Note: Descriptions are shown in the official language in which they were submitted.
73
TITLE
Alkene Polymer Composite Heat Storage Material
E3ACKGROUND OF TH:E ~NV~;NlION
Field of the Invention
This invention relates to composites which
are useful a5 heat storage materials and which are
comprised of an alkene polymer, a finel~ divided
solid and an organic latent heat storage material.
Background
As fossil fuels become scarce and more
expensive, the use of alternate energy sources, such
as solar energy and waste energy from industrial
proces~es r becomes more attractive. Since the time
periods during which such sources of energy are
15 available do not necessarily correspond to the time
periods of energy n~d, energy storage plays an
important role in the use of alternate energy sources.
Various types of heat storage are known 7
For example, heat can be stored in the form of the
20 sensible heat of a fluid such as water or the
sensible heat of a solid such as stone or in the form
of a combination of sensible heat and latent heat of
a transitionl particularly the latent heat of fusion,
using materials such as inorganic salt hydratesy
25 paraffin or organic polymers. The transition
temperature of the latent heat material used must be
below the temperature of ~he material from which heat
is to be removed and stored, and equal to or above
the temp~rature which is to be provided on removal of
30 heat from the latent heat material~
Latent heat materials undergoin~
liquid/solid phase transi~ions must be suitably
containedO One way to accomplish this is to place
the latent heat storage material in a container of
CR-8157 35 suitable size, making allowance for temperature
3Z~73
expansion of the latent heat material. This approach
using a container may give rise to a heat transfer
problem when the heat is removed from ~he latent heat
storage material. Solidification o the latent heat
storage material occurs first on the walls of the
container, and any additional heat removed must be
conducted through the solid thus formed, the solid
increasing in thickness as more of the liquid
solidifies. Conversely, when heat is being stored in
a solid latent heat material, heat transfer is
inefficient because convection, which is requisite to
efficient heat transfer, is hindered by the high
viscosity of the liquid first formed from melted
solid. Moreover, on cycling, the solid latent heat
storage m terial may contract and pull away from the
walls of the con~ainer, thereby fur~her decreasing
the efficiency of heat conduction.
The art discloses attempts which have been
made to solve some of these problems. For example, a
granular form of latent heat material may be used,
with the heat transfer medium being passed through a
bed of such granules either to supply heat or to
extract heat from the granules.
U.S. Patent 2,846,421 discloses A method for
controlling the temperature of liquid phase
reactions, ~or example, emulsion polymerization, by
means of an encapsulated latent heat material, the
capsule being formed from a metal or plastic~ the
latent heat material being commonly available
materials, including water, benzene, glycol, mercury,
&lauber's salt and Wood' 5 metal. U.S. Patent
4,182,398 discloses a method for removing heat from a
fluid by means of crystalline polyethvlene
silane-grafted-crosslinked polymer pieces crosslinked
to retain at least 70% of the heat of fusion of the
7~3
uncrosslinked crystalline polymer and suf~iciently
crosslinked for the pieces not to stick together upon
being cycled above and below the melting polnt of the
polymer. U.S. Patent 4,221,259 discloses a method
for storing heat by means of a ~usible substance,
that is, a latent heat material, which is absorbed
on a finely divided microporous carrier. Paraffin
absorbed on active coal or coke in yrains or sticks
is exemplified. Other latent heat materials which
are disclosed are fusible mineral salts, metal
hydrides, alloys, metal alloys, and polymers. U~S,
Patent 4,003,~26 discloses a heat or thermal energy
storage structure comprising a crosslinked polymeric
resinous matrix having a plurality of substantially
unconnected small closed ca~ities and a heat sink
material encapsulated within the cavities. A similar
type of heat storage composition is disclosed in U.K.
published Patent Application ~B 208603~A.
It is an object of this invention to provide
a composite material which is suitable for heat
storage. Another object is to provide such a
material which can be cycled repeatedly between heat
sink and heat source conditions without substantial
deterioration~ Still another object is to provide
such a material which can be fabricated readily from
commonly available ingredients. Other objec-ts will
become apparent h~ereinafter.
