Essay good chemistry, m hubbe

Opportunities in Wet-End Chemistry: Feature
Essay, Posted Oct. 2001
Good Chemistry - Looking towards the Future of
Papermaking Additives
Martin A. Hubbe
Dept. Wood & Paper Sci., N.C. State Univ., Box 8005, Raleigh,
NC 27695-8005
Citation (public domain):
http://www4.ncsu.edu/~hubbe/new/goodchem/
There's an old story about a public hearing in which paper
company executives were describing their plans for a green-field
mill. A spokesperson ended her presentation with a listing of the
maximum levels of various substances in the liquid effluent
from the proposed plant. "Our effluent water will have a
biological oxygen demand of less than 10 parts per million, and
it will have a pH of 7." At this point someone near the back of
the room stood up and said, "I am a citizen of this town, and I
will insist that the pH value be reduced to zero before the water
is discharged!"
Part of our challenge as papermakers is to maximize the
efficiency of our operations and make them increasingly eco-
friendly. But, as illustrated by the story above, we also need to
be proactive in explaining the steps we are taking as an industry.
Our challenge is to educate our fellow citizens that chemicals,
used appropriately, are absolutely essential in this effort and that
they also can be safe to use.

What about the chemicals that one adds at the wet end of a paper
machine? The public sometimes associates the word "chemical"
with words like "pollutants," "emissions," "toxicity," or
"hazard." As noted in an article by Reinbold (1994), "the public
no longer views technology as something beneficial." Some
advocates for the environment have described paper as a
"chemical cocktail." The goal of this essay is to consider how
we, as papermakers, can do more in the years ahead to minimize
environmental impacts and also to achieve a more favorable
impression in the eyes of the public.

Fig. 1. Full description given by Fig. 2. Full description given by
Gottsching (1993) Gottsching (1993)

Where do we look for answers? In my opinion there are
basically three answers to our situation as suppliers and users of
papermaking additives. I will spend the rest of this essay
expanding on each one of them in turn. The first answer is for us
in the industry to show that each additive to a paper machine has
a clear and beneficial role. The second answer is to demonstrate
progress in understanding and minimizing environmental

impacts of specific papermaking additives. The third answer is
to envision the types of chemical additives and their uses in a
hypothetical future paper mill. Our ideal paper mill of the future
should be both profitable and as nearly "invisible" as possible in
terms of its impact on the environment.
Part 1 - A Purpose for Each Wet-End Chemical
Think about your reaction when you see a really long list of
ingredients on the container of a processed food item. Do you
ever read down through the list and wonder whether all of those
odd-sounding chemical items are really needed? It's far worse
for those who happen to be allergic to one or more of those
additives. Unlike packaged food, paper products come with no
list of ingredients. Except for some factors that I will discuss
below, we are in a situation somewhat resembling the years
before food labels. It is possible to list about 3000 different
kinds of chemicals that have been proposed for use in
papermaking (Reinbold 1994). Ingredient labels for paper
products may or may not be a good idea; but it is also clear that
there is an opportunity for the paper industry to tell the public
what is used in paper and why.
Progress in explaining the environmental consequences of
papermaking additives already has been achieved in a series of
publications that appeared in the early 1990's. First, an article by
Reinbold (1994) clarifies just how few chemicals papermakers
actually use. If one ignores brand designations, differences in
concentration, and minor variations in molecular mass or
composition, then only about 200 individual chemicals are
commonly added to paper machines, not 3000. The relatively
low number of chemical additives used in papermaking is

consistent with the fact that this industry mainly makes low-cost,
high-volume products; we simply can't afford to use superfluous
chemicals.
An article by Göttsching (1993) makes the further point that
papermaking practices are generally compatible with the
environment. If one were to omit all chemical additives from a
papermaking process, then the consequences would include
larger increases in emissions of solids, biological oxygen
demand, and even of noxious gases - resulting from uncontrolled
growth of slime in paper machine systems. This article, together
with a publication by Webb (1993) give an excellent run-down
of the main types of chemical additives and the status of each of
these additive relative to various environmental impacts.
Saving Energy: Let's take a closer look at how wet-end
additives can reduce the energy required used in papermaking.
Removal of water uses by far the largest component of that
energy. Most water is removed by gravity drainage, application
of vacuum, inertial effects, and pressing. However, most of the
energy is expended during a subsequent process, drying by
evaporation (Hersh 1981; Specht 1992). Approximately 2 to 9
million BTU are required per ton of product, to evaporate water.
Substantial savings in energy can be achieved by shifting a
greater proportion of the water removal to the preceding unit
operations of forming and pressing (Manson 1980; Nelson 1981;
Manfield 1986; Marley 1990). One way to accomplish this goal
is to accelerate dewatering with chemical additives. There has
been much work in this area (Auhorn 1982; Allen, Yaraskavitch
1991; Litchfield 1994; Raisanen et al. 1995; McGregor, Knight
1996). I it generally agreed that each 1% increase in solids

content of a paper web should yield about a reduction of 4 to 5%
in the net drying load (Shirley 1980; Nelson 1981; Auhorn 1982;
Strawinksi 1985; Marley 1990). Pulp mills are often net
producers of energy in the form of steam or electricity, but
savings in the energy of drying has the potential to either
decrease the consumption of fossil fuels or decrease the
production of greenhouse gases.
The goal sounds great, but what chemicals are we talking about
in terms of additives? Three classes of chemicals stand out as
the major drainage chemicals in current use (Allen,
Yaraskavitch 1991; McGregor, Knight 1996; Scott 1996). These
three classes are often called "coagulants," "flocculants," and
"microparticles." Coagulants used in papermaking are generally
multivalent or polymeric compounds of high positive charge
density. Commonly used coagulants include aluminum sulfate
("papermakers' alum"), polyamines, and polyethyleneimine
(PEI). The word "coagulate" implies that the negative surface
charges of suspended solids, fibers, and colloidal material are
neutralized, removing the electrical repulsion between these
surfaces. Flocculants complete the process of bringing fine
particles together; the most widely used type of flocculants in
the paper industry are very high mass copolymers of acrylamide
(Horn, Linhart 1991). Amounts typically less than 0.05% based
on product mass are sufficient to increase the retention of fine
particle in paper as it is being formed. Microparticles are tiny
negatively charged particles such as colloidal silica, bentonite,
or highly branched carboxyl compounds; they interact with
cationic polyacrylamides or cationic starch to further promote
dewatering (Langley, Litchfield 1986; Knudson 1993; Honig et
al. 1993; Andersson, Lindgren 1996; Swerin et al. 1996). A

