GB2285406A - Modified plant material - Google Patents

Abstract

A modified plant material, suitable for press-moulding into shaped containers and other articles (particularly "one-use" or disposable articles) for such uses as fast-food and other packaging (e.g for garden plants) and generally for containing, handling or displaying foods or beverages comprises a composite pressure-formed from a plurality of pieces of stem skin material from a plant of the genus Musa, more particularly the banana plant Musa sapientum, in the presence of an amount of an adhesive (most preferably a biodegradable adhesive) effective to retain the pieces integrally together in the composite material. The material is biodegradable, yet can be substituted for conventional materials such as plastics, paper and card. The material has distinct environmental, ecological and economic advantages.

Description

MODIFIED PLANT MATERIAL The present invention relates to modified plant material and articles made therefrom.

Plant material offers potentially great economic, environmental and ecological benefits as a manufacturing material, compared with exhaustible resources such as plastics. However, while of course certain plant materials, for example wood and leaves, have been used for manufacturing articles for thousands of years, to date no satisfactory plant material has been found which can be used as a substitute for metals and plastics, particularly in relatively small moulded or pressed articles such as dishes, trays and containers.

The leaves of the banana plant Musa sapientum have been used, in India and other countries, in place of plates for the presentation of food. However, banana leaves do not provide a satisfactory material for moulded or pressed articles.

According to the present invention, there is provided a modified plant material and articles made therefrom, comprising a composite pressure-formed from a plurality of pieces of stem skin material from a plant of the genus Musa (more particularly the banana plant Musa sapientum) in the presence of an amount of an adhesive effective to retain the pieces integrally together in the composite material.

The materials of the present invention are biodegradable and may be used in place of materials (e.g. polystyrene, PVC, paper or card) conventionally used for many small (typically disposable) moulded or press-formed articles, The new material has many ecological, environmental and economic advantages over conventional materials. Such articles include disposable ("one-use") products such as, for example, "clam shell" fast food packaging, dishes, cups, containers, trays etc., or other products (e.g.

containers for garden plants) where a biodegradable article can advantageously be allowed to degrade away in situ.

According to a further aspect of the present invention, there is provided a method for preparing the modified plant material and articles made therefrom, comprising pressure-forming the material or articles as an integral composite from a plurality of the pieces of stem skin material in the presence of an amount of adhesive effective to form the integral composite, the pressureforming preferably being conducted in the presence of moisture at an elevated temperature.

The term "pressure-forming" used herein refers to any forming process carried out under pressure, for example by means of press plates, rollers or any alternative pressure applying means.

The term "stem skin material" used herein refers particularly to the outer curved layers of vegetation which constitute the stem of the Musa plants, and which in the case of bananas are traditionally cut away and discarded with the upper leaves of the plant as part of the banana-harvesting operation. The banana stem skin layers particularly constitute the outer 50-75mm of the plant's stem and are wrapped around a solid core which is approximately 50mm in diameter and which is not affected by the banana-harvesting operation.

Banana stem skin material is typically removed by simply peeling and separating away of the layers from mature banana plants to provide lengths of the unprocessed material in the form of slightly curved sheets approximately 800-lOOOmm long and approximately 150-180mm wide. It is these lengths which typically constitute the pieces from which the material and articles according to the present invention are formed.

The banana stem skin material has fibres along its length embedded in a honeycomb structure which is covered on both sides by thin membranes. In its fresh condition, the stem skin material is green, somewhat brittle, and contains as much as 80% by weight of water.

It is preferred that the fresh stem skin material as removed from the plant is first partially dried to reduce the thickness of the sheets and to increase the pliability. It is preferred to remove between about 50 and about 958 of the original moisture, more particularly between about 70 and about 85%, e.g. about 80 to about 85% of the original moisture. The removal of water should be carried out slowly to prevent uneven drying, and we have found it convenient to perform simple warm air drying by allowing air to circulate in natural convection currents over vertically or horizontally stacked stem skin pieces in well ventilated shade or in a banana field where the material is not much exposed to the direct rays of the sun.The stem skin pieces are thus partially dried to a final moisture content of most preferably about 15% (by weight) and a thickness of preferably about 1.0 to 1.5mm.

According to the invention, articles may be pressureformed directly from the stem skin pieces in the presence of the adhesive, by using a pressing system which shapes the article simultaneously with the formation of the composite material. The articles according to the invention may be made by any conventional press including press members shaped to according to the desired article, optionally including stamps, die cutters and other conventional accessories. For mass production processes, the initial manufacture of a semi-processed piece such as a board or sheet of the material is preferred, suitably by pressure-forming between rollers or between the plates of a conventional press, whereas for small scale and oneoff pressing operations the stem skin material can be laid directly in the mould in the presence of a sufficient amount of adhesive, and subsequently pressed.

