Note: Descriptions are shown in the official language in which they were submitted.
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PROCES ING AND USE OF CARBIDE LIME
The present invention relates to the processing and use of a waste by-
product of the acetylene industry known as "carbide lime", especially as a
filler and extender in thermoplastic compositions, and to the preparation of
carbide lime for such use.
°Carbide lime" i,~ the waste by-product generated in the commercial
production of acetylene gas by reacting calcium carbide with water. On a dry
weight basis, it is primarily connprised of calcium hydroxide (typically 75 to
87%), with varying amounts of calcium carbonate (1 to 15%, depending on
exposure to air), and 5~ to 10% of silicaceous, carbonaceous and inorganic
impurities derived from the calcined limestone and coke used to manufacture
the calcium carbide.
In many countries, a "wet" carbide process is used, wherein more than
double the stochiometric amount of water is used to ensure that there is no
residual unreacted cal~:ium carbide. This maximises acetylene production
and eliminates the risk of explosion from residual acetylene retained in the
carbide lime waste material. A,s a consequence, the carbide lime waste is
obtained from the settling ('dec;ant') tanks of the "wet" acetylene process as
a
thixotropic slurry with about 55 to 65% moisture content, and is commonly
pumped to outdoor lagoons or pits for storage and dewatering. In other
countries, especially in Eastern Europe, a °dry" process is employed,
using
less water and with vacuum e~;traction of remaining acetylene gas, resulting
in a drier carbide lime with only about 8-10% moisture. Large quantities of
both carbide lime by-pn~oducts are produced each year.
With very few commerciial uses of carbide lime and the unwillingness of
producers to pay the treatment and disposal costs for neutralising its high pH
to make it suitable for landfilling, millions of tons of carbide lime have
accumulated as a waste material in lagoons, pits and heaps around the world,
and the quantity is increasing ;annually.
It has been estimated that carbide lime is the third largest tonnage of
waste material in the world, after the slag from iron and steel production and
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coal slag from power stations. Known commercial uses, which collectively
account for a very small proportion of the carbide lime produced each year
are limited to, for instance, application as a neutralising agent in scrubbing
waste acid flue gases, as a constituent of various mortars and cements, use
of dried carbide lime admixed with crushed stone in an asphalt binder to
produce building blocks and paving material, and the manufacture of low-
grade agricultural calcium fertilisers. Methods of drying carbide lime sludge
by admixing and chemical reaction with quicklime or calcium carbide to keep
the carbonation levels below governmental standards as slaked lime for use
in mortars/cements are disclosed by Fedorik et al in Czech patent 214011,
issued June 1, 1984. A process for chemical conversion to purified
precipitated calcium carbonate powder has also been proposed.
A benefit of the present invention is the ability to use this waste by-
product substantially without chemical modification.
The use of fillers in polymer compositions is known, and fillers may
impart improved physical properties, such as stiffness, to the final article
compared to the unfilled resin. These are often referred to as "reinforcing
fillers".
Alternatively, fillers which are substantially lower in unit volume cost
than polymer resins may be added to the polymers to displace resin volume
and reduce overall composition raw material costs, frequently with reduced,
but adequate, physical properties in the final product. Such fillers are
sometimes known as "extenders". Frequently fillers perform both functions.
Yet other fillers may impart specific properties to the filled compound, e.g.
fire
retardency, opacity, colour etc. either used alone, or more commonly admixed
with the more general reinforcing fillers and extenders.
The most commonly used fillers are powdered inorganic materials,
although organics such as wood flour are used for special applications, as are
glass and other chopped fibres, glass microspheres etc. The inorganic fillers
are frequently of mineral origin, purified, ground and dried. The most
commercially significant are limestones ( calcium carbonates), taics, clays or
other naturally occurring minerals such as gypsum, barytes, feldspar and
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various silicates. Due to practical limitations on size reduction equipment,
the
ground mineral fillers are typically restricted to a minimum average particle
of
about 2-5 micron ESD (equivalent spherical diameter). For sub-micron
particle sizes, filler; may nE:ed to be chemically synthesized, where they are
referred to as 'precipitated' grades. These precipitated grades are much
more costly than ground mineral grades due to the extra costs of synthesis,
filtration and drying.
Insoluble metallic hydroxides, notably aluminum (frequently called
alumina tri-hydrate) and m<~gnesium, are well-known resin additives.
However, their thermochennical performance and that of zinc hydroxide are
more akin to hydrated oxides, since they decompose and lose their water of
hydration on heating to relatively low temperatures, from 108 through
210°C.
As a result, they are generally only used as fire-retardent additives in resin
compounds. They are unusable in polymers processed at higher
temperatures, e.g. nylon, due to thermal decomposition and consequent
porosity of the products obtained.
Commercial synthetic calcium hydroxide has also been investigated as
a potential fire retardent aclditive in thermoplastic resin/polymer systems by
Ashley and Rothor~, Plastics, Rubber and Composites Processing and
Applications 15 (1 ~t91 ) 19 ;21. However, the proposed use was rejected when
it was discovered that, contrary to published data, on heating in the presence
of air, calcium hydroxide does not quickly decompose endothermically to its
oxide, giving off water of albout 580°C, but instead reacts directly,
more slowly
and exothermically with carbon dioxide of the air to yield calcium carbonate
at
a lower temperature. WO 98131542 of Frijs et al proposes use of the gas
absorptive properties of calcium hydroxide with respect to carbon dioxide in
the film/foil packaging of carbon dioxide-sensitive foodstuffs. This
application
discloses a laminate having an intermediate layer of calcium hydroxide and/or
calcium oxide as gas absorbents, in low density polyethylene (LDPE) film,
protected from contact with foodstuffs by a gas-porous layer of plastic film.
In various thermosetting resin systems, the use of commercial
synthetic calcium hydroxide is disclosed as a minor additive.
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Japanese Patent 8291253, issued to Toray Industries describes blends
of polyphenylene sulphide p100 parts), olefin polymers containing halogen,
carbonyl and/or cyano groups (2-300 parts), calcium hydroxide (30-250 parts)
and fillers (0-350 parts) have improved tracking resistance for electrical and
i) 5 optical instruments.
In U5 patent 4847317, issued July 11, 1989, Dokurno et al disclose
filled carbo~;ylic acid/anhydride - grafted polyolefin blended compositions,
where the grafted reactive resin groups, preferably malefic anhydride, are
reacted with specified metallic hydroxide fillers, including calcium
hydroxide.
i) 10 It has now been found that carbide lime may be used as, for instance,
a general purpose or reinforcing filler and extender in a wide variety of
thermoplastic materials, especially in thermoplastic materials that are non-
reactive with carbide lime.
