GB2352230A

GB2352230A - Biodegradable packaging material

Info

Publication number: GB2352230A
Application number: GB9917058A
Authority: GB
Inventors: Jim Song
Original assignee: DYON Ltd
Current assignee: DYON Ltd
Priority date: 1999-07-22
Filing date: 1999-07-22
Publication date: 2001-01-24
Also published as: GB9917058D0; AU4878500A

Abstract

Biodegradable packaging material, particularly of block form, comprises an ordered structure of lengths 16 of foamed starch rod. The rod may be extruded and each length adhered to at least one adjacent length. The surface of each length may be moistened with water, eg a spray or steam, to cause the surfaces to adhere together. The lengths of rod may be in substantially axial alignment and may be arranged in layers, the lengths in successive layers being parallel and/or perpendicular. The ordered structure may comprise a cubic grid structure, a honeycomb lattice structure or a helix. Reinforcement ribs of denser material may be formed along the regions of contact of adjacent lengths. The structure may be at least partially covered with a protective or decorative coating such as wax paper.

Description

2352230 Packaging The present invention relates to biodegradable packaging

material and methods for production of - suchpackaging material.

Conventional packaging for goods such as computers and hi-fi equipment is made from synthetic polymer foams such as expanded polystyrene (EPS) or foamed polyurethane. Typically, the polymer is moulded or extruded to form blocks which are then stamped, and cut, 41 nto the desired shape before use. However, such packaging is unsatisfactory because it is not readily degraded after use and nonrenewable petroleum resources are used to manufacture the foams. Emission of gases such as carbon dioxide and chlorofluorocarbons during manufacture of the foams can also cause adverse environmental effects.

Biodegrada-ble packaging in the form of loose-fill chips can be made from extruded wheat starch. in one method (known as high temperature short time (HTST) extension cooking) used to make the loose-fill chips, wheat starch granules are softened by heat and broken, open to disperse their polymers. The polymers are plasticised by water to form a viscoelastic fluid which is then extruded at temperatures greater than 100'C to form the foamed loose-fill chips. This process does not give rise to harmful gaseous emissions.

Loose-fill chip packaging formed from extruded starch is biodegradable and water soluble, thus making it readily disposable. it has comparable cushioning properties to other types of non degradable packaging, such as polystyrene chips, and provides an excellent environmentally friendly replacement to such types of packaging. However, extrusion of starch with a large cross- sectional area is difficult because a high pressure difference at the extrusion die is required. Consequently, s.4;.zeable blocks of extruded starch cannot be made using conventional techniques.

Biodegradable b1ocks can be made by compression moulding of conventional loose-fill chips once they have been moistened with water to cause them to adhere to each other. Such blocks, however, contain large cavities which severely decrease the strength of the blocks and adversely affect thei.appearance. There is, therefore, a need to provide biodegradable blocks which are an effective replacement to conventional packaging b7ocks made from synthetic polymer foam.

According to the invention there is provided biodegradable packaging material comprising an ordered structure of lengths of foamed starch rod.

Preferably each length of rod is adhered to at least one ad4lacent length.

J Preferably, at least some of the lengths of rod are in substantially axial alignment.

Preferably the foamed starch is extruded starch.

II.e biodegradable packaging material may comprise a plurality of rods.

The ordered structure may comprise at least two layers, each laver comprising a plurality of lengths of rod. Preferably the principal axes of the lengths of rod of each layer are gene.-ally in axial alignment. The principal axes of the lengths of rod of one laver may not be in axial alignment with the principal axes of the lengths of rod of an adjacent laver. The principal axes of the lengths of one layer may be generally perpendicular to the principal axes of the lengths of an adjacent layer.

Reinforcement ribs of dense- material may be formed along the regions of contact between adjacent lengths of rod.

The ordered structure may comprise a helix.

Packaging according to tll-.e invention may be at least partially covered with a protective or decorative coating, for example with waxed papper which can protect packaging from the effects of humid_'tv.

The starch may be unmodified starch, for example wheat starch. Biodegradable packaging according to the invention made from unmodified wheat starch may be more resistant to changes in humidity than packaging made from modified starch.

Also according to the invention there is provided a method for making biodegradable packaging material which comprises: forming lengths of foamed starch in rod; and arranging the lengths into an ordered structure.

The method may -further comprise adhering each length of rod to at least one adjacent length.