DISCLOSURE OF INVENTIO~
For ~urther comprehension o~ the invention
and of the objects and advantages thereof, refererLce
may be made to the following description and to the
appended claims in which the various novel features
of the invention are more particularly set forth.
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The invention resides in the composite
consisting essentially of, by weight, with the total
being 100%:
(a) about 2 55%, preferably about 30-40%,
more preferably about 35%, o~ an organic latent heat
materlal having at least one la~en~ heat transition,
as a solid-solid transition(s) and/or a solid~liquid
transition, in the temperature range 0-100C, and
which, when liquid, wets the surface of the
polyalkene of (b) and the ~inely divided solid of (c);
(b) about 5-65%, preferably about 15-25%,
of a polyalkene having a molecular weight of at least
lO,000, preferably at least lO0,000, molecular weiqht
being weight averaye; and
(c) about 15-90%, preferably about 35 55~,
of a finely divided (particulate) solid such as a
mineral, an organic material such as a polymer, a
metal or a mixture thereof, said solid having a
melting point above that of the materials of (a) and
20 (b) and being substantially insoluble in these
materials.
The term "consisting essentially of" is used
to specify the essential components of the composite
of the i.nvention; the term is not intended to
preclude the inclusion of other components which do
not substantially. adversely affect the desirable
properties of the composite of the invention, such
other components thus being nonessential components
of the composite.
The organic latent heat compounds which are
useful in this invention have a latent heat
transition(s); ~s a solid-solid transition(sj and/or
a solid-liquid transition, singly or in combination,
in the temperature range 0-100C. The preferred
organic compounds have the highest latent heat
capacity per gram when compared to their isomers.
Thus, organic compounds having unbranched sa~urated
chains are preferred over organic compounds having
branched chains, rings or unsaturated linkages. In
addition, since it is necessary that the organic
compound be compatible wi~h the alkene polymer, it is
restricted to those organic compounds that possess a
minimum of polar groups so that, when molten, it will
wet the surface of the alkene polymer and the finely
divided solid. In order for the liquid organic
compound to wet the surface of the alkene polymer and
the solid it must have a lower refractive index than
those of the alkene polymer and the finely divided
solid. It is also desirable that the organic
compounds have a low vapor pressure in the working
temperature range, that is, in the cycling
temperature range as a heat sink and as a heat
source, be nontoxic, possess little odor, and be
thermally stable for a period of years. Preferred
organic latent heat materials are paraffin wax and
stearic acid.
It has been found that the heat storage
capacity of the composite is equal to the sum of the
sensible heat capacity of the components over the
working temperature range and the latent heat
capacity of the organic material undergoing
solid-solid and/or solid-liquid transitions. The
latent hea~ capacity of the composi~e is related only
to the amount of organic material and is not
influenced by the amount of polyalkene or type of
finely divided solid. l'he solid provides the major
portion of the heat conductivity necessary to conduct
heat in and out of the composite, thereby making the
composite useful as a heat storage element, and the
solid must provide sufficient heat conductivity for
this purpose. For example~ aluminum dust or flake
2~7~3
can be used as the solid ma~erial to provide good
heat conductivity or it can be added to supplement
the conductivity of a less conductive mineral or
polymer. The polyalkene and the solid supply
strength to the composite and also ~upply about
one-half the sensible heat capacity.
The finely divided solid used in the
composite of this invention can be a finely divided
(particulate) mineral, polymer, or metal or a
combination of these. Carbon is considered herein as
a mineral. The size of the particles or agglomerates
of particles is in the range o 1 ~m to 2 mm, passing
a 10 mesh sieve (U.S. Sieve Series).
