A METHOD OF TREATING A SUNFLOWER PLANT STEMS

Description

FIELD OF THE INVENTION

The present invention relates to a method of treating a plant-stem, particularly of extracting fibre from a sunflower stem. In particular, the treatment enables the fibre to be woven or knitted to form a wearable fabric or used as a non-woven textile alternative to down.

A further aspect of the invention relates to a method of applying a hydrophobic coating for increased water resistance of textiles, particularly using a hydrophobic coating derived from sunflower wax.

BACKGROUND TO THE INVENTION

In addition to their cultivation for oils, sunflowers can be used as a regenerative break crop as they are drought tolerant, improve soil organic matter, and increase soil nitrogen levels; thereby reducing the need for resource intensive fertilisers.

To maximise the economic value of this important break crop and to aid in reducing resource use, useful materials, with a low carbon footprint and circular label, can be derived from sunflower waste. There is an increasing drive to reduce the use of synthetic fabric materials produced from fossil fuels and to reduce the use of cotton which has resource intensive cultivation. This is being driven both from a desire to reduce energy requirements in forming the fabric and also to make the production of fabrics more carbon neutral. Moreover, many synthetic fabric materials are not readily recyclable or biodegradable.

The use of soft fibres from a plant stem is known in the art to produce a fabric which can be utilised in the manufacture of clothing and other articles. In the plant the fibres contribute to the support of the stem and are found primarily in the phloem: the softness allowing the stem to bend to a greater extent than is the case in other plants such as trees. Many different methods of liberating the fibres from the associated materials in the stem are known and are commonly referred to in the art as retting. The present invention discloses a type of retting process known as enzyme retting.

A typical retting process uses as its starting material the cut stems of a plant from which the leaves and roots are removed. Very often the stem is simply allowed to undergo natural decomposition under wet conditions, allowing bacteria present in the natural surroundings to decompose much of the surrounding tissue in the stem. To aid the process the stem is broken so that the bacteria can enter more easily. This process, however, has the disadvantage that several weeks can be required to achieve the level of degradation necessary. This means that the stems must be monitored to ensure that they do not dry out.

It would be advantageous, therefore, to provide an alternative retting method. The present invention seeks to provide such an alternative through the use of an enzymatic treatment in the retting process. A further aspect of the invention relates to the provision of a manufactured fabric, wherein the fabric produced has improved resistance to water penetration into the fabric, which obviously makes an item of clothing formed from the fabric more convenient to wear should the clothing get wet.

In a related aspect a method is disclosed of treating a fabric material to improve its water resistance. One method known in the art is described by Fawson (Carbohydrate Polymers, 227, 1-9, (2020)). In this paper cationic starches and dispersions of carnauba wax are utilised to coat a fabric material. This has the disadvantage that carnauba wax is extracted from trees in Brazil which can lead to deforestation and can displace native plant and animal species. There is also the environmental impact of shipping from overseas to international markets, whereas sunflowers are grown internationally. It would therefore be of benefit to use a material not linked to deforestation and that is widely available across geographies. The second part of this present invention seeks to provide an alternative hydrophobic material for coatings derived from sunflower wax, a by-product from the sunflower oil industry.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a method of treating a sunflower plant stem, the method comprising the steps of:

