PROCESS

The present invention relates to cellulose-containing pulps and processes for their preparation. In particular, the present invention relates to dissolving grade cellulose- containing pulps formed from a cellulose feedstock comprising at least one non-wood material.

Cellulose-containing pulps are useful in a variety of applications, for example in the production of paper/paper board, tissue, trays or other fibrous products; in the industrial manufacture of viscose, for example to form films, fibres and other shaped articles; and in the production of cellulose esters, cellulose ethers or other cellulose derivatives.

Conventionally, cellulose-containing pulps have been formed from solely wood-based materials, for example softwood or hardwood. However, more recently it has been contemplated to form cellulose-containing pulps from blends of wood and non-wood materials, or non-wood materials alone. Non-wood materials include maize, cotton, sugar cane (bagasse), wheat, rice, barley, rapeseed, switch grass, bamboo, kernel shells for example oat hulls, coconut shells and fruit bunches, for example. The use of non-wood materials is advantageous since they are readily available, tend to be more rapidly replenished in the environment, and may have a lower environmental impact than wood-based materials. Furthermore, non-wood materials may be derived from waste material, in particular agricultural waste. There are two general pulping techniques known to those skilled in the art. Firstly, pulp can be prepared mechanically, by milling or grinding the raw material(s) to physically separate cellulose fibres from hemi-cellulose and lignin.

Alternatively, the raw material(s) can be chemically treated to dissolve lignin and hemicellulose, ideally without disrupting the cellulose fibres native to the raw material(s). Examples of chemical pulping processes include the alkaline sulphate process (also known as the Kraft process), the soda process and the sulphite process.

There are also a number of hybrid pulping processes where chemical processing steps are employed in a mechanical pulping process, or vice versa. Examples of such processes include, thermomechanical processes, where, in addition to mechanical comminution, the raw material(s) is exposed to heat; and chemithermomechanical processes, where the raw material(s) is first exposed to chemicals used in chemical pulping processes before comminution and exposure to heat.

It is known in the art to form cellulose-containing pulps from non-wood materials. It is also known to form cellulose-containing pulps from a blend of a non-wood pulp with a wood-based pulp.

GB 518,887 describes a process for producing pulp from wood, bamboo, straw, grasses and such like cellulose-containing plants by treating the initial material, which may have been comminuted, with alkaline liquids at a raised temperature, characterised by the feature that the initial material is subjected in the dry state to a vacuum treatment and that, after the addition of alkali and after cooking under pressure, the pressure is suddenly released, whereupon the mass is left under atmospheric pressure until the disintegration is complete.

WO 82/01019 describes a process to produce pulp from vegetable, cellulose- containing fibrous material such as coniferous wood, hardwood, straw, bagasse etc.

US 1 ,717,795 describes a process of preparing cellulosic and ligneous materials for pulping which comprises cooking the same in a solution of an alkali-forming metal sulfate, of substantially below 1 % strength, which solution is substantially free from caustic alkalis, soluble sulphides and sulphurous acid, until the cementitious matter in said cellulosic and ligneous material, while retaining its initial physical structure, is rendered readily frangible by pressure, without thereby reducing such material to a pulp.

WO 201 1/051556 describes a process for improving the internal bond strength of paper manufactured from wood pulp, which involves adding to the wood pulp a non- wood pulp composition. The wood pulp and non-wood pulp composition are separately manufactured using chemical methods such as a sulphate, sulphite or soda method, and are then brought together.

WO 2013/158931 describes a process for manufacturing an article which involves combining a first and second fibre to form a fibre mixture, wherein the first and second fibres are obtained from discrete materials, and where at least one of the fibres is derived from an edible fruit of a plant. More specifically, the first fibres are in the form of a wood pulp and the second fibres are in the form of a fruit pulp e.g. a citrus pulp, the two pulps being blended together after their separate manufacture.

WO 03/000983 describes a process wherein comminuted Arundo Donax (also known as nalgrass - a non-wood material) is treated in a conventional pulping process to produce high tensile strength pulp that can be used in the production of paper. The pulp can be combined with wood pulp to produce a variety of products including composite panels, pulp and paper products.

WO 2007/144588 describes a process for the production of a paper pulp, comprising preparing the pulp from a raw material derived from a plant of the Araceae family (i.e. non-wood). The pulp can be mixed with a pulp derived from other species or sources, for example from another non-wood or a wood-based source.

However, the above-mentioned prior art processes require separate cooking processes to form the non-wood and wood-based pulps. This may have the disadvantage of increased manufacturing costs.

