Electrically conductive and thermoresponsive composition

Abstract

The present invention relates to an electrically conductive and thermally responsive composition comprising (a) 0.5-10% by weight of an electrically conductive material, and (b) 90-99.5% by weight of a mixture of a first oligomer or polymer having a weight average molecular weight in the range of 300-2,000 g / mol and a second oligomer or polymer having a weight average molecular weight in the range of 3,000-100,000 g / mol. Furthermore, the present invention relates to the use of the composition of the present invention to obtain irreversible change properties upon exposure to a critical temperature.

Description

[Technical field]

[0001] Technical Field The present invention relates to electrically conductive and thermally responsive compositions that can exhibit irreversible electrical resistance properties upon exposure to a critical temperature. [Background technology]

[0002] A temperature sensor is a device that relies on detecting the change in a physical property when the temperature changes. Furthermore, detecting the change in an electrical property allows for easy and direct reading by commonly used electrical equipment. For example, the decrease in electrical conductivity (i.e., increase in electrical resistance) or increase in electrical conductivity can be easily measured when the sensor is exposed to a temperature change. This temperature sensor has been developed to be more convenient and suitable for more wide-ranging applications, for example, by combining it with passive RFID or NFC systems. However, it is generally known that temperature sensor devices using passive RFID or NFC have technical disadvantages, such as low sensitivity or low accuracy, or the inability to detect temperature changes without an external power source.

[0003] Many attempts have been made to improve the electrical properties of temperature sensing device systems and / or temperature sensitive materials used in combination with passive RFID or NFC systems, for example, modifying conductive compositions to obtain a difference in electrical resistance before and after heating at a specific temperature.

[0004] China CN106046721A publication discloses a conductive polymer composite for temperature sensing applications, which is composed of a polymer matrix, which is a polymer blend of one or more polymers, such as polylactic acid, polyethylene, polypropylene, polystyrene, acrylonitrile-butadiene-benzeneethylene copolymer, polyethylene terephthalate, polyvinyl alcohol, nylon, polyformaldehyde, polyoxyethylene, polyurethane, polyvinyl chloride, etc., and further conductive fillers, such as carbon black, graphite sheets, graphene nanosheets, reduced graphene oxide, etc.

[0005] US2015 / 0262738Al discloses a conductive thin film for temperature sensing and a method for manufacturing the same. The conductive thin film is prepared by mixing a composite of silicon crystals and carbon particles, a binder, and a thinner to obtain a temperature-sensitive ink, and then printing the ink on a substrate to form a conductive thin film. The carbon particles can be selected from the group consisting of carbon black, graphite flakes, and graphene nanoplatelets. The binder can be selected from the group consisting of acrylic polymers, epoxies, silicones (polyorganosiloxanes), polyurethanes, polyimides, silanes, germanes, carboxylates, thiolates, alkoxys, alkanes, alkenes, alkynes, and diketonates. Furthermore, the solvent can be selected from the group consisting of ethylene glycol, polyethylene glycol, hydrocarbons, alcohols, ethers, organic acids, esters, aromatics, amines, water, and mixtures thereof.

[0006] International Publication WO2015 / 018619A1 discloses a device for irreversibly detecting the exceedance of a predetermined temperature and a method for its manufacture. The device consists of a substrate layer to which a layer of meltable material is applied. The meltable material layer can be prepared from a mixture of wax or alternative polymers such as polyethylene glycol, polyethylene, polyamide, polypropylene, polybutene, polylactide, etc., and conductive carbon particles.

[0007] Despite the development of conductive materials for temperature identification devices as described above, there remains a need for novel conductive and thermally responsive materials that have irreversible electrical resistance properties suitable for temperature detection at a specific critical temperature, the irreversible change allowing such detection during device operation without constant user or machine supervision or without a continuous supply of external power. Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to provide a mixed polymer matrix comprising low and high molecular weight polymers or oligomers capable of producing an irreversible change of property upon exposure to a critical temperature, in particular a mixed polymer matrix comprising low and high molecular weight polymers or oligomers capable of producing the required irreversible decrease in electrical resistance (R) upon exposure to a critical temperature in the range of 55-120°C.

