Note: Descriptions are shown in the official language in which they were submitted.
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RHEOLOGY MODIFICATION AND MODIFIERS
The present invention relates to explosives compositions and methods for
modifying
the rheology of explosives compositions using associative thickeners.
Civilian mining, quarrying and excavation industries commonly use bulk or
packaged
explosive formulations as a principal method for breaking rocks and ore for
mining, building
tunnels, excavating and similar activities. Explosive compositions typically
used in these
applications include emulsion-based explosive compositions.
Water-in-oil emulsion explosive compositions were first disclosed by Bluhm in
United
States Patent 3,447,978 and comprise (a) a discontinuous aqueous phase
comprising discrete
droplets of an aqueous solution of inorganic oxygen-releasing salts; (b) a
continuous water-
immiscible organic phase throughout which the droplets are dispersed and (c)
an emulsifier
which forms an emulsion of the droplets of oxidiser salt solution throughout
the continuous
organic phase. Where these types of emulsions comprise very little water or
adventitious
water only in the discontinuous phase they are more correctly referred to as
melt-in-fuel
emulsion explosives.
In emulsion explosives, emulsifiers are generally used to decrease interfacial
tension
between the aqueous and oil phases. Molecules of the emulsifier locate at the
interface
between the aqueous droplet and continuous hydrocarbon phase. The emulsifier
molecules
are oriented with the hydrophilic head group in the aqueous droplet and the
lipophilic tail in
the continuous hydrocarbon phase. Emulsifiers stabilise the emulsion,
inhibiting coalescence
of the aqueous droplets and phase separation. Emulsifiers also inhibit
crystallisation of
oxidiser salt in the aqueous droplets. Uncontrolled crystallisation can lead
to emulsion
breakdown and reduction in detonation sensitivity of the emulsion explosive
composition.
Generally the emulsions themselves are not detonable and in order to form an
explosive composition, the emulsion must be mixed with sensitising agents such
as a self
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explosive (e.g. trinitrotoluene or nitroglycerine) or a discontinuous phase of
void agents.
Suitable void agents include glass microballoons, plastic microballoons,
expanded polystyrene
beads and gas bubbles including bubbles of entrained air.
Emulsions are often blended with ANFO-based explosive compositions to provide
explosives which are commonly referred to as "heavy ANFO's". Compositions
comprising
blends of emulsion and AN or ANFO are described for example in US Patents
3,161,551
(Egly et al) and 4,357,184 (Binet et al).
When explosives are used in the mining industry, ore and rock is fractured by
drilling
blastholes in the area to be blasted, and then filling the blastholes with
bulk or packaged
explosive compositions which are subsequently detonated. Bulk explosives are
generally less
expensive per unit mass than packaged explosives hence bulk explosives are
preferred,
particularly at large mine sites where many hundreds of tonnes of explosives
may be needed
for a single blast. Packaged explosives also suffer the drawback that they
must be manually
loaded into blastholes whereas bulk explosives are able to be readily loaded
by mechanised
means.
Packaged explosives are manufactured at fixed site manufacturing facilities
and the
cartridges of packaged explosives are transported to the blast site and hand
loaded into
predrilled blastholes. Bulk explosives are either manufactured at a
manufacturing facility and
transported in a specially designed truck to the mine or mixed on-site in
manufacturing units
located on trucks (called mobile manufacturing units or MMU's).
The transport trucks and MMU's are provided with the mechanised means of
loading
bulk explosive into blastholes. The blasthole loading is usually carried out
by either
auguring, pouring, pumping or blow loading the bulk explosive into the
blasthole, the loading
method used depending on the physical characteristics of the type of bulk
explosive used.
Loading by pumping is usually carried out by using a mechanical or pneumatic
pump to push
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explosives compositions through a delivery hose into the blastholes. Blow
loading of an
explosive composition typically involves the use of compressed gas to blow the
explosive
through a delivery hose into blastholes and is a commonly used delivery
method.
Both MMU's and fixed manufacturing facilities store relatively large
quantities of
chemical components which can be mixed together to form explosives
compositions. For
example, MMU's comprise several large storage containers for storing fuel oil,
emulsion,
particulate oxidiser salts, water and other explosive components. These
components can be
mixed in differing proportions to provide ANFO or various formulations of
emulsion and
heavy ANFO.
The manufacturing processes carried out using MMU's and fixed manufacturing
facilities can provide various explosives formulations having various physical
characteristics
by precise control of the component flow rate, temperature and other physical
parameters
related to the manufacturing process.
One of the most important parameters in the manufacture, delivery and handling
of
emulsion explosives is the emulsion rheology. The rheology of the emulsion
impacts on
virtually every aspect of emulsion handling including the flow of the emulsion
in pipes and
hoses; adhesion to the walls of the tanks and conduits of the manufacturing
system; ease of
pumping; retention in upholes and cracked ground; and retention of voidage at
low density.
For example, explosives compositions which are very dense and viscous can only
be
pneumatically or mechanically pumped through short loading hoses; they cannot
be pumped
through long hoses without the use of excessively high pumping pressures or
the hoses block
up.
It has also been noted that a column of emulsion will fail to be retained in
an uphole
if there is adhesive failure between the emulsion column and the blasthole
walls or a cohesive
failure of the emulsion. These problems may be alleviated somewhat if the
viscosity
(effective rigidity) of the emulsion is increased.
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While it is often desirable for an emulsion to exhibit a high viscosity in the
blasthole,
this is not optimal for transport, handling or loading the emulsion into
blastholes, particularly
when pumping. In other words, an explosive emulsion which has rheological
characteristics
which make the emulsion suitable for pumping through a loading hose, may not
be suitable
for residence in a blasthole and vice versa.
