A new spotlight on fibers

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Lately a lot of focus and attention was placed on fibers and the recent development pertaining to strength developments and convertibility improvements based on fiber origin.

I would stress to say, that nothing is new under the sun, but the latest development in both test methods and raw data analysis tools have re-opened the vast opportunities that lay within the starting point in all tissue, paper and board making: the actual fiber. In retrospect, the fiber as primary root cause of both improvements and limitations seem to get attention every 20-25 years or so. We are currently at the beginning of such a, roughly, 5-year span of interest when the established view is being challenged and exchanged for new insights. Especially in tissue.

The papers presented within the technical session no 2 at Tissue World in Milan called Raw materials and fibers: properties, morphology & sustainability focused on currently used fibers, upgraded or modified fibers and new fiber resources for higher degree of sustainability. In this brief article, I will discuss the certain aspects presented and try to form an educated guess as to what we will see next within the field of fiber resources and how that will impact the global supply of fibers as well as tissue, paper and packaging product performance. It will be evident, that we at Rise are firm believers in the opportunities which now are being developed within stock preparation and fiber resources, and that there are great expectations on abilities to shape and decide final product qualities in all directions (MD-, CD- and Z-direction) in the near future. Quite literally; enabling mills to use very simple tools and plan their production accurately and consistently with 3D furnish engineering. It doesn’t appear to be the Holy Grail anymore, but rather within reach. We’re currently seeing a new dawn for the power of the fiber.

The new fiber resources

As Fibria put it in their paper; pulp is the single most important cost item in tissue. No matter how you address costs with internal controlling means, pulp is consistently a worry, risk and still paramount for production, naturally. To achieve the decided characteristics for different final products, may it be bulk, softness, absorption, tensile strength and more, choosing the right fiber resource, pulping and stock preparation technologies will continue to have a profound and very dominant standing. Add the sustainable business demand imposed by government regulations and or customer behavior and trends, and you’ll have more than good reasons to continuously research new and improved ways of achieving both a product for now and the future, as well as, sustainable profitability by keeping production costs in check.

One very interesting road to embark on would be to choose different fiber raw material than commonly used, which Mark Lewis described in his paper «Pulping non-wood fibers with lower water, energy and chemical input». As agricultural resources amount for 73 percent of the total NA biomass potential (forest and agricultural put together) there is a huge opportunity in utilizing the residual agricultural fibers otherwise lost. Especially in comparison to the actual output referred to as production rates per acre which could be up to 17 times higher than that of Douglas Fir. Over the years, it’s not far-fetched to say that almost all different fibers found globally have been examined, tried and judged based on earlier available and known processes and pulp and paper grades.

The recent nanocellulose and lignin research findings and applications have, however, opened a whole new era of possibilities to control and shape a future for a more sustainable future and worldwide bio-economy based on all kinds of natural and biodegradable materials rather than the fossil fuels of today. These new fibers have with modern technologies been proven to have quite different and perhaps even better characteristics for the applications now being developed.

And with further improved pulping processes, a deeper understanding of the characteristics of each fiber resource (e.g. wheat straw, bagasse, barley, bamboo) both from the scale of laboratories and implemented through pilot trials and full-scale machine trials at mills, there is ample potential in improving both processes and sustainability.

The Eucalyptus challenge

The most important product properties for many tissue and fluff products are strength, wet resiliency, absorbency, and haptic properties. In some cases, these properties conflict with each other or with the efficiency and runnability of the production process. Every tissue mill is in a constant struggle towards an objective to understand and quantify the relationship between fiber types, production process and properties of the final product, which should be produced at lowest cost possible.

In respect to strength properties, a common strive for the tissue makers in some parts of the world is to reach the same strength properties, both in dry and wet state, with a lower amount of fiber material. When designing the product properties, the selection of the fiber type and its treatment are critical. The use of cost-effective fibers, for example eucalyptus pulp, is increasing rapidly and gives a better softness in comparison to softwood fibres. Softwood fibers, on the other hand have advantages when it comes to strength-related properties, and the runnability in the tissue and converting machine.

