Method for Processing a Mix of Lignocellulose Fibers for the Production of a Bio-Based Composite

Abstract

A method for processing a mix of lignocellulose fibers, such as miscanthus or sorghum fibers, for the production of a bio-based composite, having the steps of: harvesting lignocellulosic crops and processing the harvested lignocellulosic crops to obtain a raw mix of lignocellulose fibers, separating the raw mix of lignocellulose fibers, such as by sieving or grinding, into a first fraction (f1) having a mix of fibers having a fiber size of approximately <s1 and having first physical/chemical properties and a second fraction (f2) having a mix of fibers having a fiber size of approximately >s1 and having second physical/chemical properties being different from the first physical/chemical properties, mixing the fibers of the first fraction (f1) or the fibers of the second fraction (f2) with a binding agent, letting the binding agent harden, to obtain the bio-based composite.

Claims

1. A method for processing a mix of miscanthus fibers for the production of a bio-based composite, comprising the steps of: harvesting miscanthus crops and processing the harvested miscanthus crops to obtain a raw mix of miscanthus fibers, separating the raw mix of miscanthus fibers, such as by sieving or grinding, into a first fraction (f1) comprising a mix of miscanthus fibers having a fiber size of approximately <s1 and having first physical/chemical properties and a second fraction (f2) comprising a mix of miscanthus fibers having a fiber size of approximately >s1 and having second physical/chemical properties being different from the first physical/chemical properties, mixing the miscanthus fibers of the first fraction (f1) or the miscanthus fibers of the second fraction (f2) with a binding agent, letting the binding agent harden, to obtain the bio-based composite.

2. The method according to claim 1, wherein the binding agent is a mortar, the miscanthus fibers have a fiber size below 1.5 mm and the amount of miscanthus fibers range between 7 and 20 wt. %, to obtain a 3D printable concrete mixture, and wherein the mortar preferably is based on a MgO/aqueous MgCl2 mortar system.

3. The method according to claim 1, wherein the binding agent is a mortar, the at least 50 wt. % of the miscanthus fibers have a fiber size between 2 and 8 mm and the amount of miscanthus fibers range between 5 and 13 vol %, to obtain a concrete mixture.

4. The method according to claim 3, further comprising the steps of a) weighing the materials b) dry mixing of powders (cement and fillers other than sand) c) adding sands and dry mixing of sands with powders d) adding 75% of required water and homogeneously mixing the content e) optionally letting the mix rest for about 1 minute f) addition of a superplasticizer+remaining 25% water and continue the slow mixing g) adding dry miscanthus fibres and continue the slow mixing h) add additional water (2.5 g water per 1 gr fiber) and continue slow mixing optionally increasing the mixing speed to separate any clumping miscanthus fibers to obtain the miscanthus containing concrete mixture.

5. The method according to claim 3, wherein the biobased concrete mixture contains between 0.01 to 1 wt. % of a superplasticizer, preferably a polycarboxylate ether plasticizer.

6. The method according to claim 1, wherein the miscanthus crop is a dry crop and the raw mix of miscanthus fibers comprises at least 80 wt. %, preferably at least 90 or 91 wt. % dry fibers and between 5-20 wt. % water.

7. The method according to claim 1, wherein the first fraction is further separated to obtain a first further separated fraction comprising miscanthus fibers having a length of 0.3-0.5 mm, optionally wherein the first fraction is further separated to obtain a first further separated fraction comprising miscanthus fibers having a length of about 0.3-0.4 mm or wherein the first fraction is further separated to obtain a first further separated fraction comprising miscanthus fibers having a length of about 0.325-0.375 mm.

8-10. (canceled)

11. The method according to claim 1, comprising the step of: separating the second fraction (f2), such as by sieving or grinding, into a third fraction (f3) comprising a mix of fibers having a fiber size of approximately >s1 and approximately <s2 and a fourth fraction (f4) comprising a mix of fibers having a fiber size of approximately >s2.

12. The method for producing a bio-based composite by using the first fraction, the second fraction, the third fraction and/or the fourth fraction according to claim 1, further comprising the steps of: mixing the fibers of the first fraction, the second fraction, the third fraction and/or the fourth fraction with a binding agent, wherein the mixing ratio is determined based on the desired properties of the bio-based composite to be produced, letting the binding agent cure, to obtain the bio-based composite.

