HYDRAULIC BINDER COMPOSITION
FIELD OF THE INVENTION
The present invention relates to dry compositions comprising a hydraulic binder,
such as cement or gypsum, and a water retention agent which is a highly
substituted hydroxypropyl guar derivative comprising an unsubstituted linear or
branched C6-C8 alkyl chain.
BACKGROUND OF THE ART
It is well known to use hydraulic binder compositions in the construction field
for making the infrastructure of buildings, works of art, apartment buildings or
articles such as paving slabs or boards and tiles, and as adhesives or jointing
compositions, particularly to adhere tiles or ceramics in general, vertically or
horizontally, to plane surfaces of different kinds, such as to concrete, plywood
or brick surfaces.
In the present text with the term "hydraulic binders" we designate mineral
substances that in the presence of water harden because of hydration chemical
reactions and can bind other materials together.
Hydraulic binder compositions that mainly consist of cement mixed with a
variable amount of sand and possibly gypsum are generally used to prepare tile
adhesives, mortars, concrete, cement plaster, finiture plaster, self-levelling
flooring; hydraulic binder compositions based on gypsum are generally used to
prepare gypsum plasters and joint compounds.
Immediately prior to use, a proper amount of water is added to the dry hydraulic
binder composition, making it a workable paste and allowing the shaping of
articles or the application on various surfaces.
The curing of the thus obtained hydraulic binder paste (from now on "paste"),
also commonly referred to as "setting", begins as soon as the composition is
admixed with water and will result in its complete hardening and its exhibiting
the necessary physical and mechanical features.
Setting is a rather complex chemical process that leads to polymeric inorganic
structures whose strong reciprocal interactions result in the formation of solid
and strong masses.
In the setting process, many features are of importance and influence not only
the speed at which setting occurs but also its final effectiveness, i.e. its solidity.
Among these features of fundamental importance are the content of water and
the capability of the composition to retain the proper amount of water during the
whole setting process. It is important that the paste retains sufficient water until
all the desired physical characteristics are obtained.
In practice, most of the surfaces onto which pastes are generally applied are
porous and absorbent and they absorb water from the paste in the area of
contact, thus creating defects in the setting which may at some point in time
result in defects of the adhesion and of the mechanical properties of the
hardened composition.
Another problem that may be encountered during the application of pastes that
is related to the capability of the paste to retain the proper amount of water
during the whole setting process is a too rapid hardening that prevents the
adjustment of the laid strata or of the shaped articles. This problem is called
"lack of open time" and/or "lack of adjustability time".
Yet another problem occurs when the content of water becomes excessive, even
if only locally or because of a lack of homogeneity of mixing. In such cases,
setting becomes too slow due to a too flowing mixture, working time grows
longer and the resulting application becomes imprecise and difficult.
Another issue in the handling of pastes is the fact that water in the mixture acts
as a lubricant for the solid particles when paste is spread on the surface of the
object to which it is to be applied. The proper amount of water gives to the
mixture the "pastiness" or "creaminess" suitable for a uniform, homogeneous
and easy laying. The rheological characteristics of the final mixture are very
important and they depend on the kind and on the amount of the different
components in the mixture.
The rheology of a mixture of sand, cement and water alone, or of gypsum and
water alone renders them unsuitable for use as pastes because of the lack of the
above-mentioned characteristics, and more generally, because of their poor
processing.
To overcome all these problems, additives are used in the formulation of
hydraulic binder compositions acting as retention agents and rheology
modifiers. These additives are generally synthetic or semi-synthetic polymers,
usually chemically modified natural polymers, exhibiting the specific
characteristic of bonding and coordinating a large amount of water once they are
dissolved in water.
These products, and among these in particular cellulose ethers, are highly
purified products whose preparation requires many sophisticated and complex
purification steps. They are rather expensive products.
In literature many mixtures are described for use as rheology modifier and
retention aid in pastes, such as in US 6,706,1 12 , US 4,028,127, EP 2355 13, US
5,432,215, and US 4,487,864, in which mixtures are also described whose
components show synergic effects.
