been rebuffed in its pursuit of Allied Colloids just months ealier. Once such approaches are in the open, it does not usually take very long for other suitors to appear and Allied Colloids was soon snapped up by another company with an interest in paper chemicals, Ciba. In both these cases, there was a complimentary fit between the combining businesses, particularly on the paper chemicals side.

No sooner had the ink dried on this deal, when Ciba announced its intention to merge with the Swiss-based multinational outfit, Clariant. But following a period of due dilengence, the deal has fallen apart and negotiations terminated.

Niche supplies

Although this M&A activity has concentrated much of the paper chemicals business in fewer and fewer hands, there are opportunities for new suppliers that identify niche opportunities or have new marketing approaches to enter the paper chemicals arena. Takeovers inevitably mean redundancies and/or disaffected employees, some of whom grab the chance to start up their own business. Many of the smaller paper chemical suppliers do not manufacture chemicals, but either formulate products by blending bought-in chemicals or simply sell the products on.

In some areas, there must be literally dozens of products under different trade names that are identical with one another chemically, although not perhaps cost-wise. What can differentiate such suppliers is the level of local technical back-up on offer, which tends to be something paper mills have an inexhaustible appetite for. In these circumstances, the over-used term "partnership" for a supplier-customer relationship takes on a special meaning, but in extreme cases can be too close for either party.

An interesting new model for supplier-customer relationships uses a "shared savings" approach, developed in North America. Under the normal system, suppliers have a vested interest in selling as much material as possible, albeit constrained by competition from other suppliers. Under the "shared savings" system, the contract is based on a fixed price per unit of production ($ per ton paper) so that both the supplier and mill have an interest in minimizing chemical use and costs. In essence, the customer is buying a service or an effect, not a chemical. The potential benefits of this approach cover not only costs, but bring environmental benefits in terms of reduced use of resources, reduced on-site chemical inventory and less waste. It has been actively taken up by the automotive industry, but is also being pioneered in the US paper industry (notably the tissue sector) by Omnikem.

Another factor that has an important bearing on choice and competition is the globalization of both paper and chemical companies and the trend to global sourcing of particular chemicals from one or a short list of preferred suppliers. Suppliers without a presence in the home market of the paper business or operating in just one or two countries would find it difficult to be considered for such contracts even though they may be very cost-effective where they do operate. In such situations, the incoming global supplier may find it difficult to match the cost-performance of the displaced supplier and may find itself in the embarrassing position of having to source its chemicals from its competitor.

Although the main reasons for choosing a supplier will remain centered on cost-performance allied to the desired level of service, paper mills are increasingly concerned with the environmental profile of raw materials and the supplier's environmental credentials. With its global "Responsible Care" programs, the chemical industry is probably in a more advanced position than the paper industry in informing everyone about its environmental performance through regular environmental reports (see PPI February 1998, p.30). The chemical industry has made significant progress toward reducing the environmental effects of paper chemicals. These developments have included:

• reducing the levels of chlorinated organics (notably dichloropropanol) in polyamidoamine-epichlorhydrin wet strength agents;
• eliminating urea as a solubiliser in dye solutions;
• developing biocides with enhanced biodegradability.

AKD sizes have always been produced in a fairly dilute form (typically 10% solids). This led to high transportation costs and associated environmental impacts. Eka have now developed a new range of zero-toluene AKD sizes at 30% solids content, but also with improved retention characteristics - a win-win situation technically and environmentally.

Biodegradability is a property that is usually considered to be desirable on environmental grounds, but this may not always be the case as it depends on where this action takes place. A biodegradable material will be broken down to some degree during papermaking, thus contributing to the costs for controlling microbial-related problems such as slime (ie biocide addition) and also impairing the material's functionality to some degree. This problem is greatest for materials with low first pass retention, but the biodegradability of non-retained residues in the mill wastewater becomes an advantage as the expressed BOD can then be removed by biological treatment. If the mill does not have a biological treatment plant, the biodegradability leads to oxygen consumption in the receiving water, which could lead to problems depending on the water's oxygen balance.

Biodegradable materials in the paper product lead to possible biodeterioration of the paper when stored under moist conditions. After use, some biodegradation is inevitable in the waste stream, even before the product is recovered for material recycling.

Lack of biodegradability (or of abiotic degradability) denotes that the material will tend to persist in the environment once it is released. In the aquatic environment, such substances may build up to levels that exert direct toxic effects on aquatic life, perhaps after bioconcentration in fatty tissue.

As there are no paper chemicals with guaranteed 100% retention in the paper, biodegradability has to be a desirable attribute for all organic papermaking materials. Unfortunately, this is not yet the case, although it is one of the motivations behind the development of new paper chemicals. Softening agents are not a major class of paper chemicals, but they are important in the manufacture of tissue grades and are also used for their anti-static properties. The normal softening chemical is a "quat", a quaternary ammonium compound substituted with methyl and tallow alkyl groups, but its hydrophobic character limits accessibility to micro-organisms.