• • 1) Selecting a sunflower plant, removing the flower head and leaves from the stem and preparing the stem for enzymatic treatment by slitting the stem lengthways, removing the inner core from the stem; or using mechanical rollers to break open the stem; or any other method including mechanical, hydrothermal or enzymatic.
  • 2) Treating the cut stem with a pectinase containing buffer solution; preferably Tris-buffer solution containing 0.01-0.20% pectinase, optionally from Aspergillus niger, for 24 hours with shaking at a pH of 3.8-8.5, and preferably 7.2 and at a temperature of from 20-60° C. and preferably, 26° C.;
  • 3) Removing the stem and washing with water, preferably, boiling water;
  • 4) Placing the stems into a buffer solution containing xylanase; preferably Tris-buffer solution containing a xylanase, at a pH of from 7.0-8.0 and preferably 8.0 and at a temperature of from 37-50° C. and preferably 37° C. for 24 hours with shaking;
  • 5) Removing the stems and washing with water, preferably boiling water;
  • 6) Placing the stems into a buffer solution containing feruloyl esterase, preferably Tris-buffer solution at a pH of 7.2-8.0 containing 0.01-0.05% feruloyl esterase, optionally from Anaeromyces mucronatus, at a temperature of from 37-50° C. for up to 24 hours, optionally 48 hours;
  • 7) Removing the stems and washing with water, preferably boiling water;
  • 8) Pressing the stems with a roller to separate the fibres within the stems or any other method that removes the unwanted plant matter;
  • 9) Treating the pressed stems with a basic solution preferably; sodium hydroxide solution (1.6%) for 12 hours at 30° C.;
  • 10) Washing the stems in water, preferably boiling water, or heating in an autoclave at 121° C. for 15 minutes;
  • 11) Carrying out a further water washing step;
  • 12) Processing the fibres for non-woven applications or combing and spinning the fibres to form a yarn.

According to a second aspect of the invention, there is provided a method of treating a fibre yarn with wax obtained from a sunflower seed to waterproof a yarn, the method comprising the steps of:

• • 1) Pre-treating the fabric with a water wash and drying the fabric;
  • 2) Contacting the fabric, either by soaking or spraying, with a solution of a cationic starch at a concentration of 2-10 g/l and preferably 5 g/l, then rinsing the fabric with water. Optionally, the rinsing stages can be omitted if the layers are sprayed onto the fabric;
  • 3) Applying a layer of a sunflower wax suspension in water to the fabric, by soaking or by spraying, the particles of wax having a particle size of from 100-160 μm;
  • 4) Repeating the application of a starch layer and wax layer alternately, preferably to give four layers of each of the starch and the wax;
  • 5) Curing the fabric, preferably at a temperature of 72-85° C. for 20-45 minutes.

DETAILED DESCRIPTION OF THE INVENTION

The drive to utilise a renewable source for fabric materials is increasing as manufacturers seek to reduce the carbon footprint of clothing and other materials and to reduce reliance on fossil fuels for the raw materials, due to the increasing costs thereof and also the finite nature of such fossil fuel resources. There is also an increased push to diversify the plant fibres that are used for clothing and textiles and to decrease our reliance on cotton, which has resource-intensive cultivation.

Cottonized hemp is being championed as a cotton alternative. However, hemp has to undergo an additional degumming process after the fibres have been obtained to achieve a cotton-like fibre. This can be lengthy and can also heavily rely on a chemical-intensive process, reducing its commercial viability to compete with cotton.

One such renewable source which has hitherto not been considered is the sunflower plant. Although the obtention of an oil from sunflower seeds is well known, the use of other parts of the sunflower, such as the stem, is less well advanced.

The present invention in one aspect relates to a multi-stage process for the provision of a fibre which can be used in the textile industry to produce a woven, knitted, non-woven textiles, or alternative down material, which is more like cotton than the equivalent retted hemp fibres, without the additional degumming process. In the disclosed process, the stems of a sunflower are treated to remove the materials surrounding the fibres in the stem, leaving the fibres available to be formed into the fabric.

In broad terms, the process used is an enzyme retting process, following a pre-treatment series of steps. The pre-treatment steps involve breaking down xylan, pectin, and hemicelluloses in the plant stem. The breakdown products can then be more easily removed from association with the fibre materials to enable intact fibres to be isolated and processed for post treatment.

