Abstract:
Disclosed are methods for manufacturing bio-based epoxy resins. The raw materials of the resins include lignin, polyol, solvent, catalyst, acid anhydride, and multi-epoxy compound. The methods of manufacturing the resins include evenly mixing the lignin, the polyol, the catalyst, and the solvent together to form a mixture. The acid anhydride is added to the mixture to process esterification for forming an intermediate product. The multi-epoxy compound is added to the intermediate product to process epoxidation for forming the bio-based epoxy resins. The bio-based epoxy resin has excellent compatibility with the solvent, such that the solvent can be added to the bio-based epoxy resins to form coatings having a tunable solid content. As a result, the coating can be applied to the surfaces of every type of base material.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application claims priority of Taiwan Patent Application No. 099143654, filed on Dec. 14, 2010, the entirety of which is incorporated by reference herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to lignin, and in particular relates to modified epoxy resins utilizing lignin, and raw materials and methods of manufacturing the modified epoxy resins. 
         [0004]    2. Description of the Related Art 
         [0005]    Gasoline supplement is running dry, such that the gasoline costs are rising. 
         [0006]    Production, usage, and waste of gasoline products are not environmentally friendly and results in a lot of carbon dioxide and pollutants. As such, plant type and bio-based materials is a major area being developed for replacing gasoline materials which are used as raw materials in critical industries. In plants, a content ration of lignin is just less than a content ratio of cellulose. A lignin source can be straw, pulp black, wood flour, lumber, or any plants. According to methods of obtaining the lignin, the lignin can be classified to kraft lignin, ororganosolv lignin, lignosulfonate, and the likes. Compared to other lignins, lignosulfonate can be industrially mass produced and is the most readily and stably sourced lignin material around. Currently, lignin is applied in additives, dispersive agents, and for organic synthesis, wherein lignin-based epoxy resins are mainly formed. 
         [0007]    Lignin-based epoxy resins are classified into two major types, depending on whether the lignin serves as a main agent or a curing agent. For lignin serving as the main agent, there are two preparation methods thereof. In the first method, the lignin is polymerized with chloropropylene oxide under an alkaline condition. In the second method, a lignin-acid anhydride pre-polymer is reacted with an epoxy compound. The main agent products of the method may be used to collocate with different curing agents. For lignin serving as the curing agent, there are three preparation methods thereof. In the first method, the lignin is not modified. In the second method, the lignin is modified by phenol to tune a hydroxyl ratio thereof. In the third method, the lignin is modified by polymerizing the lignin with polyol and acid anhydride to form a lignin-acid anhydride pre-polymer. Theses products of the methods may be used to collocate with different epoxy resin main agents. Although lignosulfonate source is stable, wide, and low cost, the stewing process of sulfite for manufacturing the lignosulfonate will change its structure, reduce its reactivity, and decrease its solubility in several organic solvents. In other words, application of lignosulfonate is difficult. The conventional lignosulfonate must be modified and purified by complicated processes, and then polymerized with chloropropylene oxide. Lignin inherently has two hydroxyl groups, e.g. hydroxyl groups on alkyl chains or phenol groups on aromatic rings, with different epoxidation rates. Moreover, the lignosulfonate with changed structure and low reactivity is difficult to epoxidize, and therefore influencing the epoxy resin performance. 
         [0008]    For solving the described problems, several patents have disclosed reacting polyols, acid anhydrides, and lignins, together, to form lignin-acid anhydride pre-polymers, such that reactivity and compatibility of the lignin and the solvents are enhanced. Thereafter, the pre-polymers are used to prepare lignin-based epoxy resins. In China Patent No. CN101348558, an enzymolysis lignin (ororganosolv lignin) is used to prepare a lignin-based epoxy resin having an epoxy value of 0.24 mol/100 g to 0.67 mol/100 g. However, when the organosolv lignin used, is replaced with lignosulfonate, a lignin-based epoxy resin cannot be produced. In Japan Publication No. JP2006/028528, ethylene glycol and acid anhydride are used to modify an enzymolysis lignin (or kraft lignin) to form a lignin-based acid anhydride pre-polymer. The pre-polymer may serve as a multi-carboxylic acid curing agent. A biodegradable epoxy resin can be prepared by using the curing agent and several epoxy resins (main agents). However, the publication fails to teach that the lignin can be replaced with lignosulfonate. 