In particular, US 6,706,1 12 discloses cementitious mortar additives including at
least a hydroxyalkyl guar ether having a molar substitution of from about 0.7 to
about 3 which is able to impart to mortars very good water retention and an
initial adhesion as good as the adhesion of mortars that include cellulose ethers.
Nonetheless, it would be desirable in the art of preparing cement and/or gypsum
pastes to provide additives that further improve the water retention properties
and, as a consequence, the whole processing of such pastes.
Surprisingly, it has now been found that highly substituted hydroxypropyl guar
ethers that further comprise a certain amount of relatively short hydrophobic
unsubstituted alkyl chains impart improved water retention and processability to
cement and/or gypsum pastes.
Hydrophobic hydroxypropyl guar derivatives bearing C 10-C32 hydrophobic
substituents have been described in the patent literature, by way of example in
US 4,870,127 and US 4,960,876; they are said to be suitable for use in many
industrial fields, such as in the manufacture of paper coatings and sizings,
adhesives, liquid detergents, emulsions used to make polishes, cleaners and
lattices, in compositions for textile printing and dyeing, and as textile binders
and adhesives, in water borne coatings, as suspending agents in agricultural
sprays and as suspending agents for pigments and inks, in the photographic
processing and in the manufacture of ceramics, in cosmetics, in the general
fields of mining, explosives and oil stimulation.
US 4,870,127 also reports the synthesis of a hydroxypropyl guar derivative
comprising a C6-alkyl chain.
US 7,355,039 describes the use of glyoxalated purified hydrophobic
hydroxypropyl guar derivatives bearing hydrophobic C10-C32 alky! chains for
use in water based paints and varnishes, wall coverings, adhesives and mortars.
None of the above prior art, however, does disclose or suggest that highly
substituted hydroxypropyl guar derivative comprising an unsubstituted linear or
branched C6-C8 alkyl chain are particularly effective as water retention agents in
compositions comprising a hydraulic binder.
SUMMARY OF THE INVENTION
In one aspect, the invention is a dry composition comprising a hydraulic binder
and from 0 .1 to 2.0 %wt of at least one compound which is a hydroxypropyl
guar derivative comprising unsubstituted linear or branched C ,-C8 alkyl chains.
In another aspect, the object of the invention is 2-hydroxypropyl-2-hydroxy-3-
(2-ethylhexyloxy) propyl guar having hydroxypropyl molar degree of
substitution (MSHP) from 1.0 to 3.0 and alkyl degree of substitution (DSA^) from
0.01 to 0.20.
In still another aspect, the invention is a hydraulic binder paste prepared by
admixing a dry composition comprising a hydraulic binder and from 0.1 to 2.0
%wt of at least one compound which is a hydroxypropyl guar derivative
comprising unsubstituted linear or branched C6-C8 alkyl chains with an amount
of water of from about 10 to about 85 parts by weight for 100 parts by weight of
the dry composition.
DETAILED DESCRIPTION OF THE INVENTION
The hydroxypropyl guar ethers are derivatives of a renewable raw material
substrate, which due to their low production cost are desirable as replacements
for other products now in use.
Guar, or guar gum, is a polysaccharide belonging to the family of
galactomannans and is extracted from a leguminosae, "Cyamopsis
Tetragonolobus", that grows in the semi-dry region of tropical countries,
particularly in India and in Pakistan.
Its hydroxyethyl and hydroxypropyl ether derivatives, obtained by reacting guar
with ethylene oxide or propylene oxide under basic conditions, are commonly
employed in the textile industry as printing paste thickeners, in the paints and
coatings industry as rheology modifiers, in the drilling industry, in paper and
explosives production and in other industry sectors (Industrial Gums 3rd Ed.,
1993, Academic Press Inc., pp 199-205).
The polysaccharidic molecule of guar consists of a main linear chain of polymannose
bearing branches of galactose units in a molar ratio of about 2:1.
The hydroxypropyl ethers commercially available generally have hydroxypropyl
molar substitution from 0.2 to 3.
