Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF MAKING A FOAMED HYDRAULIC BINDER BASED PRODUCT
BACKGROUND OF THE INVENTION
This invention relates to a method of making a product from a hydraulic
binder and a foam, and to the product so made.
Foams generated from organic compound solutions in water, for addition to
pastes formed from a hydraulic binder and water, are known. Examples of
suitable organic compounds for the manufacture of such foams are
polyvinyl alcohols, various surface active agents and proteinaceous
compounds. Foamed hydraulic binder products produced from these
foams tend to suffer from foam instability. This in turn leads to foams with a
large or irregular cell size, which in turn leads to variable density through
the thickness of the final product, limitations as to product density control,
and to the danger of foam collapse during processing.
On the other hand, when a foam is used which leads to a very fine cellular
structure, then the resulting product has excellent thermal. acoustic and fire
protection properties. Further the product can easily be nailed, sawn or
worked, and may have a density as low as 200 kg/m3.
CONFiRMATIOtJ COPY
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PCT Patent Application No PCT/GB 98/03556 to Windsor Technologies
Limited teaches a method of making a composite product by mixing
together a hydraulic binder, finely divided lignocellulosic fibres in an
amount
of from 1 % to 30% inclusive by mass of the hydraulic binder, and water
optionally containing a polyvinyl alcohol, the water being present in an
amount sufficient to form a paste. There is then introduced into this mixture
a foam generated from a polyvinyl alcohol, in an amount of from 0,05% to
15% inclusive by mass of the paste, and this is mixed to form a foamed
product. The foamed product is formed into a desired shape and the
hydraulic binder is allowed to set to form the composite product.
There is however always a need for new products formed from a hydraulic
binder and a foam.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a method of
making a composite product including the steps of:
(a) mixing:
(i) a hydraulic binder; and
(ii) water, optionally containing a polyvinyl alcohol, the water being
present in an amount sufficient to form a paste;
(b) introducing a foam into the paste in an amount of from 2% to 50%
inclusive by mass of the paste, preferably in an amount of from 25%
to 40% inclusive by mass of the paste, the foam being generated
from a mixture of a polyvinyl alcohol solution and a second
hydrophilic polymer, and mixing to form a foamed product;
(c) forming the foamed product into a desired shape; and
(d) allowing the hydraulic binder to set to form the composite product; the
composite product being formed in the absence of thermosetting
resin.
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It is to be noted that the product is formed in the absence of a
thermosetting resin. In other words the product contains no thermosetting
resin.
According to a second aspect of the invention there is provided a product
made by the method set out above.
DESCRIPTION OF EMBODIMENTS
The crux of the invention is a method of making a product, such a building
board. The first step comprises mixing a hydraulic binder and water,
optionally containing a polyvinyl alcohol and optionally containing a second
hydrophilic polymer, the water being present in an amount sufficient to form
a paste. There is then introduced into the paste a foam in an amount of
from 2% to 50% inclusive by mass of the paste, and mixing to form a
foamed product. The foam is generated from a mixture of a polyvinyl
alcohol solution and a second hydrophilic polymer. Thereafter, the foamed
product is formed into a desired shape and the hydraulic binder is allowed
to set to form the product.
The first component of the product is a hydraulic binder. The hydraulic
binder may be selected from the group consisting of a hydraulic cement,
such as a Portland cement, e.g ordinary Portland cement or rapid
hardening Portland cement, a calcium sulphoaluminate cement, a high
alumina cement such as is used in refractory applications, a gypsum
cement, calcium sulphate hemihydrate in either the alpha or beta form;
magnesium oxychloride, magnesium oxysulphate, an alkali silicate such as
sodium silicate and pozzolans such as ground granulated blast furnace
slag and mixtures of two or more thereof.
The preferred hydraulic binders are a Portland cement such as ordinary
Portland cement; a high alumina cement; a blend of a Portland cement and
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a high alumina cement; and gypsum, i.e calcium sulphate hemihydrate in
either the alpha or beta form, preferably the beta form.
When the hydraulic binder is a Portland cement, rapid gelation of the
foamed hydraulic binder may be induced by adding, between steps (b) and
(c), a gelation agent such as a high alumina cement-in-water paste or a
sodium or potassium silicate in water solution. Using these gelation
agents, gelation of the foam may be achieved within a few seconds of
addition, and thus the addition of the gelation agent must be synchronized
with process requirements.