In the past, many different techniques have been used to modify the rheology
of
explosives emulsions. Most of these approaches to rheology modification are
based on
chemical interactions such as the chemical crosslinking of components within
the emulsion.
For example United States Patent 5,387,675 (Yeh) discloses the use of
quaternary ammonium
ether(s) of polyol(s) and polysaccharides as chemical thickeners in a range of
products
including explosives. United States Patent 5,145,535 describes the use of a
cationic salt of
CMC ether as a chemical thickener.
However, chemically-based rheology modification of emulsions generally suffers
from
the problems that the chemical reaction occurs at a relatively slow rate and
is strongly
temperature dependent and irreversible.
It has now been found that effective rheology modification of emulsions for
emulsion
explosives can be provided using "associative thickeners" which are believed
to rely on a
physical interaction with components of the emulsion rather than chemical
interactions.
Associative thickeners have been previously used in technologies such as the
coating
industry. For example United States Patent 5,521,235 (Redelius and Redelius)
describes the
use of hydrophobically modified urethane ethoxylates as associative nonionic
type thickeners
in cationic type bitumen emulsion for rods, roofing and waterproofing to allow
thicker coating
layers to be formed. Canadian Patent 2079926 (Fistner) discloses an aqueous
paint
composition with high gloss for use on textiles, the paint comprising an
associative thickener,
preferably a polyurethane block copolymer or an alkali swellable acrylic
polymer or an alkali
soluble acrylic polymer. Associative thickeners have also been used in
thickening drilling
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muds, polishes, cleaners, personal care products such as cosmetics, food
products and
pharmaceuticals, hydraulic fluids and inks but not hitherto in explosives
manufactured to
control rheological characteristics.
We have now found that associative thickeners may be used in emulsions for use
in
explosive compositions, which associative thickeners provide for rapid and
reversible
changes in emulsion viscosity. Associative thickeners provide explosives
emulsions
having the desirable characteristics of (1) significant reduction in viscosity
during pumping
and (2) re-establishment of relatively high viscosity when pumping is
terminated without
damage to the emulsion components. It is believed that the associative
thickener provides
a network of physical linkages throughout the emulsion which network can be
reversibly
broken down.
Accordingly, the present invention provides an emulsion for use in emulsion
explosives wherein said emulsion comprises an associative thickener
incorporated in an
aqueous phase of the emulsion.
There is further provided an emulsion wherein the emulsion has increased zero-
shear viscosity relative to an emulsion absent the associative thickener and
exhibits
significant reduction in viscosity when subjected to applied shear force and
re-establishes
substantially the original viscosity when the applied shear force is removed.
In a first embodiment of the present invention there is provided a water-in-
oil
emulsion suitable for use in the manufacture of an emulsion explosive
composition, the
water-in-oil emulsion comprising a water-immiscible organic phase, an
emulsifier and an
aqueous phase including an oxygen releasing salt, wherein at least one
associative
thickener is incorporated into the aqueous phase of the emulsion in an amount
such that the
emulsion has increased zero-shear viscosity relative to an emulsion absent the
associative
thickener and exhibits significant reduction in viscosity when subjected to an
applied shear
force and re-establishes substantially original viscosity when the applied
shear force is
removed, wherein the associative thickener comprises a chain of hydrophilic
material
soluble in the aqueous phase of the emulsion, and hydrophobic moieties
insoluble in the
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aqueous phase of the emulsion which moieties are dispersed along the chain or
are present
as terminal groups.
In a second embodiment of the present invention there is provided an emulsion
explosive composition comprising water-in-oil emulsion of the present
invention.
In a third embodiment of the present invention there is provided a method of
manufacturing an emulsion explosive composition comprising incorporating at
least one
associative thickener into an aqueous phase and subsequently emulsifying the
aqueous
phase into a water-immiscible organic phase to form a water-in-oil emulsion,
wherein the
associative thickener comprises a chain of hydrophilic material soluble in the
aqueous
phase of the emulsion, and hydrophobic moieties insoluble in the aqueous phase
of the
emulsion which moieties are dispersed along the chain or are present as
terminal groups.
In a fourth embodiment of the present invention there is provided a use of a
water-
in-oil emulsion of the present invention in the manufacture of an emulsion
explosive
composition.
In a fifth embodiment of the present invention there is provided an emulsion
explosive composition when manufactured by a method of the present invention.
A wide variety of associative thickeners may be used in the present invention.
Suitable associative thickeners may be selected in accordance with their
compatibility with the emulsion explosive in which they are incorporated.
The associative thickener of the present invention may be polymeric or non-
polymeric and may act in the aqueous phase of the emulsion.
The associative thickener may typically comprise a backbone or chain which is
soluble in the aqueous phase of the emulsion. These associative thickeners
additionally
comprise a number of moieties which are insoluble in the aqueous phase. These
moieties
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are preferably dispersed along the backbone with insoluble moieties present
within or as
pendent or terminal groups on the chain.
The associative thickener may be a polymer soluble in the aqueous phase and
have insoluble moieties substituted thereto in substoichiometric amounts.
Preferably
the associative thickener comprises blocks of hydrophilic polymers or
copolymer
prepared with small amounts of hydrophobic comonomer. The hydrophilic polymer
or
copolymer is preferably prepared from monomers selected form the group
consisting of
vinylpyrrolidone, vinyl acetate, acrylamide, ethylene glycol, ethylene oxide,
vinyl
alcohol and propylene glycol and their hydrophilic derivatives.
The hydrophobic monomer may be any monomer polymerisable with the
hydrophilic monomer and which contains hydrophobic moieties. There are a wide
variety of suitable hydrophobic monomers which will be known to those skilled
in the
art of associative thickeners. Preferably the hydrophobic monomers are
selected from
the group consisting of N-alkylacrylamides such as N-(4-ethylphenyl)acrylamide
and
N-(4-t-butylphenyl)acrylamide. The associative thickener may be for example, a
copolymer of acrylamide (a hydrophile) and N-4-(t-butyl)phenyl acrylamide (a
hydrophobe) comprising less than 1 mol % hydrophobic comonomer.
