Application of micro- and the air permeability due to an increase in the bonded area within the fiber network that closes off the porous structure.5 nanofibrillated cellulose (MNFC) in The reduction in air permeability correlates with an increase hygiene tissue products in the sheet density.6 Addition of MNFC also reduces the drainage rate of pulp slurries. Proper selection of retention aids helps to reverse this trend to some extent.4 Franklin Zambrano, Richard Venditti, Hasan Applications of MNFC in papermaking have mainly Jameel, Ronalds Gonzalez* focused on printing and writing paper7 and, to a lesser degree, on packaging materials.8 For such grades, Department of Forest Biomaterials, North Carolina State mechanical stability represents a critical control parameter University, Raleigh, NC 27695-8005, USA. that can be enhanced by the addition of MNFC. In tissue *Corresponding author: [email protected] papers, strength properties are only necessary to meet stresses and strains requirements during manufacturing ABSTRACT operations and consumer usage.9 For this particular grade, other physical parameters highlight according to the The development of novel technologies and materials application for which each tissue product is designed. to face current and future market challenges related to fiber Softness, absorbency, and brightness are desirable for bath supply, quality and cost is a hot topic for the hygiene tissue and facial tissue, whereas absorbency and strength are more industry. Micro- and nanofibrillated cellulose (MNFC) important for napkins and kitchen towels.10 presents an opportunity to modify tissue paper features due The addition of MNFC can be regarded as a wet-end to its superior strength properties. This has triggered a strategy to control tissue properties. To the best of the growing interest in using MNFC to generate either high- authors’ knowledge, no comprehensive studies have been value applications or low-cost alternatives. This work aims published on applications of MNFC in light-weight papers to develop a systematic study on the use of MNFC in with a focus on hygiene tissue. In that regard, the objective hygiene products with a focus on tissue paper. To that end, of the present work is to study the effect of the addition of MNFCs produced from four different market pulps were MNFC on the major properties of hygiene tissue products. added to tissue-making slurries of virgin fibers at different To that end, the performance of four MNFCs prepared from loads. Results show that MNFC act as an effective strength virgin and recycled market pulps is simultaneously additive for tissue paper, however, there is a tradeoff evaluated at different loads in a tissue-making slurry. The between the strength gains and the changes in other tradeoff between the resulting tissue properties, namely properties such as bulk, water absorbency, and softness, tensile strength, softness and water absorbency, is analyzed which are negatively affected. The extent of the changes and the MNFC that performs best for each specific tissue depends on both the load and the type of MNFC. As strength application is recommended. The ultimate goal of this work requirements are necessary to withstand tissue- is to screen opportunities for value creation in the hygiene manufacturing operations, this allows tailoring the final tissue industry by using renewable nanotechnology. tissue properties according to the application for which each hygiene product is designed. EXPERIMENTAL

Keywords: Nanofibrillated cellulose (NFC); Materials Microfibrillated cellulose (MFC); Hygiene tissue paper; Micro- and nanofibrillated celluloses prepared from four Tensile strength; Softness; Water absorbency different market pulps through mechanical fibrillation in an ultra-fine friction grinder Supermasscolloider (model INTRODUCTION MKZA6-5, Masuko Sangyo Co., Ltd, Saitama, Japan) were used as strength additive for tissue paper. The MNFCs The use of nanotechnology is an emerging area that is samples were taken once a total net energy input of 6,000 finding its way into daily consumer commodities.1 Within kWh/od ton was reached during fibrillation. Table 1 this segment, micro- and nanofibrillated cellulose (MNFC) describes the market pulps selected for MNFC is the potential candidate to create high-end products or low- manufacturing, including aspects related to fiber cost alternatives for the pulp and paper industry.2 This field morphology, and “as received” moisture content. represents a promising arena for bio-nanomaterials aiming Fig 1 shows SEM images of the MNFC produced from to achieve a short-term adoption by the market.3 each feedstock along with the average fibrils width obtained In papermaking applications, adding MNFC to pulp from an image analysis software (ImageJ 1.47v, National slurries yields paper products with improved mechanical Institutes of Health, Bethesda, MD). The average width of properties. Several authors have reported the strengthening the fibrils was calculated considering a minimum of 50 capacity of MNFC in paper products.4 In addition to randomly selected particles from at least five images per increasing the strength properties of paper, MNFC decreases feedstock.