common characteristic of all of these drainage-promoting
chemicals is that, to perform their function, they adsorb onto the
surface of solids in the papermaking furnish. That means that
these chemicals tend to be retained well in the paper; relatively
little of it remains in liquid effluent from paper machines, even
before wastewater treatment.
Defoamer chemicals affect many aspects of papermaking, in
addition to drainage, but it is the drainage benefits that have the
clearest connection with environmental impact. A study by
Brecht and Kirchner (1959) was among the first to clearly show
that air bubbles in a stock suspension can have an effect very
similar to that of fiber fines in slowing the rate of drainage from
a paper web. Especially in the case of heavier weights of paper
or paperboard, higher levels of fines or bubbles can be expected
to clog the drainage channels in a wet sheet of paper (Gess 1989,
1991). Defoamers are added to the wet end in the form of
emulsions; little droplets of oily material spread rapidly on
bubble surfaces and cause the bubbles to coalesce. The result is
less entrained air coming out of the headbox. In principle,
improvements in drainage can be converted into dryer paper
going into the wet-press section. In turn, a dryer sheet coming
into the press section makes it possible to load the presses more
without squashing the sheet. The happiest situation is when
increased pressing results in a stronger, better-consolidated
sheet, with less water remaining to be evaporated. The wild card
in this situation is whether the resulting sheet still has enough
caliper so that it can be calendared to meet a specified
smoothness.

Decreasing Effluent Loads: A remarkable aspect of the "art" of
papermaking is that paper is formed on a relatively coarse,
continuous screen fabric; typically the openings in the fabric are
large enough so that between about 5 and 50% of the solids
delivered to the forming section are capable of passing through
those openings. The small particulate material in paper, the
"fines," may consist mostly of wood byproducts (Brecht, Klemm
1953; Scott 1986; Gess 1991; Luukko, Paulapuro 1999; Rundlöf
et al. 2000). Even before it is refined, a typical kraft pulp
contains about 5 to 10% by weight of such things as tiny
parenchyma cells, used for food storage or conduction. The
process of refining pulp - passing the pulp slurry between
counter-rotating metal plates or cones having raised bars - is
necessary to develop the bonding ability of fibers for most
grades of paper, but refining also increases the level of fines in
the slurry. But all of these wood-derived fines can be
overwhelmed by fine material of a different type, the mineral
fillers (Bown 1998). Calcium carbonate and clay are the major
types of fillers used, and they make it possible to achieve
opacity targets with less total materials.
To understand how retention aid chemicals can impact the
environment it is worthwhile to view papermaking operations as
the first step in a multi-step water clarification process (Leitz
1993). Though there is a great deal of overlap between
"retention chemicals" and the fore-mentioned "drainage
chemicals," the emphasis of a retention program is to increase
the relative proportion of fine materials that stay with the wet
paper web as it is being formed (Jaycock, Swales 1994; Gess
1998). The very-high-mass acrylamide copolymers,
polyethylene oxide in combination with phenolic cofactors, and

also high-mass acrylamides, in combination with microparticles,
can be very effective retention systems, even in some cases
where the surfaces of the suspended matter are far from being
neutral in charge. Higher retention efficiency implies that less
solid material is present in the water that drains from the paper.
The traditional name that papermakers used to describe the
filtrate water from papermaking is "white water." A generation
ago it used to be more common for white water to contain so
much clay, titanium dioxide, and air bubbles that it looked like
milk. Now, largely thanks to chemical additives, together with
screen devices called save-alls, solids levels of white water are
kept under control and nearly all of the fine material eventually
ends up as paper.
Avoiding Waste of Fibers: You may not think of strength aids
as fiber-saving chemicals, but you should. Consider the case of
recycled office waste fibers. Such fibers tend to loose a
significant fraction of their bonding ability each time they are
dried and reslurried (Lindström, Carlsson 1982; Klungness,
Caulfield 1982; Howard, Bichard 1992; Nazhad, Paszner 1994;
Zhang et al. 2001). The loss in bonding ability has been
attributed to essentially irreversible closure of pores in the cell
wall (Stone, Scallan 1966), resulting in a loss of flexibility of the
fiber surfaces (Paavlilainen, Luner 1986). Strength
specifications become more difficult to achieve. One approach is
to try to make up for the strength loss by increased refining.
However, the furnish is likely to already have a relatively low
freeness, so there comes a point where more refining is not the
answer. Rather, papermakers tend to use increased levels of
strength additives, such as cationic starch or acrylamides