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It will be apparent to those skilled in the art that molecules of this type
can be
synthesised by various methods. The two major synthetic routes to associative
thickeners are
through micellar copolymerisation or from the chemical modification of a water-
soluble
precursor polymer. The latter route has mainly been applied to cellulose
derivatives,
poly(acrylic acid) and ethoxylated urethane polymers. The micellar
copolymerisation process
involves essentially acrylamide-based copolymers. An additional synthetic
route which
utilises hydrophobic monomers with a built in surfactant character overcomes
the need for the
external surfactants used in the micellar technique.
Factors which influence the viscosifying ability of associative thickeners, in
the
absence of shear, are many and varied. Included in these are the molecular
weight of the
copolymer, the copolymer microstructure (hydrophobe content and hydrophobe
distribution
along the polymer chain), the hydrophobicity of the hydrophobe, the presence
of charge either
in the polymer backbone or on the pendant hydrophobic groups, the copolymer
concentration, the presence of additives (e.g. salt or surfactant) and
temperature. Depending
on the relative influence of each of these factors and the copolymer chain
flexibility, both
interchain and intrachain associations may occur.
Preferably the emulsion suitable for use as an explosives emulsion is a water-
in-oil or
melt-in-oil emulsion or melt-in-fuel emulsion. Typically the associative
thickener is dissolved
in the aqueous phase prior to emulsion formation. Typically the emulsion
comprises 0.1 % to
3 % by weight of emulsion of associated thickener. More typically the
associative thickener
is present at a concentration of 0.2 to 2 % by weight of emulsion. Suitable
oxygen releasing
salts for use in the aqueous phase of the emulsion of the present invention
include the
alkali and alkaline earth metal nitrates, chlorates and perchlorates, ammonium
nitrate,
ammonium chlorate, ammonium perchlorate and mixtures thereof. The preferred
oxygen releasing salts include ammonium nitrate, sodium nitrate and calcium
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nitrate. More preferably the oxygen releasing salt comprises ammonium nitrate
or a
mixture of ammonium nitrate and sodium or calcium nitrates.
Typically the oxygen releasing salt component of the compositions of the
present
invention comprises from 45 to 95 % w/w and preferably from 60 to 90 % w/w of
the total
emulsion composition. In compositions wherein the oxygen releasing salt
comprises a
mixture of ammonium nitrate and sodium nitrate the preferred composition range
for such
a blend is from 5 to 80 parts of sodium nitrate for every 100 parts of
ammonium nitrate.
Therefore, in the preferred composition the oxygen releasing salt component
comprises
from 45 to 90 % w/w (of the total emulsion composition), ammonium nitrate or
mixtures
of from 0 to 40 % w/w, sodium or calcium nitrates and from 50 to 90 % w/w
ammonium
nitrate.
Typically the amount of water employed in the compositions of the present
invention
is in the range of from 0 to 30 % w/w of the total emulsion composition.
Preferably the
amount employed is from 4 to 25 % w/w and more preferably from 6 to 20 % w/w.
The water immiscible organic phase of the emulsion composition of the present
invention comprises the continuous "oil phase" of the emulsion composition and
is the fuel.
Suitable organic fuels include aliphatic, alicyclic and aromatic compounds and
mixtures thereof which are in the liquid state at the formulation temperature.
Suitable
organic fuels may be chosen from fuel oil, diesel oil, distillate, furnace
oil, kerosene,
naphtha, waxes such as microcrystalline wax, paraffin wax and slack wax,
paraffin oils,
benzene, toluene, xylenes, asphaltic materials, polymeric oils such as the low
molecular
weight polymers of olefines, animal oils, vegetable oils, fish oils and other
mineral,
hydrocarbon or fatty oils and mixtures thereof. Preferred organic fuels are
liquid
hydrocarbons generally referred to as petroleum distillates such as gasoline,
kerosene, fuel
oils and paraffin oils.
Typically the organic fuel or continuous phase of the emulsion comprises from
2 to
15 % w/w and preferably 3 to 10 % w/w of the total composition.
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The emulsifier of the emulsion composition of the present invention may
comprise
emulsifiers chosen from the wide range of emulsifiers known in the art from
the preparation
of emulsion explosive compositions. It is particularly preferred that the
emulsifier used in the
emulsion composition of the present invention is one of the well known
emulsifiers based on
the reaction products of poly[alk(en)yl] succinic anhydrides and alkylamines,
including the
polyisobutylene succinic anhydride (PiBSA) derivatives of alkanolamines. Other
suitable
emulsifiers for use in the emulsion of the present invention include alcohol
alkoxylates phenol
5 alkoxylates, poly(olyalkylene)glycols, poly(oxyalkylene)fatty acid esters,
amine alkoxylates,
fatty acid esters of sorbitol and glycerol, fatty acid salts, sorbitan esters,
poly(oxyalkylene)
sorbitan esters, fatty amine alkoxylates, poly(oxyalkylene)glycol esters,
fatty acid amines,
fatty acid amide alkoxylates, fatty amines, quaternary amines,
alkyloxazolines,
alkenyloxazolines, imidazolines, alkylsulphonates, alkylarylsulphonates,
alkylsulphosuccinates, alkylarylsulpnonates, alkylsulphosuccinates,
alkylphosphates,
alkenylphosphates, phosphate esters, lecithin, copolymers of
poly(oxyalkylene)glycols and
poly(12-hydroxystearic)acid and mixtures thereof.