Treatment processes to modify the fibers for better strength – and tear-related – properties must be used carefully, as they often imply higher energy costs, deteriorated dewatering properties, and a loss in softness. Strength agents can be added, but again, the effect on other properties must be understood. Absorbency can be substantially increased through bulking of the product, however, without compromising strength properties. Here it is also important that the bulk is maintained even when the product is wet. That said, Fibria’s presentation showed a very interesting approach to improve the eucalyptus strength issues into a higher tensile niche for the pulp by improving the bonding ability. By adding a biopolymer in their preparation process, the aim is to use the enhanced bonding ability of the fibers, and hereby «shifting the tensile x drainage behavior to a new level». The new pulp quality named EucaStrong® has been tested both in laboratories and on several commercial case studies which make their case for their new pulp as: aggregating the benefits of the eucalyptus and strength brought by SWKP; reduces costs through long fiber substitution and lower energy consumption; higher softness should also be reached thanks to the above; in some cases, the output of tissue production increased due to improved drainage and drying.

FIGURA 3

Not only Fibria is targeting resource efficiency as achieving the same function with less raw material and production energy. There are recent research findings giving examples of how to achieve this by e.g., the use of strength agents and more efficient dewatering through higher wet pressing temperature.

As smooth, yet strong, as can be

Haptic properties, such as smoothness and/or softness, should be improved continuously, again however, without compromising strength and absorbency. In general, we at Rise believe strongly that there is a need for better characterization methods for in-depth analysis of the haptic appearance of the product, as well as, the structure of the raw material, the tissue base sheet and the absorption process. The softwood fiber is, paradox to its name, not optimal for softness in tissue. Instead, the hardwood fibers are giving the better haptic performance. As in life, there are always compromises to be made and sound production economics makes for softwood addition in the process for enough strength throughout the processes – not only the tissue making process, but perhaps more importantly, the converting processes.

As our senior expert Mr. Mattias Drotz also mentioned in his presentation «Influence of pulp and process parameters on the strength of low grammage sheets», one needs to understand the multivariable aspects of the compromises made in tissue and paper production. In his studies presented in Milan, the main target was to understand the differences between softwood and hardwood and study the new methods of measuring strengths – the dry state strength methods were investigated with converting issues discussed. He could show in a newly developed IR technique for evaluating tear resistance, that the tear strength in dry state is heavily dependent upon fiber resource: the crack propagation showed significant differences in both time and route, which will be researched further.

Coming back to what I stated in the beginning of this article; We’re currently seeing a new dawn for the power of the fiber. And by that, I mean that there is so much more to be researched to unlock all the secrets required to create a cookbook filled with recipes of optimal products prepared by al kinds of ingredients. In the future, the specific relationship between raw material, production process and properties of the final product in detail both using standard and new unique methods for characterization of products and their convertibility, should be researched in detail: Different raw materials need to be investigated; softwood and hardwood and mixtures thereof; modified pulps; fiber-based strength agents; CTMP, chemicals, exotic pulps, and bio-based thermoplastic fibers etcetera.

In Mattias work, the influence of the production process conditions will be correlated with the achieved product properties using unique laboratory equipment, pilot-scale trials, and full-scale implementation. One additional step has already been planned and will also be carried out under the new research programme 2018-2020: to create a database with collected toilet, napkin and handkerchief, and towel samples which could also be used for a geographical mapping of product properties.

Morpheus

Quite interestingly, Morpheus was the greek god of dreams, and the common dream for tissue producers is to find more cost-effective fibers and still keep or improve final product properties. As mentioned, the usage of cost-effective fibers, e.g. eucalyptus, is growing fast since it often gives a better softness in comparison to softwood fibers. Though, one needs to be aware of shorter fibers also having distinct disadvantages, such as runnability issues in the tissue and converting process. To study this more in detail, novel methods are currently being developed for the analysis of furnish (for example, the fiber morphology distribution), products, and their convertibility.

Related to strength properties, the influence of fiber morphology on the mechanical properties should be investigated. Tuomo Niemi from Metsä Fiber presented some very interesting analysis regarding the role of softwood fiber morphology in runnability of a toilet line. In his paper, he compared the performance of different softwood pulp morphology (fiber length and coarseness) in toilet tissue production including converting. The results were very indicative and in short could be summarized as:

  • The fiber number in SW pulp is important in base paper production and converting. It was described as Fiber number = 1 / (L * C) where L is fiber length, mm and C is coarseness, mg/m.
  • High fiber number gives better first pass retention and high formation potential; lower loss in both MD and CD tensile strength in converting
  • High hemicellulose content in SW pulp means low refining energy need; low refining energy gives higher DS at press 1% increase in DS at press leads to 3 €/t of cost savings in base paper production
  • The use of high quality NBSK is the key issue for the overall production efficiency of a toilet tissue line.

With those results, it would be really interesting to push even further and put a special focus on tearing properties, which are important both for the ball-burst strength and the embossing process in even further detail. For example, by using a thermography method, the width of the rupture zone during a tearing experiment could be investigated for different pulps as those researched by Tuomo. The influence of the moisture content on the deformation properties of low grammage webs and tissue base paper sheets could mean huge benefits in a converting process if a higher moisture ratio could give higher bulk values and softness.

