U.S. patent application number 11/258779 was filed with the patent office on 2006-06-15 for phase change material (pcm) compositions for thermal management.
Invention is credited to Raymond Joseph Reisdorf, Loic Pierre Rolland.
Application Number | 20060124892 11/258779 |
Document ID | / |
Family ID | 36293656 |
Filed Date | 2006-06-15 |
United States Patent
Application |
20060124892 |
Kind Code |
A1 |
Rolland; Loic Pierre ; et
al. |
June 15, 2006 |
Phase change material (PCM) compositions for thermal management
Abstract
The present invention relates to a Phase Change Material (PCM)
composition comprising a) from 20 to 80 wt % of a PCM; and b) from
20 to 80 wt % of one or more polymers chosen from the group
consisting of b1) Very Low Density Polyethylene (VLDPE) having a
density equal or lower than 0.910 g/cm.sup.3 measured according to
ASTM 792; b2) Ethylene Propylene Rubber (EPR) having a density
equal or lower than 0.900 g/cm.sup.3 measured according to ASTM
792; b3) Styrene Ethylene Butadiene Styrene (SEBS) copolymers; and
b4) Styrene Butadiene Styrene (SBS) copolymers. The PCM composition
of the present invention can be used in applications where thermal
management is needed, like for example in building, automotive,
packaging, garments and footwear.
Inventors: |
Rolland; Loic Pierre;
(Divonne Les Bains, FR) ; Reisdorf; Raymond Joseph;
(Attert, BE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
36293656 |
Appl. No.: |
11/258779 |
Filed: |
October 26, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60634592 |
Dec 9, 2004 |
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Current U.S.
Class: |
252/70 |
Current CPC
Class: |
B32B 2307/726 20130101;
C08K 5/14 20130101; C08L 23/16 20130101; C08L 2666/04 20130101;
C09K 5/063 20130101; B32B 15/06 20130101; B32B 2307/51 20130101;
C08F 255/02 20130101; B32B 15/20 20130101; C08L 91/06 20130101;
B32B 2307/54 20130101; B32B 2307/546 20130101; B32B 2471/02
20130101; B32B 25/08 20130101; B32B 2439/80 20130101; B32B 27/36
20130101; B32B 2307/3065 20130101; C08L 91/06 20130101; B32B
2307/72 20130101; B32B 2601/00 20130101; B32B 2264/102 20130101;
B32B 2439/70 20130101; C08L 2312/00 20130101; B32B 2419/00
20130101; B32B 2264/105 20130101; B32B 2437/00 20130101; B32B
2255/205 20130101; C08L 23/0815 20130101; C08L 23/16 20130101; C08L
91/06 20130101; C08L 2312/00 20130101; C08L 91/06 20130101; C08L
51/06 20130101; C08K 5/14 20130101; C08K 5/14 20130101; C08L
2666/04 20130101; C08L 23/0815 20130101; C08L 2312/00 20130101;
C08L 23/0807 20130101; C08L 2666/04 20130101; C08L 2207/064
20130101; C08L 2666/04 20130101; C08F 230/08 20130101; B32B 2605/08
20130101; B32B 25/16 20130101; C08L 2666/04 20130101; B32B 27/08
20130101; C08L 23/0815 20130101; C08L 23/16 20130101; C08F 255/02
20130101; B32B 2307/582 20130101; C08L 91/06 20130101; B32B 15/09
20130101; B32B 15/085 20130101; B32B 27/32 20130101; C08L 2207/064
20130101; C08L 23/0807 20130101; C08L 23/0807 20130101; B32B
2255/10 20130101; C08L 91/06 20130101; B32B 27/18 20130101; B32B
2597/00 20130101 |
Class at
Publication: |
252/070 |
International
Class: |
C09K 3/18 20060101
C09K003/18 |
Claims
1. Phase Change Material (PCM) composition comprising: a) from 20
to 80 wt % of a PCM; and b) from 20 to 80 wt % of one or more
polymers chosen from the group consisting of: b1) Very Low Density
Polyethylene (VLDPE) having a density equal or lower than 0.910
g/cm.sup.3 measured according to ASTM 792; b2) Ethylene Propylene
Rubber (EPR) having a density equal or lower than 0.900 g/cm.sup.3;
b3) Styrene Ethylene Butadiene Styrene (SEBS) copolymers; and b4)
Styrene Butadiene Styrene (SBS) copolymers; the weight percentages
being based on the total weight of the composition.