Pulp slurry preparation this context, the procedure followed for forming handsheets A tissue-making slurry consisting of 70 wt.% SBHK and for physical tests of pulp correspond to a modified version 30 wt.% NBSK was used to make 30 g/m2 light-weight of TAPPI T 205 sp-0212. This alternative method intends to paper. Two loads (1 wt.% and 2 wt.% based on od fiber) of adapt the standard procedure to the conditions used in tissue MNFC produced from the various feedstocks were added to manufacturing. Briefly, pressing and ring drying of the the slurry. MNFC and papermaking fibers were mixed handsheets are avoided. Instead, after formation and together at 3000 rpm during 5 min and 1.2 wt.% consistency couching, handsheets are dried using a cylindrical dryer using a pulp disintegrator (Testing Machines, Inc., (Formax 12”, Adirondack Machine Co., Gleans Fall, NY) Amityville, NY). After disintegration, the MNFC-pulp that simulates the yankee roll operation. The operating slurry was diluted to 0.3 wt.% consistency using tap water. conditions for the cylindrical dryer are 110°C, 20% of nominal speed, and 5 min residence time. Handsheets Table 1. Market pulps used for MNFC and tissue produced from this method are uncreped. handsheets preparation Pulp type Hardwood Softwood Recycled Handsheets testing Evaluation of handsheets mechanical and physical Southern Northern Bleached bleached bleached Deinked properties was performed according to ISO 12625. Pulp name Eucalyptus hardwood softwood pulp Handsheets samples were conditioned for 24 hours under a Kraft Kraft Kraft standard atmosphere set at 50% relative humidity and 23°C Pulp tag BEK SBHK NBSK DIP before testing (ISO 187).13 Softness, defined in this context Fiber length1 as the human sensorial response obtained when a tissue 0.802 1.101 2.343 1.111 (mm) product is stroked with fingers and crumpled by hand,15 was Mean width 15.6 17.9 25.7 17.9 assessed with a Tissue Softness Analyzer (Emtec Electronic (µm) Fines content2 GmbH, Leipzig, Germany). 31.35 73.67 56.25 55.73 (%) Moisture RESULTS AND DISCUSSION 3 7.72 7.87 6.41 7.34 content (%) 1Length weighted mean length; 2Arithmetic percent fines. Fines are defined as particles with length between 0.025 mm and 0.2 mm; 3 “As received” moisture content This section describes the changes in the physical and measured in accordance with TAPPI T 412 om-1611 mechanical properties that occur to the tissue paper due to Fiber morphology determined with fiber quality analyzer (HiRes FQA, OPTest Equipment Inc., Hawkesbury, ON, Canada) the addition of MNFC. For each property studied, results are discussed considering the effect of the load and type of MNFC used.

Tensile strength of tissue paper The addition of MNFC to the tissue-making slurry enhances the tensile strength of the resulting tissue paper. The increase in the tensile strength promoted by the MNFC addition is shown in Fig 2. Overall, the increase in tensile strength is proportional to the MNFC load in the slurry. The a) BEK-MNFC b) SBHK-MNFC Average fibrils width = 284 nm Average fibrils width = 165 nm performance of the MNFC as a tissue strength additive also varies according to the feedstock used for MNFC manufacturing. At a 1 wt.% load, small differences exist between the types of MNFC. Interestingly, differences in strength improvement become more noticeable with the increase in the MNFC load. At a 2 wt.% load, MNFC produced from NBSK yields the stronger tissue structure with an increase of 67% in the tensile strength compared to the base case. Conversely, BEK-MNFC triggers an increase c) NBSK-MNFC d) DIP-MNFC Average fibrils width = 130 nm Average fibrils width = 213 nm of 30%, which is the lowest increase obtained among the conditions studied. Fig 1. SEM images for MNFCs prepared by mechanical The differences in performances showed a correlation fibrillation of (a) BEK, (b) SBHK, (c) NBSK, and (d) DIP with the average fibrils width for MNFCs prepared from virgin fibers. NBSK-MNFC, which has the smallest fibrils Handsheets making width (130 nm) presents the major improvement in tensile In tissue manufacturing operations, wet pressing of the strength. Contrarily, BEK-MNFC, which has the largest paper web is minimized to preserve bulk as densification fibrils width (284 nm), shows the poorest performance. yields poor softness and absorbency of the paper sheet. In SBHK-MNFC, with an intermediate average fibrils width