(Marton 1980; Strazdins 1984; Howard, Jowsey 1989; Smith
1992; Iwasa 1993; Glittenberg et al. 1994).
Another situation in which strength additives can "save fiber"
arises in the case of paper grades that are specified by strength
rather than basis weight. Such is the case for containerboard
grades made in accordance with the Rule 41 criteria (Gutmann
et al. 1993). Briefly stated, the rule allows a producer to
decrease the basis weight of a product as long as the combined
board still meets various strength goals, such as crush resistance.
In practice, papermakers use a combination of refining practices,
dry-strength additives, and sometimes size-press addition to
make the premium-strength board and take advantage of Rule 41
(Smith 1992).
Can Chemicals Added Initially Benefit Recycling? It has been
shown that strength-enhancing chemicals added to never-dried
kraft fiber can also have a beneficial effect after the same fibers
are recycled (Higgins, McKenzie 1963; Grau et al. 1996;
Laivins, Scallan 1996; Zhang, Hubbe 2000). Treatments found
to be effective included cationic starch and combinations of
cationic and anionic polymers. Results were consistent with the
ability of such chemicals to act as inter-fiber bonding agents -
both in the initial paper and also in the recycled paper, even
when no additional polymeric material was added during the
second generation of papermaking.
Losses in fiber bonding ability due to drying, aging, and
recycling of paper made from kraft pulp may be minimized by
alkaline papermaking conditions. Some benefit of alkaline
conditions may result from reduced hydrolysis of cellulose
macromolecules (Wilson, Parks 1983; Nazhad, Paszner 1994).

Further benefits may be associated with reduced closure of pores
in the cell walls (Lindström, Carlsson 1982), and reduced
stiffening of fibers. Though papermakers adjust pH values in
various different ways, one type of additive stands out in terms
of adjusting the pH to minimize damage to fibers. Give up? That
additive is calcium carbonate filler. Recent recommendations for
archival papers require at least two percent calcium carbonate to
make sure that the paper remains buffered in a weakly alkaline
pH range to make it resistant to gradual embrittlement
(McComb, Williams 1981; Kelly, Weberg 1981; Anon. 1993).
Work by Pycraft and Howarth (1980) shows further that over-
drying of virgin paper is likely to harm the properties of the
fibers, if they are to be used later for recycled paper.
The Sludge Dewatering Press is Like a Little Paper
Machine: Recycling of paper requires more fossil fuels or
electrical energy, compared to new pulp and paper from wood or
sawmill waste. The recycling of paper also can produce a lot of
waste sludge. Nevertheless, recycling usually is regarded as
having a favorable net impact on the environment (Pajula, Kärnä
1995; Jorling 2000). A key goal of increased recycling helps
keep the rate of tree harvesting below the growth rate of new
trees.
Saving land-fill space is another motivation to recycle paper: it
turns out that chemicals can play a beneficial role in helping to
achieve this goal. The reason is that sludge from wastepaper
recycling can contain a lot of water (Dorica, Allen 1997;
Kantardjieff 2000). The water content adds to the weight of
sludge to be discarded, and it also makes it more fluid-like, not
the ideal characteristic for building a stable landfill. Chemicals

coagulants such as poly-aluminum chloride (PAC), essentially
the same coagulants used in paper formation, can be used to
assist pressing more water from sludge (Ghosh et al. 1985; Leitz
1993; Pawlowska, Proverb 1996). Side benefits of sludge
dewatering may include a) more stable, solid-like sludge, b) the
colloidal materials in the sludge will tend to be insolubilized in
polyelectrolyte complexes and precipitates, and c) the sludge
will be more valuable as a fuel source, if that option is
considered (Harila, Kivilinna 1999). In principle well coagulated
waste sludge is expected to have reduced rates of leaching.
Part II - Minimizing the Environmental Impacts of Each
Type of Additive
"You work for the paper industry? Then maybe you can explain
that smell when I drive into [you fill in the place name]." To put
the present discussion into context it is worth noting that most
recent public concern has been directed at issues other than
papermaking additives. Rather, greater attention has been
directed towards issues of pulping, tree harvesting practices,
paper recycling, and, yes, air emissions (Vasara 2001). Another,
possibly more authoritative measure of environmental concern
comes in the form of legislation. Pulping and bleaching have
been center-stage in the so-called "cluster rule" regulations
(Vice, Carroll 2001). While keeping this context in mind, we
still have to seriously consider the potential impacts of
papermaking additives, if and when they enter the environment.
The good news is that substantial progress has been
accomplished in the area of papermaking additives with respect
to their toxicity, their biodegradability, and their ability to be
removed from the water phase during wastewater treatment

(Jorling 2000; Hamm, Göttsching 1994; Swann 2000). Later in
Part II we will consider various papermaking additives, focusing
on their potential hazards.

Fig. 3. See article by Goettsching Fig. 4. Full description given by
(1993) Vasara (2001)

A subtle, and often overlooked influence on chemical additives
for papermaking comes in the form of Material Safety Data
Sheets. "MSDS" information often is kept in orange or yellow
loose-leaf notebooks, adjacent to places where industrial
chemicals are being used. As noted by Allen (1991), these
documents have encouraged a trend towards greater awareness
of what it being added to paper machines. Toxicity and safety
information in MSDS has provided a starting point for making
improvements, and making substitutions toward less toxic
materials.
After toxicity, perhaps the second most serious issue is
biodegradability of chemical additives for papermaking.
Essentially all excess water from US paper mills undergoes

wastewater treatment before it is discharged. Bacterial action
during the secondary wastewater treatment converts many
organic chemicals into benign forms, and most of the biological
oxygen demand (BOD) is consumed. Some approximate rules to
predict biodegradability have been proposed. For instance,
compounds that contain chlorine, nitrogen, sulfonic acid, or azo-
groups are more likely to resist breakdown during water
treatment (Hamm, Göttsching 1994). Other factors that appear to
hurt biodegradability include toxicity, long chain length of
polymers, branching, and chemical substituents along polymer
chains. Unsubstituted alkyl chains also resist biological
degradation (Swann 2000). The problem with persistent
chemicals is that they might have the potential to accumulate in
the environment or in particular organisms.
Wet-strength agents: Environmental concerns about wet-
strength chemicals are often associated with their monomer
composition, possible residual monomers, and the possibility of
regenerating these monomers and releasing them into the
environment. The traditional wet-strength resins most often used
for acidic papermaking conditions are based on formaldehyde
(Dulany 1989; Espy 1995; Spence 1999). Possibly in response to
these concerns, the usage of phenol-formaldehyde and
melamine-formaldehyde resins has decreased dramatically in the
US paper industry. Poly-amidoamine-epichlorohydrin (PAAE)
resins have been replacing the formaldehyde resins in most
paper applications requiring durable wet-strength (Espy 1995;
Fischer 1996; Spence 1999).
Besides the issues with biodegradability, users of wet-strength
agents face two additional concerns. First, difficulties in

