METHODS OF INCREASING FORMABILITY OF A PALM SHEATH MATERIAL, METHODS OF PRODUCING A PALM SHEATH-BASED PRODUCT, AND PALM SHEATH FOODWARE PRODUCED THEREBY

Abstract

Methods of increasing formability of a palm sheath material, methods of producing a palm sheath-based product, and palm sheath foodware produced thereby. The formability of a palm sheath material is increased by treating the palm sheath material with a fluid substance that weakens bonds between cellulose fibers of the palm sheath material by partially eliminating lignin and hemicellulose of the palm sheath material. The treated palm sheath material can be used to form various products, such as foodware products by deforming the treated palm sheath material into a shape. Advantageously, the treated palm sheath material can typically be deformed by stretching or punching using dies to a height to diameter aspect ratio of greater than 0.2 and/or to a limit strain of the palm sheath material greater than 0.38.

Claims

1. A method of increasing formability of a palm sheath material, the method comprising treating the palm sheath material with a fluid substance that weakens bonds between cellulose fibers of the palm sheath material by partially eliminating lignin and hemicellulose of the palm sheath material without inducing large-scale structural damage that promotes fracture.

2. The method of claim 1, wherein the fluid substance is chosen from the group consisting of ethylene glycol, hot water or boiling water, and aqueous solutions containing one or more hydroxides and/or sulfites.

3. The method of claim 2, wherein the fluid substance contains at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, and ammonium hydroxide.

4. The method of claim 1, wherein the fluid substance is an aqueous solution.

5. The method of claim 1, wherein the fluid substance is an aqueous sodium hydroxide solution.

6. The method of claim 5, wherein the aqueous sodium hydroxide solution has a NaOH concentration of about 2% to less than 10%.

7. The method of claim 5, wherein the aqueous sodium hydroxide solution has a NaOH concentration of about 5%.

8. The method of claim 5, wherein the palm sheath material is treated with the aqueous sodium hydroxide solution for a duration of not greater than twelve hours.

9. The method of claim 5, wherein the palm sheath material is treated with the aqueous sodium hydroxide solution for a duration of greater than one hour and up to about six hours.

10. The method of claim 5, wherein the aqueous sodium hydroxide solution has a NaOH concentration of about 5% and the palm sheath material is treated with the aqueous sodium hydroxide solution for a duration of about one to about six hours.

11. The method of claim 5, wherein the aqueous sodium hydroxide solution has a NaOH concentration of about 5% and the palm sheath material is treated with the aqueous sodium hydroxide solution for a duration of about two to about six hours.

12. The method of claim 5, wherein the aqueous sodium hydroxide solution consists of sodium hydroxide and water.

13. The method of claim 2, wherein the fluid substance contains at least one of potassium sulfite, calcium sulfite, magnesium sulfite, and ammonium sulfite.

14. The method of claim 1, wherein the fluid substance contains at least one of methanol, formic acid, acetic acid, chlorite, and tetrahydrofuran.

15. The method of claim 1, wherein the palm sheath material is an areca palm sheath.

16. The method of claim 1, wherein the palm sheath material is in a raw condition when treated with the fluid substance.

17. A method of producing a palm sheath-based product, the method comprising: performing the method of claim 1 on the palm sheath material to produce a treated palm sheath material; and deforming the treated palm sheath material into a shape to produce a product.

18. The method of claim 17, wherein the deforming step is accomplished by mechanical pressing, stretching, twisting, bending, punching, rolling, piercing, cutting, or some combination thereof.

19. The method of claim 17, wherein the deforming step forms a limit strain that exceeds 0.38.

20. The method of claim 17, further comprising: heating the product to preserve the shape by removing excess moisture without causing structural damage to the treated palm sheath material.

21. The method of claim 17, wherein the deforming step is performed on the treated palm sheath material with dies.

22. The method of claim 21, wherein the dies are heated to heat the product.

23. A palm sheath foodware comprising a product produced in accordance with the method of claim 17, wherein the product comprises at least one of a cup, a bowl, a plate, a utensil, a tumbler, and packaging.