It has been proposed to combine the wood-based and non-wood raw materials and then co-cook the blend of materials to produce a mixed cellulose-containing pulp.

JP 2001 -040591 describes a process for producing pulp for paper-making, comprising converting a mixture of sugar cane and woodchip into chemical pulp by means of a chemical pulping process, preferably the sulphate (Kraft) process, wherein the weight ratio of the sugar cane to woodchip is from 2:98 to 30:70. WO 201 1/072718 describes a process for forming a pulp mixture, comprising the steps of: a) providing a wood material and a first liquor; b) treating the wood material in said first liquor in order to release wood fibres; c1 ) introducing an agricultural crop/residue before or during said treatment of the wood material, and during the treatment deriving a first fraction comprising hemicellulose from said agricultural crop/residue; and/or c2) introducing a mixture of a first fraction comprising hemicellulose and a residue liquor derived from agricultural crop/residue by a liquor treatment, said introduction being done before, during or after said treatment of the wood material.

WO 2012/097380 describes a process for forming bamboo pulp or a mixed bamboo/wood pulp using Kraft cooking conditions. The mixed pulp is formed by blending bamboo chips with hardwood chips prior to loading the material in a digester. The resulting pulp can be washed and bleached and used as a blend for making paper.

GB 266, 168 describes a process for the manufacture of pulp or fibrous material from various kinds of cellulosic and ligneous vegetable matter using relatively dilute solutions of salts which have the effect of rendering the intercellular cementitious matter of the vegetable matter readily friable, without dissolving the lignin. Both single types of vegetable matter and blends of vegetable matter are described and these are selected from woods, cane, bamboo, straw, marsh grasses, banana stalks and leaves, bear grass and cocoanut husks.

However, the prior art processes have numerous disadvantages associated therewith. Notably, the resulting cellulose-containing pulps of the prior art are non-dissolving grade pulps, also known as paper grade pulps, and are not suitable for forming dissolving grade pulps. Thus, there remains a need in the art for a process for forming a dissolving grade cellulose-containing pulp from a cellulose feedstock comprising at least one non-wood material.

According to a first aspect of the present invention there is provided a process for forming a dissolving grade cellulose-containing pulp, comprising:

providing a cellulose feedstock comprising at least one non-wood material; treating the cellulose feedstock in a chemical cooking process to form a cellulose-containing pulp; and

bleaching the cellulose-containing pulp to form a dissolving grade cellulose- containing pulp.

By 'dissolving grade cellulose-containing pulp', we preferably or optionally mean a pulp which has an a-cellulose content of 92% or higher. For example, the dissolving grade pulp may have an α-cellulose content of 93% or higher, 94% or higher, 95% or higher, 96% or higher, 97% or higher, 98% or higher, or 99% or higher.

Consequently, the dissolving grade cellulose-containing pulp may preferably or optionally have a hemicellulose content of 8% or less. For example, the dissolving grade pulp may have a hemicellulose content of 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, or 1 % or less.

The inventors of the present invention have surprisingly found that a dissolving grade cellulose-containing pulp can be formed by treating a cellulose feedstock comprising at least one non-wood material, in a chemical cooking process, and bleaching the resulting cellulose-containing pulp.

Dissolving grade cellulose-containing pulps have numerous advantages over non- dissolving grade cellulose-containing pulps. Dissolving grade pulps typically have a lower hemicellulose content and a higher a-cellulose content, are more refined, have a lower degree of polymerisation (DP) and/or have a higher quality control than non- dissolving grade pulps. These characteristics make dissolving grade pulps particularly suitable for use as a feedstock for the production of viscose, to form films or fibres for example.

The non-wood material may comprise one or more of maize, cotton, sugar cane (bagasse), wheat, rice, barley, sorghum, millet, rye, buckwheat fonio, quinoa, rapeseed, switch grass, bamboo, kernel shells for example oil palm or oat hulls, coconut shells, fruit bunches and the like. Preferably, the non-wood material comprises kernel shells, more preferably oat hulls.

The non-wood material may have a cellulose content comparable to that of a wood- based material. The inventors of the present invention have surprisingly found that the use of a non-wood material having a cellulose content comparable to that of a wood- based material may help to achieve a pulp yield comparable to, or exceeding, that obtained when cooking only wood based material(s) under the same conditions. For example, the cellulose content of the non-wood material may be from about 20 wt% to about 60 wt%, from about 25 wt% to about 55 wt%, from about 30 wt% to about 50 wt%, or from about 35 wt% to about 45 wt%. The non-wood material may have a lignin content which is comparable to, or less than, that of a wood-based material. For example, the lignin content of the non-wood material may be from about 5 wt% to about 40 wt%, from about 10 wt% to about 30 wt%, or from about 15 wt% to about 25 wt%.

