Alkali-O2 oxidized lignin as dispersant
20180327311 ยท 2018-11-15
Inventors
Cpc classification
C08H6/00
CHEMISTRY; METALLURGY
International classification
Abstract
According to an example aspect of the present invention, there is provided a dispersant comprising alkaline-O.sub.2 oxidized lignin. Such dispersant may be used for example in inorganic pigments to reduce interactions between pigment particles and lower the viscosity of pigment mixtures, and thereby positively affect for example to the loading of fillers and pigments in paints and coatings, paper and board, constructions materials, printing inks and plastics. Dispersants may also be used in aiding the inorganic pigment grinding in the pigment mine. Another suitable use is as a plasticizer or as a retardant agent for construction materials, such as gypsum.
Claims
1. A dispersant comprising alkali-O.sub.2 oxidized lignin.
2. The dispersant of claim 1, further comprising being in a form of an aqueous solution and having a lignin content of 0.5-40 w-%, more preferably 5-25 w-%.
3. The dispersant of claim 1, further comprising being a water-soluble polyelectrolyte and having surface active properties.
4. The dispersant of claim 1, wherein the alkali-O.sub.2 oxidized lignin has a negative charge due to carboxylic structures and resonance stabilized quinone enol structures in lignin polymer.
5. The dispersant of claim 4, wherein the quinone enol structures are acidic hydroxyl-p-quinones.
6. A mixture or composition comprising a dispersant and at least one of: a pigment and a construction material, the dispersant comprising alkali-O.sub.2 oxidized lignin.
7. The mixture or composition of claim 6, wherein the dispersant content is 0.01-5 w-% of the mixture or composition.
8. The mixture or composition of claim 6, comprising an inorganic pigment.
9. The mixture or composition of claim 6 comprising a construction material.
10. The mixture or composition of claim 9, wherein the dispersant content is 0.1-5 w-% of the construction material.
11. A method for dispersing inorganic pigments comprising applying 0.01-5 w-% of an alkali-O.sub.2 oxidized lignin solution into a pigment mixture, thereby reducing interactions between pigment particles and lowering viscosity of the pigment mixture.
12.-15. (canceled)
16. The mixture or composition of claim 10, wherein the construction material is gypsum-based.
Description
[0022] Some of the embodiments of the present invention are described in
[0023]
[0024]
[0025]
[0026]
[0027]
[0028]
[0029] Thus, one aspect of the present invention is to disclose the dispersing performance of the alkali-O.sub.2 oxidized lignins in different inorganic pigment pastes. Reference is made to examples and figures of the present specification.
[0030] According to a preferred embodiment, the present invention discloses a novel dispersant comprising alkali-O.sub.2 oxidized lignin. Such dispersant is in a form of an aqueous solution and has a lignin content of 0.5-40 w-%, more preferably 5-25 w-%. Furthermore the dispersant is characterized by being a water-soluble polyelectrolyte and having surface active properties.
[0031] Alkali-O.sub.2 oxidation increases lignin hydrophilicity i.e. solubility, which is particularly advantageous for dispersing applications. Oxidized lignins are more soluble even though their molecular weight has increased when compared to the unmodified lignin. Unmodified soda wheat straw lignin is only soluble above pH 7, while alkali-O.sub.2 oxidized lignin is already soluble above pH 4 or above pH 5. The results indicate that oxidized lignins are also suitable for dispersing applications in the acidic pH range. According to one embodiment, the dispersant of the present invention is soluble in pH-areas above 3-4.
[0032] The method for alkali-O.sub.2 oxidation of the starting lignin material is described in WO 2015/049424, which is hereby incorporated by reference.
[0033] According to one embodiment, the alkali-O.sub.2 oxidized lignin samples have negative charge, which is originated from carboxylic structures and resonance stabilized quinone enol structures (i.e. acidic hydroxyl-p-quinones) in said lignin polymer. Part of the charge is due to the acidic, small molecular reaction products of lignin.
[0034] Furthermore, one embodiment of the present invention is a pigment mixture or a pigment composition comprising the alkali-O.sub.2 oxidized lignin as a dispersant. The pigment mixture or composition has such dispersant content of 0.01-5 w-%, more preferably 0.1-2 w-% of the pigment mixture or composition. In particular, the pigment is inorganic.