Accordingly, an aspect of the present invention provides a composition
i) 15 of theromoplastic polymer and powdered dried carbide lime, carbide lime
being a waste by-product from the production of acetylene gas by reaction of
calcium carbide with water.
A further aspect of the invention provides a composition of
thermoplastic polymer and powdered dried carbide lime, carbide lime being a
i) 20 waste by-product from the production of acetylene gas by reaction of
calcium
carbide with water, said carbide lime having a content of calcium carbonate
that is below 25% by weight and a mean particle size of 2-10 microns.
In embodiments of t:he composition of the present invention, the
composition comprises 5-60 parts by weight of carbide lime, 20-95 parts by
i) 25 weight of thermoplastic polymer and 0-60 parts by weight of at least one
additive selected from lubricants, stabilizers, antioxidants, plasticisers,
pigments and dyes; anti-blocking, anti-static, blowing and release agents;
flame-retardants; impact modifiers; coupling and wetting agents; processing
aids and fibrous reinforcing agents.
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Another aspect of the present invention provides a composition
comprising a blend of
(a) 5-60 parts by weight of powdered dried carbide lime, carbide
lime being a waste by-product from the production of acetylene gas by
reaction of calcium carbide with water;
(b) 20-95 parts by weight of at least one thermoplastic material
selected from the group consisting of thermoplastic polymer, thermoplastic
elastomer and thermoplastic rubber; and
(c) 0-60 parts by weight of at least one additive selected from
lubricants; stabilisers; antioxidants; plasticisers; pigments and dyes; anti-
blocking, anti-static, blowing and release agents; flame-retardants; impact
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modifiers; coupling and wetting agents; other processing aids and fibrous
reinforcing agents.
In embodiments, the; carbide lime is inert with respect to the
thermoplastic material, or interacts with the thermoplastic material.
Additional aspects oaf the present invention provides use of carbide
lime as a filler in a irhermop~lastic polymer, use of carbide lime as a filler
in a
thermoplastic elastomer and use of carbide lime as a filler in a thermoplastic
rubber.
In embodiments of the present invention, the thermoplastic material is
selected from at least one of polyolefins, polyvinyl chloride, polyvinylidene
chloride, copolymers of vinyl chloride or vinylidene chloride with vinyl
esters,
chlorinated polyvinyl chloride, polyamides, polyacetals, polycarbonates,
polyacrylates, therrnoplastic polyesters, polystyrene, polybutadiene,
poiybutylene, copolymers of butylene or butadiene with acrylonitrile,
polyester
and polyether urethanes, p~olyetherester elastomers, ethylene/propylene
elastomers, and ethylene/propylene/diene elastomers.
Another aspect of the present invention provides a process for the
manufacture of a carbide lime filled thermoplastic composition, comprising:
(i) feeding to apparatus for the processing of thermoplastic
materials, an admixture of:
(a) 5-60 parts by weight of dried powdered carbide lime;
(b) 20-95 parts by weight of at least one thermoplastic
material selected from the group consisting of thermoplastic polymer,
thermoplastic elastomer and thermoplastic rubber; and
(c) 0-60 parts by weight of at least one additive selected
from lubricants; stabilisers; antioxidants; plasticisers; pigments and dyes;
anti-
blocking, anti-static:, blowing and release agents; flame-retardants; impact
modifiers; coupling and wetting agents; other processing aids and fibrous
reinforcing agents;
(ii) homogeneously admixing (a), (b) and (c) at a temperature that
is above the melting processing temperature of the thermoplastic polymer and
the softening temperature of the thermoplastic elastomer or thermoplastic
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rubber, said temperature being below the decomposition temperature of
each of (a), (b) and (c), and
(iii) passing the composition so obtained from said apparatus.
In addition, an aspect of the present invention provides a process for
the manufacture of carbide lime in a form suitable for use as a filler in
thermoplastic; materials, said carbide lime being in the form of a sludge or
slurry
of solid waste by-product from the production of acetylene gas by reaction of
calcium carbide with water, such process comprising, in sequence:
(i) screening carbide lime;
(ii) drying the carbide lime to a moisture content of less than 0.6% by
weight and maintaining the calcium carbonate content below 25% by weight;
(iii) grinding the dried powder so obtained to a maximum mean particle
size of 30 microns; and
(iv) air classifying the dry, ground carbide lime powder, to separate a
fraction of lower specific gravity and having a mean particle size of 2-10
microns,
with maximum particle size of 40 microns, from coarser and/or denser material.
Additional aspects of the compositions of the invention have 5-60 parts
by weight of powdered dried carbide lime having a calcium hydroxide content of
70-85% by weight and a calcium carbonate content of 5-25% by weight, the
calcium carbonate being substantially in the form of surface carbonation on
the
calcium hydroxide.
Further aspects of the present invention provide a composition
comprising:
(a) 5-60 parts by weight of a filler having a calcium hydroxide content
of 70-85% by weight and a calcium carbonate content of 5-25% by weight, the
calcium carbonate being substantially in the form of surface carbonation on
the
calcium hydroxide;
(b) 20-95 parts by weight of at least one thermoplastic material
selected from the group consisting of thermoplastic polymer, thermoplastic
elastomer and thermoplastic rubber; and
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(c) 0-60 parts by weight of at least one additive selected from
lubricants; stabilisers; antioxidants; plasticisers; pigments and dyes; anti-
blocking, anti-static, blowing and release agents; flame-retardants; impact
modifiers; coupling and wetting agents; other processing aids and fibrous
reinforcing agents.
Further aspects of the invention are as follows:
Use of carbide lime as a filler in a thermoplastic polymer, carbide lime
being a waste by-product from the production of acetylene gas by reaction of
calcium carbide with water, said carbide lime having a content of calcium
carbonate that is below 25% by weight and a mean particle size of 2-10
microns.
Use of carbide lime as a filler in a thermoplastic elastomer, carbide
lime being a waste by-product from the production of acetylene gas by
reaction of calcium carbide with water.
Use of carbide lime as a filler in a thermoplastic elastomer, carbide
lime being a waste by-product from the production of acetylene gas by
reaction of calcium carbide with water, said carbide lime having a content of
calcium carbonate that is below 25% by weight and a mean particle size of 2-
10 microns.
Use of carbide lime as a filler in a thermoplastic rubber, carbide lime
being a waste by-product from the production of acetylene gas by reaction of
calcium carbide with water.
Use of carbide lime as a filler in a thermoplastic rubber, carbide lime
being a waste by-product from the production of acetylene gas by reaction of
calcium carbide with water, said carbide lime having a content of calcium
carbonate that is below 25% by weight and a mean particle size of 2-10
microns.
