Shape memory polymer filament and a method of manufacturing thereof

Abstract

A shape memory polymer conductive filament comprising thermoplastic polymer, wherein the thermoplastic polymer is used in an amount ranging between 70% to 95% by weight of the shape memory polymer conductive filament; and filler, wherein the filler is used in an amount ranging between 5% to 30% by weight of the shape memory polymer conductive filament.

Description

[0001] SHAPE MEMORY POLYMER FILAMENT AND A METHOD OF MANUFACTURING THEREOF

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to shape memory polymer (SMP) conductive filament, in particular, the SMP conductive filament exhibits improved conductivity, shape recovery as well as desirable activation temperatures.

[0004] BACKGROUND OF THE INVENTION

[0005] Shape memory polymer (SMP) is a stimuli-responsive material that can be programmed to respond to its surrounding. SMP are commonly used in applications such as but no limited to aerospace engineering, shape memory arrays, 4D printings, and biomedical devices.

[0006] Thermally activated SMP filaments are known to have poor activation response and speed when activated by change in environment. SMP filaments can be affected from localized or uneven heating as well as activation from other activation method. One of the methods to overcome this problem is to ensure that the SMP filaments have the conductive properties and are manufactured from suitable polymers such that ineffective activation can be minimized through Joule heating. Further, it is also crucial for the SMP filament to have a desirable range of activation temperature which is subsequently ideal for the end products such as but not limited to technical textiles, aerospace, biomedical and automotive applications.

[0007] As such, there is a need to identify a suitable material to manufacture a shape memory polymer filament such that the filament exhibits improved conductivity and minimized ineffective activation along with a desirable activation temperature.

[0008] SUMMARY OF THE INVENTION

[0009] The present invention relates to a shape memory polymer conductive filament comprising thermoplastic polymer, wherein the thermoplastic polymers is used in an amount ranging between 70% to 95% by weight of the shape memory polymer conductive filament; and filler, wherein the filler is used in an amount ranging between 5% to 30% by weight of the shape memory polymer conductive filament.

[0010] Additional aspects, features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the accompanying drawings and preferred embodiments of the invention.

[0011] BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0012] The present invention will be fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, wherein:

[0013] In the attached drawings:

[0014] FIGURE 1 represents the illustration of equation for measuring the resistivity of the SMP conductive filament.

[0015] FIGURE 2 represents the illustration of the Dynamic Mechanical Analyser (DMA) sequence to measure shape memory properties of the SMP conductive filaments of the present invention.

[0016] FIGURE 3 represents the graph that consists of the parameters such as time, temperature and stress for the shape memory properties test.

[0017] DETAILED DESCRIPTION OF THE INVENTION

[0018] Detailed description of preferred embodiments of the present invention is disclosed herein. It should be understood, however the embodiments are merely exemplary of the present invention, which may be embodied in various forms. Therefore, the details disclosed herein are not to be interpreted as limiting, but merely as the basis for the claims and for teaching one skilled in the art of the invention. The numerical data or ranges used in the specification are not to be construed as limiting.

[0019] The present invention relates to shape memory polymer (SMP) conductive filament, in particular, the SMP conductive filament exhibits improved conductivity, shape recovery, as well as desirable activation temperatures. First aspect of the present invention discusses on a shape memory polymer (SMP) conductive filament, wherein the SMP conductive filament comprises: thermoplastic polymers, wherein the thermoplastic polymers are used in an amount ranging between 70% to 95% by weight of the SMP conductive filament. The thermoplastic polymers are such as but not limited to thermoplastic polyurethane, polylactic acid, polycaprolactone, polyhydroxyalkanoates and mixtures thereof, preferably a mixture of thermoplastic polyurethane and polylactic acid. For the purpose of the present invention, the thermoplastic polymer is prepared by mixing the thermoplastic polyurethane and polylactic acid is at a ratio of 70:30 using an internal mixer at a speed ranging between 50 rpm to 60 rpm at a temperature ranging between 190°C to 200°C for a duration ranging between 7 minutes to 10 minutes.; and filler, wherein the filler is used in an amount ranging between 5% to 30% by weight of the SMP conductive filament. The filler is selected from the group consisting of carbon-based conductive materials such as but not limited to graphene, carbon fibers, recycled carbon black and carbon nanotubes, and high conductive materials such as but not limited to copper and silver.

