Anti-Microbial Fibres and Their Production

Abstract

Anti-microbial lyocell fibres incorporate an anti-microbial composition which comprises a silver compound deposited on a support material in the form of porous particles having an extended surface area and comprising an oxidic material which is essentially insoluble in water and incapable of forming hydrates. A preferred composition is silver chloride on titanium dioxide particles. The anti-microbial effect is durable to processing and the fibres are not adversely discoloured. Low concentrations of the anti-microbial composition of below 0.1 percent by weight on weight of cellulose may be used. In the process of making the fibres, the anti-microbial composition preferably is added to the pasty pre-mix of the spinning solution.

Description

FIELD OF THE INVENTION [0001] The present invention relates to anti-microbial lyocell fibres which can impart qualities of freshness and hygiene to fabrics made from the fibres. It also relates to a process for making such fibres. BACKGROUND ART [0002] There is an increasing interest in fabrics offering qualities of improved hygiene and freshness, for example for use as clothing, and also in fabrics having better protection from deterioration caused by microbes. [0003] One way of achieving this is to apply anti-microbial agents to the fabric, for example as a finishing treatment. Another way, offering greater commercial flexibility, is to provide fibres that are already anti-microbial, by virtue of having an anti-microbial agent applied to or incorporated into the fibres. [0004] Many organic anti-microbial agents have been used or proposed for use on fibres, including triclosan, biguanides, phenols and derivatives, isothiazolones, quaternary ammonium salts, tri-butyl tin oxide, halo...

AI Technical Summary

Benefits of technology

[0024] The anti-microbial composition may be added to the spinning solution or to an ingredient of that solution, for example the amine oxide solvent. However, it is preferably added to a precursor of the cellulose solution comprising a pasty pre-mix of the cellulose pulp and the amine oxide solvent. One method of forming the solution of cellulose in an amine oxide solvent such as tertiary amine N-oxide, for example N-methylmorpholine N-oxide, is to form a pre-mix of cellulose and aqueous amine oxide solvent incorporating an excess of water over the optimum required for solution to take place. The pre-mix, which is a paste or dough, is then subjected to an evaporation process, for example in a thin-film evaporator, to remove the excess water and form a solution of the cellulose. The anti-microbial composition, which has been added to the pre-mix, is effectively dispersed throughout this resulting cellulose solution.

[0027] The process of the invention may be carried out without any significant processing problems. The sequestering stabiliser, which is preferably propyl gallate, appears to remove insignificant amounts of the silver compound from the anti-microbial composition. The oxidic support material appears to stabilise the silver compound against the activity of the propyl gallate during the manufacturing process. The corollary of this is that the propyl gallate does not become excessively used up by reacting with the silver compound and instead remains in the system to scavenge radicals which could otherwise trigger explosive exothermic reactions. Propyl gallate does not leave the spinning system with the fibres and so cannot affect the anti-microbial composition once it is incorporated into the fibres.

Problems solved by technology

Unfortunately, many of the anti-microbial agents that can be incorporated into other man-made fibres are incompatible with the amine oxide spinning system used to make lyocell fibres.

For example, triclosan is too easily washed out of the fibres during processing.

Also, some silver ion complexes are deactivated by amine oxide solvents and yield a brown or yellow colouration on the fibres that is not acceptable.

The process described has not become commercial possibly because of compatibility problems and colour problems with the spinning systems.

These silver compounds produce unacceptable colour staining on the fibres.

The purpose of this stabiliser is to sequester free radicals, particularly metal ions, which can catalyse exothermic reactions in the system, leading to uncontrolled explosions.

The concern with adding silver compounds is twofold: firstly, that the stabiliser will sequester the silver, deplete it as residual anti-microbial agent and cause staining, and, secondly, that the silver compound will use up the stabiliser and leave insufficient in the system to protect against exothermic reactions.