FIBRES

The present invention relates to a process for delignification and bleaching of fibres. One particular application for such fibres is for use in reinforced composite materials.

Various industries, such as the paper and textile industries, make use of natural fibres. The natural products from which such fibres are derived must be suitably treated to produce the fibres in a form that can be used. Such treatment steps can include delignification of the fibres. The lignin present in plant cell walls lends rigidity to the original natural material, and may need to be removed to produce the desired properties in the fibres.

In the kraft process for producing paper the feedstock is woodchips, which may contain in the region of 30% lignin. The delignification step comprises sulphate/sulphide chemistry, and can typically require several hours at temperatures above 100°C.

In the textile industry, the starting materials may have around 6% by weight lignin. That lignin may be reduced by the process of retting, which uses natural micro-organisms to decompose the hemicellulose and (depending on the extent of the retting) the lignin present. The textile industry typically uses “fully retted” fibres, in which the lignin content may have been reduced to around 1-3%. These fibres are then normally bleached with no further delignification step.

It is possible to use natural fibres as the “reinforcing” component of a composite material, to form a so-called “biocomposite” material. Such materials can include fibres such as hemp fibres in a matrix of a polymer resin, to provide improved material properties compared to the polymer resin alone.

However, to produce such biocomposite materials it is necessary to prepare suitable fibres for use in the eventual composite.

Preparing such fibres using the chemistry of the kraft process is undesirable due to the environmental impact of the chemicals being used, and the waste products created. However, relying solely on a natural retting process such as in the textile industry it is also undesirable as it can lead to a product of varying quality product that can then undesirably result in a varying quality of composite material.

The present invention aims to at least partly solve the above-mentioned problems.

According to an aspect of the present invention, there is provided an apparatus for delignification and bleaching of fibres, the apparatus comprising: a reactor for containing a bed comprising fibres; and a moveable head box for dispensing liquid into the reactor; wherein the head box is configured to rest on the bed of fibres.

In an arrangement, the reactor comprises a perforated plate for supporting the bed of fibres.

In an arrangement, the reactor comprises a removable cassette for holding the fibres. In an arrangement, the perforated plate is part of cassette.

In an arrangement, the reactor is insulated.

In an arrangement, the reactor is configured to collect, in use, liquid that has passed through the bed of fibres, in the bottom of the reactor.

In an arrangement, the apparatus further comprises a line for returning liquid from the bottom of the reactor to the moveable head box.

In an arrangement, the line comprises a filter.

In an arrangement, the reactor is configured to keep, in use, the bed comprising fibres from being submerged in the liquid collected in the bottom of the reactor.

In an arrangement, the reactor does not comprise a stirrer for stirring the bed of fibres. In an arrangement, the head box comprises: at least one spray nozzle for spraying liquid, a first perforated sheet arranged beneath the spray nozzle, wherein the head box is configured such that, in use, liquid from the nozzle passes through the perforations out of the head box.

According to an aspect of the present invention, there is provided a head box for dispensing liquid to a reactor, the head box comprising: at least one spray nozzle for spraying liquid, a first perforated sheet arranged beneath the spray nozzle, wherein the head box is configured such that, in use, liquid from the nozzle passes through the perforations out of the head box.

In an arrangement, the head box is configured to dispense liquid from the perforations by drip feeding.

In an arrangement, the spray nozzle points downwards towards the perforated sheet.

In an arrangement, the head box comprises a second perforated sheet, positioned between the spray nozzle and first perforated sheet

In an arrangement, the at least one spray nozzle is arranged such that, in use, the first perforated sheet is fully wetted. According to an aspect of the present invention, there is provided a method of evenly dispersing fluid through a fibre bed in a container, the process comprising: resting a head box on a fibre bed; drip feeding fluid from the head box into the fibre bed.

In an arrangement, the method further comprises compressing the fibre bed with the head box.

In an arrangement, the weight of the head box causes the compression.

In an arrangement, the compressing comprises active squeezing of the bed with the head box.