[0020] Table 1 shows the chemical components and compositions thereof used in the SMP conductive filament of the present invention.

[0021] Table 1 : Chemical components and compositions thereof used in the SMP conductive filament of the present invention

[0022] Second aspect of the present invention discusses on a method of preparing the SMP conductive filament, wherein the method comprises the steps of: i. mixing filler into the thermoplastic polymer until homogenously distributed to produce a compound, wherein the mixing process is carried out using an internal mixer at a processing temperature ranging between 190°C to 210°C at a speed ranging between 50 rpm / min to 60 rpm / min for a duration ranging between 7 minutes to 15 minutes; ii. pelletizing the compound obtained from step (i) by using a crusher to produce pelletized compound, wherein the crushing process is carried out by using a low speed granulator; iii. drying the pelletized compound obtained from step (ii) to obtain a dried compound, wherein the drying process is carried out by using a vacuum drying oven at a temperature ranging between 60°C to 70°C for a duration of 12 hours; and iv. extruding the dried compound obtained from step (iii) to produce the SMP conductive filament of the present invention, wherein the extruding process is carried by using a desktop extruder at a temperature ranging between 190°C to 210°C at an extruded speed ranging between 50mm / s to 70mm / s.

[0023] The resultant SMP conductive filaments of the present invention has an average diameter of 1.75 ±0.05 mm. The same is used as feedstock for fused deposition modelling 3D printer.

[0024] The following example is constructed to illustrate the present invention in a non-limiting sense.

[0025] TEST RESULTS

[0026] The SMP conductive filament of the present invention is prepared using the composition as described in Table 1 adopting a method as described in the second aspect of the present invention.

[0027] Test results for the SMP conductive filament of the present invention

[0028] The SMP conductive filaments of the present invention are tested for sheet resistance, wherein the sheet resistance is measured using the two-point probe method by a digital multimeter (Keithley Instruments Inc., USA). The resistivity (p) values of the filaments are calculated from the measured sheet resistance (R) values of the conductive elements using the equation below and as illustrated in FIGURE 1 : wherein R = resistance value p = resistivity

[0029] L = length of the filament

[0030] A = area

[0031] As indicated above, the sheet resistance is measured using the two-point probe for the filaments. L, which represents the length of the filament, has a value of 10.5 cm. A is the cross-sectional area of the filaments.

[0032] For the purpose of the present invention, a total of 10 samples for each filament are measured and the average resistivity values are obtained. For the purpose of Table 2, Set 1 refers to a conventional non-shape memory conductive filament. Set 2 refers to the shape memory conductive filament of the present invention comprising 15% of filler. Set 3 refers to the shape memory conductive filament of the present invention having 20% of filler.

[0033] Table 2 shows the resistivity value of the filament samples of the present invention.

[0034] Table 2: Outcome of the resistivity value of the filament samples of the present invention

[0035] Based on Table 2, it is evident that Sets 2 and 3 of the present invention are able to exhibit a lower resistivity value as compared to a conventional non-shape memory conductive filament, indicating a good electrical conductivity in both samples. It has to be understood that the lower the resistivity, the higher the conductivity of the filament.

[0036] The shape memory filaments of the present invention are also tested for shape memory properties using Dynamic Mechanical Analyser (DMA) according to ASTM D4065. The sequence for the DMA testing is in cyclic which consists of four stages. The sample preparation is also done according to ASTM D4065. The samples are printed into thin sheets with the dimension of 0.5mm (thickness) x 10mm (width) x 40mm (height).

