TECHNICAL FIELD

The present disclosure pertains to a method for consolidating a fibrous material comprising or consisting of plant-based fibers. In particular, this disclosure pertains to a method for consolidating a fibrous material comprising or consisting of plant-based fibers with a bio-based binder. The present disclosure also pertains to a consolidated fibrous material obtained by the method, an aqueous solution comprising a cellulose derivative and an acid and a nonwoven material comprising fibers consolidated by the bio-based binder. BACKGROUND OF THE INVENTION

It is common for nonwoven materials to be based on the biological raw material cellulose, the binders used to bind the fibers together and obtain the desired features are in general fossil-based polymers, making the fabric non-bio-based. The fossil-based polymers contribute to a material which has a high level of both wet and dry strength, water absorption capacity and other characteristics which might be of importance for its planned application. Due to the well-known and appreciated properties of the fossil-based polymers it has been difficult to find a bio-based replacement suitable to use for nonwovens. Unfortunately, an issue with moving from fossil-based binders towards bio-based ones is that the finished material in general loses some of its important characteristics, such as strength or durability.

The demands on the performance of the material will however be high and it is important that the properties of the material is not compromised with to a unreasonable extent, while a more sustainable solution still is found. It is known that water-soluble modified celluloses, such as a cellulose ethers, have many desirable qualities such as binding and water absorbing properties. However, the drawback seen with these binders is that the nonwoven material becomes quite rigid and loses much of its elongation. In view of the above, it is an object of the present disclosure to consolidate a fibrous material by means an environmentally friendly method, the fibrous material having maintained absorbency performance and improved mechanical strength and flexibility. SUMMARY OF THE INVENTION

One or more of the above objects may be achieved by a method for consolidating a fibrous material in accordance with claim 1 , a fibrous material according to claim 15 consolidated by the method, an aqueous binder solution according to claim 16 and a nonwoven material according to claim 22. Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.

According to a first aspect, the present disclosure relates to a method for consolidating a fibrous material comprising or consisting of, plant-based fibers, such as cellulose fibers and/or poly-lactic acid fibers, the method comprising the steps of; - applying to the fibrous material an aqueous solution comprising a cellulose derivative, and/or a salt thereof, and an acid, the aqueous solution having a pH within the range of from 3 to 7, optionally within the range of from 3.5 to 6, and drying the bonded fibrous material, optionally at 100° C or higher. The fact that the fibrous material comprising or consisting of plant-based fibers, has been consolidated by an aqueous solution comprising a cellulose derivative, and/or a salt thereof, and an acid, the aqueous solution having a pH within the range of from 3 to 7 has been found to provide a consolidated fibrous material having improved wet strength properties and an enhanced flexibility.

Optionally the drying step may be carried out at a temperature being within a range of from 100° C to 170° C during a period of time of at least 20 seconds, or at least 50 seconds, or at least 2 minutes, or at least 5 minutes, 10 minutes, optionally at least 15 minutes. The drying may be carried at a temperature being out at within a range of from 120° C to 160° C during a time of at least of at least 20 seconds, or at least 50 seconds, or at least 2 minutes, or at least 5 minutes, or at least 10 minutes, optionally at least 15 minutes.

The drying step may be carried out directly after the step of applying the aqueous solution to the fibrous web. The cellulose derivative may be carboxymethyl cellulose and the salt thereof may be sodium carboxymethyl cellulose. The fibrous material may be an airiaid, wetlaid, foam formed or carded nonwoven material comprising or consisting of plant-based fibers.

Alternatively, the fibrous material may be pre-treated with the aqueous solution, prior to a step of forming a web of material.

The fibrous material may alternatively be a tissue material.

The acid may be a monoprotic acid. The aqueous solution may furthermore comprise a pH control agent. To adjust the pH of the aqueous solution to the required range, for example if lower amounts of the acid is added, a pH control agent may be added to the solution.

The acid may be carboxylic acid.

The carboxylic acid may be a monocarboxylic acid.

The carboxylic acid may be a polycarboxylic acid, i.e. having two or more carboxyl groups, optionally citric acid.

The aqueous solution may comprise one or more acids, for example a mix of monocarboxylic acids and polycarboxylic acids.

The method may comprise the step of adding a bio-based plasticizer, such as glycerol, to the fibrous material. The plasticizer may be added to the aqueous solution after dissolving the cellulose derivative in the aqueous solution and after the acid is added into the aqueous solution. A ratio of the cellulose derivative, and/or a salt thereof, and the acid may be within the range of from 1.5:1 to 5:1 , such as within the range of from 1.5:1 to 4:1 , or within the range of from 2:1 to 4:1 or from 2:1 to 3:1. The amount of acid may be within the range of from 0.05 wt-% to 3 wt-% of the aqueous binder solution total mass, optionally within the range of from 0.05 wt-% to 2 wt-% of the aqueous binder solution total mass, optionally 0.1 wt-% to 3 wt-% of the aqueous binder solution total mass. The amount of cellulose derivative, and/or a salt thereof, may be within the range of from 0.4 wt-% to 6 wt-% of the aqueous binder solution total mass, optionally within the range of from 0.5 wt-% to 5 wt-% of the aqueous binder solution total mass.