An example of a suitable high alumina cement for use as the hydraulic
binder is Cement Fondu Lafarge containing approximately 40% by weight
of aluminium oxide (alumina). This may optionally be blended with a
Portland cement, for example in an amount of 10 parts of high alumina
cement : 90 parts of a Portland cement to 90 parts of high alumina cement
parts of a Portland cement. The higher the proportion of high alumina
cement in the blend, the more refractory is the resulting foamed product.
Burning out of the organic components of the composition at temperatures
exceeding 700°C for a period exceeding 60 minutes may be carried out
after setting and drying of the product, to produce a refractory product.
When using a sodium silicate as a gelation agent, it will generally be added
in an amount of between 1 % and 7% by mass of the mass of the Portland
cement.
The hydraulic binder is mixed with water, preferably containing a polyvinyl
alcohol in an amount of from 0,5% to 10% inclusive, preferably in an
amount of from 1 % to 5% inclusive of the polyvinyl alcohol by mass on the
mass of the water.
The polyvinyl alcohol serves to compatiblise the hydraulic binder paste with
the foam when it is added. It also serves as a colloidal protector stabilizing
the foam, and as a polymer, it reinforces the resulting product.
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The polyvinyl alcohol which is mixed with the water is preferably a low
viscosity partially hydrolysed polyvinyl alcohol such as Mowiol 4/88 by
Clariant.
The paste water may also contain a hydrophilic polymer which may be the
same as or different from the second hydrophilic polymer.
The paste water, optionally containing the polyvinyl alcohol and the
hydrophilic polymer is mixed with the hydraulic binder in an amount
sufficient to form a paste.
The next step of the method of the invention is to produce a foam from a
mixture of a polyvinyl alcohol in water solution and a hydrophilic polymer.
Preferably the polyvinyl alcohol is dissolved in water to form a solution
containing from 1 % to 10% inclusive, more preferably from 2% or 2,5% to
7% inclusive by mass of the polyvinyl alcohol to the total mass of the
solution.
The polyvinyl alcohol used in the preparation of the foam is preferably a
higher viscosity polyvinyl alcohol such as Mowiol 18/88 by Clariant. The
preferred viscosity of the polyvinyl alcohol solution at a 5% concentration at
20°C is in the range 8mPa.s to 100mPa.s, the ideal being 50mPa.s~ which
is the viscosity of Mowiol 18/88.
Mowiol 4/88 and Mowiol 18/88 have a degree of hydrolysis of 87,7 mol
percent, and ester value of mgKOH per g of 140, and a residual acetal
content of 10,7% by weight.
The solution from which the foam is produced also contains an amount of a
second hydrophilic polymer, preferably an amount of from 0,2% to 5%
inclusive, more preferably an amount of from 0,3% to 1,5% inclusive by
mass of the second hydrophilic polymer to the total mass of the solution.
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The second hydrophilic polymer is preferably a macromolecular colloidal
protector which is either water soluble or water swellable, e.g a hydrogel,
which controls viscosity. thixotropy and rheology of the wet foamed
hydraulic binder composition, acting synergistically with the polyvinyl
alcohol to impose foam stability and minimise cell size.
The second hydrophilic polymer is preferably selected from the group:
A. Natural polymers such as:
(i) carbohydrates, i.e modified starches such as the polyhydroxy
pre-polymers;
(ii) natural carbohydrate gums, i.e guar, or seaweed colloids, i.e
agar;
(iii) proteins such as gelatin;
B. Semi-synthetic polymers such as:
(i) the cellulose ethers, particularly sodium carboxymethyl
celluloses or hydroxyethyl celluloses;
(ii) microbial gums such as xanthan gum;
C. Synthetic polymers such as:
(i) hydrogels such as the homo polymer and copolymer derivatives
of acrylic and methacrylic acid, or a polyacrylamide-polyacrylate
co-polymer;
(ii) polyacrylamide hydrophilic polymers.
Particularly suitable hydrophilic polymers are those soluble in water at
elevated temperatures i.e. above 35°C and which gel at lower
temperatures.
The preferred second hydrophilic polymer is gelatin, which is a proteinous
macromolecule derived from collagen, which is the protein of skin, bones
and connective tissues of animals. Gelatin may be obtained in a range of
molecular sizes and shapes with a broad molecular weight distribution of
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from 15 000 to 250 000. It is characterised by its viscosity in hot water in
which it is soluble, and its phenomenon of gelling on cooling, its action as a
protective colloid, its propensity to foam. its function as a binder and its
synergy with polyvinyl alcohol.