Methods according to the invention in which adjacent: lengths are adhered together may further comprise compressing the ordered structure to increase the adherence between adjacent lengths of rod. Compression may be applied in a direction generally transverse to the principal axes of the lengths of rod. A layered structure may be formed by joining a first layer to a second layer, each layer comprising a plurality of lengths of rod, and compressing the layers together, for example in a direction gene-rally transverse to the plane of the layers.

The surface of each length of rod may be moistened with water, for example as a spray or as steam, to cause the surfaces to adhere together. The surface of each length is preferably moistened with water before the lengths are arranged into the ordered structure. Other adhesives may alternatively or addJiLtionally be used to adhere the lengths of rod to one another.

If the adhesive is water or some other adhesive that breaks down the foam of the lengths of starch rod, reinforcement ribs of denser material w-4-1-1 be formed along the regions of contact between adjacent lengths of rod. Compression of the ordered structure may cause reinforcement ribs of denser material to be formed along the regions of contact formed between adjacent lengths of rod as a result of the compression.

Packaging according to the invention which comprises a coating may be adhered to the coating by moistening the surface of the packaging or the coating with water and applying the coating to the packaging.

At least some of the lengths of rod are preferably arranged in substantially axial alignment.

The lengths of foamed starch are preferably formed by extrusion. Lengths of foamed starch having a desired shape in cross-section may be formed by extrusion through a suitable shaped die. L:ngths of foamed starch may be formed into a desired shape in cross-section after extrusion.

Packaging according to the invention which comprises a helix may be formed by winding a length of rod around a drum.

Embodiments of the invention will now be described in detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a schematic perspective view of a first, a second and a third embodiment of the invention; Figure 2 shows a schematic perspective view of an arrangement of extruded starch rods similar to that used to make the first and second embodiments of the invention shown in figure 1; Figure 3 shows the results of compression analysis of embodiments of the invention in comparison with conventional packaging; Figure 4 shows a schematic perspective view of an arrangement of extruded starch rods used to make an alternative embodiment of the invention; and Figure 5 is a schematic view of five alternative embodiments of the invention in cross section.

The first embodiment of the invention show-, in figure la comprises a block 10 of biodegradable packaging having a network of relatively dense reinforcing ribs 12 which extend throughout the block 1.0 in directions generally parallel with, and transverse to, its principal axis. Less dense material 14 is located between the reinforcing ribs 12. The block 10 is generally rectangular in cross-section and is made from horizontally packed lengths of extruded starch rod 16 (shown in figure 2).

The second embodiment of the invention shown in figure lb comprises a block IS of biodegradable packaging having a network of relatively dense reinforcing ribs 20 which extend throughout the block 18 in directions generally parallel with, and transverse to, its principal axis. Less dense material 22 is located between the reinforcing ribs 20. The block 18 is generally rectangular in cross-section and is made from vertically packed lengths of extruded starch rod 16.

The third embodiment of the invention shown in figure lc comprises a block 24 of biodegradable packaging having a net-work of relatively dense reinforcing ribs 26 which extend throughout the block 24. Less dense material 28 is located between the reinforcing ribs 26. The block 24 is generally -ectancular in cross sect-on and is made From 'our layers of horizontally packed lengths of extruded starch rod 16. The principal axes of the lengths of rod in each layer are generally in axial alignment. However, the principal axes of the lengths of rod of each layer are generally transverse to those of the adjacent layer or layers.

The lengths of extruded starch rod 16 used to make the i5 embodiments of the invention described are resistant to compression forces applied along their principal axes, but are less resistant to compression forces acting in directions generally transverse to their principal axes. it will be appreciated that the blocks 10, 18 of the first and second embodiments of the invention are relatively cormcressible in a first direction generally transverse to the principal axes of the lengths of rod 16 forming them.

The blocks 10, 18 are also relatively compressible in a second direction which is generally transverse to the first direction and to the principal axes of the lengths of rod 16 forming them. In contrast, the block 24 of the third embodiment of the invention is relatively resistant to compression in a first direction along the principal axes of the lengths of rod -of one, layer of the block 24 and in a second, generally perpendicular direction, acting along the principal axes of the lengths of rod of an adjacent layer of the block 24. The block 24 is relatively more compressible when subjected to compression forces acting in a third direction generally transverse to the first and second drections.