The latent heat storage composites of this
invention can be prepared by three general
procedures. In the first procedure a solution of
organic latent heat material, for example, paraffin
wax in any solvent that dissolves a reasonable amount
of the organic latent heat material, but preferably
with a solubility of at least 5% W/W7 iS slurried
with a m;xture of finely divided solid and finely
divided polyalkene. The solvent is removed and the
resultant powder is pressed in an appropriate mold to
give the desired shape. Preferably, the mold is
heated above the melting point of the polyalkene
since, in this case, it is not as critical that the
polyalkene be finely divided. In the second
procedure, molten organic latent heat material, for
example, paraffin wax is added to the finely divided
solid and the resultan~ mixture is then melt blended
with a polyalkene. In the third procedure, a finely
divided solid, polyalkene and an organic latent heat
material, for e~ample, paraffin wax are melt b~ended
together. The solid products recovered after
carrying out the last two procedures can be remelted
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and pressed into the desired shape. Al~ernatively,
the solid products can be ground and the resulting
powder can be pressed into ~he desired shape,
optionally being heated above the melting point of
the polyalkene. As a fuxther alternative, the
products can be extruded into the desired shape.
The following examples are intended to
illustrate but not limit the invention. Unless
otherwise noted, all parts and percentages are byO weight and all tempera~ures are in degrees Celsius.
EX~MPLES 1-8
These examples demonstrate the preparation
of composites using a mixture of hexane, finely
divided (particulate) solid, polyalkene, and organic
latent heat ma~erial. In each example, 10 g
quantities of composite consisting of 4.7 g of
mineral, 1.8 g of polyalkene, and 3.5 g of paraffin
wax (m.p. 52-54C) were prepared by slurrying the
components together in hexane which was heated to a
temperature above the melting point of the wax but
below the boiling point of the hexane (about 69C);
the mineral and polyalkene components are shown in
Table I. The hexane was removed at 0.01 mm (1.3 Pa)
pressure while heating at 95C for 2 h. The
resultant powders were pressed at room temperature
(20-25C) into cylindrical pellets at 5,000 psi
(35,000 KPa). The pellets from Examples 1, 3, 5, and
7 were then pressed for 5 min at 3,000 psi (21,000
KPa) in a mold that was heated to 160C. The pellets
were then cooled to 20-25C~ The pellets were
weighed and measured. The pellets were then measured
for creep crush according to ASTM D 2990-77~ The
pellets were placed in a heatable press and subjected
to a pressure of 2~ psi (140 ~Pa). The press
temperature was varied cyclically, ~ h heating from
~g~æ~7~3
20C to 95~C, 8 h at 95C, 4 h cooling from 95~C to
20C, and 8 h at 2~C. After 72 h (3 complete
cycles) creep crush was measured. The pellets were
removed from the press. Any wax which was lost
appeared as a solidiied meniscus around the base of
the cooled pellet. ~his wax was carefully removed by
scraping with a razor blade and the pellet was then
weighed to determine the amount o wax lost during
the creep crush tes~. The results appear in Table
II. All wax loss was less ~han 1%. A negative wax
loss indicate~ tha~ the mineral absorbed some water
from the air and caus~d a sligh~ weight gain for the
pellet. The ~ creep was less than 5%. A negative
creep crush arises from relaxation of compression
produced in the pellet during the preparation of the
pellet.
In order to be useful as heat storage
elements, these pellets should exhibit creep crush
results of less than 20%, preferably less than 3~,
and most preferably less than 1%.
Examples 1-8 show that shaped structures of
the composite can be made either by cold-pressing the
powder or by hot-pressing the powder above the
melting temperature of the wax and the polyalkene and
that, with either preparation, the composites have
substantially the same good mechanical properties.
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TABLE I
Ex. Mineral Polyalkene
1 Optiwhite~ clay 1220 Allied LPE*
2 H
5 3 Attagel** 50 n
4 n n
Optiwhite~ clay Ultrahigh
molecular
weigh~ linear
polyethylene
7 Attagel 50 n
B n n
*1220 Allied LPE is ultrahigh molecular weight
polyethylene with a MW in the range 1-3x106
TABLE II
Example% Wax Lost % Creep
1 0.~ 2.515
2 0.22 2.199
3 0.25 1.343
4 -0.30 -2.721
0~39 4.129
6 0.23 - 1.0~5
7 -0.69 0.~79
8 -1.34 -2.716
3~
\
** denote~ trade mark
73
EXAMPLES 9-16
Polyalkene pellets were cooled with liquid
nitrogen and ground in a Janke and Kunkel* grinder t~
yield a fine powder~ The composites were prepared by
slurrying together in hexane heated to a temperature
above the melting point of the w~x but below the
boiling point of the hexaneo 3.5 9 of paraffin wax
(melt;ng point 52-54C), 1.8 9 of polyalkene powdPr,
and 4.7 g of mineral. The hexane was removed at 0.01
mm ~1.3 Pa) pressure while heating at ~5C for 2 h.