German supplier, Henkel, has developed a quat with an ester linkage in the substituent groups that aids biodegradation under both aerobic and anaerobic conditions. Like other surface-active chemicals, it does still have some toxicity to aquatic life, but its biodegradability means that this should rarely be expressed.

Less horny pulps

The efficiency in using paper chemicals is intimately related to the chemical and physical properties of the dominant material (excluding the water) on all paper machines, namely the pulp or mix of pulps used. There has been little change in the chemistry of mechanical or unbleached chemical pulps in recent years, but environmental pressures have led to changes in the bleaching stage for chemical pulps (both virgin and deinked grades), which has changed the chemistry of the pulp passing to the paper machine. The reason why some mills experience significant differences in their process chemistry and the functioning of added paper chemicals with some totally chlorine-free (TCF) pulps has become clearer following research carried out at the Helsinki University of Technology over the last few years.

Two important things happen when pulps are used in papermaking - the particle size distribution of the fibers gets smaller and some substances in the pulp dissolve. Both have an adverse effect on the pulp's retention, particularly the dissolved substances as their overall retentions are low, except on machines with closed water systems. However, by then they have built up to high concentrations, which may cause various problems depending on their chemical character (Figure 1). One of the problem areas is the dissolution of anionic substances, which then interfere with the action of cationic additives, such as strength and retention aids. Virgin pulp is an important source of such substances in the form of various charged hemi-celluloses, such as the glucuronoxylans. During kraft pulping, this particular set of substances is converted partially to hexeneuronic acids, which are degraded during chlorine and chlorine dioxide bleaching. However, they are not degraded during TCF bleaching with oxygen/peroxide, although they are by TCF bleaching that includes an ozone stage (Figure 2).

The effect of charged substances within the pulp is not wholly undesirable as, provided that these groups remain within the fiber wall, they aid the swelling of fibers and therefore the strength of the resulting paper. For similar reasons, charge also influences the so-called hornification of fibers - the loss of swelling ability that usually accompanies drying the pulp or the paper. As high charge minimizes hornification, peroxide-bleached kraft pulps may lose less of their strength on recycling than other bleached chemical pulps, but a systematic study on the relative recycling characteristics of ECF and the range of TCF pulps is still awaited. The rush to produce pulps with a better environmental profile during the bleaching stage seems to have ignored the important changes (good or bad) that this could introduce later in the life cycle of paper.

The chemistry of recycled pulps is more varied than that of virgin pulps due to the range of chemicals that may remain from the original papers. There may also be residues of new chemicals introduced during deinking, such as silicates. The actual transfer of dissolved substances to the paper machine depends on many factors including the direction of water movement and the degree of water closure within the deinking and papermaking circuits. Several studies have shown that the extent of dissolution from recovered paper is minimized under neutral, rather than alkaline, deinking conditions. The wide range of dissolved charges found in an Australian study is illustrated in Figure 3.

Given the variability of these figures for both virgin and recycled pulps, plus the contribution from mill broke, it is not surprising that change control early in the papermaking system (or at the end of the pulping/deinking system) is fast becoming an accepted technology.

Drain and retain

Although retention is a more central concept within wet end chemistry, achieving an acceptable rate of water removal on the wire and in the press section is also critical in several ways, for example:

• to machine runnability, by maximizing the strength of the wet web in order to minimize breaks;
• to costs, by minimizing energy consumption during final drying;
• to productivity, by allowing the machine speed to be maximized;
• to paper quality, by defining the lowest flowbox consistency for the best paper formation.

The rate of water removal is affected by many factors, but each of the three pre-dryer dewatering stages (free drainage, vacuum drainage and pressing) has its own key variables. Chemistry comes into play across all three areas, but in different ways. Free drainage is governed by the permeability of the fibrous mat, which in turn depends on the particle geometry and mat porosity. The state of aggregation of the particulate matrix (combination of pulps and filler) is critical and is determined largely by the coagulants/flocculants employed as retention/drainage aids.

The response to vacuum is also affected by these chemicals, but here the floc structure is paramount with an even, micro-floc structure being best for holding the vacuum through to the couch.

After dewatering on the wire, the sheet structure remains important to its "pressability", but the ultimate moisture content after pressing is determined by the water-holding capacity of the fibers. Recent Finnish work has shed some interesting light on the nature of the water within the cell wall that remains after pressing. Three fractions are identifiable in relation to their freezing point:

• unbound water within macropores, which freezes at the same temperature as the bulk water outside the cell wall and disappears at a solids content of 55-67% for an unbleached kraft pulp;
• bound water within micropores, which freezes at a lower temperature and disappears at a solids content of just under 80% for an unbleached kraft pulp;
• water that does not freeze at all and is considered to be hydrogen-bonded to the hemi-celluloses and cellulose.