The aqueous solution may be applied by spraying. The aqueous solution may alternatively be applied by coating. The aqueous solution may be added to/mixed with a fiber mix of plant-based fibers prior to forming a material web or after a material web has been formed.

The present disclosure relates according to a second aspect to a fibrous material obtained by the method according to the first aspect.

The fibrous material may be an airlaid, wetlaid, foam formed, or carded fibrous material. It may be a nonwoven material. The fibrous material may comprise one or several types of plant-based fibers, for example, the fibrous material may be a mix of cellulose fibers and PLA fibers.

The fibrous material may alternatively be a tissue material and the aqueous solution may then be added to the fibre suspension and provide wet strength to the tissue material.

According to a third aspect, the present disclosure relates to an aqueous binder solution comprising a cellulose derivative, and/or a salt thereof, and an acid, the aqueous solution having a pH within the range of from 3 to 7, optionally a pH within the range of from 3.5 to

6. The cellulose derivative may be carboxymethyl cellulose and the salt thereof may be sodium carboxymethyl cellulose.

The acid may be a carboxylic acid, optionally a monocarboxylic acid.

The aqueous solution may furthermore comprise a pH control agent.

A ratio of the cellulose-based binder and the acid may be from 1.5:1 to 5:1 , such as from 1.5:1 to 4:1 , or from 1.5:1 to 3:1.

The amount of acid may be within the range of from 0.2 wt-% to 3 wt-% of the aqueous binder solution, optionally within the range of from 0.2 wt-% to 2 wt-% of the aqueous binder solution. Optionally, within the range of from 0.4 wt-% to 2 wt-% of the aqueous binder solution

According to a fourth aspect, the present disclosure relates to a nonwoven material comprising plant-based fibers, the plant-based fibers being consolidated together by a bio-based binder, the bio-based binder being a cellulose derivative, and/or a salt thereof, such as carboxymethyl cellulose or a salt thereof, bonded with carboxylic acid, the nonwoven having a wet maximum tensile strength in machine direction (MD) of 100 N/m or more, and wet maximum tensile strength in cross direction (CD) of 100 N/m or more, as measured according to NWSP 110.4R0 (15).

The fibers may be cellulosic fibers or polylactic acid (PLA) fibers. Cellulose fibers include viscose and lyocell fibers and the nonwoven material may include one or more types of the fibers, such as a mix of plant-based fibers.

The nonwoven material may have an elongation in machine direction (MD) of at least 6%, optionally at least 7%, and an elongation in cross direction (CD) of at least 6%, optionally at least 7%, as measured according to NWSP 110.4R0 (15).

The nonwoven material may be an airlaid nonwoven material.

The bio-based binder may be carboxymethyl cellulose or a salt thereof, optionally sodium carboxymethyl cellulose. The carboxylic acid may be a monocarboxylic acid or a polycarboxylic acid, for example citric acid. The EDANA standard method NWSP 110.4R0 (15) “Breaking Force and Elongation of Nonwoven Materials” (Strip Method) is used for measuring tensile strength and elongation. The type of specimen is according to Option B - 50 mm strip tensile and with the Style of tensile testing machine option a) i.e. a Constant-rate-of-extension (CRE). Nonwoven material is defined as a web or sheet of fibers which are bonded together thermally, mechanically or chemically thus they are not knitted nor woven, unlike textile fabrics. The appearance and characteristics of the nonwoven can be very different, depending on the choice of raw materials as well as production process and every nonwoven is designed for a specific application. Even though the properties of the fabric may differ, it is common to use a nonwoven which has absorbent, strong, elongated and durable properties.

The manufacturing of a nonwoven begins with the arrangement of fibres into a web structure. This arrangement can be performed in different ways, some possible methods are airlaid, wetlaid and spunlaid web formation among others. There is also a wide range of different fibers that may be used and they can be either synthetic or natural. Which fiber to use depends on the application and required properties for the specific nonwoven. One of the most popular natural fibers for nonwoven fabrics is cellulose due to several reasons. Cellulose is the most abundant natural polymer on earth, which means that it is easily accessible, but furthermore it is highly biodegradable and contributes to a material with high moisture absorbency. The use of cellulosic fibers in nonwoven is especially suitable for hygiene products as it is a nontoxic, bio-based fiber. However, it is also common to use synthetic fibers from fossil-based polymers, since they are flexible and durable.

As the web formation on its own has limited strength it is necessary to consolidate it and bind the fibers together to enhance its strength. This can be done through thermal, mechanical or chemical bonding, and once again the choice of method depends on the desirable properties for the end-product. When bonding the web thermally the thermoplastic properties of synthetic fibers are utilized to form bonds under heating. The synthetic fitbers can either be the web fibre itself or components added to the web for the sole purpose of binding the web together. In mechanical bonding the fibres are physically bonded with each other through inter-fibre friction which is achieved through needlepunching or hydroentanglement.