repulping wet-strength paper increase the likelihood that the
fiber will be sent to landfills after its first use. Second, if
papermakers decide to repulp the wet-strength paper, one needs
to be concerned about the chemicals used as repulping aids.
Hypochlorite bleach is sometimes used to repulp wet-strength
broke (Espy 1992; Fischer 1997). Elevated pH or temperature
also may be required to redisperse the fibers. At a minimum,
recycling of wet-strength paper is likely to require higher energy
input in the repulping operation. That means that there is an
environmental price to wet-strength treatment; sometimes the
price is paid in terms of increased landfilling, sometimes in
increased water treatment requirements, and sometimes in
increased energy expenditures. The ideal, in terms of wet-
strength treatments, would be to find a non-toxic, biodegradable
material that provided efficient, durable wet-strength under
conditions of use, but which also repulped easily under slightly
higher temperatures and hydrodynamic shear conditions in a
repulping operation.
Dyes: Papermaking colorants tend to have relatively poor
biodegradability (Webb 1993; Wahaab 2000). Fortunately there
has been a trend towards dyes with relatively high affinity for
solid surfaces. That means that the dyes tend to leave the paper
machine as part of the product, not in the water to be treated. In
addition, dyes entering the wastewater plant tend to be removed
with biological sludge (Webb 1993). High affinity onto solid
surfaces is generally achieved by development and use of
relatively large, planar molecules - the so-called "direct" dyes.
Affinity for fibers is further promoted by the trend for more use
of cationic direct dyes, in cases where these are appropriate.
Jackson (1993) noted that dye suppliers can minimize adverse

environmental impacts by careful selection of adjunct materials
used to stabilize liquid dyes.
Acrylamide copolymers: Considering their benefits in reducing
the waste of unretained fines, it is easy to love retention aids.
Copolymers of acrylamide are the most widely used very-high-
mass flocculants to promote fine-particle retention. On the one
hand, acrylamide products are expected to contribute much less
to biological demand (BOD), compared to the amounts of starch
products needed to render equivalent benefits in terms of either
retention or dry strength (Iwasa 1993). On the other hand, they
are not easily biodegradable (Webb 1993), as is to be expected,
based on their molecular mass (Hamm, Göttsching 1994). The
maximum permissible level of monomers present in acrylamide
copolymers is 750 ppm, compared to 100 ppm in the case of
other polymers (Swann 2000). Acrylamide products have
received the more lenient limits due to their history of 40 years
of use in the paper industry without evidence of harm.
Another issue to consider is the use of mineral oil as the
continuous phase of common retention aid emulsion products
(Swann 2000). Oil introduced with retention aids probably is
mostly adsorbed by fibers, with no adverse effects. However, it
is possible to imagine a bad effect resulting from the following
sequence: a) a low-grade mineral oil, having a significant
aromatic content, is used in the formulation; b) some of the same
paper is recycled in a batch that includes colored papers; and c)
the paper is bleached with elemental chlorine (Fleming 1995;
Lancaster et al. 1992). Fortunately, this combination of
circumstances is probably rare these days due to the use of
purified, alkyl mineral oils and the elimination of elemental

chlorine from most pulp bleaching operations in the US
(Deardorff 1997).
Another way to address concerns about oils in retention aid
products is to eliminate them from the formulation. One of the
side-benefits of oil-free formulation can be a substantial
reduction in shipping weight and transportation costs for a given
amount of active materials. Many water-in-oil retention aid
emulsions have active solids contents in the range of 25 to 50%
(Horn, Linhart 1991). Dry granular or "bead" acrylamide-type
flocculants, which have been available for many years, have
nearly 100% active content. If it weren't for the perceived
convenience of pumpable liquid formulations it is likely that dry
products would enjoy more widespread use. An especially
elegant solution to this dilemma involves a dispersion of
acrylamide-copolymer particles in aqueous solutions (Feng et al.
2001). Normally such copolymers would dissolve in water, but
the ion concentrations can be adjusted to prevent this from
happening.
Highly cationic copolymers: Efforts by papermakers to
conserve fiber resources and water have led to increased usage
of highly charged cationic polymers. One of the ways to
conserve fiber resources is to use high-yield pulps, such as
thermo-mechanical pulp (TMP). Wood pitch from TMP can be a
source of tacky deposits on papermaking equipment, forcing the
mill to shut down often for cleanups (Back, Allen 2000).
Another way to conserve fiber is through recycling. Wood pitch
is less of a problem with recycled fibers, but the problem is
replaced by stickies from pressure-sensitive adhesives and
coating latex (Hsu 1997; Douek et. al. 1997; Venditti et al. 1999;