(165 nm), shows a performance that is between the two preserve bulk, even though pressing is a cost-effective MNFCs mentioned before. The strengthening mechanism of technique to partially dewater the paper web and promote MNFC is based on the increase of the total bonded area by consolidation of the sheet. In practice, finding an optimum promoting fiber-fiber bonding, and the formation of ratio between the tensile strength and the bulk represents a embedded nano-networks along larger fibers that serve as challenge. points of high resistance for the macroscopic network.16 The Overall, the addition of MNFC yields a tissue product expansion in surface area that results from the reduction of with a lower bulk compared to that of the base case. MNFC the fibrils size increases the ability of the MNFC to act as an closes off the porous network, which causes densification adhesion promoter in the tissue structure, and at the same and decreases the compressibility of the tissue structure. The time, to form stronger and more rigid nano-structures extent to which this occurs is a function of both the load and through both mechanical interaction and hydrogen bonding. type of MNFC as demonstrated in Fig 3. Bulk losses are In the case of DIP-MNFC, the increase obtained in tensile proportional to the MNFC load. An abrupt decrease is strength is comparable to that of the SBHK-MNFC at a 2 obtained with 1 wt.% load, however, the rate of densification wt.% load. Hence, for applications that aim to exclusively levels off as the load increases up to 2 wt.%. As densification enhance the strength of the tissue paper, MNFC produced progresses fewer porous sites are available to be filled by the from recycled fibers has the potential to perform as a MNFC nanofibers, which hinders the rate of densification. produced from hardwood virgin fibers at a lower Bulk changes are highly dependent on the type of MNFC manufacturing cost. used. Among the MNFCs manufactured from virgin fibers, When used as tissue strength additives, MNFCs NBSK-MNFC, with the smallest fibrils width, yields the produced from NBSK and SBHK pulp fibers showed a greatest decrease in bulk, whereas for SBHK and BEK- performance that is not significantly different from each MNFCs the reduction in bulk is comparable. In the case of other within the range evaluated. Considering that both DIP-MNFC, an abrupt decrease in bulk occurs with 1 wt.% MNFCs present a quite similar average particle size, this load and it levels off for the subsequent addition being finding suggests that at the nanoscale the strengthening equivalent to that of the NBSK-MNFC. As previously capacity is primarily driven by the size of the fibrils rather discussed, inorganic particles in the DIP potentially than their chemical composition. At the macroscale, the grounded to the nanoscale might promote a quick latter factor plays a key role in determining the bonding densification of the web structure. However, the loss in bulk ability of pulp fibers. However, differences in paper does not contribute to the tensile strength to the same extent properties associated with the fiber chemistry at the as it does for the NBSK-MNFC. macroscale might be mitigated at the nanofibrils level, i.e., possible variations in performance due to differences in chemical composition might be outweighed by the extensive surface area. From a practical point of view, this has huge implications on costs associated with MNFC manufacturing and application.

