Gypsum compositions containing crosslinked cellulose ethers for mortars with reduced stickiness

Abstract

The present invention provides dry mix compositions for use in making gypsum plasters or mortars comprising gypsum, preferably, phosphorous gypsum one or more retarder, and one or more crosslinked cellulose ethers containing polyether groups. The compositions enable the provision of gypsum dry mixes, such as those from phosphorus gypsum, that make gypsum mortars with less stickiness while reducing the amount of cellulose ether in the dry mix.

Claims

1. A dry mix composition for use in making gypsum plasters or mortars having reduced stickiness comprising gypsum, one or more retarder, and one or more crosslinked cellulose ethers containing polyether groups in an amount of from 0.1 to 0.4 wt. % of total solids.

2. The dry mix composition as claimed in claim 1, wherein the gypsum comprises from 20 to 100 wt. %, based on the total weight of gypsum solids, of a phosphorous gypsum.

3. The dry mix composition as claimed in claim 1, wherein the amount of the gypsum ranges from 60 to 99.7 wt. % of total solids in any composition other than a lime plaster and wherein, in lime plaster, the amount of the gypsum ranges from 40 to 96.7 wt. % of total solids and the amount of lime ranges from 3 to 20 wt. % of total solids.

4. 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.

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

6. The dry mix composition as claimed in claim 1, wherein the polyether group in the one or more crosslinked cellulose ethers is a polyoxyalkylene which has from 2 to 20 oxyalkylene groups.

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

8. The dry mix composition as claimed in claim 1, wherein the one or more crosslinked cellulose ethers is a polyoxypropylene group containing hydroxyethyl methylcellulose.

9. The dry mix composition as claimed in claim 1, wherein the amount of the one or more retarder ranges from 0.02 to 0.1 wt. % of total solids.

10. A method of using the dry mix composition as claimed in claim 1, comprising combining the dry mix composition with water or aqueous liquid to make a mortar and applying the mortar to a substrate and letting the applied mortar dry.

Description

EXAMPLES

(1) The following materials were used.

(2) Phosphorous gypsum dry powder (a mixture of hemihydrate gypsum, multiphase gypsum & perlite (Engis, BE), containing, as indicated, air-entrainment agents, retarders and other additives, such as starch ethers.

(3) The phosphorus gypsum material was mixed with 4% wt. lime hydrate, 0.025% wt. sodium lauryl sulfate, 0.05% wt. tartaric acid, 0.035% wt. starch ether and 0.25% wt. cellulose ether. The resulting material was used as a dry mix powder.

(4) Unless otherwise indicated, the hydroxyethyl methylcellulose (HEMC) cellulose ether used was that available as WALOCEL MKX 40,000 PP01 cellulose ether (Dow, Midland, Mich.). Viscosity of a 2% aq. solution is 40,000 to 50,000 mPas, Haake Rotovisko RV 100, shear rate 2.55 s.sup.1, 20 C.

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

(6) ##STR00001##
wherein n is 5.7-6.7.

Synthesis Example 1

(7) Ground cellulose flock (1.5 mol) was added to a 5 L autoclave. After purging the autoclave trice with nitrogen gas, the reactor is heated to 40 C. Then dimethylether (DME, 4.7 mol/mol AGU), and methyl chloride (MCI 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.

(8) Then the amount of crosslinker (Epilox M985 crosslinker) specified in Table 1, below, (from 0 to 0.0025 mol crosslinker/mol AGU) was dissolved in 20 ml isopropanol and added to the cellulose ether (HEMC) product in six increments in 30 second intervals. Using this poly(propyleneglycol) diglycidylether crosslinker, no additional reaction time other than dosage time was required to crosslink the cellulose ether.

(9) The mass was heated to 80 C. in 45 minutes. At 80 C. MCL 2 (1.3 mol/mol AGU) is 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. Following this, the product was washed in hot (>95 C.) water, neutralized with formic acid, granulated, dried and milled.

(10) Cellulose ethers were tested and characterized as discussed below in the form of aqueous solutions and, as well, in gypsum mortars having the indicated compositions.

(11) Gypsum mortars in tests discussed below contained the above mentioned gypsum dry mix composition of 95.6 wt. % of a phosphorous gypsum material, having a particle size of 73%<0.063 mm as determined by air jet sieving. Each indicated cellulose ether was added as an aqueous solution to eliminate the influence of different cellulose ether particle sizes or particle size distributions on the stickiness. To make the aqueous solutions, the indicated cellulose ethers were added to water as needed to arrive a final water/solid weight ratio of 0.55; the water/solid ratio of 0.55 was kept constant for all experiments. Each cellulose ether aqueous solution was added to phosphorous gypsum dry mix material in the amount of indicated in Table 2, below, as a wt. % of total solids.