2. The PCM composition according to claim 1, wherein the EPR having
a density equal or lower than 0.900 g/cm.sup.3 is Ethylene
Propylene Diene Methylene (EPDM), Ethylene Propylene Methylene
(EPM) and mixtures thereof.
3. The PCM composition according to claim 1, wherein the one or
more polymers is VLDPE having a density equal or lower than 0.910
g/cm.sup.3.
4. The PCM composition according to claim 1, wherein the PCM is one
or more crystalline alkyl hydrocarbons.
5. The PCM composition according to claim 1, further comprising
from 10 to 40 wt % of an inert powder having an absorption capacity
of at least 50 wt %, the weight percentages being based on the
dried mass of the inert powder.
6. The PCM composition according to claim 5, wherein the inert
powder has an absorption capacity of at least 120 wt %, the weight
percentages being based on the dried mass of the inert powder.
7. The PCM composition according to claim 5, wherein the inert
powder is silicate, one or more flame retardant fillers and
mixtures thereof.
8. The PCM composition according to claim 7, wherein the one or
more flame retardant fillers are chosen among aluminum trihydrate,
magnesium hydroxide, melamine pyrophosphate, melamine cyanurate,
one or more brominated fillers and mixtures thereof.
9. The PCM composition according to claim 1 comprising from 30 to
50 wt % of the one or more polymers.
10. The PCM composition according to claim 1 comprising from 50 to
70 wt % of PCM.
11. The PCM composition according to claim 1, wherein the one or
more polymers are grafted with 0.2 to 3 wt % of a carboxylic acid
or carboxylic acid anhydride functionality, the weight percentages
being based on the total weight of the one or more polymers.
12. The PCM composition according to claim 1, wherein the density
of the VLDPE is between 0.800 and 0.910.
13. The PCM composition according to claim 1, further comprising
antioxidants and UV filters.
14. The PCM composition according to claim 1, wherein the one or
more polymers are cross-linked.
15. A sheet made with a PCM composition as claimed in claim 1.
16. The sheet according to claim 15 having a thickness between 0.5
and 10 mm.
17. A multilayer structure comprising at least one PCM sheet (A)
according to claim 15 which is adjacent to at least one layer (B)
made of aluminum, polyester vacuum coated with aluminum, one or
more flame retardant polymer composition, plaster, rock-wool
insulation, glass-wool insulation and foamed polystyrene.
18. The multilayer structure of claim 17 wherein the at least one
sheet (A) is positioned between two layers (B1, B2) independently
made of aluminum, polyester vacuum coated with aluminum, one or
more flame retardant polymer composition, plaster, rock-wool
insulation, glass-wool insulation and foamed polystyrene.
19. The multilayer structure of claim 17, comprising in the
following sequence: c) at least one sheet (A); d) at least one
layer (B) positioned adjacent to the at least one sheet (A); e) one
or more additional layers (C) positioned adjacent to the at least
one layer (B), said one or more additional layers (C) being
independently made of aluminum, polyester vacuum coated with
aluminum, one or more flame retardant polymer composition, plaster,
rock-wool insulation, glass-wool insulation and foamed
polystyrene.
20. The multilayer structure of claim 18, further comprising one or
more additional layers (C) positioned adjacent and externally to
one or more of the layers (B1, B2), said one or more additional
layers (C) being independently made of aluminum, polyester vacuum
coated with aluminum, one or more flame retardant polymer
composition, plaster, rock-wool insulation, glass-wool insulation
and foamed polystyrene.
21. A molded part made of a PCM composition as claimed in claim 1.
Description
FIELD OF INVENTION
[0001] The present invention relates to Phase Change Material (PCM)
compositions for the thermal management in different applications
like for example in building, automotive, packaging, garments and
footwear. The present invention also relates to sheets and molded
parts comprising the above PCM composition.
BACKGROUND OF THE INVENTION
[0002] There is a general desire in all technical fields to be
energy efficient. In the building industry, for example, there is a
permanent need to decrease the energy costs related to heating and
cooling indoor rooms. The same applies also in the textile
industry, for instance for life and personal protection clothing,
where the heat excess produced by the wearer must be removed and
managed away from his body in order to increase the overall wear
comfort.