[0009] Another object of the present invention is to provide an electrically conductive and thermally responsive composition suitable for temperature sensor applications, e.g., RFID- or NFC-based temperature sensing devices, to obtain irreversible change properties upon exposure to a critical temperature. [Means for solving the problem]

[0010] The present invention relates to an electrically conductive and thermally responsive composition comprising: (a) 0.5 to 10 mass % of a conductive material, and (b) 90 to 99.5% by mass of a mixture consisting of a first oligomer or polymer having a weight average molecular weight in the range of 300 to 2000 g / mol and a second oligomer or polymer having a weight average molecular weight in the range of 3000 to 100,000 g / mol. The present invention is characterized in that the conductive and thermally responsive composition comprises:

[0011] In another aspect, the present invention relates to the use of the conductive and thermally responsive composition of the present invention to obtain irreversible change properties upon exposure to a critical temperature, particularly in the range of 55-120°C. [Brief description of the drawings]

[0012] A preferred embodiment of the present invention will be described with reference to the drawings.

[0013] [Figure 1]FIG. 1 shows the electrical resistance measurement of a polymer composition containing polyethylene glycol with a weight-average molecular weight of 1450 g / mol (PEG1450) and containing acetylene black at contents of 1 mass %, 2.5 mass %, 5 mass %, 7.5 mass %, 10 mass %, and 20 mass % of the polymer composition when heated to approximately 60° C.

[0014] [Diagram 2] 2 shows electrical resistance measurements of polymer compositions containing variations of low molecular weight polyethylene glycol (PEG600) with a weight average molecular weight of 600 g / mol and high molecular weight polyethylene glycol (PEG6000) with a weight average molecular weight of 6000 g / mol (PEG6000) and 10000 g / mol (PEG10k) when heated at about 60° C. The mass ratio of low molecular weight polyethylene glycol to high molecular weight polyethylene glycol is 80:20, and the content of acetylene black in the polymer composition is 2.5% by mass.

[0015] [Diagram 3] 3 is a diagram showing electrical resistance measurements of a polymer composition containing a low molecular weight polyethylene glycol (PEG1000) with a weight average molecular weight of 1000 g / mol and variations of high molecular weight polyethylene glycol with weight average molecular weights of 3000 g / mol (PEG3000), 6000 g / mol (PEG6000), and 10000 g / mol (PEG10k) when heated at about 60° C. The mass ratio of the low molecular weight polyethylene glycol to the high molecular weight polyethylene glycol is 80:20, and the content of acetylene black in the polymer composition is 2.5% by mass.

[0016] [Figure 4]4 is a diagram showing electrical resistance measurements of a polymer composition containing a low molecular weight polyethylene glycol (PEG1450) with a weight average molecular weight of 1450 g / mol and variations of high molecular weight polyethylene glycol with weight average molecular weights of 3000 g / mol (PEG3000), 6000 g / mol (PEG6000), and 10000 g / mol (PEG10k) when heated at about 60° C. The mass ratio of the low molecular weight polyethylene glycol to the high molecular weight polyethylene glycol is 80:20, and the content of acetylene black in the polymer composition is 2.5% by mass.

[0017] [Diagram 5] 5 is a diagram showing electrical resistance measurements of a polymer composition containing polyethylene glycols with weight-average molecular weights of 1450 g / mol (PEG1450) and 10000 g / mol (PEG10k) when heated at approximately 40° C., 50° C., and 60° C. The mass ratio of PEG1450 to PEG10k is 80:20, and the content of acetylene black in the polymer composition is 2.5% by mass relative to the mass of the polymer composition.

[0018] [Figure 6] 6 is a diagram showing the electrical resistance measurement of a polymer composition containing polyethylene glycols with weight-average molecular weights of 1450 g / mol (PEG1450) and 10000 g / mol (PEG10k) when the polymer composition was repeatedly heated for three cycles at about 60° C. The mass ratio of PEG1450 to PEG10k was 80:20, and the content of acetylene black in the polymer composition was 2.5% by mass relative to the mass of the polymer composition.

[0019] [Figure 7]7 is a diagram showing a stability test of a temperature sensor in a low electrical resistance state after storage in a desiccator for 88 days. The temperature sensor uses a polymer composition containing polyethylene glycols with weight average molecular weights of 1450 g / mol (PEG1450) and 10000 g / mol (PEG10k). The mass ratio of PEG1450 to PEG10k is 80:20, and the content of acetylene black in the polymer composition is 2.5% by mass relative to the mass of the polymer composition. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Detailed Description of the Invention Unless otherwise specified, the embodiments described below are intended to encompass applications to other embodiments of the present invention.