The non-wood material may have a hemicellulose content comparable to, or less than, that of a wood-based material. For example, the hemicellulose content of the non- wood material may be from about 10 wt% to about 40 wt%, from about 15 wt% to about 35 wt%, or from about 20 wt% to about 30 wt%.

Where the cellulose feedstock comprises at least one non-wood material and one or more wood-based materials, it may be preferable for the non-wood material to have a composition which is comparable to that of the wood-based material, for example a comparable cellulose content, lignin content and/or hemicellulose content. Advantageously, the use of a non-wood material having a composition which is comparable to that of the wood-based material may allow the conditions of the chemical cooking process to be optimised such that both the non-wood and wood- based materials are simultaneously refined. This may help to achieve a high purity cellulose-containing pulp while avoiding the loss of yield as a result of Over cooking' (excessively depolymerising) one or more of the components.

The cellulose feedstock may comprise at least about 1 wt% of non-wood material. Preferably, the cellulose feedstock comprises at least about 5 wt%, at least about 10 wt%, at least about 15 wt%, at least about 20 wt%, at least about 25 wt%, at least about 30 wt%, at least about 35 wt%, or at least about 40 wt% of non-wood material. The cellulose feedstock may comprise from about 1 wt% to about 40 wt% of non-wood material, from about 5 wt% to about 35 wt% of non-wood material, from about 10 wt% to about 30 wt% of non-wood material, or from about 15 wt% to about 25 wt% of non- wood material.

The cellulose feedstock may additionally comprise one or more wood-based materials. The one or more wood-based materials may comprise a softwood, for example spruce, pine, fir, cedar or the like; and/or a hardwood, for example oak, ash, beech, birch or the like.

The cellulose feedstock may comprise about 99 wt% or less of wood-based material. Preferably, the cellulose feedstock comprises about 95 wt% or less, about 90 wt% or less, about 85 wt% or less, about 80 wt% or less, about 75 wt% or less, about 70 wt % or less, about 65 wt% or less, or about 60 wt% or less of wood-based material. The cellulose feedstock may comprise from about 60 wt% to about 99 wt% of wood-based material, from about 65 wt% to about 95 wt% of wood-based material, from about 70 wt% to about 90 wt% of wood-based material, or from about 75 wt% to about 85 wt% of wood-based material.

The ratio of the non-wood material(s) to the one or more wood-based materials in the cellulose feedstock may be from 1 :99 to 40:60, or from 5:95 to 35:65, or from 10:90 to 30:70, or from 15:85 to 25:75. The use of a cellulose feedstock comprising at least one non-wood material alone or in combination with one or more wood-based materials, is advantageous over a cellulose feedstock formed solely of wood based material(s), since non-wood materials are readily available, tend to be more rapidly replenished in the environment, and may have a lower environmental impact than wood-based materials. In addition, non-wood materials may be derived from waste material, in particular agricultural waste. Furthermore, the cost of non-wood materials tends to be much lower than that of wood-based materials.

The chemical cooking process may be any known chemical cooking process for pulping cellulose feedstocks, for example the alkaline sulphate process (also known as the Kraft process), the soda process or the sulphite process. Preferably, the alkaline sulphate process is used.

The alkaline sulphate process typically uses a cooking liquor comprising sodium hydroxide and sodium sulphide, to at least partially dissolve the cellulose feedstock. The effective alkali concentration of the cooking liquor may be dependent on the type of cellulose feedstock used. For example, the effective alkali concentration (as sodium hydroxide) of the cooking liquor may be from about 10% to about 30%, or from about 15% to about 25%, or from about 18% to about 22%.

The cooking liquor may be heated. The temperature to which the cooking liquor is heated may be dependent on the type of cellulose feedstock used. For example, the cooking liquor may be heated to a temperature of from about 150°C to about 200°C, or from about 160°C to about 180°C. The cooking time may vary depending on the type of cellulose feedstock used. For example, the cooking time may be from about 60 minutes to about 180 minutes.

The cooking liquor to cellulose feedstock ratio (CLCF) may be dependent on the type of cellulose feedstock used. For example, the CLCF ratio may be from about 1 l/kg to about 10 l/kg, or from about 2 l/kg to about 7 l/kg, or from about 3 l/kg to about 5 l/kg, or from about 2.5 l/kg to about 5 l/kg.

