New polyurethane and process for preparing same

Abstract: A new class of polyurethanes is provided in which the polyurethane contains a hard segment derived from the reaction of at least one polyisocyanate with cellulose, hemi-cellulose and/or lignin. The polyurethane preferably contains also a soft segment derived from a polyol conventionally used in the manufacture of polyurethanes. The new polyurethane containing such a hard segment exhibit improved mechanical and thermal characteristics

Description: This invention relates to a new polyurethane, and to a process of preparing the polyurethane. Various kinds of polyurethanes derived from various polyhydroxy ingredients and various polyisocyanates are known in the field of resins and plastics. In the production of polyurethanes, the polyhydroxy ingredient to be polycondensed with a polyisocyanate ingredient is generally a polyol compound or a sugar which is called a soft segment component capable of forming a soft segment by the reaction with a polyisocyanate. Up to the present, however, polyurethanes derived from lignocellulose or cellulose as a hard segment component have not yet been known in this art. In general, cellulosic substances including cellulose itself and derivatives thereof having unreacted hydroxyl groups are polymeric polyhydroxy compounds, i.e. polyhydroxy compound having a skeleton as a macromolecular polymer, and behave differently from monomeric polyhydroxy compounds such as saccharides. Among the cellulosic substances broadly termed, lignocellulose is contained not only in pulp as a main product in pulp industry but also in various kinds of by-products, agricultural waste materials, etc and is now regarded as a substance whose effective utilization is strongly desired. On the other hand, chemical modifications in various resinous materials including polyurethane are continuously studied in this art to improve their useful properties. Under the above mentioned circumstances, there is a great demand in the field of the agricultural industry, including the pulp industry, to find an effective use for lignocellulose as a chemical starting material and thereby developing a new art for improving the quality of various synthetic materials. WO86/07070 discloses a method for producing polyurethane by polymerizing polymeric isocyanate, polyol and kraft or other technical lignin which has been freed of high molecular weight fractions. Similarly, US-A-3577358 discloses the production of polyurethane by reacting lignin and an organic polyisocyanate in a solvent. WO-A-8103332 teaches a process in which a cellulose-containing plant is first reacted with a substantial amount of an alkali metal hydroxide at a high temperature in order to produce a water-soluble broken down alkali metal cellulose-containing plant polymer, which in turn is reacted with a salt-forming compound to produce a lignin-cellulose resinous product. This lignin-cellulose resinous product may then be dissolved in a solvent such as polypropylene glycol and reacted with an organic polyisocyanate such as tolylene diisocyanate so as to form a polyurethane-lignin cellulose product. DD-A-136845 discloses a process for the dissolution of lignocellulose in which the lignocellulose is first treated with a mineral acid such as sulfuric acid. The resulting mixture is filtered, dried at elevated temperature and then extracted using a polyol such as diethylene glycol. It is suggested that the resulting polyol solution could be used inter alia for the preparation of polymers. The present inventors have carried out extensive research on the effective utilization of lignocellulose and cellulose as a chemical starting material for producing synthetic materials. As a result of the research it has now been found that lignocellulose and cellulose which have not been digested with an acid or alkali have an excellent effect as a hard segment component for producing polyurethane and that the polyurethane thus obtained which contains therein a hard segment derived from the hard segment component is remarkably superior in mechanical and thermal characteristics to the existing polyurethanes usually derived from a polyol compound and a polyisocyanate. Accordingly, in accordance with the present invention in one aspect there is provided a new polyurethane which has been prepared from at least one polyhydroxy ingredient and at least one polyisocyanate ingredient, characterized by containing therein a hard segment derived from at least one polyhydroxy compound selected from lignocellulose and cellulose which have not been digested with an acid or an alkali. In accordance with a further aspect of the present invention, there is also provided a process for the preparation of a polyurethane, which comprises reacting a polyisocyanate ingredient with a solvent solution of a polyhydroxy ingredient comprising a polyhydroxy compound which is selected from lignocellulose and cellulose which have not been digested with an acid or alkali. As indicated, the polyhydroxy compound used in the present