Polymer composition and its use as a phase change material

Abstract

A polymer composition comprising: (a) from 50% by volume to 99% by volume, preferably from 70% by volume to 95% by volume, of at least one homopolymer or copolymer of ethylene; (b) from 1% by volume to 50% by volume, preferably from 5% by volume to 30% by volume, of at least two fillers having different thermal conductivity; (c) from 100 ppm to 4000 ppm, preferably from 200 ppm to 3500 ppm of at least one fluoropolymer; the sum of (a)+(b) being 100. Said polymer composition can be used as a phase change material (PCM), in particular for thermal energy storage (TES), more in particular for the storage of solar energy.

Claims

1. A phase change material that is adapted for thermal energy storage, comprising a polymer composition comprising: (a) from 80% by volume to 99% by volume of at least one homopolymer or copolymer of ethylene; (b) from 1% by volume to 20% by volume of at least two fillers having different thermal conductivity: (b.sub.1) fillers having a thermal conductivity lower than or equal to 15 W/mK; (b.sub.2) fillers having a thermal conductivity higher than or equal to 50 W/mK; from 100 ppm to 4000 ppm of at least one fluoropolymer; wherein said at least one homopolymer or copolymer of ethylene and said at least one fluoropolymer, are the only (co)polymers of the composition, and the sum of (a)+(b) is 100.

2. A phase change material that is adapted for thermal energy storage, comprising a polymer composition according to claim 1, wherein said homopolymer or copolymer of ethylene is selected from: high-density polyethylene (HDPE); medium-density polyethylene (MDPE); low-density polyethylene (LDPE); linear-low-density polyethylene (LLDPE), very-low-density polyethylene (VLDPE), ultra-low-density polyethylene (ULDPE), which are copolymers of ethylene with at least one aliphatic α-olefin having the formula CH.sub.2═CH—R in which R represents a linear or branched alkyl group containing from 1 to 12 carbon atoms, selected from: propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene; or mixtures thereof.

3. A phase change material that is adapted for thermal energy storage, comprising a polymer composition according to claim 1, wherein said fillers (b.sub.1) are selected from: talc H.sub.2Mg.sub.3(SiO.sub.3).sub.4, calcium carbonate (CaCO.sub.3), magnesium hydroxide [Mg(OH).sub.2], mica, barium oxide (BaO), boehmite [g-AlO(OH)], diaspore [g-AlO(OH)], gibbsite [Al(OH).sub.3], barium sulfate (BaSO.sub.4), wollastonite (CaSiO.sub.3), zirconium oxide (ZrO.sub.2), silicon oxide (SiO.sub.2), glass fiber, magnesium aluminate [MgO.sub.xAl.sub.2O.sub.3 in which x=from 1.5 to 2.5], dolomite [CaMg(CO.sub.3).sub.2], clay, hydrotalcite, or mixtures thereof.

4. A phase change material that is adapted for thermal energy storage, comprising a polymer composition according to claim 1, wherein said fillers (b.sub.2) are selected from: boron nitride (BN), aluminum nitride (AlN), magnesium silicon nitride (MgSiN.sub.2), silicon carbide (SiC), graphite, ceramic coated graphite, expanded graphite, graphene, carbon fiber, carbon nanotubes (CNT), graphitized carbon black, or mixtures thereof.

5. A phase change material that is adapted for thermal energy storage, comprising a polymer composition according to claim 1, wherein said fillers (b.sub.1) and said fillers (b.sub.2) have: an aspect ratio, said aspect ratio being defined as the ratio between the diameter and the thickness of said fillers, ranging from 5 to 1000; and/or at least one of the three dimensions ranging from 0.1 μm to 1000 μm.

6. Polymer composition according to claim 1, wherein said at least one filler (b.sub.1) and said at least one filler (b.sub.2) are present in a ratio by volume ranging from 4:1 to 1:2.

7. A phase change material that is adapted for thermal energy storage, comprising a polymer composition according to claim 1, wherein said fluoropolymer (c) is selected from fluoroelastomers, mixtures comprising a fluoroelastomer and an ethylene (co)polymer, masterbatches comprising a fluoroelastomer and a (co)polymer of ethylene.

8. A phase change material that is adapted for thermal energy storage, comprising a polymer composition according to claim 1 comprising from 200 ppm to 3500 ppm of said at least one fluoropolymer.

9. A phase change material that is adapted for thermal energy storage, comprising a polymer composition according to claim 1 wherein said fillers (b1) have a thermal conductivity ranging from 1 W/mK to 10 W/mK and said fillers (b.sub.2) have a thermal conductivity ranging from 80 W/mK to 500 W/mK.