The chemical cooking process may be carried out in any suitable digester, for example a circulation digester or a Pandia ^R ™ digester. Preferably, a circulation digester is used for the chemical cooking process.

Advantageously, where the cellulose feedstock comprises at least one non-wood material and one or more wood-based materials, a single chemical cooking process, for example the Kraft process, can be used to form the dissolving grade pulp.

The high mineral content of non-wood materials, particularly silica, has previously been found to be problematic in pulping processes. In alkaline cooking processes, for example the Kraft process, the silica is solubilised into the cooking liquor. When the cooking liquor is evaporated for recovery (after the chemical cooking process is complete), the concentration of the silica in the cellulose-containing pulp increases to such an extent that it may cause downstream processing problems, for example if the pulp is used to form fibres it may clogging in the spinnerets. However, the inventors of the present invention have surprisingly found that the blending of one or more wood-based materials with the non-wood material(s) in the same chemical cooking process, decreases the overall silica concentration in the cellulose-containing pulp, thus, reducing or eliminating any downstream processing problems. Without wishing to be bound by any such theory, it is believed that by incorporating one or more wood-based materials, which have a lower silica content, into the cellulose feedstock, the overall silica content is reduced.

The inventors of the present invention have surprisingly found that the yield of the cellulose-containing pulp following the chemical cooking process, may be comparable to, or exceed, the yield obtained when using a cellulose feedstock formed solely from wood-based material(s). The yield of the cellulose-containing pulp may be dependent on the type of cellulose feedstock used. For example, the yield of the cellulose- containing pulp may be at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, or at least about 40%. The yield of the cellulose-containing pulp may be from about 10% to about 50%, from about 20% to about 40%, or from about 30% to about 35%.

After the chemical cooking process, the cellulose-containing pulp is bleached to form a dissolving grade cellulose-containing pulp. Bleaching is a process for removing residual lignin from pulps. Lignin contains chromophoric groups, thus its removal may result in an increase in the brightness and/or cleanliness of the pulp. Any suitable bleaching process may be used to bleach the cellulose-containing pulp. For example, a suitable bleaching process may be Elemental Chlorine Free (ECF) bleaching, which is a well-known process in the art.

Unexpectedly, it has been found that the dissolving grade cellulose-containing pulp formed according to the process of the invention exhibits similar or improved properties compared to a dissolving grade cellulose-containing pulp formed from solely wood-based material(s).

R10 and R18 values may be indicative of the quality of a cellulose-containing pulp. An R10 value is the amount (wt%) of pulp that is insoluble in 10% sodium hydroxide. An R18 value is the amount (wt%) of pulp that is insoluble in 18% sodium hydroxide. The soluble portion of the pulp will likely comprise hemicellulose and/or degraded low molecular weight cellulose - both of which are undesirable in dissolving grade pulps. Thus, higher R10 and R18 values may indicate a higher quality pulp.

The dissolving grade cellulose-containing pulp of the invention may have an R10 and/or an R18 value that is comparable to or greater than the R10/R18 value of a dissolving grade cellulose-containing pulp formed solely from wood-based material(s). The R10 and/or R18 value may be dependent on the type of cellulose feedstock used. For example, the R10 and/or R18 value of the dissolving grade cellulose-containing pulp may be 92% or higher, 93% or higher, 94% or higher, 95% or higher, 96% or higher, 97% or higher, 98% or higher, or 99% or higher. The Kappa number may be indicative of the quality of a cellulose-containing pulp. The Kappa number relates to the lignin content in the pulp and is determined using the standard test method ISO 302:2004. The Kappa number is given as a number in the range of 0 to 100. The lower the Kappa number, the less lignin present in the pulp which may indicate a higher quality pulp.

Following the chemical cooking process (but prior to the bleaching process), the cellulose-containing pulp may have a Kappa number which is comparable to, or less than, that of a cellulose-containing pulp formed solely from wood-based material(s). The Kappa number may be dependent on the type of cellulose feedstock used. For example, the Kappa number may be from about 1 to about 20, from about 5 to about 15, or from about 8 to about 12.

Following the bleaching process, the dissolving grade cellulose-containing pulp may have a Kappa number which is comparable to or less than that of a dissolving grade cellulose-containing pulp formed solely from wood-based material(s). The Kappa number may be dependent on the type of cellulose feedstock used. Preferably, the Kappa number of the dissolving grade cellulose-containing pulp is 1 or less, for example from about 0.1 to about 1 , from about 0.2 to about 0.9, or from about 0.3 to about 0.8.