Typically the emulsifier of the emulsion comprises up to 5 % w/w of the
emulsion.
Higher proportions of the emulsifying agent may be used and may serve as
supplemental fuel
for the composition but in general it is not necessary to add more than 5 %
w/w of
emulsifying agent to achieve the desired effect. Stable emulsions can be
formed using
relatively low levels of emulsifier and for reasons of economy it is
preferable to keep the
amount of emulsifying agent used to the minimum required to form the emulsion.
The
preferred level of emulsifying agent used is in the range of from 0. 1 to 3.0
% w/w of the
water-in-oil emulsion.
If desired, other optional fuel materials, hereinafter referred to as
secondary fuels may
be incorporated into the emulsion in addition to the water immiscible organic
fuel phase.
Examples of such secondary fuels include finely divided solids and water
miscible organic
liquids which can be used to partially replace water as a solvent for the
oxygen releasing salts
or to extend the aqueous solvent for the oxygen releasing salts. Examples of
such secondary
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fuels include finely divided solids and water miscible organic liquids which
can be used to
partially replace water as a solvent for the oxygen releasing salts or to
extend the aqueous
solvent for the oxygen releasing salts. Examples of solid secondary fuels
include finely
divided materials such as sulphur, aluminium, urea and carbonaceous materials
such as
gilsonite, comminuted coke or charcoal, carbon black, resin acids such as
abietic acid, sugars
such as glucose or dextrose and vegetable products such as starch, nut meal,
grain meal and
wood pulp. Examples of water miscible organic liquids include alcohols such as
methanol,
glycols such as ethylene glycol, amides such as formamide and urea and amines
such as
methylamine.
Typically the optional secondary fuel component of the composition of the
present
invention comprises from 0 to 30 % w/w of the total composition.
The water-in-oil emulsion composition may be prepared by a number of different
methods. One preferred method of manufacture includes: dissolving said oxygen
releasing
salts in water at a temperature above the crystallization point of the salt
solution, preferably
at a temperature in the range from 20 to 110 C to give an aqueous salt
solution; combining
an aqueous salt solution, a water immiscible organic phase, and an emulsifier
with rapid
mixing to form a water-in-oil emulsion; and mixing until the emulsion is
uniform.
It lies within the invention that there may also be incorporated into the
emulsion other
substances or mixtures of substances which are oxygen releasing salts or which
are themselves
suitable as explosive materials. For example the emulsion may be mixed with
prilled or
particulate ammonium nitrate or ammonium nitrate/fuel oil mixtures.
Other optional additives may be added to the emulsion explosive compositions
hereinbefore described including non-associative thickening agents or chemical
thickening
agents such as zinc chromate or a dichromate either as a separate entity or as
a component of
a conventional redox system such as for example, a mixture of potassium
dichromate and
potassium antimony tartrate.
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Without wishing to be bound by theory, it is believed that the associative
thickener
increases the zero-shear viscosity by the non-soluble moieties of different
associative thickener
molecules associating together in the solvent, giving localised points of
linkage between the
soluble backbones of the molecules. These associations are believed to give
rise to an
extensive three-dimensional structure of the associative thickener molecules
in the solvent,
the 3-dimensional structure acting to hinder solvent flow and therefore raise
the emulsion
viscosity.
The points of association are not permanent as they are only formed through
relatively
weak physical forces. Under the influence of applied shearing force, the
points of association
can be disrupted and the emulsion can flow normally. However the disruption
only subsists
while the shearing force is applied. If the shearing force is removed the
points of association
can rapidly be re-formed, re-establishing the 3-dimensional network.
It is believed that the driving force for formation of the associations has a
primarily
thermodynamic basis. For example, where the associative thickener constitutes
a
hydrophobically modified water-soluble polymer, the driving force for the
associations is a
large entropic increase (accompanied by a small enthalpic change) arising from
the breakdown
of the ordered structure of water molecules around the hydrophobes as they are
removed from
solution. This aggregation is therefore favoured due to the large decrease in
the free energy
resulting from a net decrease in the number of hydrophobe-water contacts. The
aggregation
in aqueous solution of the hydrophobic groups on the polymer chains thus
results in
intermolecular associations, forming physical linkages between the chains.
These linkages
produce polymolecular structures with a high hydrodynamic volume and
consequently,
enhanced viscosification properties.
Advantageously, the incorporation of an associative thickener into the aqueous
phase- of an emulsion for use in an emulsion explosive composition provides a
marked viscosifying effect, especially for emulsions having a dispersed phase
with
a small average droplet size. We have found that the apparent viscosity of
such
an emulsion may display an increase of 150% or more. We
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observed that the apparent viscosity, when measured as a function of shear
rate, demonstrated
an apparent viscosity far greater than for emulsions unmodified by associative
thickeners over
relatively low shear rates. The apparent viscosity of the emulsions comprising
an associative
thickener coincided with the apparent viscosities of an unmodified emulsion at
higher shear
rates. This clearly shows that emulsions comprising associative thickeners may
be pumped,
augured or otherwise transported as readily as standard emulsions yet may
exhibit apparent
viscosities far greater than for standard emulsions at low or zero shear such
as when loaded
in a bore hole.
When the associative thickener is incorporated into the dispersed phase of the
emulsion, the droplets have been observed to be significantly harder to deform
although at
relatively high shear rates, the resistance to deformation is overcome. In a
preferred
embodiment of the present invention, the associative thickener is incorporated
into the
dispersed aqueous phase of a water-in-oil emulsion.
We have observed that in a number of the emulsions prepared incorporating an
associative thickener demonstrate increased stability with respect to an
unmodified emulsion.
We have also observed that the average droplet size and droplet distribution
is similar to and
exhibits similar general behaviour to standard emulsions over time.
