Ethylene vinyl acetate (EVA) foams with good cushioning and durability have been widely applied as packing materials and sport equipment. Recently, EVA blended with polyethylene (PE) has been studied in order to improve the lightness and cushioning property. Because of cross-linkage of the blended foam, it is difficult to distinguish them by the conventional analysis techniques. In this study, a new analytical method with acetic acid elimination treatment technique is investigated. The crystallization temperature (T_c) of original and treated EVA/PE blended foam was both analyzed by using differential scanning calorimetry (DSC). As a result, after the treatment, T_c of EVA became higher while T_c of PE did not change. Therefore it was confirmed that the cross-linked EVA/PE blended foam can be analyzed. However, this method was not applicable to the specific foams consisting mainly of linear low density polyethylene (LLDPE) and of small amount of EVA. In these foams, T_c of PE also became higher after the treatment. In the above foams, a trace amount of non-cross-linked components was focused. They were extracted with tetrahydrofuran, fractionated with gel permeation chromatography (GPC) and analyzed with Fourier transform infrared spectroscopy (FT-IR). The content of vinyl acetate in EVA and the blended ratio of EVA and PE can be analyzed by this method.

Appearance of bubbles in the rubber has been observed in real time by using X-ray imaging method in SPring-8. The behavior of diameter and quantity of bubbles has been measured for the samples which have the various contents of cure agent and moisture. The babbles appear after 30 to 50 sec from releasing curing pressure at the place where there are no any feature in the X-ray images pixel size is 0.5 μm. The diameter of bubbles increases linearly with time at first, and then it grows up to be closer to the limit diameter finally. This final diameter changes with cure time and amount of cure agent. And the quantity of bubbles changes with amount of moisture. The result shows the one of origin of bubble is moisture, and even if the moisture content changes, the size of moisture particles does not change, the quantity of particles changes. The crosslink density participates in whether this particle changes to a bubble or keeps that state. That also participates in the final diameter of bubble. X-Ray experiments were performed at BL19B2, BL46XU in the SPring-8 with approval of the Japan Radiation Research Institute (JASRI) (Proposal No. 2014A1571, 2014A1572).

Large scale coarse-grained molecular dynamics simulations of rubber-filler composite systems which are models of rubber compositions have been conducted on the K-computer. Different structures of filler aggregates are modeled by reverse Monte Carlo method from a part of USAXS data of rubber compounds obtained in the large synchrotron radiation facility SPring-8. The difference of experimental stress-strain curves between end-modified SBR and non-modified SBR has been reproduced qualitatively by simulation. Behaviors of large strain region of experimental stressstrain curves can be explained by the difference of maximum elongation of network chains due to the difference of numbers of bonds between fillers in end-modified SBR and non-modified SBR. Difference of small strain region of experimental SS curves between end-modified SBR and non-modified SBR can be reproduced qualitatively by models that filler aggregates are defined. This result suggests that filler aggregates play an important role for behavior of small strain region of stress-strain curves of filled rubbers.

To extend the wear lives of tribomaterials, the proper control of wear rate is desired. The description of wear rates is shown at the first portion. The fundamental wear mechanisms for rubbers and polymeric materials, such as abrasive wear and adhesive wear, are explained in this paper.

Strain-induced crystallization (SIC) of rubber is a self-reinforcing mechanism of rubber. The phenomenon was found in 1925, however, the elucidation of it has been a controversial topic since then. In 2002, synchrotron X-ray made it possible to measure stress-strain relation and SIC simultaneously. In 2012, the time constant of SIC is revealed as less than 60 msec by very fast experimental facilities. SIC is created instantaneously compared to practical deformation processes.
1. SIC is a common phenomenon of rubber and rubber compounds because several rubbers such as natural rubber (NR), synthetic polyisoprene rubber (IR), butadiene rubber (BR), butyl rubber (IIR), chloroprene rubber (CR), thermoplastic elastomer (TPE) and reinforcement filled rubber perform SIC.
2. During deformation, rubber perform several phenomena such as SIC with temperature upturn, cavitation due to void or crack, creation of radical due to breakdown of network, stress softening and hardening, and limited extensibility of chains between crosslinks simultaneously. Therefore, we should distinguish each phenomenon and analyze the contributions of them to a whole rubber performance.
3. Rubber is in-homogeneous material. Synthetic rubbers may include 2-10% of hard gel, remained catalysis and anti-oxidants. Natural rubber include about 6% of non-rubber components such as protein, carbohydrate, phospholipids, metal ions and others. Sulfur vulcanization system add zinc oxide and stearic acids as catalysts. Some of carbohydrates, zinc oxide and stearic acids are crystal. Protein aggregates, phospholipids and fatty-acids micelles are non-crystalline solid materials. Those solid materials may cause stress or strain concentrated points because solid particles are unable to be deformed in liquid-like matrix. Vulcanization is a chemical reaction of solid particle such as sulfur and catalysts with polymer chains in high viscous matrix. Therefore, crosslinks are unable to be distributed homogeneously. These heterogeneity may play important role for SIC of rubber.

The polymer materials, such as rubber and plastics, are easily degradable compared to metal materials, therefore, the degradation of polymer causes many troubles in products. The cause of such troubles must be studied immediately to take measures against a recurrence. Solution for the trouble is just not only aimed to satisfy the product liability but often useful for a development or improvement of products. Polymer materials, of course, have both of advantages and disadvantages in their physicochemical properties, however, most of the engineers do not well understand the disadvantages, which often lead a cause of trouble. Therefore, it is very important to know a disadvantage of polymer materials. For example, the accident of Space Shuttle Challenger is known to be caused by a fuel-leaking from some parts made of fluoro-elastomer (Viton), an extremely-low-cold-resisting polymer. In particular, moisture in the materials induces an extraction of antioxidant and hydrolysis of polymeric materials to promote the degradation, such as decrease in strength and bacterial damage. Therefore, rubber and plastic product must be carefully designed by considering what factor may cause trouble in actual use.