When the web is instead consolidated through chemical bonding, special binders are added to generate formation of bonds between the fibres. There are different methods of applying the binders to the web including spraying, coating or impregnating. Commonly, the binders used in commercial products are fossil-based polymers produced through emulsion polymerisation, often referred to as latex binders. However, as the interest in producing more sustainable nonwoven materials is growing so is the investigation and applications of bio-based and biodegradable binders. There are currently however few bio-based commercial options available. Not only do the different fibers, web forming methods and bonding methods affect the final properties but it is also possible to further customize the fabric with finishing treatments. For certain nonwovens materials the water absorbing property is a key parameter. However, it is also important with good wet and dry tensile strength, appropriate elongation and a suitable basis weight. To obtain these desirable characteristics the chemically bonded nonwoven may contain some sort of fossil-based polymer which has well documented effects on the tensile strength of the material. When now shifting focus from the fossil-based polymers in an effort to find a biodegradable replacement one large challenge is to find a biodegradable binder which still contributes to a strong and durable end-material.

Cellulose ethers are important and highly commercial cellulose derivatives. The most significant characteristic of cellulose ethers is that they are well soluble in water, but most of them are also nontoxic and odor- and tasteless making them appropriate for food and skin contact. However, they are also used as solution thickeners, binders and film formers in paint, building material and textiles. Furthermore, the moisture absorbent properties of cellulose ethers have been utilized in the area of superabsorbent material. The etherification of cellulose is usually performed with activated alkali cellulose which is typically treated with alkyl chlorides. A generalised reaction described by R.A. Young (2002) is presented below. Cell(OH) + NaOH + RCI → Cell(OR) + NaCI + H2O

Commercially, the most important cellulose ether is the anionic ether carboxymethyl cellulose (CMC). Due to its anionic nature CMC is easily soluble in water already at low DS. When carboxymethylation is performed on cellulosic fibres the fibres obtain enhanced hydrophilic properties as well as a high bonding strength. The enhanced hydrophilic properties contribute to greater plasticity, meaning it gains a greater flexibility, and increased bond area as well. It is common to use CMC in its sodium form. Other important cellulose ethers are methyl or ethyl cellulose, hydroxypropyl methyl cellulose (HPMC) and hydroxyethyl cellulose (HEC). HEC have similar properties as CMC and is, just like CMC, currently used for applications such as preparations for superabsorbent materials.

Cross-link is an irreverstole covalent bond which is formed between two polymer chains by a chemical reaction. The cross-linking of polymers is utilized in material to obtain higher mechanical strength, fluid absorbency and fluid retention.

The polymers which are currently the most popular ones to use as binders for nonwoven Fabric, are prepared through emulsion polymerisation, where they are customised and adapted for specific requirements. These binders are referred to as latex binders.

Key parameters that are optimised are the glass transition temperature (Tg), the molecular weight and the solubility in water. Other important parameters to consider are viscosity and particle size. The introduction of a cross-linking agent in the emulsion polymerisation is important for the latex binder’s ability to contribute to higher durability of the end-material.

The formation of covalent bonds between polymer chains increases the molecular weight of the polymer and makes it less vulnerable to external stresses. If the polymer is too cross-linked however, it loses much of its flexibility. Thus it is important to introduce a functional group which interrupts the packing of the polymer chains in the emulsion, and preserve some of the desired flexibility of the polymer. Ethylene vinyl acetate (EVA) is a polymer customized through emulsion polymerisation which is suitable for applications with airlaid nonwoven based on cellulosic fibers. Since cellulose and most cellulose ethers are easily soluble in water, a cross-linking agent is necessary if they are to be used as binders, to provide the end-material with a desirable level of wet strength. The cross-linking of a cellulosic material is achieved by linking two or more of the hydroxyl groups in a cellulose molecule or in a neighboring cellulose molecule. Thus, it is crucial that the cross-linking agent used for CMC and similar substances is difunctional with respect to cellulose to ensure that this reaction is possible. For example, one of the most investigated cross-linking agents for CMC has been formaldehyde which, even though it is monofunctional in several reactions, is difunctional with respect to cellulose. While cross-linking appears to be essential for obtaining an end-material with acceptable levels of mechanical strength, studies have shown that a higher level of cross-linking in a cellulosic material does not only contribute to higher mechanical strength, but also to less swelling and less flexibility of the material.

As formaldehyde is no longer a potential cross-linking agent, it has become popular to investigate the hydrogel formation from the combination of CMC together with the polycarboxylic acid citric acid, which would be working as a cross-linking agent

These studies have been performed mainly in the area of superabsorbents. As mentioned earlier the stiffness of the end-material increases and the swelling decreases as the level of cross-linking increases, making it undesirable to obtain an excessively large level of cross-linking.