Wilhelm et al. 1999). Some of the tackiness problems can be
minimized by use of talc (Braitberg 1966; Allen et al. 1993).
Also the furnish usually can be treated with highly charged
cationic materials such as polyethylene-imine (PEI),
polyamines, or poly-diallyldimethyl-ammonium chloride (poly-
DADMAC). Such cationic treatments can help to bind the tacky
materials to fibers so that they can be purged from the system
(Gill, 1993; Fogarty 1993; Shetty et al. 1994; Magee, Taylor
1994; Moormann-Schmitz et al. 1994). Highly cationic
polymers or soluble aluminum compounds are used for the
neutralization of excess anionic colloidal charge in papermaking
furnish - often the first key step in optimization of drainage and
retention systems (see references cited in Part I). Yet another use
of highly cationic polymers is in the spraying or forming fabrics
or press felts to inhibit deposition of tacky substances from the
paper (Allen 1991; Sawada 1997); here again, the use of these
agents is helping in the effort to use wastepaper and high-yield
pulps, both of which are worthy environmental goals.
Highly substituted, synthetic polymers of the type used for
precipitation of tacky materials and the neutralization of excess
colloidal charge are not expected to be highly biodegradable
(Hamm, Göttsching 1994). For example Wahaab (2000)
observed very poor biodegradability in the case of a commercial,
highly cationic polymer used for treatment of forming fabrics.
One step towards addressing concerns about possible
environmental impacts of highly cationic polymers is to avoid
using more than is needed. For instance in the spraying of
forming fabrics it is possible to minimize the chemical use by
proper dilution and by use of a well-designed spray boom

(Sawada 1997). When used to neutralize excess colloidal charge,
it is possible to avoid overdose of highly cationic polymers by
carrying out online or laboratory charge titrations with streaming
current instruments (Bley 1992; Stitt 1998; Phipps 1999; Gill
2000; Rantala, Koskela 2000; Chen et al. 2001). Charge control
to the neutral range has the advantage of tending to maximize
precipitation of most polymers and fines onto fiber surfaces,
reducing the amounts of polymeric and colloidal substances that
are sent to the wastewater treatment system.
Recently there is yet another option to consider, the use of
highly cationic polymers based on starch or other natural
products. Already a highly cationic polymer based on starch has
been used for charge neutralization and optimization of wet-end
operations (Vihervaara, Paakkanen 1992). Presumably such
materials might be more easily biodegraded, compared to their
synthetic counterparts. "Not necessarily so," says Reinbold
(1994). Rather, there is a wide range of variability in the
biodegradation of both natural and synthetic polymers.
Biocides: Conventional slimacides are highly toxic. They have
to be to perform their function. Many do not break down readily
during treatment of wastewater (Webb 1993). Concerns over
these types of biocides have resulted in pressure against biocide
use for papermaking in Sweden (Swann 2000). One of the goals,
then, is to develop biocides that do their job and then self-
destruct (Allen 1991).
Enzymes are very good at self-destruction. The fragile nature of
enzymes is due to the fact that they consist of complex proteins
with many loops and coils that have to fit together in an exact
way to perform some kind of function. Even moderate changes

in pH or temperature can temporarily or permanently destroy the
enzyme's activity. Enzymes such as amylases are already used
for cleaning up deposits on starch-preparation equipment and
paper machine wet-ends (Swann 2000).
Another way to minimize the need for toxic agents to control
slime involves biodispersants (Crill 1993). Biodispersants make
sense because bacteria attached to surfaces, the so-called
"sessile" bacteria, tend to cause more problems than freely
floating bacteria in paper mill systems. Although it is premature
to expect that biodispersants can eliminate the need for toxic
biocides, or of oxidizers such as chlorine dioxide, it is
reasonable to expect the dependency on such materials to be
reduced.
Starch: Starch products probably wouldn't even be included in
the present discussion, but for the fact that the paper industry
uses so much of them. The largest proportion of starch is added
to the surface of paper at the size press or in coating
formulations. Additional starch is commonly added at the wet
end in levels up to about 1% on paper mass. Native,
underivatized starch is close to ideal in terms of its
biodegradability (Hijiya 1999). In addition to providing strength
and helping certain retention aid programs, starch products also
are based on a renewable resource. The most common grade of
starch used in the US is a byproduct of processing corn
sweetener for soft drinks and other processed foods. The trouble
is, size-press starch often makes up 1 to 5% of the mass of
various paper products. This is certainly true of printing papers.
Since the kinds of starch most often used at the size press are
poorly attached to fibers, large amounts of starch can become

solubilized through the repulping of dry-end broke. Such starch
is likely to be a major contributor to BOD of liquid effluent from
the mill. In other words, the problem is in the large amount of
starch products in the effluent water, not in their rate of
degradation in a well-run biological wastewater treatment
system.
Work carried out by Roberts et al. (1987) showed a very
effective way to minimize BOD contribution of starch in
effluent from paper machine systems. The answer is to use
cationic starch (Webb 1994). Roberts showed a case in which
about 85% of cationic starch was retained at neutral pH, whereas
only about 10% was retained when the experiments were
repeated with unmodified starch. It should come as little surprise
that most starch now added at the wet-end of paper machines is
either cationic or amphoteric (i.e. having both positive and
negative charged groups attached to the chain). The down side is
that cationization of starch appears to make it less biodegradable
(Hamm, Göttsching 1994). In summary, the higher retention of
cationic starch and its good, though not perfect biodegradability
make it highly beneficial in terms of overall environmental
impact of paper mills.
Sizing Agents: Internal sizing agents are truly remarkable in
their ability to transform the nature of paper, even when the
added dosages are typically well below 1% of the dry mass of
product. The chemical composition of wood-derived fibers
makes them highly water-loving. Paper uses for cups, bags,
cartons, and various printing applications can require that it
resist water absorption and penetration.

