DESC:Field of Invention
The present disclosure relates to a biocomposite material and a method for preparing said biocomposite material. Particularly, the present disclosure relates to lignin-based biocomposite material which can be used for various applications, such as particleboards.
Background
Particleboards or medium density fiber (MDF) boards currently available on the market have been manufactured using formaldehyde-based adhesives such as urea formaldehyde (UF), phenol formaldehyde (PF), and melamine urea formaldehyde (MUF). Urea and phenol formaldehyde-based adhesives are more popular due to their lower cost. However, it is desirable to avoid formaldehyde-based adhesives as they are known to be carcinogenic and have an emission limit of 0.1 PPMV/m3 of air.
Formaldehyde-free adhesives are known for manufacturing particleboards, such as those using polyurethane and PVC resins. However, such adhesives are expensive, making them less attractive for commercial purposes. Also, such resins are derived from fossil fuels and are therefore not sustainable. They also require the addition of other chemicals for increasing their water resistance and microbial resistance, which result in a higher cost of production.
In recent years, research has turned to the use of wholly renewable, sustainable, and/or biodegradable materials to replace traditional resins used for making wood composites. However, purely natural additives like those using different sources of protein, starch, etc. have lower water resistance. Hence, they either partially replace the formaldehyde-containing resins or need additional chemicals (usually derived from fossil fuel) to increase their water resistance.
Summary
The present disclosure relates to a biocomposite material. Said biocomposite material comprises of 5 to 70 wt % of lignin, 5 to 30 wt % of a binder, and 25 to 90 wt % of a filler.
The present disclosure also relates to a process for preparing the disclosed biocomposite material. Said process comprises mixing 5 to 70 wt % of lignin, 5 to 30 wt % of a binder, and 25 to 90 wt % of a filler in the presence of an aqueous medium; followed by compressing the obtained mixture to obtain the biocomposite material.
Brief Description of Drawings
Figure 1A shows a sample of particleboard prepared in accordance with an embodiment of the present disclosure.
Figure 1B shows a comparison of the particleboard (B) prepared in accordance with an embodiment of the present disclosure with the commercially available MDF (A) and particleboard (C).
Figure 2A shows the results of water absorption and color leaching for biocomposite materials prepared in accordance with an embodiment of the present disclosure using varying gluten%.
Figure 2B shows the visual appearance of water upon color leaching from the biocomposite material prepared in accordance with an embodiment of the present disclosure using varying gluten%.
Detailed Description
For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the disclosed composition and method, and such further applications of the principles of the disclosure therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the disclosure and are not intended to be restrictive thereof.
Reference throughout this specification to “one embodiment” “an embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The terms "comprise", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion and are not intended to be construed as “consists of only”, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method.
Likewise, the terms “having” and “including”, and their grammatical variants are intended to be non-limiting, such that recitations of said items in a list are not to the exclusion of other items that can be substituted or added to the listed items.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods, and materials are now described. All publications mentioned herein are incorporated herein by reference.
The term “biocomposite” refers to blends of different materials, one of which may be derived from natural resources, for realizing the material properties, depending upon end use.
The term “lignin” refers to a oxygen-containing organic polymer that, with cellulose, forms the chief constituent of wood. The major source of lignin is the paper industry, which through the pulping processes separates lignin from cellulose.
The term “Kraft lignin” refers to lignin recovered from the black liquor obtained from kraft pulp manufacturing process via precipitation method by adjusting the pH, followed by separation, drying and powdering.
In its broadest scope, the present disclosure relates to a biocomposite material and a method for preparing said biocomposite material. Specifically, the present disclosure relates to a biocomposite material comprising 5 to 70 wt % of lignin, 5 to 30 wt % of a binder, and 25 to 90 wt % of a filler.
In an embodiment, the lignin used in the biocomposite material is Kraft lignin. In an embodiment, the biocomposite material comprises 30 to 50 wt % of lignin.
In an embodiment, the binder is selected from the group consisting of protein source, natural resins and gums such as guar gum, glyoxal or similar chemical entities, pulp/paper powder and mixtures thereof. In an embodiment, the protein source is a plant-based protein selected from the group consisting of wheat gluten, zein (corn protein), soy protein, chitin, and mixtures thereof. In some embodiments, the protein source is gluten. The protein source used in the present biocomposite material was obtained from commercial sources. In an embodiment, the biocomposite material comprises 5 to 25 wt % of binder. In some embodiments, the biocomposite material comprises about 20 wt % of binder.
In an embodiment, the filler is any powdered or granulated material obtained from any wood source. In accordance with an embodiment, the filler is selected from the group consisting of saw dust, wood powder, agricultural waste, and a combination thereof. Suitable agricultural waste are straws, rice husk etc. The fillers used in the present biocomposite material were obtained from commercial sources. In an embodiment, the biocomposite material comprises 40 to 70 wt % of filler.