13. The method according to claim 1, comprising the further steps of: compressing the miscanthus fibers of the first fraction, the second fraction, the third fraction and/or the fourth fraction into pellets under the addition of an adhesive agent, such as maltodextrin, mixing the pellets containing the miscanthus fibers of the first fraction, the second fraction, the third fraction and/or the fourth fraction with the binding agent and letting the binding agent cure to obtain the bio-based composite, and processing the bio-based composite into the granulate, and optionally compressing the granulate into a foil.

14. (canceled)

15. The method according to claim 1, wherein the method comprises the further steps of: processing the bio-based composite, the granulate or the foil into a product, such as a product intended for absorption of moisture, such as a packaging for a food product or a diaper.

16. The method according to claim 1, wherein the first fraction constitutes at least 70%, more preferably at least 80%, even more preferably at least 90%, most preferably around 100%, of the miscanthus fiber mix to be mixed with the binding agent.

17. The method according to claim 1, wherein, when the bio-based composite is a bio-based concrete mixture, the method further comprising the step of: prior to letting the mortar cure, printing the fluid mortar/fiber mixture in a desired shape using a 3D-printer.

18. The method according to any claim 10, wherein, when the granulate or the foil is processed into a product by means of thermoforming, such as a product intended for absorption of moisture, such as a packaging for a food product or a diaper, the thermoforming process temperature is around 110-130 C., preferably around 120 C.

19-24. (canceled)

25. A biobased concrete mixture having between 5 and 13 vol % of miscanthus fibers, wherein at least 70 wt. % of the fibers have a miscanthus fibers have a fiber size between 2 and 8 mm and optionally containing between 0.01 to 1 wt. % of a superplasticizer (relative to the total weight of the concrete mixture), and wherein the superplasticizer preferably comprises a polycarboxylate ether plasticizer.

26-29. (canceled)

30. A 3D printable concrete mixture containing between 7 and 20 wt. % of miscanthus fibers having a particle size less than 1.5 mm, and the mixture is based on an MgO/aqueous MgCl.sub.2 mortar system.

31-32. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0074] The present invention will be explained hereafter with reference to exemplary embodiments of a method according to the invention and with reference to the drawings. Therein:

[0075] FIG. 1 schematically shows a method for processing a mix of lignocellulose fibers for the production of a bio-based composite;

[0076] FIG. 2 schematically shows a method for processing a mix of lignocellulose fibers for the production of a bio-based composite, wherein the bio-based composite is processed into a granulate;

[0077] FIG. 3 schematically shows a method for compressing the mix of fibers into pellets and mixing the pellets with the binding agent;

[0078] FIG. 4 schematically shows a method for processing the granulate into a foil; and

[0079] FIG. 5 shows a graph depicting bulk density and moisture content for several fiber fraction samples.

DETAILED DESCRIPTION OF THE INVENTION

[0080] FIG. 1 schematically shows a method 100 for processing a mix of lignocellulose fibers, such as miscanthus or sorghum fibers, for the production of a bio-based composite 1. The method 100 comprises the steps of: harvesting 101 lignocellulosic crops and processing the harvested lignocellulosic crops to obtain a raw mix of lignocellulose fibers 2. According to the invention, the method 11 is characterized by separating 102 the raw mix of lignocellulose fibers 2, such as by sieving or grinding, into a first fraction f1 comprising a mix of fibers having a fiber size of approximately <s1 and having first physical/chemical properties and a second fraction f2 comprising a mix of fibers having a fiber size of approximately >s1 and having second physical/chemical properties being different from the first physical/chemical properties. Preferably, s1=1.0-3.0 mm, more preferably 1.5-2.5 mm, such as 2 mm. Preferably, the harvesting step comprises chopping of the fibers. The separation step preferably comprises (in a consecutive manner) one or more subsequent sieving and grinding steps.

[0081] To characterize for instance the moisture content (as physical property) of the first fraction f1 and the second fraction f2, the individual fractions f1, f2 (i.e. samples thereof) can be heated, such as overnight, to a temperature of 90-110 C., such as around 105 C., to determine their respective moisture content. Thus, by experimenting with different values for s1, an optimal value for s1 can be determined in order to have a first fraction f1 or second fraction f2 with a certain desired moisture content.