[0021] Unless otherwise defined, technical and scientific terms used herein have definitions that are understood by those of ordinary skill in the art.

[0022] Throughout the present invention, the term "about" is used to indicate that a value indicated or presented herein may be subject to variation or deviation. Such variation or deviation may represent the error in the device or method used to determine the value.

[0023] The terms "consisting of" (variations of "consist(s) of", such as "consisting of", "consisted of", and "consisted of"), "including" (variations of "comprise(s)", such as "comprising" and "comprised"), "containing", and "having" (variations of "include(s)", such as "has / have / having", "contain(s), "including", and "included") are open-ended verbs. For example, a method that "comprises", "has", or "consists of" one or more components or steps is not limited to only one or more components or steps, but also includes unmentioned components or steps.

[0024] The terms "a," "an," "the," and "the" when referring to a singular noun, are intended to include the plural of that noun, unless specifically stated otherwise.

[0025] The means, devices, methods, materials, or chemicals described in this specification refer to means, devices, methods, materials, or chemicals commonly used or practiced by those skilled in the art, unless otherwise specified.

[0026] All disclosed materials, polymers, components, and / or methods, as well as the claims of the present invention, are intended to cover aspects of the present invention resulting from any action, implementation, modification, or change made to the factors without significant experimentation from the present invention, and are also intended to include those that, although not specifically indicated in the claims, have similar properties, utility, and effects to the aspects of the present invention according to those skilled in the art. Thus, objects equivalent to or similar to the aspects of the present invention should be considered within the spirit, scope, and concept of the present invention, including slight modifications or changes that are obvious to those skilled in the art.

[0027] According to a first aspect, the conductive and thermally responsive composition of the present invention comprises: (a) 0.5 to 10 mass % of a conductive material, and (b) 90 to 99.5% by mass of a mixture consisting of a first oligomer or polymer having a weight average molecular weight in the range of 300 to 2,000 g / mol and a second oligomer or polymer having a weight average molecular weight in the range of 3,000 to 100,000 g / mol; The conductive and thermally responsive composition comprises:

[0028] In a preferred embodiment, the first oligomer or polymer has a weight average molecular weight in the range of 300 to 1,600 g / mol.

[0029] In another preferred embodiment, the second oligomer or polymer has a weight average molecular weight in the range of 3,000 to 12,000 g / mol.

[0030] In exemplary specific embodiments, the mass ratio of the first oligomer or polymer to the second oligomer or polymer ranges from 50:50 to 98:2. For example, the mass ratio of the first oligomer or polymer to the second oligomer or polymer can be 50:50, 65:35, 80:20, 90:10, 95:5, 97.5:2.5, and the like.

[0031] According to the present invention, the selective combination of two different specific molecular weight polymers or oligomers can provide the surprising technical effect of irreversible electrical resistance (R) properties at critical temperatures in the range of 55-120°C, such as 60±5°C, 70±5°C, 80±5°C, 90±5°C, 100±5°C, 110±5°C, etc. Specifically, for irreversible properties, the electrical resistance (R) of the composition starts in a high resistance state and remains in or returns to such a high resistance state during or after the composition is exposed to a temperature below the critical temperature. What is important is that after the composition is exposed to a temperature equal to or above the critical temperature, the electrical resistance (R) of the composition is significantly reduced and irreversibly transitions to a low resistance state. More preferably, the reduction in electrical resistance associated with the irreversible change should be two orders of magnitude. That is, the difference (ΔR) between the initial electrical resistance and the final electrical resistance after exposure to the critical temperature is about 100 times. For irreversible properties, after the initial exposure to the critical temperature, the electrical resistance should remain in the low resistance state independent of further exposure to any temperatures below or above the critical temperature, except for some fluctuations during the heating or cooling process.

[0032] According to exemplary preferred embodiments of the present invention, the conductive and thermally responsive compositions of the present invention comprise a mixture of two different molecular weight oligomers and / or polymers, such as: The first oligomer or polymer has a weight average molecular weight in the range of 300 to 500 g / mol and the second oligomer or polymer has a weight average molecular weight in the range of 3,000 to 12,000 g / mol. The first oligomer or polymer has a weight average molecular weight in the range of 500 to 700 g / mol and the second oligomer or polymer has a weight average molecular weight in the range of 3,000 to 12,000 g / mol. The first oligomer or polymer has a weight average molecular weight in the range of 900 to 1,200 g / mol and the second oligomer or polymer has a weight average molecular weight in the range of 3,000 to 12,000 g / mol. The first oligomer or polymer has a weight average molecular weight in the range of 1,300 to 1,600 g / mol, and the second oligomer or polymer has a weight average molecular weight in the range of 3,000 to 12,000 g / mol.

