WO2014070036A1

WO2014070036A1 - Lignin composite material

Info

Publication number: WO2014070036A1
Application number: PCT/RU2012/000901
Authority: WO
Inventors: Alexei Alexeevich GRIDNEV
Original assignee: Gridnev Alexei Alexeevich
Priority date: 2012-11-02
Filing date: 2012-11-02
Publication date: 2014-05-08

Abstract

The present invention provides a composite material comprising lignin, carboxylic anhydride binder and cross-linking agent (hardener). Carboxylic anhydride binder is a polymeric material with amount of carboxylic anhydride 2 or more carboxylic anhydride fragments per molecule of the binder. The binder can be synthesized by copolymerization of different anhydrides with ethylenically unsaturated monomers in the presence of lignin. The hardener comprises chemical groups that are capable to react with carboxylic anhydride moieties, like polyols, polyepoxides or polyamines with amount of such groups 2 or more. Neither the binder, not the hardener contains solvents or water. The composite is obtained by cure of all ingredients together on heating and, optionally, pressing, and with optional catalyst. Catalysts can be applied to reduce process temperature or to improve properties of the composite material. Fillers can be introduced into the lignin composite to improve mechanical strength.

Description

LIGNIN COMPOSITE MATERIAL.

DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION

The most common approach of making copolymers with lignin is, first, to graft a reactive group onto a lignin molecule. Then, this reactive group reacts with other reagents to form a polymer with lignin. ( T. Q. Hu (edd.). Chemical

Modifications, Properties and Usage of Lignin. Kluwer Publishers, New York, (2002) p. 57). Thus, cross-linked polymer was obtained by grafting

polymerizable vinyl group, like methacyloyl group, on lignin followed by free radical copolymerization with methacrylate, acrylamide and other vinylic monomers (US Pat. 5, 138,007; 5,121,801 ; 5,037,931 ; 4,931 ,527). This approach requires two steps for making lignin composites. First step, grafting reactive group on lignin, utilizes reagents dissolved in organic solvents. Removal of these solvents after the grafting is complete creates fire hazards and is expensive.

Lignin can be treated with formaldehyde and/or added to phenol-formaldehyde resins to form a polymeric material (US 4,769,434; 4,221,708). In both cases formaldehyde should be utilized for the synthesis of polymeric material.

Formaldehyde is known carcinogen and its usage is supposed to be avoided as much as possible, especially in consumer product.

Lignin was converted into a polymeric material by heating with sulfur (US 4, 107, 1 1 1). The material has unpleasant odor.

Each of the sited above methods of producing polymeric material from lignin has its own disadvantages preventing noticeable production of lignin-based polymers and composites.

] The present invention have endeavored to solve the problem of converting lignin into a structural material by reaction with polyanhydrides of carboxylic acids. In some cases, like maleinized vegetable oils, essentially natural binders can be applied. Taking into consideration that lignin itself is naturally occurring material, a composites with more than 90% natural components can be obtained.

STATEMENT OF THE INVENTION

In accordance with the present invention, lignin forms a composite material with polymers containing carboxylic anhydride groups and a cross-linking agent (hardener).

Lignin is not very reactive polymer so that chemical bonding with other polymers is problematic. We found that polymers with carboxylic anhydride groups form with lignin a composite with sound mechanical properties. Most likely, anhydrides react with hydroxyl groups of lignin.

Polymers with anhydride groups are known. Mostly, these polymers are solid materials due to high polarity of anhydrides. Lignin is, laso, a solid material. Making composite material using two solid polymers requires good mixing of these two polymers. Such mixing can be made only with special blenders that have relatively low productivity and high energy consumption. The other approach, usage of polymer solutions, as it was mentioned above, requires removal of solvents that creates additional technological problems. Most likely, these problems of compatabilization of lignin with polymeric anhydride prevented discovery of corresponding composites earlier. The solution was found in the present invention. First method utilizes concept of synthesis of a polymeric anhydride in lignin by methods or radical

polymerization of monomeric anhydride with vinylic monomers. This method is considered impossible due to presence of phenolic group in lignin. Phenols are considered inhibitors of radical polymerization (Dyumaev K. M. et al. Izv. Akad. Nauk SSSR (1961) 167). Leading experts in lignin believe that no polymers can be formed by radical polymerization of vinylic monomers in the presence of lignin ( Gandini A. Polymers from renewable resources in: Comprehensive Polymer Science, edited by Aggrawal S. L. and Russo S. Pergamon Press; Oxford 1992. Supplement V. l, pp. 527-573). This is why chemical blocking of phenolic hydroxyl is considered essential for making copolymers of lignin by free radical polymerization (i.g. grafting a vinylic monomer onto them as described on the first page).

