EP4003931A1

EP4003931A1 - Gypsum compositions

Info

Publication number: EP4003931A1
Application number: EP20746576.6A
Authority: EP
Inventors: Max GIUDICI; Barbara CALLONI; Giuseppe PIRRONE; Alberto CESTONARO; Giovanni Floridi; Giuseppe Li Bassi
Original assignee: Lamberti SpA
Current assignee: Lamberti SpA
Priority date: 2019-07-22
Filing date: 2020-07-17
Publication date: 2022-06-01
Also published as: IT201900012597A1; WO2021013751A1

Abstract

The present invention relates to gypsum compositions comprising an alkyl hydrogenpolysiloxane and a depolymerized carboxymethyl cellulose and to a method for producing waterproof gypsum products, which comprises the use of said gypsum compositions.

Description

GYPSUM COMPOSITIONS

FIELD OF THE INVENTION

The present invention relates to a method for producing waterproof gypsum products which comprises the use of gypsum compositions comprising an alkyl hydrogenpolysiloxane and a depolymerized carboxymethyl cellulose.

The invention also relates to gypsum compositions comprising an alkyl hydrogenpolysiloxane and a depolymerized carboxymethyl cellulose. BACKGROUND OF THE ART

Certain properties of gypsum make it very popular for use in making industrial and building products. It is an abundant and inexpensive raw material which, through a process of dehydration and rehydration, can be cast, molded, extruded or otherwise formed into useful products. It is also non-combustible and relatively dimensionally stable.

Typical examples of gypsum products are gypsum wallboards, also known as plasterboards, which consist of a rehydrated gypsum core sandwiched between multi-ply paper cover sheets, that are commonly used for interior wall and ceiling applications.

Unfortunately, gypsum products, such as wallboards, gypsum tiles, gypsum blocks, gypsum bricks, and the like, are largely hydrophilic and easily absorb water which causes problems of degradation in their thermal insulation and heat retaining properties, generation of cracks, changes in size, etc.. Many attempts have been made in the past to reduce the water absorption (waterproofing) of gypsum products by hydrophobization of the gypsum raw materials. These attempts include the addition to the gypsum compositions used for the preparation of gypsum products of water-repellent compounds such as metallic soaps, asphalts, waxes, resins and polysiloxanes, in particular alkyl hydrogenpolysiloxanes.

The use of alkyl hydrogenpolysiloxanes to confer waterproofing properties in gypsum-based products is described, for example, in the patents US 3,455,710, EP 0 171 018 and US 5,814,411 among others. There are a number of theories that have been developed to try to explain the waterproofing mechanism of the alkyl hydrogenpolysiloxanes. The simplest involves two main reactions. The first hydrogenpolysiloxane reaction happens during the gypsum rehydration step and is a reaction with water at the hydrogen site to generate a hydroxyl group on the siloxane with a resulting hydrogen gas (H2) generation. The second reaction involves the cleavage of trimethylsilanol end groups to allow the formation of a highly crosslinked silicone resin, which forms a thin hydrophobic waterproof film on the surface of the gypsum particles.

The alkyl hydrogenpolysiloxanes are quite efficient water-repellent compounds, but, unfortunately, they are quite expensive and many efforts have been made to find compounds which allowed to reduce the amount of the hydrogen polysiloxanes that are required for giving appropriate waterproofing properties to the gypsum products. Some polysaccharides and/or derivatives thereof are among the compounds described in the art which are able to improve the waterproofing effect of alkyl hydrogenpolysiloxanes

For example, WO 99/50200 describes a method for damp-proofing gypsum plaster by adding to the plaster an alkyl hydrogenopolysiloxane and a galactomannan.

DE 10 220 659 relates to a composition for rendering gypsum water- repellent comprises an organosiloxane containing Si-bonded hydrogen atoms (hydrogenpolysiloxane) together with a starch ether.

US 2009/036572 discloses a method for waterproofing a gypsum-based product formed from a plaster-based composition comprising a linear or cyclic hydrogenpolysiloxane and a pregelified starch.