The ability of certain retention aid systems to maximize drainage is now well proven for many paper grades, during which the particulate fines are also aggregated in an optimal way for good formation. However, there is one other component of the colloidal wet end matrix that impacts on drainage (and formation), namely the gas content of the thin stock. Previously, this might have been referred to as the air content, but there are other significant sources of stock gas such as carbon dioxide generated in situ by dissolution of calcium carbonate filler and by uncontrolled biological activity. Dissolved gases cause few problems directly, but they can become visible when the system changes in some way, such as a drop in pressure/pH or rise in temperature. At 30C in contact with air at atmospheric pressure, the saturation concentrations of oxygen, nitrogen and carbon dioxide correspond to gas contents of 1.1%, 1.7% and 0.1% respectively, but the dissolution of 100 mg/l of calcium carbonate would generate a carbon dioxide content of about 11% if it was all retained in the stock. This level is much higher than is measured on most paper machines, where entrained gas contents above about 0.5% in the thin stock can give problems.

Small gas bubbles are stabilized by surface active chemicals, of which there are many sources in papermaking - pulps, sizes, cleaning compounds, etc. The presence of foam is an extreme manifestation of the presence of dispersed gas and surfactant (and water), most commonly occurring on top of the wire pit or whitewater silo. A common way of removing stock gases to minimize their adverse effect on paper formation and drainage is by application of vacuum to the thin stock, but chemicals are also widely used to help degassify stock and control foam accumulation. Foam control agents can be classified in relation to whether they are able to prevent foams building up in the first place and/or whether they are able to knock down pre-existing foams. Chemical foam prevention is achieved by neutralizing the surfactant in some way, whereas foam destruction relies on a combination of film penetration, displacement and spreading.

Commercial defoamers are nearly always a mixture of several ingredients, which tend to be described rather generically by the manufacturers. In fact, there is sometimes more clarity about what isn't there than what is, an example being the claim for many defoamers to be free from alkylphenolethoxylates, a class of chemicals that have been receiving a bad press in recent years due to their claimed activity as endocrine disrupters.

Most defoamers have a strong hydrophobic character, which allows them to change the orientation of the surfactant molecules. Like sizing agents, hydrophobic defoamers are best used in an aqueous emulsified form otherwise they may cause more problems than they cure such as deposits. It is difficult to find a chemical supplier to the paper industry that doesn't have at least one defoamer on its books, but at the same time there are suppliers, for example Blackburn Chemicals in the UK, that have chosen to specialize in this relatively small market. Although foam control costs are not high compared to the cost of other chemicals, the purchase of a few metallic foam controllers (better known as spanners) is usually a wise investment.

Hotting up

One of the general trends in wet end chemistry in recent years has been the rising temperature of water circuits. This is caused predominantly by increased closure, but it does not take much energy (no more than about 0.5 GJ/ton paper) to be dissipated from stock pumping/refining for the wet end temperature to be elevated well above the fresh water baseline. One of the few areas of papermaking that benefits from a high temperature is the removal of water (due to its lowered viscosity), but this effect is best achieved by steam boxes on the wire rather than heating the whole wet end. However in most other respects, high temperatures cause problems such as:

• increased rate of chemical and microbiolog-ical reactions, usually leading to undesirable degradation and deposition;
• increased mobility of tacky materials such as pitch and stickies;
• increased tendency to form stable foams.

Perhaps the biggest synergy between the thermal and material concentration effects of closing up (Figure 5) relates to microbiological growth within the process. As this synergy is not exactly wanted within papermaking, it is often the factor that limits closing up beyond a certain level. Temperature is itself a good selector between different types of microorganism and can be used to minimize some types of microbial infection, eg sulfate-reducers at about 45C, but it is not a full-proof technique.

The concentrating effect of a closed water system is handy when it comes to maintaining a high dose of an anti-microbial treatment and the high temperature should help penetration into the slime. The greater effectiveness of non-cidal reagents (eg Stockhausen's Tallofin) for on-machine bio-control at high process temperatures is probably a factor in the increased popularity of biodispersants rather than biocides. This can include enzymatic products, not only for stock dosing, but also for incorporation in milder cleaning compounds used for system cleaning at sub-boiling temperatures, such as some of Buckman's products.

Today's wet end chemicals have to contend with a much more demanding wet end environment than previously and at the same time have to minimize their impact on the environment outside the mill. The future means even faster and wider machine speeds operating with tighter constraints on water use and more demanding targets to reduce broke. For all paper grades, broke means waste even when the broke is recycled, as some materials are not retained and the drying energy is irrecoverable. For many, but not all, paper grades, reduced broke would go some way towards compensating for the greater pressures imposed on paper chemicals by the other changes taking place. To paraphrase a common saying in industry - "if it is broke, do fix it". n

Leslie Webb provides on-site training courses in paper chemistry. He can be contacted
on tel/fax + 44.1372. 276.599 or email leswebb@compuserve.com