[0033] In one embodiment, the first oligomer or polymer can have a melting point in the range of 15 to 46°C and the second oligomer or polymer can have a melting point in the range of 53 to 85°C.

[0034] In another embodiment, the first oligomer or polymer can have a melting point in the range of 55-58°C and the second oligomer or polymer can have a melting point in the range of 100-120°C.

[0035] Examples of the first and second oligomers or polymers that can be used in the present invention are those selected from the group consisting of oligoethers, oligoolefins, polyethers, polyolefins, and combinations thereof. For example, the first oligomer or polymer can be an oligoolefin or polyolefin, and the second oligomer or polymer is a polyolefin. More specifically, the oligoolefin is a linear or branched alkane, or a combination thereof, and the polyolefin is selected from the group consisting of polyethylene, polypropylene, polybutylene, and combinations thereof.

[0036] According to one embodiment, the first oligomer or polymer is an oligoether or polyether and the second oligomer or polymer is a polyether. Preferably, the oligoether is selected from the group consisting of polyoxymethylene, poly(ethylene glycol), poly(ethylene oxide), poly(propylene glycol), poly(tetramethylene glycol), poly(butylene glycol), and combinations thereof. More preferably, the polyether is selected from the group consisting of polyoxymethylene, poly(ethylene glycol), poly(ethylene oxide), poly(propylene glycol), poly(tetramethylene glycol), poly(butylene glycol), and combinations thereof.

[0037] In a preferred embodiment, the conductive material contained in the composition of the present invention is in the range of 0.5 to 5 mass %, more preferably in the range of 0.5 to 2.5 mass %.

[0038] The conductive material used in the present invention can be, for example, a carbon material such as carbon black, acetylene black, graphite, graphene, carbon nanotubes, and the like.

[0039] The compositions of the present invention are suitable for use in obtaining irreversible change properties when exposed to a critical temperature, particularly in the range of 55 to 120° C. For example, the critical temperature may be 60±5° C., 70±5° C., 80±5° C., 90±5° C., 100±5° C., 110±5° C., and the like. EXAMPLES

[0040] The present invention will now be further described by the following examples, which are intended for illustrative purposes and are not intended to limit the scope of the present invention. (1. Preparation of Electrically Conductive and Thermoresponsive Composition) The samples of the conductive and thermoresponsive composition of the present invention can be prepared by melting a mixture of selected oligomers and / or polymers of two different molecular weights at a predetermined temperature between 60 and 100°C. For example, when polyethylene glycol is used, the melting temperature is 100°C. The resulting molten mixture was then mixed with a predetermined amount of acetylene black. To measure the electrical resistance of the samples, the prepared compositions were blade coated on a substrate, such as a printed circuit board (PCB), with a certain thickness in the range of 100 to 600 μm, for example 300 μm. Before measuring the initial electrical resistance (initial R), the samples were left overnight in a room at a temperature of 20°C and a relative humidity (RH) of 30%. The final electrical resistance (final R) of the samples was measured after heating to about 60°C. The initial R before heating, the final R after heating, and the ratio of initial R / final R for each condition were reported.

[0041] (2. Experimental Results) (2.1 Effect of conductive material content on single polymer composition) Samples of polymer compositions containing polyethylene glycol (PEG 1450) with a weight average molecular weight of about 1450 g / mol and acetylene black in various amounts of 1%, 2.5%, 5%, 7.5%, 10%, and 20% by weight of the resulting composition were prepared and their electrical resistance was measured before heating (initial R) and after heating at about 60° C. (final R). The results of the tests are shown in FIG. 1 and Table 1.

[0042] [Table 1]

[0043] The test results showed that samples with an acetylene black content of less than 10% by mass (1 to 7.5% by mass) exhibited reversible electrical resistance, i.e., electrical resistance decreased as the temperature increased and increased again as the temperature decreased, whereas samples with an acetylene black content of 10% by mass or more (10% by mass and 20% by mass) did not show any heat-dependent change in electrical resistance.