Aspects of the present invention provide a process for the preparation
and manufacture of carbide lime into a form suitable for use as a filler in
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thermoplastic compositions, starting from the sludge or slurry solid waste-
product produced as the by-product from the manufacture of acetylene using
the reaction of calcium carbide with water. Such carbide lime sludge or slurry
may have a wide range of moisture content e.g. from 8% to 65%, depending
on the type of process i.e. "wet" or "dry". As noted above, the slurry
directly
from the process settling or decant tanks of a wet process, usually in the
form of a thixotropic pumpable slurry, typically has 55 to 65% by weight
moisture. From storage ponds or lagoons where gravity dewatering and
evaporation reduces the moisture content, the moisture content is typically 35
to 55% by weight. The moisture content of the slurry from the process decant
tanks may be reduced by conventional vacuum filtration to 10 to 30%, or
more slowly, by gravity dewatering in tanks or ponds to 30 to 55% by weight.
Carbide lime from a dry process has a lower moisture content e.g. 8-10%.
The particle size of the carbide lime, as obtained from a wet or dry
process, is generally in the range of 0.5 to 100 microns. However, due to the
caking characteristics of the principal component, calcium hydroxide, in air,
agglomerates of primary particles and clumps of agglomerates can form, with
lumps of material up to several metres in size. These need to be
mechanically broken into smaller pieces, by conventional means, and passed
through a grid, typically having square openings about 2.5 to 10 cms per side,
or a conventional screen, such that the maximum size of the pieces is smaller
than any critical dimensions of any subsequent apparatus to avoid blocking of
the flow. Filler cake from dewatered decant tank slurry may be fed directly to
the process.
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From either of these sources, the following steps may be performed,
in sequence:
i) preliminary indirect heating and drying of the material to a moisture
content of 5 to 20%, preferably 5 to 15%, in an apparatus with minimal
contact with air, to reduce the rate of surface carbonation, and with
simultaneous mechanical agitation to reduce the particle size of agglomerates
and prevent caking;
ii) course sieving of the partially-dried carbide lime with coarse
material returned to the first-stage drying and the finer material conveyed to
an apparatus for further drying;
iii) secondary drying of the material to less than 0.6% moisture,
preferably less than 0.25% moisture, in a conventional direct or, preferably,
indirect dryer or by microwave drying at high temperature and with short
residence time to minimize surface carbonation, such that total calcium
carbonate content is kept below 25% by weight, preferably below 20% and
even more preferably below 15%;
iv) size reduction e.g. by grinding, pulverising, milling or crushing of
the dried powder to a maximum mean particle size of 30 micron, preferably
15 microns and even more preferably 5 to 10 microns, with the maximum
individual particle size of 100 microns, preferably 50 microns in a
continuous,
non-batch conventional pulveriser. The pulveriser is preferably of the impact
or air jet mill type, where there is particle-to-particle impact;
v) air classification of the dry, ground carbide lime powder to
separate and purify the finer sized and lower specific gravity particles. The
product preferably has a mean particle size of 2-10 microns, with maximum
particle size of 40 microns, preferably 20 microns. Coarser material and
higher specific gravity impurities such as calcium carbonate and silicates
which form the classifier tailings, may be discarded, used in mortar mixes or
recycled and mixed with wet feedstock to the first stage dryer. The fines
product from the classifier may be separated from its airstream by
conventional cyclone and/or dust collection equipment and stored or bagged
under sealed, dry conditions.
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Use of the feedstock from the "dry" process may obviate the need for
step (i) since its moisture is typically below 10% and it has low surface
carbonation if freshly produced.
Preferentially, the preliminary drying of stage (i) may also incorporate
windrowing to reduce high ex-pond moisture. Alternatively or additionally,
such drying may also involve mixing of the wet feedstock with dried carbide
lime recycled as part of the output from any of the stages, (iii) after
secondary
drying, (iv) after grinding andlor (v) after classifying, preferentially using
the
coarse "tailings" from the latter.
Optionally, the airstream from the secondary dryer and the fines
cyclone separator may be further filtered e.g. by the bag filters andlor
electrostatic precipitators to prevent or reduce solid emissions to the
environment. The fines that are collected may also be recycled by
continuously mixing with the wet feedstock entering the first-stage dryer, to
reduce feed moisture. Suitable continuous mixers include trough
mixersldryers, ribbon mixers and pug mills.
In an embodiment of the invention, the apparatus is constructed
primarily of stainless steel to prevent both iron pick-up in the filler, which
may
discolour certain resins, and to prevent corrosion of the equipment due to the
corrosive pH nature of the carbide lime when moist.
It should be understood that one of the primary benefits of carbide lime
as a filler derives from its lower specific gravity compared to conventional
fillers such as calcium carbonate (SG 2.7) or talc (SG 2.8), enabling
advantages of lower filler usage by weight, for the same filler volume, and
lighter-weight finished compositions and shaped articles. The carbide lime
specific gravity may be in the range 2.29 to 2.32 gmlcc, which represents a 14
to 18% lower filler density. As surface carbonation of the calcium hydroxide
in the carbide lime increases, its specific gravity increases and the weight
benefit is reduced.
Furthermore, the greater the extent of surface carbonation, the lower is
the available particle surface area containing resin-accessible hydroxyl
groups, which are more hydrophilic and reportedly provide better bonding
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strengths between resin-filler interfaces than carbonate or silicate groups.
Conversely, a benefit of surface carbonated carbide lime is that the inert and
pH-neutral calcium carbonate thin outer coating, chemically bonded to the
calcium hydroxide of the carbide lime interior, may provide a protective
layer,
preventing polymer degradation caused by contact with the high pH calcium
hydroxide, in the presence of trace amounts of surface moisture, in resins
which are sensitive to high pH environments.
For these reasons, it is therefore important to minimize the extent of
carbonation during processing, and also, desirably, in the original slurry
feedstock. It is preferable to use freshly prepared carbide lime slurry either
from the decant tanks of the "wet" process, or taken directly from the "dry"
process, where the initial calcium carbonate content is commonly less than
5% by weight, and typically 1 to 3%. Conversely, if carbide lime slurry has
been stored outdoors in exposed storage ponds for lengthy periods, the initial
calcium carbonate content may be as high as 15%, and it is more difficult to
keep the final carbonation level below 15-20% in the final processed product.
It has been found that the extent of carbonation of the hydroxide in
carbide lime in a drying process is a complex matter dependent on a number
on inter-related variables including material temperature and moisture
content, air temperature and relative humidity, particle-size and surface area
of the filler, exposure time and the extent of initial feedstock surface
carbonation. In the case of direct dryers, the air velocity and the carbon
dioxide content of the dryer inlet air are factors, which varies with fuel and
combustion. The carbonation also interacts with the ability to dry the
product,
since extra moisture is chemically generated in the carbonation reaction in
the
stochiometric proportion 18:44 of the carbon dioxide reactively absorbed.
