Background One of the essential driving forces in the development work concerning utilization of wood fibre based pulp, as main raw material for e. g. package products is to maximize the strength properties of the material without increasing the weight thereof. This is important for an efficient utilization of raw material as well as for utilization of transports.

The strength properties of such package products depend among other things on the number of bonds between individual fibres, the strength and shape of the fibres, the density distribution in the thickness direction and distribution of the orientation of the fibres in different directions, as well as how the fibre matrix has contracted during the drying process.

It is a general opinion that bonds between fibres are created predominantly through intramolecular hydrogen bond formation during the drying process (Clark 1985). The contact surfaces between fibres and the chemical composition of the fibre surfaces are important in this context (Nissan 1977, Robinson 1980). Beating reveal the fibrilles and microfibrilles on the fibre surfaces. The amount of, the dispersion and the disintegration of the fibrilles and microfibrilles are considered to be of essential importance for the binding force between fibres (Mitikka-Eklund et al. 1999).

On the whole it is evident that it is desirable to find a method of producing cellulosic articles, e. g. package products, in which the strength properties are maximized without increasing the weight of the articles.

Description of the invention The present invention provides an aqueous fibre suspension that can be used for production of moulded cellulosic articles.

The fibre suspension of the invention is based on cellulase enzyme-treated microfibrillar sulphate pulp (eMFC) and carboxymethylcellulose (CMC).

The term"microfibrillar cellulose (MFC) "is here intended to describe wood fibres that have been disintegrated to small fragments with a large proportion of the microfibrilles of the fibre wall uncovered. In addition, a large amount of very fine material is formed. The fragments and the fines can thus, if they are applied in the right way, contribute to the creation of a closed surface structure with reduced surface porosity and a smoother board

surface. Furthermore, the uncovered microfibrilles on the fines contribute to strengthen the fibre-fibre bonds that are developed during the drying process of the fibre suspension.

Common microfibrillar cellulose (MFC) can be produced by mechanically disintegrating the fibres. This technique has been tried in the so-called the Recell project at the Institute for Fibre and Polymer Technology (Ohisson et al. 2000). The MFC is in this case produced with the aid of a bead beater. The result from the project indicates that mechanically produced MFC pulp has a high specific surface that gives a strong binding capacity in the paper structure, high water retention, good stability in water dispersions and is an insoluble adhesive in colloidal form that does not give the environmental drawbacks as soluble alternatives such as starch-based preparations.

The cellulose fibres can also be disintegrated to microfibrillar cellulose by enzyme treatment, especially treatment with cellulases. This type of microfibrillar cellulose is herein designated eMFC. Enzymes have a totally different effect on the fibres than a beater, and therefore there are essential differences between the resulting two types of microfibrillar cellufose. The method of producing eMFC by enzyme treatment is an essential part of the manufacturing process of the new type of fibre suspension according to the present invention.

The present invention comprises a special fibre suspension that is suitable for a number of different moulded cellulosic articles. The suspension comprises fibres from sulphate pulp that have been subjected to a special enzyme treatment and optionally subsequently been dispersed and stabilized with carboxymethylcellulose (CMC).

The aqueous fibre suspension of the invention is produced by treatment of sulphate pulp with the enzymes endoglucanase and cellobiohydrolase followed by addition of carboxymethyl- cellulose (CMC). The enzyme treated hard or soft wood fibres give a combination of properties regarding surface charge, flexibility, particle size and particle size distribution that substantially differ from conventional sulphate pulp. The enzyme treated fibres of the invention result in microfibrillar cellulose (eMFC). More precisely, the eMFC designates cellulose fibres that have been disintegrated by enzymatic treatment to small fragments with a large proportion of the microfibrilles of the cell wall uncovered. Furthermore, a large amount of very fine material is formed. The fragments and the fines contribute to reduction of the surface porosity and creation of a smoother surface. The uncovered microfibrilles contribute to strengthening the fibre-fibre bonds that develop during the drying process.