However, we found that this is not true. In our experiments, polyanhydrides were obtained when various anhydrides, i.g. ithaconic, maleic, methacrylate, with different ethylenically unsaturated compounds were radically

copolymerized in lignin matrix (Examples 3-5). Solvent are capable to extract a polymer with broad range of molecular weights, from few hundred to several thousand Daltons from lignin matrix after this free radical polymerization.

Second method of making mixtures of lignin with polyanhydrides is to use liquid, low molecular weight polyanhydrides. Maleinized vegetable oils are the example of such low molecular weight polyanhydrides, with average number of maleic anhydride moieties in the 2-4 range per molecule (Chakrabarty, M. M. Chemistry And Technology Of Oils And Fats. Allied Publishers. 2003).

Oligomeric anhydrides, also, can be synthesized by catalytic chain transfer polymerization (Sanders G.C. et al.. Macromolecules, 2012, 45 (15), pp 5923- 5933). We found, also, that polyanhydrides, especially low molecular weight one, do not form composites with lignin with acceptable mechanical properties when heated and pressed together at high level of lignin in such composites. A cross- linking agent (hardeher) is required. Such hardeners can be reagents that react with anhydrides. For example, polyols (examples 4-6), polyepoxides (examples 1 and 2) or imines (Examples 8 and 9) react with polyanhydrides to form a cross- linked composite materials with polymeric anhydride/lignin mixture with sound mechanical properties. In some cases (example 3) hydroxyl group can be introduced into a polyanhydride polymer during copolymerization.

Polyols are chemical compounds bearing hydroxyl (OH) groups. Imines are chemical compouds bearing R_tR₂C=NR₃ group, wherein R,, R₂, and R₃ are independently H or hydrocarbon substituents.

Cured lignin compositions were tested and reasonable shear strength, from 3 to 12 MPa was determined. These values of tensile strength are comparable with shear strength of standard MDF (http://www.spanogroup.be/upload/docs/MDF- manual%20ENG%20LOW%20RES.pdf).

Shear strength of invented lignin composite materials can be increases even further by mixing with fillers (Example 10 and 1 1). There is no doubt that fillers other than glass fiber or wood particles, described in the example 10 and 1 1 , can be applied the invented lignin composite due to high adhering properties of polyanhydrides to various surfaces.

In the provided examples content of lignin in the invented lignin composites was used above 30 wt. % of the final material to keep composite cost low.

Apparently, content of lignin in the composite can be reduced to less than 30% if technological, esthetical or other reasons require less amount of lignin in the invented composite.

The lignin composites of the present invention have relatively low swelling in water (Example 7), less then 20% after 24 h immersion in water. Most important, after drying the composite restored its dimensions and shear strength. The higher is the content of binder, the less is swelling of the lignin composite in water.

Curing rate of the present lignin composites depends on chemical origin of lignin, type of carboxylic anhydride, the hardener, temperature and catalyst. Reaction of hydroxy groups of polyols with anhydrides, acids and other reactive groups is known to be catalyzed by different catalyst including but not limited to acids, amines, phosphines and metallochelates. Examples 3-6 utilized only few of such catalysts. Examples 1-2 and 8-9 employed no catalysts.

Preferred curing catalysts in this invention are tertiary amines due to good solubility of such amines in the invented composition, low cost and no leaching of the amine catalyst from the cured material. Apparently, acidic groups that are formed during reaction of polyanhydrides with the hardeners hold the amine catalyst by forming a salt.

EXAMPLES

Maleic anhydride, methacrylic anhydride, ithaconic anhydride, DABCO, tetraethyleneglycol, hexanal, 2-(aminomethyl)-2-methyl-l,3-propanediamine (Aldrich, USA) were used as received. All oils were purchased in local grocery stores. Maleinization of oils was performed according to Tran P., Seybold ., Grayver D., Narayan R. J. Amer, Oil. Chem. Soc. 82(2005)169. Epoxide resins ED20 (Karbokhim, Russian Federation) were used as received. ED20 resin consists of diglycidyl ether of bisphenol A by 90 wt % with the rest 10% of a corresponding dimer bearing hydroxyl groups. Sulfolignin (lignin sulfate) was received from Segezh and kraft-lignin from Svetogorsk (Russian Federation) paper mills.