It was also found that the propensity of the carbide lime to cake, or
agglomerate, increased at moisture contents greater than about 15-20%,
such that most feedstocks having moistures greater than this could not be
introduced into conventional dryers, since the material caked and plugged the
dryer or related conveying and feed metering systems. Furthermore, the
longer residence time required for drying these higher moisture feedstocks in
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air, caused excessive carbonation. However, it was found that this caking
and blocking did not occur if the feed to the dryer could be controlled below
15 to 20% moisture, and farther that the carbonation created in the dryer
could be controlled) below 15 to 20% in direct dryers having co-current air.
Less carbonation vvould be: expected in counter-current indirect rotary
dryers,
with less airflow, and even less with microwave or flash dryers. It has been
found that flash dryers, operated at high air temperatures and with high air
velocities can advantageously be employed, wherein the short resident time
can keep added carbonation below 5% and with de-agglomeration of larger
particle sizes caused by particle-to-particle impact in the high velocity
airstream.
Aspects of this invention therefore include a two-stage drying
procedure for the carbide Time, where feedstock moisture exceeds the 20%
caking moisture, as is common, or where initial carbonation levels are high.
Preliminary, or first stage dlrying, is required to reduce the moisture
content
below about 20% vvhile minimizing the extent of carbonation. This requires
minimal contact with air, wiith concurrent mechanical agitation to prevent and
break down agglomerates from caking. It has been found that the most
suitable apparatus is a screw-conveyor, or "trough", dryer with exterior
jacket
heated by fluid or steam, preferably with multiple screws, or paddle
mechanisms, for agitating and conveying the material through the dryer.
Jacketed ribbon blenders and pug mills are also suitable. The use of hollow
screws or paddles to improve heat transfer coefficients in particularly
preferred. In thesE; types of apparatus, which preferably have a cover, the
moisture is effectively steamed off as the material is turned over, with
minimal
surface area exposed to air.
While such apparatus may optionally be operated under vacuum, or
under a blanket of inert gas, the simplest and most economic operation is with
a low capacity fan drawings minimal airflow countercurrently through the
chamber and using the high water vapour content of this air as a blanket to
slow the rate of carbonation. To maximize heating and drying efficiencies, the
heating fluid temperatures should be 150 to 350°C, preferably 250 to
350°C
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and operated countercurrent to material flow direction. The material
temperature should be maintained between 100 to 150°C to slow the rate
of
carbonation. Increasing the rotation speed of the screws or paddles improves
the heat transfer coefficient and increases the breakdown of agglomerated
caked lumps of material, but also increases throughput rate, thereby reducing
residence drying time. Consequently it may be necessary, or more efficient,
to operate several such dryers in series.
Such apparatus may advantageously incorporate admixing of any dry
material recycled as superfines from dust collection equipment andlor as
tailings from the air classifier. Such admixing with dry recycle streams
reduces feed moisture, and heating may not be required. As well as
improving overall heat and mass efficiency, it can act as a means of
controlling variable pond-feed moisture.
Further aspects of the invention provide a composition of thermoplastic
polymer and carbide lime, especially in which the composition contains 5-60%
by weight of carbide lime. In embodiments, the composition comprises 5-60
parts by weight of carbide lime, 20-95 parts by weight of thermoplastic
polymer and 0-60 parts by weight of at least one additive selected from
lubricants, stabilizers, antioxidants, plasticisers, pigments and dyes; anti-
blocking, anti-static, blowing and release agents; flame-retardants; impact
modifiers; coupling and wetting agents; processing aids and fibrous
reinforcing agents. Uses of carbide lime include use as a filler in
thermoplastic polymer compositions.
Other aspects of the invention are directed to a composition
comprising 5-60 parts by weight of powdered carbide lime, 20-95 parts by
weight of at least one thermoplastic material selected from the group
consisting of thermoplastic polymer, thermoplastic elastomer and
thermoplastic rubber; and 0-60 parts by weight of at least one additive
selected from lubricants; stabilisers; antioxidants; plasticisers; pigments
and
dyes; anti-blocking, anti-static, blowing and release agents; flame-
retardants;
impact modifiers; coupling and wetting agents; other processing aids and
fibrous reinforcing agents. The carbide lime may interact with the
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thermoplastic material e.g. the thermoplastic material may be a modified
thermoplastic material, but in preferred embodiments the carbide lime is inert
with respect to the thermoplastic material.
In embodiments, the thermoplastic material is selected from at least
one of polyolefins, polyvinyl chloride; polyvinylidene chloride; copolymers of
vinyl chloride or vinylidene chloride with vinyl esters; chlorinated polyvinyl
chloride; polyamides; polyacetals; polycarbonates; polyacrylates;
thermoplastic polyesters, polystyrene, polybutadiene; polybutylene;
copolymers of butylene or butadiene with acrylonitrile; polyester and
polyether
urethanes, polyetherester elastomers, ethylenelpropylene elastomers, and
ethylene/propylene/diene elastomers. It is preferred that the carbide lime has
a mean particle size of less than 10 microns.
Examples of thermoplastic materials also include a copolymer of
ethylene and an ester selected from vinyl acetate and ethyl acrylate,
propylene-ethylene and ethylene-butene copolymers, polyethylene
terephthalate, polybutylene terephthalate and mixtures thereof, polyolefin
elastomer of octene, impact polystyrene, a homopolymer of ethylene or
propylene, a copolymer of ethylene or propylene with another alpha-olefin,
olefin co-polymer, thermoplastic polyester, a polyolefin elastomer,
styrenelbutadiene rubber, chlorinated polyethylene or polypropylene oxide.
In embodiments of the invention, the thermoplastic material is a
thermoplastic polymer with a melt index of 0.5 to 30 dg/min.
In preferred embodiments of the invention, the carbide lime has a
moisture content of less than 0.6% by weight. Preferably, the carbide lime is
air classified carbide lime, as described herein, and especially carbide lime
with a specific gravity of 2.29-2.69 gmlcc. In further embodiments, the
compositions of the invention contain 5-60% by weight of carbide lime. In
addition preferred embodiments, the carbide lime contains less than 25% by
weight of calcium carbonate and has a mean particle size of 2-10 microns.
While the compositions described herein may be fed directly to
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subsequent thermoforming or melt processing apparatus, they are
usually formed into comminuted shapes, e.g. pellets, or into slabs, which are
more convenient suitable for storage, transport and feeding to subsequent
forming equipment.