Fig 3. Effect of the addition of MNFC on the bulk of tissue paper

Water absorbency of tissue paper Absorbency properties are an important price driver for tissue products designed for wiping purposes. For two-plies Fig 2. Effect of the addition of MNFC on the tensile strength tissue products, water locates between plies, among fibers, of tissue paper and inside fibers. In the case of one-ply products, which correspond to the condition considered in this study, water Bulk of tissue paper location is limited to the spaces between fibers and inside Bulk is an important quality standard in tissue paper. the fiber structure. Manufacturing operations avoid pressing of the wet sheet to Fig 4 shows the effect of the addition of MNFC on the

water absorbency. Overall, the addition of MNFC yields a softness and bulk softness. Surface softness is the perception tissue product with a lower water absorbency compared to obtained from the lightly brushing of the fingertips over the the base case. This effect is proportional to the MNFC load surface of the tissue paper. Bulk softness is the perception of in the paper web. MNFC is well-known for being a ease to crumple the tissue paper between the hands. superabsorbent in a wet state. The experimental data shows Softness is a price driver in tissue grades as customers are however that once the MNFC incorporates into the fiber willing to pay a premium for products that exhibit an network and transitions into a dry state upon drying of the improved hand feel comfort. tissue paper, these super absorbance features are either lost Fig 5 shows how softness of the tissue paper responds to or outweighed by other physical changes. the addition of MNFC. Changes in softness depend on both The decrease in the water absorbency is intimately the load and the type of MNFC added to the tissue furnish. related to the loss in bulk of the sheet when MNFC is For the softness measurement, a lower TS7 value is incorporated in the tissue web. Water absorbency showed 85% associated with a softer product. The addition of MNFC linear correlation to the bulk for all the conditions evaluated triggers an increase in the TS7, which is proportional to the in this study. The increase in MNFC load implies a higher load of MNFC in the paper web. MNFC have been reported number of nanofibrils available to produce fiber bridging to improve the surface smoothness,17 which is beneficial for and fill the porous network what yields a more compact surface softness. However, it densifies the sheet, which hurts structure with less free spaces for water holding. compressibility and increases the rigidity of the fiber This effect changes depending on the type of MNFC structure. Both factors negatively affect bulk softness, used, which directly correlates with the fibrils dimensions. yielding to an overall loss in tissue softness. BEK-MNFC, with the largest fibrils width, presents a lower The type of MNFC used influences the changes in tissue number of fibrils available to fill the voids in the tissue softness. The extent to which each MNFC affects the network and less surface area to produce bridging between properties previously discussed is what determines the fibers, compared to the NBSK-MNFC, with the smallest resulting softness for each product, i.e., there is a tradeoff particle size, which means a larger number of fibrils to between properties that leads to the final tissue softness. promote both mechanisms. SBHK-MNFC with an average MNFC prepared from BEK, SBHK and DIP performed width between these two MNFCs shows an intermediate similarly for the conditions studied. The improvements in water absorbency. Yet, DIP-MNFC shows an atypical tensile strength promoted by the addition of these MNFCs behavior. Even though the bulk of the resulting tissue is as compromise softness, however, the loss in softness is low as the one from the sheets containing NBSK-MNFC, the buffered with a moderated decrease in the tissue bulk. water absorbency presents a different value. Structurally Conversely, the addition of NBSK-MNFC promotes an speaking this suggests a different internal configuration of abrupt change in strength and bulk of the tissue paper that both tissue papers, with the NBSK-MNFC containing tissue causes the TS7 value significantly to increase, resulting into having a less porous structure. a poor softness. Particularly for the DIP-MNFC, even though the addition causes an important loss in bulk, the results suggest that densification of the fiber network occurs in such a way that the rigidity of the web is affected similarly as for the MNFCs produced from hardwood fibers.

Fig 4. Effect of the addition of MNFC on the water absorbency of tissue paper

Softness of tissue paper Softness is a human sensorial response to the action of Fig 5. Effect of the addition of MNFC on the softness of rubbing a paper sheet with the fingers and crumpling it in tissue paper. The lower the TS7 value the softer the product. the hands. The hand feel, typically referred to as softness, results from a combination of two factors namely, surface

