Functional Polymer Blends: electrochemical & bio-based applications
Biodegradable polymer blends using polycarbonates
Silk fibroin polymer blends for tissue-engineering materials
SPE/elastomer blends for antistatic materials
Since plastics and rubber products are insulators, various static electricity disturbances will occur by electrification. In order to prevent this, it will lead to expansion of use by giving level of conductivity to the material according to purpose of use. For this reason, antistatic technology has become a very important position in recent years, mainly in electronics related fields. The commonly used antistatic technology is a method of imparting conductivity by kneading a conductive filler such as carbon black (CB) to a polymer material as shown in the left figure. However, with these technologies, problems such as difficulty in precise control of conductivity and low durability are issues. Tominaga Group focused on the use of ion-conductive SPE. With the use of SPE, there is a possibility of realizing precise control and uniformity of conductivity as an antistatic material with particularly large industrial needs. However, SPE generally has high hygroscopicity, which limits the usage environment. Therefore, by blending both in a method of "in situ" polymerization of SPE in the base polymer, we aimed to develop new antistatic materials that can achieve both excellent ionic conductivity and reduced humidity dependency [1-5].
The figure above shows the method of making an ion-conductive elastomer blend by solvent casting method prepared in this research . M(EO/PO) and various metal salts were vacuum dried at room temperature for 24 hours before preparing the blended sample. Predetermined amounts of acrylonitrile butadiene rubber (NBR), M(EO/PO), metal salt and AIBN (1 mol% based on monomer) were stirred in THF for 24 hours. After casting the mixed THF solution obtained to a Teflon Petri dish, vacuum drying at room temperature for 6 hours and vacuum drying for 24 hours were carried out. Thereafter, heating was carried out in a dry N2 gas atmosphere at 100 °C for 24 hours to radical-polymerize the monomers, thereby obtaining various target blends (film thickness 400 to 500 μm). The filling amount of the metal salt was set to 5 wt% with respect to the total amount of the sample.
On the left figure to the left, values of log (σdry), log (σwet), |log (σwet/σdry)| at 30 °C of each blend are summarized . In all blends, the ionic conductivity was 10-8 S/cm order or more and |log (σwet/σdry)| was 0.5 or less, showing excellent ion-conductive behavior as an antistatic material. In addition, each blend of medium to high nitrile NBR30, NBR43, and NBR50 showed higher conductivity than the blend of NBR18 which has low nitrile unit. As a factor of this, the cyano group (-C≡N) of the nitrile moiety of NBR may contribute to the improvement of ionic conductivity. Since the cyano group of the polymer in the polymer electrolyte interacts with the dissociated cation (Li+) like ether oxygen, many ionic conductors using polymers with C≡N groups have been reported. As a representative research example, in the polyacrylonitrile (PVA) electrolyte having a cyano group in the main chain, due to the effect of a cyano group having a strong electron-withdrawing property, ionic conductivity is exhibited even below Tg, so that segment motion and Isolated ion transport mechanism is also expected. In recent years, research on electrolytes in which a cyano group is introduced into a polymer side chain has also progressed, and it can be seen that a cyano group expresses high ionic conductivity by promoting dissociation of a metal salt. In this study, it is considered that the cyano group (-C≡N) of NBR in the blended sample interacts with the dissociated K+, thereby contributing to the improvement of ionic conductivity. These relationships are also confirmed by the interaction between CN group and K+ by FT-IR measurement.
The left figure shows the HAADF-STEM image and the TEM-EDS mapping image of the blend of NBR18 and NBR50 . From the HAADF-STEM image, it was confirmed that both blends formed a polyether island phase of 10-20 nm. Mapping S (sulfur) element and K (potassium) element derived from KSCN metal salt with red and green, respectively. In the blend of NBR18, it was observed that both elements localized to the polyether island phase. In addition, the element K is scattered also in the NBR marine phase compared to the S element. It can be considered that the K element was confirmed also in the NBR phase by the interaction between the cyano group of NBR and K+. On the other hand, in the blend of NBR50, it was observed that both elements were uniformly dispersed in the NBR marine phase/polyether island phase. This is thought to be influenced by the increased interaction between cyano group and K+ in the blend of NBR50 with higher AN content. By the TEM-EDS observation, it was visually confirmed that the cyano group of NBR and K+ interacted with each other. From these results, in the blend using the low nitrile NBR, K+ preferentially interacts with the ether oxygen of the polyether, and K+ which interacts with the cyano group increases as the AN content increases which was revealed that the element K in the NBR phase increased.
- Y. Kubota, Y. Tominaga*, Nihon Gomu Kyokaishi (Japanese), 90 (2), 23-29 (2017).
- Y. Kubota, Y. Tominaga*, Materials Today Communications, 4, 124-129 (2015).
- Y. Kubota, Y. Tominaga*, e-Journal of Soft Materials, 9, 9-13 (2013).
- Y. Tominaga, Nihon Gomu Kyokaishi (review in Japanese), 85 (3), 93-100 (2012).
- Y. Tominaga*, S. Asai, M. Sumita, Nihon Gomu Kyokaishi (Japanese), 82 (12), 499-506 (2009).