[0003] PCM materials are highly-productive thermal storage media
which are capable of absorbing and releasing high amounts of latent
heat during melting and crystallization, respectively. During such
phase changes, the temperature of the PCM materials remains nearly
constant and so does the space surrounding the PCMs, the heat
flowing through the PCM being "entrapped" within the PCM itself.
Paraffin waxes are known to be particularly efficient as PCMs.
[0004] FIG. 1 shows a temperature profile simulation of the inside
surface of three building wall structures (wood timber frames)
during a typical summer day (latitude 45.degree.; azimuth
180.degree.; air T.sub.min 15.degree. C.; air T.sub.max 35.degree.
C.). Such three wall structures comprise an external layer (wood
siding, thickness 20 mm), a stone wool layer (thickness 250 mm)
adjacent to such external layer and an internal gypsum board
(thickness 10 mm). The first wall structure (W1) does not include
PCM, while the second and third wall structures (W2,W3) further
comprise a PCM composition layer positioned between the stone wool
layer and the gypsum board layer, the PCM composition layers
consisting of 7.15 wt % of PCM and 92.85 wt % of an hypothetical
polymer and 45 wt % of PCM and 55 wt % of an hypothetical polymer,
respectively. The PCM considered for this simulation is
commercially available from Rubitherm under the trade name
Rubitherm.RTM. RT20 (melting point 22.degree. C.).
[0005] FIG. 1 shows that the variation of the inside wall
temperature during the day is reduced with increasing PCM amount in
the wall structure or, in other words, that the heat management
performance of the wall structure increases with increasing amount
of PCM included therein.
[0006] WO 2004/044345 discloses a wall covering assembly comprising
phase change materials like crystalline alkyl hydrocarbons as a
thermal storage mean. The assembly comprises 1) a cover layer of
fabric or paper covered by a vinyl coating; 2) an intermediate
layer made of an acrylic coating compound which contains finely
divided PCM and a rear layer made of a liquid ceramic compound
facing the wall during use. However, the capacity of the acrylic
coating to incorporate PCM is limited due to the polarity and the
elevated crystallinity degree of the acrylic material itself, so
that the heat storage capacity of the overall assembly is limited
to a certain extent.
[0007] U.S. Pat. No. 5,053,446 discloses a composite useful in
thermal energy storage, said composite being a polyolefin matrix
having a PCM (for example a crystalline alkyl hydrocarbon)
incorporated therein. The polyolefin matrix is crystalline and must
be thermally form stable up to temperatures of 150-180.degree. C.
This is due to the fact that the PCM imbibition of the matrix must
take place at temperatures up to the above values in order to
enable the PCM material itself to penetrate into the narrow spaces
of the crystalline matrix. The thermal stability is usually
achieved by reticulating the polyolefin prior to the imbibition
process. This is an additional step for the preparation of the
composite material, which additional step renders the overall
manufacturing process more complicated and expensive. Furthermore,
because of the limited space available within the matrix itself,
proper retention of the PCM, particularly at temperatures below the
PCM melting point, is very difficult, thus leading to a strong
decrease in the heat management performance of the overall
composite.
[0008] The problem at the root of the present invention is
therefore to provide a PCM composition for the thermal management
in different applications like for example in building, automotive,
garments and footwear, which PCM composition can overcome the
problems mentioned above.
SUMMARY OF THE INVENTION
[0009] Now, it has been surprisingly found that the above-mentioned
problems can be overcome by a PCM composition comprising:
[0010] a) from 20 to 80 wt % of a PCM; and
[0011] b) from 20 to 80 wt % of one or more polymers chosen from
the group consisting of: [0012] b1) Very Low Density Polyethylene
(VLDPE) having a density equal or lower than 0.910 g/cm.sup.3
measured according to ASTM 792; [0013] b2) Ethylene Propylene
Rubber (EPR) having a density equal or lower than 0.900 g/cm.sup.3
measured according to ASTM 792; [0014] b3) Styrene Ethylene
Butadiene Styrene (SEBS) copolymers; and [0015] b4) Styrene
Butadiene Styrene (SBS) copolymers; the weight percentages being
based on the total weight of the composition.
[0016] It is another aspect of the present invention to provide a
sheet made with the PCM composition described above, as well as a
multilayer structure including said sheet.
[0017] It is a further aspect of the present invention to provide a
molded part made of the PCM composition described above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a temperature profile simulation of the inside
surface of three building wall structures (wood timber frames)
during a typical summer day (latitude 45.degree.; azimuth
180.degree.; air T.sub.min 15.degree. C.; air T.sub.max 35.degree.
