CEMENTITIOUS TILE ADHESIVE COMPOSITIONS CONTAINING CROSSLINKED CELLULOSE ETHERS FOR MORTARS WITH ENHANCED GEL-STRENGTH

Abstract

The present invention provides cementitious tile adhesives comprising ordinary Portland cement, sand or another inorganic filler, and from 0.12 to 0.6 wt. % of total solids of one or more polyether group containing crosslinked cellulose ethers. The present invention also provides methods of making the polyether group containing crosslinked cellulose ethers comprising crosslinking a cellulose ether at 90 C. or less, in an inert atmosphere, e.g. nitrogen, in the presence of a polyether group containing crosslinking agent and in the presence of alkali; the process may comprise part of a stepwise addition process of making of a cellulose ether itself in which the crosslinking of the cellulose ethers precedes at least one addition of alkyl halide or alkylene oxide to form, respectively, alkyl or hydroxyalkyl groups on the cellulose.

Claims

1. A dry mix composition for use in making cementitious tile adhesives or mortars comprising from 20 to 35 wt. % of ordinary portland cement, from 64.7 to 79.9 wt. % of sand or an inorganic filler, and one or more crosslinked cellulose ethers containing polyether groups in the amount of from 0.12 to 0.6 wt. % of total solids.

2. The dry mix composition as claimed in claim 1, wherein at least one of the one or more crosslinked cellulose ethers is a mixed cellulose ether that contains hydroxyalkyl groups and alkyl ether groups.

3. The dry mix composition as claimed in claim 2, wherein the one or more crosslinked cellulose ethers is chosen from hydroxyethyl methylcellulose (NEMC), hydroxypropyl methylcellulose (HPMC), methyl hydroxyethyl hydroxypropylcellulose (MHEHPC), and ethylhydroxyethyl cellulose (EHEC).

4. The dry mix composition as claimed in claim 1, wherein the polyether group in the crosslinked cellulose ethers is a polyoxyalkylene which has from 2 to 100 oxyalkylene groups.

5. The dry mix composition as claimed in claim 1, wherein the polyether group in the crosslinked cellulose ethers is a polyoxyalkylene chosen a polyoxyethylene, a polyoxypropylenes and combinations thereof.

6. The dry mix composition as claimed in claim 1, wherein the crosslinked cellulose ether is a polyoxypropylene group containing hydroxyethyl methylcellulose.

7. A method of using the dry mix compositions as claimed in claim 1, comprising combining the dry mix composition with water or aqueous liquid to make a mortar, applying the mortar to the unfinished side or backside of one or more tiles, placing the mortar containing backside of the one or more tiles on a substrate, and letting the mortar set.

8. A method of making polyether group containing crosslinked cellulose ethers comprising crosslinking at 90 C. or less, in an inert atmosphere, a cellulose ether in the presence of a polyether group containing crosslinking agent in an amount of from 0.0001 to 0.05 eq to form a crosslinked polyether group containing cellulose ether, wherein the unit eq represents the molar ratio of moles of the respective crosslinking agent relative to the number of moles of anhydroglucose units (AGU) in the cellulose ether; and, granulating and drying the resulting crosslinked polyether group containing cellulose ether.

9. The method as claimed in claim 8, wherein the polyether group containing crosslinking agent having two or more crosslinking groups chosen from halogen groups, glycidyl groups, epoxy groups, and ethylenically unsaturated groups that form ether bonds with the cellulose ether in crosslinking the cellulose ether.

10. The method as claimed in claim 8, wherein the crosslinking of the cellulose ethers takes place in the reactor in which the cellulose ether itself is made and in the presence of caustic or alkali.

11. The method as claimed in claim 8, wherein the crosslinking of the cellulose ethers precedes one or more addition of alkyl halide in the presence of alkali to form alkyl ethers of the cellulose.

Description

EXAMPLES

[0048] The following materials were used:

[0049] Epilox M985 poly(propyleneglycol) diglycidylether crosslinker (Leuna-Harze GmbH, Leuna, Del.) is a linear poly(propyleneglycol) diglycidylether made from polypropylene glycol (PPG) having a molecular weight of 400 daltons and having the formula below;

##STR00001##

wherein n is 5.7-6.7.

Synthesis Example 1A

[0050] Ground cellulose flock (1.5 mol) was added to a 5 L autoclave. After purging the autoclave trice with nitrogen gas, the reactor was heated to 40 C. Then dimethylether (DME, 4.7 mol/mol AGU), and methyl chloride (MCl 1; 3.2 mol/mol AGU) were injected into the autoclave. Caustic soda (NaOH, strength 50 wt. % aqueous, 1.9 mol NaOH/mol AGU) was added in 3 portions during 2 minutes at a temperature of 40 C. The reaction mixture was held at 40 C. for 30 minutes. Ethylene oxide (0.45 mol/mol AGU) was then added and the reaction mixture was held for 10 min at 40 C.

