Extruded cellulose products are formed from recovered cellulose obtained from natural cellulose sources, such as wood pulp. The recovered cellulose is dissolved to form a solution suitable for extrusion according to the amine- oxide process.

In the so called"amine-oxide"process cellulose is dissolved in a mixture of water and an amine-oxide solvent.

A commonly used amine-oxide solvent is the tertiary amine- oxide NMMO (N-methyl morpholine N-oxide). This solvent is able to dissolve cellulose without having to first derivatise the cellulose, as for example in the viscose process. Once solubilised the cellulose will precipitate from the solution as a recovered cellulose product by contacting the solution with a precipitation liquid which is a non-solvent for cellulose and a solvent for NMMO. The most frequently used precipitation liquid for the amine- oxide process is water or dilute NMMO solution.

Being derived from natural sources by a breakdown process, it is often difficult to adequately control the quality of the recovered cellulose produced in this manner.

In particular, the mechanical properties may be variable or inadequate. It is an object of the present invention to address this.

It is known that in nature cellulose is produced by microorganisms or bacteria from glucose, sugar or other organic substrates. Acetobacter xylinum is a prolific cellulose-producing non-photosynthetic bacterium.

Synthetic bacterial cellulose produced in this way is a pure material with defined and controllable properties. It may be produced on a commercial scale'by fermentation techniques and a commercial product has been available under the trademark Cellulon as a cellulose fibre for use as a binding agent. Other applications of bacterial cellulose include food and drink products and medical products. However, bacterial cellulose is more expensive than recovered cellulose.

Useful introductory material is available on the internet web site of R. Malcolm Brown, Jr, Department of Botany, The University of Texas at Austin, USA. The product Cellulon is discussed in an article by Frank J.

Miskiel, Tappi Journal Vol. 81; number 3, pl83. The production of bacterial cellulose and investigation of the supramolecular structure is given in Hans-Peter Fink et al.

Macramol. Symp. 120,207-217 (1997). Furthermore, German published patent application DE19633405 describes the use of bacterial cellulose together with cellulose from the amine-oxide process, but envisages relatively high bacterial cellulose contents in the range 5 to 90% by weight.

The present invention is based on the surprising discovery that amounts of bacterial cellulose (generally less than 5% by weight of total cellulose in the amine- oxide process are effective in significantly improving the mechanical properties of extruded products formed from recovered cellulose.

Thus, the present invention provides a process for the production of an extruded cellulose product, which comprises -forming a cellulose solution which is a solution in an amine-oxide solvent, which contains non-bacterial cellulose and bacterial cellulose in an amount of 0.01 to 5% by weight of the total cellulose weight; and -extruding the cellulose solution to form an extruded cellulose product.

The invention also relates to a corresponding product.

It has been found that the inclusion of amounts of bacterial cellulose gives rise to improved mechanical strength properties and increased tear resistance in the extruded product, typically a film, sheet, tube or fibre.

In the present invention, it is only necessary to include a small concentration of bacterial cellulose into the extrusion solution according to the amine-oxide process.

Another benefit of the inclusion of bacterial cellulose is the enhanced ability to retain water, which results in improved peeling properties for tubular sausage casings.

It is known in the alternative viscose process to embed a fibre composite material into the film structure to improve the mechanical properties of so produced fibres and sausage casings. As the fibre composite material, a cellulose paperweb mainly consisting of hennep fibres has been used. However, the present invention offers a simpler, faster and more economical solution to the problem of improving mechanical properties in the amine oxide produced product such as tensile strength and tear resistance without the requirement of embedded fibres.

The bacterial cellulose to be used in the process may be from any suitable source. And is particularly that obtained from the fermentation of Acetobacter. Bacterial cellulose referred to as"nata de coco"is one of the many types that may be employed.

The non-bacterial cellulose is preferably cellulose from natural sources (such as wood pulp) which is recovered according to the amine-oxide process.

The bacterial cellulose may be included in the so- called"dope"as a non-dissolved fibre prior to extrusion according to the techniques of the amine-oxide process.

The bacterial cellulose may be mixed with non-bacterial cellulose (eg. wood cellulose) prior to dissolving with NMMO whereby the bacterial cellulose will dissolve partially or completely into the"dope"prior to extrusion.

Thus, the present invention requires almost no modification to the existing process and can therefore be carried out economically.

The extruded cellulose product may be a film, sheet, tube or fibre. The inclusion of bacterial cellulose may enhance the water retention of the cellulose casing thereby improving its properties. Thus, the process is particularly applicable to the production of wrappings or tubular casings for sausages, salami or other cased food products. The cellulose casing may be either used during the production of the food product and removed thereafter or may be retained in place.

Embodiments of the present invention will now be described by way of example only in the following Example.

Example 1 A product may be prepared according to the amine-oxide process as follows. A cellulose solution for extrusion is prepared by mixing cellulose pulp with an aqueous NMMO solution containing about 50% by weight NMMO. To this is added up to 5 weight % of bacterial cellulose. Water is removed from the mixture by applying heat and reduced pressure. Water boils off at approximately 70°C and vapours may be recovered in a condenser. Once the water content is reduced to about 12%, the NMMO monohydrate forms and the cellulose begins to dissolve in the NMMO monohydrate solution. A stabiliser is added to the solution to inhibit thermal degradation of NMMO. The temperature is then increased to about 95°C and all the cellulose fibres dissolve to form an extrusion solution. The pressure is then further reduced to remove air bubbles from the cellulose solution. At a temperature of about 100°C the cellulose solution is a visco-elastic melt with a high viscosity and a pronounced elastic behaviour. The time required to produce the cellulose solution is about 3 hours.

The cellulose solution is then stirred in a storage vessel and extruded through an annular die so as to form an NMMO-cellulose tube. The tube is passed through a precipitation bath containing a precipitation medium, such as water or aqueous NMMO solution. A positive pressure is applied into the air gap between the extrusion die and the precipitation bath so as to keep the tube inflated. The inner volume of the tube is also kept filled with precipitation liquid, the composition of which is controlled to be constant.

The extruded cellulose tube has enhanced mechanical properties due to the inclusion of the bacterial cellulose.