C.).
DETAILED DESCRIPTION OF THE INVENTION
[0019] The polymers used in the present invention have low polarity
and crystallinity. The low polarity degree of the polymer is
important to enable compatibility between the polymer itself and a
PCM of non-polar nature. Moreover, due to their amorphousness, the
polymer matrices used in the present invention have sufficient
absorption capacity to incorporate and retain high amounts of PCM,
even at temperatures which are above or below the melting point of
the PCM itself. The capacity of the above polymers to efficiently
retain the PCM within their own matrix confers to the composition
of the present invention an excellent heat management performance
over long periods of time.
[0020] The density of polymers is directly correlated to the
percentage of crystallinity by the following equation (D. Campbell
and J. R. White, Polymer Characterization, Chapman and Hall, 1989,
page 328): %
crystallinity=.rho..sub.s-.rho..sub.a/.rho..sub.c-.rho..sub.a where
.rho..sub.s is the density of a given polymer, .rho..sub.a is the
density of the same polymer having an amorphous structure and
.rho..sub.c is the density of the same polymer having 100%
crystalline structure.
[0021] For the purpose of the present invention, the one or more
polymers can be chosen among all types of SEBSs and SBSs copolymers
which are well known to be amorphous and which typically have
densities varying between 0.900 and 1.1 g/cm.sup.3. It is also
possible to use EPR copolymers having densities equal or lower than
0.900 g/cm.sup.3 as well as VLDPEs having densities equal or lower
than 0.910 g/cm.sup.3, preferably between 0.800 and 0.910, all
densities being measured according to ASTM 792.
[0022] According to a preferred embodiment of the present
invention, the PCM composition includes EPRs which are chosen among
Ethylene Propylene Diene Methylene (EPDM), Ethylene Propylene
Methylene (EPM) and mixtures thereof. Alternatively, the sole
polymer used in the PCM composition of the present invention is
VLDPE having a density equal or lower than 0.910 g/cm.sup.3.
[0023] Advantageously, the PCM composition of the present invention
comprises from 30 to 50 wt % and still more preferably about 40 wt
% of the one or more polymers, the weight percentages being based
on the total weight of the PCM composition.
[0024] In accordance with a preferred embodiment of the invention,
the PCM is chosen among one or more alkyl hydrocarbons (paraffin
waxes). Paraffin waxes are saturated hydrocarbon mixtures and
generally consist of a mixture of mostly straight-chain n-alkanes
with the chemical formula CH.sub.3--(CH.sub.2).sub.n--CH.sub.3. The
crystallization of the --(CH.sub.2).sub.n-- chain releases a large
amount of the latent heat. Both the melting point and the heat of
fusion increase with increasing chain length. Therefore, it is
possible to select the paraffin waxes, which are products of
petroleum refining, in such a way that the phase change temperature
range matches with the temperature of the operation system to which
the PCM is applied.
[0025] The thermal properties of three different paraffin waxes are
given in Table 1. TABLE-US-00001 TABLE 1 Melt. Heat of Spec. Heat
No. Point Fusion C.sub.pkJ/ State Alkane of C .degree. C. KJ/kg
kg.degree. C. at RT Tetradecane 14 5.8 227 2.18 liquid Pentadecane
15 9.9 206 liquid Hexadecane 16 18.1 236 2.22 solid
[0026] Preferably, the PCM composition of the present invention
includes from 50 to 70 wt % of PCM, preferably 60 wt %, the weight
percentages being based on the total weight of the PCM
composition.
[0027] According to another embodiment, the PCM composition of the
present invention further comprises from 10 to 40 wt % of an inert
powder having an absorption capacity of at least 50 wt % and
preferably of at least 120 wt %, the weight percentages being based
on the dried mass of the inert powder itself. The use of the inert
powder further improves retention of the PCM within the polymeric
matrix. Advantageously, the inert powder used in the PCM
composition of the present invention is silicate, one or more flame
retardant fillers and mixtures thereof. The one or more flame
retardant fillers are advantageously chosen among aluminum
trihydrate, magnesium hydroxide, melamine pyrophosphate, melamine
cyanurate, one or more brominated fillers and mixtures thereof.