[0035] A method for dispersing inorganic pigments also belongs to the scope of the present invention. Such method comprises applying 0.01-5 w-%, more preferably 0.1-2 w-% of an alkali-O.sub.2 oxidized lignin solution into a pigment mixture, and thereby reducing interactions between pigment particles and lowering viscosity of the pigment mixture.
[0036] Inventors of the present invention have found out that the alkali-O.sub.2 oxidized lignin is at least equally as good dispersant as a typical synthetic dispersant, when used at least 1.5 times, such as 2 times more than said synthetic dispersant. Further observations conclude that the present alkali-O.sub.2 oxidized lignin is clearly better dispersant than non-oxidized lignin or lignosulfonate-based dispersant when used in same amounts. These findings are also described in the examples below.
[0037] Another aspect of the present invention is to disclose the performance of alkali-O.sub.2 oxidized lignin for plasticization and retarding of raw gypsum in comparison to traditional commercial plasticizers and set-retardants, such as citric acid (CA), tartaric acid (TA) and lignosulfonate. Reference is made especially to example 5 and
[0038] Herein gypsum is intended to cover its dihydrate (CaSO.sub.4*2H.sub.2O), hemihydrate (CaSO.sub.4*0.5H.sub.2O) and anhydrate (CaSO.sub.4) forms. It was observed by the inventors, that modified lignins of the present invention worked well under slightly acidic conditions (at about pH 6), whereas for example tartaric acid functions only at pH 9 or higher. Citric acid is a good plasticizer and retarder for acidic gypsum mix. However, in some cases both qualities might not be desired. For example, gypsum mortars might benefit from high dispersion state (high workability and density), whereas porous gypsum might need only retarding effect. Such effects can be modified in alkali-O.sub.2 oxidized lignins by altering the oxidation process.
[0039] Thus, one embodiment of the present invention is a construction material comprising the alkali-O.sub.2 oxidized lignin as a dispersant. The construction material has such dispersant content of 0.1-5 w-%, more preferably 0.1-2 w-% of the construction material. In particular, the construction material is gypsum-based, such as gypsum mortar or gypsum plasterboard.
[0040] Furthermore, a method for gypsum plasticization and hydration retarding belongs to the scope of the present invention. Such method comprises mixing 0.1-5 w-%, more preferably 0.1-2 w-% of an alkali-O.sub.2 oxidized lignin solution together with gypsum, and thereby dispersing gypsum particles and also slowing down the hydration effect.
[0041] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.
[0042] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases in one embodiment or in an embodiment in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.
[0043] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.
[0044] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.
[0045] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.
[0046] The verbs to comprise and to include are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of a or an, that is, a singular form, throughout this document does not exclude a plurality.
INDUSTRIAL APPLICABILITY
[0047] At least some embodiments of the present invention find industrial application as dispersants for inorganic pigments in paint and coating industry (for example for decorative coatings, industrial coatings, automotive coatings, as well as printing ink and packaging applications), in construction materials, in paper and board industry and in plastics. Another suitable application area is additives, for example in pigment mining, grinding, and storage. Inorganic pigments comprise for example TiO.sub.2, color-pigments, different forms of gypsum, clay, CaCO.sub.3 and carbon black. In addition to the plasticizing function, in gypsum (such as gypsum plaster, gypsum wall board and gypsum molds) the alkali-O.sub.2 lignins can be used as a retardant agent to slow down the typical fast reaction (hydration) of the material.
ExamplesMaterials and Methods
[0048] Production and characteristics of the oxidized lignin samples:
[0049] The alkali-O.sub.2 oxidations were conducted and the samples were characterized as described in WO2015/049424 (examples 1, 2, 5 and 6). The oxidation method and the sample characteristics have also been recently published by Kalliola et al. (2015). The alkali-O.sub.2 oxidation treatment increases the water solubility of lignin, thus converting it desirable for dispersing applications. In addition, the molecular weight of the lignin can be controlled using the oxidation parameters, especially by the pH.
[0050] Description of lignin samples, reference products, and inorganic pigments used in the examples are shown in the summary tables 1-3 below.