All these polysaccharides and/or derivatives thereof provides good performances, however, there is still the need in the field of finding other compounds which allow a further reduction of the concentration of the hydrogenpolysiloxanes in gypsum compositions.

Now, we have found that the addition of a specific depolymerized carboxymethyl cellulose markedly improves the performances of the alkyl hydrogenpolysiloxanes and provides to obtain waterproofing results superior to those obtained with other polysaccharides, thus allowing a further optimization of the production costs. In addition, the depolymerised carboxymethyl cellulose of the invention is easily soluble in water and it can be provided in the form of pourable concentrated aqueous solutions, allowing faster and easier preparation of gypsum compositions compared to the prior art polysaccharides.

As far as the Applicant knows, no one has described the use of a depolymerised carboxymethyl cellulose in combination with an alkyl hydrogenpolysiloxane for the production of waterproof gypsum products. US 7,294,195 describes a water-repellant composition for the production of wallboard containing a metal salt of an alkylsiliconate, such as NaOSi(OH)₂(CH₂)3NH2 NaO(OH)Si(CH₃)(CH₂)₃NH₂ or

KOSi(OH)₂(CH₂)₃NH₂, and a hydroxybased cellulose. Carboxymethyl cellulose is mentioned among the suitable hydroxybased cellulose, but no further specific information are provided and only hydroxyalkyl or alkyl hydroxyalkyl cellulose were used in the Examples. Moreover, the waterproofing mechanism of the metal salts of alkylsiliconates is completely different from that of the alkyl hydrogen siloxanes.

The term "gypsum", as used in the present application, includes calcium sulfate hemihydrate, calcined gypsum, anhydrite, stucco and gypsum.

In the following description, all parts and percentages are by weight, unless otherwise specified. DESCRIPTION OF THE INVENTION

It is therefore an object of the present invention a method of producing waterproof gypsum products which comprises the use of gypsum compositions comprising, based on 100 part by weight (pbw) of gypsum, a) from 0.005 to 2 pbw (active substance) of a depolymerized carboxymethyl cellulose (depolymerized CMC) having a weight average molecular weight comprised between 10,000 and 90,000 dalton (Da);

b) from 0.01 to 2 pbw of an alkyl hydrogenpolysiloxane.

It is another object of the invention a gypsum composition comprising, based on 100 pbw of gypsum :

a) from 0.005 to 2 pbw (active substance) of a depolymerized CMC having a weight average molecular weight comprised between 10,000 and 90,000 Da;

b) from 0.01 to 2 pbw of an alkyl hydrogenpolysiloxane.

DETAILED DESCRIPTION OF TH E I NVENTION

Preferably, the gypsum composition of the invention comprises, based on 100 pbw of gypsum :

a) from 0.01 to 1.5 pbw (active substance) of said depolymerized CMC; b) from 0.03 to 1.5 pbw of an alkyl hydrogenpolysiloxane.

In the gypsum compositions, the weight ratio of depolymerized CMC to alkyl hydrogenpolysiloxane is preferably from 10: 1 to 1 : 10, more preferably from 3: 1 to 1 : 3. The gypsum suitable for the realization of the present invention, can be, for example, plaster (CaS04_*l/2H₂0) in the form of building plaster, plaster of Paris or insulating plaster, or other types of gypsum, such as floor gypsum, Keene's cement, phosphogypsum, FGD gypsum, anhydrite or mixtures of plaster and slaked lime.

In one embodiment of the invention, the gypsum composition comprises more than 60 % by dry weight, preferably more than 80 % by dry weight, of gypsum.

According to a preferred embodiment of the invention, the depolymerized CMC has a weight average molecular weight comprised between 15,000 and 50,000 Da, more preferably from 17,000 to 45,000 Da.

The molecular weight of the depolymerized CMC is determined by gel permeation chromatography using a 0.1 M aqueous solution of ammonium acetate as eluent and a pullulane standard kit (see Characterization Method).

Advantageously, the depolymerized CMC has a degree of substitution (DS) ranging from 0.4 to 1.6, more preferably 0.6 to 1.2.