[0051] The mass was heated to 80 C. in 45 minutes. At 80 C., methyl chloride MCl 2 (1.3 mol/mol AGU) was injected quickly to the mass. Afterwards, NaOH (0.67 mol/mol AGU) was added in 7 portions over 30 minutes followed by a 70 minute cook-off time at 80 C. Thus, an extra addition of methyl chloride followed the crosslinking reaction. Following this, the product was dewatered and washed in hot (96 C.) water, neutralized with formic acid, granulated, dried and milled.

Synthesis Example 2

[0052] The synthesis in Example 1 was repeated except on a larger scale, where ground cellulose flock (400 mol) was added to a 1000 L autoclave.

Synthesis Example 3

[0053] The synthesis in Example 1 was repeated, except that after ethylene oxide addition and heating to 40 C. for, 10 min, the crosslinker (Epilox M985 crosslinker, 0.0025 mol crosslinker/mol AGU) was dissolved in 20 ml isopropanol and added to the cellulose ether (NEMC) product in six increments in 30 second intervals. Then the mass was heated to 80 C. for 45 minutes and MCl was added and the synthesis completed.

[0054] Using this poly(propyleneglycol) diglycidylether crosslinker, no additional reaction time other than dosage time was required to crosslink the cellulose ether.

Synthesis Example 4

[0055] The synthesis in Example 3 was repeated, except that 0.003 mol/mol AGU of the crosslinker was added.

Synthesis Example 5

[0056] The synthesis in Example 4 was repeated, except on a larger scale, where ground cellulose flock (400 mol) was added to a 1000 L autoclave.

[0057] Cellulose ethers were tested and characterized as discussed below in the form of aqueous solutions and, as well, in tile adhesive mortars having the indicated compositions.

[0058] Gel Strength: A rheological oscillation test was run with the indicated cellulose ethers as a 1 wt. % aqueous solution similar to the manner described in U.S. patent pub. no. 2004/0127700A1 at pages 2 and 3, paragraphs [0035]-[0044], page 6, paragraphs [0095] to [0105]). The test was run with each indicated cellulose ether solution at 20 C. using a Universal Dynamic Spectrometer UDS 200 rheometer (Physica Messtechnik GmbH, Stuttgart, Del.). The indicated cellulose ether or crosslinked cellulose ether was dissolved in water in the amount of 1.0 parts by weight of the cellulose ether, on a dry basis, and 99.0 parts per weight of water. To make the aqueous solution, the cellulose ether was dispersed over 1 minute in the water at room temperature with stirring to avoid the formation of lumps. Afterwards the mixture was stirred at 1000 rpm for 10 min. Then over 24 h, the solution was stored in a round glass vessel tightly sealed with a lid and rotated slowly about its longitudinal (horizontal) axis for the full 24 hours.

[0059] In the test, a cone/plate of 50 mm diameter, cone of 1 cone angle and 0.05 mm flattening of the cone point was used and, its angular frequency () in radians/s was changed in the range of () from 0.1 to 100 with a deformation of 0.5%. The storage modulus (G) and loss modulus (G) in Pascal were measured as a function of angular frequency (). The material being measured is called a gel if G is greater than G. A plot of modulus (in Pa) versus angular frequency (in rad/s) reveals two lines sloping up to the right, one for each of G and G. At a lower angular frequency, loss modulus (G) will be greater than storage modulus (G). The angular frequency () at the intersection of the lines G and G, where G and G are identical, is defined as the Crossover point. At angular frequencies lower than this cross over point the materials show no gel characteristics above the cross over point is shows gel characteristics. The earlier the crossover point, the greater the gel strength of the cellulose ether.

[0060] The characteristics of the various cellulose ether materials tested in the Examples are shown in Table 1, below.

TABLE-US-00001 TABLE 1 Characteristics of Crosslinked Cellulose Ethers 1* 1A* 2* Example (HEMC) (HEMC) (HEMC) 3 4 5 Crosslinker w/o w/o w/o 0.0025 0.003 0.003 (mol/mol AGU) DS-M 1.60 1.52 1.64 1.53 1.55 1.67 MS-HE 0.28 0.25 0.3 0.24 0.21 0.27 Viscosity.sup.1 9460 5212 9800 14150 12990 12800 (mPas, 1%) Crossover 18.9 6.0 1.3 4.8 2.7 Point () Viscometer, shear and T (a 1 wt. % in water, Haake Rotovisko RV 100 rheometer, shear rate 2.55 s.sup.1 20 C.); *Denotes Comparative Example.