[0082] The density of the respective fraction f1, f2 can be determined using one of the abovementioned (dried) samples, and a He-Pycnometer. Thus, analogously, by experimenting with different values for s1, an optimal value for s1 can be determined in order to have a first fraction f1 or second fraction f2 with a certain desired density.

[0083] Water absorption, for instance, can be determined using a hydrostatic balance for each individual size fraction f1, f2 as an indication of the amount of water the bio-based composite 1 or the final product comprising such fractions f1, f2 can absorb. When the bio-based composite 1 is a bio-based concrete mixture, comprising a cement or mortar, the influence of the fibers of the first and second fractions f1, f2 on cement hydration, isothermal calorimetry can be used (with relatively small samples of for instance 10 ml). The fractions f1, f2 can for instance by ground in a mill, such as a ball mill, and then mixed with cement. The heat generated during hydration can be measured and compared to neat cement paste. The lignocellulose fibers are boiled in water to leech organics from the fibers. The water is then mixed with cement and the influence on hydration measured. After initial assessment with isothermal calorimetry, larger volume/lignocellulose mixes can be made in insulated moulds and the temperature measured during hydration. The lignocellulose will be mixed as-is, giving less accurate but more realistic information about the influence of lignocellulose on cement hydration.

[0084] Based on the above measurements/characterizations, in case of a bio-based concrete as the bio-based composite 1 to be obtained, multiple recipes with varying lignocellulose/cement/water ratios can be made and tested for physical/chemical properties (such as mechanical properties, densities, rheological properties).

[0085] Ways to pre-treat the lignocellulose fibers, such as by soaking in water or salt solutions, can be tested and applied in cement.

[0086] Preferably, the above steps are to be repeated with lignocellulose harvested in a different year, season, location, soil type, et cetera to obtain an indication of the natural variation of physical/chemical properties.

[0087] As shown in FIG. 1, the second fraction f2 can be separated 103 further, such as by sieving or grinding, into a third fraction f3 comprising a mix of fibers having a fiber size of approximately >s1 and approximately <s2 and a fourth fraction f4 comprising a mix of fibers having a fiber size of approximately >s2. Preferably, s2=3.0-5.0 mm, more preferably 3.5-4.5 mm, such as 4 mm.

[0088] FIG. 2 schematically shows a method 200 for producing a bio-based composite 1 by using the first fraction f1, the second fraction f2, the third fraction f3 and/or the fourth fraction f4, further comprising the steps of: mixing 201 the fibers of the first fraction f1, the second fraction f2, the third fraction f3 and/or the fourth fraction f4 with a binding agent 3, wherein the mixing ratio is determined based on the desired properties of the bio-based composite 1 to be produced, letting the binding agent 3 cure 202, to obtain the bio-based composite 1.

[0089] A further step of the method 200 could comprise the further step of: processing 203 the bio-based composite into a granulate 4.

[0090] The method 200 could comprise the further steps of: [0091] compressing 204 the fibers of the first fraction f1, the second fraction f2, the third fraction f3 and/or the fourth fraction f4 into pellets 6 under the addition of an adhesive agent 5, such as maltodextrin, [0092] mixing 201 the pellets 6 containing the fibers of the first fraction f1, the second fraction f2, the third fraction f3 and/or the fourth fraction f4 with the binding agent 3 and letting the binding agent 3 cure to obtain the bio-based composite 1, and [0093] processing 203 the bio-based composite 1 into the granulate 4.

[0094] As mentioned before, preferably, the binding agent 3 is a plastic and the mixing of the pellets 6 with the binding agent 3 is performed with a plastics extruder. More preferably, s1 is chosen at around 0.5 mm and a first fraction f1 having fibers of a size smaller than 0.5 mm is then used to create the pellets 6. Such pellets 6 are easy to create by compression, are easily mixable with the binding agent 3 and are easy to process into the granulate 4.

[0095] Maltodextrin, by the way, advantageously becomes warm, e.g. as a result of friction in the press, and consequently sticky, when compressed (i.e. during compression of the pellets 6).