Many attempts have been made to positively modify the characteristics of guar
derivatives and specifically of hydroxypropyl guar ethers and to make them
suitable for use in mortars, as reported by way of example in US 6,706,1 12 and
in US 7,355,039.
Surprisingly, it has now been determined that hydroxypropyl guar derivatives
characterized by comprising unsubstituted linear or branched C6~C 8 alkyl chains
are particularly suitable as additives for the preparation of pastes based on
cement or gypsum, being able to impart to them excellent water retention
properties, without altering their additional applicative characteristics, such as
adhesion and final strength.
A further relevant advantage of the guar derivatives of the present invention is
the fact that they can be used in crude form as they guarantee good
performances without the need of a purification step after their preparation, and,
as a consequence, they are obtainable at a substantially low factory cost.
The hydroxypropyl guar derivatives useful for the present invention are
hydroxypropyl guar derivatives having MSHP from 1.0 to 3.0, preferably from
1.5 to 2.0, and DS^ from 0.01 to 0.20, preferably from 0.02 to 0. 10.
For the purposes of the present invention, the hydroxypropyl molar degree of
substitution, that is the average number of moles of hydroxypropyl groups
linked per monosaccharidic unit, is abbreviated "MSHp" and is determined by
Ή-NMR (effective molar substitution).
For the purposes of the present invention, the C6-C8 alkyl degree of substitution,
that is the average number of moles of unsubstituted linear or branched C6-C8
alkyl chains linked per monosaccharidic unit, is abbreviated "DSA k " and is also
determined by 1H-NMR (effective degree of substitution).
The unsubstituted linear or branched C6-C8 alkyl chains may be introduced by
reacting the hydroxypropyl guar with a linear or branched C6-C8 alkyl halide, or
with a linear or branched Cg-C 10 1,2 epoxide, or with a linear or branched C6-C8
alkyl glycidy] ether, obtaining respectively an alkyl ether derivative, a
hydroxyalkyl ether derivative and a 2-hydroxy-3-(alkyloxy) propyl ether
derivative.
Particularly preferred for use as water retention agents in compositions
comprising a hydraulic binder are hydroxypropyl guar derivatives comprising nhexyl
chains or 2-ethylhexyl chains.
The most preferred hydroxypropyl guar derivative is 2-hydroxypropyl-2-
hydroxy-3-(2-ethylhexyloxy) propyl guar.
The dry compositions of the present invention generally contain from 5 to 80 %
by weight of cement and/or gypsum as the hydraulic binder; preferably, in case
the hydraulic binder is gypsum, the amount of hydraulic binder is from 40 to
80% by weight, while in case the hydraulic binder is cement, its amount ranges
from 5 to 60% by weight.
The cement may be Portland cement or a Portland cement admixture or a non-
Portland hydraulic cement, such as calcium aluminate cement, calcium
sulfoaluminate cement, pozzolan lime cement.
Preferred cements are Portland cement and Portland cements admixtures (by
way of example, slag Portland cement, pozzolan Portland cement, fly ash
Portland cement, blastfurnace Portland cement and all the Portland cement
admixtures defined in standard EN 197-1 A3).
The gypsum may be calcium sulphate hemihydrate or anhydrite, most preferably
is calcium sulphate hemihydrate.
Dry compositions comprising cement mixed with a variable amount of sand and
possibly gyspum serve as the base materials for producing mortars, grouts,
concrete, tile adhesives, cement plaster, finiture plaster, self-levelling flooring
Cement based dry hydraulic binder compositions may also be reinforced with
fibres for the manufacture of fibrocements used, for example, as a material for
making articles for covering roofs, pipework or tanks.
The hydroxypropyl guar derivative comprising unsubstituted linear or branched
C6-Cg alkyl chains is also an efficient additive for controlling the filtration of
liquids from cement compositions. Moreover, it exhibits a better resistance to
high temperatures than the natural polymers currently used in the cementing of
oil wells. As a consequence, the dry compositions according to the invention in
which the hydraulic binder is cement may also serve as the base material for
hydraulic binder pastes useful for the cementation of oil wells.
