Study on Electro-induced Shape Memory Polycaprolactone Carbon Black Composite Conductive Polymer Material

Materials and Performance Electro-Reactive Shape Memory Polycaprolactone/Carbon Black Composite Conductive Polymer Materials Qin Ruifeng, Zhu Guangming, Du Zongxi, Cui Xiaoping, Zhang Longbin (Department of Applied Chemistry, Northwestern Polytechnical University, Xi'an 710072, Shaanxi, China). The results show that the composite conductive polymer material with cross-linked polycool as the polymer matrix and conductive carbon black as the conductive filler has good electromechanical shape memory properties. The deformation recovery rate of the CB30025 sample that was stretched 2 times at 200 V was 100%. The response time was 140 s. The sample with the carbon black mass content of 25% was compared with the sample with 20% carbon black content. The response time is shorter and the deformation recovery rate is also higher. As the voltage increases, the response time of the sample decreases, and the recovery rate of deformation increases.

1 If the shape-memory effect of a shape-memory polymer is combined with the electro-thermal effect of Lian-Lian 6ChhaAcadco's leg alElectronic Publishing and the shape memory effect of the polymer, the shape memory effect of the shape memory polymer is specifically expressed as follows: Lights or changes in pH, etc.) The deformed state can be maintained; when it is heated, illuminated, or changed in pH, the sample can return to its original shape. Compared with shape memory alloys and shape memory ceramics, shape memory polymers have the advantages of large memory effect, low induction temperature, low cost, easy processing and molding, wide application range, and the like, and have received much attention in recent years. According to different conditions for achieving shape recovery, shape memory polymers can be classified into different types such as thermal, photo, electro- and pH-sensitive types. At present, shape memory polymers that have been researched more and have been applied on a large scale are mainly thermally induced. Thermotropic shape memory polymers generally consist of a stationary phase that maintains the shape of a molded article and a reversible phase that undergoes a softening-hardening reversible change with temperature. The stationary phase is used to remember the shape of the initial molding, and the reversible phase ensures that the molded product can change shape. Thermally-induced shape memory polymers that have been developed include polynorbornene, cross-linked polyolefins, trans-1,4-polyisoprene, styrene-butadiene copolymers, and polyurethanes. Due to its electrothermal effect, composite conductive polymer materials have been used in self-controlling heaters (with) current limiters and circuit overload protectors. The self-controlled temperature heating tape has been used in the anti-frozen and thermal insulation of gas-liquid transmission pipelines, instrument pipelines, and tanks in the petroleum and chemical industries and various types of snow melting devices. It can be seen that the shape memory performance of the sample is proportional to the elastic modulus E when the sample is in a high elastic state, and E can be obtained from (3): g entanglement factor k Boltzmann constant a linear distortion factor V unit volume The number of molecular chains P density N Avogadro constants The number average molecular weight of Mn molecular chains The relative molecular mass of the segments between Mc crosslinks It can be seen that the greater the degree of cross-linking, the greater the entanglement point More, Mc becomes smaller, V becomes larger, then E is greater, and the shape memory performance is better.

It can be seen from Table 1 that the recovery rate of the deformation of the sample with the irradiation dose of 100 kGy is low, and the recovery rate of the deformation of the sample with the radiation dose of 200 kGy and 300 kGy reaches more than 90%, and when the carbon black content is At the same time, as the irradiation dose increases, the deformation recovery rate of the sample increases. This is due to the difference in the gel content of the sample, and the recovery rate of the deformation of the sample with a high gel content is also high. The gel content of the sample also confirmed this point. When the carbon black content is the same, the gel content of the sample increases with the increase of the irradiation dose. It can be seen that the irradiation of the sample is a decisive factor influencing the shape memory performance of the sample.

Table 1 Thermal shape memory properties of POZCB specimens. For PCL/CB specimens, after applying a voltage across the specimen after stretching, it can be observed that a point on one end of the specimen is first softened, thereby producing a deformation recovery. As the pressurization time increases, the softened region gradually expands, extending toward the unsoftened portion, and the length of the sample is continuously shortened. After a certain period of time, the entire specimen was completely softened and the length of the specimen no longer changed.

During the deformation recovery of the sample, it was found that the recovery rate of deformation did not change much.

This phenomenon can be explained by the fact that in the PCL/CB specimens, the resistance distribution is relatively uniform, and after the voltage is applied, the parts with the larger resistance are softened due to the electrothermal effect and are first softened and contracted. If the temperature is kept at room temperature, since the conductive network of the sample after shrinkage is more dense than that of the tensile sample, the resistance will decrease. However, due to the PTC/NTC effect, the resistance of the softened part does not change much, and therefore, in the entire circuit, The current does not change much, it will always be kept at a high level, and the electric heating effect is also strong. With the soft part near the site, due to the influence of heat conduction, the temperature will be higher, due to the PTC effect, the resistance will be greater, the electrothermal effect will be dominant, and will be preferentially softened. It is for this reason that during the recovery of the deformation of the specimen, the softening starts from the part and then extends toward the unsoftened part until the entire specimen is completely softened. Since the current does not change much, the recovery rate is also more uniform throughout the recovery process.

Carbon black content is one of the key factors that determine the shape memory performance of PCL/CB samples. The effect of carbon black content on the electromechanical shape memory performance of the sample shows that the sample with the carbon black content of 15% has the same length after voltage is applied, ie, there is no electromechanical shape memory effect. It can be seen that the samples with carbon black content of 20% and 25% can recover after voltage application. Compared with the sample with 20% carbon black, the response time of the sample with 25% carbon black was shorter, the response time was 3 minutes, the response time of the former was 12 minutes, and the recovery rate of the sample with 25% carbon black was also higher. High, can reach more than 90%.

The influence of the carbon black content on the electromechanical shape memory performance of the CB200 sample is a key factor that influences the recovery of the sample deformation. It can be seen that as the voltage increases, the response time of the sample decreases and the deformation recovery rate also decreases. improve. When the voltage is 125V, the sample is not completely melted, so the deformation recovery rate is low; when the applied voltage is above 150V, the deformation recovery rate of the sample is large; when the voltage is 175V and 200V, the deformation recovery rate of the sample is Up to 90% or more.

The magnitude of the voltage mainly affects the electrothermal effect of the sample. The higher the voltage, the stronger the electrothermal effect, and the softening of the sample is faster and more complete, so that the deformation recovery rate and the deformation recovery rate are large.

From Table 2, it can be seen that the response time and deformation recovery rate of the sample in the first three stretching-recovery cycles have no significant changes, and it can be seen that the three cycles have no significant effect on the electromechanical shape memory performance of the sample. After 3 cycles of stretching and recovery, the recovery rate of the deformation of the sample did not change much, and the response was increased. It may be recied several times after Mfe cycle experiment. Conclusion The cross-linked polycaprolactone is a polymer matrix conductive carbon black as the conductive filler, and the prepared composite conductive polymer material has good electro-active shape memory characteristics. For the samples with 200kGy and 300kGy irradiation dose and 25% carbon black, the deformation recovery rate can reach over 90%. The CB300-25 sample still has good electromechanical shape memory characteristics after 3 cycles of stretching and recovery.

The carbon black content in the sample is one of the key factors that determine the shape memory performance of the sample. Samples with 25% carbon black and 20% carbon black have a shorter response time of 3 minutes and a higher recovery rate of deformation, which can reach over 90%. The magnitude of the applied voltage is also a key factor that influences the recovery of the deformation of the sample. With the increase of the voltage, the response time of the sample is shortened, and the recovery rate of deformation is improved.