FLEXIBLE HIGH-DENSITY FIBERBOARD AND METHOD FOR MANUFACTURING THE SAME

Abstract

The present invention provides a flexible high-density fiberboard which is essentially free of formaldehyde and isocyanates and comprises 70 to 90% by weight of straw fibers, and 30 to 10% by weight of a thermoplastic elastomer and one or more optional additive(s). Furthermore, the present invention provides a method for manufacturing such a flexible high-density fiberboard comprising the steps of providing straw fibers, providing a thermoplastic elastomer in powder form, optionally providing one or more additive(s), dry mixing the straw fibers, the thermoplastic elastomer powder and optionally the one or more additive(s), such that a mixture comprising 70 to 90% by weight of the straw fibers, and 30 to 10% by weight of the thermoplastic elastomer and one or more of the optional additive(s) is obtained, extruding the obtained mixture at a temperature such that the thermoplastic elastomer powder is in a molten state, and pressing the extruded mixture.

Claims

1. A flexible high-density fiberboard essentially free of formaldehyde and isocyanates and comprising 70 to 90% by weight of straw fibers, and 30 to 10% by weight of a thermoplastic elastomer and one or more optional additive(s).

2. The flexible high-density fiberboard according to claim 1, wherein the flexible high-density fiberboard comprises 80 to 90% by weight of straw fibers and 20 to 10% by weight of a thermoplastic elastomer.

3. The flexible high-density fiberboard according to claim 1, wherein the straw fibers are selected from the group consisting of wheat straw fibers, corn straw fibers, rice straw fibers, oat straw fibers, barley straw fibers and rye straw fibers.

4. The flexible high-density fiberboard to claim 1, wherein the straw fibers have a length of 5.0 mm.

5. The flexible high-density fiberboard according to claim 1, wherein the one or more optional additive(s) is/are selected from the group consisting of color pigments, preferably matte pigments applied in thermoplastic-based and flexible-PVC products, without being wetted or transformed into liquid forms, coupling agents, preferably silane coupling agent and maleic anhydride, water-repelling agents, preferably calcium chloride, and fire retardants, preferably phosphorous-based/mineral-based flame-retardant additives.

6. The flexible high-density fiberboard according to claim 1, wherein the straw fibers are rice straw fibers and wheat straw fibers.

7. The flexible high-density fiberboard according to claim 1, wherein the thermoplastic elastomer is a vinyl acetate based copolymer, preferably a vinyl acetate-ethylene-vinyl ester copolymer.

8. The flexible high-density fiberboard according to claim 1, further comprising a veneer on one or both surfaces thereof.

9. A method for manufacturing a flexible high-density fibreboard according to claim 1, comprising the steps of providing straw fibers, providing a thermoplastic elastomer in powder form, optionally providing one or more additive(s), dry mixing the straw fibers, the thermoplastic elastomer powder and optionally the one or more additive(s), such that a mixture comprising 70 to 90% by weight of the straw fibers, and 30 to 10% by weight of the thermoplastic elastomer and one or more of the optional additive(s) is obtained, extruding the obtained mixture at a temperature such that the thermoplastic elastomer powder is in a molten state, and pressing the extruded mixture.

10. The method according to claim 9, wherein the straw fibers are selected from the group consisting of wheat straw fibers, corn straw fibers and rice straw fibers, preferably wherein the straw fibers have a length of 7.0 mm.

11. The method according to claim 9 further comprising the step of applying a veneer on one or both surfaces of the flexible high-density fiberboard.

Description

EXAMPLE

[0053] In the following, a preferred example of a flexible high-density fiberboard according to the present invention manufactured by the method of the present invention is described. However, it should be noted that the scope of the present invention is by no means restricted by said example.

[0054] Starting Materials

[0055] Straw: rice straw

[0056] Thermoplastic elastomer: VINNEX 2505 Vinylacetate-ethylene-vinylester copolymer powder (available from Wacker Chemie AG, Munich, Germany)

[0057] Straw analysis and preparation before compounding

[0058] Chemical Analysis

[0059] Straws 1 and 2 were chopped and burnt at 550 C. to prepare straw ash samples. The inorganic chemical components of the two straw ash samples were analyzed and the results shown in table 1 were obtained.

TABLE-US-00001 TABLE 1 Chemical composition of the inorganic ash components of straws 1 and 2 mg/kg Ash Al Ca Fe K Mg Mn Na P S Si Zn Straw 1 3.566 16.630 3.599 80.573 11.657 1.561 33.071 2.326 4.666 313.113 129 Straw 2 2.065 18.801 1.553 80.218 6.893 2.937 1.917 6.451 4.628 343.817 70

[0060] Humidity Assessment

[0061] The humidity of straws 1 and 2 was measured according to American Society of Agricultural and Biological Engineers Standards (ASAE S358.2, 2006).