Prior to the chemical cooking process, the cellulose feedstock may be subjected to pre-hydrolysis, which involves the cellulose feedstock being hydrolysed with water. The pre-hydrolysis temperature may be dependent on the type of cellulose feedstock used. For example, the pre-hydrolysis temperature may be from about 150°C to about 200°C, or from about 160°C to about 180°C. The time at the pre-hydrolysis temperature may also be dependent on the type of cellulose feedstock used. For example, the time at the pre-hydrolysis temperature may be from about 30 minutes to about 120 minutes, or from about 60 minutes to about 90 minutes.

Once pre-hydrolysis of the cellulose feedstock is complete, the pre-hydrolysis liquor may be drained off. Subsequently, the pre-hydrolysed cellulose feedstock may be washed with de-ionized water. The temperature of the de-ionized and the washing time may be dependent on the type of cellulose feedstock used. As an example, the de-ionized water may be at a temperature of from about 130°C to about 150°C and/or the cellulose feedstock may be washed for about 10 minutes to about 30 minutes.

The pre-hydrolysis step may be carried out in any suitable digester, for example a circulation digester or a Pandia ^R ™ digester. Preferably, the pre-hydrolysis step is carried out in the same digester as the chemical cooking process.

The dissolving grade cellulose-containing pulp formed by the process of the invention may be used to produce a cellulosic solution by the application of a viscose process. The viscose process may include one or more of: slurrying the pulp in a caustic soda, steeping the pulp in a caustic solution, mercerisation, xanthating with carbon disulphide, and dissolving the xanthate in an aqueous caustic solution to form viscose.

Alternatively, the dissolving grade cellulose-containing pulp formed by the process of the invention may be used to produce a cellulosic solution by dissolving the pulp in an ionic liquid or in NMMO. The cellulosic solution may be used to form cellulose-shaped articles, for example cellulosic films or fibres. The cellulosic film may be used in packaging, labelling, banknotes or security documents. The cellulose fibre may be used in fabric or clothing.

To form a cellulosic film, the cellulosic solution may be extruded through a slit or rollers, or to form fibres the cellulosic solution may be extruded through a spinneret. The shaped cellulosic solution may then be contacted with an acidic casting solution, for example a solution of sulphuric acid and sodium sulphate, to regenerate the cellulose from the solution.

In addition, the extruded cellulose film may be passed through rollers and/or baths to clean, soften and/or improve optical and mechanical properties of the film.

Additionally or alternatively, the dissolving grade cellulose-containing pulp formed by the process of the present invention may be used in the production of cellulose esters, for example cellulose acetates, cellulose propionates, cellulose butyrates and cellulose nitrates; and/or in the production of cellulose ethers, for example carboxymethyl cellulose, ethyl cellulose and methyl cellulose. Suitable methods for the production of such cellulose-based products are known in the art.

Additionally or alternatively, the dissolving grade cellulose-containing pulp formed by the process of the present invention may be used in the production of paper, paperboard, tissue, trays and/or other fibrous products. According to a second aspect of the present invention there is provided a cellulose- containing pulp derived from a cellulose feedstock comprising at least one grain-based material.

The cellulose-containing pulp is preferably a dissolving grade cellulose-containing pulp.

The inventors of the present invention have surprisingly found that a cellulose- containing pulp derived from a cellulose feedstock comprising at least one grain-based material may be a dissolving grade pulp.

The grain-based material may be selected from the list of non-wood materials outlined above. In particular, the grain based material may comprise a cereal grain-based material, for example maize, wheat, rice, barley, sorghum, millet, oats, rye, buckwheat fonio, quinoa and the like.

The grain-based material may comprise kernel shells i.e. the hulls of the grain which have been stripped from the grain kernels. Preferably, the grain-based material comprises oat hulls.

According to a third aspect of the present invention there is provided a process for forming a cellulose-containing pulp according to the second aspect of the invention, comprising: providing a cellulose feedstock comprising at least one grain-based material; and treating the cellulose feedstock in a chemical cooking process. For the avoidance of doubt, all features relating to the first aspect of the invention may apply to the second and third aspects of the invention and vice versa. For example, features relating to the 'non-wood material' described in the first aspect of the invention may apply to the 'grain-based material' of the second and third aspects of the invention.

The invention is more specifically described in the following, non-limiting examples, and with reference to the figures, in which:

Figure 1 shows SEM images of three different pulp types following ECF bleaching.

Figure 2 is a graph showing the rate of oxidative degradation of two alkali cellulose samples formed from different pulp types.

Figure 3 shows images of viscose produced from different pulp types.