[0028] In another aspect of the present invention, the one or more
polymers of the PCM composition are grafted with 0.2 to 3 wt % of a
carboxylic acid or carboxylic acid anhydride functionality, the
weight percentages being based on the total weight of the one or
more polymers. While this small quantity of carboxylic acid or
carboxylic acid anhydride does not affect the overall polarity of
the polymer matrix, it is desirable to have such functionality in
such amount if the PCM composition is used in combination with, for
example, aluminum foils since the carboxylic acid or carboxylic
acid anhydride functionality strongly improves adhesion of the PCM
composition to metal surfaces.
[0029] The polymer matrix of the PCM composition according to the
present invention may be cross-linked after the PCM has been
incorporated into it by means of any conventional method known in
the art like for example by using cross-linking agents based on
silane and/or peroxide groups. During this process, it is important
to avoid that cross-linking of the PCM takes place. This is
possible, for example, by grafting silane groups onto the polymer
molecules prior to incorporating the PCM. Such grafting can occur
by means of conventional techniques, such as by extruding the
polymer at temperatures above 150.degree. C. after adding 0.2 to 2
wt-% of vinyl-tri-methoxy-silane or vinyl-tri-ethoxy-silane
together with 0.05 to 0.5 wt-% peroxide. The PCM can then be
incorporated into the silane grafted polymer and the resulting
blend can be cross-linked, in presence of water or water moisture,
by using catalysts like di-butyl-tin-laureate. Such cross-linking
of the polymer matrix enables to increase the mechanical and
thermal properties of the composition itself when used in the
different applications listed below.
[0030] The PCM composition of the invention may further comprise
conventional additives such as antioxidants and UV filters. These
additives may be present in the composition in amounts and in forms
well known in the art.
[0031] The PCM composition according to the present invention can
be produced by soaking the different components all together at
temperatures which are slightly above the melting point of the PCM
but below the melting point of the one or more polymers. Soaking is
a natural absorption of the molten PCM by the polymer matrix.
Usually the components are mixed together in a tumble blender
during a certain period of time which can vary in function of the
rotational speed of the tumble blender itself. Typical periods of
time are around eight (8) hours.
[0032] Another possibility for obtaining the PCM composition of the
present invention is by melt blend extrusion whereby the components
are blended at temperatures above the melting point of both the one
or more polymers and the PCM, the thus obtained mixture being
subsequently extruded into granules or directly into sheets or any
other suitable form.
[0033] Sheets made with the PCM composition described above are
also an object of the present invention. Preferably such sheets
have a thickness varying between 0.5 and 10 mm and can be
manufactured either directly by melt blend extrusion as described
above, or alternatively by preparing the PCM composition which is
subsequently processed by means of any conventional technology such
as extrusion, calendering and hot lamination.
[0034] Another object of the present invention is a multilayer
structure comprising at least one sheet (A) of the above PCM
composition, which is adjacent to at least one layer (B).
Preferably, such sheet (A) is positioned between two layers
(B1,B2). One of the functions of the at least one layer (B), or
preferably of two layers (B1,B2) is to help keep the PCM material
of the sheet (A) within the polymer matrix, thus enabling to
maintain the heat management performance of the PCM sheet (A) at a
high level over a long period of time. Furthermore, undesired
grease stains on the surfaces adjacent to the PCM composition are
hereby avoided.
[0035] According to one embodiment of the present invention, the
multilayer structure comprises in the following sequence:
[0036] a) at least one sheet (A);
[0037] b) at least one layer (B) positioned adjacent to the at
least one sheet (A);
[0038] c) one or more additional layers (C) positioned adjacent to
the at least one layer (B).
[0039] According to another embodiment of the present invention,
the multilayer structure further comprises one or more additional
layers (C) positioned adjacent and externally to one or more of the
layers (B1, B2).
[0040] The at least one layer (B) and the one or more additional
layers (C) can also have the function of conferring to the overall
multilayer structure improved fire retardancy and heat conductivity
so that heat is easily conveyed through such at least one layer to
the PCM composition and vice versa.
[0041] The at least one layer (B) and the one or more additional
layers (C) can be made of aluminum. It is also possible to use
polyester vacuum coated on one side with aluminum, the aluminated
side facing the PCM sheet (A), in order to achieve optimum
adhesion. The use of aluminated polyester also confers to the
overall PCM multilayer structure an excellent mechanical strength
as well as an excellent elasticity.
[0042] The at least one layer (B) and the one or more additional
layers (C) can be made of other materials instead of (or in
addition to) the above mentioned aluminum and/or polyester vacuum
coated material, according to the specific use and application.