In an arrangement, the method is performed in an apparatus for delignification and bleaching of fibres.

According to an aspect of the present invention, there is provided a process for delignification and bleaching of fibres, the process comprising: a step of washing the fibres with water, the water being 70°C or above; and a step of treating the fibres with a delignification and bleaching agent.

In an arrangement, the fibres comprise or consist of one or more of natural fibres, hemp, flax, recycled textile, wheat straw, rice straw, bast fibre and/or agricultural straw.

In an arrangement, the fibres comprise or consist of natural fibres and the step of treating comprises treating the fibres having their full natural lignin content.

In an arrangement, the delignification and bleaching agent comprises or consists of one or more of, and enzymatic agent, hydrogen peroxide and/or sodium hydroxide.

In an arrangement, the fibres have a maximum length of 100 mm or less, preferably 50 mm or less, more preferably 25 mm or less, still more preferably 10 mm or less.

In an arrangement, the fibres are not wood fibres.

In an arrangement, a weight ratio of liquid to fibres in the step of treating is 10: 1 or less, preferably 5:1 or less, more preferably 2:1 or less.

In an arrangement, less than 15% by volume of the fibres are submerged in liquid during the step of treating, preferably less than 10%, more preferably less than 5%, and still more preferably wherein none of the fibres are submerged.

In an arrangement, the temperature of the step of washing is 80°C or above, optionally 90°C or above, further optionally 100°C or above.

In an arrangement, the step of treating comprises drip feeding agent onto a bed of the fibres. In an arrangement, the process further comprises compressing the bed of fibres during the step of treating.

In an arrangement, the step of treating further comprises collecting agent that has passed through the bed of fibres and recycling it for re-use in drip feeding.

According to an aspect of the invention, there is provided a process for producing a biocomposite comprising fibres in a matrix material, wherein the process comprises: the process for delignification and bleaching of fibres as above; and following the step of treating the fibres, using the fibres to form a biocomposite material.

According to an aspect of the invention, there is provided a biocomposite material obtained by the above process, fibres obtained by the above process and a fibre pellet comprising such fibres.

The invention is described below, by way of example only, with reference to the enclosed Figures, in which:

Fig. l is a schematic diagram of a unit operation for delignifying and bleaching fibres; and

Fig. 2 is a schematic representation of the arrangement of perforations in a mesh;

Fig. 3 is a schematic representation of the cross-section of an arrangement of a head unit; and

Fig. 4 is a schematic representation of the plan view of an arrangement of a head unit.

Fig. 1 illustrates an example system 1 for use in a process of delignifying and bleaching fibres 50.

The apparatus 1 comprises a reactor 100. The reactor 100 is constructed from suitable materials for withstanding the mechanical and chemical conditions of the process, which the skilled person would be able to readily ascertain. By way of example, the reactor 100 may be made from stainless steel. Similarly, the reactor 100 may have any desired shape, and may for example be square, rectangular or circular in cross-section.

As shown in Fig. 1, the reactor 100 has an outer cassette 10 and an inner cassette 20. The inner cassette 20 fits within the outer cassette 10, and can be removed from the outer cassette 10.

Such an arrangement allows for easy loading and removal of fibres 50. This is because the inner cassette 20 can be removed from the outer cassette 10, loaded with fibres 50, inserted back into the outer cassette 10 and then can subsequently be removed again once the process is complete. This arrangement also provides advantages for quickly moving from batch to batch, as a new inner cassette 20 containing fibres 50 can be loaded into the outer cassette 10 whilst the previous inner cassette 20 is still being emptied.

However, whilst this arrangement of an inner and outer cassette has advantages for preforming the process, it is not essential to the process itself, and other arrangements may be used.