24. The palm sheath foodware of claim 23, wherein the product has a height to diameter aspect ratio of greater than 0.2 and a limit strain of the palm sheath material greater than 0.38.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1A is an image depicting the leaf, stem, and sheath of an areca palm tree.

[0020] FIG. 1B contains images depicting a raw areca palm sheath with directional arrows and a scale.

[0021] FIG. 1C contains images identifying features and surfaces of an areca palm sheath.

[0022] FIG. 1D contains images depicting various existing palm sheath foodware items.

[0023] FIG. 2A schematically represents a limiting dome height (LDH) test employed to test formability and tensile strength of a palm sheath material.

[0024] FIG. 2B is a load-displacement curve graph evidencing forming limits for palm sheaths tested when dry, hydrated, and treated with an aqueous NaOH solution.

[0025] FIG. 2C contains an image depicting a cup of a depth of approximately 10 mm formed from areca palm sheath during an LDH test after undergoing a hydration treatment.

[0026] FIG. 2D contains an image depicting a cup of a depth of approximately 10 mm formed from a copper sheet during an LDH test.

[0027] FIG. 3 is a graph evidencing the effects of NaOH concentration and treatment time on forming strain on an areca palm sheath. Dry refers to a sheath in the as-received condition, and a NaOH (%) of 0 identifies sheaths treated with only a water hydration treatment (in other words, without NaOH).

[0028] FIG. 4A contains SEM images showing surfaces (top row) and transverse cross-sections (bottom row) of sheaths following three different treatment conditions: an original (dry and untreated) sheath and two sheaths that underwent two-hour treatments in 5% and 15% NaOH solutions.

[0029] FIG. 4B is a graph indicating weight loss due to the NaOH treatments.

[0030] FIG. 4C contains FTIR spectrum plots of dry (untreated) sheath and a sheath (dry) and a sheath that underwent a two-hour treatment in 15% NaOH solution.

DETAILED DESCRIPTION OF THE INVENTION

[0031] The intended purpose of the following detailed description of the invention and the phraseology and terminology employed therein is to describe what is shown in the drawings, which depict and/or relate to one or more nonlimiting embodiments of the invention, and to describe certain but not all aspects of the embodiment(s) depicted in the drawings. The following detailed description also identifies certain but not all alternatives of the embodiment(s) depicted in the drawings. As nonlimiting examples, the invention encompasses additional or alternative embodiments in which one or more features or aspects shown and/or described as part of a particular embodiment could be eliminated, and also encompasses additional or alternative embodiments that combine two or more features or aspects shown and/or described as part of different embodiments. Therefore, the appended provisional claims, and not the detailed description, are intended to particularly point out subject matter regarded to be aspects of the invention, including certain but not necessarily all of the aspects and alternatives described in the detailed description.

[0032] According to some nonlimiting aspects of the invention, a palm sheath material, for example, a sheath of an areca palm, can be treated with a fluid substance that weakens bonds between cellulose fibers of the palm sheath material by partially eliminating lignin and hemicellulose of the palm sheath material prior to undergoing a forming operation to increase its formability. Particular but nonlimiting examples of suitable fluid substances include ethylene glycol, hot water (liquid), water vapor, and aqueous (liquid) solutions containing one or more hydroxides (which release OH.sup.? groups that aid in the partial elimination of lignin) and sulfites, such as sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, ammonium hydroxide, potassium sulfite, calcium sulfite, magnesium sulfite, and ammonium sulfite. Further nonlimiting examples of suitable fluid substances are believed to include methanol, formic acid, acetic acid, chlorite, and tetrahydrofuran. In investigations leading to the present invention, tests were performed evidencing the efficacy of sodium hydroxide, ethylene glycol, sodium sulfite, and hot water or boiling water. Some of the investigations using aqueous sodium hydroxide (NaOH) solutions as the fluid substance to treat areca palm sheaths are described below.