Rosin size has been criticized for its toxicity and for the fact that
rosin sizing usually requires the use of aluminum compounds
(Webb 1993). But rosin products can claim a positive attribute
not shared by the common alternative sizing agents; rosin is a
byproduct of wood pulping. Rosin is a renewable, biodegradable
material (Webb 1993). There is an interesting balance between
rosin's efficiency and its biodegradability; most rosin is reacted
with maleic or fumaric anhydride to produce "fortified" rosin
size. The fortified size is more storage-stable and more efficient
in use. However, it also is less biodegradable than natural rosin
(Webb 1993).
Though it still is worth considering environmental implications
of rosin size products, there has been a strong trend over the past
20 years towards alkaline papermaking conditions and the use of
calcium carbonate filler (Gill, Scott 1987; Laufmann et al.
2000). Values of pH higher than about 7 make it increasingly
harder to size paper with conventional rosin products (Liu 1993;
Schultz, Franke 1996; Wang et al. 2000). Fortunately, two
widely used "alkaline sizing agents" are available.
Alkenylsuccinic anhydride (ASA), which is very popular for
production of printing papers and gypsum board liner, is a
byproduct of petroleum (Webb 1993). By contrast, alkylketene
dimer (AKD) is made from fatty acids, a renewable resource. In
either case, alkaline sizing agents tend to be much more efficient
than rosin in terms of the amounts needed to reach equivalent
levels of resistance to fluids.
Surfactants: Some surface-active materials are added to paper
intentionally, whereas others come along for the ride as
stabilizers for other chemicals or as residuals from de-inking. If

we use a broad definition, then the list of intentionally added
surfactants would include sizing agents (e.g. rosin soap size),
components of certain defoamers (i.e. water-insoluble
surfactants), certain deposit-control additives, and debonding
agents used in certain tissue products. Various nonionic and
fatty-acid-based surfactants are used in flotation de-inking
(Johansson, Ström 1998; Rao, Stenius 1998) and for the
agglomeration of xerographic toners (Darlington 1989;
Heitmann 1994; Bast-Kammerer, Salzburger 1995). Nonionic
surfactants also are used to stabilize such additives as retention
aid emulsions, dyes, and certain sizing agents.
Probably the most obvious adverse environmental impact of
surfactants would be cases of visible foam. But the more serious
impacts should be evident to anyone who has opened their eyes
in soapy water, or when shampooing. Has anyone interviewed a
fish on this subject?
Issues of toxicity and persistence have been raised in the case of
non-ionic surfactants (Hamm, Göttsching 1994). Nonylphenol-
ethyoxylate products have been replaced, especially in Europe,
due to concerns about their toxicity (Swann 2000). Linear alkyl
(or alcohol) ethoxylates have taken their place in many
applications. Though the latter are not regarded as toxic, the
saturated alkyl chains tends to make them poorly biodegradable
(Swann 2000). Perhaps the next logical extension is to use
unsaturated aliphatic (alkenyl) poly-ethers. Alternatively,
perhaps the most economical solution is to do a better job at
removing surfactants before effluent water is discharged.
Chelating Agents: The most common function of chelating
agents such as diethylenetriaminepentaacetate (DTPA) in

papermaking is to keep certain metal ions from interfering with
peroxide bleaching of mechanically defibered pulps. Strictly
speaking this is not an issue of wet-end chemistry; usually the
pulping and bleaching operations are regarded as separate from
papermaking. That matter aside, the problem with chelating
agents is that they resist biodegradation (Göttsching 1993;
Hamm, Göttsching 1994; Reinbold 1994). The potential adverse
effect of persistent chelating agents follows from their likely
tendency to interfere with natural uses of calcium and other
metals in aquatic organisms. Since peroxide bleaching is often
used for recycled pulp, especially when it contains mechanical
fibers, there is active interest in finding biodegradable
alternatives to chelating agents. One approach is to use
sequesterants such as silicates. In layman's terms, a sequesterant
is something that binds objectionable metal ions less efficiently
than a chelating agent, but enough to permit peroxide bleaching.
Since the byproducts of peroxide bleaching tend to be non-toxic,
it would be highly beneficial to find other ways of increasing its
efficient use in pulp mixtures that are likely to contain
manganese, iron, and other divalent transition metal ions.
While on the subject of metals, it is worth considering the
environmental consequences of heavy metals in effluent from
paper mills. In the past there were concerns about heavy metals
in various printing inks. As noted by Göttsching (1993),
papermakers have to work with their associates in publishing
and converting companies to avoid contaminating the waste
fiber supply with persistent hazardous materials. D'Souza et al.
(1998) observed that between 75% and 100% of various metals
entering a paper mill system by way of waste paper were
removed as a component of sludge. However, the levels of metal

in the sludge, and also in the product, were both below the level
of concern.
Part 3 - A Vision for the Future
"I don't know what they do in those buildings next door. They
seem to do a lot of business and process a lot of waste materials.
They seem to ship a lot of product. They always keep their lawn
mowed and the people are always polite." My vision for the
future paper mill is that it should be "invisible" in terms of its
effects on the environment. Neighbors, from urban people to
rural fish, ought to hardly notice its presence. The goal of Part 3
is to consider what kinds of wet-end additives and related
processes are likely to take place in that paper mill.

Fig. 5. Paper technologist thinking of Fig. 6. Using the other dictionary
word "chemistry." definition of "chemistry"

"Fiber-Friendly"
A lot of effort and capital goes into the production of fibers from
wood, as well as from alternative fiber sources such as sugar

cane residues (bagasse), straw, and cotton. These are renewable
resources. When managed properly, every tree that gets
converted into pulp for paper products gets replaced by new
planting and new growth of trees or other fibrous materials.
Actually, the situation is even a bit more complicated than that.
Rather than using all trees cut from the forest, the paper industry
gets much of its wood fiber in the form of used paper an waste
from lumber mills and related operations (Smith 1984; Kramer,
Jurgen 1998).
Even before one considers the effect of papermaking additives,
plant fibers already have the following highly desirable
attributes: a) they easily bond to each other without needing any
glue; b) they can easily be redispersed in water and formed into
recycled paper; c) they do not originally contain toxic materials;
and d) after they have become too degraded or contaminated to
be worth recycling, they still can be used for energy generation
(Göttsching 1993; Delefosse 1993; Norris 1998; Weigard 2001).
By using fibrous waste products to fuel power boilers at the
paper mill it is possible to displace some of the need for fossil
fuels and also reduce landfill requirements. Landfilling of paper
products can result in production of greenhouse gases such as
methane (Wiegard 2001), so it makes more sense to use waste
wood products for fuel and leave more petroleum, natural gas,
and coal reserves in the ground.
Having said all these nice things about plant fibers, especially
those from wood, one of our high priorities as an industry ought
to be aimed at preserving their quality and in continuing to use
renewable plant fibers as the main component in our products.
Calcium carbonate is known to inhibit aging of paper by