In the arrangement shown in Fig. 1, the inner cassette 20 is for containing the fibres 50 during the process. The bed of fibres 50 is held on a mesh or perforated sheet 21, forming the bottom of the inner cassette 20. The mesh 21 contains holes or perforations to allow process liquid to pass through the bottom of the inner cassette 20. The holes or perforations are sized in order to retain the fibres 50 within the inner cassette 20, whilst allowing adequate drainage. By way of example, the mesh may comprise circular perforations 1 mm in diameter, arranged on a triangular array with an interval of 2 mm (e.g. as illustrated in Fig. 2, showing diameter d and interval /). However, other sizes and configurations are possible.

The outer cassette 10 of the reactor 100 has a bottom/reservoir portion 11. This reservoir portion 11 is under the inner cassette 20, for collecting liquid from the inner cassette 20.

The reactor 100 also comprises a head unit 30. The head unit 30 is configured to provide liquid to the fibre bed 50. The construction of the head unit 30 is considered in further detail later. However, in one arrangement, the head unit 30 may rest upon the fibre bed 50, during one or more of the process steps, to compress the bed of fibres 50 whilst it is wet.

The reactor 100 further comprises a pipework recycle loop 40 which can recycle liquid from the reservoir 11 at the bottom of the inner cassette to the head unit 30.

The loop 40 may include a pump 41, to drive the recycle. The pump 41 may be provided with a filter, to help prevent stray fibres from the process damaging or impacting the performance of the pump 41.

The loop 40 may also include a heater 44 for heating fluid circulated through the loop 40. In other arrangements, the heater 44 may be provided within the reactor 100, for example within the reservoir 11. The form of the heater 44 may take any suitable form, such as an electrically powered resistive heating element, or a heat exchanger for integrating waste heat from other processes.

The pipework 40 may also include an inlet 42 and outlet 43 for adding and removing liquid to/from the process. Alternatively, in other arrangements, the process liquid may be added in a batch-wise fashion directly to the outer cassette 10, for example, and subsequently circulated via the pipework 40.

In use, feedstock fibres 50 are loaded into the reactor 100. As explained above, the fibres 50 are loaded into the inner cassette 20 when using the arrangement shown in Fig. 1. Depending on the ultimate composite product to be produced, the fibres may be natural fibres such as hemp or flax fibres, or any form of bast fibre. The fibres may be in the form of an agricultural straw, such as wheat straw or rice straw, for example. By way of example, the bed of fibres 50 may have a dry weight of around 50-75kg.

The fibres may have already undergone some retting. For example, the fibres may be partially retted, so that they retain their full natural amount of lignin (e.g. 4% or more) but e.g. the hemicellulose in the fibres has started to be removed.

The fibres may also include recycled textile fibres.

Preferably, the fibres are not wood fibres.

The fibres may be relatively short in length. The fibres may have a length of 100 mm or less, optionally 50 mm or less, further optionally 25 mm or less and still further optionally 10 mm or less.

Once the fibres 50 have been loaded into the reactor 100, the head unit 30 can be positioned. The head unit 30 may either be fixed as a “static” lid to the reactor 100, or may rest directly upon the bed 50 to compress the bed 50, as mentioned above.

Once the fibres 50 have been loaded, a first process step of washing the fibres 50 takes place. This step of washing helps removes contaminants. Further, by performing the washing at an elevated temperature, the washing step starts the delignification process.

That is, by using elevated temperature the delignification occurs even though the fibres are being washed with conventional process water (e.g. with a pH in the range of 5-7). This not only reduces the overall process time (by combining the start of the delignification with the washing) but also allows for less environmentally impactful chemicals to be used in the subsequent delignification and bleaching. Preferably, the temperature of the water during the washing step is 70°C or more, more preferably 80°C or more, still more preferably 90°C or more, and can be 100°C or more if the step is performed under pressure.

In one example, the washing step may last around 30 minutes. The temperature of the water may be maintained by the heater 44 in the recycle loop 40. During the washing, in the arrangement of Fig. 1, water is provided to the bed via the head unit 30, passing through the bed 50 and its collected in the reservoir 11, from where it is heated by heater 44 and circulated by pump 41 back to the head unit 30 by the pipework 40. In order to operate as efficiently as possible, the reactor 100 may be insulated, to assist with retaining the heat in the reaction mixture. Such insulation can be provided as an integral part of the construction of the reactor walls, or may be provided as additional/ separate component that fits around the reactor.