~he specific polyalkenes and minerals used are shown
in Table III. For each example the resulting powder
was ground to approximately 10 ~m and a cylindrical
pellet was pressed at 10,000 psi (69~000 RPa). The
pellets of Examples 10, 12, 14 and 16 were heated to
165C and hot-pressed at tha~ ~emperature at a
pressure of 1,500 psi ~10,000 RPa). Creep crush
testing and determination of ~ wax loss after creep
crush were done for each sample as described for
~xamples 1-8; the results are shown in Table IIIL
Example 9 is considered outside the invention. % Wax
loss could not be determined because the sample was
crushed and the particulate could not be recovered
and weighed accurately. Although not wishing to be
bound by this explanation, it is believed that the
experiment failed because the polyalkene was not
sufficiently finely divided and admixed with ~he
mineral, as is necessary when the pellets are
prepared by cold pressing.
* denotes trade mark
.
TABLE III
%
Creep % Wax
Ex. Polyalk.ene* Mineral Crush Loss
9~B 301Satintone** #1 50.17
10 1~ n 1.82 --0.. 18
11 ~ Atta~el 50 -4.15 -0.36
12 n ~7 1.53 6.()7
13190~ Satintone #1 -1.16 0~12
10 14 n n 13 . 53 0 . 06
n Attagel 50 ~3~05 -0O71
16 n n 1.60 -0.74
*Both polyalkenes used are high molecular weight
polyethylenes; ~B 301 is ~ercules* HB 301
polyethylene resîn ~MW = 1.5 x 106); 1900 is
Hercules 1900 polyethylene resin (MW = 5 x
6)
EXAMPLES 17-20
These examples demonstrate the preparation
of composi~es by mel~ blending the components, and
the use of polye~hylenes of differen~ densities~ In
each example, 109~5 9 of paraffin wax, 131.5 g of
mineral and 7~ 9 of polyethylene were blended at
160C, first in a Readco** M~xer and then in a
two-roll rubber mill. Each sample had 0.3 g of
Irganox~ 1010 antioxidant (pentaerythritol ester of
3,5-di-tert-butyl-4-hydroxyphenylacetic acid
manufactured by Ciba Geigy) added to it during melt
mixin~. The recovered materials were ground u~ing a
Janke and ~unkel grinder cooled with liquid nitrogen
to give a powder (about 10 ~m particle size).
Cylindrical pellets were prepared by pressing the
powder at 10,000 psi (699000) kPa in a mold heated to
180C~ The pellets were weighed and tested for creep
~* denotes trade mark
.1
12
crush as in Examples 1-8. ~he results after 72 h of
creep crush testing are shown in Table IV, along with
a description of the minerals and polyethylenes
used. The free radical stabilizer is not detrimental
to the mechanical properties o~ the resul~ing product.
TABLE IV
%
Polyethylene Creep % Wax
Ex.Mineral (Aldrich) Crush Loss
17Attagel 50low density PE 6.71 6.3
18 n high density PE 1~76 3.1
195atintone #llow density PE 3.24 4.0
n high density PE 1.50 4.2
EXAMPLES 21-24
These examples demonstrate the use of
polyethylene and isotactic ~olypropylene of
intermediate melt flow and the use o a combination
of charcoal and Satintone #l as the mineral. For
each example, 317.8 9 of paraffin wax was melt
blended with the quantities of mineral and polymer
shown in Table V, using subs~antially the same
procedure described in Examples 17-20. In each
example r the recovered powder was pressed into a
cylindrical pellet in an evacuated mold and heated to
200C for 30 min, cooled and examined for creep crush
and wax loss as in Examples 1-8. The results are
given in ~able V.