In more detail, in an exemplary process, the following stages and stage-steps are undertaken. In the first stage, a xylanase enzyme is obtained for use in the subsequent treatment of the plant stem. In the second stage, the stems are prepared and the pectin removed to loosen the links between cells in the plant-stem cell walls, and thus allow the cellular material to be more easily disrupted. This is followed by removal of cinnamoyl residues from the plant cell wall to further aid the degradation of the plant cell walls. Finally, the degraded plant cell walls can be further removed in a mechanical or chemical washing procedure to leave the required plant fibres for purification and drying.

In more detail, the first stage of isolating a suitable hemicellulase, xylanase, is described. The purified xylanase can be commercially purchased or obtained through recombinant expression in a microbial system. The steps undertaken to purify xylanase from a recombinant expression system in E. coli are described below. This method provides a cheaper and more sustainable alternative to purchasing pre purified enzymes commercially and can be scaled up as desired. A version of this process can also be applied to other enzymes used in this text.

Step (i)

Steps (i)-(iii) are for protein expression & scaling and can be applied to obtain all enzymes outlined with appropriate modifications. Commercially available enzymes can also be used which skip out steps (i)-(iii).

A vector expressing xylanase under a Isopropyl β-D-1-thiogalactopyranoside (IPTG) inducible promoter is inserted in Escherichia coli strain BL21 competent cells by chemical transformation. Other methods are equally suitable. The BL21 containing the xylanase vector is selected by growing the cells in Luria Broth Agar plates containing selective antibiotic and grown at 37° C. overnight.

Step (ii)

In this step, 5 single colonies are selected and transferred to 10 ml Luria Broth liquid media containing the appropriate selective antibiotics. The mixture obtained is then incubated overnight at 37° C. with shaking at 180 rpm.

Step (iii)

In this step, the bacterial culture grown in Step (ii) are scaled-up in size. The 10 ml overnight cultures are inoculated in a total volume of 1 L Luria Broth culture containing suitable antibiotics and placed in 2 L Erlenmeyer flasks for optimal aeration. These are then incubated at 37° C., with shaking at 200 rpm until the optical density (OD_600nm) reaches 0.6. IPTG is then added to a final concentration of 0.2 mM to each flask, which is then incubated overnight at 18° C. with 200 rpm shaking.

The cells produced are then harvested, by firstly centrifuging the incubated suspension at 5000 rpm for 10 minutes. The cell pellets obtained are then suspended in an aqueous Tris-buffer solution (15 ml), having a pH of 8 and containing tris(hydroxymethyl)aminomethane (Tris) (at 2.42 g/L) sodium chloride (17.53 g/L). At this stage the suspension can be frozen at −20° C. for later use if so desired. The suspension is sonicated for 5 minutes, while kept in an ice bath, using 30 s pulses, and then centrifuged at 6000 rpm for 5 minutes. The xylanase enzyme aqueous mixture is collected from the supernatant and kept for further use.

Step (iv)

The xylanase generated in the above steps is then utilised in the retting process as now described. The stems from sunflowers are prepared by the removal of the head and the leaves from the stem. The prepared stems are prepared by crushing or cutting lengthways, and, optionally, its inner core removed. Other methods known in the art, including mechanical, hydrothermal or enzymatic can also be used, followed by the inner core preferably being removed. The cut stems are then added to a vessel containing a buffer solution preferably; Tris-buffer solution at a pH of from 3.8-8.5 , and preferably 7.2. Pectinase, such as the commercially available ones obtained from Aspergillus niger, is added to the buffer solution at a concentration of 0.01-0.20 v/v. At this stage it is advisable that the stems are at least 50% to 100% submerged in the buffer mixture. Optionally, a buffer solution can be sprayed onto the stems to reduce reagent consumption. The container holding the buffer solution and the stems is closed and incubated at a temperature of from 20-60° C. and preferably 26° C. for between 18 and 48 hours, preferably 24 hrs with shaking. The stems are then removed from the buffer solution and washed with boiling water.