During the washing step, the weight ratio of water to fibres may be 10:1 or less, preferably 5: 1 or less, more preferably 2: 1 or less.

Following the washing step, a step of treating the fibres 50 with a delignification and bleaching agent occurs. Any suitable agent may be used, but preferable options for their relatively low environmental impact are enzymatic agents, hydrogen peroxide and/or sodium hydroxide. Hydrogen peroxide, for example, is an attractive option as it reacts with the lignin to form water as a waste product, which is thus relatively simple to dispose of.

During the treatment step, the delignification and bleaching agent is provided to the bed of fibres 50 via the head unit 30, passes through the bed 50 and its collected in the reservoir 11. From the reservoir, the agent can be circulated by pump 41 back to the head unit 30 by the pipework 40.

During the treatment step, the head unit 30 preferably rests on the bed of fibres 50, compressing the bed 50 as it reacts. It has been found that this compression results in a more thorough and even reaction of the bed 50, with a relatively small amount of liquid. Without wishing to be bound by theory, it is thought that that the compression helps prevent “tunnelling” in which liquid passing through the bed 50 forms preferential channels through the fibre material, and instead keeps the fibres together in a way which encourages the liquid to wick through the entire bed 50. It has been found that this improvement occurs without any ‘active’ compression of the bed - that is, the self-weight of the head unit itself is enough to produce the improvement. However, the bed may also be actively compressed by applying a force to the bed.

To facilitate the compression, preferably the reactor 100 has no stirrer, which could otherwise get in the way. That is the fibre bed 50 is not agitated during the reaction. Instead the bed is “still” (except for movement caused by the compression or the introduction of the reaction liquid) or unstirred. In an arrangement, the fibre bed may have a volume of 500 litres or more, preferably 1,000 litres or more.

In any case, liquid introduced to the bed via the head unit 30 passes through the bed and reacts with the fibres to delignify and bleach the fibres. The treatment step can be performed with very high ratios of fibre to liquid. The instantaneous holdup weight ratio of liquid to fibres in the bed 50 during the step of treating is preferably 10:1 or less, preferably 5: 1 or less, more preferably 2: 1 or less.

By way of comparison, delignification steps during a typical paper process operate at more than 10% fibre in liquid. Such low ratios of fibre to liquid help enable a continuous process in which the reacting mixture can be stirred and pumped from one step to the next.

In contrast, when the present process is implemented as a batch operation, the reaction can be characterised as occurring in a static wet matt of fibres 50, as opposed to in a suspension as in the typical paper processes.

During the treatment step, the liquid passes through the bed 50 and is collected in the reservoir 11 at the bottom of the reactor 100 as mentioned above. Preferably, less than 10% by volume of the fibre bed 50 is submerged in the reservoir, more preferably less than 5% and still more preferably less than 2%. Most preferably, the bottom of the fibre bed 50 is not submerged in the liquid reservoir 11 at all.

The step of treatment can be performed, for example, with e.g. 3% v/v hydrogen peroxide in water. The treatment step can last for as long as required to reach the required delignification, but could be around 30 mins.

The temperature of the treatment step can depend on the reactants used. For example, enzymatic processes may operate at a lower temperature than non-enzymatic processes. By way of example, the temperature may be 40°C or more; 50°C or more; 60°C or more; 70°C or more; 80°C or more; 90°C or more; or 100°C or more.

The liquid from the treatment step, with the broken down lignin and hemicellulose, is a waste stream from the process under consideration, but can be a useful product in its own right.

Following the treatment step, the fibre bed 50 can be washed with water to remove any remaining reactants and reaction products. This can be performed in the reactor 100 itself.