It is most preferred that the composite is formed by steam pressing, and for this purpose the stem skin material, which as stated above is preferably partially dried after removal from the plant, is suitably moistened (e.g. by sprinkling with hot water) immediately before pressing, and the pressing takes place between press members (e.g. metal plates perforated to allow the escape of steam) at an elevated temperature. The press members may suitably be coated with a releasing or non-stick material such as Teflon @(es ) The plates may be electrically heated or may be preheated by a non-electrical heat source to a temperature in excess of 1000C by any conventional press heating means. The hot plates lead to substantial drying of the composite.The heat and pressure are maintained during the entire pressing/drying process, to ensure that the shape is retained in the finished article and that the surface of the composite material is smooth.

The nature of the adhesive is not critical, provided that it confers the desired strength, integrity and flexibility on the resulting composite material and is not degraded or dissolved in a steam pressing process.

Biodegradable adhesives are preferred, in order to provide a fully ecologically and environmentally acceptable composite material. Particularly preferred adhesives include starch glues derived from tapioca, tamarind, etc, used for bookbinding, textile sizing etc, resins such as phenolic resins (e.g. phenol/ formaldehyde), natural gums such as polysaccharide gums, synthetic gums, edible gums, wood and furniture adhesives, and sugar-derivative adhesives. Where the articles and materials are likely to be exposed to moisture, an insoluble adhesive must be used.

The composite can be coated or surface-treated in any conventional way, for example to improve water resistance, aesthetic appeal, or to provide commercial logos, advertising or other printed matter. Coatings may be applied to provide a desirable "finish" or smooth surface to the composite, or to improve its durability, particularly maintenance of the form and shape of the articles, or to improve the ability of the composite to carry printed matter on its surface. It is preferred that any such coatings or surface-treatment agents will be biodegradable.

The composite can be sterilised by conventional means, e.g. by gamma radiation, heat or gas sterilisation.

In cases where the composite is initially formed as a semi-processed piece of simple shape such as a sheet or board, the subsequent post-processing into an article is suitably carried out in any suitable conventional manner.

We have found that it is convenient to steam the semiprocessed sheet sufficiently to soften it, before hotpressing the desired articles from the sheet in conventional manner. The press conditions in this case are similar in general to the press conditions required to initially form the composite, as described above.

In all cases, care must be taken that the conditions of heat and moisture required to work both the stem skin pieces and the semi-processed composite pieces are not damaging to the adhesive or its properties. However, any necessary adjustments are well within the capability of a worker of ordinary skill in this art.

The present invention enables for the first time biodegradable and environmentally acceptable substitutes, made from banana stem skins for articles conventionally pressed or moulded from metals and plastics such as polystyrene and PVC, most particularly disposable articles used in the commercial and domestic preparation and handling of food, for example "clam shell" hamburger containers, plates, dishes and trays.

In any automated form of the process, after collection and washing of the skin pieces the drying process may take place on a conveyor under artificial drying conditions. An adhesive spray will suitably be applied automatically and a second layer of skin pieces overlain on the sprayed skin pieces for forming, after pressing, a semi-processed stiff board of the composite. Heat and compression between rollers can be applied as an alternative to press forming. The emerging material is in the form of a sheet which can be used for producing, via conventional subsequent processing techniques such as pressing, bending, cutting, rolling, surface-coating, surface-treating and sterilisation, various packaging containers and other articles with domestic or industrial purposes.

In a modification of the invention, also included within the scope of this application, the adhesive may be dispensed with and a single piece of stem skin material employed, to prepare an article (particularly a fast-food package or an article for containing, handling or displaying foods or beverages) comprising a material pressure-formed from said stem skin material. The details described herein for the invention apply, with appropriate modifications as will be readily understood by persons of ordinary skill in this art, to articles made according to such a modified process (and to the modified process itself).

For ease of understanding of the present invention, embodiments will now be described in more detail, without limitation and with reference to the accompanying drawings, in which: Figure 1 shows in schematic vertical section a manually operated press mould for forming bowls from a semi processed flat sheet of a banana stem skin composite material; Figure 2 shows in perspective a bowl formed in the press mould of Figure 1; Figure 3 shows in (a) top and (b) side view the semiprocessed flat sheet of a banana stem skin composite material; Figure 4 shows in schematic vertical section a manually operated press for forming the sheet of Fig. 3; Figure 5 shows in schematic vertical section a steaming chamber for moistening the sheet of Fig. 3 prior to pressing in the press of Fig. 4; Figure 6 shows a section of a banana stem; and Figure 7 shows in perspective a stem skin piece separated from the stem of Fig. 6.