Clearly, the converting process faces many issues ranging from micro and macroscale deformation to the dusting propensity of different pulps and tissue products. Many of these require quite detailed and novel technologies to be analyzed properly. What Tuomo presented is a very good indication on the potential that lays therein.

The power of existing equipment

Finally, even if we’re declaring our current process status as “Back to Basics” with the argument for the Fiber Source as the most valuable tool, there are also the process equipment to consider in ensuring to utilize the fibers to their potential and not destroy any properties, may it be through forming, creping or converting. Stratified headboxes, foam forming, fractionation, high-level refining, specific MFC-additions, different production processes (DCT, Hybrid, TAD) and converting optimization have shown and still hold great promise and are available for commercial implementation already. It will be the combination of fiber source and finding the least destructive way of moving from fiber to converted tissue which will be the key to the most profitable tissue products of the future.

Missing pieces of the puzzle

A new spotlight on fibers should also mean further progress in determining the effect fibers and fiber treatments have on the other part of the tissue process. Though not discussed at Tissue World in Milan, the following process areas should be researched and discussed to complete the picture:

  • Different fiber raw material and mixtures vs. base paper properties during the creping process which highly affects strength properties, stretchability and softness
  • Benchmarking dynamic absorption properties of different pulps, leading to results of the absorption capacity vs absorption rate by pulp
  • Influence of wet strength agents on the adsorption properties
  • Benchmarking of softness of different pulps with both established and novel commercially available methods
  • Improving the dewatering on the tissue machine through optimal PMC design and introduction of novel techniques
  • Improved converting process, for example by operating at an increased relative humidity
  • Also related to the converting process, the effect of embossing pattern (dot size, height, shape) and rubber blanket softness vs fiber lengths and origin should be investigated
  • The winding process, and in particular the web tension, influences the product properties, e.g. bulk and stretch-at-break, but how much and in what respect could different fiber sources be effective.

So, what does the future hold?

Both new and old insights will combine to form a formidable recipe book of 3D furnish engineering to cover almost all productions processes; that’s what the future holds in a nut shell. For instance, a very interesting concept could be to combine base sheets from different production processes such as DCT, hybrid processes (e.g. NTT and ATMOS) and TAD into one product to optimize the bulk, absorption, softness and strength properties of the final product. Such concepts would mean putting a special focus on final product properties after the converting process and working upstream, layer by layer to involve the whole value chain from fiber to final product properties. With the new flexibility in choice of fibers together with new applications of stock preparation tools used, new exciting high performing and cost-efficient tissue products will be developed.

It can also be foreseen that, due to the recent strength improvement findings, the increased usage of cost-effective fibers will continue. Earlier held truths, e.g. that shorter fibers give disadvantages in terms of runnability in the tissue machine as well in the converting units will become less clear and evident thanks to new possibilities with tailored strength agents. This will lead to reduction in grammage and consequently the raw material cost for a given tissue product. Consider also an addition of different fiber-based dry strength agents, for example glue pulp, FE (Fines-Enriched) pulp, HF (Highly-Fibrillated) pulp, and cellulose nanofibrils – these dry strength additives can be produced in larger quantities on-site at the mill.

In the end, selection criteria for raw materials such as softwood, hardwood, mixtures thereof, chemically modified pulps, CTMP, and bio-based thermoplastic fibers will all be re-evaluated for their new optimized performance and final product characteristics. Further, we expect process compromises and production efficiency balances will become more intricate. This is not bad, it’s an opportunity to find an optimal fiber source for a better production process and cost efficiency. To mention one example, the addition of a strength agent can result in higher energy costs, and reduced softness which also need to be addressed.

Conclusion

To make this short and rather simple, the main conclusions drawn from the presentations regarding fibers can be summarized as:

New research insights have shown great advantages of both additives and modifications of pulps, blurring the former strict lines of application between softwood, hardwood and recycled fibers

  • The fiber types are as strong and flexible as they come originally, the main trick is to lessen the impact of both tissue production and converting processes
  • In the near future, technology, research and development will enable tissue producers to improve their bottom lines in specific products and processes to tailor make products based on their favored raw material
  • Established applicable knowledge on how to optimize the converting process and efficiently select and treat the raw materials will help the producers optimize and improve the performance of their products
  • 3D Furnish Engineering is already here in pilot scale trials. It won’t be long until we see it applied commercially.

 

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