Microfibrilles, and in particular well-dispersed disintegrated microfibrilles, have a marked effect on the creation of strong interfibrillar bonds (Mitikka-Eklund et al. 1999).

Thus, the present invention is directed to a moulded cellulosic article obtainable by drying and optionally pressing an aqueous fibre suspension comprising cellulase enzyme- treated microfibrillar sulphate pulp (eMFC) in a casting mould to obtain the article.

In an embodiment of the invention the fibre suspension additionally comprises carboxymethylcellulose (CMC).

In another embodiment of the invention the cellulase enzyme is endoglucanase and/or cellobiohydrolase, and the CMC has an average molecular weight of more than 50 000, and the suspension has a viscosity in the range of 100 to 3000 mPas (Brookfield, 100 r. p. m. sp4).

In a preferred embodiment of the invention the sulphate pulp is a bleached sulphate pulp.

In yet another preferred embodiment the dry weight of the suspension is in the range of 2 to 15 In yet another embodiment of the invention the suspension additionally comprises inorganic coating pigments and/or fillers.

In still another embodiment of the invention the cellulosic article according to the invention is selected from the group consisting of package products, such as troughs and trays for food and feed, or is selected from the group consisting of toys, ornaments, fancy goods, golf pegs and plantation pots.

The invention will now be illustrated with the aid of the examples and the drawings, but it should be understood that the scope of protection is not limited to any specifically mentioned details.

Description of the drawings Figure 1 is a diagram that shows the fibre shortening during enzyme treatment and post treatment, for different enzyme treatment durations (1-6 hours). The enzyme dosage was 10 g/kg for all test points except for B06 (15 g/kg).

Figures 2 shows the fibres before and after 1 and 6.5 hour's enzyme treatment.

Specifically, Figure 2a shows a light microscopy image of bleached kraft pulp fibres before the enzyme treatment; Figure 2b shows a light microscopy image of bleached kraft pulp fibres after 1 hour enzyme treatment; and Figure 2c shows a light microscopy image of bleached kraft pulp fibres after 61/2-hours enzyme treatment.

Figure 3 illustrates a test bar for testing of stress strain properties and its dimensions.

Figure 4 is a diagram that shows the tensile stress plotted against the strain at break for the test plates prepared of different types of eMFC fiber suspensions. Sample 1 was made of properly dispersed eMFC with the addition of 10% CMC; Sample 3 was the same without addition of CMC.; Sample 2 was made of the same eMFC pulp, but with an inappropriate dispersion and mixing.

Figure 5 shows one of the trays made of eMFC used as test specimen.

Figure 6 is a diagram that shows the fibre length of the prepared pulps and the density of the trays.

Figure 7 is a diagram that shows the Young's modulus and the tensile stiffness for test specimens made of the different trays.

Figure 8 is a diagram that shows strain at break and work at break index for test specimens made of the different trays.

Figure 9 is a diagram that shows absorption rate characterized with the EMCO test for the different trays.

Examples First the preparation of the aqueous fibre suspension is described and then examples are given of its applications.

Preparation of fibre suspension A typical example of the procedure for preparation of the enzyme-treated fibre suspension is given below. Even though the proportions and treatment times are optimized for the respective applications mentioned below, the enzyme treatment of sulphate pulp is the same.

The enzyme used was Ecostone L900 from Röhm Enzyme Finland Oy and it consists essentially of two cellulases, namely cellobiohydrolase and endoglucanase. ECF bleached softwood sulphate pulp having a dry content of 34% was withdrawn from the press filter of Korsnäs board machine PM5. The CMC quality was FF10 from Noviant AB having an average molecular weight of 66 000.

Approximately 150 litres of water were heated to 55°C in a double-jacket mixer for controlled temperature regulation and the pH was adjusted to 4.8 with citric acid since the pH was expected to rise at the addition of the pulp. Then 24 kg of dry pulp was successively added. The enzyme was added when approximately half of the amount of pulp had been mixed in, followed by addition of the remaining amount of pulp during two hours. Altogether 66 g of citric hydrate was required to keep a pH between 5 and 5.5 during the enzyme treatment. When the enzyme treatment had proceeded for 7 hours, the treatment was stopped by raising the pH to 9.5 for 20 minutes by addition of sodium hydroxide, 0.5 moles.