CONCLUSIONS Nord. Pulp Pap. Res. J. 29, 156–166 (2014). 6. Su, J., Mosse, W. K. J., Sharman, S., Batchelor, W. Micro- and nanofibrillated cellulose can be used as an J. & Garnier, G. Effect of tethered and free effective wet-end additive for tissue paper. The changes in microfibrillated cellulose (MFC) on the properties the mechanical and physical properties caused by the MNFC of paper composites. Cellulose 20, 1925–1935 addition are proportional to the load in the tissue-making (2013). furnish and the type of cellulosic fiber used for the MNFC 7. González, I. et al. Nanofibrillated cellulose as paper manufacturing. The addition of MNFC improves the tensile additive in Eucalyptus pulps. BioResources 7, strength of the tissue paper so that it can withstand stresses 5167–5180 (2012). during manufacturing operations and consumer usage. That 8. Hellström, P., Heijnesson-Hultèn, A., Paulsson, M., improvement in strength compromises other properties such Håkansson, H. & Germgård, U. Fenton pre-treated as bulk, water absorbency, and softness, which are microfibrillated cellulose evaluated as a strength negatively affected. The changes in properties can be more enhancer in the middle ply of paperboard. Nord. or less severe depending on the type of MNFC used. This Pulp Pap. Res. J. (2014). doi:10.3183/NPPRJ-2014- allows tailoring the tissue properties to specific applications. 29-04-p732-740 For example, for a less strong but bulkier and softer product 9. Nanko, H., Button, A. & Hillman, D. The World of SBHK-MNFC would be the best fit, whereas for a stronger Market Pulp. (TAPPI Press, 2010). but less soft product NBSK-MNFC would be the best option. 10. Zou, X. Overview of tissue grades and their pulp At the same time, the results highlight potential scenarios furnish selection. in Paper Conference and Trade for value creation in MNFC applications. Manufacturers Show: Renew, Rethink, Redefine the Future, that do not consider differences in performance so PaperCon 2017 370–383 (TAPPI Press, 2017). significant can used the cheapest feedstock for MNFC 11. TAPPI T 412 om-94. Moisture in pulp, paper and preparation, or manufacturers that are paying high prices for paperboard. (1994). MNFCs that outperform their products can select the one 12. TAPPI T 205 sp-02. Forming handsheets for that best fits their needs. physical tests of pulp. (2006). 13. ISO 187. Paper, board and pulps - Standard ACKNOWLEDGMENTS atmosphere for conditioning and testing and procedure for monitoring the atmosphere and This work was financially supported in part by the conditioning of samples. (1990). Tissue Pack Innovation Lab (Department of Forest 14. ISO 12625-8. Tissue paper and tissue products - Biomaterials, College of Natural Resources, North Carolina Part 8: Water-absorption time and water- State University, USA) and by the USDA-NIFA project, absorption capacity, basket-immersion test method. Preparing Diverse and Rural Students to Meet the (2005). Challenges in the Bioproducts and Bioenergy Industry, 15. Hollmark, H. & Ampulski, R. S. Measurement of award #2017-67009-26771. tissue paper softness : A literature review. Nord. Pulp Pap. Res. J. 19, 345–353 (2004). REFERENCES 16. Boufi, S. et al. Nanofibrillated cellulose as an additive in papermaking process: A review. 1. Wijnhoven, P., Dekkers, S. & Hagens, W. I. Carbohydr. Polym. 154, 151–166 (2016). Exposure to nanomaterials in consumer products. 17. Svending, P. Commercial break-through in MFC Public Health 1–47 (2009). processing. in Tappi International Conference on 2. Dufresne, A. Nanocellulose: A new ageless Nanotechnology for Renewable Materials (2014). bionanomaterial. Mater. Today 16, 220–227 (2013). 3. Osong, S. H., Norgren, S. & Engstrand, P. Processing of wood-based microfibrillated cellulose and nanofibrillated cellulose, and applications relating to papermaking: a review. Cellulose 23, 93– 123 (2016). 4. Taipale, T., Österberg, M., Nykänen, A., Ruokolainen, J. & Laine, J. Effect of microfibrillated cellulose and fines on the drainage of kraft pulp suspension and paper strength. Cellulose 17, 1005–1020 (2010). 5. Brodin, F. W., Gregersen, Ø. W. & Syverud, K. Cellulose nanofibrils: Challenges and possibilities as a paper additive or coating material - A review. Application of Micro- and Nanofibrillated Cellulose (MNFC) in Hygiene Tissue Products Franklin Zambrano, Dr. Ronalds Gonzalez, Dr. Richard Venditti, Dr. Hasan Jameel Tissue Pack Innovation Lab, Department of Forest Biomaterials, North Carolina State University Outline

