Fiber engineering: the key to industry change: imagine major benefits in our industry's efficiency, economics and product quality--without changing the basic papermaking processes. Fiber modification can make it possible.

Editor's note. This article is part of a continuing series of reports from the Forest, Wood and Paper Industry Technology Summit, held in May 2001 in Peachtree City, Georgia, USA. The Technology Summit was sponsored by TAPPI, AF&PA and the U.S. Department of Energy's Office of Industrial Technology.

All paper grades are dependent on the attributes of the fibers from which they are made. Mills use certain types of fibers in particular grades to achieve the most desirable properties. According to calculations using the Institute of Paper and Science Technology (IPST) Economic Model, fiber costs are typically the single largest component of manufacturing costs, ranging roughly from 22% (for newsprint) to 42% (for linerboard). Papermakers often must use fibers readily available to them at low cost even though these may not always be the ideal fibers for a particular grade. Mills could improve their operations if they had a way to modify, fibers so that any given fiber could be used effectively in the production of any grade. While this may not be a realistic goal, the ability to modify the bulk or surface properties of fibers, so that they provide new or enhanced benefits or reduced costs, is a very worthwhile objective.

Since papermaking unit operations also create unwanted (and harmful) changes in the cell wall structure, it is currently impossible to obtain all of the beneficial structural changes (both physical and chemical) in fiber cell walls desired for key product attributes. Operations such as chemical pulping and bleaching, relining of chemical pulps, fiber separation, development of fibrillation in mechanical pulping, and dislodging ink particles and other foreign material flora recycled fibers typically do not contribute just a single beneficial change to the cell wall structure. Instead, they often provide a multitude of structural changes in the cell wall structure. The simultaneous appearance of wanted and unwanted structural changes in the fiber cell wall means that paper product attributes made from these fibers are always a compromise. Many operations used to enhance fiber properties are not precision processes; rather, they resemble sledgehammer-style operations.

FIBER ENGINEERING BASICS

Paper is unique in that pulp fibers come together during consolidation of the web via surface tension threes and then bond naturally through hydrogen bonding. No adhesive is required to produce a reasonably strong sheet. Yet the strength of the bonds, as well as other web properties, depend on a number of factors: the type of fibers, fiber morphology, the nature of the pulping method, the extent of fibrillation, and so on. Some argue that the building blocks of paper are not the fibers at all but rather the cell wall material of the fibers.

While strength is required in virtually all paper grades, there are other attributes that may play an equal or greater role than strength in the end product (for example, opacity, brightness or absorbency), for which certain fiber properties will be more important than just the ability to develop strength. (It is rather amazing that so many grades of paper, with different end use requirements, can be made from the same fiber type. The diversity of such grades must also be considered when contemplating the engineering of certain fiber attributes.) Because wood pulp fibers are the foundation of the papermaking industry, it is surprising that the area of fiber modification--the development of superior wood pulp fibers-has not received more emphasis.

Based on these facts, there is a compelling need for fiber engineering (modification) that can yield specific fiber attributes required for converting and end-use performance. Researchers expect fiber engineering to be an integral part of: higher value raw material supply, significantly reduced manufacturing costs, improved energy performance, and new forest based materials; plus, it quite possibly will lead to products and processes with superior environmental performance. Enhanced fiber attributes are needed to deliver higher value and, most likely, will be required to assure new forest based materials. Enhanced fiber attributes could be significant in the drive to reduce manufacturing costs. Improved energy performance opportunities are strongly related to mechanical fiber liberation processes. In fact, as depicted in Fig. 1, one could say that fiber modification is the key to change in our industry.

[FIGURE 1 OMITTED]

Clearly, the development of superior engineered fibers must be a high priority for all these areas, with this in mind, the broad goals of fiber modification must be:

* To seek innovative ways to enhance fiber-fiber bonding so that fewer fibers are required to produce the same sheet strength

* Develop innovative ways to enhance fiber performance in grades where attributes other than just strength are of primary importance

* Find ways to use the fibers developed above in other grades, or in completely new grades of paper.

GAP-FILLING TECHNOLOGIES

There are at least four ways fibers can be modified, or "engineered":

Genetic modification: This is a long-term approach to providing higher fiber value. There is considerable overlap here with the areas of sustainable forestry (see Solutions! June 2002, pg. 55) and new forest based materials (see Solutions! May 2002, pg. 55). The primary difference between these and fiber modification is that the latter is very focused on sheet structure and product attributes. A major question is "What fiber attributes would you attempt to change genetically?" For example, should we strive to eliminate the $3 layer (which contributes little to sheet properties), make S1 as thin as possible or eliminate it, or perhaps strengthen the interface between S1 and S27 Can we control the relative amounts of cellulose, hemicellulose, and lignin?