Dynamic shear studies of emulsions comprising the associative thickener
demonstrate
elastic character in the emulsions over a wider range of frequencies and
strains than would
be expected in unmodified emulsions.
Advantageously, the emulsions incorporating the associative thickener
demonstrate less
rheopectic behaviour than would be expected with unmodified emulsions.
Throughout this specification and the claims which follow, unless the context
requires
otherwise, the word "comprise", and variations such as "comprises" and
"comprising", will
be understood to imply the inclusion of a stated integer or step or group of
integers or steps
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but not the exclusion of any other integer or step or group of integers or
steps.
The invention is now demonstrated by but in no way limited to the following
examples:
Example 1
In this example, a copolymer of acrylamide and N-(4-t-butylphenyl) acrylamide
was
used as an associative thickener. The associative thickener was synthesised
using an
aqueous micellar free radical polymerisation route. The resultant copolymer
contained no
more than 1 mol % of the hydrophilic monomer.
The effect of ammonium nitrate and sodium chloride on the solution properties
of the
associative thickener were investigated. The concentration of associative
thickener was 0.50
% w/w with ammonium nitrate levels ranging from 10 % w/w to 60 % w/w. The
shear rate
range was varied from 0.00186 S-1 to 1470 S-1 with a constant delay time of 5
sec and an
integration time of 5 sec using a Bohlin VOR' rheometer. The samples were
examined as
a function of shear rate and also as a function of shear time at a constant
rate.
The results are shown in Figures 1 to 3. Figure 1 shows the apparent viscosity
at
25 C as a function of shear rate (sweep up and down) for 0.50 % w/w aqueous
associative
thickener solutions containing various levels of ammonium nitrate. The arrows
indicate the
direction of sweep. Figure 2 shows the apparent viscosity at 25 C at a
constant shear rate of
0.583 S-1 as a function of the ammonium nitrate concentration for 0.50 % w/w
aqueous
associative thickener solutions.
The results indicated that in aqueous ammonium nitrate solution the
associative
thickener offered significant enhancement of the viscosity but that under the
influence of shear
the associative thickener led to shear thinning, achieving viscosities closer
to that of pure
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water at high shear rates (that is greater than 100/s). Time dependent effects
were also seen,
with the associative thickener exhibiting rheopexy (increased viscosity as a
function of shear
time) at low shear rates and thixotropy (decreased viscosity as a function of
shear time) at
higher shear rates.
Example 2
In this example, a copolymer of acrylamide and N-(4-t-butylphenyl) acrylamide
was
used as an associative thickener.
The effect of sodium chloride on the solution properties of the associative
thickener
were investigated. The concentration of associative thickener of 0.50% w/w and
1.50% w/w
with sodium chloride levels ranging from 5 % w/w to 25 % w/w. The shear rate
range was
varied from 0.00186 S' to 1470 S'' with a constant delay time of 5 sec and an
integration
time of 5 sec using a Bohlin VOR rheometer. The samples were examined as a
function of
shear rate and also as a function of shear time at a constant rate.
The results are shown in Figures 4 to 6. Figure 4 shows the apparent viscosity
at 25
C as a function of shear rate (sweep up and down) for 0.50 % w/w aqueous
associative
thickener solutions containing various levels of sodium chloride. The arrows
indicate the
direction of sweep. Figure 5 shows the apparent viscosity at 25 C at a
constant shear rate of
0.583 1/s as a function of shear time for 0.50 % w/w aqueous associative
thickener solutions
containing various levels of sodium chloride. Figure 6 shows the apparent
viscosity at 25 C
at a shear rate of 0.583 S-' as a function of the sodium chloride
concentration for 0.50 % w/w
aqueous associative thickener solutions.
The results indicated that in aqueous NaCl solution the copolymers offered
significant
enhancement of the viscosity but that under the influence of shear they showed
shear thinning,
achieving viscosities closer to that of pure water at high shear rates (that
is greater than
100/s). Time dependent effects were also seen, with the copolymer exhibiting
rheopexy
(increased viscosity as a function of shear time) at low shear rates and
thixotropy (decreased
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viscosity as a function of shear time) at higher shear rates.
Example 3
Preparation of a Water-in-Oil Emulsion
A water-in-oil emulsion of the following composition was prepared for use in
the
example; Oxidiser Solution - 91.5 % w/w
ammonium nitrate (78.9 % w/w)
water (20.7 % w/w)
buffer (0.4 % w/w)
Fuel Phase - 9 % w/w
hydrocarbon oil/emulsifier mix (9% w/w).
The emulsifier was an uncondensed amide form of the reaction product of an
alkanolamine and poly(isobutylene)succinic anhydride (PiBSA). The emulsion was
prepared
by dissolving ammonium nitrate in the water at elevated temperature (98 C)
then adjusting
the pH of the oxidiser solution so formed to 4.2. The fuel phase was then
prepared by mixing
the emulsifier with the hydrocarbon oil. The oxidiser phase was then added in
a slow stream
to the fuel phase at 98 C with rapid stirring to form a homogeneous water-in-
oil emulsion.
Emulsion of this formulation was suitable for use in forming an explosives
emulsion.
A first portion of the water-in-oil emulsion was set aside as a control
sample. The
associative thickener of Example 1 was incorporated at a concentration of 1.5
% w/w into
the aqueous phase of a second test sample of the emulsion.
A comparison of the test sample with the control sample showed that the
associative
thickener enhanced the zero shear viscosity of the test sample. Furthermore
the test sample
exhibited shear thinning as a function of applied shear rate, the test sample
having the same
viscosities as the control sample at higher shear rates. Upon relaxation of
the shear force, the
test sample immediately regained high zero shear viscosity .