1. Introduction: Nanocellulose - Definition & Production

2. Objectives: What we want to know

3. Experimental: Production of MNFC and tissue-making

4. Results: Performance of MNFC in tissue products

5. Case study: Using MNFC to reduce product weight

6. Conclusions

2 INTRODUCTION Nanocellulose: Definition & Production

3 INTRODUCTION Digging into the fiber structure: Nanocellulose Bundle of Cellulose Cellulose Tree Fibers Cellulose fibers cellulose fibrils fibrils molecule

Fiber surface Amorphous domains

Crystalline domains

Wood Wood tissue Width = 20-30 µm Width > 15 nm Width ~ 3 nm Width = 0.4 nm Length = 1-3 mm Length > 2 µm Length ~ 500 nm Crystallinity = 70-90% 4 INTRODUCTION Cellulose nanocrystals and micro- and nanofibrils

Chemical CNC treatment

Pulp CNC: cellulose nanocrystals Biomass > 85% cellulose Purification We will MFC: microfibrillated cellulose Usual focus on MNFC NFC: nanofibrillated cellulose starting point Lignin Hemicellulose Extractives Inorganic compounds Pre- Mechanical MFC Necessary step treatment treatment NFC Optional step 5 OBJECTIVES What we want to know

6 OBJECTIVES

Study the effect of the MNFC load on the tissue-making furnish and tissue paper

MNFC load I prefer the I like the super absorbent “ultra-soft” tissue! paper towels! Facts: Most of the literature on use of MNFC in paper applications focused on copy/writing and packaging.

No mention to the use of MNFC in hygiene tissue products.

7 OBJECTIVES

Study the effect of the fiber source on the MNFC performance

Fiber source

15% electricity

60% pulp

Source: de Assis (2017) 8 EXPERIMENTAL Production of MNFC and tissue-making

9 EXPERIMENTAL Production of micro- and nanofibrillated cellulose (MNFC)

Wood fibers used for production of MNFC Production scheme Length Mean Fines Pulp Weighted Width (%) Pulp slurry Recirculation loop (Pass) (mm) (µm)

BEK 0.80 15.60 31.4 Readings • Power SBHK 1.11 17.95 73.7 • Time

NBSK 2.34 25.70 56.3 Characterization Fiber quality DIP 1.11 17.85 55.7 • MNFC analysis (FQA) sample • Morphology and BEK: bleached Eucalyptus Kraft size (SEM) SBHK: southern bleached hardwood Kraft • Water retention NBSK: northern bleached softwood Kraft value (WRV) DIP: deinked pulp 10 EXPERIMENTAL MNFC production: Fiber length & Fines content vs. Energy 3.00 100 BEK 90 SBHK 2.50 MNFC used as NBSK 80 additive for tissue DIP 70 2.00 60

1.50 50

40 % Fines content Fiber length (mm) 1.00 30 BEK Fines: Particles with length between SBHK 20 0.50 25 and 200 µm % Fines content: calculated based on NBSK 10 number of particles DIP 0.00 0 0 2,000 4,000 6,000 8,000 10,000 0 2,000 4,000 6,000 8,000 10,000 Cumulative energy (kWh/OD ton) Cumulative energy (kWh/OD ton) 11 EXPERIMENTAL MNFC characterization: Fibrillation process

Starting SBHK fiber SBHK sample after extensive fibrillation Untreated sample Energy input: 6000 kWh/OD ton

Author: Heather Starkey

Mean width = 17.9 µm Mean width of fibrils = 165 nm 12 EXPERIMENTAL MNFC characterization: Morphology & Fibrils size

BEK DIP SBHK NBSK

Mean width = 284 nm Mean width = 213 nm Mean width = 165 nm Mean width = 130 nm WRV = 55.7 (0.2) g/g WRV = 57.7 (0.7) g/g WRV = 59.5 (0.2) g/g WRV = 63.71 (0.02 ) g/g