Summarv of Reference Numerals 1) Bowl (or alternatively a cup or container) 2) Male mould part 3) Female mould part 4) Press plate (upper) 5) Press plate (lower) 6) Flat sheet made from stem skin material 7) Aluminium body (7a,7b upper and lower respectively) 8) Bolts 9) Contact block 10) Solid core 11) Skin pieces 12) First layer of skin 13) Second layer of skin 14) Fibres 15) Steaming chamber 16) Stem of banana plant Press construction Referring to the Figures, two press constructions are shown, that in Figure 1 consisting of a mould having male 2 and female 3 mould parts to yield a bowl 1 in the pressing operation. The apparatus shown in Figure 4 is of generally similar construction, except that the press plates 4,5 are flat to yield a flat sheet 6 during the pressing operation.Alternative mould or press arrangements may be readily envisaged by a skilled worker, and in particular an arrangement (not illustrated) for making a hamburger container in the form of two hinged "clam shell" halves may be mentioned. As an alternative, the hamburger container may be made by gluing together two separately formed clam shell halves, each half having a tab and a slot, and the halves being joinable by inserting a tab of one half into the slot of the neighbouring half and gluing the tab in place.

In general, the presses comprise a two-piece cast aluminium body 7, the pieces 7a, 7b being bolted together at the four corners by bolts 8 to give the pressure necessary for forming the bowl 1, sheet 6 or other shape.

One or both parts of the press or mould can have a grid of small channels (not shown) cut into it to allow water vapour to escape. In the mould apparatus shown in Figure 1, the male 2 part of the mould is urged towards the female part 3 via a contact block 9 provided on the underside of the upper body piece 7a.

Automated and mechanised forms of the manual presses illustrated will be readily envisaged by a reader of ordinary skill in this art, and are intended to be embraced within the scope of this invention.

Preparing the stem skin material As shown in Figure 6, the stem 16 of a banana plant has a solid core 10 of about 50mm diameter on which crescent shaped stem skin material 11 is wrapped, as shown in Figure 7. The total diameter of the stem is 150 to 200mm. The stem skin pieces 11 can be easily peeled and separated from the stems, to provide slightly curved lengths of material of stem skin material typically approximately 800-1000 mm long and typically approximately 150-180 mm wide. Because of the relatively high initial moisture content (approximately 80%), a preliminary partial dehydration is carried out to improve flexibility and reduce the thickness of the material, by atmospheric drying in the sun or in well ventilated shade. The skin pieces are preferably stacked loosely (not shown), for example in a wire cage, to allow air to circulate between the pieces.

Prior to the present invention such stem skin pieces have been simply discarded by banana growers.

During the partial drying, natural convection currents of warm air circulate around the pieces of skin and slowly remove moisture from the honeycombed structure 12 progressively, so that the skin shrinks in thickness to about 1 to 1.5mm and becomes pliable with moisture content of about 15% by weight.

Preparation of the stem skin pieces for moulding directly into an article The partially dried pieces of skin 11 are typically first sprinkled with tepid water to soften them before moulding. The softened skin pieces should then ideally be rolled to remove any wrinkles, but this is not essential.

It is typically necessary to stick two skin pieces together along their edges to form a two-piece sheet, using any starch or other biodegradable paste. The starch paste is applied just before moulding takes place.

Starch paste adhesive is suitable only for small scale and one-off pressing operations, where the moistened leaf pieces are assembled in the mould individually before pressing, and then the adhesive is applied at the last stage of the pre-pressing preparation. Furthermore, if the article is required to have water-resistance, starch paste cannot be used and a water-insoluble alternative adhesive must be used instead.

The pressing process In the small scale or one-off process, the moistened leaf pieces are laid in the female part 3 of the mould, and covered with adhesive. In the mass-production process, the steamed semi-formed piece 6 is placed between the mould parts 2,3. The mould parts and/or the press parts 7a,7b may be heated electrically or by any other convenient means (e.g. in an oven) to a temperature of typically between about 30C and about 1200C. The female part of the mould is typically at the bottom of the press, two skin pieces or one semi-processed sheet piece is placed over the female part of the mould and the male part of the mould then placed on top and pressed down.

Edge cutters or trimmers (not shown) may also be used in conventional manner. In a manual press, corner bolts are typically inserted and screwed down tight using spanners.