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Example 4
The following chemicals were used in the preparation of the samples used in
this example:
* E25/66T (emulsifier, ex Orica Australia)
* Paraffin Oil (ex Orica Australia)
* Sodium Chloride (98 + %, Aldrich Chemical Company, Inc.)
* Water (MilliporeTM "Milli-Q" Grade)
All chemicals were used as supplied without further purification.
The continuous phase (oil phase) for the comparative emulsions was prepared
using
30% w/w E26/66T and 70% w/w paraffin oil, while the dispersed phase (aqueous
phase) was
a 25 % w/w sodium chloride solution. All emulsions were prepared at ambient
temperature
from continuous and dispersed phases at this temperature.
A Sunbeam BeatermixTM JM-040 five-speed electronic hand mixer with a whisk-
type
stirrer was employed in the preparation of the emulsions. The speed setting
used was
dependent on the droplet size required for the emulsion.
The highly concentrated emulsions were prepared as follows: 94g of aqueous
phase
was slowly added to 6g of constantly mixing oil phase over a 5 minute time
period.
Emulsification and refinement was then continued for a further specified
period of time, with
the emulsion vessel being moved in a circular motion during this time to
ensure complete
dispersion of the aqueous phase in the oil phase.
Emulsions of approximately 6 m average droplet size were prepared using the
highest
speed setting (Speed 5) and a refinement time of 5 minutes.
An emulsion of approximately 12 m average droplet size was prepared using the
lowest speed setting (Speed 1) and a refinement time of 2.5 minutes.
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An emulsion of approximately 18 m average droplet size was prepared using the
lowest speed setting (Speed 1) and a refinement time of 45 seconds.
These emulsions will hereon be referred to as Emulsion S6, Emulsion S12 and
Emulsion S 18 respectively.
The acrylamide/N-(4-butylphenyl)acrylamide copolymer used to thicken the
internal
phase of the emulsions was obtained from a free-radical copolymerisation in an
aqueous
micellar medium. This polymerisation technique produces a copolymer with an
essentially
block-like structure, with hydrophobic regions being dispersed along the
hydrophilic polymer
backbone. It is believed that the copolymer is polydisperse in nature, with
polymer chain
compositions ranging from hydrophobe rich to pure acrylamide.
The copolymer/salt solution was prepared by dissolving 1.5% w/w of copolymer
in
a 25% w/w sodium chloride solution using gentle magnetic stirring at ambient
temperature.
The thickened emulsions were prepared using essentially the same method as for
standard emulsions. However, due to the increased viscosity of the dispersed
phase, small
amounts of the copolymer/salt solution were continuously added to the oil
phase in the
emulsion vessel until all of the dispersed phase had been added. This occurred
over a 5
minute period.
All emulsions were prepared using the highest speed setting (Speed 5) on the
mixer.
Thickened emulsions of approximately 6 m, 12 m and 18 m were prepared using
refinement times of 40 minutes, 10 minutes and 4 minutes 45 seconds
respectively. They will
hereon be referred to as Emulsion T6, Emulsion T12 and Emulsion T18
respectively.
The measuring system utilised in all measurements was a Bohlin VOR rheometer
with
a stainless steel concentric cylinder (C14) geometry consisting of a cup of
diameter 15.4 mm
and a bob of diameter 14.0 mm. The base of the bob was conical with cone angle
150 , the
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purpose of which was to minimise any end effects on the flow of the sample.
The 86.6 g.cm torsion bar was used for all shear time, shear rate sweep and
flow/relaxation measurements, together with the oscillatory measurements of
Emulsion T6.
The oscillatory measurements on the remaining emulsions employed the 18 g.cm
torsion bar.
Each was selected to ensure maximum sensitivity.
The available method of measurement enabled the shearing of the emulsion
sample at
each particular shear rate for a specified time, prior to the measurement at
that shear rate
being taken. This initial period of pre-shear is known as the delay time.
Taking the
measurement at a particular shear rate involved averaging a number of
instantaneous torque
readings taken over a specified time period to produce the reported data
value. This period
of measurement is known as the integration time.
The torque signal was zeroed manually prior to the start of each measurement.
All measurements were preformed at a temperature of 25 C.
The apparent viscosity as a function of time was recorded in what will be
referred to
as "shear time" measurements. For these measurements, the sample was
continuously sheared
at a single fixed shear rate and data collected at fixed intervals. A shear
rate of 0.581 S4,
together with a delay time of 5 seconds and an integration time of 5 seconds,
was used in each
measurement.
The initial shear time measurement on each emulsion was performed within 15
minutes of manufacture and the apparent viscosity was monitored over a 5000
second time
period. This measurement gave an indication of the structure formation and
relaxation of the
emulsions immediately after manufacture.
The apparent viscosity of each emulsion was then monitored over time (days),
with
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one shear time measurement being taken at the beginning of the day of
interest, with the
duration of the measurement being 500 seconds.
Shear rate sweeps were performed over the full shear rate range of 0.00186 S-'
to 1470
S'. Two types of shear rate sweep measurements were conducted.
The first involved the sequential step-wise increase of shear rate to high
shear rates
followed by the sequential step-wise decrease of shear rate back to low shear
rates. These
will be referred to as "Up-Down" shear rate sweep measurements. An integration
time of 5
seconds was employed for all measurements, while delay times of 5, 30, 60, 180
and 600
seconds were used for each emulsion. These measurements gave an indication of
the
destructuration and restructuration times for the emulsions.
In addition, for Emulsion S6 only "Down-Up" experiments, in which the shear
rate
was sequentially decreased then increased in a step-wise fashion, were also
conducted,
enabling the comparison of Up-Down and Down-Up measurements. These
measurements
were conducted over five shear rate ranges, namely 0.00186 S-' to 0.116 S'',
1.16 S-', 11.6
S-', 116 S-' and 1160 S-' respectively. These measurements gave an indication
of the shear
rate range over which most destructuration of the emulsion occurs.