Reduction in fibrils width

Increase in water retention value (WRV) 13 EXPERIMENTAL Procedure for making uncreped tissue handsheets

Source: adapted TAPPI T 205

Market pulp MNFC Disintegration Pulp/MNFC + water Handsheets making 70% SBHK – 30% NBSK 1% - 2% OD basis @ 0.3% consistency Basis weight = 30 g/m2 (from BEK, SBHK, NBSK, DIP) (Freeness measurement)

Properties testing Conditioning Drying Couching Tensile strength, Bulk, @ 50% RH - 23 ˚C @ 110˚C - 20 rpm Water absorbency, Softness 14 RESULTS Performance of MNFC in tissue products

15 RESULTS MNFC addition vs. Tensile strength 450 ISO 12625-4 400 Effect on tensile strength of tissue 350 1. Enhancement of tensile strength 300 proportional to the MNFC load 250 BEK 2. Fiber source affects the MNFC SBHK 200 NBSK performance

Tensile strength (N/m) 150 DIP 3. Correlation between performance and size 100 of MNFC 0.0% 0.5% 1.0% 1.5% 2.0% MNFC load (%) Pulp NBSK SBHK DIP BEK 80 67 70 Avg fibrils width 130 165 213 284 60 52 52 (nm) 50 40 30 28 30 23 4. Strengthening mechanism based on the 20 15 13 increase of total bonded area and 10 formation of embedded nano-networks % increase% in tensile strength 0 1% 2% 1% 2% 1% 2% 1% 2% within fiber structure BEK SBHK NBSK DIP 16 RESULTS MNFC addition vs. Bulk 6.0 5.8 BEK SBHK Effect on bulk of tissue 5.6 NBSK 5.4 DIP

/g) 1. MNFC addition yields tissue with 3 5.2 5.0 lower bulk 4.8

Bulk (cm 4.6 2. MNFC closes off porous structure of 4.4 the tissue sheet 4.2 4.0 3. Bulk losses proportional to MNFC 0.0% 0.5% 1.0% 1.5% 2.0% load MNFC load (%) 4. Rates of densification levels off with BEK SBHK NBSK DIP increasing MNFC load 1% 2% 1% 2% 1% 2% 1% 2% 0 5. Correlation between bulk changes -2 and fibrils size -4 -6 -8 Pulp NBSK SBHK DIP BEK -10 -9 -8 -12 -11 Avg fibrils width

% reduction in bulk -11 130 165 213 284 -14 -12 -12 (nm) -13 -16 -14 17 RESULTS MNFC addition vs. Water absorbency 8.0 BEK 7.5 SBHK Effect on water absorbency 7.0 NBSK DIP 1. MNFC addition yields tissue products with 6.5 6.0 lower ability to absorb water 5.5 2. Drop in water absorbency proportional to

(g water/g fiber) 5.0 MNFC load Water absorbency absorbency Water 4.5 ISO 12625-8 3. Less free spaces for water holding 4.0 4. Super absorbance features of MNFC either 0.0% 0.5% 1.0% 1.5% 2.0% lost or outweighed MNFC load (%) 5. Decrease in absorbency intimately related BEK SBHK NBSK DIP to the loss in bulk 1% 2% 1% 2% 1% 2% 1% 2% 6. Correlation between water absorbency 0 and fibrils dimensions -2 -4 -6 Pulp NBSK SBHK DIP BEK -6 -8 -7 -7 -10 Avg fibrils width absorbency -12 -10 -10 130 165 213 284 -11 (nm)

% decrease in water -14 -15 -13 -16 18 RESULTS Softness of tissue paper Softness is a human sensorial response

Tissue stroked with fingers Tissue crumpled by hand Surface Softness Bulk Softness

SUBJECTIVE perception 19 RESULTS Evaluating softness of tissue paper How is softness objectively “measured” in the lab?