[0096] As shown in FIG. 4, the method 200 could comprise the further step of: compressing 204 the granulate 4 into a foil 7.

[0097] Finally, the method 200, comprises the further steps of: processing the bio-based composite 1, the granulate 4 or the foil 7 into a product, such as a product intended for absorption of moisture, such as a packaging for a food product or a diaper. Other (consumer) products are of course also conceivable, such as vases for flowers, lampshades, cat litter, (packaging) trays, et cetera. Preferably, when a diaper is produced, the bio-based composite 1 is incorporated in a pad or similar holder/container, the pad therein acting as a desiccant (much like a silica gel). The diaper pad is thus not produced by thermoforming, extruding, et cetera, unlike several of the other (consumer) products, such as crockery, trays, vases, et cetera. Preferably, the pad or similar holder/container comprises one or more layers (acting as a membrane) comprising miscanthus fibers.

[0098] Applicant has also found that producing a foil 7 having a plurality of layers, such as 1, 2, 3, 4, 5, but preferably 3 layers, could further optimize the mechanical and/or chemical properties of the final product. Preferably, the layers are then applied in an alternating pattern, such as A-B-A (when 3 layers are used), with the outer layers having mechanical or chemical properties A and the middle layer having mechanical or chemical properties B. For instance, the middle layer (in particular when an odd number of layers is used) may be reinforced with other types of fibers, such as jute or sackcloth. Preferably the layer A does not contain miscanthus and is prepared from a biocompatible resin (like for example PLA) and the layer B contains miscanthus fibers.

[0099] Preferably, in particular when a diaper or a packaging product is produced, a thermoforming or thermomolding process is used to produce the foil 7 into the product. More preferably, a thermoforming process is used wherein the process temperature is around 110-130 C., preferably around 120 C. Applicant has advantageously found that when the foil 7 mainly (i.e. >50%, preferably >70%, more preferably >80% or even >90%) comprises fibers with a fiber size of about 0.3-0.5 mm (wherein s1=about 0.3 mm and s2=about 0.5 mm), preferably about 0.3-0.4 mm, more preferably about 0.325-0.375 mm, such as around 0.35 mm, the process (oven) temperature can be lowered (i.e. versus the usual temperature of around 180 C.). This leads to substantial energy savings during the thermoforming process. Applicant has found that 20-30% energy savings are realistic, improving and emphasizing the durable character of the products.

[0100] Applicant has also found from practice that a first further separated fraction comprising fibers with the mentioned fiber size of about 0.3-0.5 mm, preferably about 0.3-0.4 mm, more preferably about 0.325-0.375 mm, such as around 0.35 mm, reduces friction during the extrusion process of the foil 7. At the same time this fiber size surprisingly leads to very good moisture absorption properties and mechanical properties of the final (consumer) product.

[0101] In an embodiment, the first fraction f1 could constitute at least 70%, more preferably at least 80%, even more preferably at least 90%, most preferably around 100%, of the fiber mix 2 to be mixed with the binding agent 3.

[0102] When cutting the edges of the foil 7, before rolling the foil 7 up into or onto a roll, preferably round knives (i.e. pizza knives) are used to obtain a neat edge (instead of e.g. Stanley knives).

[0103] Preferably, the fibers are mixed with a natural polymer (instead of relatively unnatural polymers such as PE and PP) to improve compostability of the product, leading to a lower burden on the environment.

[0104] The bio-based composite 1 could be a bio-based concrete mixture and the binding agent 3 could be a mortar.

[0105] Alternatively, the third fraction f3 could constitute at least 70%, more preferably at least 80%, even more preferably at least 90%, most preferably around 100%, of the fiber mix 2 to be mixed with the mortar.

[0106] The method could furthermore comprise the step of: prior to letting the mortar cure, printing the fluid mortar/fiber mixture in a desired shape using a 3D-printer.

[0107] It should be clear that the description above is intended to illustrate the operation of preferred embodiments of the invention, and not to reduce the scope of protection of the invention. Starting from the above description, many embodiments will be conceivable to the skilled person within the inventive concept and scope of protection of the present invention.