The second type of shear rate sweep measurement, which will be referred to as
a
"shear rate sweep under continuous measurement", involved the gradual increase
and decrease
of the shear rate over the shear rate range, with instantaneous readings
recorded throughout.
In contrast to the previous shear rate sweeps, these measurements did not
require delay and
integration times to be specified by the user. These measurements were
conducted in each
of the three rheometer gears, namely Gear 0 (18.2 S-' to 1460 S-'), Gear 1
(0.182 S-' to 14.6
S-') and Gear 2 (0.00182 S"' to 0.146 S-'). The selected sweep time was 600
seconds, with
the entire measurement involving an increase in shear rate over 600 seconds
followed by a
decrease in shear rate over a further 600 seconds (1200 seconds in total).
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Flow/relaxation, or stress relaxation, experiments involve shearing the
emulsion at a
specified shear rate for a specified period of time, thus applying an
accumulated strain to the
emulsion, and monitoring the decay of the torque on the bob for a specified
period of time
following the cessation of shear. The measurement gave information about the
recovery of
the emulsion after shear.
The flow/relaxation behaviour of Emulsion S6 was studied most thoroughly. For
this
emulsion, shear rates of 0.116 S-', 0.581 S-', 1.16 S', 4.61 S-' , 11.6 S', 46
S-', 116 S` 461
S-' and 1160 S-' were employed together with shear times of 30 seconds and 600
seconds.
The relaxation was monitored for 100 seconds. The relaxation curves were then
normalised
by dividing all shear stresses in each curve by the value of the first shear
stress recorded,
allowing further comparison of relaxation behaviour.
For remaining emulsions, shear rates of 0.116 S', 1.16 S-', 11.6 S` and 116 S-
' with
shear times of 30 seconds and 600 seconds were used. The relaxation was
monitored over
a 200 second time period and normalised curves were also produced.
Two types of oscillatory measurements were conducted.
The first, known as an "Oscillation Test", measured various dynamic variables,
including G' (storage modulus), G" (loss modulus) and phase angle S, over a
frequency range
of 0.004 Hz to 20Hz. Amplitudes of 10%, 20%, 30% and 40%, corresponding to
strains of
0.0206, 0.0412, 0.0618 and 0.0823 respectively, were employed for these
measurements.
Oscillation of the sample occurred only during measurement at each frequency.
The second type of measurement, known as a "Strain Sweep", measured the
dynamic
variables over a range of strains, namely 0.000206 to 0.206 (0.1 % to 100%
amplitude).
Frequencies of 0.1 Hz 1 Hz 10 Hz and 20 Hz were employed.
Results were interpreted using plots of tan 6 as a function of frequency and
strain
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respectively. This is due to the fact that tan S = G"/G'. Thus tan S > I
indicates that the
emulsion is behaving predominantly as a viscous or liquid material, which tan
S < 1 indicates
elastic or solid-like behaviour. Finally, tan S = 1 marks the transition from
"flow" to
"oscillation" of the emulsion.
Three further points should be noted for all measurements. Firstly, with the
exception
of the initial shear time measurements, rheological measurements were not
commenced until
one day after the manufacture of the emulsion. This length of time enabled a
state of
equilibrium to be attained. Secondly, any data point with a torque range of
less than 1.0 %
was considered to be unreliable and was therefore omitted from the data
presented. Finally,
a new emulsion sample was used for each measurement, so that results could be
directly
compared without having to account for shear history of the sample.
Droplet sizing of each emulsion was performed using a Malvern MasterizerTM and
a
magnetically stirred cell. The general procedure for analysing an emulsion was
as follows.
The cell was filled with paraffin oil and a background reading taken. A small
sample of
emulsion was collected on the end of a Pasteur pipette. The magnetic stirrer
was then
switched on and emulsion added to the paraffin oil by shaking the pipette in
the oil until a
sufficient concentration had been obtained. After allowing the sample to stir
for a short time
(around 10 seconds), the stirrer was switched off and a measurement
immediately taken.
For freshly manufactured emulsions, further measurements were taken in five
minute
intervals for a 2.5 hour time period so that the stability of the droplets
could be monitored.
On subsequent days, measurements were taken in five minute intervals over a 15
minute time
period, allowing the average droplet size of the emulsions to be monitored
over time.
The droplet size distributions of these emulsions are shown in Figure 7, while
their
average droplet sizes (on the day of manufacture) and apparent viscosities (as
measured on
the second day, at which time it is thought than an equilibrium droplet
packing, and thus a
stable apparent viscosity is attained) are listed in Table 1.
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TABLE 1
Average droplet size and apparent viscosities for standard and
thickened emulsions of various droplet size
Emulsion Average Droplet Apparent Viscosity
Size ( m) (Pa. s)
S6 6.18 180
S12 11.04 90
S18 17.72 65
T6 6.09 500
T12 11.19 200
T18 18.24 125
As can be seen from the data, the average droplet size and droplet size
distributions
of Emulsions S6 and T6 are very closely matched. Thus any differences in
rheological
behaviour as discussed below may be attributed predominantly to the
incorporation of the
associative thickener into the dispersed phase droplets. For Emulsions S12 and
T12,
however, while possessing similar average droplet sizes, it can be seen in
Figure 7 that the
droplet size distributions of these two emulsions are significantly different,
with the thickened
emulsion displaying a wider distribution. Similarly, Emulsions S18 and T18
exhibit similar
average droplet size but significantly different droplet size distributions.
Thus, for these latter
emulsions, any observed differences in the rheological behaviour of the
corresponding pairs
of standard and thickened emulsions may be partly due to this difference in
droplet size
distribution, in addition to the incorporation of associative thickener into
the internal phase
droplets.