In step (b) of the method of the invention, the foam is preferably generated
by injecting air into a moving stream of the solution of the polyvinyl alcohol
and the second hydrophilic polymer. Alternatively, the solution containing
the polyvinyl alcohol and the second hydrophilic polymer may be atomized
with air.
When the second hydrophilic polymer is gelatin, the solution of the polyvinyl
alcohol and gelatin in water is preferably formed at an elevated temperature
and kept at that elevated temperature up to and including the stage at
which the foam is generated therefrom and introduced into the paste which
is at ambient temperature. By elevated temperature there is meant a
temperature in the range of from 35°C to 95°C. Immediately upon
introduction of the foam into the paste, the gelatin gels to form a stable
foam of very fine cell size, after which the hydraulic binder is allowed to
set
to form the final product.
Agar exhibits a similar phenomenon at concentrations as low as 0,5%.
Various additional components may be added to the mixture as set out
below.
A suitable thixotropic agent or rheological controller may be added to the
paste before the introduction of the foam, or to the solution from which the
foam is generated. Examples of suitable agents of this type include high
density polyethylene fibrids of bulk density less than 50 grams per litre,
with
or without an amorphous silica such as Stewathix by Schwarzwalder Textil-
Werke; fumed silica such the Aerosils by Degussa; bentonite; hollow glass
balloons; added in an amount of about 1 % or less on the mass of the
hydraulic binder.
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A suitable gelation agent may also be added, particularly in the case of
Portland cements, as set out above.
When the hydraulic binder includes a high alumina cement, a suitable
accelerator may be added such as for example lithium carbonate in an
amount of from about 0,1 % to about 0,8% inclusive by mass on the mass of
the high alumina cement.
In order to minimise the sensitivity of gypsum foams to high atmospheric
humidity, silicone water repellents or hydrophobic agents may be added to
the hydraulic binder paste before the addition of the foam. Those preferred
are the anhydrous silicones based on hydrogen-polysiloxane, added to the
gypsum paste at the level of 0,1 % to 0,5% on the mass of the gypsum. At
an addition rate of 0,25% subsequent water absorption on submersion of a
gypsum foam acoustic ceiling panel is reduced from of the order of 50% to
below 5%, in this way avoiding any tendency to sag with increasing
humidities. An example of a suitable product is Silicone Masonry Water
Repellent BS94 by blacker. Cohesion property of the composite is also
improved, particularly at lower densities.
The paste may also include an amount of reinforcing fibres which
preferably have a high aspect ratio, the fibres having lengths of from 1 mm
to 6mm, more preferably from 1,5mm to 4mm and preferably chosen from
the group consisting of polyacrylonitrile, polyvinyl alcohol, polyester,
polyethylene, polypropylene, glass fibre, ceramic fibre, mineral wool,
aramid, or naturally occurring fibrous or high aspect ratio minerals such as
wollastonite.
The composition may also contain reinforcing particles such as mica,
phlogopite, delaminated exfoliated vermiculite such as FPSV by W R
Grace, these particles having a diameter of less than 0.75mm, preferably
less than 0,25mm.
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Such reinforcing fibres or particles are preferably added in an amount of
from 0,1 % to 2%, more preferably in an amount of from 0,25% to 1,5% by
mass of the mass of the hydraulic binder.
Suitable inorganic compounds, in small particles sizes may also be added
to the hydraulic binder pastes, such as for example a silica flour, a talc,
calcium carbonate, a diatomaceous earth and the like
In addition, contributors to syntactic elements within the foam may be
included in the hydraulic binder paste, such as for example an expanded
mineral, e.g perlite, clays, aluminas, vermiculites, hollow glass balloons and
silica fumes, or expanded organic particles such as ground or milled
polymer foams such as polyurethanes, polyvinyl chlorides, or polystyrenes.
In step (c) of the method of the invention, the foamed product is formed into
a desired shape, for example by conventional techniques such as casting
or pouring or otherwise dispensing into a suitable mould or onto a moving
belt or the like.
In step (d) of the method of the invention, the hydraulic binder is allowed to
set to form the final product.
Thereafter, the final product may be used directly or may be cured and
dried and thereafter machined into suitable sizes and the like
The essential feature of the method of the invention is the use of a
combination of a polyvinyl alcohol and a second hydrophilic polymer, which
work synergistically together to produce the foam. Both the polyvinyl
alcohol and the second hydrophilic polymer are colloidal protectors working
together to encapsulate tiny bubbles of air and preventing their
coalescence, thus maintaining foam stability and keeping the heavier
particles of hydraulic binder in uniform suspension.