LIST OF REFERENCE NUMERALS

[0108] 1. Bio-based composite [0109] 2. Raw mix of lignocellulose (miscanthus) fibers [0110] 3. Binding agent [0111] 4. Granulate [0112] 5. Adhesive agent [0113] 6. Pellets [0114] 7. Foil [0115] 100. Method for processing a mix of lignocellulose fibers for the production of a bio-based composite. [0116] 101. Harvesting step [0117] 102. Separating step (1) [0118] 103. Separating step (2) [0119] 200. Method for producing a bio-based composite [0120] 201. Mixing step [0121] 202. Curing step [0122] 203. Processing into granulate step [0123] 204. Compression into pellets step [0124] 205. Compression into foil step

EXAMPLE 1

[0125] A miscanthus based mortar is prepared with the following process:

Weigh the Materials

[0126] 1st minute: dry mixing of the powders [0127] 2nd minute: add sands; dry mixing of sands with powders [0128] 3rd minute: add 75% of required water and check if everything is mixing thoroughly [0129] 4th minute: let the mix rest for 1 minute [0130] 5th & 6th minute: add the superplasticizer+remaining 25% water and continue the slow mixing [0131] 7th minute: add the dry fibers and continue the slow mixing [0132] 8th & 9th minute: add the additional (2.5 g water per 1 gr fiber) and continue slow mixing (level 1) [0133] 10th & 11th minute: increase the mixing speed to separate any clumping fibers.

[0134] Particle Size Distribution for Mortar Production

TABLE-US-00002 Standard Cumulative Fraction Average Deviation Percentage percentage sizes (g) (g) (%) (%) Unsieved 91.83 0.05 <2 mm 1.53 0.45 23.15 23 .sup.2-4 mm 4.90 0.75 55.10 78 4-5.6 mm 9.93 2.00 14.84 93 5.6-8 mm 54.07 1.45 5.48 99 >8 mm 24.20 3.05 1.40 100

EXAMPLE 2

[0135] A 3D printable concrete mixture is produced having different levels of fibers having a size below 1.5 mm

TABLE-US-00003 Pre-saturated fibres Dry fibres specimens specimens Fresh Average Fresh Average density slumpflow density slumpflow Mixtures (kg/m.sup.3) (cm) (kg/m.sup.3) (cm) Reference 0% 2237.1 50 .sup.30.25 0.5 2237.1 50 .sup.30.25 0.5 Miscanthus 2% 2102.2 50 28.25 1 2084.4 50 28.75 1 Miscanthus 3% 2100.4 50 28 0.5 2132.1 50 27.25 1 Miscanthus 4% 2002.8 50 25.75 1 2010.8 50 26.5 1 Miscanthus 5% 1864.3 50 24.75 1 1891.2 50 24 1 Miscanthus 9% 1804.4 50 12.5 0.5 1770.7 50 12 0.5

[0136] The 3D printable concrete mixture is based on an MgO/aqueous MgCl.sub.2 mortar system. Magnesia cement, also called Sorell cement or Magnesia Oxychloride cement (MOC), is used, which is produced by mixing MgO with MgCl.sub.2 solution. A reaction takes place that forms magnesium chloride hydroxide hydrates: [0137] 5Mg(OH).sub.2-1MgCl.sub.2-8H.sub.2O 5-1-8 (normally forms first, metastable) [0138] 3Mg(OH).sub.2-1MgCl.sub.2-8H.sub.2O 3-1-8 (stable phase, normally formed from 5-1-8)

[0139] The recipe for the 3D printable biobased concrete mixture comprises the following ingredients: [0140] Miscanthus (milled to 1.5 mm) 14, 19 and 24 wt. % of dry mass [0141] 28, 35 and 40 vol % of dry volume [0142] MgCl.sub.2x6H.sub.2O mixed with tap water (ratio 0.7 by weight) [0143] MgO mixed with MgCl.sub.2x6H.sub.2O (ratio 1.25 g/ml) [0144] High solid/liquid ratio to account for water adsorption of Miscanthus

[0145] The figure below shows the hydration reaction of magnesia cement incorporating different wt. % of Miscanthus. Heat flow is normalized to mass of magnesium oxide:

[0146] The mixes are prepared by mixing the dry ingredients first by hand, adding the solution and then mixing everything by hand again for about 30 s until a homogenous mass is produced.

