Lignocellulosic materials, e.g. fibrous materials of cellulose, are used widely in a variety of applications, and they have many advantages, including that they are relatively inexpensive, as compared to, for example, synthetic plastics material fibres. Lignocellulosic materials include Jute, Hemp, Wood, Paper, Flax and so on.

As to uses of these materials, jute is much used in the form of sacks for the transport and storage of food, but much food stored this way is destroyed or discarded because jute is susceptible to decay, and the sacks disintegrate as a result of absorption and adsorption o f moisture. In general lignocellulosic fibres are highly moisture absorptive and therein lies a first significant disadvantage of use of these fibres.

Lignocellulosic fibres also tend to lack stability and strength and therefore they do not offer themselves as significant substitutes for synthetic fibres which have greater stability and strength.

More recently however, it has been proposed to "acetylate" fibres so that they become "acetylated". See in particular Eupopean Patent No. 0213252. The process o f acetylation has been used for treating wood fibres and the treatment has improved the dimensional stability and susceptibility to decay (R.M.Rowell, Rune Simonson and A.M.Tillman Paperi ja Puu, 68,(10), 740(1986)) . In another study the acetylation o f jute was considered (Mona Anderssen and A.M.Tillman, J ournal o f Applied Polymer Sciences, Vol 37, 3437, 1989) . The basic process of acetylation involves the use o f acetic anhydride to change the basic

chemistry o f the cell wall polymers . Specifically, in relation to the cellulose and hemicellulose components, for example, the highly specific, biological enzymatic reactions cannot take place because the chemical configuration and molecular conformation of the substrate have been altered. By using reacting chemicals to bulk the cell wall polymers reduces the tendency o f the fibres to swell with changes in moisture in that the lignocellulosic material becomes in a partially if not completely swollen state, all as described in the said European Patent No . 0213252.

B asically, in the preferred arrangement in said European Patent, use is made of acetic anhydride to esterify the hydroxyl groups in the cell wall, resulting in resistance to attack from organisms and improved dimensional stability.

Heretofore the use o f acetylated lignocellulosic fibres has been very limited for various reasons including that the acetylation proces s involves the use of toxic materials which must be effectively disposed of or rendered neutral.

As far as we are aware, the only use for these acetylated fibres has been the use o f wood fibres in the so called composition board, known as "chip board", which is widely used as a substitute for natural wood board. Chip board is however still susceptible to absorption o f water and it deteriorates in use.

The present invention concerns the utilisation of acetylated fibres, especially acetylate jute fibres . Jute fibres are of particular interest to us for a number o f reasons, the first o f which is that the fibres are available in copious supply, and consequently are inexpensive, as

compared to the fibres which are at present used in the application in which we are interested. Secondly, the acetylated Jute fibres are stronger than the conventionally used fibres, and also can be crimped, which lends another advantage to the use of the acetylated fibres in the application with which we are concerned.

It has been shown furthermore that an enhanced effect can be achieved in the application in question by the combining o f the fibres and the surrounding matrix in which the fibres are contained to produce a functional article. The composition o f the matrix is also contributory to the effect as indeed is the specific construction o f the article.

The present invention provides that acetylated fibres, especially but not exclusively jute fibres, are arranged as part of a composite in flexible sheet material form, of which the other part is a viscous mass of a type containing at least a curable resin component so that the sheet material can be shaped and the mass can be rigidified (when thermoplastics resin is used) and cured (when a thermosetting resin is used) to a rigid form with the acetylated fibres therein, and specifically the composite may be arranged as a flexible tubular structure, which can be inflated either to form a pipe or positioned to line a pipeline or passageway whilst the tubular structure is still flexible, and when it has been so inflated or positioned, the resin (preferably thermo setting) is cured or caused to cure so that the structure forms a rigid lining on the pipeline or passageway surface.

A considerable advantage is surprisingly attained that the acetylated fibres absorb and adsorb the resin component o f the mass with the result that a very good bond develops between the fibres and the

cured resin component, providing a finished product which is rigid and strong. The fibres, when in loose dispersed form which is preferred, disappear and by the absorption of the resin become resin rich and provide enhanced strengthening of the finished rigid product specifically the lining on the pipeline or passageway surface. This effect happens in the case of a tubular product, even when the fibres are for example in the form of a felt or in the form o f yarns which are wrapped circumferentially o f the tubular structure.