The expression "degree of substitution" means the number of carboxymethyl groups for each anhydroglycosidic unit of the cellulose; the DS is measured following the ASTM Standard Test Method D1439-

03. The Brookfield viscosity of the depolymerized CMC measured at 20 rpm and 20 °C in water solution at 25 wt% concentration is usually below 6500 mPa_*s, preferably below 4000 mPa_*s.

Usually, the depolymerized CMC of the invention is salified with alkali metal ions, such as sodium or potassium, or ammonium or quaternary ammonium ions. Preferably, the depolymerized carboxymethyl cellulose of the invention is salified with potassium or sodium ions, more preferably with sodium ions.

Many methods useful for the depolymerisation of carboxymethyl cellulose are known; we cite, by way of example, those reported in : EP 382 577, where enzymatic hydrolysed from cellulose derivative are described; GB 2,281,073, where the procedure for obtaining solutions of low viscosity carboxymethyl cellulose from the dissolution of solid mixtures of carboxymethyl cellulose and enzymes is described; EP 465 992, where a procedure for the depolymerisation of cellulose ethers with hydrogen peroxide in water is described; EP 708 113, where the obtainment of low molecular weight cellulose ethers by irradiation is described; and WO 2005/012540, which describes a procedure for the enzymatic depolymerization of medium viscosity carboxymethyl cellulose in the form of dispersed powder in a hydro-alcoholic heterogeneous medium.

Practically, all these methods are utilizable for the preparation of a depolymerized CMC suitable for the composition of the invention. Depolymerized CMC obtained from an enzymatic depolymerization process is the preferred choice.

The depolymerization methods can be applied both on purified or technical grade carboxymethyl cellulose having a DS ranging from 0.4 to 1.6, preferably from 0.6 to 1.2.

For example, the depolymerized CMC can be obtained from a technical grade carboxymethyl cellulose having a content of active substance of from 55 to 75 % by dry weight. Technical grade CMC are not washed after the etherification reaction and usually contain from 25 to 45 % by dry weight of the carboxymethylation by-products. These by-products are normally salts of chloride and glycolate, such as sodium chloride and sodium glycolate

Preferably, the depolymerized CMC of the invention is obtained from a purified CMC containing more than 96 by dry weight of active substance. The depolymerized CMC of the invention can be incorporated into the gypsum composition as solid or can be added as a concentrated liquid form. Generally, it is preferred to add the depolymerized CMC of the invention as a concentrated liquid solution or dispersion, more preferably as a concentrated solution.

According to a preferred aspect of the invention, the depolymerized CMC is added as a concentrated aqueous solution containing from 20 to 45 wt% (active substance) of depolymerised CMC, preferably from 27 to 37 wt% (active substance). Any alkyl hydrogenpolysiloxane commonly used in the field can be utilized for the realization of the present invention. The alkyl hydrogenpolysiloxanes described in the above mentioned patents are examples of suitable polysiloxanes.

For example, said alkyl hydrogenpolysiloxane can be chosen among the linear or cyclic hydrogenopolysiloxanes of Formula (I) or (II) shown below:

wherein

n and m are integers comprised between 0 and 200 and 1 and 200 respectively, m and q are integers comprised between 1 and 5 and 1 and 10 respectively, with l<n + m<200 and 3<p+q<10;

Ri and F are identical or different and represent independently: • a Ci-Cs linear or branched alkyl group, such as a methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, isobutyl, pentyl, hexyl and octyl group;

• a C₁-C₄ alkoxy group, such as a methoxy, ethoxy, propoxy, isopropoxy and n-butoxy group;

• a C₃-C₁₀ cycloalkyl group, such as a cyclopentyl or cyclohexyl group;

• a C₆-C₁₄ aryl group, unsubstituted or substituted by at least one Ci- C₄ alkyl radical or a C₂-C₁₂ alkenyl radical, such as a phenyl, naphthyl, tolyl, xylyl and ethylphenyl group;

· a aralkyl group in which the aryl portion is C₆-C₁₀ and the alkyl portion is C₁-C₄, such as a benzyl, phenylethyl, phenylpropyl or naphthylmethyl group, wherein said aryl groups can be substituted or non-substituted;

• a C₅-C₁₂ monocyclic or bicyclic heteroaryl group comprising at least one heteroatom chosen from 0, N and S;

• a C₂-C₁₂ alkenyl group, such as example a vinyl, allyl or crotonyl group.