Packaging blocks according to the first, second and third embodiments of the invention may be orientated appropriately relative to the goods to be packaged, depending on whether it is desired to provide cushioning or more rigid protection. In some cases, the goods being packaged may require cushioning protection in one direction and more rigid protection in a different direction. Packaging according to the invention can provide both these types of protection.

In the embodiments of the invention described, each length of starch rod 16 has a foamed cellular structure in which each cell is elongate in shape and is generally aligned with its longitudinal axis approx4Lmately parallel to the principal axis of the length of starch rod of which it forms a part. It is believed that this cellular structure may account for the relative incompressibility of the lengths of extruded starch rod along their principal axis as compared with their relative compress -ibi lity in directions generally transverse to their principal axis.

To make the block 10 or 18, the lengths 16 of starch rod are first formed by conventional HTST extrusion. The lengths of rod are then sprayed with water to cause them to adhere together when they are in contact with each other, and are a.-ranged in parallel in rows one length of rod on top of another, as shown in figure 2. The principal axes of lengths of rod in vertically adjacent rows are aligned in a plane generally perpendicular to the plane in which the principal axes of lengths in horizontally adjacent rows are aligned and there is a single point of contact between adjacent lengths. This arrangement is referred to as a cubic grid structure. After the lengths are assembled, they are compressed together in a direction generally transverse to their principal axes so that the surfaces of adjacent lengths contact each other. As the surfaces contact eath other, they adhere together and the reinforcing ribs of denser material are formed at the points of contact between the adjacent lengths.

The block 24 of the third embodiment of the invention is formed by spraying lengths of extruded starch rod (made by HTST extrusion cooking) with water and joining the lengths of rod to form separate layers comprising parallel lengths of rod. The separate layers are then joined together so that the principal axes of the lengths of rod of adjacent I m. - transverse are in parallel p'anes but are gene-ally.

to one another. The layers are then compressed together in a direction gene-rally transverse to the planes of the lavers.

The blocks of the first, second, and third embodiments of the invention were analysed using static compression tests complying with International Standard BSEN ISO 3386-1:

1997. According to this standard, a block to be tested is Placed in a test machine capable of compressing the block be:ween a support surface and a compression plate at a rate of motion in the vertical direction of 100 + 20 mm/min.

From the compression force and sample thickness recordings, stress-strain curves for each block can be obta4ned.

L - - The results of th 4 s analvsis are used to calculate values for the cushion factor (C) of the block being tested using the following formula':

C= [cr/E] where CT is the stress applied; and E is the accumulated energy absorbed, calculated from the stress-strain curve - s.

I L.J. Gibson and M.F. Ashby Cellular Solids (2" Edition) 1997. Cambridge University Press, pp. 309-343.

The higher the C value, the poorer the material I s ef f iciency as an energy absorber and, therefore, the more material that is required to protect the goods being packaged compared to materials with. a lower C value. The cushion factor varies with the stress level and reaches a minimum value (C,,,,,). The blocks of the first, second, and third embodiments of the invention were compared with conventionall packaging blocks and with conventional loose starch chips in a test chamber 150 x 150 x 150mm. Four different conventional packaging blocks were tested. Three of these, EPS-A, EPS-B, and EPS-C, were made using steam chest moulding from different size spheres of expanded polystyrene (7-PS) and had different bulk densities (see table 1). A fourth conventional packaging block made from foamed polyurethane (PU) was also tested. Two types of conventional loose starch chips were tested; standard chips (LF-SD) at a bulk density of 6-7 kg/ml and heavy duty chips (LF-HD) at a bulk density of 10 kg/mI. The results of the minimum cushion factor determination for each type of block are given in table I toczether with the density of each block.

Type of block Block density C (Kg/m-') LF-SD 10.5 3.79 LF-HD.9.97 3.33 First embodiment 26.9 3.19 Third embodiment 26.8 3.30 Second embodiment 26.7 2.0 PU 18.6 2.8 EPS-A 10.1 3.17 EPS-B 15.4 2.77 EPS-C 25.5 2.57 Table 1

The results in table I show that the starch block of the second embodiment of the invention has better cushioning efficiency than any of the other blocks tested, including conventional blocks of similar density (EPS-C). The blocks of the first and third embodiments of the invention have almost identical cushioning efficiency to the EPS-A block and have comparable cushioning efficiency to other types of conventional block. All the blocks have better cushioning efficiency than the loose chips (LF-SD and LF-HD).