Following that, the fibre bed 50 can be removed and dried. The resulting fibres 50 have good, consistent, mechanical properties, for example compared to other sources of extracted fibres that may have a higher amount of impurity and/or a lower overall weight percentage of cellulose. These fibres can then be used as the reinforcing material in biocomposites formed of the fibres and matrix material such as conventional thermoplastics or biodegradable starch-based binders for example. This may involve pelletising the fibres before they are combined with the matrix material to produce the biocomposite. The head unit 30, also known as a head box, 30 has been discussed above. To assist with the dispersion of liquid through the fibre bed 50 during the process, the head unit 30 can be designed to provide a consistent drip feed of liquid across the entire bed 50.

A cross section through an example of a head box 30 is depicted schematically in Fig. 3. The head box 30 comprises a nozzle 33 for spraying liquid, and a first sheet 31. First sheet 31 is perforated, and arranged beneath the nozzle 33. In use, liquid supplied by pipe 40 to nozzle 33 is distributed by the nozzle 33 across the first sheet 31. As such, liquid from the nozzle 33 passes through the perforations and out of the head box 30.

The nozzle 33 may take any form, but is preferably configured to disperse liquid across the first sheet 31 so that the sheet 31 is fully wetted in use. As such, the nozzle 33 may be pointed down towards the first sheet 31. In larger systems, there may be more than one nozzle 33 in order ensure a thorough distribution of liquid across the first sheet 31.

Fig. 4 shows, in plan, a schematic representation of an example head box 30 having 4 nozzles. The pipe 40 supplying liquid to the head box 30 is divided into a dedicated nozzle supply pipe 45 for each nozzle 33. That is each nozzle 33 has its own nozzle supply pipe 45, so that the number of nozzle supply pipes 45 is the same as the number of nozzles 33.

In Fig 4, it can be seen that the overall head box 30 (and thus the first sheet 31) is divided into substantially equal areas (four, in this case, indicated by dashed lines 34) each containing a single nozzle 33, that nozzle 33 being located substantially centrally within its respective area. In embodiments such as this, each nozzle 33 is intended to cover its own area, and so it is desirable that each nozzle supply pipe 45 provides the same amount of liquid to each nozzle 33, to ensure even coverage of the first sheet 31. As such, the nozzle supply pipes 45 are preferably hydraulically similar. That is, they preferably have substantially the same diameter and length, and the same profile, so that liquid from the pipe 40 is split evenly among the pipes. Less preferably, the nozzles 33 could be fed from a common manifold, in series, suitably configured to give an even flow from each of the nozzles 33.

In some systems, nozzles 33 of different sizes may be used to cover different sized areas of the first sheet 31. In that case, the supply of liquid to each nozzle 33 needs to be appropriate to ensure that a good distribution of liquid across the first sheet 31 is achieved.

In use, the head box 30 drip feeds liquid out of the perforations in the first sheet 31. That is, the head box 30 is preferably not dispensing liquid in the manner of a pressurised sprinkler (in the manner of the nozzles 33 internal to the head box 30), but instead is allowing liquid to drip through the perforations in the first sheet 31. To assist with this, and to assist with ensuring an even distribution of liquid across the first perforated sheet 31, a second perforated sheet 32 may be positioned between the nozzle(s) 33 and the first sheet 31. The second perforated sheet 32 pay be substantially similar to the first sheet 31. As such, liquid from the nozzle(s) 33 is dispersed across the second sheet 32, from where it drips on to the first sheet and then drips again out of the head box 30. This can provide a more even distribution than spraying directly onto the first perforated sheet 31.

In some arrangements, the first perforated sheet 31 may be 5 cm or more from the nozzle(s) 33, optionally 10 cm or more from the nozzle(s) 33, optionally 15 cm or more from the nozzle(s) 33. The second perforated sheet may be 1 cm or more from the first sheet 32, optionally3 cm or more from the first sheet 32, optionally 5 cm or more from the first sheet 32.

The above description is by way of example only. The invention is defined in the appended claims.