[0033] Though NaOH is known to soften wood to increase its bendability and to increase the densification of natural wood by compression, the action of a NaOH solution in all of these cases is to weaken the bonding between cellulose fibers in natural wood by partially removing hemi-cellulose and lignin. An advantageous increase in the formability of a palm sheath due to a NaOH treatment was not expected given that palm sheaths have a structure intermediate that of wood and a plant leaf.

[0034] Formability conferred by NaOH treatments to palm sheaths was investigated using a limiting dome height (LDH) test, an illustrative example of which is shown in FIG. 2A. In the investigations, 3 mm-thick samples of areca sheaths were clamped along their peripheries in an LDH die and then axi-symetrically stretched (expanded) into cup (bowl) form. See FIGS. 2A and 2C. As represented in FIG. 2A, stretching was accomplished by pressing a hemispherical surface (diameter, d.sub.p=25 mm) of a punch against the unclamped central region (diameter, 30 mm) of the sample, as is typical of LDH testing. The sheath surface that forms the inner side of a cup formed by deformation is thus in contact with the punch, while the opposite surface (the side facing away from the punch) forms the outer side of the cup. A solid lubricant (TEFLON? film) was placed between the sample and punch surfaces to reduce interface friction. The LDH test closely resembled stretch-forming processes used to manufacture areca foodware such as plates and bowls, except that there was no bottom die in the LDH tests as there would be in a foodware manufacturing process.

[0035] A series of LDH experiments was carried out with areca sheaths under dry (original untreated), hydrated, and aqueous NaOH treatment conditions to assess sheath formability with specific relevance to foodware manufacturing. The sheaths were obtained in a raw condition, meaning that they had not undergone any previous treatments that would alter their structures or microstructures. The LDH test samples were cut from central regions of the sheaths to each have a size of about 40 mm?40 mm?3 mm (thickness). Sheath formability was assessed in terms of maximum punch displacement and maximum strain (forming limit) developed at the bottommost point of the punch (inside surface of the resulting cup) at failure, as well as the forming force.

[0036] All hydrated test samples were hydrated by immersion in water (0% NaOH) for two hours. Aqueous NaOH solutions at different NaOH concentrations were used to treat the NaOH-treated samples. NaOH concentrations evaluated were 2%, 5%, 10%, and 15% by weight in a solution of water, and all NaOH-treated samples at each concentration were treated by immersion in the solution for a duration of one, two, six, or twelve hours. Forming limit strains were obtained with five tests performed at each set of parameter conditions.

[0037] Formability was assessed in terms of the capacity for shape change (limit strain, ?) and the forming force to produce a given shape change. Results for dry samples, hydrated samples treated with water for two hours, and samples treated with 5% NaOH for two hours are plotted in FIG. 2B. The penetration depth at failure (h) for the dry sheath samples, hydrated sheath samples, and sheath samples treated with a 5% NaOH aqueous solution for two hours were 3.8 mm (h/d=0.13), 10.2 mm (h/d=0.34) and 13 mm (h/d=0.43), respectively. The corresponding forming limit (pole) strains in the cup samples are 0.06, 0.38, and 0.56, respectively. Based on both the penetration depth and forming limit strain, it was evident that the hydration and NaOH treatments resulted in a significant increase in the formability compared to the dry condition. The aspect ratios achieved with the hydration and NaOH treatments were 2.5 to 3.5 times that of the dry samples, while the forming limit strains were six to nine times that of the dry samples. While both the hydration and NaOH treatments produced impressive increases in the forming limit strain, the forming limit of ?=0.56 produced by the NaOH treatment was approximately 50% greater than that of the hydration treatment (=0.38). Interestingly, the high limit strain of the hydrated sheath samples exhibited in FIG. 2B was essentially the same as that of very ductile copper, as can be seen by comparing FIGS. 2C and 2D.