[0147] Compressive strength tests results for different wt. % of miscanthus fibers:

TABLE-US-00004 Age Strength Density Mix (h) (Mpa) (g/cm.sub.3) 14 wt. % 1 0.1 5 0.38 7 1.03 24 55 1.51 19 wt. % 1 0.05 5 0.12 7 0.72 24 50 1.57 24 wt. % 24 26 1.34

[0148] Spread flow tests according to standard C1437 with 10 cm cone results:

TABLE-US-00005 MgCl.sub.2 MgO solution Miscanthus Miscanthus Flow Mix (g) (ml) (g) (wt. % of solids) (cm) 1 250 200 40 14 13.2 2 250 200 55 18 no flow 3 250 200 70 22 no flow

[0149] All 3 mixes show very low or now flow. This is a desired property for 3D printing, because it allows printed lines to keep their shape until they are sufficiently hardened. The hydration visible with isothermal calorimetry is not significantly retarded by the addition of Miscanthus and the reaction maximum is reached after 9 h.

[0150] The early compressive strength of the prisms is low. After 1 h the prisms can be handled, but are still soft. But due to their low flowability it is still possible to print with the material. After 24 h the strength is very high with 50-55 MPa for mix 1 and 2. Even mix 3 with 22 wt % Miscanthus has a strength of 26 MPa. This is sufficient for 3D printed objects, but its workability is entirely unsuitable, because the mix is too dry and likely cannot be pumped.

[0151] SEM pictures show excellent adhesion between the dense magnesia cement matrix and the Miscanthus fiber. This is the reason magnesia cement can incorporate high amounts of natural fibers without loss of strength.

[0152] Overall mix 2 seems to be the most suitable one for printing, but the advantage of magnesia cement is that the mix can be adjusted over a wide range to get optimal workability without significant loss of strength or delay in hardening.

EXAMPLE 3

[0153] Alternative Magnesium Oxide

[0154] In order to improve the early compressive strength of the magnesia cement for 3D printing, highly reactive magnesium oxide was tested. A mix consisting of pure magnesia cement without Miscanthus is used for this purpose. The composition of these mixes is as follows: 250 g MgO and 150 ml MgCl.sub.2 solution with the same concentration as described previously. However the MgO was so reactive that an extreme heat development was observed to the point that the material became too hot to touch and cracks appeared. For this reason a new approach was decided. The low reactivity MgO used in the previous mixes was only partially replaced (10 and 20 wt. %) with the highly reactive MgO and the influence on spread flow and setting time measured.

[0155] From the results below it can be seen that the partial replacement with highly reactive MgO decreases the setting begin by up to 40% and reduces the heat produced during setting and hydration. This makes the material suitable for 3D printing in combination with the low spread flow of the material.

[0156] Spread flow and setting begin of magnesia cement produced with low reactivity MgO and mixes of low and high reactivity MgO:

TABLE-US-00006 MgO High reactivity Low reactivity Flow Setting begin (wt. %) (wt. %) (cm) (h) 0% 100% 12.5 1.5 10% 90% 15 1.2 20% 80% 13 0.9

[0157] It is thus possible to produce magnesia cement/Miscanthus mixes with no or very low spread flow and a fast setting begin that are suitable for 3D printing. The addition of 18 wt. % Miscanthus is easily possible but should be adjusted to get the optimum workability for 3D printing. This is easily possible without influencing the hydration behavior or negatively influencing strength.

[0158] For the magnesia cement itself a combination of small amounts of highly reactive with less reactive magnesium oxide is the most promising, because they show the fastest setting begin. A high heat development might lead to problems such as cracking, but can be counteracted in several ways: [0159] The addition of Miscanthus will effectively dilute the system and lower the overall temperature. [0160] Inert filler material in the form of limestone powder or similar material can be added to the mix, replacing part of the MgO. This would dilute the system further without negatively influencing workability or setting time. [0161] The concentration of the MgCl.sub.2 used in the magnesia cement production can be lowered to slow down the reaction. However, this might have negative influence on the setting speed and the final strength of the printed material.