These results indicate that packaging according to the invention can provide a biodegradable alternative for conventional packaging w it- h significantly better, or comparable, cushioning efficiency to conventional packaging. For embodiments of the invention which have better cushioning efficiency than conventional packaging, the packaging bulk may be reduced whilst providing the same cushioning protection to goods as conventional packag-ing, or goods may be more effectively protected using the same packaging bulk as conventional packaging.

The static compression tests also enable the recommended stress range for each material to be calculated. This is done by reading the stress range corresponding to 50-70% comoression deformation of the material from the stressstrain curves. The recommended stress range encompasses the C,, value of the material. It provides a measure of its load bearing capacity and of the weight of goods that will be most effectively protected by a particular thickness of that material. For example, the higher the range, the better the material-will be at protecting heavy goods. The recommended stress range also provides information about the supporting area that should be provided by a material for it to protect a g-4ven weight of goods. The results are shown in table 2.

Type of block Reco=ended stress range (KPa) LF-SD 13-26 LF-HD 15-24 First embodiment 35-81 Second embodiment 30-64 Third embodiment 22-54 PU 22-56 EPS-A 178-283 EPS-B 295-500 EPS-C 155-265 Table 2

Tatle 2 shows that the recommended stress ranges of the blocks of the fIrst, second and third embodiments of the invention are much higher than the ranges for the LF-SD and LF-HDI loose chios. The recommended stress ranges for the blocks of the first and second embodiments of the invention are overlapping with, but higher than, the recommended stress range of "the foamed PU block. The block of the third embodiment of the invention has a similar recommended stress 20.-a.-Ige to the foamed PU block. The recommended stress ranges of the EPS blocks are h-iz,',er than all the other blocks tested.

These results indicate tha::, for the same contact area, packaging made from blocks similar to the first and second embodiments of the invention packaging is more effective at protecting heavier goods than the foamed PU packaging. Alternatively, less support area is required to be provided from packaging made from blocks similar to the first and second embodiments of the invention compared to foamed PU packaging to adequately protect a given weight of goods. Packaging made from blocks similar to the third embodiment of the invention is effective at protecting similar weight goods as the foamed PU packaging. Consequently, similar supporting area is required to be provided from packaging made from blocks similar to the third embodiment of the invention comna-red to foamed PU packaging to adequately protect a given weight of goods.

Thestarch blocks of the first, second and third embodiments of the invention were also compared with conventional EPS-A type blocks in dynamic compression tests complying with European Standard EN ISO 4651, 1995. In these tests, the block to be tested was placed on the anvil of the test apparatus and impacted by a drop hammer at a predetermined height and weight. The peak deceleration (peak G) of the drou hammer on the imoact- was measured using an accelerometer connected to a da:a acqu';sition system of a computer. The peak G values were then plotted against the static s 1. r e s s levels o the impacts to produce a deceleration-static stress diagram.

The peak G value provides a measure of the cushioning protection provided by a given thick,ness of packaging block to a particular level of impact. The lower the peak G value, the better the block is at cushioning the impact.

Comparison of the peak G values of similar thicknesses of different types of packaging block over a range of static stress levels prov.-Ides an indication of which type of packaging block will be most effective at protecting goods of a certain weight and/or which will be most effective at providing protection from a certain level of impact. For example, packaging with lower peak G values at high static stress levels than other types of packaging will be more effective at cushioning heavy goods and/or protecting goods from high level impacts than other packaging types.

Similarly, packaging with lower peak G values at low static stress levels than other types of packaging will be more effective at cushioning light goods and/or goods protecting - 13 goods from low level impacts than those other packaging types.

Blocks of similar cross-sectional area (100mm x 100mm) and thickness (50 mm) were analysed. The deceleration-static stress diagrams for the blocks are shown in figure 3.

Figure 3 shows that the starch blocks of the first, second, and third embodiments of the invention have comparable ability to absorb impacts to the conventional EPS-type blocks over the range of static stresses tested.

The block of the second embodiment of the invention was better able to cushion impacts at static stress levels between about 0.06 and about 0.09 kg/sq.cm than all the conventional EPS-type blocks tested. This block was also better able to cushion impacts at higher static stress levels (upto about 0.17 kg/sq.cm) than the EPS-A block, and had very similar cushioning ability to the E-PS-B and EPS-C blocks at these stress!evels. At lower static stress levels (below about 0.06 k---/sq.cm) the block of the second embodiment of the invention was better able to absorb impacts than the EPS-C block and at static stress levels between about 0.045 kg/sq.cm and 0.06 kg/sq.cm this block was better able to absorb impacts than the EPS-B block.