In an embodiment, the biocomposite material comprises lignin and the binder in a w/w ratio ranging between 1:1 to 4:1. In some embodiments, the biocomposite material comprises lignin and the binder in a w/w ratio of 2:1. The present inventors found that the ratio of lignin and binder and its source for example, the protein source is critical to achieving the biocomposite material with desired properties. In an exemplary embodiment, it was observed that the ratio of lignin (Kraft lignin) and protein source (gluten) affects water absorption as well as color leaching of biocomposite material. Water absorption percentage as well as color leaching by samples having low percentage of gluten is high. Water absorption percentage as well as color leaching by samples reduce as percentage of gluten is increased. However, water absorption % starts increasing beyond certain percentages of gluten.
It is understood that said effect is obtained due to interaction between gluten and Kraft lignin. At high temperature, thiol radicals are generated from gluten and gluten-disulfide bonds are formed. Lignin captures these radicals and avoids formation of gluten di-sulfide bonds thereby forming a network of lignin and gluten. Lignin helps in reducing hydrophilicity of gluten by bonding with it and reducing its interaction with water molecules. At low percentage of gluten, owing to its hydrophilic nature there is less bonding between gluten and lignin. Hence, more pores are available in the sample for absorbing water. Also, when gluten% is low, free lignin (unbonded with gluten) is present. This causes leaching of lignin into water and hence coloration of water is observed. However, when percentage of gluten is high, its hydrophilic nature becomes dominant causing an increase in water absorption%. Minimum water absorption as well as less leaching is observed at optimum ratio of lignin and gluten.
The present disclosure also relates to a process for preparing the disclosed biocomposite material. Said process comprises mixing 5 to 70 wt % of lignin, 5 to 30 wt % of a binder, and 25 to 90 wt % of a filler in the presence of an aqueous medium; followed by compressing the obtained mixture to obtain the biocomposite material.
In an embodiment, the process comprises preparing a mixture of lignin and binder; adding an aqueous medium to said mixture of lignin and the binder to obtain a solution thereof; mixing the obtained solution with the filler; and subjecting this mixture to compression to obtain the biocomposite material. In an alternate embodiment, the process for preparing said biocomposite material comprises preparing a pre-mix by mixing lignin, binder and filler; adding an aqueous medium to said pre-mix to obtain a mixture; and subjecting this mixture to compression to obtain the biocomposite material. Both the embodiments avoid the formation of protein agglomerates, a problem observed when protein-based binder is mixed with water.
In accordance with an embodiment, lignin is Kraft lignin, obtained by precipitation of lignin from black liquor obtained from Kraft process. For the purposes of present biocomposite material, it was found that lignin must be precipitated at a pH 4-7. The precipitated lignin is separated from the slurry through centrifugation or filtration. Separated lignin can be washed using washing liquor to recover remaining quantity of filtrate and some salts. The washed and purified lignin is dried at below 100oC using any known means of drying. In an embodiment, drying is carried out by drying in an oven, vacuum oven, under sun or by using natural or forced convection drying at room temperature. The dried lignin is powdered using any blender, ball mill, mechanical grinder etc.
In accordance with an embodiment, the filtrate obtained after centrifugation/ filtration of lignin is recycled to waste heat recovery boiler wherein the filtrate contains 30 to 40 wt% inorganic salts which are recycled into the pulping process, thereby making the process ecofriendly and economical. In accordance with an embodiment, the washing liquor can be mixed with the filtrate obtained during centrifugation or filtration.
In an embodiment, the aqueous medium is water.
Compression is carried out using any known means of compressing a material. In an embodiment, the compression is carried out using compression molding machine with a three plate mold.
Examples:
In order that this invention may be better understood, the following examples are set forth. These examples are for the purpose of illustration only and the exact compositions, methods of preparation and embodiments shown are not limiting of the invention, and any obvious modifications will be apparent to one skilled in the art.
Also described herein are method for characterizing the biocomposite material, formed using embodiments of the claimed process.
Example 1:
Process for obtaining Kraft lignin: Black liquor was obtained from Kraft based pulp process. The pH of solution was reduced using sulfuric acid (98% acid diluted by 10%-40%) to cause precipitation of lignin. The obtained precipitated mass was separated from the solution using centrifugation and was dried at below 100°C. This dried mass was powdered in a mill to obtain kraft lignin.
Preparation of mixture comprising lignin, binder and saw dust: Saw dust (SD), lignin (SD/L ratio 1:1 to 4:1) and binder (gluten alone or mixture of gluten with other binder/s or other binder/s without gluten) were mixed using a mixer. Water (10%-100% by weight of solid) was added to the solid mass comprising lignin, binder and saw dust, followed by uniform mixing for a sufficient period ranging between 1-5 minutes so that it moistens uniformly.
Compression of mixture to obtain biocomposite material: The moist mass was placed in a mold (2 or 3 plate) of a suitable design to transmit the pressure on the material. Herein, three-plate mold was used for making the biocomposite material. The mixture for making particleboard was filled in the cavity in the middle plate. Top plate had projections of different height. Thickness of the composite was governed by the height of these projections. The moist mass was cured at a predetermined pressure (20-40 bar) and temperature (140-200°C) for a sufficient period ranging between 5-60 minutes. The biocomposite material was taken out from the mold followed by analysis of its properties viz. Modulus of elasticity (MOE), modulus of rupture (MOR), % water absorption as per IS 3087:2005.