Techniques and apparatus for the admixing, melt processing, extrusion
or thermoforming of filled thermoplastics, elastomers and rubbers are known
in the art. For admixing and melt processing, suitable equipment will include,
for example, high-dispersion internal mixers, twin-screw extruders and the
like, especially for thermoplastic polymers. For admixing certain elastomers,
two-roll shear mills may be preferred. Suitable extrusion, thermoforming or
other melt fabrication processes may include injection or blow moulding,
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profile or film extrusion, vacuum and compression moulding, casting and
calendering and rotational moulding. Articles made from compositions of the
invention using extrusion, injection moulding and calendering may find use in,
for instance, rigid duct and drainage piping, building panels such as siding,
flexible vinyl flooring, garden/patio furniture, rigid packaging and
transportation products.
The present invention relates to the processing and preparation of
carbide lime to a form suitable for its use as an economic filler in resin and
polymer compounds, and its use therein. Resin, polymer and elastomeric
compounds, particularly thermoplastics, and especially polyolefins and
polyvinyl chloride, are used in a wide variety of end uses in the form of
film,
sheet fibres, moulded, extruded or thermoformed articles, pipes, fittings,
profiles etc.
The present invention is illustrated by the following examples.
EXAMPLE 1
A carbide lime sludge from a "wet-process" storage pond, with 35%
moisture content, and having an initial composition of 83% calcium hydroxide,
11 % calcium carbonate and 6% silica/iron/alumina/carbon and magnesium
oxide impurities was fed at 800 Iblhour ( 364 kg/hr) to a stainless steel
jacketed conveyor dryer with two counter-rotating hollow heated screws
rotating at 3 rpm. The screws were heated co-currently by a DowthermT""
heat transfer fluid having an inlet temperature of 150°C. The partially-
dried
powdery material leaving this first-stage dryer had a moisture content of
14.3% and an outlet temperature of 100°C.
The partially dried material was fed by a belt conveyor into a stainless
steel, direct gas-fired rotary dryer, 5 feet (1.5 m) in diameter and 20 feet
(6.1
m) long, operating co-currently and rotating at 1.3 rpm. The inlet and outlet
air temperature were 260 and 155°C, respectively. The 600 Ib/hour (270
kg/hr) dried material output from the dryer was fed to a PremaT"" fine impact
grinder model M20, operating at 117 metres/sec with an air-flow pressure
drop of 6" w.g. The ground material was fed directly to a °Rema
AeroSplit"T""
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Model MAC 0, 3 HP, air classifier operating with a pressure drop of 8" w.g.
The moisture content of the classifier output was 0.52%. The particle size
distribution, as measured on a MicroTracT""-SRA9200, is shown in Table 1.
The coarse material from the classifier, having a mean particle size of 15-20
microns was recycled back in with the wet feed to the first-stage dryer feed
hopper.
The calcium carbonate contents of the fine product and of the coarse
tailings were 22% .and 24°ro, by weight, respectively. The specific
gravity of
the fine product was 2.35 gm/cc. The untamped bulk density of the fines
product was 22 Ib/cu. ft. (370 kg/m3).
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TABLE 1
Run Ratio
No. Product! Particle Size (microns)
Tailings
Mean 50% < 10% < 90% < Smallest Largest
Grinding
1 N/A* 14.3 9.6 2.5 33.6 0.69 114
2 NIA 15.6 11.2 2.7 35.4 0.69 81
3 NIA 12.9 8.4 2.4 27.6 0.70 114
3A NIA 9.6 6.3 2.0 22.3 0.69 57
Air-Classifying - Fines/Product
2 65:35 7.3 5.3 1.9 14.7 0.69 40
3 78:22 7.5 5.6 2.0 15.3 0.69 40
4 71:29 7.0 5.3 2.0 14.2 0.69 40
52:48 6.0 4.9 1.9 11.9 0.69 29
6 50:50 5.8 4.9 1.9 11.0 0.69 20
5 * NIA = not applicable.
EXAMPLE 2
A carbide lime sludge obtained from decant tanks in a "wet process"
for manufacture of acetylene, having a feed moisture content of 57.6% and a
calcium carbonate content of only 2%, was fed directly to the equipment
described in Example 1 but at a reduced throughput. The product material
from the rotary dryer, which had a moisture content of 0.42% and a calcium
carbonate content of 17%, was ground and classified to produce a mean
particle size of 2-3 microns. This example demonstrates the ability of the
process to achieve lower carbonation levels in the final material by the use
of
a lower carbonate content feed material from the decant tanks.
EXAMPLE 3
The same carbide lime sludge feedstock as in Example 1, with 35%
moisture, was continuously admixed with an equal weight of dried carbide
lime "tailing" obtained from the rejected coarse oversize stream from the
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"Rema AeroSplit" model MAC 0 air classifier described in Example 1. This
mixing was done in the same jacketed conveyor dryer, or trough dryer,
described in Example 1, operating at a screw speed of 3 rpm, with the heating
only on the jacket shell. A production rate of 600 Ibs/hour (272 kg/hr) was
obtained from the preliminary drying stage, with the product having a moisture
content from 16 to 18.5%.
The partially dried carbide lime was then continuously fed to a 14"
(35.5 cm) diameter ThermoJetT"" flash-dryer, manufactured by Fluid Energy
Aljet, at feedrates (wet basis) of 2300 to 4500 Ib/hr (1045-2045 kg/hr). The
dryer was heated by 2100 SCFM air at an inlet temperature from 200-
255°C,
with the material collected in a cyclone hopper and superfines removed in a
dust collection system. Output production rates of 1900 to 3500 Ib/hr (860-
1590 kg/hr) (dry basis) were obtained, with product moisture contents from
0.4% to 0.7%, depending on process variables.
It was found that this type of dryer, operating with high air velocities of
50 to 60 feet per second (15.2-18.3 m/s) in a donut shaped loop also
advantageously caused particle to particle impact with consequent
deagglomeration of carbide lime particles, and a consequent significant
reduction in mean and topsize particle size. The particle size distribution of
this dryer feed and output streams, measured by a Coulter unit using
isopropyl alcohol as dispersant, are shown below.
The dried product was then size reduced, using a small jet-mill with
integrated air classifier and oversize recycle. The jet-mill, manufactured by
Fluid Energy Systems, and operated by Ortech International, Mississauga
produced outputs of up to 100 Ib/hr using 100 psig compressed air. The
median and maximum particle size and size distribution fell well within the
typical limits of 5-6 micron median size ("D50 value") and 30 micron topsize
("D100 value"), commonly used for mineral fillers used in plastics. The jet-
milled product particle size data, tested on a "MicroTrac" analyser, also
using
isopropanol dispersant, is shown below.