(12) Rheology Test Methods:

(13) Loss Factor at Yield Point (Tan ):

(14) A rheological oscillation test was run with each gypsum mortar to measure the ratio of loss modulus (G) to shear storage modulus (a) to get the loss factor (tan =G/G), or a loss factor (tan ) taken at the yield point of the gypsum mortar. The yield point itself is the point at, and beyond which, the gypsum mortar becomes viscous. The tan is a function of plaster stickiness; thus, a lower tan value indicates less stickiness of a given material; the lower the tan , the better. The indicated materials containing cellulose ether and phosphorous gypsum dry mix material were mixed in a Z2-DIN-beaker using a Krups 3 (speed) Mix 3003 mixer (Krups GmbH, Solingen, DE) for 15 s at mixer level 1 and then an additional 45 s at mixer level 3. The test was run with each gypsum mortar at 20 C. using a Universal Dynamic Spectrometer UDS 200 rheometer (Physica Messtechnik GmbH, Stuttgart, DE). In the test, the indicated gypsum mortar and the indicated cellulose ether was filled into a cylinder and deformed in an oscillatory fashion with a vane spindle at a shear flow at 2 Hz. The measurement followed the method described in the literature of Baumann, R. et al., Controlling the application performance of cement renders with cellulose ethers, ZKG 4 2010, ZKG (Cement Lime Gypsum) International, Bauverlag BV, GmbH, Guterslh, DE, pp 68-75. The phosphorous gypsum plaster was subjected to a sweep of the stress amplitude from 0-1500 Pa.

(15) The tan stickiness of the crosslinked cellulose ethers of the present invention was tested in the indicated gypsum mortar compositions and, as a compared with the tan of the same amount of the same cellulose ether, absent crosslinking, in the same gypsum mortar composition. Results are shown in Table 2, below.

(16) Gel Strength or n/m:

(17) A rheological oscillation test was run with the indicated cellulose ethers as a 1.5 wt. % aqueous solution in 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 cellulose ether solution at 20 C. room temperature using a Universal Dynamic Spectrometer UDS 200 rheometer (Physica Messtechnik GmbH, Stuttgart, DE). In this test, the cellulose ether solution has an enhanced gel strength if n/m is between 0.8 and 1.2.

(18) In the test, a vane spindle was used and, its angular frequency () in rad/s was changed in such a manner that there were in total 6 measured points in the range of () from 0.1 to 1. The storage modulus (G) and loss moduls (G) in Pascal were measured as a function of angular frequency (). In a logarithmic plot of modulus in Pascal versus angular frequency (), where n and m are, respectively, the slope of a line defined by log G and the slope of a line defined by the log G, the value of n/m corresponds to the gel strength of the cellulose ether.

(19) Measurements of storage modulus (G) and loss moduls (G) in Pascal and angular frequency () for the various cellulose ethers tested in the Examples are given in Tables A-1 to A-2, below.

(20) TABLE-US-00001 TABLE A-1 Gel Strength of Hydroxyethyl Methyl Cellulose Ether (HEMC) Example 1* log log G log G 0 1.06069784 1.2764618 0.19997064 0.88195497 1.15533604 0.40011693 0.6919651 1.02938378 0.60032628 0.48572143 0.88817949 0.80134291 0.26717173 0.74193908 1 0.04532298 0.57634135 slope 1.0176 0.6970 R: 0.9982 0.9967 n/m 1.46 *Denotes Comparative Example

(21) TABLE-US-00002 TABLE A-2 Gel Strength of Cellulose Ethers Example 3 log log G log G 0 1.478566496 1.42488164 0.199970641 1.411619706 1.32221929 0.400116928 1.336459734 1.26007139 0.600326279 1.235528447 1.17318627 0.801342913 1.146128036 1.09342169 1 1.041392685 0.99694925 slope 0.4402 0.4159 R: 0.9940 0.9968 n/m 1.06

(22) The ratio n/m (gel strength) is reported in Table 1, below. As shown in Table 1, the ratio (n/m) of the inventive polyether group containing crosslinked cellulose ethers is in the desired range of from 0.8 to 1.2. The gel strength of the inventive polyether group containing crosslinked cellulose ethers is greater than that of the same cellulose ether in comparative Example 1 that is not crosslinked. This is surprisingly the case even with the very slight degree of crosslinking.

(23) TABLE-US-00003 TABLE 1 Crosslinked Cellulose Ether Compositions EXAMPLE 2 3 *1 (HEMC) Crosslinker 0.0025 0.0025 0.0000 (mol/mol) V.sup.1 mPa .Math. s 4888 5367 4370 DS(M) 1.51 1.49 1.59 MS(HE) 0.22 0.24 0.32 Gel Strength or 1.20 1.06 1.46 Ratio n/m.sup.2 .sup.1V = Viscosity of a 1 wt. % in water, Haake Rotovisko RV 100 rheometer, shear rate 2.55 s.sup.1, 20 C.; *Denotes Comparative Example.

(24) TABLE-US-00004 TABLE 2 Tan Values for Cellulose Ethers In Gypsum Mortar Cellulose Ether Example Addition Rate (%) tan .sup.1 1* HEMC from Table 1 0.25 0.52 1* HEMC from Table 1 0.19 0.51 2 from Table 1 (invention) 0.19 0.45 3 from Ex. 3, Table 1 0.19 0.42 (invention) .sup.1standard deviation <1%; *denotes Comparative Example.

(25) As shown in Table 2, above, at an amount of 0.19 wt. %, a comparative cellulose ether (HEMC) gives a tan value (within margin of error) of about 0.51. Using the same amount of an inventive crosslinked cellulose ether (CL HEMC) in Examples 2 and 3 significantly decreased the tan values. Accordingly, the inventive gypsum mortar has a much lower stickiness compared to the comparative gypsum mortar containing HEMC, and gives acceptable stickiness in a phosphorous gypsum containing mortar. It was not expected that a phosphorous gypsum mortar would give acceptable smooth running application characteristics like a gypsum mortar containing a natural gypsum source.