Figure 4 shows images of film samples produced from the viscose samples in Figure 3.

Examples

Two types of cellulose feedstock were used:

1. 100% softwood - spruce and pine mixture (comparative example)

2. 80% softwood - spruce and pine mixture; 20% oat hull (non-wood material) Pre-hydrolysis

The cellulose feedstocks were pre-hydrolysed with water at 170°C for 63 minutes in a circulation digester. The pre-hydrolysis liquor to cellulose feedstock ratio was 3.5 l/kg.

After the pre-hydrolysis, the digester was cooled down, the pressure released, and the pre-hydrolysis liquor drained off. The pre-hydrolysed material was then washed with de-ionized water at a temperature of 140°C for 15 minutes.

Kraft Cooking

Following pre-hydrolysis, the cellulose feedstocks were treated in a Kraft cooking process. The cellulose feedstock was cooked in a cooking liquor composed of sodium hydroxide and sodium sulphide. The effective alkali concentration (as sodium hydroxide) was 20%. The cooking liquor to cellulose feedstock ratio was 3.5 l/kg. The cooking process was carried out at a temperature of 170°C for 120 minutes.

Once the Kraft cooking process was complete, samples of the resulting cellulose- containing pulps were tested. In particular, the Kappa number, ISO-brightness, viscosity, cooking yield, rejected amount, R10 value, R18 value and residual alkali concentration were determined. The results are shown in Table 1 .

Table 1

Cooking yield % 34 34.3

Reject % 0.03 0.05

R10 % 94.6 94.6

R18 % 96.5 95.9

Residual Alkali g/i 13.9 10.2

Note - ISO brightness was determined according to ISO 2470. ISO brightness refers to the diffuse illumination at 0° viewing angle, expressed as absolute reflectance, and is a measure of pulp brightness.

From the results it can be seen that the cellulose-containing pulp formed from the wood/non-wood cellulose feedstock via the process of the invention (Sample 2) has comparable properties to the cellulose-containing pulp formed from a purely wood- based cellulose feedstock (Sample 1 ).

Bleaching

Each of the cellulose-containing pulps from the Kraft cooking process were screened to remove knots and clumped, uncooked fibre bundles. Subsequently, the pulps were bleached using a standard 5-stage Elemental Chlorine Free (ECF) bleaching process to form dissolving grade cellulose-containing pulps.

The first stage (OO) involved oxygen bleaching of the pulp. The pulp was bleached with oxygen at a pressure of 6 bar, and at a temperature of 105°C for 60 minutes. The oxygen bleaching was carried out under basic conditions of 15 kg NaOH/oven dried ton (ODT) with a pulp consistency of 10%. After the first stage of bleaching was complete, the pulp was analysed and the results are shown in Table 2. Table 2

The second stage (Do) involved bleaching of the pulp with chlorine dioxide. The pulp was bleached with 15 kg active chlorine/ODT at a temperature of 65°C for 70 minutes. The pulp consistency was 12%. After the second stage of bleaching was complete, the pulp was analysed and the results are shown in Table 3.

Table 3

The third stage (EP) involved alkaline extraction reinforced with hydrogen peroxide. This stage was carried out with 10 kg NaOH/ODT and 4 kg H2O2/ODT at a temperature of 75°C for 80 minutes. The pulp consistency was 12%. After the third stage was complete, the pulp was analysed and the results are shown in Table 4.

Table 4 Sample 1

Analysis Unit Sample 2

(comparative)

Residual H2O2 kg/ODT 0 0

Kappa number - 0.8 0.8

End pH - 12.3 12.3

Viscosity mL/g 478 587

ISO-brightness % 81.1 80.8

The fourth stage (Di) involved bleaching of the pulp with chlorine dioxide for the second time. The pulp was bleached with 13 kg active chlorine/ODT at a temperature of 70°C for 180 minutes. The pulp consistency was 12%. After the fourth stage of bleaching was complete, the pulp was analysed and the results are shown in Table 5.

Table 5

The fifth stage (D2) involved bleaching of the pulp with chlorine dioxide for the third time. The pulp was bleached with 6 kg active chlorine/ODT at a temperature of 75°C for 180 minutes. The pulp consistency was 12%. After the fifth stage of bleaching was complete, the pulp was analysed and the results are shown in Table 6.