[0061] As shown in Table 1, above, Examples 3, 4 and 5 exhibit a crossover point at a substantially lower angular frequency versus comparative Examples 1 A and 2 by anywhere from 20% to over 90%. Accordingly, the data consistently show enhanced gel strength of the crosslinked cellulose ether of the present invention when compared to commercial HEMC in the same use.

[0062] The gel strength of the inventive crosslinked cellulose ethers surprisingly results even with the very slight degree of crosslinking.

[0063] Cementitious tile adhesive formulations for an economic tile adhesive were tested. Tile adhesives in Batch A comprised ordinary portland cement (OPC, CEM I 42.5) 30 wt. %, and silica sand (Type F34 Quarzwerke Frechen, Frechen, PSD 99%<0.355 mm as measured by sieve machine EML 200 digital plus, Haver & Boecker, Oelde, Del.) 70 wt. %, and the indicated crosslinked or comparative cellulose ether in the indicated amounts, all amounts being wt.% of total solids. See Tables 3 and 4, below. Tile adhesives in Batch B comprised ordinary portland cement (OPC, CEM I 42.5) 30 wt. %, and silica sand (Type F34, Quarzwerke Frechen, Frechen, DE, PSD 100%<0.500 mm as measured by sieve machine EML 200 digital plus, Haver & Boecker, Oelde, Del.) 70 wt. %, and the indicated crosslinked or comparative cellulose ether in the indicated amounts, all amounts being wt. % of total solids. See Table 2, below.

[0064] All tile adhesive materials were combined as dry mix to which water was added to make a mortar in following manner: Water was filled into a Toni Technik laboratory mixer (Toni Technik, Berlin, Del.) and 1 kg of the dry mix was added within 15 seconds while mixing on speed 1 (lower speed). After addition of the dry mix was completed, mixing was continued for another 30 seconds. After waiting for one minute during which the mortar was removed from the mixer blade, the mortar was again mixed for one minute at speed 1. After this the mortar was allowed to ripen for five minutes. After this period the mortar finally was mixed for 15 seconds on speed 2 (high mixing speed).

[0065] Test Methods: Cement Tile Adhesives were tested, as follows:

[0066] Adhesive Strength: The adhesive strength of CBTA compositions was determined according to European Standard EN 1348 (DIN EN 1348, Beuth Verlag GmbH, Berlin, Del, 2007). In such tests, the tensile adhesive strength is determined following storage of adhered tiles under the conditions: Normal storage (7 d) adhered tiles stored for 7 days under standard climate conditions of 23 C. and 50% relative humidity; and, normal storage (28 d) adhered tiles stored for 28 days under standard climate conditions of 23 C. and 50% relative humidity.

[0067] Stirring test in order to determine water demand: This test determines the consistency of the mortar and the optimum water-to-solid ratio. One mixes 100 g of a dry mix for a tile adhesive into a 150 ml cup with a defined quantity of water. The mixture is stirred for 30 s with a wooden stirrer (hardwood, 250135 mm), stirring for up to an addition 60 s if the mixture fails to become homogeneous after 30 s. The consistency of the adhesive, its initial thickening behavior (i.e. time thickening begins after mixing), shear stability, and stirring resistance are observed. Then, the entire sample is removed from the cup using the wooden stirrer and its surface and standing strength is determined. To determine standing strength, as much of the mortar sample as can be held on narrow side of the stirrer is removed from the cup and is visually observed after 30 s to assess mortar paste consistency. To determine shear stability, the mortar sample is returned to the cup and is left to set for 5 min. Then, the sample is stirred again for 1 min, during which its thickening behaviour, shear stability and stirring resistance are assessed. Then the standing strength (shear stability after further stirring) on the wooden stirrer and the surface of the adhesive are assessed for the second time. Standing strength and shear stability are visually assessed for mortar paste consistency, as follows:

TABLE-US-00002 100% = full standing strength 97.5% = almost no movement of the tile adhesive 95% = slow continual movement 92.5% = faster continual movement 90% = faster continual movement, still good cohesion, but runs off 85% = adhesive is difficult to pick up and tears off abruptly <80% = adhesive cannot be properly taken up onto the wooden stirrer, adhesive has a thin/runny consistency. [0068] An acceptable result is at least 95%; a preferred result is at least 97.5%.

[0069] Water Demand: The stirring test is used to assess a proper water dosage for preparing a mortar paste with a laboratory mixer. The water demand is reported as the fraction of the total weight of the mortar which comprises water. The amount of water (dosage) reported for evaluating each CBTA formulation is that which resulted in 100% for standing strength assessment and 97.5% or more for assessment of shear stability for the mortar pastes.