The block of the third embodiment of the invention was better able to absorb impacts than the EPS-C block at static stress levels below about 0.075 kg/sq.cm, and than the EPS-B block at static stresses below about 0.065 kg/sq.cm. The block of the first emodiment of the invention was better Able to absorb impacts than the EPS-C block at static stress levels below about 0.07 kg/sq.cm and than the EPS-B block at static stress levels below about 0.05 kg/sq.cm.

These results show that packaging according to '.-he invention has comparable or better impact absorption qualities to conventional EPS-type packaging over a wide range of static stress levels.

Figure 3 a'-so shows that the ability of the embodiments of the invention to cushion impacts over a range of stress levels varies. For impacts over the middle part of the range of static stresses tested (from about 0.06 to about 0.22 kg/sq.cm), the block of the second embodiment of the invention has better cushioning ability than the block oj third embodiment of the invent-ion which had, in turn, better cushioning ability than the block of the first embodiment of the invention. For impacts at low static stress (below about 0. 05 kg/sq. cm), the peak G values recorded for the block of the second embodiment of the invention increased and were higher tlan those recorded for the blocks of the first and third embodiments. For impacts at high static stress (above about 0.22 kg/sq.cm), the peak G values for the second embodiment were higher than those recorded for the third embodiment but remained below those for the first embodiment. Thus, at high static stress levels the third embodiment is better than the first and second embodiments at cushioning impacts and at lower stress levels, the first and third embodiments were better than the second embodiment at cushioning impacts.

It is believed that the differing ability of the first, second, and third embodiments of the invention to cushion impacts can be explained by their differing structures. The prIncipal axes of the lengths of rod of the first embodiment of the invention were generally transverse to the direction of impact of the drop hammer in the dynamic compression tests It is thought that because the lengths of rod are relatively compressible in this direction, the first embodiment had comparatively low cushioning ability over the range of static stress levels tested.

The principal axes of the lengths of rod of the third embodiment were also generally transverse to the direction of impact of the drop hammer in the static compression tests. However, because the lengths of rod of adjacent layers in this block are generally transverse to each other, the network of reinforcing ribs in the third embodiment runs in different directions in alternate layers of that block. This more complex reinforcement structure is believed to provide better cushioning against impacts than that of the first embodiment.

The principal axes of the lengths of rod of the second embodiment were generally parallel. to the direction of imDact of the drop hammer in the dynamic compression tests. Because the lengths of rod are relatively resistant to compression forces acting along their principal axes, the second embodiment had better cushioning ability than the first and third embodiments over most of the range of static stress levels tested.

In summary, the results described indicate that packaging according to the invention can provide an excellent biodegradable alte.-native to conventional packaging and that some embodiments of the invention have superior qualities to conventional packaging.

The cushioning properties of blocks according to the invention are affected by the extent, spatial distribution, and thickness of the reinforcing ribs. For a given volume, packaging blocks formed from smaller diameter lengths of rod have a higher proportion of reinforcing ribs than similarly compressed blocks formed from larger diameter lengths of rod and are more resistant to compression than such blocks. The extent of formation of the network or reinforcing ribs depends on the packing arrangement of the lengths of rod, the amount of water sprayed onto the lengths of rod before assembly, and on the degree to which the lengths of rod are subsequently compressed together. In some embodJLments of the invention, the lengths are simply arranged into the desired structure without any, or only slight, subsequent compression. In other embodiments, the lengths are compressed together so that their surfaces are substantially in contact with each other. Packaging formed by compressing lengths of rod under relatively low pressure is softer, and is more suited to packag'Lng light and fragile goods such as computer board and other electronic components. Packaging formed by compressing lengths of rod under relatively MLgh pressure is more suitable for packaging heavier goods.

The properties of packagLng acclordJLng to the invention are also affected by the pack'na arrangement of lengths of rod in the packaging and by the orientation of the packaging relative to the goods being packaged.