Such materials can be independently chosen from one or more of
flame retardant polymer compositions (polymers filled with flame
retardant inorganic fillers like aluminum trihydrate, magnesium
hydroxide, calcium carbonate, brominated fillers and melamine
pyrophosphate), plaster (plaster boards and panels, gypsum boards),
rock-wool insulation, glass-wool insulation, foamed polystyrene and
other materials conventionally used in the construction
industry.
[0043] The at least one layer (B) and the one or more additional
layers (C) may have a thickness varying from 5 .mu.m up to 20 cm in
accordance with the materials used. Aluminum layers, for example,
will have thicknesses typically varying from 5 to 500 .mu.m,
preferably from 20 to 80 .mu.m and, still more preferably, of about
50 .mu.m.
[0044] The multilayer structure of the present invention can be
manufactured by conventional methods. This includes extrusion
coating the PCM material onto the at least one layer (B), extrusion
laminating the PCM material between two of such layers (B1, B2),
and co-extruding the PCM material with the at least one layer (B)
if the material of such at least one layer (B) makes it possible
(for example if the at least one layer is made of a flame retardant
composition).
[0045] An additional aspect of the present invention relates to a
molded part made of a PCM composition as described above. Such
molded part can be manufactured by any process suitable for
transforming thermoplastic materials including injection molding,
blow molding, thermoforming and rotomolding.
[0046] The PCM composition of the present invention can be used in
several applications where thermal management is needed. While
temperature management inside buildings is one of the most relevant
applications, the PCM composition of the present invention may also
be used in automotive applications (for example in the ceiling,
seats and tires of vehicles); air filters in air ducts;
transportation applications; food packaging (to keep food chilled
or warm); medical packaging; woven and nonwoven fabrics for
garments and sport wear; footwear; tree wraps, hand grips (in
tools, sporting goods and vehicles); bedding; carpets; wood
composites; electric cables and plastic tubes for hot media
including water.
[0047] The invention will be further described in the following
Examples.
EXAMPLES
Example 1
[0048] 55 g of paraffinic wax (PCM) commercially available from
Rubitherm under the trade name Rubitherm.RTM. RT20 (melting point
22.degree. C.) and 45 g of granules of VLDPE (density 0.863
g/cm.sup.3) grafted with 0.5 wt % of maleic anhydride, commercially
available from E. I. du Pont de Nemours and Company under the trade
name Fusabond.RTM. 493 D, were simultaneously introduced into an
one liter tumble blender. Blending was carried out during eight (8)
hours at 25.degree. C. in order to enable sufficient time for
maximal incorporation of the liquid paraffinic wax into the polymer
matrix (soaking). The granules soaked with the paraffinic wax were
taken out of the blender and filtered in order to remove rests of
liquid paraffin wax from their external surface. The difference in
the granules weight before and after soaking was measured, thus
allowing to calculate the weight percentage of wax absorbed by the
polymer matrix.
[0049] Slabs were compression molded using the PCM composition
obtained above. The granules were placed in a frame (thickness of 2
mm) between 2 steel slabs and the whole system was subsequently
pressed at a jaw temperature of 100.degree. C. and at a pressure of
1 bar during the first minute and of 80 bars during the subsequent
2 minutes. The jaws were then cooled down to 25.degree. C. during a
period of 4 minutes always under a pressure of 80 bars. The
pressure was eventually released and the produced polymer slabs
removed from the frame.
[0050] The flexibility of the molded slabs was tested. Tensile
strength and elongation at break were also measured on dumble bar
samples cut out from two of these slabs, according to method DIN
53504 S2.
[0051] The results are shown in Table 2.
Example 2 (Comparative)
[0052] Example 1 was repeated using granules of ethylene methyl
acrylate, comprising 25 wt % of methyl acrylate, commercially
available from E. I. du Pont de Nemours and Company under the trade
name Elvaloy.RTM. AC 1125. No slabs were made with the PCM
composition obtained under this Example 2.
[0053] The results are shown in Table 2.
Example 3
[0054] Example 1 was repeated using granules of VLDPE (density
0.863 g/cm.sup.3), commercially available from Dow Chemicals under
the trade name Engage.RTM. 8180. No slabs were made with the PCM
composition obtained under this Example 3.
[0055] The results are shown in Table 2.