Figure 1 shows how the average fibre length varied during the enzyme treatment. Figures 2a-c show the fibres before and after 1 and 6.5 hours enzyme treatment, respectively. The breakdown of the fibres becomes evident, both as fibre shortening and the release of microfibrilles.

The fibre suspension was subjected to an intense mixing after the enzyme treatment in order to mechanically fragment the fibres that had been weakened by the enzyme treatment. In industrial scale a careful refining could carry this out.

An additional type of suspension was obtained by further adding 9.6 kg of CMC under vigorous stirring which was maintained for 45 minutes. The eMFC mixture has a dry content of 15%.

The eMFC mixture is shown in the following to give unique possibilities of being used as renewable raw material for moulded package products such as e. g. troughs and trays for food and feed, and moreover for toys, ornaments, fancy goods, golf pegs and plantation pots.

Example 1 Preparation and characterization of test bars of eMFC for comparison with some thermoplastics Special test bars (Figure 3) for testing of mechanical strength were manufactured of microfibrillar cellulose produced by enzyme treatment (eMFC). The eMFC pulp was prepared as described above. The eMFC pulp was poured into a special casting mould and was dewatered by pressing (<100 kPa) and drying (room temperature >12 h).

The properties of the material were characterized in tensional load (Figure 4) and were matched against the properties of some common thermoplastics in Table 1. The test bars (Samples) 1 and 3 were relatively rigid and in that respect comparable to several of the thermoplastics. This concerns especially Sample 1 that has been dispersed with CMC.

Sample 2, wherein the eMFC pulp had not been mixed completely, did not seem to be of interest for applications wherein the mechanical properties are important. However, the Samples 1 and 3 are rather brittle, and neither the stress at break, approx. 4 MPa, nor the strain at break, 0.1-0. 3%, were particularly high compared to the plastics used as references.

This is likely a consequence of that the materials are non-homogenous (built-up of fibres) and therefore sensitive to defects. Probably the impact strength is also rather low.

Even though the moulded material based on eMFC pulp and CMC cannot match the thermoplastics in every respect regarding mechanical properties, the comparison in Example 2 shows that its stiffness is substantially higher than for conventional wood fibres based moulded materials.

Table 1. Results from tensile strength testing of the plates prepared according to the disclosed method. These are compared to the corresponding properties for some common thermoplastics. Stress at Strain at Material E-modulus, GPa break, MPa break, % Sample 1 eMFC +10 pph CMC, , 3. 4 4.0 0.1 dispersed Sample 2 eMFC, no CMC, not dispersed 0.14 0. 1 2. 3 Sample 3 eMFC, no CMC, dispersed 1.8 4.3 0.3 HDPE*2 0.8 30 up to 1000 LDPE*3 0.2 10 up to 500 PC*'2. 3 70 100 PA 6*5 1.4 65 200 pS*6 3. 3 50 3

*1 Dispersed for 5 minutes in a laboratory mixer.

*2 HD-polyethylene, common"everyday plastic", used for tubes, reservoirs etc.

*3 LD-polyethylene, common"everyday plastic", used for plastic bags, films etc.

*4 Polycarbonate, structural plastic, used for protective helmets, cassettes etc.

*5 Polyamide, Nylon, structural plastic, used for gear wheels, bearings, hoods etc.

*6 Polystyrene, common"everyday plastic", used for packages, disposable articles etc.

Example 2 Manufacture and characterization of tray prototypes made of eMFC.

Special trays were made of eMFC prepared from bleached softwood sulphate Kraft pulp and a corresponding pulp that were not subjected to the enzyme treatment. The trays made of eMFC pulp that were prepared in a so-called Finnish Hand Sheet Former and then press dried at room temperature to the shape depicted in Figure 5. Table 2 shows the trial points. Some of the trials points were dispersed and fragmented in a laboratory mixer before the moulding.