Table 6 Sample 1

Analysis Unit Sample 2

(comparative)

Residual CI0 ₂ Kg/ODT 1 .2 1 .1

End pH - 3.7 3.8

Viscosity mL/g 449 552

ISO-brightness % 90.6 91.3

R10 % 93.3 93.9

R18 % 95.8 96.8

The results from the bleaching process show that the dissolving grade pulp formed from the wood/non-wood cellulose feedstock via the process of the invention (Sample 2) has comparable and in some cases improved properties compared to the dissolving grade pulp formed from a purely wood-based cellulose feedstock (Sample 1 ). In particular, Sample 2 shows higher R10, R18 and brightness values than Sample 1 , after bleaching.

SEM images were taken of Sample 1 and Sample 2 following ECF bleaching and were compared to an SEM image of a Neucel ^R ™ dissolving grade pulp following the same treatment. Figure 1 shows the SEM images as follows:

• Image 1 - Neucel ^R ™ dissolving grade pulp

• Image 2 - Sample 1

• Image 3 - Sample 2

All of the pulps show fibres of between around 20 pm and 25 pm in width and between 0.5 mm and 4 mm in length.

Viscose Production Following bleaching, Sample 1 , Sample 2 and a sample of Neucel ^R ™ dissolving grade pulp formed from a purely wood-based cellulose feedstock (Sample 3 - comparative), were used as a feedstock for the production of viscose.

Preparation of Alkali Cellulose

1800 ml of a caustic solution (17 wt% NaOH) was added to a 3 litre plastic container and heated to 48°C using a water bath. 4 ml Berol ^R ™ 44 (1.784 wt% solution), 1 ml Berol ^R ™ 388 (10 wt% solution) and 6 ml MnS0 ₄ (0.225 wt% solution) were added to the container, followed by 89.2 g of the bleached pulp sample.

The components were mixed using a Silverson ^R ™ shear mixer at 8000 rpm for 1 minute and then returned to the heated water bath. The resulting slurry was then mixed at 400 rpm for 30 minutes using an overhead stirrer. The slurry was poured into a stainless steel cylinder, press-fitted with a wire mesh, and allowed to drain. The slurry press piston was inserted, the assembly placed into a hydraulic jack, and 10 tonnes of pressure applied for 30 seconds in order to remove the remaining excess caustic solution. The resultant alkali cellulose cake was weighed and then shredded in a blender for 60 seconds to form an alkali cellulose crumb.

The alkali cellulose crumb was analysed and the results are shown in Table 7.

Table 7

NaOH content % 14.8 15.0 16.0

Oxidative Degradation/DP Control

Oxidative degradation of cellulose pulps is required in order to achieve the optimum degree of polymerisation (DP) for the processing of viscose into cellulose-shaped articles, for example films and fibres. Thus, the oxidative degradation may be indicative of the suitability of a pulp for use in the production of films and fibres.

The rate of oxidative degradation of the alkali cellulose crumb, was determined for Sample 1 and Sample 2. A 2 L Pyrex ^R ™ vessel was preheated in an oven to 48°C. A portion of the alkali cellulose crumb was added to the vessel and the vessel sealed. The vessel was returned to the oven and the alkali cellulose crumb was sampled at 15 minute intervals. The alkali cellulose samples were neutralised using 10 wt% acetic acid and washed with water.

The average DP of the alkali cellulose samples was estimated by determining the viscosity of a 0.5 wt% solution in copper (II) ethylenediamine. 0.252 g of dry pulp was weighed into a HDPE bottle. 25 ml of distilled water was added to the bottle along with 4 glass beads. The bottle was agitated on a mechanical shaker for at least 30 minutes at full speed. 25 ml of copper (II) ethylenediamine solution (DIN 54270) was added to the sample. The bottle was purged with nitrogen for 30 seconds, and then agitated on the mechanical shaker at full speed for a minimum of 4 hours. The resulting solution was allowed to de-aerate for 10 minutes prior to testing. The viscosity of the resulting cellulose solution was determined using a Cannon- Fenske ^R ™ viscometer (TAPPI T230). 5 ml of sample solution was added to a 150 Cannon-Fenske ^R ™ viscometer. The viscometer tube was placed in a 25°C water bath until the temperature had equilibrated. The solution was drawn above the measurement mark by suction. The time taken for the solution to pass between the upper and lower measuring marks (efflux time) was recorded in seconds. The viscosity (V) and the degree of polymerisation (DP) of the sample was calculated using the following equations:

X = C x t x d

X = viscosity of copper (II) ethylenediamine solution at 25°C (cP)

C = viscosity constant of the viscometer tube

t = efflux time

d = density of cellulose sample (1 .052 g/cm ³ )

DP = (499.48 x (In X)) - 136.35

The rate of oxidative degradation was calculated for both Sample 1 and Sample 2 and the results are displayed in Figure 2.