Table 1 clearly shows that incorporation of associative thickener into the
internal phase
droplets of an emulsion has a marked viscosifying effect, especially for the
emulsions of
approximately 6 m average droplet size.
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The standard and thickened emulsions display similar behaviour under steady
shear
flow, with both sets of emulsions exhibiting shear thinning and thixotropic
behaviour in their
apparent viscosities as a function of shear rate. In addition, the emulsions
of larger average
droplet size, both thickened and unthickened, display some rheopectic
behaviour, especially
when long delay times are employed.
The apparent viscosities of Emulsions S6 and T6 as a function of shear rate
are given
in Figure 8. The displayed curves were obtained using a 60 second delay time
and 5 second
integration time and is representative of the curves produced using all five
delay times for
each of the three emulsion droplet sizes. The figure clearly illustrates that
the sweep up curve
for the thickened emulsion lies above that of the standard emulsion for the
majority of the
shear rate sweep up, with the curves merging at the highest shear rates. This
behaviour is
believed to be attributed to the relative deformability of the droplets of the
standard and
thickened emulsions. The fact that the sweep up curve of the emulsion
containing associative
thickener lies above that of the standard emulsion indicates that the droplets
of the thickened
emulsions have increased resistance to deformation. Thus the apparent
viscosity of the
thickened emulsions remain higher than for the standard emulsions during the
shear rate
sweep up, since the thickened emulsion has less tendency to flow as a result
of the decreased
deformability of the emulsion droplets. This increase in resistance to
deformation of the
droplets of the thickened emulsions would be expected, since these droplets
are of greater
apparent viscosity due to the incorporation of associative thickener and are,
therefore,
effectively "harder" and subsequently more difficult to deform, than the
droplets of the
standard emulsions. At high shear rates however, this increased resistance to
deformation is
overcome, and the droplets of the thickened emulsions are distorted to a
similar extent to that
of the standard emulsions. Consequently, the sweep up curves coincide at high
shear rates.
In addition, Figure 8 shows that the thickened emulsion displays increased
hysteresis relative
to that of the standard emulsions. Indeed, this observation is generally
observed for each of
the emulsions of different average droplet size for all delay times employed.
This suggests
that, once deformed, the emulsion droplets containing associative thickener
regain their
original shape and packing less rapidly than the droplets of the standard
emulsions, that is,
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the thickened emulsions display increased resistance to the reformation of
structure following
destructuration at high shear.
The shear stress as a function of time following cessation of 30 seconds of
shear at a
shear rate of 1.16 s 1 is shown for each of the standard and thickened
emulsions in Figure 9.
As can be seen from Figure 9, the initial shear stresses observed for the
thickened emulsions
are greater than those attained by the corresponding standard emulsions. This
behaviour is
believed to imply that the thickened emulsions tend to display increased
elastic behaviour
relative to the standard emulsions. This tendency is further supported by
comparing the
plateau values of the shear stress maintained by each of the emulsions. For
example, Figure
9 shows that the stress maintained by each of the thickened emulsions is
greater than that of
the corresponding standard emulsions. Indeed, this was the case for all of the
shear rates
employed in this study, with the trend being more apparent at the lower
applied shear rates.
In addition, the normalised curves show that the relaxation of the thickened
emulsions is
significantly slower than that of the standard emulsions, as evidenced by the
gradients of the
curves of the standard emulsions being greater than those of the thickened
emulsions. This
is believed to indicate that the shear stress is dissipated more quickly for
the standard
emulsions or, in other words, that the thickened emulsions are more capable of
maintaining
the accumulated strain. In addition, this suggests that the thickened
emulsions "solidify" at
increased strains, which again shows that the thickened emulsions are able to
store more
energy than the standard emulsions. These observations, by definition, again
indicate the
increased elastic behaviour of the thickened relative to the standard
emulsions.
The standard and thickened emulsions generally show very similar behaviour
under
dynamic shear flow. Both sets of emulsions display significant Maxwellian
behaviour, with
consideration of tan S as a function of frequency at several amplitudes
revealing that the
transition from flow to oscillatory behaviour for the emulsions occurs at
higher frequency for
increasing amplitude.
Tan 6 as a function of frequency at 30% amplitude is shown in Figure 10 for
all
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emulsions prepared in this study. It can be clearly seen from the figure that
the frequency at
which the transition from predominantly viscous to primarily elastic behaviour
occurs is
significantly decreased for the thickened relative to the corresponding
standard emulsions.
This was the case for all amplitudes studied. In fact, for the thickened
emulsions, the value
of tan S remains below unity over the entire frequency range studied in many
cases, that is,
the thickened emulsions display predominantly elastic behaviour over the whole
frequency
range. These observations clearly illustrate the increased elastic component
of the rheological
behaviour of thickened emulsions relative to that of the standard emulsions.
Similarly, consideration of tan 6 as a function of strain for a number of
different
frequencies reveals that, for both sets of emulsions, the transition from
predominantly elastic
to primarily viscous behaviour occurs at higher strain for increasing applied
frequency.
Tan 6 as a function of strain at a frequency of 0.1 Hz is shown in Figure 11
for
Emulsions S6, S12, T6 and T12. It can be clearly seen from the figure that the
aforementioned transition point occurs at higher strains for the thickened
relative to the
standard emulsions. This appears to be the general trend for all pairs of
corresponding
emulsions at all frequencies studied. These observations again imply that the
thickened
emulsions show increased elastic behaviour relative to that of the standard
emulsions.
While the invention has been explained in relation to its deferred embodiments
it is
to be understood that various modifications thereof will become apparent to
those skilled in
the art upon reading the specification. Therefore, it is to be understood that
the invention
disclosed herein is intended to cover such modifications as fall within the
scope of the
appended claims.
