| POLYMERS Vol.70 No.5 |
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COVER STORY
Polymers Shaping the Future Society with Reliability and Safety |
| COVER STORY: Highlight Reviews |
| Fracture of Polymeric Materials | Koh-hei NITTA |
| <Abstract> The complexity of the fracture behavior of polymers is associated with the fact that both intra and inter-molecular interactions coexist under tension. Fracture theory for polymers has been developed for explaining why the bond strength for chain scission is considerably higher than the experimental strength of the actual polymeric materials. For glassy polymers, macroscopic craze-cracks that grow perpendicular to the direction of stretching are the origin of fractures. For crystalline polymers, the origin of macroscopic fracture is a interchain dissociation leading to slippage between extended chain bundles. Keywords: Fracture / Failure / Brittle / Ductile / Craze / Crack |
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| Degradation Diagnosis for Polymeric Materials | Hideaki HAGIHARA |
| <Abstract> The degradation mechanism of polymeric materials needs to be understood in order to improve the reliability of the materials. Progress of analytical equipment and technologies for the polymer structure helps us to clarify the structure of degraded polymers precisely, eventually to realize elucidation of the degradation mechanism. Recent topics of degradation analysis using cutting-edge analytical methods are briefly picked up in this report; the 2D-mapping technologies for the huge data of high-resolution mass spectrometry and infrared spectroscopy, the free volume analysis by positron annihilation, the evaluation of additives and degradation-reaction species. Keywords: Polymer Degradation / Structural Analysis / Mass Spectrometry / Infrared Spectroscopy / Positron Annihilation / Oxidation / Antioxidant / Hydrolysis |
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| COVER STORY: Topics and Products |
| Causes of Fracture of Polymer Materials and Their Analysis Methods | Kazumi NAKAYAMA |
| <Abstract> This paper summarizes the types and causes of fracture in polymer materials and introduces failure analysis methods. The development of essentially durable products continues even now. Nevertheless, fracture do not disappear. This is because fractures are caused by multiple factors. In addition to the strength of the material itself, major factors that affect product strength include degradation, shape, foreign substances, voids and weld lines. While identification of the failure mode is an important part of the product failure analysis, specifying the failure mode is not the ultimate goal. The ultimate goal is to understand why the product has broken in that failure mode. Sometimes observation of fracture surfaces is enough to determine the failure mode, but it is necessary to make a full use of multiple material analysis methods to achieve the ultimate goal. Keywords: Fracture / Analysis / Polymer Material / Fracture Surfaces |
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| High Impact-Resistance Carbon Fiber Composite for Safe and Ustainable Society | Kentaro HANZAWA |
| <Abstract> Carbon Fiber Reinforced Plastic (CFRP) is rapidly expanding its applications in various industries such as aviation, automotive, power generation and construction with replacing metals originally used in these industries due to its light weight and high rigidity. However, the application to structural members for safety is carefully proceeded because CFRP is still behind metals in terms of the fracture property, such as impact resistance. To improve the impact resistance of CFRP, several methods using elastomer have been proposed, and some of them have been commercialized. On the other hand, the application of elastomers to CFRP cause a decrease in rigidity. It is necessary to achieve both, high impact resistance and high rigidity, for a further expansion of applications. We have developed a new concept of Carbon Fiber Reinforced Thermo Plastic (CFRTP), which can achieve both of required properties by compounding elastomers in PA6 matrix and controlling its orientaiton. CFRTP showed higher impact resistance than aluminum alloy without large decrease in rigidity. Further, we analyzed impact fracture mechanism with Finite Element Method (FEM) for advanced performance design. Keywords: CFRP / CFRTP / Impact Resistance / Fracture Analysis |
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| Wet Processed High-Barrier Structure for Flexible OLED Panels | Yoshiyuki SUZURI |
| <Abstract> OLED (Organic Light-Emitting Diode) is an emitting diode that has been attracting significant attention especially for flexibility and printability. Since OLEDs are sensitive to degradation by water vapor, a high barrier structure for flexible panels is necessary. Flexible OLED displays achieve high barrier performance with alternating layers of inorganic films by a vacuum process. The key to the widespread use of OLEDs is the “innovative flexible technology” that provides flexible panels at low cost. We have achieved the world’s first high barrier structure by wet process on OLEDs. A unique feature of our laboratory is obtaining dense inorganic films from precursor polymers by VUV light (λ=172 nm) irradiation at room temperature and under nitrogen atmosphere. This is an innovative technology that can be used not only for OLEDs, but also for other devices and packages that need to be protected from water vapor. Keywords: OLED / Flexible Device / High Barrier / Wet Process / VUV |
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| Degradation Index of Rubber based on Non-Linear Viscoelasticity | Rika TAKEDA, Kyoichi TSURUSAKI |
| <Abstract> Concerning rubbers, the non-linear viscoelasticity (NLVE) appears in the large amplitude oscillatory shear (LAOS) measurement in the region of amplitude γ0>10％. We introduced a novel NLVE index Θ given by a line integral of the geometrical curvature κ of a 3-dimensional closed curve consisting of points at strain γ, strain rate γ and stress σ (3D-Lis). We found that Θ at γ0＝50％ decreases as increasing exposure time of the weathering test. More precisely, two peak heights of κ near a half period decrease even though the exposure time is less than 200 hours. The result suggests that the NLVE analysis will give a sensitive degradation index for rubbers. NLVE has much possibility as a physical characterization of not only rubbers but also soft matters. We expect that the NLVE analysis will be useful in many fields of readers. Keywords: Non-Linear Viscoelasiticity / LAOS / Rubber / Degradation Index / NLVE Index / Geometrical Curvature |
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| Polymer Science and I: A Personal Account |
| Become Intrigued | Yukiya KITAYAMA |
| <Abstract> Background of the author and interfacial photo-crosslinking as his recent hot research are introduced in this column. |
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| Front-Line Polymer Science |
| Development of Rational Interfacial Design Strategy for Batteries | Noriyoshi MATSUMI |
| <Abstract> In the field of lithium ion secondary batteries, active development of component materials has been carried out on electrodes, electrolytes, separators, polymer binders and so forth. In addition to these, another important research frontier will be strategic design of solid electrolyte interface (SEI) in battery systems. It has been recognized that SEI is playing a quite important role and having dramatic impacts on battery performance by affecting both electron transfer and diffuson process. However, in traditional types of batteries, SEI has been formed by unintended electrochemical decomposition of electrolytes, and SEI had a complicated composition, which prevented us from deep understanding of their structure and stucture-property relationship. This article introduces several promissing approaches on rational SEI design. One approach is a suitable binder design by tuning of HOMO-LUMO level of binder materials which affects the extent of electrolyte degradation at electrolyte-electrode interface. The use of n-type conjugated polymer binders, self-healing binders and polymerizable additives will also be described in details. Keywords: Lithium Ion Secondary Batteries / Polymer Binders / Conjugated Polymers / Self-Healing Polymers / Silicon Anode / LiNMC / Additive / Organoboron Electrolytes |
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