12
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TABLE V
%
Mineral Polyalkene Creep % Wax
~x.(~) (g) Crush Loss
21Satintone Du Pont 2.28 6.2
~l (426.7) Alathon~
7030* (163.5~
22Satintone Du Pont 2~42 1~3
~l ~499.4) ~lathon~
703~* (90.8)
lO 23 Satintone Du Pont l.39 3.l
~l (372.3)/ Alathon~
Charcoal 7030* ~l63.5)
(54.5)
24 Satintone Hercules 0.95 less
~l (426.7) Profax~ than
6523** 1163'5) 0-5
* Du Pont Alathon~ 7030, low density
polyethylene resin.
**Hercules~ 6523 polypropylene resin.
EXAMPLES 25-29
These examples demonstrate the effect of
varying the amount of paraffin wax on ~ creep crush,
% wax loss on thermal cycling and latent heat
capacity. The amounts of materials used are ~hown in
~able VI; Satintone #l was used as the mineral and
~he polyalkene used was Aldrich* isotactic
polypropylene. The paraffin wax (mp 52-54C) was
weighed into a l L beaker and then melted on a steam
bath . The polypropylene pellets were added ~ followed
30 by the mineral. The mixture was well stirred,
cooled, and melt blended on a ~cwo-roll blender at
185CI, The mixture was then cooled with liquid
nitrogen and ground at 20, 000 rpm in a Janke and
~unkel grinder to yi21d a fine powder. The powder
35 * denotes ~rade mark
13
,~L A~ 7~ 7 3
14
from each example was pressed at 100,000 psi (690,000
~Pa) for 20 min at 25~C in~o a cylindrical pellet.
The pellets were subject0d to a 72 h creep crush test
as in Examples 1-8. The results are shown in Table
VI. All pellets had a wax loss of less than 0.1%.
The latent heat was measured for two heating and
cooling cycles and the average latent heats given in
Table VI are, therefore, the average of 4
determinations.
TABLE VI
Avg.
Paraffin ~ Latent
Wax Mineral Polyalkene Creep Heat
Ex. (9~ (~) (9) Crush (cal/g)
2~ 20 144 36 0.22 4.7
26 40 124 n 0 . 569 . 5
27 60 104 " 1.4813 . 6
2S 70 94 1~ 0 . 0618 . 6
29 80 84 n 3 . 5520 . 6
EXRMPLE:S 30~34
Examples 25-29 were repeated using Hercules
Profax~ 6523 polypropylene in place of Aldrich
isotactic polypropylene~ The compositions of the
composites are shown in Table VII. The pellets were
examined for creep crush properties (shown in Table
VII) and wax loss. All had wax losses of less than
0.1%. The latent heat was measured for two hea~ing
and cooling cycles and the average latent heats given
in Table VII are, therefore, the average of 4
determinations.
14
73
TABLE VI I
Avg.
Paraffin ~ Latent
Wax Polyalkene Mineral Creep Heat
Ex. (g) (g)(g) Crush (cal/g)
18 72 -1.34 3.0
31 20 n ~;2 ~0 . 39 8 .6
32 30 n 52 --1.32 13.6
33 35 n 47 0 . 26 13 . 9
3~ 40 " 42 1~00 18.0
EXAMPLE 35
This example demonstrates ~he sensible and
latent heat storage by a melt hlended composite and
demonstrates a utility for ~he material, namely,
heating water.
A 151.87 g sample of composite prepared
according to ~he procedure described in Example 31
was pressed in an unheated (25C) mold at 10,000 psi
~69,000 KPa) ~v form a disk 2'~ dia. x 1" ~hick (5.08
cm dia. x 2.54 cm thick). The disk was heated in a
water bath to 95.1C for 1 h. A Dewar flask
contain;ng 372.49 g of water was thermally
preequilibrated at 32.8C. The warm disk was removed
from the water bath and transferred to the Dewar
together with 16.73 9 of water, also at 95.1C. Five
minutes later the temperature of the water in the
Dewar was 41.2~C. The bomb constant for ~he Dewar
was previously found to be 95.38 cal/C, From these
measurements and the known composition of the
composite, a sen~ible heat capacity of 0.272 cal/g~C
was de~ermined. This compares with a calculated heat
capacity of 0.276 cal/gC for a composite con~ain;ng
62~ Satintone ~1 clay, 18~ polypropylene, and 20%
paraffin wax having sensible heat capacities of 0.179
cal/gC, 0.44 cal/~C and 0.43 cal/~C, respec~ively,
'7~
16
together with a latent heat capacity of 52 cal/g for
the paraffin wax.