10. A phase change material that is adapted for thermal energy storage, comprising a polymer composition according to claim 5 wherein said fillers (b.sub.1) and said fillers (b.sub.2) have: said aspect ratio ranging from 10 to 500; and/or said at least one of the three dimensions ranging from 3 μm to 500 μm.

11. A phase change material that is adapted for thermal energy storage, comprising a polymer composition according to claim 1, wherein said at least one filler (b.sub.1) and said at least one filler (b.sub.2) are present in a ratio by volume ranging from 2:1 to 1:1.

12. A phase change material that is adapted for thermal energy storage, comprising a polymer composition according to claim 1 wherein said at least one fluoropolymer does not reduce a thermal conductivity of said polymer composition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Part of the granules obtained in EXAMPLE 3 below were subjected to DSC (Differential Scanning Calorimetry), for determining the phase transition enthalpy as shown in FIG. 1 in which Heat Flow (W/g) was determined as a function of Temperature (° C.).

(2) For the purpose of understanding the present invention better and to put it into practice, below are some illustrative and non-limiting examples thereof.

EXAMPLE 1 (COMPARATIVE)

(3) 100% by volume of high-density polyethylene (HDPE) (Eraclene® MR 80 U by Versalis spa), were loaded into a co-rotating twin-screw extruder (D=30 mm; L/D=28) equipped with a die plate having cylindrical holes with a diameter of 3 mm, a length of 20 mm and flow rate per individual extrusion hole of 4.50 kg/h. The whole was extruded operating at a constant temperature profile of 200° C., at a constant pressure profile of 26 bar, at a flow rate of 4.50 kg/h per individual hole, and at a screw rotation speed of 100 rpm. The material extruded in “spaghetti” form was cooled in a water bath, dried in air, granulated using a chopper. Part of the granules obtained were compression molded at 240° C., 100 bar, for 5 minutes, obtaining a plaque with dimensions of 20×20×2 cm, which was subjected to thermal conductivity analysis: the datum obtained is reported in Table 1.

(4) The thermal conductivity analysis was carried out operating according to the methodology described in: Gustafsson S. E. et al., “Journal of Physics D: Applied Physics” (1979), Vol. 12, No. 9, pg. 1411-1421 in relation to the equipment used; Gustafsson S. E., “Journal of Applied Physics” (1982), Vol. 53, No. 9, pg. 6064-6068 in relation to the thermal conductivity calculation.

(5) Part of the granules obtained were compression molded at 200° C., 100 bar, for 5 minutes, obtaining a specimen with dimensions 15×40×4 mm which was subjected to Vicat softening temperature measurement operating in accordance with standard ISO 306:2004, Method A50 (1 kg−50° C./h), which was equal to 126° C.

EXAMPLE 2 (COMPARATIVE)

(6) 80% by volume of high-density polyethylene (HDPE) (Eraclene® MR 80 U by Versalis spa), 10% by volume of talc (aspect ratio=15; largest dimension: 35μm) (Imerys-FGRM) and 10% by volume of boron nitride (aspect ratio=30; largest dimension: 20 μm) (Boron Nitride Cooling Filler Platelets Grades 15/400), were loaded into a co-rotating twin-screw extruder (D=30 mm; L/D=28) equipped with a die plate having cylindrical holes with a diameter of 3 mm, a length of 20 mm and flow rate per individual extrusion hole of 1.50 kg/h. the whole was extruded operating at a constant temperature profile of 200° C., at a constant pressure profile of 26 bar, at a flow rate of 1.50 kg/h per individual hole, and at a screw rotation speed of 100 rpm. The material extruded in “spaghetti” form was cooled in a water bath, dried in air, granulated using a chopper. Part of the granules obtained were compression molded at 240° C., 100 bar, for 5 minutes, obtaining a plaque with dimensions of 20×20×2 cm, which was subjected to thermal conductivity analysis operating as described in Example 1: the datum obtained is reported in Table 1.

(7) Part of the granules obtained were compression molded at 200° C., 100 bar, for 5 minutes, obtaining a specimen with dimensions 15×40×4 mm which was subjected to Vicat softening temperature measurement operating in accordance with standard ISO 306:2004, Method A50 (1 kg−50° C./h), which was equal to 126° C.

(8) During extrusion the formation of die build up was observed on the die plate after about 3 hours of operation of the extruder. It is to be noted that the formation of die build up can cause the formation of irregularities on the surface of the extruded material which can lead to its breaking and to the consequent need to stop the extruder in order to clean the die plate.