Specific examples of alkyl hydrogenpolysiloxanes suitable for the realization of the present invention are methyl hydrogenopolysiloxanes such as SILRES® BS 94 and SILRES® BS 46 from Wacker Chemie AG.

Preferably, the alkyl hydrogenpolysiloxane of the invention is used as such in the form of an oil or in the form of an oil-in-water emulsion. The composition can comprise further additives commonly used in the field, such as dispersants, for example polyphosphates or low molecular weight polyacrylic acids, foaming agents, such as ethoxylated alcohols or ethoxylated alcohol sulfates, ethoxylated fatty acids and the like; setting accelerators, such as potassium sulfate and aluminum sulphate; setting retarders, such as proteins or tartaric acid salts; lightening products, rheology modifiers, fillers or fibers, such as silica or cellulose fibers; other functional additives such as starch, silicone oil, waxes and the like.

The gypsum composition can be in the form of powder or of moldable mass.

Usually, the gypsum composition in the form of moldable mass contains, based on 100 pbw of gypsum, from 30 to 110 pbw, preferably from 40 to 80 pbw, of water.

The gypsum composition can be prepared following any conventional method and equipment known in the art.

Preferably, a concentrated solution of depolymeryzed CMC is diluted with water and mixed with the alkyl hydrogenpolysiloxane. Then the dry gypsum powder or a aqueous gypsum slurry is added to this mixture for obtaining, after stirring, the inventive gypsum composition.

The gypsum compositions of this invention can be used to prepare waterproof gypsum products, such as cast, molded or extruded articles, for example plasterboards, gypsum tiles and gypsum bricks, or to prepare wallboard coatings and products for filling joints or similar spaces, for example, in preparing filler materials, joint sealants, plaster cements and gypsum plasters.

EXAMPLES

Characterization Methods

The Brookfield (BRK) viscosity of the CMC solutions was measured with a DV-E Brookfield® viscometer at 20 °C and at 20 rpm.

The degree of substitution (DS) of the carboxymethyl cellulose was measured following the ASTM Standard Test Method D1439-03 (Degree of Etherification).

The active matter content of the carboxymethyl cellulose is determined following the ASTM Standard Test Method D 1439-03 (Purity).

The active matter content of the solution of depolymerized carboxymethyl cellulose was calculated from the matter content subtracting the amount of salts (acids, bases, buffers, and the like) added in the depolymerization process.

Gel permeation chromatography (GPC) was used to determine the weight average molecular weight (Mw), by using the following method. The determinations were performed on depolymerized CMC solutions prepared by dissolving at a concentration of 0.3 % w/vol of sample in 0.10 M ammonium acetate ("mobile phase solution").

Pullulanes with molecular weights ranging from 180 to 788000 Da were used as molecular weight standards. 25 microliters of each solution, filtered on a 0.45 micron membrane filter, were injected into a HPLC equipped with an evaporative light scattering detector.

The following columns were used at a temperature of 60 °C: SupelcoProgel - TSK G3000 PWXL, G5000 PWXL, G6000 PWXL, and Progel-TSK PWXL guard columns. The HPLC was set at a flow rate of 0.8 ml/min for 50 minutes.

Water Uptake Tests

The water uptake tests were performed following the standard UNI EN 520: 2009 with some modification.

The lower the water uptake, or percent uptake, the more hydrophobic the gypsum composition can be considered and, as a consequence, the more waterproof a gypsum product prepared by using this composition can be.

Scagliola Extra (CaS0_4*l/2H₂0 provided from Nuova Siga S.r.L, Italy) was used in all the Examples.