Trials performed on the combination of CMC and citric acid have shown that the end- material becomes extremely rigid and loses most of its elongation. This implies that even though the cross-linking can be obtained with a cellulose derivative and carboxylic acid alone, a plasticizer or softener might be a necessary additive to increase the softness and flexibility of the finished product. It has surprisingly been found by the present inventors that it may be possible to increase the softness by altering the ratio between the cellulose derivative and acid and at the same time improve or maintain the tensile strength. As discussed a high level of cross-linking may lead to increased stiffness and decreased softness of a material. It might therefore be relevant to add a substance to the material which will increase the flexibility and softness while still ensuring high mechanical strength. Such a substance is often referred to as plasticizer. Although this term includes a wide variety of materials it is mostly used when discussing additives in plastics. Some well-known plasticizers include Phthalates, such as di-2-ethylhexyl phthalate (DOR). The plasticizer is mixed and incorporated into the polymer matrix of the material to which it is supposed to improve. The incorporation can be obtained through a few different processes, such as heating and mixing, and there are some different theories which explain the observable characteristics of the plasticizer. One theory, the lubricating theory of plasticization, suggests that the plasticizer molecules diffuse into the polymer during heating, and there, weaken the polymer-polymer bonding. This prevents the formation of a static polymer network and reduces intermolecular forces and thus increasing the softness, flexibility and elongation of the polymer. Most plasticizers today are fossil-based polymers but if biodegradability is a desired characteristic of the end- material a biodegradable option needs to be used. Possible commercial bio-based plasticizers are glycerol or citric acid derivatives such as acetyl tributyl citrate. For the specific application as a softener in the nonwoven wipes produced by Essity and any subsidiary thereof, one essential characteristic is that the plasticizer must be water- soluble. Furthermore, studies have shown that as the molecular weight of the plasticizer decreases, the efficiency of the plasticizer increases. Increasing plasticizer concentration increases flexibility, decreases tensile strength and reduces hardness, meaning that a compromise has to be made between mechanical strength and flexibility. For the purpose of using plasticizer in nonwoven together with a cellulose-based binder, the added amount should be around 10% of the cellulose derivative mass. This level of additive should be high enough to increase the softness and elongation, while still keeping a desirable level of mechanical strength.

EXPERIMENTAL SECTION Method Following section will describe the experimental part including equipment, chemicals and laboratory methods. A detailed description of physical testing on material properties will be included as well.

Equipment and material The equipment used for laboratory testing is listed in table 1. Table 1: Summary of equipment

Nonwoven material

Throughout the description all testing will be performed on a nonwoven cloth based on cellulose fibers derived from wood. The nonwoven cloths are produced by airlaid web formation and have no additives beyond the basic cellulosic fibres. This means that the fabric lacks cohesion and is therefore extremely delicate and must be handled with much caution. The trials will be performed on different combinations and ratios of the substances, to gain a deeper understanding of the binding behaviors and how they can be implemented. The combinations of substances as well as the amount of each substance are presented in a full list in table 8, and a summarized list is presented below in table 2. The samples will be compared to a reference binder which is a typical EVA binder. Each of the chemicals are chosen for a specific reason. As the combination of CMC and citric acid is known and studied for this specific application the experiments will begin by examining different ratios of this combination to further investigate the structure and behavior of both the binder and the nonwoven cloth. For the experiment sodium CMC will be used, but will continuously be referred to simply as CMC.

The combination of CMC and citric acid will also be investigated with the addition of glycerol which will work as a softener or plasticizer. The hope is that the addition of glycerol will improve the softness and flexibility of the nonwoven material, as it otherwise becomes quite rigid and stiff when CMC and citric acid is used on its own.

Table 2: Summary of the different combinations of chemicals used to prepare 5 binder-samples for spraying and testing.

CMC- Carboxymethyl cellulose, HEC -Hydroxyethyi cellulose, CA - Citric add, GLY-Glycerol, HCW Hydrochloric add

Formation of binder The amount of each chemical presented in table 8, is added to a 100 g solution containing de-ionized water and 0.3 g of the blue pigment Irgalithe Blue R-LW. The addition of pigment is necessary to ensure an even distribution of binder over the nonwoven cloth. More de-ionized water is then added until the total mass of the solution is 300 g. The mixture of water, pigment, cellulose derivative, acid and in some cases glycerol, is stirred on a magnetic stirrer overnight. This is to enable dissolution of the cellulose derivative. The added mass of each substance to the mixture is calculated through equation 2.

(2) Where m _for solution is the mass of the substance used for the binder solution, s is the dry content of the binder and c is the concentration of the commercial product.

Soraving and drvino of binder

The mixed solutions of water together with the additives of each sample are added to a manual spraying equipment. 20 g of the mixed solution is added per nonwoven cloth. The nonwoven cloth is placed on a steel tray with cavities which is placed in a fume cupboard. The cloth and the tray may be angled or leaned against the wall of the fume cupboard to provide optimum spraying range. Thus it is of importance to ensure that the cloth is properly fixed to the tray, perhaps with help of clamps or the like. The cloth is then evenly sprayed with binder solution at one side on a distance of circa 10 cm, and dried in an oven directly afterwards for 15 minutes at 150 °C. After drying for 15 minutes the procedure is repeated for the remaining side of the cloth. The mass of binder on should be approximately 10 g per side of each cloth. 8 cloths are sprayed per sample, meaning that the described method is repeated 8 times per sample.