Tissue Softness Analyzer (TSA) Sound analysis Moving head 50 45 TS7 Lower TS7 peak Rotor with blades 40 TSA Softness 35 Higher softness Measuring cell 30 Stiff fibers Fixing ring 25 Load cell 20 Microphone Flexible fibers 15 10

Cancellation of (dB) Level Sound Pressure 5 surrounding noise 0 0 2 4 6 8 10 12 14 16 18 20 Frequency (kHz)

Source: emtec Electronic GmbH 20 RESULTS MNFC addition vs. TS7 (Softness) 50 BEK 45 SBHK Effect on softness of tissue 40 NBSK DIP 1. MNFC addition triggers an increase in TS7 35 (less soft tissue) 30

TS7 (dB)TS7 2. Increase in TS7 proportional to MNFC load 25 in paper web 20 3. Sheet densification hurts compressibility 15 and increase rigidity of structure 0.0% 0.5% 1.0% 1.5% 2.0% 4. The extent to which each MNFC affect MNFC load (%) 120 physical properties determines the 109 resulting softness 100 5. Similar performance for MNFC from BEK, 80 68 64 65 SBHK and DIP 60 54 6. Significant increase in TS7 with addition of 40 16 25 23 MNFC from NBSK 20 % increase % in TS7 (dB) 0 1% 2% 1% 2% 1% 2% 1% 2% BEK SBHK NBSK DIP 21 RESULTS MNFC addition vs. Freeness 700 BEK 680 SBHK Effect on freeness of slurry 660 NBSK 1. MNFC addition affects negatively the 640 freeness of the tissue-making slurry 620 2. Negative effect associated with 600 mechanisms governing wet web formation Freeness (mL CSF) Furnish: 70% SBHK – 30% NBSK 580 (no retention/drainage aid) 3. Freeness losses depend on type of MNFC 560 and intensify with the increase in MNFC 0.0% 0.5% 1.0% 1.5% 2.0% load MNFC load (%) 4. MNFC produced from NBSK yields the BEK SBHK NBSK DIP higher freeness drop 1% 2% 1% 2% 1% 2% 1% 2% 5. Comparable freeness drop at 1 wt.% load 0 but noticeable difference at 2 wt.% load -2 6. Use of cationic polymers can compensate -4 -3 -4 -3 -6 -5 freeness losses -8 7. Freeness values at suitable levels despite -10 -8 -12 freeness losses -14 -12

% decrease in freeness -14 -16 -14 22 RESULTS What we have learned with MNFC:

The addition of MNFC improves the tensile strength of tissue paper but affects negatively the bulk, water absorbency, and softness. The extent of the change is proportional to the load.

The changes in properties can be more or less severe depending on the type of MNFC.

Potential to tailor tissue properties to specific applications using MNFC:

• SBHK-MNFC offers good combination between strength, softness and absorbency • NBSK-MNFC is suitable for grades that require good strength attributes with moderate softness and absorbency 23 CASE STUDY Reduction of product weight with MNFC addition

24 CASE STUDY Fiber reduction by means of MNFC addition 500 R² = 0.9711 600 mL CSF

450

400

350 17% basis weight 627 mL CSF reduction 300 Tensile strength (N/m) strength Tensile

250 Base case 2% MNFC + additive 24.8 g/m2 200 23 24 25 26 27 28 29 30 31 Basis weight (g/m2) CASE STUDY Fiber reduction by means of MNFC addition 40

35

30 TS7 (dB) - No change in TS7 25 Softness

20 Base case 24.8 g/m2 2% MNFC + additive 17% reduction 15 23 24 25 26 27 28 29 30 31 Basis weight (g/m2) CONCLUSIONS

27 CONCLUSIONS

MNFC can be used as a strength additive for tissue paper

More promising application:

Engineered use of MNFC can help to reduce fiber without affecting product performance

2% MNFC costs ~15% fiber reduction translates into < USD 35 per ton USD 75/ton DIP and USD 130/ton MP

28 Tissue Pack Innovation Lab

THANK YOU

Franklin Zambrano Department of Forest Biomaterials North Carolina State University [email protected] www.go.ncsu.edu/tissue 29