[0070] Table 2, below summarizes the findings of the assessment of cement tile adhesives formulated as a Batch B containing the indicated amount of the indicated crosslinked cellulose ethers of the present invention in comparison to cellulose ethers which are not crosslinked.

[0071] In Table 2, below, the cellulose ether of comparative Example 1*, above was used in comparative Example 6*; and, the cellulose ether of Example 3, above was used in Examples 7, 8 and 9.

[0072] As shown in Table 2, below, at an addition rate of 0.3 wt. % of total solids, in the same mortar compositions with various cellulose ethers, the water demand of the crosslinked cellulose ethers of the present invention in Example 7 is higher than the same cellulose ether in comparative Example 6 which is not crosslinked; this effect is caused by the higher viscosity of the inventive crosslinked cellulose ethers. The adhesion strength in one case, Example 7, (after 28 d) is at the same level with the HEMC in comparative Example 6. However, in Examples 8 and 9 containing a significantly lower addition rate of the inventive crosslinked cellulose ethers show that the water demand is as low as with the comparative HEMC of Example 6 in the same mortar; however, the adhesion strength values in Examples 8 and 9 are significantly higher than in the comparative Example 6. Apparently, a lower absorption of the crosslinked cellulose ether to cement particles in early (first few hours) cement hydration at the lower low cellulose ether loading below 0.29 wt. %), thereby resulting in faster cement hydration and higher final adhesion strength.

TABLE-US-00003 TABLE 2 Cement Tile Adhesives with Crosslinked Cellulose Ethers 6* (0.3 wt. % 7 (0.3 8 (0.27% 9 (0.25% EXAMPLE HEMC) wt. %) wt. %) wt. %) Viscosity.sup.1 (mPas) 9460 14150 14150 14150 water demand 0.21 0.225 0.215 0.21 stirring test standing strength (%) 100 100 100 100 shearing strength (%) 97.5 97.5 97.5 97.5 adhesive strength 0.69 0.87 0.96 (N/mm.sup.2) EN 1348 7 d; nc (23 C./50%) adhesive strength 0.72 0.72 0.83 0.85 (N/mm.sup.2) EN 1348 28 d; nc (23 C./50%) .sup.11% aq. soln (Haake Rotovisko RV 100 rheometer, shear rate 2.55 s.sup.1, 20 C.); *Denotes comparative Example.

[0073] In a separate Batch A, cementitious tile adhesives were made with cellulose ethers produced on a laboratory scale and the results are shown in Table 3, below. The HEMC of comparative Example 1 was used in Example 10 and the Crosslinked cellulose ether of Example 4 was used in Examples 10 and 11.

TABLE-US-00004 TABLE 3 Cement Tile Adhesives with Crosslinked Cellulose Ethers 10* (0.3 wt. % 11 12 EXAMPLE HEMC) (0.3 wt. %) (0.27 wt. %) Viscosity.sup.1 (mPas) 9460 12990 12990 water demand 0.21 0.23 0.225 stirring test standing strength (%) 100 100 100 shearing strength (%) 97.5 97.5 97.5 adhesive strength (N/mm.sup.2) 0.72 0.75 0.8 EN 1348 28 d; nc (23 C./50%) *Denotes comparative Example; .sup.11 wt. % sol'n in water, Haake Rotovisko RV 100 rheometer, shear rate 2.55 s.sup.1, 20 C.

[0074] As shown in Table 3, above, at the same loading of crosslinked cellulose ethers in comparative Example 10 and Example 11, the crosslinked cellulose ethers of the present invention provide slightly higher adhesion strength; however, at lower cellulose ether addition rates, the crosslinked cellulose ethers of the present invention provide substantially higher adhesion strengths.

[0075] In another separate Batch A, cementitious tile adhesives were made using cellulose ether that had been produced on a pilot plant scale and the results are shown in Table 4, below.

TABLE-US-00005 TABLE 4 Cement Tile Adhesives with Crosslinked Cellulose Ethers 12* (0.2 wt. % 13 (0.18 wt. % EXAMPLE Ex 2* HEMC) Ex. 5 CL CE) Viscosity.sup.1 (mPas) 9800 12800 water demand 0.21 0.21 stirring test standing strength (%) 100 100 shearing strength (%) 97.5 97.5 adhesive strength (N/mm.sup.2) 0.51 0.8 EN 1348 28 d; nc (23 C./50%) *Denotes comparative Example; .sup.11 wt. % sol'n in water, Haake Rotovisko RV 100 rheometer, shear rate 2.55 s.sup.1, 20 C.

[0076] As shown in Table 4, above, the inventive crosslinked cellulose ether in Example 13 gave a tile adhesive having a substantially higher adhesion strength than the same tile adhesive with the same cellulose ether that was not crosslinked in comparative Example 12. The remaining tile adhesive properties were comparable.