Measurement of pH-level pH-levels of selected samples of binder combinations are measured with a pH-meter of the brand VWR Symphony, which is shown in figure 8. An electrode is rinsed with de-ionized water and then placed in a small beaker containing the binder mixture. The electrode is kept still until the display stops blinking and the final pH-value is logged. Results from the pH-measurements are presented in table 3.

Testing of material properties As the material has dried after the preparation and spraying of binder. The properties and qualities of the material is to be tested and evaluated. There are several characteristics that are essential for nonwovens for use as wipes. Thus to ensure that these are obtained some tests need to be performed and the tests chosen are basis weight, thickness, dry and wet tensile strength, absorption capacity and absorption time.

Thickness and basis weight

The first test that is conducted is a measurement of the basis weight. The basis weight is measured by weighing the cloth on a scale which give the results in gram. However, the results are then recalculated by adding the dimensions of the cloth and presented in g/cm2. This is done on all cloths from each sample. The thickness is measured by means of a measuring foot with a fixed load which is lowered onto the sample at a given rate.

The thickness is read off at the digital thickness gauge. The pressure plate gives a static load of 0.5 kPa. These measurements are repeated 5 times for different part of each cloth and the results are given in millimeters. Dry and wet tensile strength

When testing the tensile strength of the nonwoven a tensile tester of the brand Lloyd is used. A sample with determined dimensions is stretched to break at a constant rate of elongation in the tensile strength apparatus. The tensile strength is recorded as a function of the elongation. From received data, the different parameters are calculated. Measurements are performed on 5 dry pieces of each sample in machine direction (MD) and 5 pieces of each sample in cross direction (CD). Furthermore, measurements are also conducted on wet samples as well. For the wet testing one sample with determined dimensions is soaked in water just before stretching to rupture/break at a constant rate of elongation. The tensile strength will record as a function of the elongation at this measurement as well. From received data, the parameters are calculated. As for dry testing, wet testing is conducted for 5 pieces of each samples in both MD and CD direction. Water absorption time and capacity

To determine the water absorption time and the water absorption capacity of the nonwoven a basket immersion method is used. A test piece of defined width and total mass is placed in a cylindrical basket which is dropped from 2,5 +/- 0,5 cm above a water surface. The time is measured from when the basket is dropped until the test piece has been fully wetted and the results serve as water absorption time. The amount of absorbed water is determined from the dry and wet weight of the test piece. The results from the water absorption time and capacity tests are presented in table 7.

Results In following section results from binder distribution and material testing will be presented in summarized tables where they are compared to the value of the latex reference binder. pH A measurement of pH-values of selected binder mixtures were conducted to obtain a deeper understanding of the behavior of the binder. The results from the pH- measurements are presented in table 3. Table 3: Summary of pH-levels for chosen samples Binder add-on

The binder solution is prepared and sprayed upon the nonwoven fabric as described above. The binder add-on is shown both as the mass of the CMC and the acid in the binder solution, as well as the percentage these components represent of the total weight of the treated nonwoven. The add-on is different for each sample, although the add-on of CMC is in many cases kept constant for comparison reasons. The dry weight of the nonwoven fabric, the wet add-on of binder and the dry add-on of cellulose derivative and carboxylic acid for each sample are presented in table 9.

The dry weight of the nonwoven fabric is measured, and so is the mass of the wet add-on. The dry add-on of the binder on the nonwoven fabric in grams is calculated through equation 3 and the add-on in percentage is calculated through equation 4.

(3) Where d is the dry add-on and w is the wet add-on of the sprayed binder. (4)

Where a is the add-on of the binder and indexes 1 and 2 represent the cellulose derivative and carboxylic acid respectively.

When preparing the binder solution with HEC and citric acid it was soon clear that the viscosity of the solution was very high. Due to the high viscosity of the mixture it was hard, impossible almost, to distribute it over the nonwoven material through spraying.

The solution was therefore diluted with water to half the concentration, and while it was still challenging to use the spraying equipment with the binder mixture it was a clear improvement. This of course leads to a lower add-on of binder for these samples in comparison to samples containing CMC, which might affect the results from the physical testing. Thickness and basis weight

Thickness and basis weight of each sample is analyzed as described above and a summarized version of the results from these tests are presented in table 4. Full results are available in table 10.

Table 4: Basis wight and thickness of nonwoven cloth, after binder spray

* Increased amount of glycerol in comparison to previous trials

Tensile strength

Mechanical strength, elongation and wet strength is analyzed through a tensile tester, further described above. Full results from dry tensile tests are presented in tables 11 and 12, while full results from the wet tensile tests are presented in table 13 below. In tables 5 and 6 the results are presented in comparison to the reference binder.