TABLE-US-00001 TABLE 1 Lignin samples (oxidized lignins i.e. dispersants of the invention and unmodified lignins) used in the following examples. Negative charge M.sub.w M.sub.n at pH 6 Sample code Description of sample (g mol.sup.?1) (g mol.sup.?1) M.sub.w/M.sub.n (mmol g.sup.?1) SL Commercial soda wheat 3880 2070 1.9 1.5 straw lignin*, unmodified SL 25% 1ox Commercial soda wheat straw 7320 2600 2.8 3.4 lignin, oxidized SL 15% 2ox Commercial soda wheat straw 6270 2390 2.6 5.1 lignin, oxidized SL constant Commercial soda wheat straw 4580 2020 2.3 6.5 pH ox lignin, oxidized SL constant Commercial soda wheat straw 3200 1650 1.9 6.9 pH 2ox lignin, oxidized IndAT Commercial softwood kraft 4500 2100 2.1 n.d. lignin**, unmodified IndAT c. pH ox Commercial softwood kraft 9670 2850 3.4 n.d. lignin, oxidized *Protobind? 1000 by GreenValue SA, **Indulin at by MeadWestvaco Corp. n.d. not determined.
TABLE-US-00002 TABLE 2 Reference products (dispersants, plasticizers, chemical) used in the following examples. Sample Description M.sub.w M.sub.n code of sample (g mol.sup.?1) (g mol.sup.?1) M.sub.w/M.sub.n WRDA 90D Commercial 3000 1700 1.8 lignosulfonate-based plasticizer Marasperse AG Commercial n.d. n.d. n.d. lignosulfonate-based dispersant Glenium Commercial synthetic 15900 5100 3.1 superplasticizer, Glenium C151 DISPEX Commercial synthetic 4510 1770 2.5 AA140 dispersant Citric acid Chemical used as 192 gypsum plasticizer and retarder, C.sub.6H.sub.8O.sub.7
TABLE-US-00003 TABLE 3 Pigments used in the following examples. Mean particle pH in Description size paste Pigment of pigment Supplier (?m) () PCC Precipitated CALOFORT?U 0.1 9.6 Calcium by Specialty Carbonate, CaCO.sub.3 Minerals Inc. Titanium TiO.sub.2 Uula v?ripigmentti 1.4 8.4 dioxide by Uula Kaolin Aluminum silicate, by Aquaminerals 2 6.7 Al.sub.2Si.sub.2O.sub.5(OH).sub.4 Kaolin Aluminum silicate by Aquaminerals 10 6.3 Gypsum ?-hemihydrate, by Knauf n.d. 6.0 CaSO.sub.4*0.5H.sub.2O
[0051] Dispersing performance of the oxidized lignins in different inorganic pigment pastes (examples 1-3);
[0052] Dispersing performance of the oxidized lignin solutions (dispersants of the invention) was evaluated in different inorganic pigment pastes in laboratory scale. Pigment and water were mixed efficiently using Heidolph DIAX 600 for 2 min. Thereafter, the oxidized lignin solutions were added in the paste and the mixing was continued for 2 min. Unmodified lignins and reference products were used in comparison. The pastes contained 34 to 70 w-% of pigment in water (including the dispersant solution). Dispersant dosages of 0.04-1.0 w-% (active matter) of pigment were used. The fluidity of the pastes was evaluated by measuring the shear stress as a function of shear rate by using a rheometer, Bohlin Visco. In general, the lower the shear stress, the better is the dispersing of the pigment particles.
[0053] Pastes were mixed with magnetic stirrer and ultrasound (Hielscher UP400S) with two 30 seconds sonication periods. Total mixing time was 2 minutes. Prepared pastes were measured with (Rheotest RN, measuring cell S1) rheometer. First experiments had constant 0.12% dispersion agent dosage (example 4).