invention as a hard segment component is selected from chemically unmodified cellulose and lignocellulose. A mixture of these substances, or a composite cellulose such as pectocellulose can also be used in the present invention. It is important that substantially all the hydroxyl groups of the cellulose or lignocellulose should remain unmodified, since otherwise the polycondensation reaction with a polyisocyanate cannot generally proceed in a satisfactory manner. Thus, the use of, for example, acetylcellulose, methylcellulose or similar modified cellulose or modified lignin is not suited for the purpose of the present invention. Further, no merits are feasible by the use of such modified materials and, rather, modification causes considerable increase of costs. Examples of lignocellulose sources which can be used in this invention include wood dust, various kinds of pulp and their residues, bagasse, coconut shell, coffee bean parchment and the like plant tissues. If necessary, such lignocellulose can be extracted from wood by treating it, for example, with cresol-water under heating. The polyhydroxy compound can be used singly or as a mixture of at least two such compounds for polycondensation with the polyisocyanate ingredient. By the word "poly" used with respect to the polyhydroxy substance and the polyisocyanate ingredient is meant herein a number of two or more. Accordingly, the polyisocyanate may be a diisocyanate. The polyisocyanate ingredients to be reacted with the polyhydroxy compound in this invention are widely known in the production of polyurethane and are commercially available. Any of the known polyisocyanates such as those of aromatic series, aliphatic series and heterocyclic series can be used in the present invention. Illustrative of the polyisocyanate are, for example, 4,4'-diphenylamine diisocyanate (MDI), tolylene diisocyanate, phenylene diisocyanate and hexamethylene diisocyanate. These polyisocyanates are normally used singly, but may be used as a mixture of at least two such compounds. In the present invention, a polyol compound capable of forming, after the reaction with the polyisocyanate ingredient, a soft segment may be omitted but is usually employed together with the polyhydroxy compound. In case the polyol compound is used jointly with the polyhydroxy compound, the polyol compound may be used in excess. In this case, excess polyol compound can serve as a solvent for the polyhydroxy compound. The polyol compounds per se are widely known as reactants for the production of polyurethanes or polyesters and commercially available. The polyol compounds are roughly classified into those of polyether type and those of polyester type and any of these can be used in the present invention. Preferable examples of the polyol compound include polyethylene glycol, polypropylene glycol, polyethylene adipate, and polyethylene terephthalate. The polyurethane of this invention can be prepared according to a method known per se for the production of polyurethane by polycondensation. Any of the conventional catalyst known for the production of polyurethane, such as those of amine type and those of tin type can be used for accelerate the polycondensation reaaction. The use of a catalyst of tin type such as dimethyltin laurate is preferable. In accordance with the process of this invention, the polyhydroxy compound is dissolved, if necessary, together with the polyol compound in a solvent. Examples of the solvent in this case include tetrahydrofuran, dimethylsulfoxide and dioxane and other conventional solvents inert to the reaction. In case the polyol compound is used together with the polyhydroxy compound, the polyol compound can be used in excess, as described hereinbefore, whereby the polyol compound has a dual function as the polyhydroxy reactant and as a solvent for the polyhydroxy compound. The solution is then mixed under heating with the polyisocyanate ingredient to effect a polycondensation reaction of the reactants normally in the presence of the catalyst. In one embodiment of the process of this invention, water is allowed to exist in the polycondensation reaction system whereby the polyisocyanate is decomposed to form a polyurethane of foamy type. In this case, a conventional foam-controlling agent of silicone series may be added to the reaction system so as to obtain a uniformly foamed product. In another embodiment of the process of this invention, water is not allowed to exist in the reaction system whereby the product is obtained in the form of a solid resinous substance. Preferably, the proportion of the polyol compound to the polyhydroxy compound is 0-50, more preferably 0-30 per part by weight, or in other words, the polyol compound is used in an amount of 0-5000, preferably 0-3000 parts by weight per 100 parts by weight of the polyhydroxy compound. When the polyhydroxy compound and the polyol compound are dissolved in the solvent such as tetrahydrofuran, the proportion of the polyol compound to the polyhydroxy compound preferably is 0-0.95, more