[0044] (2.2 Effect of Conductive Material Content on Mixed Molecular Weight Polymer Compositions) Samples of polymer compositions were prepared containing polyethylene glycol (PEG1450) having a weight average molecular weight of about 1450 g / mol, polyethylene glycol (PEG10k) having a weight average molecular weight of about 10000 g / mol, and acetylene black at 0.25%, 0.5%, and 2.5% by weight of the resulting composition. The weight ratio of PEG1450 to PEG10k is 80:20. The electrical resistance of the samples was measured before heating (initial R) and after heating at about 60° C. (final R). The test results are shown in Table 2.

[0045] [Table 2]

[0046] The above test results show that samples with an acetylene black content of 0.5 mass% or more (0.5 mass% and 2.5 mass%) exhibited irreversible electrical resistance characteristics, whereas samples with an acetylene black content of less than 0.5 mass% (0.25 mass%) did not exhibit irreversible electrical resistance characteristics.

[0047] (2.3 Effect of selected molecular weight of polymer and its mass ratio) Samples of two different polymers, a polyethylene glycol composition and a polyethylene composition, were prepared and their electrical resistance (R) was measured before heating (initial R) and after heating at about 60° C. (final R).

[0048] The first polymer composition sample contains polyethylene glycols of different weight average molecular weights mixed in various weight ratios and acetylene black in the resulting composition at a content of 0.5% and 2.5% by weight. The test results of the polyethylene glycol composition sample containing 0.5% by weight of acetylene black are shown in Table 3 (Tables 3-1 and 3-2). The test results of the polyethylene glycol composition containing 2.5% by weight of acetylene black are shown in Figures 2, 3 and 4.

[0049] The second polymer composition sample consisted of polyethylenes of different molecular weights mixed in various weight ratios with acetylene black at 0.5% and 2.5% by weight of the resulting composition. Test results for the polyethylene composition samples are shown in Table 4.

[0050] [Table 3-1]

[0051] [Table 3-2]

[0052] As shown in Table 3 (Tables 3-1 and 3-2), the test results of the polyethylene glycol composition containing 0.5% by weight of acetylene black revealed that all samples exhibited irreversible electrical resistance properties. According to the test results, the higher the proportion of high molecular weight polyethylene glycol, the higher the initial R and the lower the final R, thus improving performance in terms of the ratio of initial R / final R. However, the higher the amount of high molecular weight polyethylene glycol, the worse the mechanical properties, for example, the more brittle the composition becomes or the composition peels off from the substrate. For the same low molecular weight polyethylene glycol, the higher the molecular weight of the high molecular weight polyethylene glycol, the higher the initial R and the lower the final R. As a result, the ratio of initial R to final R increases. Furthermore, the viscosity of the high molecular weight polyethylene glycol with a molecular weight of 100,000 g / mol is too high, so that a proportion of 20% (samples No. 16 and 24 in Table 3-1) is already too high for successful coating on the substrate. The test results also show that increasing the molecular weight of the low molecular weight polyethylene glycol improves performance, mainly due to the higher initial R.

[0053] Figures 2, 3 and 4 show the test results of a polyethylene glycol composition containing 2.5% by mass of acetylene black and a mass ratio of low molecular weight polyethylene glycol to high molecular weight polyethylene glycol of 80:20. The test results show that compositions containing mixtures of low molecular weight and high molecular weight polyethylene glycol, including PEG600 / PEG6000, PEG600 / PEG10k, PEG1000 / PEG3000, PEG1000 / PEG6000 and PEG1450 / PEG10k, exhibited irreversible electrical resistance characteristics, while compositions containing mixtures of low molecular weight and high molecular weight polyethylene glycol, including PEG1450 / PEG3000 and PEG1450 / 6000, did not exhibit irreversible electrical resistance characteristics.

[0054] In addition, samples of a mixture of low molecular weight polyethylene glycol and high molecular weight polyethylene glycol, PEG1450 / PEG10k, in which the mass ratio of PEG1450 to PEG10k is 80:20, and a polyethylene glycol composition containing 2.5% by mass of acetylene black in the polymer composition, were subjected to additional tests, such as measuring the electrical resistance at approximately 40°C, 50°C, and 60°C, and testing the stability of the sensor in the low electrical resistance (LR) state after storage in a desiccator for 88 days. The test results are shown in Figures 5 to 7.

[0055] The test results showed that the polymer composition samples exhibited irreversible electrical resistance properties only when heated to approximately 60° C. (FIG. 5). Furthermore, the electrical resistance did not change even after multiple heatings (FIG. 6), and the electrical resistance did not change over time (Examples 1 and 2 in FIG. 7).