The treated stems are then added to a buffer solution preferably Tris-buffer solution at a pH of from 6.0-9.0 and preferably 8.0 and at a temperature of from 37-50° C. and preferably 37° C., and it is advisable that the stems are at least 50% to 100% submerged. Optionally, a buffer solution can be sprayed onto the stems to reduce reagent consumption. The buffer solution contains the xylanase from step (iii) or equivalent commercially available enzyme above at a concentration of from 0.01-1.00% v/v, although the concentration chosen depends on the activity of the xylanase obtained. The container holding the buffer solution and the stems is closed and incubated at a temperature of 25-60° C. and preferably 37° C. for between 18 and 48 hours, preferably 24 hrs with shaking. The stems are then removed from the buffer solution and washed with boiling water.

The stems from the previous stage are then added to a buffer solution preferably Tris-buffer solution, at a pH of from 5.0-8.5, preferably from 7.2-8.0, and it is advisable such that the stems are at least 50% to 100% submerged. Optionally, a buffer solution can be sprayed onto the stems to reduce reagent consumption. Feruloyl esterase as a solid or in solution, optionally from Anaeromyces mucronatus, is added to a concentration of 0.01-0.05 % v/v. The container holding the buffer solution and the stems is closed and incubated at 37-50° C. for 24 hours with shaking. If preferred, the incubation can be carried out for up to a 48 hour period. The stems are then removed from the buffer solution and washed with boiling water. The washed stems are then pressed with a roller to flatten them out and separate the fibres. Any other known method including mechanical, hydrothermal or enzymatic treatment can be used for stem post processing.

Step (v)

The next stage of the process to soften the fibres is optional depending on end use of the fibre. The treated stems from the previous stage are then soaked in a hydroxide solution, preferably; sodium hydroxide solution (1.6% w/v), overnight at 26-30° C., preferably 30° C. to further soften the fibres or washed with industrial soap. If the separation is acceptable, the stems are washed with boiling water or autoclaved at 120-130° C., preferably 125° C. for 15 minutes to remove excess degraded plant material. Other steam-based methods known in the art can be used. The stems are further washed to remove degraded plant material and processed suitably for desired end use.

Step (vi)

The fibres thus obtained can be used as a down alternative, for non-woven fabrics or are suitable for being spun together to form a yarn which is suitable for knitting or weaving. The fibres can optionally also be blended with other natural fibres such as flax, hemp or cotton, if desired.

With regard to a second aspect of the invention relating to a method for rendering a fibre yarn such as that obtained above to be waterproof, then the following exemplifies such a method in accordance with the current invention.

To boiling water, a cationic starch is added to give a final concentration of 2-10 g/L, preferably 5 g/L, with agitation, such as stirring for 15 minutes. Separately, sunflower wax is added to boiling water at a concentration of 10 g/L and with sonication to obtain a homogeneous solution. <Does this form a solution or a distribution of liquid wax in water?> The sonicated mixture is cooled quickly in an ice bath and the suspension is passed through a sieve with pores ranging from 100-160 μm with the flow-through being collected and retained for the further stages.

The fabric to be treated is pre-washed with water and fully dried. As examples of fabrics treated, then 100% cotton poplin and 100% hemp can be cited. The coating is applied using an alternate layer of the starch solution and the wax solution prepared as above. The fabric is coated with the starch solution by either fully soaking in the solution or spraying therewith. The fabric is then rinsed in water, particularly if soaking has been used to deposit the layer. Where spraying has been used to apply the layer, then the rinse stage can be omitted. The starch-coated fabric is then soaked or sprayed with the wax suspension. A rinse step is then carried out, especially where soaking has been used. These steps are then repeated 7-10 times to give 4 or more coats of each of the starch and the wax. The fabric is then left to dry overnight. Finally, the fabric is cured in an oven at 72-85° C. for 20-45 minutes. Utilising the above process, a fabric can be produced which holds a water droplet for over 90 minutes. After the waterproof ability is reduced, the treatment can be repeated as many times as needed.