For the preparation of gypsum composition of the invention, an aqueous solutions of depolymerized CMC (D-CMC), obtained by enzymatic depolymerization of a purified sodium CMC having a DS of about 0.75, was used. The solution had a active matter content of 35 wt% and a BRK viscosity of about 4,000 mPa_*s. The weight average molecular weight of the CMC obtained from the depolymerisation was about 23,000

Da. A low viscosity hydroxyl propyl guar (HPG) in powder form was used as comparative polysaccharide. The HPG had a hydroxypropyl molar substitution (MS) of about 0.25 and showed a BRK viscosity at 20 °C and 20 rpm, measured on a 10 wt% water solution, of 16,450 mPa_*s.

The gypsum compositions were prepared by adding the depolymerized CMC solution or the HPG into a plastic beaker containing 330 g of water. The mixture were stirred for about 20 seconds (180 sec for HPG) using a MAVER ALC W 750 rod stirrer equipped with a cowles blade (1400 rpm). Subsequently, an methyl hydrogenpolysyloxane (SILRES® BS 94 from Wacker Chemie AG) was added to the beakers and mixed for another 30 seconds. 750 g of Scagliola Extra were then slowly poured into the mixture to minimize dusting. The gypsum compositions so obtained were mixed for 120 seconds and, after this period, were transferred into disc PVC molds having inside dimensions of 8 cm (diam.) by 4 cm (h.).

The gypsum compositions were allowed to solidify in the moulds for 1 hour in a climatic chamber set at 23 °C and 50% humidity. The gypsum discs so obtained were then removed from the molds and transferred in an oven at 40 °C for 24 hours. After the drying step, the discs were removed from the oven and allowed to cool in a desiccator for 1 hour at room temperature.

The gypsum discs were then weighed and immersed in water for two hours. After the extraction from water, the discs were allowed to drain and wiped up. Finally, the gypsum discs were weighed to determine the amount of water uptake.

These tests were conducted at differing weight percents of methyl hydrogenpolysiloxane and depolymerized CMC (or HPG) in comparison with gypsum compositions which did not contain polysaccharides. The amount in grams of the additives and the % water uptake (average of three replicates) of each Example are shown in Table 1.

Table 1

^comparative

The results demonstrate that the depolymerized CMC of the invention is able to markedly increase the waterproofing performances of the alkyl hydrogen siloxanes and allows to reach waterproofing effects near the limit of determination of the standard method.

Claims

1) A gypsum composition comprising, based on 100 part by weight (pbw) of gypsum :

a) from 0.005 to 2 pbw as active matter of a depolymerized carboxymethyl cellulose (depolymerized CMC) having a weight average molecular weight comprised between 10,000 and 90,000 Dalton (Da);

b) from 0.01 to 2 pbw of an alkyl hydrogenpolysiloxane.

2) The gypsum composition of claim 1, comprising, based on 100 pbw of gypsum :

a) from 0.01 to 1.5 pbw as dry matter of said depolymerized CMC; b) from 0.03 to 1.5 pbw of an alkyl hydrogenpolysiloxane.

3) The gypsum compositions of claim 1 and 2, wherein the weight ratio of depolymerized CMC to alkyl hydrogenpolysiloxane is from 10: 1 to 1 : 10.

4) The gypsum compositions of claim 3, wherein the depolymerized CMC has a weight average molecular weight comprised between 15,000 and 50,000 Da.

5) The gypsum composition of claim 1, comprising, on 100 parts by weight of gypsum, from 30 to 110 parts by weight of water.

6) The gypsum composition of claim 5, comprising, on 100 parts by weight of gypsum, from 40 to 80 parts by weight of water. 7) A method of producing waterproof gypsum products, which comprises the use of gypsum compositions according to claims from 1 to 6.

8) A method for the preparation of gypsum compositions according to claims from 1 to 6, comprising the use of a concentrated depolymerized CMC aqueous solution containing from 20 to 45 % by weight as active matter of depolymerized CMC.

9) The method of claim 8, wherein said concentrated aqueous solution is diluted with water and mixed with an alkyl hydrogenpolysiloxane; subsequently, a dry gypsum powder or an aqueous gypsum slurry is added to the obtained mixture.

10) The method of claim 9, wherein the alkyl hydrogenpolysiloxane is used as such in the form of an oil or in the form of an oil-in-water emulsion.