[0038] Concurrent with the increased capacity for shape change, there was a corresponding large reduction in the forming force due to the hydration and NaOH treatments. For example, the maximum load, which occurs almost at the failure limit (h about 3.8 mm), was about 350 Newtons (N) in the dry sample, whereas the corresponding load at the same penetration depth of 3.8 mm with the hydrated sample was just less than 50 N, an approximately 85% load decrease. This failure limit load was even further lowered with the NaOH treated samples relative to the hydrated samplesabout 130 N vs about 410 Na nearly 70% reduction in the forming force with the NaOH treatment. The large forming force reduction was concluded to be another manifestation of the significantly increased formability due to hydration and even more so due to the NaOH treatment. Such reductions in forming force confer advantages in energy requirements when forming foodware as well as other products from areca palm sheath materials, and therefore reduces the embodied energy of such products.

[0039] Areca sheath samples subjected to aqueous NAOH solution treatments at 2%, 5%, 10%, and 15% concentrations for durations of one, two, six, and twelve hours also underwent a series of LDH tests, the results of which are depicted in FIG. 3. For two-hour durations, limit strains were observed to increase with NaOH concentrations up to 5%. Steep decreases in limit strains were observed in concentrations over 5%. A decrease in formability also occurred in the 5% NaOH sample when the time duration of the treatment was increased to 12 hours. In contrast, with the pure hydration treatment (0% NaOH), the formability was not influenced by the duration of the time exposure. In summary, the 5% NaOH aqueous solution treatment for a two-hour duration produced the largest increase in forming limit strain, being also much greater than that realized with a pure hydration treatment. NaOH concentrations greater than 5% did not promote formability. A NaOH concentration of 2% coupled with treatment durations of two hours or more, and a NaOH concentration of 5% coupled with treatment durations of one to six hours were most effective in promoting formability among the tested samples.

[0040] SEM analysis of the sheath samples subjected to the 5% and 15% NaOH treatments (two-hour exposures) suggested that the observed forming limit changes were a consequence of microstructure modifications resulting from the treatments. FIG. 4A shows SEM images of surfaces (top row) and transverse (thickness?width) cross-sections (bottom row), respectively, of the original (dry and untreated) sheath samples and the sheath samples subjected to the 5% and 15% NaOH treatments. There is no discernible difference in the structure of the sheath surface or of the sheath cross-section between the dry and 5% NaOH treated samples. However, the surface of the 15% NaOH treated sample showed significant swelling and cracking. Furthermore, the cell walls in the 15% NaOH treated sample appeared to have disintegrated and dissolved, with significant structural damage to the material (FIG. 4A, bottom row, righthand column).

[0041] Mass measurements and FTIR analysis on dry (untreated) sheath samples and sheath samples subjected to the 15% NaOH treatment confirmed and reinforced the SEM observations of the structural changes in the sheath samples seen in FIG. 4A. Weight (mass) occurred in the samples after the NaOH treatments. FIG. 4B plots weight loss as a percentage change, with the initial mass of the sample serving as the datum. The weight loss was about 1% for the 5% NaOH-treated samples, and about 8% for the 15% NaOH-treated samples. The data coupled with FTIR analysis of the samples discussed below, and previously reported observations with respect to wood indicated that more mass in the form of hemicellulose and lignin is removed when the sheath is treated with a 15% NaOH solution. This larger-scale removal of hemicellulose and lignin with the 15% solution damages the material structurally, in addition to weakening the bonds between the cellulose fibers. In contrast, the 5% NaOH treatment appeared to only weaken the bonds between the cellulose fibers, while removing only smaller (negligible) amounts of hemicellulose and lignin. This would appear to explain why the forming limit strain for the sheath samples increased with % NaOH at the lower concentrations (5% and below), wherein there is only intra-cellulose bond weakening with negligible structural damage (FIG. 4A, middle column). Formability was rapidly lowered beyond the 5% threshold concentration due to extensive structural damage to the material (e.g., FIG. 4A, righthand column). An optimum NaOH treatment was thus concluded to cause a weakening of the bonds between the cellulose fibers to enhance material deformation capacity, but without inducing large-scale structural damage that can promote fracture.