The tubular product may be a seamless tube, or it may have a seam, or it may be formed by means of a flat web wrapped to tubular form with the edges simply overlapping, the overlap becoming a bond when the curing takes place. In such case, the wrapped web would require to have an outer supporting means, such as the passageway surface during the inflation, at least until the resin is cured.

Tubular structures comprising fibres and curable resin for pipe lining are known and are used in very large volumes throughout the world, and the conventional fibres which are used for the formation of these linings are polyester fibres. Comparing conventional linings using the polyester fibres with the linings produced using solely acetylated fibres, in particular the jute fibres, the linings according to the invention it has been found are surprisingly not only cheaper but are as much as 50% stronger. Of course it is possible to use mixtures of acetylated fibres and the conventional fibres.

The acetylation treatment improves the resistance to biodegradation, but a most important feature o f the use of the acetylated fibres in the instant invention is that the acetylated fibres have voids in the surface which become filled with the resin and therefore in the resulting

lining the bond between the fibres and the resin becomes strong, and the lining can accommodate more o f the resin than the conventional lining. This is important in the present invention, as compared to the known use o f acetylated fibres, because in the invention, the tubular structure is subjected to much manual handling and manipulation as it must, when it is to line a pipe, be taken to the site and then inserted in the pipe and be inflated.

The fibres may be given a solvent epoxy wash followed by drying, to improve the bond between fibres and the resin.

As indicated above, a significant advantage o f the invention is that as the resin "enters" the voids in the fibres, the fibres and resin hang together better than in the conventional arrangement, whilst still flexible, and the flexible tubular structure can be handled easier. This is important, because the flexible tubular structure, o f which an example is given in our co-pending application GB No . 9510019.4, in many instances as indicated above, has to be manipulated e. g. everted as it is being positioned on the pipeline or passageway surface. It has been found that the use of the fibres, especially the jute fibres, prevent elongation of the flexible tubular structure during the eversion process.

This invention is usable in connection with the inventions disclosed in our GB co-pending applications Nos.9510019.4; 9519575.6; 9521457.3; 9522689.0;9522862.3; 9600520.2; 9600639; to which reference is made for information.

The invention can be used with great advantage in tubular structures which comprise and extruded matrix comprising the resin and the

loose fibres intermixed with the resin, or in the alternative arrangement where the structure is a web of the fibres which is pre¬ formed into a tube which is subsequently impregnated with the resin. In the latter case, the fibres o f the web may be acetylated first and then formed into a web , or alternatively the web may be acetylated after being formed.

It is envisaged that the fibres may be in the form o f yarns which extend circumferentially o f the tubular structure, and in such case the yarns may be pre impregnated with a resin which is the same as or compatible with the resin used for the tubular structure so that they effectively bond thereto . The fibres of the yarns may be acetylated before or after being formed into the yarns.

The acetylation o f the fibres which are used in this invention may take place by any suitable process, for example as set forth in any of the above prior publications, or by the new methods set forth by us in UK patent applications Nos. 9614495.1 and

It has to be mentioned that the fibres may be o f any length, but there is a relationship between the fibre length and sheet material tensile strength (before rigidifying) and therefore it is expected that the use of longer fibres, such as jute will be preferred.

The resulting sheet material is one which can in effect be moulded to a desired shape and then the resin is rigidified, resulting in the creation o f a rigid product. Clearly, although we are interested in the pipe lining art, the invention has a wide range of application. For example it could be used for producing small boat hulls, shower trays,

baths and roo f linings, and indeed any application where conventional materials such as those known as "pre-pregs" are used.

A further significant advantage of the material is that in its preferred form, it has the texture of leather sheet, and therefore it can be handled quite easily, can be shaped to the required form and then the material can be cured (thermosetting resin) resulting in a moulded finished product. Complicated processing machinery can be avoided.