EXAMPLE 3 (INVENTION)

(9) 80% by volume of high-density polyethylene (HDPE) (Eraclene® MR 80 U by Versalis spa), 10% by volume of talc (aspect ratio=15; largest dimension: 35 μm) (Imerys-FGRM) and 10% by volume of boron nitride (aspect ratio=30; largest dimension: 20 μm) (Boron Nitride Cooling Filler Platelets Grades 15/400) and 500 ppm of fluoropolymer (Viton® Freeflow™ GB by DuPont), were loaded into a co-rotating twin-screw extruder (D=30 mm; L/D=28) equipped with a die plate having cylindrical holes with a diameter of 3 mm, a length of 20 mm and flow rate per individual extrusion hole of 1.70 kg/h. The whole was extruded operating at a constant temperature profile of 200° C., at a constant pressure profile of 26 bar, at a flow rate of 1.70 kg/h per individual hole, and at a screw rotation speed of 100 rpm. The material extruded in “spaghetti” form was cooled in a water bath, dried in air, granulated using a chopper. Part of the granules obtained were compression molded at 240° C., 100 bar, for 5 minutes, obtaining a plaque with dimensions of 20×20×2 cm, which was subjected to thermal conductivity analysis operating as described in Example 1: the datum obtained is reported in Table 1.

(10) Part of the granules obtained were compression molded at 200° C., 100 bar, for 5 minutes, obtaining a specimen with dimensions 15×40×4 mm which was subjected to Vicat softening temperature measurement operating in accordance with standard ISO 306:2004, Method A50 (1 kg−50° C./h), which was equal to 126° C.

(11) During extrusion no formation of die build up was observed on the die plate even after 5 hours of operation of the extruder.

(12) Part of the granules obtained were also subjected to DSC (Differential Scanning calorimetry), for the purpose of determining the phase transition enthalpy through a Perkin Elmer Pyris differential scanning calorimeter. For that purpose, 10 mg of granules were analyzed, with a scanning speed of 20° C./min in cooling and 5° C./min in heating, in an inert nitrogen atmosphere: the results obtained are reported in FIG. 1, from which it can be deduced that the polymer composition obtained as described above has a phase transition enthalpy of 151.6 J/g in fusion and 170.7 J/g in crystallization.

EXAMPLE 4 (INVENTION)

(13) 80% by volume of high-density polyethylene (HDPE) (Eraclene® MR 80 U by Versalis spa), 10% by volume of talc (aspect ratio=15; largest dimension: 35 μm) (Imerys-FGRM) and 10% by volume of boron nitride (aspect ratio=30; largest dimension: 20 μm) (Boron Nitride Cooling Filler Platelets Grades 15/400) and 3000 ppm of fluoropolymer (Viton® Freeflow™ GB by DuPont), were loaded into a co-rotating twin-screw extruder (D=30 mm; L/D=28) equipped with a die plate having cylindrical holes with a diameter of 3 mm, a length of 20 mm and flow rate per individual extrusion hole of 2.15 kg/h. The whole was extruded operating at a constant temperature profile of 200° C., at a constant pressure profile of 26 bar, at a flow rate of 2.15 kg/h per individual hole, and at a screw rotation speed of 100 rpm. The material extruded in “spaghetti” form was cooled in a water bath, dried in air, granulated using a chopper. Part of the granules obtained were compression molded at 240° C., 100 bar, for 5 minutes, obtaining a plaque with dimensions of 20×20×2 cm, which was subjected to thermal conductivity analysis operating as described in Example 1: the datum obtained is reported in Table 1.

(14) Part of the granules obtained were compression molded at 200° C., 100 bar, for 5 minutes, obtaining a specimen with dimensions 15×40×4 mm which was subjected to Vicat softening temperature measurement operating in accordance with standard ISO 306:2004, Method A50 (1 kg−50° C./h), which was equal to 126° C.

(15) During extrusion no formation of die build up was observed on the die plate even after about 5 hours of operation of the extruder.

(16) TABLE-US-00001 TABLE 1 THERMAL CONDUCTIVITY FLOW RATE Die build up EXAMPLE (W/mK) (kg/h) time (h) 1 (comparative) 0.4 4.50 — 2 (comparative) 2.4 1.50 3 3 (invention) 2.4 1.70 >5 4 (invention) 2.4 2.15 >5

(17) From the data reported in Table 1 it can be deduced that the presence of fluoroelastomer [Example 3 (invention) and Example 4 (invention)] does not affect the thermal conductivity which remains unvaried with respect to Example 2 (comparative) which, however, shows a lower extrusion flow rate per individual hole (equal to 1.50 kg/h) with respect to the extrusion flow rate per individual hole of both Example 3 (invention) (equal to 1.70 kg/h), and Example 4 (invention) (equal to 2.15 kg/h). Furthermore, it can be deduced that the presence of fluoroelastomer [Example 3 (invention) and Example 4 (invention)] allows die build up to be prevented on the die plate even after 5 hours of operation of the extruder.