In other embodiments of the invention, the lengths of rod used to make the packaging may be stacked in an arrangement other than that of the cubic lattice structure of Figure 2. For example, the lengths may be arranged in generally parallel rows one on top of another with the lengths of each row being disposed direcz'Ly above the point of contact between adjacent lengths JLn the row immediately underneath. This arrangement of lengths of rod is shown in f4Lgure 4 and is termed a honeycomb lattice structure.

In other embodiments of the invention, the 'Lengths of rod may have any desired shape in cross-section. Lengths of rod with the desired shape in cross-section may be made, for example, by extruding starch through a suitably shaped die, or by forming the lengths into the desired shape after extrusion. In one preferred embodiment, the lengths of starch rod are triangular in cross section.

Figure 5 shows five alternative preferred embodiments of the invention in schematic cross section. Figure 5a shows a schematic cross section of a fourth embodiment of the invention. The fourth embodiment comprises a block 30 made from extruded starch rods 32 arranged in a cubic grid structure. A network of relatively dense reinforcing ribs 34 (represented by the darker lines in the figure) is formed along the regions of contact between the extruded starch rods 32.

Figure 5b shows a schematic cross section of a fifth embodiment of the invention. The fifth embodiment comprises a block 36 made 'from extruded starch rods 38 arranged in a honeycomb grid structure. A network of relatively dense re4A.nforcing ribs 40 (represented by the darker lines in the figure) is formed along the reg-Lons of contact between the extruded starch rods 38.

i5 Figure 5c shows a schematic cross section of a sixth embodiment of the invention. The sixth embodiment comprises a block 42 made from five layers of extruded starch rods 44.

The principal axes of the extruded starch rods 44 of the different layers are in generally parallel planes. However, the principal axes of theextruded starch rods 44 of adjacent layers are generally transverse to one another. A network of relatively dense reinforcing ribs 46 (represented by the darker lines in the figure) is formed along the regions of contact between the extruded starch rods 44.

Figure 5d shows a schematic cross section of a seventh embodiment o f the invention. The seventh embodiment comprises a block 48 made from three layers of extruded starch rods 50. The principal axes of the starch rods 50 of one of the outer layers lie in a plane generally parallel to the plane in which the principal axes of the starch rods 50 of the other outer layer lie. The starch rods 50 of the middle layer are in a cubic grid arrangement. The principal axes of the starch rods 50 of the middle layer are generally transverse to the planes in which the principal axes of the starch rods 50 of the outer layers lie. A network of relatively dense reinforcing ribs 52 (represented by the darker lines in the figure) is formed along Che regions of contact between the extruded starch rods 50.

Figure 5e shows a schematic cross section of an eighth embodiment of the invention. The eighth embodiment comprises a block 54 madle from extruded starch rods 56 of generally triangular cross-section. The extruded starch rods 56 are packed together so that the flat surfaces of adjacent lengths are substantially in contact with one another. A network of relatively dense reinforc'Lng ribs 58 (represented by the darker lines in the figure) is formed along the regions of contact between the extruded starch rods 56. This embodiment has been found to have particularly good resistance to compression forces of relatively high static stress levels and is, therefore, especially suited for protecting heavier goods.

The lighter lines in F-Lgures 5a, b, c, d, and e show schematically the internal cellular structure of the extruded starch rods 32, 38, 44, 50 and 56 used to make the fourth to eighth embodiments of the invention.

Alternative preferred embodiments of the invention are described below. one preferred embodiment comprises three blocks having a cubic grid structure arranged generally transverse to one another to define the corner of a cube.

This embodiment is suitable for protecting the corner of an item. Another preferred embodiment comprises two blocks having a cubic grid-structure arranged generally transverse to one another to define a L-shape in cross section. This embodiment is suitable for protecting the edge of an item.

Another preferred embodiment comprises a length of rod wound into a helix structure and is suitable for protecting cylindrical items. Another preferred embodiment is a packaging block comprising three layers, the principal axes of the lengths of rod of the middle layer being generally transverse, and in a parallel plane, to the principal axes of the lengths of rod of the outer layers. A layer of wax coated paper is adhered to the upper surface of the block.

Another preferred embodiment is a packaging block comprising five layers. The lengths of rod of each layer are generally transverse, and in a parallel plane, to the lengths of rod of the adjacent layer or layers.

From the differing properties o IL embodiments of the invention described it will be appreciated that biodegradable packaging material according to the invention can readily be made to suit the requirements of the goods being packaged. Packaging with the desired load bearing, cushioning efficiency, and impact absorption qualities can be made by using appropriate diameter lengths of rod, appropriately stacking the lengths of rod, by moistening and compressing the lengths of rod to the appropriate extent, and by orientating the packaging appropriately relative to the goods.