         [0009]    Accordingly, a novel method of modifying lignins to form a lignin-based and bio-based epoxy resin with low cost and high performance is called-for. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    One embodiment of the invention provides raw materials of a bio-based epoxy resin, comprising: 100 parts by weight of lignin; 10 to 100 parts by weight of polyol; 200 to 1000 parts by weight of a solvent; 0.01 to 30 parts by weight of a catalyst; 50 to 300 parts by weight of acid anhydride; and 50 to 1000 parts by weight of a multi-epoxy compound. 
         [0011]    One embodiment of the invention provides a method of manufacturing a bio-based epoxy resin, comprising: mixing 100 parts by weight of lignin, 10 to 100 parts by weight of polyol, 0.01 to 30 parts by weight of a catalyst, and 200 to 1000 parts by weight of a solvent to form a mixture; adding 50 to 300 parts by weight of acid anhydride to the mixture for a heating reaction to form an intermediate product; adding 50 to 1000 parts by weight of a multi-epoxy compound to the intermediate product for another heating reaction to form a bio-based epoxy resin solution; and removing the solvent of the bio-based epoxy resin solution to form a bio-based epoxy resin. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0013]    In one embodiment, a method of forming a bio-based epoxy resin is provided. First, lignin, polyol, catalyst, and solvent are mixed to form a mixture. Acid anhydride is added to the mixture for a heating reaction to form a homogeneous solution of a modified lignin intermediate product. In one embodiment, the heating reaction is performed at a temperature of 110° C. to 140° C. for a period of 2 hours to 5 hours. An overly high temperature and/or an overly long period will not obviously enhance ring-opening polymerization of the heating reaction. An overly low temperature and/or an overly short period will not complete ring-opening polymerization of the heating reaction. 
         [0014]    Polyol is a compound having at least two hydroxyl groups, such as diol (e.g. ethylene glycol or propylene glycol, or triol (e.g. glycerol), or combinations thereof. The polyol may serve as a surfactant between a solvent and the lignin, such that an original lignin without modification can be a little bit dissolved in a solution. Furthermore, the polyol reacts with the acid anhydride to process ring-opening polymerization. Based on 100 parts by weight of the lignin, an amount of the polyol is 10 to 100 parts by weight thereof, and preferably 10 to 50 parts by weight thereof. An overly high amount of the polyol influences the reactivity of the acid anhydride and the lignin. An overly low amount of the polyol increases mixture viscosity and reduces the lignin compatibility, thereby influencing ring-opening polymerization. 
         [0015]    The catalyst is the so-called Lewis acid, such as phenylsulfonic acid or derivatives thereof (e.g. toluenesulfonic acid), sulfuric acid, or combinations thereof. A little catalyst may help with condensation reaction. Based on 100 parts by weight of the lignin, an amount of the catalyst is 0.01 to 30 parts by weight thereof, and preferably 10 to 20 parts by weight thereof. An overly high amount of the catalyst cannot dramatically help the condensation reaction but influence a subsequent epoxidation. An overly low amount of the catalyst lowers condensation. 
         [0016]    The solvent can be polar aprotic solvent such as N,N-dimethylformamide (DMF) or dimethylacetamide (DMAc). Generally, the lignin is dissolved in water rather than most solvents, but embodiments of the invention reverse normal ways. The lignin and other reagents are firstly dispersed in the solvent, and the modified lignin is then gradually dissolved in the solvent during reaction. In one embodiment, the lignosulfonate is chosen to be modified and dissolved in the solvent. Based on 100 parts by weight of the lignin, an amount of the solvent is 200 to 1000 parts by weight thereof, and preferably 400 to 600 parts by weight thereof. An overly high amount of the solvent will reduce a solid content of the reaction product, which is not beneficial when adjusting material ratios of the product in subsequent steps. An overly low amount of the solvent leads to an overly high reaction viscosity and poor compatibility between the reactants and the solvent. 