Drv tensile strength

Below is shown trends in dry mechanical strength. Table 5; Summary of dry maximum tensile strength and elongation

Cellulose Acid Ratio Additives Strength Elongation

Reference 0 0

CMC 1 0 -0,5

CMC CA 2 to 4 f 0,3 -0,7

CMC CA 4 to 2 41,5 -0,4

CMC CA 1 to 3 -0,5 -0,7

CMC CA 1 to 2 0 -0,7

CMC CA 1 to 1 -0,1 -0,6

CMC CA 2 to 1 40,5 -0,5

CMC CA 3 to 1 40,8 -0,4

CMC CA 1 to 3 GLY -0,4 -0,5

CMC CA 3 to 1 GLY i 1,5 -0,4

CMC CA 3 to 1 GLY* 40,6 -0,4

CMC HCl pH 3 ^• ♦ ^• 0,2 -0,4

CMC HO pH 4 40,4 -0,4

CMC HQ pH 5 ^■ +0,6 -0,3

CMC HCl pH 6 ^■ ·:· 1 ,4 -0,3

HEC CA 1 to 3 -0,4 -0,7

HEC CA 3 to 1 -0,6 -0,4

CMC + HEC CA 1 to 3 -0,2 -0.7

CMC 4 HEC CA 3 to 1 ; 0,5 -0,5

* Increased amount of glycerol in comparison to previous trials

Table 6: Summary of wel maximum tensile strength and elongation

Cellulose Add Ratio Additives Strength Elongation

Reference 0 0

CMC 1 -0,6 41,5

CMC CA 2 to 4 ! 0,3 -0,7

CMC CA 4 to 2 ^• f-0,1) -0,5

CMC CA 1 to 3 -0,6 -0,8

CMC CA l to 2 -0,3 -0,7

CMC CA 1 to 1 -0,2 -0,6

CMC CA 2 to l -0,1 -0,5

CMC CA 3 to 1 rO,l -0,4

CMC CA 1 to 3 GLY -0,4 -0,7

CMC CA 3 to 1 GLY f0,5 -0,3

CMC CA 3 to 1 GLY* 0 -0,3

CMC HCl pH 3 -0,2 -0,3

CMC HO pH 4 -0,3 -0,2

CMC HQ pH 5 -0,3 -0,2

CMC HQ pH 6 -0,2 -0,3

HEC CA 1 to 3 -0,6 -0,7

HEC CA 3 to 1 -0,7 -0,3

CMC + HEC CA l to 3 -0,3 -0,6 CMC ψ HEC CA 3 to 1 0 -0,5

* Increased amount of glycerol in comparison to previous trials

Table 7: Summary of water absorption time and capacity results

*Increased amount of glycerol in comparison to previous trials

It may be seen from the results, that the elongation of the nonwoven material decreases as a large amount of cross-linking agent is added to the binder, in comparison to using CMC by itself. The wet strength is rapidly increased as well when a cross-linking agent is added. These results can be observed in tables 5 and 6 and both phenomena were expected. However, even when CMC is used on its own the elongation is still not at the same level as the elongation of the reference binder, which also can be seen in tables 5 and 6. This might be due to the fact that CMC has high molecular immobility which prevents the polymer chains to slip past each other, and thus leading to a stiffer material.

From the same tables it is possible to deduct that with increased add-on of the binder the mechanical strength increases as well, which is an additional expected consequence. The elongation of the material is however less affected by the increase of binder add-on, which once again is possible to observe in table 5. The dry elongation is slightly higher with more add-on but just barely. A possible explanation for this is that there are no cross-links between the cellulosic fiber and the binder, but only between the citric acid and the CMC molecules. In that case there is no increase in level of cross-linking, only an increase of binder add-on. Furthermore, the absorption time increases and the absorption capacity decreases as the level of binder add-on gets higher, which table 7 shows. This indicates that increased binder add-on decreases the swelling properties of the material, and therefore less water can be absorbed.

As shown by results presented in tables 5 and 6, the elongation of the nonwoven material is surprisingly increased when the amount of carboxylic acid in the solution is decreased.

A further surprising result from tables 5 and 6 is that the mechanical strength, both dry and wet, of the material is increased as well when the level of carboxylic acid in the binder solution is decreased. The ratio between dry and wet strength is however decreasing with lower levels of carboxylic acid, which means that the wet tensile strength is less affected by the level of acid in the binder solution. This result is surprising as a higher level of citric acid may be expected to contribute to higher levels of cross-linking and thus higher levels of mechanical strength due to strong bonds between molecules. A possible explanation for these unexpected results is that the mechanical strength is affected not only by the cross-linking, but also by the pH of the binder solution. As expected, and presented in table 3, there is an increase in pH when decreasing the amount of carboxylic acid, which might provide an explanation to this behavior.