buffering the pH in the alkaline range. By contrast, acidic paper
tends to become embrittled during drying and storage, and the
cellulose molecules gradually suffer hydrolysis (McComb,
Williams 1981). In addition to its beneficial buffering ability,
calcium carbonate may be preferred over clay products due to a
relatively high purity of its deposits, so that mining of CaCO3
generates less volume of "pits" in the ground and "piles" of
tailings (Webb 1993). In cases where sludge from treatment of
paper mill wastes is used for compost, the calcium carbonate
provides useful pH buffering.
Mineral fillers, though abundant, are non-renewable, so there
seems little point in trying to load up paper with high
percentages of calcium carbonate, beyond what is needed to
achieve opacity and smoothness specifications; rather it has been
suggested that papermakers ought to concentrate on achieving
high smoothness and covering the paper with relatively thin
layers of mineral-based coatings (Lindström 1994; Swann
2000). In that way any printing inks are likely to adhere to the
coating materials and the fibers can be more readily recovered
"clean" when the resulting wastepaper is de-inked and recycled.
A recent project at North Carolina State University has involved
efforts to minimize or compensate for loss of bonding ability of
kraft fibers when they are dried (Zhang et al. 2000). The vision
that comes out of this type of work is that fibers ought to be
treated gently during each cycle of papermaking. One of the key
strategies in this regard is to avoid excessive drying
temperatures or very low moisture contents, i.e. "over-drying"
(Pycraft 1980). It also is recommended to avoid excessive
energy or intensity of pulp refining (Baker 1995). In this regard,

dry-strength chemicals such as cationic starch can help to
achieve strength objectives with moderate savings in refining
energy. Our recent work indicates that the proportional effect of
dry-strength additives added to never-dried pulp may be greater
when the fibers are recycled, compared to their effect on the
initial paper.
"Water-Friendly"
In a paper mill of the future I envision that not only fiber, but
also water, is handled as a precious resource. Future mills are
likely to be choosing between the following two alternatives: a)
continue the gradual trend of many years towards operation with
less and less fresh water per unit of product (Springer 1978;
Swann 1999); and b) operate with zero or very little discharge of
liquid effluent - in a so-called "closed water cycle" mode
(Pietschker 1996; Wiseman, Ogden 1996). In either case I
envision that paper mill operations will increasingly turn to their
own wastewater treatment systems as a source of "fresh" water.
The logic is as follows: Some level of treatment is required even
of "clean" water from rivers or springs to remove sand, humic
acids, and to control microbes. On the other hand, a paper mill
will already have expended considerable effort in purifying the
wastewater; it may be cleaner in some respects than untreated
"fresh" water. In fact, some system already in place to condition
white-water for internal re-use are very similar to conventional
primary clarification of wastewater (Sugi 1997).
Not only are future paper mills likely to reuse some of their
wastewater, but it appears likely that some of them will
essentially "bring the wastewater treatment plant into the paper
mill." The motivation for this trend is a need to control the

build-up of biological oxygen demand and colloidal materials - a
probable consequence of increased recycling of both fibers and
water (Pietschker 1996; Zhang 1999). Successful applications of
this type of technology have been reported (Delefosse 1993;
Norris 1998). In some cases it is possible to justify the cost of
such processes as ultrafiltration (Norris 1998) and ozonization to
purify water to be reused in papermaking, whereas the same
treatments would be considered too expensive if the wastewater
were to be discharged (Demel, Kappen 1999). Combinations of
aerobic and anaerobic treatment have been recommended to
minimize the volume of sludge (Göttsching 1993; Demel,
Kappen 1999). Compact reactors for biological treatment may
make sense in terms of minimizing the volume of water as paper
mills begin to incorporate these operations as part of their
system (Tenno, Paulapuro 1999; Gubelt et al. 2000). The most
important attribute of paper chemicals, in order to be compatible
with the biological treatment systems just described, is
biodegradability. Some progress has been made in this area
(Hamm, Göttsching 1994; Wahaab 2000), but much more work
is needed.
Another essential part of efforts to reduce water usage is to
select combinations of additives that tend to "self-purge"
themselves from the system by becoming retained on fibers. In
principle that implies avoiding substances like simple salts,
sugars, and oils that have little affinity for fibers, even in the
presence of coagulants or retention aids. In isolated cases it may
make sense to remove excess salts by evaporation or reverse
osmosis (Wigsten 1995; Norris 1998; Tenno, Paulapuro 1999).
In principle it is possible to maximize the retention of both
colloidal and fibrous materials in paper by control of highly

cationic additives to achieve near neutral zeta potential (Bley
1992; Moormann-Schmitz 1994), followed by very-high-mass
flocculants to collect primary particles into a particles large
enough to be mechanically retained (Horn, Linhart 1991). It is
remarkable the extent to which these principles parallel those
used in treatment of fresh water and wastewater (Leitz 1993).
"Frugal of Energy and Raw Materials"
I envision the ideal paper mill of the future as being frugal in
terms of energy and raw materials. Losses of fine materials can
be reduced to very low percentages in the paper forming process
by use of an effective retention aid program on a paper machine,
plus the use of a saveall to recover fine material from white
water. Closing up the water system it is possible to conserve
heat (Springer 1978; Wigsten 1995). Hot water promotes more
rapid drainage, and extra heat energy has to be supplied to the
extent that fresh water is used. In these respects the paper
industry already seems to be doing a very good job.
Though the paper machine tends to be frugal, relatively large
amounts of fiber fines, fillers, and fibers can be lost when paper
is recycled (Paula, Kärnä 1995; Dorica, Allen 1997; Kantardjieff
2000). It is likely that much of such waste consists of ink,
colloidal materials, and fiber fines too small to be of much value
in papermaking. However there may be opportunities to recycle
the mineral content of waste paper or of sediment in the
clarifiers at paper mills. Studies have shown that it is possible to
"burn off" various organic materials and recover gray filler
particles that are useful for paper products with intermediate
brightness targets (Sohara, Westwood 1997; Johnston et al.
2000; Moilanen et al. 2000; Wiseman et al. 2000).