Dry compositions based on gypsum are used to prepare gypsum plasters, joint
compounds, gypsum mortars and grouts.
Typical additional ingredients of cement based dry hydraulic binder
compositions are fine and coarse aggregates (sand and/or gravel).
Beside cement and/or gypsum, water retention agent and possibly aggregates,
there are several other additives that can be added to the hydraulic binder
composition of the invention before or during mixing with water.
Organic polymeric binders are typical additional ingredients of hydraulic binder
compositions for tile adhesives, joints compounds and self-levelling floorings;
calcium carbonate is usually present in gypsum and cement mortars and plasters,
in joint compounds and self levelling flooring compositions.
Other chemical additives that may be present are usually classified according to
their function; they act as air-entraining, water-reducing, retarding, accelerating,
plasticizers and superplasticizers aids.
Other varieties of additives fall into the specialty category, whose functions
include corrosion inhibition, shrinkage reduction, workability enhancement,
bonding, damp proofing, and colouring.
Hydraulic binder pastes may be prepared from the above described dry
compositions, by adding gradually the dry composition to water and mixing.
The correct amount of water is the one that allows to obtain the paste in the form
of a uniform slurry that has good workability.
Normally this amount ranges from about 10 to about 85 parts by weight of water
per 100 parts by weight of dry composition, and preferably from about 10 to
about 45 parts by weight per 100 parts by weight of dry composition when the
hydraulic binder is cement, from 35 to 80 parts by weight per 100 parts by
weight of dry composition when the hydraulic binder is gypsum.
EXAMPLES
Preparation of the water retention agents.
Preparation of n-hexyI-2-hydroxypropyl guar (nC6HPG)
In a 5 litres stirred reactor, 800 g of guar flour are charged at room temperature,
the reaction atmosphere is made inert by means of vacuum/nitrogen washings,
and, under vigorous stirring,106 g of a 30% solution of NaOH mixed in 250 g of
a water/isopropanol solution are added. The stirring is continued for 15 minutes
at 20°C.
The reactor is evacuated and filled three times with nitrogen and 530 g of
propylene oxide are added in three batches while stirring for 4 hours at 65-70°C.
When the pressure into the reactor is stable 127g of n-hexyl bromide,
previously dissolved in isopropanol, are added and the stirring is continued at
70-75°C over 2h.
The reaction mixture is cooled down to 40°C and neutralised by addition of
acetic acid to pH about 5 - 6.5.
The isopropanol is distilled in vacuum for 20 minutes.
The obtained reaction mixture is dried on a fluid bed drier by using hot air until
the humidity content is about 3% by weight, milled and analysed.
The obtained product (WRA No. 1) has DSAk - 0.05 and MSliP = 1.6.
Analogously, the water retention agents (WRA) reported in Table 1 were
prepared.
The RVT Brookfield ® viscosities (VB) of the water retention agents are
measured in aqueous solutions at 2 % by weight (WRA No. 1-6) or at 1% by
weight (WRA No. 7), at 20°C and 20 rpm, and are reported in Table 1.
Table 1
^comparative
1) n-propyl-2-hydioxypropyl guar
2) n-butyl-2-hydroxypropyl guar
3) n-decyl-2-hydroxypropyl guar
4) at 2% by weight
5) at 1% by weight
Preparation of 2-Hydroxypropyl-2-hydroxy-3-(2-ethyIhexyloxy) propyl
guar (bCgOHPG)
In a 5 litres stirred reactor, 800 g of guar flour are charged at room temperature,
the reaction atmosphere is made inert by means of vacuum/nitrogen washings,
and, under vigorous stirring, 106 g of a 30% solution of NaOH mixed in 250 g
of a water/isopropanol solution are added.
The stirring is continued for 15 minutes at 20°C temperature; 43 g of 2-ethylhexyl
glycidyl ether diluted in isopropanol (50 g) are added and the mixture is
stirred over 15 minutes.
The reactor is evacuated and filled three times with nitrogen and 530 g of
propylene oxide are added in three batches while stirring for 6 hours at 65-70°C.
The reaction mixture is cooled to 40°C and neutralised by addition of acetic acid
to pH about 5 - 6.5.