Finally, it is possible to observe in table 7 that the water absorption capacity and absorption time are less affected by the different ratios of CMC and citric acid than the mechanical strength. It is easy to obtain an acceptable level of capacity and an acceptable time, quite independent of the amount of citric acid in the binder.

Cross-linked HEC with citric acid When the cellulose ether HEC was combined together with citric acid, the binder solution became highly viscous. This characteristic made it difficult to distribute it by spraying, as it got gummed in the spraying nozzle and very low amounts were distributed over the cloth. Because of this the solution was diluted into half, which affected the results of the physical testing. Due to the dilution it is difficult to compare the results of HEC and citric acid with the results of CMC and citric acid, but it is still possible to analyze trends in the results. In contrast to the results when using CMC, the material seems to gain slightly higher mechanical strength if more citric acid is used, but lower elongation. This can be explained by the levels of cross-linking; higher amounts of cross-linking agent provides higher levels of cross-linking and higher levels of mechanical strength, but the material becomes less flexible. This is however not the case for CMC and citric acid. There might be a difference in the bonds created for CMC and citric acid and HEC and citric acid or perhaps the HEC molecule is less affected by pH, making the cross-linking more essential for HEC and citric acid.

Combination of CMC and HEC

As HEC was combined with CMC the spraying of the binder solution was possible to perform without a dilution being necessary, thus the levels of mechanical strength are higher for these samples than for the samples with only HEC and citric acid. The elongation of the material seems to decrease when HEC and CMC are combined, in comparison with if only HEC is used. However once again as the add-on for samples with only HEC is lower, it is complicated to compare them with each other. When comparing the combination of CMC and HEC to when only CMC is used, the mechanical strength is not improved. Neither is the elongation of the material improved, even though the hypothesis was that it would be. The one thing that is improved when using this combination is the wet/dry strength ratio, where a combination of CMC and HEC shows a higher wet strength relative to the dry strength than when CMC is used on its own. These results suggest that the intermolecular cross-linking might not be as essential as some studies have proposed.

CMC together with HCI

The tensile strength as can be seen in table 5 and 6 increase with lower amount of added citric acid. To investigate how the pH effects the CMC capability to provide tensile strength, trials with CMC and HCI were conducted. Surprisingly it was found that by setting the pH with HCI to pH 6, 5, 4 and 3, the highest tensile strength was obtained with the higher pH and the fact that the tensile strength decreases as the pH decrease suggests that an acid catalysis may take place which enables bonding between CMC and the cellulose fibers. Reviewing the series of CMC - Citric acid trials with a pH perspective, it may be deduced that lower amount of added Citric acid will provide higher pH and also here the acid catalysis can be seen as the major contribution to the tensile strength. Further indication of the role of acid catalysis is in the comparison with the low tensile strength obtained with CMC alone.

A Full list of chemicals

Table 8: Full list of binder-samples prepared for spraying and testing.

Sample Modified Cellulose m (g] Carboxylic acid m lei Additive

Ref. Conventional hinder 13,90

0.1 CMC 1,88

1.1 CMC 3,75 CA 7,50

1.2 CMC 3,75 CA 1,88

1.3 CMC 1,88 CA 1,88

1.4 CMC 1,88 CA 3,75

1.5 CMC 1,88 CA 0,94

1.6 CMC 1,88 CA 5.63

1.7 CMC 1,88 CA 0,63

1.8 CMC 1,88 CA 5,63 GLY*

1.9 CMC 1,88 CA 0,63 GLY*

1.10 CMC 1,88 CA 0.63 GLY**

3.1 HEC 0,94 CA 2,81

3.2 HEC 0,04 CA 0,31

4.1 HEC -r CMC 1,88 CA 5.63

4.2 HEC :· CMC 1,88 CA 0,63

6.1 CMC 1,88 HCl 52,00

6.2 CMC 1,88 HCl 25,00

6.3 CMC 1,88 HCl 7.00

6.4 CMC 1,88 HQ 2,80

The total mass of the binder solution is 3G0g.

* The mass of glycerol in solution is 10% of the mass of cellulose derivate

**Thc mass of glycerol in solution is 40% of the mass of cellulose derivate B Results of material testing

Table 9: Wei and dry average add-on of binder on nonwoven cloth

Wet add¬

Dry

Sample on/sheet Dry add-on/sheet (g) Add-on/ sheet |%] weight |g)