[0054] Plasticization and reaction retarding performance of the oxidized lignins in raw gypsum (?-hemihydrate) paste (example 5):
[0055] Oxidized lignin solutions (dispersants of the invention) were used for gypsum paste plasticization and hydration retarding. Water and dispersants were mixed together. Thereafter, water/dispersant-solution was mixed with gypsum in 1:1-ratio vigorously for 30 seconds. Dispersant dosage of 0.5 w-% (active matter) of gypsum was used. Unmodified lignin and reference products were used in comparison. Immediately after mixing, the gypsum paste samples were placed into conduction calorimeter (TAM-Air). Hydration of hemihydrate is a highly exothermic reaction:
CaSO.sub.4*0.5H.sub.2O+1.5H.sub.2O.fwdarw.CaSO.sub.4*2H.sub.2O+Q
[0056] Gypsum hydration kinetics was followed by measuring heat flow of the paste. Time for maximum heat evolution and total heat content were measured. Also, the gypsum plaster height was measured after the complete hydration. Dispersant retardation effect was determined from the time to maximum heat evolution. Longer the time to reach maximum heat flow, greater is the retardation effect. Total evolved heat was used to evaluate total hydration degree. More heat the gypsum is able to generate, higher is the hydration degree. Gypsum plaster height presents the dispersant ability to disperse gypsum particles. Lower the plaster height, better the dispersing of the particles.
Example 1
PCC (Precipitated Calcium Carbonate, CaCO.SUB.3.) 34 w-% in Water (Including Dispersant Solution)
[0057] Dispersants of the invention decreased the yield stress in PCC paste demonstrating the dispersing performance. With a dose of 1.0 w-% on pigment, SL 25% 1 ox provided roughly the same yield stress than commercial synthetic dispersant (DISPEX AA140) with a dose of 0.25 w-%. The constant pH oxidation indicated also to be a means of producing an efficient dispersant: with a dose of 1.0 w-%, IndAT c. pH ox showed equal performance than DISPEX AA140 with a dose of 0.5 w-%. The dispersing performance of commercial lignosulfonate (Marasperse AG) was clearly lower than that of the oxidized lignin. Unmodified lignins were not providing decent dispersing effect (
Example 2
Titanium Dioxide (TiO.SUB.2.) 70 w-% in Water (Including Dispersant Solution)
[0058] Dispersant of the invention (SL c. pH ox) decreased the yield stress in TiO.sub.2 paste clearly better than the unmodified lignin (SL): about 45 Pa vs. 160 Pa with an equal dosing of 0.06%. The dispersing performance of SL c. pH ox was almost the same with a dosage of 0.06% than in the case of DISPEX AA4140 with 0.05%. Marasperse AG (0.05%) did not plasticize the paste enough, and thus the yield stress was too high to be measured.
[0059] In PCC paste (Example 1), the dispersants of the invention (SL 25% 1 ox, IndAT c. pH ox) functioning well had clearly higher molecular mass (Mw) if comparing to the results in the case of TiO.sub.2 paste, wherein the dispersant of the invention (SL c. pH ox) having rather low Mw showed high dispersing performance (
Example 3
Kaolin (Aluminum Silicate, Average Particle Size 2 ?m) 50 w-% in Water (Including Dispersant Solution)
[0060] Dispersants of the invention (SL c. pH ox) decreased the yield stress in kaolin more than the unmodified lignin (SL). With a dose of 0.12 w-% on pigment, SL c. pH ox provided roughly the same yield stress than commercial synthetic dispersant (DISPEX AA140) with a dose of 0.08 w-% (
[0061] After 3 days of preparing the kaolin paste with the dispersant of the invention (SL c. pH ox, 0.12%) the paste turns stable by light shaking. In the case of the reference dispersant (DISPEX AA4140, 0.12%) the paste could not be turned to a stable form by heavy shaking (since most of the pigments had settled/packed in the bottom of the plastic tube,
Example 4
Kaolin (Aluminium Silicate, Average Particle Size 10 ?m) 50 w-% in Water (Including Dispersant Solution)
[0062] Oxidation of lignin improved dispersing effect slightly. Commercial lignosulfonate (Marasperse AG) had lower effect than the lignin samples, whereas commercial synthetic dispersant (DISPEX AA4140) had better dispersing effect (
Example 5
Gypsum (CaSO.SUB.4.*0.5H.SUB.2.O) 50 w % in Water (Including Dispersant Solution)
[0063] According to the results, WRDA90D and unmodified lignin were not able to disperse the gypsum particles. Citric acid, Glenium and oxidized lignins (dispersant of the invention) showed almost equally high performance to disperse gypsum (
CITATION LIST
Patent Literature
[0064] WO 2015/049424
Non Patent Literature
[0065] Kalliola, A., Vehmas, T., Liiti?., T., Tamminen, T., 2015. Alkali-O2 oxidized ligninA bio-based concrete plasticizer. Industrial Crops and Products 74, 150-157.