[0062] The chopped straw samples were weighed before and after their dehydration for 24 hours within a vacuum oven at 105 C. The humidity of the samples ranged from 6-7%, which indicates that the fibres were in an acceptable state to be mixed with the thermoplastic elastomer without further drying procedures. The moisture content of natural fibers before being mixed with the polymer should range between 3-8%. Accordingly, the straw fibres of straws 1 and 2 were directly applied in their natural dry state having a humidity of 6-7% without further dehydration.

[0063] Straw fibre Chopping and Grinding

[0064] A chopping machine provided from FRITSCH GmbH, Idar-Oberstein, Germany, was applied in the chopping procedure of the straw fibres before compounding. This machine has a combined system of a shredder and an absorbing apparatus, linked to a collector, which is an environmentally-friendly chopping process without released dust or fumes. The fibre length of the obtained straw fibers is 0.5 to 5 mm, which is, however, further shortened during the compounding process by means of the revolving extruder screws.

[0065] Compounding Process and Parameters

[0066] The straw fibres were not chemically modified prior to compounding. The straw fibres and the VINNEX 2505 powder were mixed at room temperature in a ratio of 80:20 in terms of weight, where the straw amounts to 80% of the total weight of the mixture and the VINNEX 2505 powder amounts to 20% of the total weight of the mixture. The mixture was then fed gradually to a batch mixing machine, HAAKE Rheocord 90, Thermo Fisher Scientific LLC, Asheville, N.C., U.S.A., simulating a lab-scale twin screw extruder at 50 rpm and 180 C.

[0067] Specimen Preparation [0068] a. The discharge (straw-binder mixture) was taken from the batch mixing machine and applied on a copper plate with Teflon foil and a high temperature releasing agent, and then pressed with a laboratory bench-top press-machine (Type P 200 E) from Dr. Collin GmbHEbersberg, Germany at 180 C. and 200 bar for 3-5 minutes. [0069] b. The resulting plates had a thickness of 2 mm and were cut using a small saw machine to produce the test specimen.

[0070] The physical characteristics of the obtained test specimen are the same:

[0071] Density: 1099.9 kg/m.sup.3 (according to DIN 53479 or DIN EN ISO 1183-1)

[0072] Tensile strength: 2.60 N/mm.sup.2

[0073] Tensile modulus: 28.91 N/mm.sup.2

[0074] (both the tensile strength and the tensile modulus were tested with the following conditions: Pre-load: 0.01 N/mm.sup.2, Pre-load speed: 10 mm/min, test speed: 50 mm/min, machine heads displacement: 250 mm)

[0075] Thickness swelling (TS) as an indication of water absorption was measured according to the same conditions of DIN EN 317, 1993, but using smaller square-shaped probes of 1010 mm.sup.2 and an original thickness of 2 mm. TS was recorded in this case to be 21.3%. According to the regulated accepted properties of dry-processed MDF (EN 622-5, 2010-03), TS is accepted till 45% for the plates of thicknesses from 1.8-2.5 mm in case of dry interior applications. Accordingly, this indicates that the straw-based fiberboard lies in the acceptable range of thickness swelling. These values were recorded without lamination, surface treatment or additives. Hence, it is expected to have much lower TS when modified accordingly.

[0076] Fire resistance: by means of phosphorous based/mineral-based additives, DIN 4102-B1 class can be achieved. The high-silica straw showed high improvement in the flame-resistance attitude of the biocomposite that can be further optimized by means of the above suggested flame-resistant additives.

[0077] Indentation resistance: 0.02 mm after 24 hours from load removal and 3 N residual load appliance according to DIN EN 1516 (the acceptable value is up to 0.5 mm (for being suitable for flooring applications in gymnasiums) after applied standard conditions).

[0078] Biodegradability: to investigate the biodegradability, a special soil-burial field-test was applied with samples of 2 mm thickness. The test was settled for a period of 15 months, where biodegradability/micro-organismal interference was controlled each 3 months, for a total period of 15 months, by means of visual inspectiondocumented by photosand weight-loss control, summing them up in the form of a table and a graph. This test simulated aerobic compost conditions to examine the possible aerobic bio-degradability in the presence of oxygen in the soil's upper surface, 3 inches (8 cm) deep; to allow the possibility of living micro-organisms existing normally in the upper surface of normal soils to attack and digest parts of the samples. The outcome was that biodegradability was detected since the probe having 80% or more fiber load lost 41% of its weight after 15 months, despite of having a thickness of 2 mm, and was visually observed of having apparent damages.

[0079] Summarizing the above results, the flexible high-density fiberboard according to the present invention has excellent physical properties which makes the same suitable for many applications, like for example, furniture, in particular free-form furniture, partition walls, flooring having anti-slip and anti-shock function (for example, in gymnasiums), and flooring replacing cork flooring in living spaces, and also in flooring system combinations, wherein, for example, flooring tiles have an underlayer of the present flexible high-density fiberboard, without any negative impact on humans and the environment.