Chemical or enzymatic modification: Either of these approaches to fiber modification may focus on the bulk of the fiber or just the surface of the fiber. For example, could we modify the surface of mechanical pulp fibers so that they behaved more like chemical pulp fibers with respect to bonding?

Mechanical modification: We know a lot about refining, but clearly, there are still things we need to understand. Is it possible, for example, to develop mechanical (microsurgical-type) modifications of fibers in fiber separation during mechanical pulping, or carry out controlled modification of the fibrillar structure of the cell wall? Mechanical separation technologies based on certain fiber characteristics (such as coarseness, curl, or surface energy) could let us obtain .just the population of fibers that need treatment. This could save refining energy, since we would not treat fibers that did not need it. Are there alternative refining methods that could optimize the transfer of energy to the fiber that would enhance and control fiber quality?

If the industry could use these modification approaches on a commercial scale, it should be able to obtain papermaking fibers that improve the efficiency and economics of paper production and give papers better converting and product attributes. Thus, the creation of new genetic, enzymatic or microchemistry, and micromechanical modification technologies form the most promising approaches for creating (only) beneficial changes in the cell wall structure. This was the starting point for the work of the Fiber Engineering Team at the Technology Summit.

The team used two other boundary conditions: (1) that the applications of the engineered fibers should be for "ordinary" paper and board grades and (2) that modification costs should be modest. In other words, the team did not consider exotic new applications for engineered fibers and assumed that treatments should have a minimal additional cost contribution to the overall cost of the fiber.

PROPOSED RESEARCH AREAS

The Fiber Engineering Team discussed a broad number of possibilities in each area. These were reduced to the following high priorities.

For genetic fiber engineering area, the team identified the following research priorities:

1. Lignin modification: Identifying mechanisms that control lignin quantity and quality

2. Biosynthesis interactions: Identifying interaction mechanisms between various wood components

3. Glucomannan: Identifying the formation pathway and eliminating glucomannan formation

4. Improved fiber bonding: Identifying the pathway for xylan and then controlling its content, distribution and structure

5. Cell wall model: Developing micromechanical models to predict fiber properties for different physicochemical structures of the cell wall.

These priorities are also linked with the Sustainable Forestry platform. The team also listed a number of topics that would likely be of prime importance for the genetic fiber engineering area. For example:

* Fiber engineering through tree breeding and genetic engineering will likely proceed faster in hardwoods.

* Hardwoods will likely be developed for fine papers, tissue, and print surface on packaging grades, whereas softwoods will be developed for packaging and mechanical printing grades.

* Complete lignin control will significantly impact pulp yields and enhance fiber liberation, yellowing, mechanical pulping, chromophores, bleached pulp yield, and perhaps growth rate.

* Hemicellulose control will affect bonding and thus opportunities to lower basis weight at constant strength and/or increased filler.

* Exploiting natural variation through tree breeding remains key. Rapid analytical techniques will be needed to map natural variation of wood properties.

In the microchemical/enzymatic fiber engineering area, the team identified the following most important research areas:

1. Microbial genomics evaluation, in order to discover more effective enzymes and to modify the enzymes for specific (customized) activity in pulp and paper applications

2. Modification of fiber surfaces with additives or enzymes to provide new properties to fibers and subsequently papers and boards

3. Intelligent fibers that respond to external triggering

4. High-yield fibers that behave in certain properties like chemical pulp fibers

5. Specialized treatments of fibers to achieve given properties, such as fiber fractionation (springwood vs. summerwood) for different chemical/enzymatic treatment

6. Precipitation of (nanoparticle) fillers into the cell wall pores and into the lumen cavity to improve on existing technologies.

In the mechanical fiber engineering area, the team listed the following 10 research areas as most relevant:

1. Develop new methods for energy transfer to fibers during mechanical pulping

* Shear vs. compressive forces in refining

* Treatment of individual fibers vs. flocculated fibers

* Apply principles of fracture mechanism to improve understanding

2. Alternatives for traditional (bar-groove) refining of chemical fibers for better control of cell wall modification

3. Pretreatment of fiber surfaces prior to refining to better control modification of the cell wall (for instance, enzymes or absorption of suitable swelling agents)

4. Fiber selection by coarseness, degree of collapse, etc.

5. Engineer processes for strong, long, high-yield, high-scattering fibers

6. Engineer hydrophobic and hydrophilic surfaces to fibers

7. Engineer white lignin (lignin without chromophores)

8. Engineer fibers that can be easily reduced chemically

9. Generate covalent bonding sites on the fiber surface

10. Engineer non-yellowing mechanical fiber.

In this subclass, there are interactions with the proposed topics to other platforms and to other subclasses inside the fiber engineering generic class. For example, energy saving in mechanical pulping is related to the platform "Energy Performance." The contribution from the fiber engineering aspect should be that the new mechanical pulping processes can produce desirable structural changes to the cell wall and prevent (or minimize) the simultaneous occurrence of non-desirable changes.