[0056] [Table 4]

[0057] From the test results in Table 4, it was found that all the samples exhibited the irreversible characteristic of electrical resistance. Furthermore, the sample of the polyethylene composition including 4000 g / mol of high molecular weight polyethylene and about 366 g / mol of low molecular weight polyethylene (i.e., hexacosane) exhibited the highest value of the initial R / final R ratio compared to the sample of the polyethylene including 4000 g / mol of high molecular weight polyethylene and about 310 g / mol of low molecular weight polyethylene (i.e., docosane) and the sample of the polyethylene composition including 4000 g / mol of high molecular weight polyethylene and about 338 g / mol of low molecular weight polyethylene (i.e., tetracosane).

[0058] According to the above experimental results, the conductive and thermally responsive composition consisting of a selected mixture of two different polymer molecular weights in combination with the effective amount of acetylene black has an unexpected technical effect of having an irreversible property of reducing electrical resistance at a critical temperature, for example, about 60°C. In particular, the higher the ratio of initial R / final R, the better the performance in temperature sensing. More preferably, the ratio of initial R / final R is the same or is greater by two or more orders of magnitude.

Claims

1. 1. An electrically conductive and thermally responsive composition comprising: (a) 0.5 to 10% by weight of a conductive material; and (b) an electrically conductive and thermally responsive composition comprising 90 to 99.5 wt. % of a mixture of a first polymer having a weight average molecular weight in the range of 300 to 2,000 g / mol and a second polymer having a weight average molecular weight in the range of 3,000 to 10,000 g / mol, the composition having a reduced resistance to electrical conductivity when exposed to a heating temperature, the reduced resistance being irreversible when the heating temperature reaches a critical temperature.

2. The composition of claim 1 , wherein the first and second polymers are the same polymer.

3. The composition of claim 1, wherein the first polymer has a melting point in the range of 15 to 46°C and the second polymer has a melting point in the range of 53 to 85°C.

4. 10. The composition of claim 1, wherein the first polymer and the second polymer are selected from the group consisting of polyethylene, polypropylene, polybutylene, and combinations thereof.

5. 10. The composition of claim 1, wherein the first polymer and the second polymer are selected from the group consisting of polyoxymethylene, poly(ethylene glycol), poly(ethylene oxide), poly(propylene glycol), poly(tetramethylene glycol), poly(butylene glycol), and combinations thereof.

6. The composition according to claim 1 or 5, wherein the first polymer and the second polymer are poly(ethylene glycol) and have a mass ratio of 50:50 to 65:

35.

7. The composition according to claim 1 or 4, wherein the first polymer and the second polymer are polyethylene and have a mass ratio of 97.5:2.5 to 90:

10.

8. 2. The composition of claim 1, wherein the critical temperature is 60°C.

9. The composition of claim 1 , wherein the conductive material is a carbon material.

10. An electrically conductive and thermally responsive composition comprising: (a) 0.5 to 10% by weight of a conductive material; and (b) an electrically conductive and thermally responsive composition comprising 90 to 99.5 weight percent of a mixture of a first polymer having a weight average molecular weight in the range of 1,000 to 1,600 g / mol and a second polymer having a weight average molecular weight in the range of 3,000 to 10,000 g / mol, the first polymer and the second polymer being polyethylene glycol in a mass ratio of 95:5, the composition having a reduced resistance to electrical conductivity when exposed to a heating temperature above room temperature, the reduced resistance being irreversible when the heating temperature reaches a critical temperature.

11. An electrically conductive and thermally responsive composition comprising: (a) 0.5 to 10% by weight of a conductive material; and (b) An electrically conductive and thermally responsive composition comprising 90 to 99.5 wt. % of (i) a mixture of a first polymer having a weight average molecular weight in the range of 1,000 g / mol and a second polymer having a weight average molecular weight in the range of 3,000 to 10,000 g / mol, or (ii) a mixture of a first polymer having a weight average molecular weight in the range of 1,000 to 1,600 g / mol and a second polymer having a weight average molecular weight in the range of 10,000 g / mol, wherein the first polymer and the second polymer are polyethylene glycol in a mass ratio of 80:20, and the composition has a reduced resistance to electrical conductivity when exposed to a heating temperature above room temperature, the reduced resistance being irreversible when the heating temperature reaches a critical temperature.

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