Id Cellulose ; Acid Cellulose 4- Acid

Ref. 5,4 19,9 0,50* 8,5*

0.1 5,4 20,1 0,13 2,5

1.1 5,2 19.0 0,24 4 0,48 4,1 4 8,1

1.2 5,2 19,5 0,24 · 0,12 4,3 'ί" 2,2

1.3 5,0 20.0 0,13 t 0,13 2,4 4 2,4

1.4 5,0 20,0 0,13 ··· 0,25 2,3 ·}· 4,7

1.5 5,1 20.0 0,13 4 0,06 2,4 4 1,2

1.6 5,2 20,0 0,13 · 0,38 2,2 t 6,6

1.7 5,1 20, 1 0,13 4 0,04 2,3 4 0,8

1.8 5,1 20,1 0,13 4 0,38** 2.3 4 6,6**

1.9 5,1 20.1 0.13 ; 0,04** 2,4 f 0,8**

1.10 5,4 20,0 0,13 ί 0,04*** 2,4 0,8***

3.1 5,1 19.7 0,12 4 0,12 2,3 4 2,2

3.2 5,2 19,9 0,12 ·:· 0,03 2,3 4 0,5

4.1 5,5 20.1 0,13 t 0,38 2,1 4 6,1

4.2 5,4 19,8 0,12 ί 0,04 2,24- 0,7

6.1 5.4 20.0 0,13 t 0,35 2,1 4 5,9

6.2 5,4 20,0 0,13 ί 0,17 2,24· 2,9

6.3 5,4 19.9 0,13 4 0,05 2,2 4 0,9 6.4 5,4 20,0 0,13 t 0,02 2,2 4 0,3

Calculations of values presented in table [9 are shown in equations

* Neither cellulose derivates nor carboxylic acid is used, bat conventional latex binder

**Also contains 0,013 g glycerol vthich is 10% of the added (rllulose

**Also contains 0,052 g glycerol which is 40% of the added cellulose

Table 10: Basis weight and thickness of nonwoven cloth after binder spray

The value of the reference binder is an average value from all of the tests conducted.

Table 11: Dry maximum tensile strength

Sample MD (N/m| CD fN/mj Ratio MD/CD {%]

Ref. 225 222 1,0

0.1 215 211 1,0

1.1 256 310 0,7

1.2 577 558 1.4

1.3 203 199 0Λ

1.4 212 218 1,0

1.5 327 342 1,0

1.6 121 113 1.0

1.7 408 382 1,1

1.8 154 133 1,3

1.9 553 568 14

1.10 355 363 1,0

3.1 134 126 1,1

3.2 113 79 1,3

4.1 210 159 1,2

4.2 345 304 1,2

6.1 288 270 1,1

6.2 328 292 1,1

6.3 362 345 1,0

6.4 537 548 L0 the value of the reference binder i» an average value from all of the tests conducted.

Table 12: Dry tensile elongation /%/

Sample Elongation MD Elongation CD Strain index MD/CD

Ref. 7,8 7,5 7,7

0.1 3,8 3,6 3,7

1,1 2.0 2,6 2,3

1.2 -4.3 4,8 4,5

1.3 3,2 3.1 3,2

1.4 2,5 2,5 2,5

1.5 4,0 3,6 3,8

1.6 2,2 2,1 2,2

1.7 5.2 4,2 4,7

1.8 2,6 2.3 3,5

1.9 4,6 5.0 4,8

1.10 4,4 4,5 4,5

3.1 2,2 2,5 2,3

3.2 4.9 5.0 5,0

4.1 2,0 2,2 2,1

4.2 3,8 3,9 3,9

6.1 4,3 4,5 4,4

6.2 4,3 5,2 4,8

6.3 4,7 5,6 5,2

6.4 5,7 5,7 5,7

The value of the reference binder is an average value from all the tests conducted

Table 13: Wet maximum tensile strength

Sample MD |N/m| CD |N/m| Elongation MD |%) Elongation CD |%]

Ref. 115 114 12,9 12,6

0.1 51 47 6.2 7,4

1.1 142 157 3.9 4,1

1.2 222 231 7,8 7,7

1.3 94 93 M 5,5

1.4 91 82 4,2 4,2

1.6 119 109 7 _: 4 7,6

1.0 59 52 4 _: 0 .1,2

1.7 119 132 9,7 8,2

1.8 76 82 5:1 4,6

1.9 173 195 10,7 9,5

1.10 128 112 8,7 9,1

3.1 Cl 45 5,6 4.3

3.2 33 39 101) 8.1

4.1 91 68 5,0 4.2

4.2 111 110 6.5 7,5

0.1 95 84 7.9 9,2

0.2 84 79 10,1 9,2

6.3 83 87 10,1 9,6

6.4 91 87 8.5 8,4

The value of the reference hinder ts an average value from all of the testa conducted.

Table 14: Water absorption time and capacity results

Sample Absorption time [sj Absorption capacity [g/gj

Ref. 3.0 13,5

0.1 1,6 13,1

1.1 3,3 15,0

1.2 2.1 14,6

1.3 2,1 11,7

1.4 1,9 15,9

1.5 1,8 16,6

1.6 4,6 17,9

1.7 1,6 17,5

1.8 3,7 16,8

1.9 1,7 16,3

1.10 1.6 14,6

3.1 1.7 16,0

3.2 2,0 16,0

4.1 1.4 15,0

4.2 1,4 14,5

6.1 1,6 14,1

6.2 1,6 14,6

6.3 1,7 14,6 6.4 1.5 14,4

The value of the reference binder is an average value from all of the tests conducted .