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Size - microns (gym)
Feed to Dryer Ex Dryer Ex Jet-mill
Median size ~m fi0 ~m 15 pm 5.2pm
> #30 mesh 22% 0.35% 0%
(>600 pm)
Analysis of < 600 p,m material
10% < 1.7 ~m 1.9 pm 1.2 pm
25% < 5.3 pm 5.8 ~m 2.4 ~m
50% < 15.6 p,m 14.4 pm 5.2 pm
75% < -- 20.0 ~tm 9.2 ~tm
90% < 51.9 ~m 46.7 ~zm 13.1
~m
100% < 176 pm 134 ~,m 28.1
~m
EXAMPLE 4
A number of different filled resin compositions were made from the
dried, ground, classified carbide lime powder made from Run #6 in Example
1. The powder had a mean particle size of 5 microns. The compositions
were made using the methods described above, and comparable
compositions were also made under the same conditions by substituting a
conventional, commercial filler, ground calcium carbonate, with the same (5
micron) average particle size. The components were preweighed, admixed
and melt processed in a 3-litre capacity MoriyamaT"" high dispersion mixer, to
a temperature of 140°C for the high density polyethylene compositions
and to
200°C for the PVC compositions, cooled and then ground into flakes for
subsequent thermoforming. The compositions used one or more of the
following materials;
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(a) #25~~55N high density polyethylene resin (HDPE), having a
density of 0.955 gm/cc and a melt index of 25 dg/min obtained from Dow
Chemical;
(b) GeonT"" 30 suspension homopolymer polyvinyl chloride resin
(PVC), having a density of 1.40 gm/cc, a "K" value of 70 and an inherent
viscosity of 1.02, obtained from The Geon Company;
(c) KemamideT"" U, a polyolefin lubricant and release agent
additive, having a density of 0.96 gm/cc and obtained from Witco Chemical, a
division of Humko Chemical;
(d) VicronT"" 25-11, a ground, non-coated, calcium carbonate filler
having the same (.5 micron) average particle size and a similar size
distribution as the carbide-lime. This filler had a density of 2.70 gm/cc, and
was made by Speciality Minerals Inc of CA, and obtained via Stochem Inc of
Brampton, ON.
(e) #404~C, an organo-tin stabiliser for PVC, obtained from Reagens
(Canada) Ltd;
(f) #AC629-A, an anti-oxidant/lubricant additive for PVC, obtained
from Canada Colors & Chemicals Ltd;
(g) Zinc Stearate, a PVC lubricant agent, obtained from Witco
Chemical.
Tensile strength and elongation were measured at 23°C using the
procedure of ASTIV1 D-638, while Gardner impact resistance was tested,
using 20 specimens, by the procedure of ASTM D5628-95 using the Bruceton
Staircase technique. The type IV dumbbells for tensile testing and the
circular specimens for Gardner impact tests for the HDPE compositions, both
0.120" (3 mm) thick, were injected moulded at 200°C. For the PVC
compositions, 6" ~; 6" square plaques, of 0.150" (3.8 mm) thickness were
produced by compression moulding at 200°C, from which the tensile bars
and
Gardner specimens were cut.
Further details and results obtained are given in Table 2.
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TABLE 2
A) HDPE Compositions
Sample Sample Sam ple
1 2 3
%by %by %by %by %by %by
wt vol wt vol wt vol
HDPE 59.5 80.2 62.3 80.2 59.5 78.4
KemamideT"" U 0.5 0.7 0.5 0.7 0.5 0.6
VicronT"" 25..11 (CaCO~)40.0 19.1 -- -- -- --
Carbide Ilme -- -- 37.2 19.1 40.0 21.0
Max Tensile strength 2715 2883 3010
(psi)
Elongation at Break (%) 6.0% 6.2% 5.4%
Gardner Impact resistance13 11 n/a
(in-Ib)
Density, gm/cc
1.26 1.20 1.23
B) PVC Compositions
Sample Sample 5
4
by % by % by % by
wt vol wt vol
PVC homopolymer 77.8 85.1 79.8 85.1
404C tin stabiliser 1.6 2.2 1.6 2.2
AC629-A antioxidant 0.4 0.5 0.4 0.5
Zinc stearate 0.8 1.2 0.8 1.2
VicronT"" 25-11 (CaC03)19.5 11.0 -- --
Carbide lime -- -- 17.4 11.0
Yield Tensile strength 7610 7432
(psl)
Elongation at Yield 5.0% 5.0%
(%)
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Break Tensile strength (psi) 5555 6527
Elongation at Break (°%) 12.9% 9.7%
Gardner Impact resistance 22 18
(in-Ib)
Density, gm/cc
1.5 1.45
In this example:
Samples No. 2, 3 (in HDPE) and 5 (in PVC) illustrate compositions of
the invention.
Samples No. 1 (HDPE) and 4 (PVC) are comparative examples
illustrating the properties of the the same resin when filled with a Vicron 25-
11, a commercial ground calcium carbonate filler of the same particle size
and distribution.
Samples No 2 and 5 are filled at the same percentage by volume by as
their comparable calcium carbonate-filled samples No. 1 and 4, respectively.
Sample No. 3, in HDPE, is filled at the same percentage by weight as
the No 1 filled with Vicron 25-11, and exhibits a higher tensile strength but
slightly lower break elongation due to the consequent higher filler loading by
volume.
This example illustrates that compositions of the invention have useful
tensile and impact strength properties with values generally equal to those of
equivalent compositions filled with the same size calcium carbonate filler. It
also illustrates the advantageous lower density (specific gravity) of the
compositions of the inventiion, i.e. lower weight per unit volume of finished
product, with equal physical properties (per unit volume), such lower density
benefits being greatest, compared to conventional fillers, when the carbide
lime is filled to equal volume.
EXAMPLE 5
A number of further compositions of the invention were made, using
the carbide lime produced in Run No. 5 of Example 1 and using the method of
the invention, to illustrate the application and physical properties in other
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common resin and elastomer systems, carbide lime compatability with other
common additives such as pigment fillers, silane surface bonding agents,
plasticisers and the like, and a wide range of high and low typical filler
loadings.
As in Example 4, the components were preweighed, admixed and melt
processed in a 3-litre capacity MoriyamaT"" high dispersion mixer, to a
temperature of 140°C for the HDPE compositions, to 150°C for the
polypropylene compositions and 120°C for the plasticised polyethylene
elastomer composition, cooled and then ground into flakes for subsequent
thermoforming.