         [0017]    The acid anhydride can be an organic compound having at least one acid anhydride group, such as maleic acid anhydride, 1,2,4,5-benzenetetracarboxylic anhydride, derivatives thereof, or combinations thereof. The hydroxyl groups of the lignin may react with the acid anhydride to form carboxylic acid groups. The terminal carboxylic acid group may further react with the hydroxyl groups of the polyol, and another hydroxyl group of the polyol may react with the other acid anhydride to form carboxylic acids. The above reaction is the so-called esterification polymerization. Note that a lot of un-reacted carboxylic acid groups of the acid anhydride will remain after the esterification polymerization, and a lot of un-reacted hydroxyl groups of the polyol will remain after the esterification polymerization, too. Based on 100 parts by weight of the lignin, an amount of the acid anhydride is 50 to 300 parts by weight thereof, and preferably 100 to 160 parts by weight thereof. An overly high amount of the acid anhydride influences epoxidation modification in subsequent steps. An overly low amount of the acid anhydride lowers epoxidation modification effect of the lignin. 
         [0018]    A multi-epoxy compound is added to the homogeneous solution of the modified lignin intermediate product for a heating reaction to form a bio-based epoxy resin solution. In one embodiment, the heating reaction is performed at a temperature of 70° C. to 140° C. for a period of 0.5 hour to 6 hours. In another embodiment, the heating reaction is performed by a two-step heating method, wherein the first step is performed at a temperature at 70° C. to 140° C. for a period of 0.5 hour to 6 hours, and the second step is performed at a temperature at 150° C. for a period of 1 hour to 6 hours. 
         [0019]    The multi-epoxy compound can be an organic compound having at least two epoxy groups, such as glycidyl ether, diglycidyl ether, bisphenol A diglycidyl ether, epoxidized vegetable oil, derivatives thereof, or combinations thereof. Part of the epoxy groups of the multi-epoxy compound react with the carboxylic acid groups and/or the hydroxyl groups of the pre-modified lignin to form the bio-based epoxy resin solution. It should be understood that the bio-based epoxy resin has un-reacted carboxylic acid groups, hydroxyl groups, and epoxy resins. In one embodiment, the multi-epoxy compound has an epoxy value of 0.02 mol/100 g to 0.8 mol/100 g. An overly low epoxy value of the multi-epoxy compound reduces the epoxidation reactivity and ratio of the lignin. Based on 100 parts by weight of the lignin, an amount of the multi-epoxy compound is 50 to 1000 parts by weight thereof, and preferably 100 to 300 parts by weight thereof. An overly amount of the multi-epoxy compound would require additional curing agents to totally crosslink the bio-based epoxy resin applied as a coating. An overly low amount of the multi-epoxy compound reduces the epoxidation ratio, thereby degrading the properties of the bio-based epoxy resin applied as a coating. 
         [0020]    The bio-based epoxy resin solution can directly serve as a coating, or an additional solvent can be added thereto for tuning its solid content. The bio-based epoxy resin solution can be coated on a substrate such as glass, ceramic, stone, plastic, metal, or polymer, and then dried to form a film. The coating method includes spin coating, dip coating, brush coating, spray coating, roll coating, or combinations thereof. In one embodiment, drying or removing the solvent of the bio-based epoxy resin solution is performed at a temperature of 150° C. to 200° C. for a period of 0.5 hour to 3 hours. 
         [0021]    As described above, the raw material of the embodiments can be mass produced with stable supplements. The compatibility of the lignin and the solvent and the epoxidation rate of the lignin can be enhanced by simple modification, such that the modified lignin is suitable to be coated on metal building materials. The bio-based epoxy resin may replace the conventional gasoline-based epoxy resin. Furthermore, the bio-based epoxy resin can be developed as an epoxy resin free of bisphenol A for application in the lining of food cans. 