Example 4 (Comparative)
[0056] Example 1 was repeated using granules of HDPE (density 0.965
g/cm.sup.3), commercially available from E. I. du Pont de Nemours
and Company under the name DuPont.TM. 6611. No slabs were made with
the PCM composition obtained under this Example 4.
[0057] The results are shown in Table 2.
Example 5 (Comparative)
[0058] Example 1 was repeated using granules of HDPE (density 0.965
g/cm.sup.3), commercially available from E. I. du Pont de Nemours
and Company under the name DuPont.TM. 6611. Blending was carried
out during eight (8) hours at 180.degree. C.
[0059] The results are shown in Table 2. TABLE-US-00002 TABLE 2
Example 1 Example 2 Example 3 Example 4 Example 5 Soaking Temp.
(.degree. C.) 25 25 25 25 180 Weight %.sup.1 100 23 100 13 100
Flexibility of the very very very molded slabs flexible flexible
brittle Tensile strength (Mpa) >4.6.sup.2 2.1 Elongation at
break (%) >2293.sup.2 5.9 .sup.1Weight percentage of paraffin
wax absorbed by the polymer matrix after eight (8) hours soaking.
100% means total absorption, that is 55 g of paraffin wax absorbed
into 45 g of polymer. .sup.22293% (4.6 Mpa) is the maximal value
measurable with the testing equipment.
Table 2 shows that the polymer matrices according to the present
invention (Examples 1 and 3) can absorb the whole amount of PCM (55
g PCM per 45 g polymer) at 25.degree. C. while polymers having high
degrees of polarity (Example 2) or high degrees of crystallinity
(Example 4) can absorb PCM only to a limited extent. In order to
achieve full absorption of the PCM with high crystallinity HDPE
matrices, it is necessary to increase the soaking temperature up to
180.degree. C. (Example 5). Slabs obtained by molding the PCM
compositions according to the present invention are very flexible
and show excellent mechanical properties. On the other hand,
Example 5 shows that slabs prepared with PCM compositions based on
crystalline polymers (HDPE) are very brittle. Therefore, from a
mechanical point of view, such compositions are not suitable in the
thermal management applications described above even if their PCM
content is quite high.
Example 6
[0060] 44.6 g of granules of VLDPE (density 0.863 g/cm.sup.3),
commercially available from Dow Chemical under the trade name
Engage.RTM. 8180, were extruded, at a temperature of 220.degree.
C., with 0.4 g of a mix of vinyl-tri-methoxy-silane and peroxide
catalyst (XL-Pearl.RTM. 23 commercially available from General
Electric, Osi Specialities) so to obtain a blend. 55 g of
paraffinic wax (PCM) commercially available from Rubitherm under
the trade name Rubitherm.RTM. RT20 (melting point 22.degree. C.),
0.03 g of di-butyl-tin-laureate and 45 g of the VLDPE based blend
obtained above, were simultaneously introduced into an one liter
tumble blender. Blending was carried out during eight (8) hours at
25.degree. C. in order to enable sufficient time for maximal
incorporation of the liquid paraffinic wax and
di-butyl-tin-laureate into the polymer matrix (soaking). The
granules soaked with the paraffinic wax and di-butyl-tin-laureate
were taken out of the blender.
[0061] Slabs were compression molded using the PCM composition
obtained in this Example 6 as well as the one obtained in Example
3. The granules were placed in a frame (thickness of 2 mm) between
2 steel plates and the whole system was subsequently pressed at a
jaw temperature of 150.degree. C. and at a pressure of 1 bar during
the first minute and of 80 bars during the subsequent 2 minutes.
The jaws were then cooled down to 25.degree. C. during a period of
4 minutes always under a pressure of 80 bars. The pressure was
eventually released and the produced polymer slabs removed from the
frame. The slabs were then immerged in water during 4 hours and
dumble bar samples were cut out from these slabs, according to
method DIN 53504 S2.
[0062] A weight of 52 g was hanged to each of the dumble bars which
were fixed inside an oven. Tests were performed at different
temperatures and during a period of 15 minutes. The temperature at
which each sample broke was recorded. The results are shown in
Table 3. TABLE-US-00003 TABLE 3 Example 3 Example 6 Temperature at
which sample 40 80 broke (.degree. C.)
Table 3 shows that the cross-linked composition obtained in Example
6 has a significantly improved resistance to heat deformation if
compared to the same uncross-linked composition (Example 3).
* * * * *