RECOMMENDED RESEARCH AREAS

A four-person working group of the Fiber Engineering Team examined this list of potential fiber engineering research areas and recommended four major research areas:

1. Fiber modification: Modification of fibers and fiber surfaces with additives or enzymes to provide new properties that will (1) enhance fiber bonding, (2) use less fiber to provide desired product attributes, and (3) lead to new product lines. This recommended research area cuts across all paper and board product lines. This research area represents a mixture of basic research and process development.

2. Cell wall polymer biosynthesis: Identify molecular mechanisms regulating cell wall polymer biosynthesis, especially cellulose and hemicellulose formation, with the expectation that this understanding can lead to the control and impact of cellulose and hemicellulose on fiber properties. This recommended research area cuts across all the product lines. This topic represents mainly fundamental and basic research.

3. Micromechanical modeling of the fiber cell wall: Develop and validate a micromechanical model that predicts the properties of the fiber as a function of composition, geometry, and architecture. Such a model should provide guidance and opportunities to bioengineer desirable fiber properties. This topic represents both fundamental research and knowledge generation for deeper understanding of the behavior of the cell wall as a function of its physical and chemical composition. Models need to be verified with experimental data.

4. Alternative refining methods: Develop alternative refining methods that optimize energy transfer to the fiber to control specific structural modifications in the cell wall to enhance and control fiber quality and improve energy efficiency. This research area cuts across all product lines and covers both mechanical pulping and low-consistency refining of chemical pulp fibers. This topic represents a major process breakthrough.

Of the four recommended fiber engineering research topics, two deal with genetic, one with microchemistry/enzymatic, and one with mechanical fiber engineering.

RELEVANT CENTERS OF EXCELLENCE

The team developed this list of relevant centers of excellence (not prioritized) for each recommended research area. The team also provided an approximate timeline for each recommended research area, assuming a sufficiently well focused and capable team of scientists from two or three leading institutes.

1. Fiber modification: IPST, Paprican, HUT, STFI, VTT and plant-based macromolecule research institutes; timeline is 5 years and commercialization

2. Cell wall polymer biosynthesis: MTU, OSU, NCSU, IPST, U. Tolouse, Carnegie Institute; timeline is 5-10 years for lignin, 10-15 years for celluloses

3. Micromechanical modeling of the fiber cell wall: IPST, U. Karlstad, STFI, Paprican; timeline is 5 years

4. Alternative relining methods: GIT, Paprican, Tampere U. Technology, HUT, STFI, VTT, Abo Akademi, Finebar, and enzyme, metallurgical and material processing institutes; timeline is 5 years for chemical pulping, 5-10 years for mechanical pulping.

POTENTIAL FUTURE ISSUES

Some of the research challenges are so large that they offer the possibility of collaboration between the North American and European paper industries, using the Framework Research money from the European Union and corresponding federal money in the United States and Canada. One must keep in mind that paper and packaging grades compete against other materials, such as electronic media and polymers.

The recommended research areas proposed by the Fiber Engineering Team are central to the industry's competitive future. They are linked to the effective use of raw materials, the efficiency and economics of papermaking, and the delivery of new product attributes in the final product. They also do not require any radical changes in current papermaking or converting equipment or final product use environment.

IN THIS ARTICLE YOU WILL LEARN;

* Why current chemical and mechanical processes are not enough to unlock fiber's true potential.

* How fiber engineering has the potential to affect every grade and papermaking process.

* Four ways fibers can be engineered to produce superior results.

* What research is still needed, and how long experts expect that research to take.

ADDITIONAL RESOURCES:

* For Technology Summit information: www.tappi.org/ctosummit.asp

* The U.S. Department of Energy's Office of Industrial Technology's home page: http://www.oit.doe.gov/forest/forest.shtml

Session Membership:

Kari Ebeling, (Co-chair)UPM-Kymmene Gary A. Bourn, (Co-chair)IPST Dan Cullen. U.S. Forest Products Laboratory Ergilio Claudio DaSilva, Aracruz Celuloses S.A. Robert Eckert, Weyerhaeuser Company Guy Goldstein. Georgia Pacific Europe Stephen Kelley, U.S. National Renewable Energy Laboratory David E. Knox, Meadwestvaco David McDonald, PAPRICAN John MacKay, IPST (Alternate) Gary Peter, IPST David Robinson, Fine Bar Tapani Vuorinen, HUT

About the author: Gary A. Baum, former vice president-operations at IPST, retired at the end of June after more then 24 years with the Institute. His new company, PaperFuture Technologies LLC, is devoted to application of new techniques end uses for paper.