       EXAMPLES 
     Example 1 
       [0022]    40 g of lignosulfonate (DP651, commercially available from Bonegaard), 8 g of ethylene glycol, 5.6 g of 4-toluenesulfonic acid, and 200 g of DMF were mixed to form a mixture. Subsequently, 54.3 g of 1,2,4,5-benzenetetracarboxylic anhydride was added to the mixture for a heating reaction at 130° C. for 3 hours, thereby forming a homogeneous solution of a modified lignosulfonate intermediate product. 45.6 g of a multi-epoxy compound (NPEL127, epoxy value of 0.5453 mol/g, commercially available from Nanya Plastic Co.) was added to the homogeneous solution of the modified lignosulfonate intermediate product for a heating reaction at 130° C. for 1 hours and then 150° C. for 1 hour. As such, a bio-based epoxy resin solution was obtained. The solvent of the bio-based epoxy resin was removed to obtain a bio-based epoxy resin having an epoxy value of 0.070 mol/100 g. A co-solvent of 5 parts by volume of DMF and 1 part by volume of methoxy polyethylene glycol (mPEG) was added to the bio-based epoxy resin to form a coating having a solid content of 30%. The coating was coated on an aluminum foil by a wire rod, and then heated to 180° C. for 1 hour to solidify the coating, remove the solvent thereof, and intermolecular crosslink and/or intramolecular crosslink the epoxy groups and hydroxyl groups of the bio-based epoxy resin. The coating was solidified to form a film having a smooth and bright appearance, a pencil hardness of H, an adhesiveness of 100/100 as measured by a scotch tape test, and a solvent rub resistance for mPEG, isopropanol, or DMAc. 
       Example 2 
       [0023]    40 g of lignosulfonate (DP651, commercially available from Bonegaard), 8 g of ethylene glycol, 5.6 g of 4-toluenesulfonic acid, and 200 g of DMF were mixed to form a mixture. Subsequently, 54.3 g of 1,2,4,5-benzenetetracarboxylic anhydride was added to the mixture for a heating reaction at 130° C. for 3 hours, thereby forming a homogeneous solution of a modified lignosulfonate intermediate product. 40 g of a multi-epoxy compound (epoxidized soybean oil, epoxy value of 0.4125 mol/g) was added to the homogeneous solution of the modified lignosulfonate intermediate product for a heating reaction at 130° C. for 1 hours and then 150° C. for 1 hour. As such, a bio-based epoxy resin solution was obtained. The solvent of the bio-based epoxy resin was removed to obtain a bio-based epoxy resin having an epoxy value of 0.063 mol/100 g. A co-solvent of 5 parts by volume of DMF and 1 part by volume of mPEG was added to the bio-based epoxy resin to form a coating having a solid content of 30%. The coating was coated on an aluminum foil by a wire rod, and then heated to 180° C. for 1 hour to solidify the coating, remove the solvent thereof, and intermolecular crosslink and/or intramolecular crosslink the epoxy groups and hydroxyl groups of the bio-based epoxy resin. The coating was solidified to form a film having a smooth and bright appearance, a pencil hardness of H, an adhesiveness of 100/100 as measured by a scotch tape test, and a solvent rub resistance for isopropanol or DMAc, but no solvent rub resistant for mPEG. Compared to Example 1, the film in Example 2 lacked of solvent rub resistance for mPEG should come from the low reactivity at the high temperature solidification. Therefore, the film had a low crosslink density and low solvent rub resistance. 
       Comparative Example 1 
       [0024]    25 g of lignosulfonate (DP651, commercially available from Bonegaard), 12.5 g of ethylene glycol, and 7.5 g of sulfuric acid (50% aqueous solution) were mixed to form a mixture. Subsequently, 25 g of 1,2,4,5-benzenetetracarboxylic anhydride was added to the mixture for a heating reaction at 130° C. for 3 hours, thereby forming a homogeneous liquid. 25 g of a multi-epoxy compound (epoxidized soybean oil, epoxy value of 0.4125 mol/g) was added to the homogeneous liquid for a heating reaction at 130° C. for 1 hours and then 150° C. for 1 hour. As such, a heterogeneous and dark brown liquid was obtained. The heterogeneous liquid stood to separate into two layers, which could not be coated on any substrate. 
         [0025]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.