Further savings in energy, per ton of paper, are likely to come in
two areas. The use of chemicals to promote dewatering and
reduce the need to evaporate water was discussed already in an
earlier section. It is possible that further savings will be achieved
by reducing the amount of water that needs to be pumped. Said
another way, it will be possible to save electrical energy
expended at the fan pump by increasing the typical consistency
of headbox furnish. Higher-consistency forming has been
considered in various publications (Case 1990; Waris 1990).
Already, modern headbox designs have been helpful in being
able to still form uniform paper with slightly less water
(Kiviranta, Paulapuro 1990). But it seems that chemical
additives will be needed to that minimize fiber flocculation at
the higher solids levels. Conventional "formation aid" strategies
can have a devastating effect on drainage (Wasser 1978; Lee,
Lindström 1989). This is an area of wet-end chemistry that may
become important in the future.
"High-Tech"
It seems that no vision of the future ought to be complete
without the words "high tech." In terms of papermaking
chemicals, the key "high tech" trends to look out for will include
automation, new sensors, bio-engineered processes or additives,
and nano-technology. Recently it seems that nano-technology is
a growth area for research. In fact, papermakers have been
involved in nano-technology for many years. How big are the
colloidal silica "microparticles" used in drainage-enhancing
programs? The answer is "usually about 1 to 5 nm" (Moffett
1994; Andersson, Lindgren 1996; Swerin et al. 1996). So, in
fact, we already use nano-technology.

Bio-tech solutions are recently becoming important in the use of
enzymes for deposit control and slime control (Webb 1994).
Enzymes also can be used to reduce the cationic demand of
process water, especially in cases involving thermomechanical
fiber (Buchert et al. 1996). In the future we can expect to see
more progress in the use of enzymes to assist with strength
development and to promote more rapid drainage (Eriksson et
al. 1997).
The large-scale, continuous, capital-intensive nature of
papermaking operations make them attractive subjects for
improved process control strategies. The last couple of decades
have brought substantial progress in the development and
implementation of tray-water solids sensors (Bernier, Begin
1994; Artama, Nokelainen 1997). These have made it possible
to even out swings in first-pass retention by varying the addition
rates of retention aids. However, in at least one case it was
shown that the demand for retention aid was strongly correlated
with variations in cationic demand of the furnish (Tomney et al.
1997). Therefore it makes sense to control cationic demand as
well, with a goal of getting closer to the root cause of the
variations. Significant progress has been achieved in online
charge control, especially with automated streaming current
titrating devices (Tomney et al. 1997; Gill 2000; Rantala,
Koskela 2000). In principle the same type of data can be
obtained more accurately and reliably by a new streaming
potential titration method (Hubbe 1999). Other devices that are
likely to become more common, especially in large papermaking
facilities, include automated freeness testers (Lehtikoski 1991),
online evaluation of fiber flocculation (Wågberg 1985; Alfano et
al. 1998; Hubbe 2000), and automated monitoring of bio-films

related to the growth of slime deposits (Robertson, Rice 1998;
Dickinson 1999; Flemming et al. 2000).
Earning the "Good Chemistry" Label
The goal of "good chemistry" with the public, with our clients,
and with our investors will require a long-term approach. We
have to face the fact that papermaking is a highly capital
intensive enterprise with long lead times for new construction
and replacement of existing facilities. We cannot expect to keep
up with every new change in focus of environmental issues
(Vasara 2001). The challenge will be continue to make
meaningful, practical improvements in our practices affecting
the environmental even through changes of issues and economic
cycles.
So what about the "chemistry" between the paper industry and
the public? We need to encourage an atmosphere of "working
together" on environmental issues for the sake of long term
progress is exemplified by a Wisconsin initiative to create a
private-public partnership (Schmidt 1998). A focus on headlines
sometimes can lead to a view that our society is highly polarized
around issues of environmentalism versus profitability
(Reinbold 1994). However, a more cautious analysis of public
opinions reveals that the bulk of the American public tends to
see issues in a much more balanced light, compared to their
politicians (Wolfe 1998). Technical people in the paper industry
have a responsibility to be environmental advocates. Some
worthy environmental goals for papermakers include a)
continuing to rely mainly on a renewable, recyclable resource -
wood fibers, b) taking steps to avoid deforestation - by
replanting, recycling, and avoiding waste, c) minimizing water

pollution by careful development, selection, and use of wet-end
chemicals, and d) minimizing energy use. As noted by Siekman
(1998), some environmentally sound practices can be profitable,
in addition to their intrinsic benefits.
No, it probably wouldn't do much good to place an ingredients
label on each sheet of paper, or even on each ream wrap, carton,
or jumbo roll. But already there have been proposals to label
certain products as "eco-friendly" (Rogers 1993). For instance,
such labels could be awarded by an independent agency based
on a point system, with part of the score coming from such
issues as wet-end chemical practices, bleaching practices, or the
amount of energy used in the life-cycle of a product. Ideally this
ought to be a voluntary system, something like the ISO
certifications of paper mill practices. In that way, paper
companies will have the incentive to get their products certified
so that they have the right to label their products as "eco-
friendly."
Achieving "good chemistry" on the paper machine and with the
public will require more than good intentions. It will require
significant technological input and a long-term commitment on
the part of us in the industry to continue to make the needed
progress.
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