Biodegradable packaging material according to the invention provides an excellent alternative to non biodegradable packaging, such as synthetic polymer foam packaging. Biodegradable packaging material according to the invention has comparable or better cushioning efficiency and load bearing capacity to conventional EPS packaging blocks at relatively low stress levels and has better cushioning efficiency and load bearing capacity than conventional foamed polyurethane packaging blocks. Packaging according to the invention also has comparable or better impact absorption qualities to conventional EPS-type packaging over a wide range of static stress levels.

Packaging according to the invention has a high quality appearance and is made using environmentally friendly techniques which may be fully automated. Protective or decorative coatings can readily be applied to packaging according to the invention using water as an adhesive agent.

Claims

1. Biodegradable packaging material comprising an ordered structure of lengths of foamed starch rod.

2. Biodegradable packaging material according to claim 1 in which each length of rod is adhered to at least one adjacent length.

3. Biodegradable packaging materiall according to claim 1 or 2 in which at least some of the lengths are in substantially axial alignment.

4. Biodegradable packaging material according to any preceding claim in which the foamed starch is extruded starch.

5. BiodegradabLe packaging material according to any preceding claim comprising a plurality of rods.

6. Biodegradable packaging material according to any preceding claim in which the ordered structure comprises a cubic grid structure (as herein defined).

7. Biodegradable packaging material according to any preceding claim in which the ordered structure comprises a honeycomb lattice structure (as herein defined) -

S. Biodegradable packaging material according to any preceding claim in which the ordered structure comprises at least two layers, -each layer comprising a plurality of lengths of rod.

9. Biodegradable packaging material according to claim 8 in which the principal axes of the lengths of rod of each layer are generally in axial alignment with each other.

10. Biodegradable packaging material according to claim 8 or 9 in which the principal axes of the lengths of one layer are generally perpendicular to the principal axes of the lengths of an adjacent laver.

11. Biodegradable packaging material according to any of claims 1 to 5 in which the ordered structure comprises a helix.

12. Biodegradable packaging material according to any preceding claim in which one or more lengths of starch rod io are generally of triangular cross-section.

13. Biodegradable packaging material according to any preceding claim in which adjacent lengths of rod are adhered together with water.

14. Biodegradable packaging material according to any preceding claim in which reinforcement ribs of denser material are formed along the regions of contact between adjacent lengths of rod.

15. Biodegradable packaging material according to any preceding claim which is -at leas-, partially covered with a protective or decorative coating such as wax paper.

16. Biodegradable packaging material according to any preceding claim in which the starch is unmodified starch.

17. A method for making biodegradable packaging material which comprises: - forming lengths of foamed starch in rod form; and arranging the lengths into an ordered structure.

18. A method according to claim 17 which further comprises adhering each length to at least one adjacent length.

19. A method according to claim 18 in which adherence of adjacent lengths to each other causes reinforcement ribs of denser material to be formed along the regions of contact between the adjacent lengths.

20. A method according to claim 18 or 19 which further comprises compressing the ordered structure to increase the adherence between adjacent lengths of rod.

21. A method according to claim 20 in which the compression causes reinforcement ribs of denser material to be formed in the ordered structure along the regions of contact formed between adjacent lengths of rod as a result of the compression.

22. A method according to any of claims 18 to 21 in which the surface of each length is moistened with water to cause the surfaces to adhere together.

23. A method according to claim 22 in which the surfaces of at least some of the lengths are moistened with water be-fore they are arranged into the ordered structure.

24. A method according to any of claims 17 to 23 in which at least some of the lengths are arranged in substantially axial alignment.

25. A method according to any of claims 17 to 24 in which the lengths of foamed starch are formed by extrusion.

26. A method according to claim 25 in which the lengths of foamed starch are formed into a desired shape in cross section by extrusion through a suitable shaped die.

27. A method according to claim 25 in which the lengths of foamed starch are formed into a desired shape in cross section after extrusion.

28. Biodegradable packaging mate jal substantially as described.

29. Biodegradable packaging material substantially as described with reference to figure la, lb, 1c, Sa, 5b, 5c, 5d, or 5e of the accompanying drawings.

30. A method substantially as described.