In addition to the material described in Example 4, the compositions
used one or more of the following materials:
(h) KY6100, a polypropylene copolymer resin with EPDM, having a
density of 0.904 gm/cc and a melt index of 25 dg/min, obtained from Shell
Chemical;
(i) EngageT"" 8100, a polyethylene elastomer having a density of
0.85 gm/cc obtained from Dow Chemical;
(j) RCL4, a titanium dioxide white pigment, having a density of 4.0
gm/cc and an average particle size of 0.5 microns, obtained from L. V. Lomas
& Co;
(k) A-1120, a silane-based filler bonding additives for polyolefins,
supplied by OSI Chemicals, manufactured by Union Carbide Chemicals;
(I) SuperpflexT"", a high-grade precipitated calcium carbonate filler,
coated with 0.2% stearic acid for lubrication, and having an average particle
size of 0.7 microns, obtained from Stochem Inc, and manufactured by Pfizer;
(m) Calcium stearate, a polyolefin lubricant additive, obtained from
W itco;
(n) SunparT"" 2150, a high viscosity paraffinic oil suitable as a
plasticiser for polyethylene elastomers, having a density of 0.8956 gm/cc and
a viscosity of 21.6 cSt at 100°C, obtained from Noco Lubricants Ltd,
made by
Sunoco Ltd.
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Tensile strength and elongation were measured as in Example 4. The
type IV dumbbells for tensile strength for the polypropylene compositions,
0.120" (3 mm) thick, were injection moulded at 220°C. For the HDPE
compositions, as in Example 4. For the plasticised polyethylene elastomer
compositions, 6" x. 6" square plaques, of 0.150" (3.8 mm) thickness were
produced by compression moulding at 140°C, from which the tensile bar
specimens were cut.
Further details and the results obtained are given in Table 3.
SENT BY:SIMBAS ; 2- 1-01 ;10:51AM ; SIMBA51 819 994 1989;# 4
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TABLE 3
A) HDPE Compositions
Sample Sample
6 7
by wt % by vol % by % by vol
wt
HDPE 61.7 80.3 59.5 80.3
Kemamide''"" U 0.5 0.6 0.5 0.6
SuperplfexT"" (CaC03)-- -- 40.0 19.1
Carbide lime 35.7 18.5 -- --
RCL4 - TIOZ pigment 2.1 0.6 -- --
Sub-total fillers 37.8 19.1 40.0 19,1
Max Tensile strength 3440 3050
(psi)
Elongation at Break 2.6% 10.0%
(%)
Density, gm/cc 1.21 1.26
B) Polypropylene Compositions
Sample S ample 9
8
by wt % by vol % by % by vol
wt
Polypropylene 51.0 73.0 48.5 73.0
Calcium stearate 1,0 1.3 1.0 1.3
Silane bonding agent 0.5 0.5 0.5 0.5
SuperpflexT"' (CaC03)-- -- 50.0 25.2
Carbide lime 45.7 24.7 -- --
RCL4 - Ti02 pigment 1.8 0.5 -- -
Sub-total fillers 47.5 25.2 50.0 25.2
Max Tensile strength 4010 3750
(psi)
Elongation at Break 1.6% 2.2%
(%)
Density, gm/cc 1.25 1.32
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C) Polyethylene Elastomer Compositions
Sample Sample
10 11
by wt ~ by vol % by 8~ by
wt vol
EngageTM PE elastomer 65.0 76.5 63.3 76.5
KemamideT"" U lubricant0.7 0.7 0.7 0.7
SunparT"' 2150 plasticiser13.3 14.1 13.0 14.1
oil
SuperpflexT"~ (CaC03) -- - 23.0 8.7
Carbide lime 21.0 8.7 --
Max Tensile strength 410 500
(psi)
Elongation at Break 890% 1190%
(%)
Density, gm/cc 0.998 1.03
In this example:
Samples No 6, 8 and 10 illustrate the use of carbide lime filler, having
micron mean size, in three different polymer and elastomer compositions,
5 while Samples No 7, 9 and 11 show the comparable tensile properties of
equivalent compounds filled with the same loading, by volume, of
SuperpflexTM precipitated coated calcium carbonate of 0.7 micron average
size.
Samples No 6, 8 and 10 demonstrate the use of carbide lime filler In a
wide range of filler concentrations, from 21 to ~+5% by weight, 8 to 25% by
volume.
Samples 6, 8 and 10 illustrates the compatibility of the carbide lime
filler with lubricants, release agents, pigments, surface bonding agents and
plasticisers, without loss of useful tensile properties.
Samples No 6 and 8 show the ability to pigment carbide lime filled
compositions.
Sample No. 10 shows the use of carbide lime filler in an elastomer
composition, with plasticising oil, and the use of the compression moulding
process used in the preparation of tensile test specimens.
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Sample No. 8 and 8 illustrate the compositions typical of admixing and
processing in high melt index, 20-30 dg/min, resins suitable as injection
moulded compounds and show the processability of these compositions
whose tensile bar/dumbbell test specimens were injection moulded under
normal processing conditions.
Samples No 6, S and 19 show the lower density benefits of the
compositions of the invention, being 3 to 5% lighter then equivalent
compositions filled with calcium carbonate at the same volume, without loss
of tensile properties. Sample 10 shows an application of such lower density,
where the carbide lime filled composition has a specific gravity below 1.0
g/cm3, which would float in fresh water, whereas the calcium carbonate-filed
equivalent compound, Sample 11, with a density of 1.03 gm/cc would sink.
This example shows that compositions of the invention In polyethylene
(high density) and polypropylene have 7 to 12% higher tensile strength
compared to equivalent calcium carbonate-filled compositions at the same
filler loading by volume. This higher tensile strength remains even when
compared to known low resin-matrix bonding resins, such as polypropylene,
when surface treated with silane bonding agents (Sample 8 vs Sample 9).
The initial slope of a tensile stress-strain curve and the maximum
(yield) tensile strength, and break (yield) elongation data obtained for these
samples also indicate the compositions of the invention have greater stiffness
than the equivalent SuperpfIexTM filled compositions. Thus for HDPE, 3440
psi (987 MPa) at 2.6% strain for carbide lime, compared to equivalent 3050
psi (875 Mpa) at 10% for SuperpflexT""; for PP 401D psl (1'150 MPa) at 1.6%
compared to 3750 psi (1076 Mpa) at 2.2%, respectively.
The lower break elongation values of the carbide lime filled
compositions, compared with SuperpflexT"" calcium carbonate filled
equivalents ace believed to be due to the much finer particle size of the
SuperpflexT"' filler, 0.7 micron average, and its stearlc acid coating,
compared
with the uncoated carbide lime at 5 micron average. The prior Example 4
illustrates the physical properties and equal break elongations when the
filler
is compared to uncoated calcium carbonate on an equal particle sire basis.