The pressure and heat are maintained for a length of time sufficient to allow the adhesive to cure and the composite to form having sufficient integrity and strength to be removed from the mould. Typically, the pressure and heat may be maintained for at least 10 minutes, for example approximately 20 minutes.

During the pressing operation it is important that the mould parts allow the escape of steam. Incomplete escape of steam can lead to bubbles forming in the composite, or wrinkling of the surface of the composite. It is preferred that at least the lower female part of the mould is provided with perforations and/or a grid of small channels in it, to allow water vapour to escape.

After the required length of time, the male mould part is raised and the article or semi-processed piece is removed. For forming hamburger containers in the form of clam shell halves it is particularly striking that articles are formed with well defined and clean edges, with good plasticity and flexibility and with well-formed and sharp corners which do not exhibit wrinkling or cracking.

Preparing the pieces and Pressing them into a semiprocessed sheet Referring now in particular to Figure 3, the skin pieces 11 are moistened as before and laid flat in a first layer 12 and a biodegradable adhesive is applied to the top surface. A second layer 13 of skin with adhesive on the bottom surface is laid so that the fibres 14 of the bottom 12 and top 13 layer are preferably at right angles to each other. This sheet is then place between the two perforated metal plates 4,5 in the press as shown in Fig.

4 and pressure is applied. The sheet is allowed to dry so that the adhesion between the two layers becomes strong. Thus, adopting the above described process, thin boards 2 to 3mm thick can be formed, which have good strength and are acceptably large in size. The board or sheet so may be used for making dishes and containers by a pressing process. It is observed that the stiff sheet has thermoplastic properties and the sheet becomes again pliable when exposed to steam. So, for preparing dishes or containers from the stiff board, pieces of required size may first be cut. Then these pieces are steamed in a steaming chamber 15 (see Figure 5) and made pliable for pressing in the mould.

The mould and die parts typically comprise conventional features such as cutters or stamps to create a sharp edge on the article or semi-processed piece. The heated male/female mould parts when brought together through the movement of the press can act to kill off any living bacteria (at 600C) and/or fungi (at 1200C) rendering the container fit for containing cooked food, frozen food e.g. meat which could subsequently be shrink wrapped.

The containers, dishes, plates, cups etc when formed, can be colour sprayed or painted upon to coat them and/or to render them aesthetically appealing.

Claims (18)

1. Modified plant material comprising a composite pressure-formed from a plurality of pieces of stem skin material from a plant of the genus Musa in the presence of an amount of an adhesive effective to retain the pieces integrally together in the composite material.

2. Modified plant material as claimed in claim 1, wherein the plant is the banana plant Musa sapientum.

3. Modified plant material as claimed in claim 1 or 2, when in the form of a sheet or board comprising one layer of stem skin pieces having overlapping edges and adhesive therebetween, and in which the fibres of adjacent pieces are substantially parallel.

4. Modified plant material as claimed in claim 1 or 2, when in the form of a sheet or board comprising two or more layers of stem skin material having adhesive between adjacent layers and in which the fibres of the stem skin pieces of each layer are substantially parallel.

5. Modified plant material as claimed in claim 4, wherein the fibres of adjacent layers are substantially at right angles to each other.

6. An article comprising a modified plant material as claimed in any preceding claim.

7. An article as claimed in claim 6 when in the form of a fast-food package or an article for containing, handling or displaying foods or beverages.

8. A method of preparing a material or article as claimed in any preceding claim, which comprises pressureforming an integral composite from a plurality of pieces of stem skin material from a plant of the genus Musa in the presence of an amount of adhesive effective to form the integral composite.

9. A method as claimed in claim 8, wherein the pressure-forming is conducted in the presence of moisture at an elevated temperature.

10. A method as claimed in claim 8 or 9, further including the step of moistening the stem skin material immediately before pressure-forming.

11. A method as claimed in any one of claims 8 to 10, wherein the stem skin material used is a partially dried form of natural stem skin.

12. A method as claimed in any one of claims 8 to 11, wherein the material or article is subjected to a sterilisation treatment.

13. A material, article or method as claimed in any preceding claim, wherein the adhesive is biodegradable.

14. A material, article or method as claimed in any preceding claim, wherein the adhesive is a waterresistant resin.

15. An article, more particularly a fast-food package or an article for containing, handling or displaying foods or beverages, comprising a material pressure-formed from stem skin material of the banana plant Musa sapientum.

16. A modified plant material substantially as herein described with reference to the accompanying drawings.

17. An article made from a modified plant material substantially as herein described with reference to the accompanying drawings.

18. A method for preparing a modified plant material or articles made therefrom, substantially as herein described with reference to the accompanying drawings.