In Figure 2, it can be seen that Sample 2 had a higher initial average DP compared to Sample 1 , however, the DP of the two samples converged at around 120 minutes.

Viscose Preparation

The alkali cellulose samples were placed into a glass churn and cooled using a compressed air line. A 3-way stopcock and vacuum gauge were then placed into the cooled glass churn and the churn was evacuated to 26 mm Hg. The required volume of CS2 was injected into the glass churn using a glass syringe. The churn was then placed in an oven at 27°C and rotated using a rock tumbler for 100 minutes. The vacuum regain was monitored to ensure there were no leaks to the vessel and that xanthation was complete.

Following completion of the xanthation reaction, the churn was removed from the oven, the vacuum released and the cellulose xanthate transferred into a steel container. The churn was then washed with NaOH solution (18.3 wt%, 17.3°C) to dissolve any remaining cellulose xanthate. The washings were then combined with the cellulose xanthate in the steel container.

The steel container was then placed in a 17.3°C water bath and the cellulose xanthate mixed on full power for 2 hours using an overhead stirrer.

Table 8 shows the specific conditions and chemicals used for each of the pulp samples.

Table 8

Alkali cellulose ageing

Min 103 100 100 time

Xanthation temperature °C 27 27 27

Carbon disulphide ml 19 18.6 18.4

NaOH solution (18.3 wt%) ml 85.9 37.2 46.3

Water ml 540.3 554.0 532.1

Variations in the composition of the alkali cellulose crumb are likely to result from laboratory-scale pressing of the samples, which impacts on the subsequent levels of sodium hydroxide solution.

Figure 3 shows images of the viscose produced from Sample 1 and Sample 2, as follows:

Image 1 - Sample 1 Image 2 - Sample 2

Table 9 shows the cellulose in viscose content (CiV), soda in viscose content (SiV), ball fall velocity, fibre count and filter value (Rv) of the viscose produced from each of the three different pulp samples.

Ball fall velocity, fibre count, and filter value (Rv) are all measures of the filterability of the viscose.

Ball fall velocity, was determined by measuring the time taken (in seconds) for a steel ball weighing 0.13 g +/- 0.02 g to sink to the bottom of the sample of viscose having a depth of 205 mm. Fibre count was determined by measuring the quantity of residual fibres in the viscose.

Rv was determined by loading a viscose sample into a steel laboratory filtration rig and pressuring it to 2 bar. The pressure was maintained at 2 bar throughout the test. When the viscose was visibly passing through the filtration membrane, the timer was started and the weight of the viscose collected was recorded at 5 minute intervals for a total of 30 minutes.

To calculate Rv from the experimental data, the following equation was used:

Fw = the filter value used to describe the filterability of the viscose

So = a constant calculated as the initial and instantaneous flow of viscose through the filtration membrane in m ³ /t, where t is the period of filter operating time in hours

Fw was calculated as follows:

Fw =—

Kw

Kw = the filter clogging value (the clogging constant (kw) x 10,000)

The clogging constant (kw) was calculated as the gradient of the line generated when t/M is plotted against t. Kw was calculated from the expression:

_{Kw =} 10,000 x ((f ₂ / ₂ ) - ( _tl I M _x ))

(t ₂ - t _x x 0.6 x ^7 )

the amount of filtrate

Typically, the higher the Rv value, the higher the quality of viscose, as it does not clog or block the filtration membrane. The Rv value for laboratory viscose is usually considerably higher than that of the equivalent industrial viscose (manufactured on plant).

Table 9

The results show that the viscose of Sample 2 is of sufficient quality (e.g. filterability) for forming cellulose-shaped articles therefrom, for example films or fibres. Variations in CiV are likely to be the main cause of the difference in viscosity between the viscose samples. Higher levels of SiV are also likely contribute to a lower viscosity in the wood-based samples.

Film Casting

Film samples were prepared by casting viscose onto a glass plate at a uniform thickness, and subsequently regenerating the cellulose by immersion in a bath containing 14 wt% sulphuric acid and 20 wt% sodium sulphate. Each film sample was then washed for 40 seconds in each of: i) water at 20°C; ii) 0.4 wt% sodium hydroxide solution at 90°C; and iii) water at 20°C. The film sample was then immersed in a 6 wt% solution of glycerol, placed in a metal frame, and dried in an oven at 100°C for 8 minutes.

Figure 4 shows images of the film samples produced from the viscose of Sample 1 and Sample 2, as follows:

Image 1 - Sample 1

Image 2 - Sample 2