EXPERIMENTS 1 and 2
These showings demonstrate the failure of
composites prepared from paraffin wax and high
molecular weight polyethylene when the finely divided
solid is omitted. The composi~es were prepared using
the hexane slurry technique as in Examples 1-8,
except that in each experim~nt 3.5 g of paraffin wax
and 6.5 g of high molecular weight polyethylene were
used. Hercules HB 301 polyethylene was used in
Experiment 1 and Hercules 1900 polye~hylene was used
in Experiment 2. The hexane slurry was evaporated at
0.02 mm (2.7 Pa) for 2 h at 20C and the recovered
powder was pressed into cylindrical pellets at 10,000
psi (69,000 RPa~. The pellets, tested for creep
crush as in Examples 1-8, were completely crushed.
EXPERIMENTS 3 to 6
These experiments demonstrate the use of
isotactic polypropylene and various amounts of
paraffin wax without the finely divided solid.
Hercules Profax~ 7523 was ground to about a 10 ~m
particle size using a Janke and Kunkel liqu;d
nitrogen cooled grinder. The resultant powder was
slurried wikh a hexane solution of paraffin wax. The
hexane was removed as in the examples and a
cylindrical pellet from the powder recovered from
each experiment was pressed at 10,000 psi (69,000
KPa) at 20C for 5 min. The compositions are shown
in Table VIII. The pellets of ~xperiments 4 and 6
were placed in a mold, heated to 200C, and
hot-pressed at 800 psi (5,500 KPa) for 4 min. The
polymer appeared to be fused i.n ~hese two pellets~
The results of creep crush tests and the ~ wax loss
are shown in Table VIII. The materials of
16
'7~3
17
Experiments 4 and 6 would not be suitable for heating
storage elements because the heat conductivities are
too low.
TABLE VIXI
Paraffin %
Wax PolyalkeneCreep % Wax
Expt~(g) (g) Crush Loss
3 305 6.5 Crushed
4 3.5 6.5 2054 1.3
4.5 5.5 Crushed
6 4.5 505 17.99 0.4
EXPERIMENTS 7-9
Example 25 was repeated eY.cept that the
amount of Satinkone $1 was 164 g and no paraffin wax
was added. The % creep crush was 0.51 and the
average latent heat was 0.
Example 30 was repeated except that the
amount of Sa~intone #1 was 82 g and no paraffin wax
was added. The % creep crush was -0.01 and the
average latent heat was 0.
Example 30 was repeated except that the
amount of paraffin wax was 100 9 and no mineral or
polyalkene was added. Creep crush could not be
determined because the wax melts under the tes~ and
~5 the average latent heat was 51.2.
BEST MODE FOR CARRYIN~ OUT THE lNv~NlION
The best mode presently contemplated for
carrying out the invention is represented by Examples
~5 ~o 34.
INDUSTRIAL APPLICABILITY
The industrial applicability of heat
sink/heat source composikes is well Icnown and is
adequately discussed in the baclcground section of
this specification. The composites of this invention
provide an improvement over the artO
17
18
Disclosed and claimed in a copending
commonly assigned Canadian Application No. 449,426
of A.G. Anderson and E.G. ~Ioward, Jr. filed
simultaneously herewith is an invention which also
is directed to a composite heat storage material,
the composite consisting essentially of an organic
latent heat material and a filled ethylene polymer
which is prepared by polymeriziny the monomer(s)
in the presence of particulate filler so that
substantially all of the polymer is deposited on
filler and substantially all o the -filler has
polymer deposited thereon. The invention herein
resides in an improvement over the invention of the
commonly assigned application in that it has been
discovered, surprisingly, that a useful composite,
that is, one which can be cycled repeatedly without
loss of the organic latent heat material, for
example, paraffin wax, can be prepared by carefully
admixing the requisite components, thus avoiding
the less economical step of first preparing filled
ethylene polymer.
18
, .
. . ~