Table 2. The trial points for the trial prototypes.

Notation Pulp Mixing time Ref Not enzyme treated Kraft pulp 0 Ref 300s-"-300 seconds MFC Os Enzyme treated Kraft pulp 0 seconds MFC 30s-"-30 seconds MFC 60s-"-60 seconds MFC 300s-"-300 seconds <BR> <BR> MFC + CMC 60s Enzyme treated Kraft pulp + addition of 60 seconds<BR> <BR> <BR> <BR> 30% dry weight CMC The properties of the trays were characterized by conventional test methods for paper testing. Figure 6 shows the fibre length and the density of the different trays. It is clear that the enzyme treatment solely does not reduce the fibre length. The intense mixing is necessary for obtaining a substantial fibre shortening. In industrial scale the mixing may be carried out in a refiner. This is most likely an effect of debonding of glucoside bonds. Note that there was only a minor fibre shortening for the pulp that has not been enzyme treated.

The fibre shortening seems to be the major cause for the densification of the material, probably to due ability for a closer packing. An increased fibre flexibility and activated microfibrilles may also contribute. The addition of CMC gave a substantial increase in density. As pointed out before the CMC may disperse the microfibrilles, which promotes an enhanced fibre-fibre bonding.

The Young's modulus and the tensile stiffness of the trays were characterized (Figure 7). The eMFC treatment more or less doubled these stiffness properties compared to the trays made of not enzyme treated pulp at similar mixing time. Longer mixing time promoted the stiffness. Once again it is clear that the CMC addition gave a substantial contribution to the stiffness properties.

Figure 8 shows strain at break and work at break for the trays. All the trays made of eMFC pulp were rather brittle. The CMC and the mixing time did not reduce the brittleness.

This indicates that the material is not suitable for applications where the impact resistance is important if the brittleness is not compensated by an increased thickness.

Figure 9 shows that the water absorption time and the wetting resistance are significantly influenced by the enzyme treatment as well as the mixing time. The dynamic water absorption was characterized by an ultrasonic technique (Emtec EST 4.0). A fast declination of the IR-value (i. e. the transmittance) indicates rapid absorption. At short contact times it is the amount and characteristics, (e. g. tortuosity and surface energy) of the small pores that control the absorption behaviour. The sample that had not been enzyme treated but mixed

for 300 seconds had fast initial absorption (the bold line) and so had also the sample that had been enzyme treated but not mixed. Increasing the mixing significantly reduced the water absorption. For the sample that had been enzyme treated and mixed for 300 seconds the absorption characteristic was completely different from the other sample. Almost no absorption occurred within this time scale. The sample that also contained CMC showed a complex behaviour. The absorption was initially very small, probably due to the fact that the CMC addition promotes an enhanced and compact fibre structure. However, as CMC dissolves in water, the absorption starts to increase within a second. These results indicate that the absorption behaviour can be controlled to a great extent by adjusting the enzyme treatment, the mixing time and CMC addition. This may have important industrial relevance for several applications, e. g. plant vessels or carriers of pharmaceutical substances.

References Ohlsson, J. , Gabrielli, I., Thilén, M. (2000) "Förnyelsebara material", Struktur 1, p. 3-5 Mitikka-Eklund M, Mari Halttunen, Melander M, Ruuttunen K. and Vourinen T. (1999):"Fibre engineering", 10th International symposium on wood and pulping chemistry, Yokohama, Japan, vol. 1, pp 432.

Nissan A, (1977):"Lectures in fiber science in paper, in Pulp and Paper Technology series (W. C. Walker ed. ), TAPPI PRESS, Atlanta.

Robinson J. V. , (1980):"Fiber bonding", in Pulp and paper chemistry and chemical technology, Vol. 2, (J. P: Casey, Ed. ), John Wiley and Son, New York, p. 915.