Various samples were prepared using above process, and raw material specifications, composition ratios and processing conditions stated below:
S. No. Raw material/ Process parameter Specification
1. Lignin Powdered form with particle size 0.1-10 micron, pH 4-7, moisture content: 1-20%, Composition range: 1%-70%
2. Binder
(Alone or in combination) -Wheat gluten, protein content > 80%, Composition range: 0%-30%;
- Guar gum (0-30%);
- pulp/paper powder (0-15%);
- glyoxal (0-10%)

3. Filler Saw dust: Pine, bamboo, Eucalyptus;
particle size 0.5-2.5 mm, Composition range: 30%-90%

4. Solid to water ratio 1:0.1 to 1:1
5. Mixing time 1-5 minutes
6. Curing time 5-90 minutes
7. Curing temperature 125-200°C
8. Curing pressure 20-60 bar

Characterization methods:
1. IS 3087:2005- Measurement of Modulus of Elasticity (MOE), Modulus of Rupture (MOR)
MOE and MOR are measured through the three-point bending test using a universal testing machine (UTM). Sample’s dimensions are measured, and it is kept on the fixture attached to the UTM. The sample is supported at the two ends using a pivot while load is applied at the center. Stress-strain curve/ data is generated until the sample breaks. The collected data is analyzed to compute MOE and MOR. MOE calculation uses the force and deflection related to the elastic limit, while MOR uses the maximum force at which the material breaks.

2. Measurement of water absorption after 2 and 24 hours.
For measuring the water absorption, the edges of the sample are dipped in molten wax to avoid water ingress through them. This leaves only top and bottom surfaces exposed to water when the sample is dipped into it. Mass of sample after applying wax at the edges is considered as the initial mass. Increase in mass of the sample due to water absorption at 2 hours and 24 hours is used to calculate the % water absorption by the sample.

3. Measurement of Color leaching:
Color leaching refers to unbonded lignin/ its chromophores which leave the particleboards and leach into the water. Color leaching was measured qualitatively by observing color of water in which sample was dipped.

Observation and Results:
Table 1 shows the % water absorption, MOE and MOR for samples prepared (Solid: water ratio for these samples was 1:0.5 and density of prepared samples was in the range of 0.7-0.8 gm/cm3) using different compositions of lignin, gluten and saw dust. Target values for these parameters were as follows:
MOE = 1800-200 N/mm2,
MOR = 10-11 N/mm2,
Water absorption = <25% in 2 hours and < 50% in 24 hours.

Table 1: Properties of biocomposite material prepared using different compositions of
lignin, gluten and saw dust


Expt. No. Lignin Gluten Sawdust Pressure Pressing time Temp Water absorption MOE MOR
% % % bar minutes °C % in 2 hours % in 24 hours N/mm2 N/mm2
1 38.5 10 51.5 20 90 150 30.1 44.0 854.0 4.9
2 34.3 20 45.7 20 90 150 16.9 44.19 1072 8.6
3 30 30 40 20 90 150 24.16 50 1310 10.1
4 18 8 74 40 60 165 42 45 1110 13.2
5 23 8 69 40 60 165 33 38 1156 9.7
6 17 14 69 40 60 165 35 36 1510 15.8
7 29 14 57 40 60 165 31 35 1967 12.5
8 16 20 64 40 60 165 29 36 2164 14.5
9 20 20 60 40 60 165 30 36 2202 13.4

Table 2 summarizes experiments using different protein sources such as paper pulp, guar gum, glyoxal etc. to reduce or replace gluten. All samples in these experiments were found to have density in the range of 0.7-0.8 gm/cm3.