preferably 0-0.9 per part by weight, or in other words, the polyol compound is used in an amount of 0-95, preferably 0-90 parts by weight per 100 parts by weight of the polyhydroxy compound. The proportion of the diisocyanate ingredient to the polyhydroxy ingredient (the polyhydroxy substance alone or in mixture with the polyol compound) preferably is 0.1-10, more preferably 0.1-9 per part by weight, or in other words, the polyisocyanate ingredient is used in an amount of 10-1000, preferably 10-900 parts by weight per 100 parts by weight of the polyhydroxy ingredient. In order to obtain a foamy product, the proportion of water to both of the polyhydroxy ingredient and the polyisocyanate ingredient is 0.001-0.2, preferably 0.005-0.1, per part by weight, or in other words, water is used in an amount of 0.1-20, preferably 0.5-10 parts by weight per 100 parts by weight of both of the polyhydroxy ingredient and the polyisocyanate ingredient. The foam-controlling agent suitably is used in an amount of 0.001-0.5, preferably 0.02-0.25 parts by weight per 100 parts by weight of both of the polyhydroxy ingredient and the polyisocyanate ingredient. In case the polyol compound is used in excess as a solvent for the polyhydroxy compound in the process of this invention, a polyurethane derived from 5-90, preferably 10-70 % by weight of the polyhydroxy compound, 5-90, preferably 10-70% by weight of the polyol compound, and 5-90, preferably 10-70% by weight of the polyisocyanate ingredient can be obtained. In case a solvent other than the polyol comopund is used, a polyurethane derived from 5-90, preferably 10-70% by weight of the polyhydroxy compound, 0-90, preferably 10-70% by weight of the polyol compound and 0-90, preferably 10-70% by weight of the polyisocyanate ingredient can be obtained. It is generally preferable that the ratio by weight of the polyol compound to the polyhydroxy compound is set within the range of 0-20, preferably 0-10. The polyurethane of this invention containing a hard segment derived from at least one polyhydroxy compound selected from cellulose and lignocellulose is excellent in mechanical and thermal characteristics and is very economical in cost. In the polyurethane of this invention, its properties can easily be modified by allowing a soft segment derived from a polyol compound to exist together with the hard segment and varying the proportion of the hard segment to the soft segment. The new polyurethane may be incorporated with a conventional auxiliary substance such as anti-oxidant, UV-protecting agent or a colorant thereby improving weather-resisting property and appearance. The polyurethane of this invention can be used in the form of a foamy substance or a solid resinous substance in various fields of industry where existing polyurethanes are used. The present invention will now be illustrated by way of examples. Example 1 One part of a thermomechanical pulp residue from pine wood was mixed under heating (250°C) with 2 parts of polyethylene glycol 400 to form a solution. To 3g of this solution were added 6g of polyethylene glycol 400 and then 20g of crude MDI, 0.7g of a mixture of a foam-controlling agent of silicone series and water (1:1) and 5 drops of dimethyltin laurate, and the mixture was vigorously stirred. At the time of foaming being commenced, however, the stirring of the mixture was stopped. After the foaming proceeded completely, the foamed product was allowed to stand overnight. The polyurethane foam thus obtained was subjected to a compression test, as a result of which it was found that the foam had a compression elasticity (E/ρ) of 7.9 expressed in terms of 10²MPa.m²/kg. Example 2 One part of coffee bean parchment was mixed under heating with 2 parts of polyethylene glycol 400 in the same manner as in Example 1 to obtain a solution. To 3g of this solution was added 6g of polyethylene glycol 400, and the mixture was treated in the same manner as described in Example 1 to obtain a polyurethane foam, which had a compression elasticity (E/ρ) of 9.5. Example 3 One part of coffee bean parchment and 2 parts of polyethylene glycol 400 were mixed under heating to prepare a solution. To 3g of this solution was added 6g of polyethylene glycol 400, and the resultant mixture was incorporated at room temperature with 5 drops of dimethyltin laurate and then with 20g of crude MDI to effect polycondensation reaction whereby a polyurethane in the form of a solid mass was obtained, which had a tensile elasticity of 30 MPa. Example 4 One part of wood meal of pine was mixed with 1 part of polyethylene glycol 400 to form a solution. To 1.5g of this solution was added 6g of polyethylene glycol 400, and the mixture was treated in the same manner as described in Example 1 to obtain a polyurethane foam having a compression elasticity of 2.4 MPa. It is understood that the preceding representative examples may be varied within the scope of the present specification, both as to the reactants and conditions, by those skilled in the art to achieve essentially the same results.