(2,4,6-tris(dimethylaminomethyl)phenol), toluenesulfonic acid, diethylene glycol, hexamethylenediamine, azo-bis(isobutironiril), benzoyl peroxide ( Reakhim, Russian Federation) were used as received. Glycidyl methacrylate (Reakhim) was vacuum distilled prior the use.

Example 1. Maleinized oil.

0.8 g of maleinized sunflower oil (20% content of maleic anhydride) and 0.15 g of ED20 bisphenol A diglycidyl ether were mixed with 9 g of sulfolignin.

Obtained brown powder was pressed at 10 kg/cm² and heated at 210°C for 10 min. Shear strength of the cured composite - 3.2 MPa.

Example 2. Different maleinized oil, different epoxide.

Glycidyl methacrylate was oligomerized to low oligomers (Mn=540) according to Polymer Journal, 24 ( 1992) 613. 0.3 g of this oligo glycidylmethacryiate and 1.7 g of maleinized soybean oil (17% content of maleic anhydride) were mixed with 8 g of sulfolignin. Obtained brown powder was pressed at 10 kg/cm² and heated at 170°C for 20 min. Shear strength of the cured composite - 5.3 MPa.

Example 3. Anhydride and hardener are in the same polymer.

1.2 g of methacrylic anhydride, 2.2 g of butyl aery late, 0.2 g of benzoyl peroxide and 0.6 g of hydroxy ethylmethacrylate were mixed with 6 g of sulfolignin and heated under nitrogen lh at 70 C, then 30 min at 80 °C and, finally 20 min at 100°C. Obtained brown powder was mixed with 0.03 g of 2,4,6-2,4,6- tris(dimethylaminomethyl)phenol, pressed at 10 kg/cm² and heated at 130°C for 1 h. Shear strength of the cured composite - 12.0 MPa.

Example 4. Different hardener are in the same polymer.

0.8 g of maleic anhydride, 2.5 g of butyl acrylate, 0.2 g of benzoyl peroxide and 1.1 g of tetraethylene glycol were mixed together and 3.5 g of obtained solution were with 6. 5 g of sulfolignin and heated under nitrogen lh at 70 C, then 30 min at 80 °C and, finally 20 min at 100°C. Obtained brown powder was mixed with 0.03 g of 2,4,6-tris(dimethylaminomethyl)phenol, pressed at 10 kg/cm and heated at 170°C for 1 min. Shear strength of the cured composite - 1 1.6 MPa.

Example 5. Different anhydride, different hardener

0.8 g of ithaconic anhydride, 2 g of styrene, 0.12 g of azo-bis(isobutironiril) , 0.02 g of DABCO and 0.25 g of 1,4-hexanediol, were mixed with 7 g of hydro lytic (kraft) lignin and heated under nitrogen 1 h at 70 C, then 30 min at 80 °C and, finally 10 min at 100°C. Obtained brown powder was pressed at 10 kg/cm² and heated at 1 10° C for 50 min. Shear strength of the cured composite - 8.6 MPa.

Example 6. Different catalyst.

A composite material was made similar to the Example 4 but toluenesulfonic acid was taken instead of 2,4,6-tris(dimethylaminomethyl)phenol. Shear strength of the cured composite - 8.9 MPa.

Example 7. Water swelling.

3 g sample of cured lignin composite from example 2 was immersed in water for 24 h. Weight of the sample increased by 38% while volume of it increased by 19%. After drying in air both the weight and the volume of the sample returned to the initial numbers. Shear strength of dry sample was found to be 4.7 MPa. Swelling ration for sample from example 4 was found 10% and 3% for sample from example 3.

Example 8. Imine hardener.

100 g of toluene, 50 g of cyclohexanone and 30 g of hexamethylenediamine were refluxed under nitrogen with Dean-Stark trap. When all water was collected in the Dean-Stark trap, all volatiles were distilled off to yield diimine as colorless liquid.

2 g of maleic anhydride, 2.1 g of styrene and 0.1 g of benzoyl peroxide were mixed together and 3 g of obtained solution was mixed with 7 g of

SLilfolignin and heated under nitrogen lh at 80 C, then 30 min at 90 °C and, finally 20 min at 100°C. Then 2 g of diimine hardener were added and after mixing the mixture was kept at 170°C for 40 min under 10 kg/cm² pressure. Shear strength of the cured composite - 7.0 MPa.

Example 9. Different imine hardener.