Table 2: Samples prepared using different materials to replace or reduce saw dust and/or gluten

S.
No. Lignin Gluten Saw
dust Other material Solid:
water ratio Pressure Pressing time Temp Water absorption % MOE MOR
% % % % Bar minutes °C in 2 hours in 24 hours N/mm2 N/mm2
10 31 8 30.5 50% Saw dust replaced by cotton rag 1:0.5 40 60 165 33 35 1667 8.33
11 29 8 57 6% gluten replaced by paper pulp 1:0.5 40 60 165 32 45 1369 8.55
12 29 4 57 10% gluten replaced by guar gum 1:0.27 40 30 165 29 118 Not measured as samples absorbed water and lost strength
13 29 4 57 10% gluten replaced by guar gum 1:0.17 40 10 165 90 171
14 29 4 57 10% gluten replaced by 4% guar gum + 6% paper pulp 1:0.17 40 10 165 82 116 1216 8.03
15 32.5 0 65 No gluten. 2.5wt% glyoxal used instead 1:0.1 40 7 165 NA 200 0.1

Smell of raw materials as well as finished products was taken (inhaled). No obnoxious smell was felt.
Figures 2A shows percentage water absorption and color leaching from samples prepared in Example 1. Figure 2B shows the visual appearance of water upon color leaching from the biocomposite material prepared in accordance with an embodiment of the present disclosure using varying gluten%.

Industrial Applicability
The disclosed biocomposite material exhibits particleboard like properties and can be used to manufacture all products that are produced from solid wood or wood materials such as particleboards, chipboard or Oriented Strand Board (OSB), Medium Density Fiberboard (MDF), etc.
The disclosed biocomposite material exhibits the following advantages- (1) they can be used to manufacture particleboards, MDF which are free from formaldehyde-based adhesives, (2) they exhibit improved resistance to water absorption, (3) they are UV Resistant and thus do not undergo color fading when exposed to sunlight, and (4) they are antimicrobial due to the lignin incorporation in the composition.
The disclosed biocomposite material is equivalent to particle board/MDF board available commercially and are as per the IS 3087:2005 (For particle boards) and IS 12406:2003 (For MDF) standards. Figures 1B and 1C show the appearance of particleboard obtained from biocomposite material of present disclosure, in comparison with MDF (Leoclassic TM) and particleboard samples collected from Akruti Boardlam Pvt. Ltd.
The disclosed biocomposite material is environment friendly and inexpensive. The raw material used to prepare the biocomposite material are by-products of other industrial processes and do not require chemical treatments to make them suitable for the manufacture of disclosed biocomposite material. It is advantageous to use Kraft lignin as it is a byproduct from kraft pulping process. The Kraft lignin is obtained from Kraft pulp process and does not undergo any chemical treatment steps. Further, Kraft process is flexible and can use a wider range of wood sources as compared to other pulping processes. Hence, this process is used by >80% plants producing paper or dissolving grade pulp making the bulk availability of Kraft lignin. Further, gluten obtained from wheat is one of the cheapest and abundant protein available commercially. Saw dust is a byproduct from wood industry.
Additionally, the disclosed composition avoids usage of additional chemicals that are used in particleboards/MDF produced currently in market, thereby making the composite ecofriendly and economical.
,CLAIMS:1. A biocomposite material comprising 5 to 70 wt % of lignin, 5 to 30 wt % of a binder, and 25 to 90 wt % of a filler.

2. The biocomposite material as claimed in claim 1, comprising the lignin and the binder in a w/w ratio ranging between 1:1 to 4:1.

3. The biocomposite material as claimed in claim 1, wherein the lignin is Kraft lignin.

4. The biocomposite material as claimed in claim 1, wherein the binder is selected from the group consisting of protein source, natural resins, pulp or paper powder, and mixtures thereof.

5. The process as claimed in claim 4, wherein the protein source is a plant-based protein selected from the group consisting of wheat gluten, zein (corn protein), soy protein, chitin and mixtures thereof.

6. The biocomposite material as claimed in claim 1, wherein the filler is a powdered or granulated material obtained from a wood source.

7. A process for preparing a biocomposite material, the process comprising mixing 5 to 70 wt % of lignin, 5 to 30 wt % of a binder, and 25 to 90 wt % of a filler in the presence of an aqueous medium; followed by compressing the obtained mixture to obtain the biocomposite material.

8. The process as claimed in claim 7, wherein the lignin is Kraft lignin.

9. The process as claimed in claim 7, wherein the Kraft lignin is obtained by precipitation of lignin from black liquor obtained from Kraft process at a pH of 4-7.

10. The process as claimed in claim 7, wherein the binder is selected from the group consisting of protein source, natural resins, pulp or paper powder, and mixtures thereof.

11. The process as claimed in claim 10, wherein the protein source is a plant-based protein selected from the group consisting of wheat gluten, zein (corn protein), soy protein, chitin, and mixtures thereof.

12. The process as claimed in claim 7, wherein the filler is a powdered or granulated material obtained from a wood source.