When the second hydrophilic polymer is a gelatin, the hot foam is added to
the paste which is at ambient temperature. The gelatin fraction gels,
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"freezing" the foam whilst the polyvinyl alcohol maintains the liquid,
workable nature of the foam before setting of the hydraulic binder.
Both components, but particularly the polyvinyl alcohol, improve the
mechanical properties of the set foam, which cannot be achieved with
conventional foaming agents.
Examples of the invention will now be given.
Example 1
A. A solution of 1 000 units by weight of water including 40 units by
weight of Mowiol 18/88 polyvinyl alcohol by Clariant, and 15 units by
weight of gelatin, is prepared at a temperature of 75°C.
B. A hydraulic binder paste comprising of 2 000 units by weight of
Portland cement, 600 units by weight of a 3% solution of Mowiol 4/88
polyvinyl alcohol-in-water by Clariant, 15 units by weight of Dolanit
acrylonitrile fibres having a length of 3mm and a diameter of 27
microns with 500 000 fibres per gram, and 200 units by weight of
undensified silica fume, are blended at ambient temperature.
C. The mixture from step A is coverted into a foam by the atomisation of
air in the solution in a foam generator and the foam is added to the
hydraulic binder paste from step B at the rate of 500 units by weight
and mixed thoroughly.
D. Immediately 75 units by weight of Silchem 3379 sodium silicate of a
composition of silicon dioxide 29%, sodium oxide 8%, at a solids-in-
water percentage of 37,88, and a weight ratio of silicon to sodium of
3.3:1, is added to the foamed hydraulic binder and thoroughly
blended.
E. The foam is spread upon a moving belt to a thickness of 25mm
whereupon it immediately gels followed by curing accelerated if
necessary by steam, to produce a final product.
Where autoclaving is selected as the cure method the Portland cement
percentage of the composite is about 800 units by weight and a fine silica
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flour typically a 300 mesh, i.e ground silica sand is included at about 1 200
units by weight. The gelled composite is cured after 24 hours precure in an
autoclave at 180°C at elevated pressures of up to 10 bar for fourteen
hours
giving a cured product capable of being nailed with a total organic
percentage in the composite of less than 2,5%.
The open cellular structure allows for the drainage of water after water
wetting, the product is inflammable, is proof to biological degradation and is
suitable for roof under-lays, floor under-lays, exterior siding, bath backer
boards and the like, with densities in the range 300 to 900 kg/m3, exhibiting
good thermal and acoustic insulation properties, good mechanical
properties and reduced cost of distribution.
Example 2
A. A solution of 4% by weight of Mowiol 18/88 polyvinyl alcohol by
Clariant and 0, 75% by weight of polyacrylamide by PRP Resins,
South Africa, in 500 units by weight of water is prepared at ambient
temperature.
B. A hydraulic binder paste comprising of 2 000 units by weight of the
beta hemihydrate of calcium sulphate, 1 400 units by weight of a 3%
in water solution of Mowiol 4/88 polyvinyl alcohol by Clariant is made.
C. The polyvinyl alcohol/polyacrylamide solution is foamed in a foam
generator by the atomisation of air in the solution to produce a low
bulk density "dry" foam which is added to the paste from step B at the
rate of 600 units by weight.
D. The foamed hydraulic binder is spread on a moving belt to a
thickness of 50mm, allowed to set and subsequently dried to produce
a fire protection composite suitable for door cores, panel cores and
the protection of steel from fire by fabricated encapsulation.
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Example 3
Foam Stability Trials
475 grams of the follow three solutions were foamed and the foam volume
measured immediately and then again after standing for two and a half
hours at 22°C:
A. Polyvinyl alcohol Mowiol 18/88 at 5% concentration in water.
B. Polyvinyl alcohol Mowiol 18/88 at 4% concentration in water plus
polyacrylamide at 2% concentration.
C. Polyvinyl alcohol Mowiol 18/88 at 4% concentration plus 2% of gelatin
in water at 70°C.
Resu It:
Solution ' Volume in Volume in cm Foam volume
cm after 2'/2 hoursreduction
immediately at
after 22C
foaming
A 2419 0 100%
i B 2083 1747 16%
C ~ 4839 4301 11%