[0037] As illustrated in FIGURES 2 and 3, the cyclic testing starts, wherein at the first stage the sample specimen is subjected to deformation under stress at 0.2 MPa and temperature condition up to 70°C above the material glass transition temperature, Tg for a duration of 50 minutes. At the second stage which is known as shape fixity, the sample shape was fixed at 0.2 MPa pressure point while the temperature condition was reduced to ambient. During this stage, the specimen shape was monitored for a duration of 50 minutes and the changes in shape were recorded. Next, the sample was subjected to the unloading stage which is stage 3 by reducing the stress applied while maintaining the temperature at ambient. The final stage is the recovery stage, wherein the temperature is increased back to 70°C above the glass transition temperature. During this stage, the percentage of recovery of specimen shape was recorded. This sequence of measurement was conducted repetitively, and the results are tabulated in Table 3.

[0038] Table 3 shows the shape memory properties of the filament samples of the present invention. For the purpose of Table 3, Set 1 refers to a conventional shape memory non-conductive filament. Set 2 refers to the shape memory conductive filament of the present invention comprising 15% of filler. Set 3 refers to the shape memory conductive filament of the present invention having 20% of filler.

[0039] Table 3: Outcome of the shape memory properties of the filament samples of the present invention Based on Table 3, it is evident that the filament samples of the present invention exhibit improved shape recovery as compared to the conventional shape memory non- conductive filament sample.

[0040] The shape memory conductive filaments of the present invention are also tested for their activation temperatures. This is to ensure that the present invention is able to cater the requirements of the end product.

[0041] Table 4 shows the activation temperature of the filament samples of the present invention. For the purpose of Table 4, Set 1 refers to a conventional shape memory non-conductive filament. Set 2 refers to the shape memory conductive filament of the present invention comprising a mixture of thermoplastic polyurethane and polylactic acid as its thermoplastic polymer. Set 3 refers to the shape memory conductive filament comprising a mixture of the polycaprolactone and thermoplastic polyurethane as its thermoplastic polymer. Set 4 refers to the shape memory conductive filament comprising a mixture of the thermoplastic polyurethane (TPU) and polyhydroxyalkanoates as its thermoplastic polymer.

[0042] Table 4: Outcome of the activation temperature of the filament samples of the present invention

[0043] Based on Table 4, it is evident that the shape memory activation of Sets 2 to 4 which are the filament samples of the present invention are desirable, whereby sets 3 and 4 have a lower activation temperature ranging between 29°C to 35°C. It should be understood that the addition of polycaprolactone and polyhydroxyalkanoates with thermoplastic polyurethane ensures the lowering of the activation temperature respectively. This subsequently enables the utilization of the thermoplastic polymers in end products that require lower activation temperature such as but not limited to technical textiles and biomedical applications. Similarly, the addition of polylactic acid with thermoplastic polyurethane ensures a higher activation temperature. This also subsequently enables the utilization of the thermoplastic polymer in end products that require higher activation temperature such as but not limited to the aerospace and automotive applications.

[0044] As a whole, SMP conductive filament of the present invention is able exhibit improved conductivity shape recovery as well as desirable activation temperatures which can be subsequently used in various end products.

[0045] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises", "comprising", “including”, and “having” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups therefrom.

[0046] The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. The use of the expression “at least” or “at least one” suggests the use of one or more elements, as the use may be in one of the embodiments to achieve one or more of the desired objects or results.

Claims

CLAIMS1 . A shape memory polymer conductive filament comprising thermoplastic polymers, wherein the thermoplastic polymers is used in an amount ranging between 70% to 95% by weight of the shape memory polymer conductive filament; and filler, wherein the filler is used in an amount ranging between 5% to 30% by weight of the shape memory polymer conductive filament.

2. The shape memory polymer conductive filament as claimed in claim 1 , wherein the thermoplastic polymers are such as but not limited to thermoplastic polyurethane, polylactic acid, polycaprolactone, polyhydroxyalkanoates and mixtures thereof.

3. The shape memory polymer conductive filament as claimed in claim 2 wherein the thermoplastic polymers are mixed in a ratio of 70:30.

4. The shape memory polymer conductive filament as claimed in claim 1 , wherein the filler is selected from the group consisting of carbon-based conductive materials such as but not limited to graphene, carbon fibers, recycled carbon black and carbon nanotubes, and high conductive materials such as but not limited to copper and silver.

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