The isopropanol is distilled off in vacuum for 20 minutes.
The obtained reaction mixture is dried on a fluid bed drier by using hot air until
the humidity content is about 3% by weight, milled and analysed.
The obtained product (WRA No. 8) has DSAK = 0.03 and MSHP = 1.7.
Analogously, the other water retention agents reported in Table 2 were prepared;
the comparative WRAs were prepared from butylene oxide and from hexadecyl
glycidyl ether.
The RVT Brookfield ® viscosities (VB) of the water retention agents are
measured in aqueous solutions at 1% by weight (WRA No. 8-9) or at 2% by
weight (WRA No. 10- 12), at 20°C and 20 rpm, and are reported in Table 2.
Application tests
The application tests were done to determine the water retention properties and
consistency of compositions comprising the water retention agents of the
Examples.
The methods used in the application tests are the following:
Water Retention (WR) is measured according to standard test method ASTM
C1506-09.
Consistency (C) is measured according to standard test method ASTM
C230/230M-08.
The tests were performed both on a cement plaster composition and on a
gypsum plaster composition.
The cement plaster composition comprising Portland cement as the hydraulic
binder was prepared by adding 2 1 parts by weight of water and 0.1 parts by
weight of WRA per 100 parts by weight of dry mix (Composition 1).
The results are reported in Table 3.
The plaster composition comprising gypsum as the hydraulic binder was
prepared by adding 64 parts by weight of water and 0.25 parts by weight of
WRA per 100 parts by weight of dry mix (Composition 2).
The results are reported in Table 4.
The results show that the additional presence of unsubstituted linear or
branched C6-C8 alkyl chains remarkably improves the water retention properties
of highly substituted hydroxypropyl guar and makes them excellent rheology
modifiers and water retention agents for hydraulic binder compositions, both
based on gypsum and on cement.
Table 2
Comparative
1) 2-hydroxybutyl-2-hydroxypropylguar
2) 2-hydroxypropyl-2-hydroxy-3-hexadecyloxypropyl guar
3) determined by GC-MS
) at 1% by weight
5) at 2% by weight
Table 3 - Cement plaster
*comparative
I) hydroxypropyl guar having MSHP = 1.7
Table 4 - Gypsum plaster
*comparative
hydroxypropyl guar having MSHP
CLAIMS
1. Dry composition comprising a hydraulic binder and from 0.1 to 2.0 %wt
of at least one compound which is a hydroxypropyl guar derivative
comprising unsubstituted linear or branched C6-Cg alkyl chains.
2. Dry composition according to claim 1 wherein the hydraulic binder is
cement and/or gypsum.
3. Dry composition according to claim 2 comprising from 5 to 80 wt% of
hydraulic binder.
4. Dry composition according to claim 2 wherein the hydraulic binder is
Portland cement or a Portland cement admixture.
5. Dry composition according to claim 2 wherein the hydraulic binder is
calcium sulphate hemihydrate.
6. Dry composition according to any of claims from 1 to 5 wherein the
hydroxypropyl guar derivative has a MSHP from 1.0 to 3.0 and DSAk from
0.01 to 0.20.
7. Dry composition according to claim 6 wherein the hydroxypropyl guar
derivative has a MSHP from 1.5 to 2.0 and DSAk from 0.02 to 0.10.
8. Dry composition according to claim 6 or 7 wherein the hydroxypropyl
guar derivative is 2-hydroxypropyl-2-hydroxy-3-(2-ethylhexyloxy)
propyl guar
9. Dry composition according to any of the claims from 1 to 8 comprising
from 0.1 to 7 wt% of a polymeric organic binder.
10. 2-Hydroxypropyl-2-hydroxy-3-(2-ethylhexyloxy) propyl guar having
MSHp from 1.0 to 3.0 and DSAk from 0.01 to 0.20.
11.Hydraulic binder paste prepared by admixing a dry composition
according to any of claims from 1 to 9 with an amount of water of from
about 10 to about 85 parts by weight for 100 parts by weight of the dry
composition.