[0042] FIG. 4C plots FTIR spectra confirming the large-scale removal of hemicellulose and lignin due to the 15% NaOH treatment. The spectrum peaks clustered around 1231 cm.sup.?1 and 1727 cm.sup.?1 from a dry untreated sheath (FIG. 4C, upper graph) are typical of plant material with cellulose, hemicellulose, and lignin as the main constituents. Both of these peaks are seen to disappear following the 15% NaOH (2-hour) treatment (FIG. 4C, lower graph). The 1231 cm.sup.?1 peak corresponds to CO (bond) stretching in lignin, while the 1727 cm.sup.?1 peak is due to the stretching of C?O in ester linkages of carboxyl group of lignin and hemicellulose. Hence, the disappearance of these peaks indicates structural degradation with partial removal of the lignin and hemicellulose, and the observed larger weight-loss for this treatment.

[0043] In light of the above, a preferred embodiment is believed to entail the treatment of palm sheath, particularly an areca palm sheath, with an aqueous NaOH solution in which the NaOH concentration is about 2% to less than 10%, for example, about 5%, with treatments of no greater than twelve hours, preferably greater than one hour and up to about six hours. Particularly suitable treatments are believed to use a 5% NaOH concentration and a treatment duration of about one to about six hours. Palm sheaths treated in this manner are believed to be suitable for producing products through a deformation process, as nonlimiting examples, foodware, food packaging, and/or cooking and eating utensils.

[0044] The cutting and forming processes of the present aspect of the invention are roughly analogous to sheet metal cutting and forming and processes known to those skilled in the art. Specifically, the shape of a finished product can be determined by the shape cut into the sheet of material, in this case a palm sheath, and by the depth of deformation. In a nonlimiting embodiment of the present invention, the forming process can be achieved by deforming the sheath by stretching, punching, or pressing it, as nonlimiting examples, mechanical pressing, stretching, twisting, bending, punching, rolling, piercing, cutting, or some combination thereof between two shaping dies. The process may further involve heating the deformed sheath material, possibly by heating the die once it is formed into a desired shape. In certain embodiments, the dies may be heated for about three minutes, which is believed in many cases to be capable of locking in the desired shape by removing excess moisture without causing structural damage to the sheath material.

[0045] The LDH force-displacement curves described above can also be used to estimate the specific energy for the forming process, an important measure of product sustainability. The specific energy is the energy required to form a given unit mass of the material, and can be estimated as the area under a load-displacement curve (e.g., FIG. 2B) divided by the mass of the sheath material deformed in the test. This calculation gives the following specific energies for the associated processes: 0.89?10?3 MJ/kg (dry), 2.5?10?3 MJ/kg (hydrated) and 1.18?10?3 MJ/kg (5% NaOH, 2 hrs.). These specific energy values are very small, approximately two orders of magnitude smaller than for forming commonly used metals into similar shapes. Given the very low process specific energy, and coupled with the fact that a palm sheath is essentially waste material discarded by a tree, the embodied energy of area palm sheath foodware is near-zero, and at least five to six orders of magnitude smaller than those of equivalent plastic or paper products. This very low embodied energy is another attractive feature of the palm sheath products, and of their production by a direct single-step forming process from raw leaf-sheath.

[0046] As previously noted above, though the foregoing detailed description describes certain aspects of one or more particular embodiments of the invention, alternatives could be adopted by one skilled in the art. For example, any number of tools, products, or utensils could be produced with the method provided by the present invention, especially as the capabilities of palm sheath materials are fully explored by those skilled in the art. Such utensils may expand to include cups, bowls, tumblers, and shell-type packaging. Additionally, those skilled in the art may expand upon the method of the present invention in terms of scaling and improved efficiency, thereby increasing production rates and reducing manufacturing costs. Finally, the LDH test used as empirical validation in the present invention could therefore explore the viability of employing the method of the present invention on similar plan materials, beyond areca palm sheath materials specifically. As such, and again as was previously noted, it should be understood that the invention is not necessarily limited to any particular embodiment described herein or illustrated in the drawings.