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EXAMPLE B
A further series of compositions of the invention were made to illustrate
the lack of sensitivity of the properties of carbide lime filled compounds to
the
source and process from which the by-product waste carbide lime is derived
and to its carbonation content. Furthermore, such samples, prepared in the
manner described above, were admixed and processed in a low melt index
linear low-density polyethylene (LLDPE), typical of resin compounds used far
extrusion or blown film applications, to show application in such uses and
products.
In addition to the materials in Examples 4 and 5, the compositions
used one or more of the following materials:
(o) DowIexTM 530C, a linear low density polyethylene homopolymer,
having a density of 0.922 gm/cc and a melt index of 2.0 dg/min, obtained from
Dow Chemical.
The compositions were admixed, melt processed and ASTM dumbbell
tensile specimen bars were Injection moulded. Tensile testing was pertormed
as in Examples 4 and 5.
TABLE 4
LLDPE Compositions
Sample Sample Sample Sample
12 13 14 15
by % by % by % by % by % by % %
by by
wt vol wt vol wt vol wt vol
LLDPE 530 69.3 85.2 69.3 85.2 69.3 85.2 69.3 86.4
Kemamide 0.7 0.8 0.7 0.8 0.7 0.8 0.7 0.8
U
Superpflex -- -- -- -- -- -- 30.0 12.8
( .~ra~r~3)
RCL4 - Ti02 1.0 0.3 1.0 0.3 1.0 0.3 -- --
pigment
Sub-total 30.0 14.0 30.0 14.0 30.0 14.0 30.0 12.8
fillers
~, , , , ; . , ~ _.
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Max Tensile 2160 2050 2058 2080
strength (psi)
Elongation at 55% 100% 85% 106%
Break (%)
Density, gm/cc 1.12 1.11 1.11 1.134
In Sample 12, the carbide lime source was from a storage pond of Air
Products Co, which when processed in Example 1, Run 5 had a calcium
carbonate content of 22% by weight.
In Sample 13, the carbide lime source was from the decant tanks of
the "wet" process of Carbide Graphite Group Inc, which when processed by
the method of Example 2, had a calcium carbonate content of 17% by weight.
In Sample 14, the carbide lime was obtained from a Carbide Graphide
Group Inc storage pond but had been previously chemically dried by mixing
with quicklime prior to processing by the method of Example 1. Its initial
calcium carbonate content was 8.4% by weight.
In this example:
Samples 12, 13 and 14 illustrate the consistency of tensile properties
of the carbide lime filled compositions, irrespective of the source of such
material and with wide variation of calcium carbonate content. The somewhat
higher break elongation values of Samples 13 and 14, compared to Sample
12 are believed due to smaller average particle size, 2-3 microns vs 5-6
microns.
Sample 15 is a comparative composition, with the same filler loading,
by weight, using Superpflex, a 0.7 micron coated calcium carbonate filler.
The compositions of this example show useful tensile properties,
comparable to a composition using high grade, fine calcium carbonate, even
when loaded at the same percentage by weight. This results in a higher filler
loading by volume, which typically would reduce break elongation values.
They also exemplify application in a fow melt index resin system, 2.0 dglmin,
typical of extrusion compounds.
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EXAMPLE 7
Compositions of the invention were prepared to evaluate the effect on
physical properties of increasing the filler content of the carbide lime and
to
compare such properties against equivalent talc-filled compounds. In
addition, the effect ~of incoporating coupling agents was evaluated.
The samples were prepared and test specimens made and tested in
the manner described in E~;ample 4.
The compositions used dried, ground carbide lime produced in
Example 3 with ones or more materials selected from:
(p) a high molecular weight high density extrusion grade
polyethylene (HMV1JHDPE), having a density of 0.94 g/cm3 and a melt index of
10 dg/min, from Nova Corp;
(q) a "Luaenac" talc of 4 micron median particle size;
(r) FusabondT"~ MB 1100, a coupling agent made of maleic-
anhydride-grafted polyethylene, obtained from Du Pont Canada Inc.
The composition and their physical properties are shown in Table 5.
TABLE 5
HMWHDPE Compositions
Sample 16 Sample 17 Sample 18 Sample 19
%o by /~ % by % by % by % by % by % by
by
~n~t vol wt vol wt vol wt vol
HMWHDPE 100 100 90 95.70 80 90.90 70 85.40
Carbide lime0 0 10 4.3 20 9.10 30 14.6
Max* tensile3735 3615 3545 3284
strength
(psi}
Yield 21 % 20% 18% 16%
elongation
(%)
Break 59% 36% 33% 27%
elongation
(%)
Density, 0.94 1 1.07 1.15
gmlcc
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Sample 18 Sample Sample 21
20
by % by % % by % by % by
by
wt vol wt vol wt vol
HMWHDPE 80 90.90 78 88.6 77 90.90
Carbide lime 20 9.10 20 9.10
Talc -- -- - -- 23 9.10
Fusabond MB110D -- -- 2 2.30 -- --
Max* tensile strength3545 3737 4090
(psi)
Yield elongation (%) 18% 18% 16%
Break elongation (%) 33% 33% 33%
Density, gm/cc 1.07 1.07 1.11
* Max tensile strength equalled yield strength.
in this example, Samples No. 16 to 19 illustrate the effect on the
tensile properties of the compositions of increasing the filler content from
0%
to 30% by weight (0% to 14.6% by volume). The gradual reduction in tensile
properties with increasing filler loading is comparable to effects of addition
of
other mineral fillers.
Sample No. 20, when compared against Sample No. 18, at the same
filler loading, shows the slight improvement in maximum tensile strength from
incorporating 2% of a malefic anhydride grafted polyethylene coupling agent.
Such improvement restores tensile strength values to those of the unfilled
virgin polymer.
Sample No. 18, compares the tensile properties and density of a 20%
by weight carbide lime filled composition to those of Sample No. 21, an
equivalent composition filled to the same volumetric loading, 9.1 %, with a
typical commercial filler-grade talc, of comparable 4 micron mean particle
size
and distribution. Sample No. 18 shows slightly lower maximum tensile
strength, but higher yield elongation, compared to talc, and a 4% lower
composition density.
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Samples No~ 17 to 20 demonstrate the usefulness of carbide lime as a
general purpose filler over a wide range of typical filler loadings.
EXAMPLE 8
A composition was formed from an impact grade of polystyrene,
carbide lime and processing additives, in the form of a blend. The blend was
extruded as a sheet and then vacuum formed into door panels.
It was found that they sheet and thermoformed articles obtained from
the blend processed well and with good physical characteristics of stiffness
and surface finish.