10 g of toluene, 3 g of hexanal and 3 g of 2-(aminomethyl)-2-methy 1- 1 ,3- propanediamine were refluxed under nitrogen with Dean-Stark trap. When all water was collected in the Dean-Stark trap, all volatiles were distilled off to yield triimine as colorless liquid.

2 g of maleic anhydride, 1.9 g of vinylacetate and 0.05 g of azo- bis(isobutironiril) were mixed together and 2 g of obtained sojution was mixed with 8 g of sulfolignin and heated under nitrogen 2 h at 70°C, then 30 min at 75 °C and, finally 10 min at 100°C. Then 1.2 g of triimine hardener were added and after mixing the mixture was kept at 170°C for 30 min under 10 kg/cm² pressure. Shear strength of the cured composite - 5.2 MPa. Example 10. Fiber reinforced lignin composite.

7 g lignin composite according example 1 was mixed with 3 g of chopped glass fibers and cured similar to the example 2. Shear strength of this 3-component cured composite - 12.3 MPa.

Example 11. Wood reinforced lignin composite.

7 g lignin composite according example 2 was mixed with 2 g of wood chips (<5 mm length) fibers and cured similar to the example 2. Shear strength of this 3- component cured composite - 7. 1 MPa.

Example 12. Low content of lignin.

Glycidyl methacrylate was oligomerized to low oligomers (Mn=540) according to Polymer Journal, 24 ( 1992) 613. 0.9 g of this oligo glycidylmethacrylate and 5.1 g of maleinized soybean oil ( 17% content of maleic anhydride) were mixed with 4 g of sulfolignin. Obtained brown powder was compacted and heated at 170°C for 20 min. Shear strength of the cured composite - 9.3 MPa.

Claims

1. A composite material comprising lignin, carboxylic anhydride binder and cross-linking agent (hardener).

2. Composite material of claim 1, wherein carboxylic anhydride binder comprises 2 or more than 2 carboxylic anhydride fragments.

3. Carboxylic anhydride binder of claim 2, wherein fragments of carboxylic anhydride binder are of the following structure

and/or

and/or wherein Ri, R₂, R3, R4 , R₅ , Re and R₇ are independently H, alkyl, alkenyl, ethylenically polyunsaturated alkenyl, OOC-Alk, OOC-Alkenyl, OAlk, CI, CN, phehyl, substituted phenyl, aryl, substituted aryl, COOZ, wherein Z is indepedently H, alkyl, substituted alkyl, hydroxy alkyl, dihydroxyalkyl, glycidyl, ethylenically unsaturated alkyl, CO(NR₈R₉) wherein R₈ and R₉ are independently H, alkyl, substituted alkyl, hydroxyl

4. Composite material of claim 1, wherein carboxylic anhydride binder

obtained by copolymerization of maleic anhydride with ethylenically unsaturated compounds.

5. Composite material of claim 1, wherein carboxylic anhydride binder obtained by copolymerization of ithaconic anhydride with ethylenically unsaturated compounds.

6. Composite material of claim 1 , wherein carboxylic anhydride binder

obtained by copolymerization of methacrylic anhydride with ethylenically unsaturated compounds.

7. Composite material of claim 1 , wherein cross-linking agent comprises a polyol with number of hydroxy 1 groups is 2 or more than 2 per molecule of cross-linking agent.

1. Composite material of claim 1, wherein cross-linking agent comprises a polyepoxide with number of epoxy groups per molecule in the range of 1 to 8, preferably, 2 or 3.

8. Composite material of claim 1, wherein cross-linking agent comprises a polyimine compound with number of imine groups is 2 or more than 2 per molecule of cross-linking agent.

9. Composite material of claim 1, wherein cross-linking agent comprises a compound bearing both hydroxyl and epoxy groups with number of hydroxyl groups and epoxide groups combined is 2 or more than 2 per molecule of cross-linking agent.

10. Composite material of claim 1 , wherein cross-linking agent and

carboxylic anhydride binder are chemically bound together.

1 1. A process of making lignin composite material of claim 1, where lignin, the binder and the hardener are heated together at temperatures from 30 to 250⁰ C, preferably, 60-200⁰ C with or without a catalyst.

12. A process of making lignin composite material of claim 12, wherein the catalyst is a tertiary amine.

13. A process of making lignin composite material of claim 12, wherein the catalyst is a mineral acid.

14. A composite formed from the adhesive composition of claim 1 and one or more filler, wherein the weight ratio of the filler and the adhesive ranges from 250: 1 to 1 :250.