Claims: A process for preparing a polyurethane comprising reacting a polyisocyanate ingredient with a solvent solution of a polyhydroxy ingredient comprising a polyhydroxy compound selected from lignocellulose and cellulose which have not been digested with an acid or alkali. A process according to Claim 1, wherein said polyhydroxy ingredient also comprises a polyol compound different from said polyhydroxy compound. A process according to Claim 2, wherein said polyhydroxy compound is soluble in said polyol compound, and wherein said polyol compound is present in excess and said excess polyol compound serves as solvent for said polyhydroxy compound. A process according to any preceding claim, wherein said polyisocyanate ingredient is present in the reaction mixture in an amount of 0.1 to 10 parts by weight per part by weight of said polyhydroxy ingredient. A process according to Claim 4, wherein said amount of said polyisocyanate ingredient is 0.1 to 9 parts by weight per part by weight of said polyhydroxy ingredient. A process according to any preceding claim, wherein the reaction is carried out in the presence of water whereby there is formed a foamed product. A process according to Claim 6, wherein said water is present in an amount of 0.001 to 0.2 part by weight per part by total weight of polyisocyanate ingredient plus polyhydroxy ingredient. A process according to Claim 7, wherein said amount of said water is 0.005 to 0.1 part by weight per part by total weight of polyisocyanate ingredient plus polyhydroxy ingredient. A process according to any one of Claims 6-8, wherein the reaction mixture also includes a foam-controlling agent for improving the uniformity of the foamed product. A process according to Claim 9, wherein the amount of said foam-controlling agent is from 0.00001 to 0.005 part by weight per part by total weight of said polyisocyanate ingredient plus polyhydroxy ingredient. A process according to Claim 3, or to any one of Claims 4-10 when appendant to Claim 3, wherein the amount of said polyol compound is up to 50 parts by weight per part by weight of said polyhydroxy compound. A process according to Claim 11, wherein said amount of said polyol compound is up to 30 parts by weight per part by weight of said polyhydroxy compound. A process according to Claim 2, or to any one of Claims 4-10 when appendant to Claim 2, wherein a separate solvent is used for said polyhydroxy compound and said polyol compound, and wherein the amount of said polyol compound is up to 0.95 part by weight per part by weight of said polyhydroxy compound. A process according to Claim 13, wherein said amount of said polyol is up to 0.9 part by weight per part by weight of said polyhydroxy compound. A polyurethane prepared by reaction between a polyisocyanate ingredient and a polyhydroxy ingredient, wherein the polyurethane contains a hard segment derived from a polyhydroxy compound selected from lignocellulose and cellulose which have not been digested with an acid or an alkali. A polyurethane according to Claim 15, wherein the polyurethane also contains a soft segment derived from a polyol which is different from said polyhydroxy compound. A polyurethane according to Claim 15 or Claim 16, which is in a foaming form. A polyurethane according to Claim 15 or Claim 16, which is in the form of a film or a solid mass.

Inventors: HATAKEYAMA HYOE, HIROSE SHIGEO, NAKAMURA KUNIO, YANO SHOICHIRO, HATAKEYAMA, HYOE, HIROSE, SHIGEO, NAKAMURA, KUNIO, YANO, SHOICHIRO
Applicants: AGENCY IND SCIENCE TECHN, DIRECTOR-GENERAL OF THE AGENCY OF INDUSTRIAL SCIENCE AND TECHNOLOGY
Application year: 1989
Main classification: C08G18
IPC codes: C08G18