Hideko T. Oyama

Crystallite Size Effect on Thermal Conductive Properties of Nonwoven Nanocellulose Sheets.

The thermal conductive properties, including the thermal diffusivity and resultant thermal conductivity, of nonwoven nanocellulose sheets were investigated by separately measuring the thermal diffusivity of the sheets in the in-plane and thickness directions with a periodic heating method. The cross-sectional area (or width) of the cellulose crystallites was the main determinant of the thermal conductive properties. Thus, the results strongly indicate that there is a crystallite size effect on phonon conduction within the nanocellulose sheets. The results also indicated that there is a large interfacial thermal resistance between the nanocellulose surfaces. The phonon propagation velocity (i.e., the sound velocity) within the nanocellulose sheets was estimated to be ∼800 m/s based on the relationship between the thermal diffusivities and crystallite widths. The resulting in-plane thermal conductivity of the tunicate nanocellulose sheet was calculated to be ∼2.5 W/mK, markedly higher than other plastic films available for flexible electronic devices.

Influence of the Polymer/Inorganic Filler Interface on the Mechanical, Thermal, and Flame Retardant Properties of Polypropylene/Magnesium Hydroxide Composites

The relationship between the interface structure and the macroscopic properties of composites composed of isotactic polypropylene (iPP) and magnesium hydroxide (MH) was investigated with a focus on mechanical properties, thermal stability, and flame retardancy. Surface treatment of MH was carried out using dodecanoic acid (DA) and dodecylphosphate (DP), both of which interacted with MH to form submonolayer coverages. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed that both organic reagents adhere to the MH surface via ionic interactions. Even low amounts of organic reagents on the MH surface were sufficient to improve the mechanical, thermal, and flame retardant properties of the composites. The incorporation of 1.8 wt% of DP in (70/30) iPP/MH-DP composite decreased the peak heat release rate (PkHRR) to 39% compared with that of neat iPP. Since the effects of DA with the same dodecyl chains were not significant, it is concluded that the phosphate groups in DP provide flame retardancy.

Thermally conductive and optically transparent flexible films with surface-exposed nanocellulose skeletons

Heat management has become a serious bottleneck that has limited the development of thin flexible paper electronics. Therefore, there is a huge demand to develop superior flexible film materials with higher thermal conductivities and transparencies. In this study, thermally conductive and optically transparent flexible films with flexible nanocellulose skeletons have been fabricated by using a membrane-assisted method. The films simultaneously exhibit in-plane thermal conductivity as high as 2.5 W m−1 K−1 with a thermal conductivity enhancement of 234% from the matrix acrylic resin, and a parallel beam transmittance of 73% at 600 nm. We demonstrate that removal of heat-insulating surface resin layers achieved by our membrane-assisted method is the key to exploit the high thermal performance of intrinsic nanocellulose skeletons with a markedly high fiber content of ∼80%. The thermal and optical properties of membrane-assisted films are controlled by changing the fiber content. We believe that this approach could provide a way to solve the critical bottleneck of modern electronics by advanced thermal management.

Impregnation of paclitaxel into poly(DL-lactic acid) using high pressure mixture of ethanol and carbon dioxide

Paclitaxel (PT) is a mitotic inhibitor used in cancer chemotherapy. Impregnation of PT into amorphous poly(DL-lactic acid) (PDLLA) in mixtures of high-pressure ethanol (EtOH) and carbon dioxide (CO2) at various compositions was investigated at 313 K and 20 MPa. It was demonstrated that the high pressure EtOH–CO2 mixture is a promising solvent for fabrication of polymer-based drug delivery systems (DDS) materials, which enables the avoidance of drug deterioration due to processing at elevated temperatures. A mixture with 25 mol% EtOH allowed impregnation of the largest amount of PT in the PDLLA matrix. The amount of impregnated PT in the EtOH–CO2 mixtures was 10 times and 28 times larger than those in supercritical CO2 and liquid EtOH, respectively. The composition of the EtOH–CO2 mixture affected the amount of PT that could be impregnated. The increase in the amount of impregnated PT in the mixture is probably attributed to plasticization of PDLLA and increased solubility of PT into the EtOH–CO2 mixture. The degree of swelling observed in the PDLLA caused by plasticization depended on the composition of the EtOH–CO2 mixture, with the volume increasing to 1.7 times the initial size for a mixture containing 40 mol% EtOH at 313 K and 20 MPa. Physical aging was induced after the swollen PDLLA in supercritical CO2 was vitrified by pressure drop from 20 MPa to atmospheric pressure at 313 K, whereas vitrification hardly occurred in the EtOH–CO2 mixture under the same conditions.

Biologically Safe Poly(l-lactic acid) Blends with Tunable Degradation Rate: Microstructure, Degradation Mechanism, and Mechanical Properties

Although poly(l-lactic acid) (PLLA) is reputed to be biodegradable in the human body, its hydrophobic nature lets it persist for ca. 5.5 years. This study demonstrates that biologically safe lactide copolymers, poly(aspartic acid-co-l-lactide) (PAL) and poly(malic acid-co-l-lactide) (PML), dispersed in the PLLA function as detonators (triggers) for its hydrolytic degradation under physiological conditions. The copolymers significantly enhance hydrolysis, and consequently, the degradation rate of PLLA becomes easily tunable by controlling the amounts of PAL and PML. The present study elucidates the effects of uniaxial drawing on the structural development, mechanical properties, and hydrolytic degradation under physiological conditions of PLLA blend films. At initial degradation stages, the mass loss was not affected by uniaxial drawing; however, at late degradation stages, less developed crystals as well as amorphous chains were degradable at low draw ratio (DR), whereas not only highly developed crystals but also the oriented amorphous chains became insensitive to hydrolysis at high DR. Our work provides important molecular level results that demonstrate that biodegradable materials can have superb mechanical properties and also disappear in a required time under physiological conditions.

Setsuro Tamaru and Fritz Haber: Links between Japan and Germany in Science and Technology

Setsuro Tamaru was my grandfather. He worked with Fritz Haber in Germany on researching the ammonia synthesis process and contributed substantially to the development of scientific research and education in Japan. Although I had never met him, I felt his existence while I grew up, since our house was built by him and had many artifacts brought back from Germany by my grandfather; e.g., a Bechstein upright piano upon which I practiced piano every day and Fritz Habers portrait with his handwritten message hung on the wall. This is an account of my grandfathers life, concentrating on his relationship with Fritz Haber. This story goes back to a time more than a century ago.

Change in thermal transitions and water uptakes of poly(l-lactic acid) blends upon hydrolytic degradation

This article reports experimental data related to the research article entitled “Poly(malic acid-co-l-lactide) as a Superb Degradation Accelerator for Poly(l-lactic acid) at Physiological Conditions” (H.T. Oyama, D. Tanishima, S. Maekawa, 2016) [1]. Hydrolytic degradation of poly(l-lactic acid) (PLLA) blends with poly(aspartic acid-co-l-lactide) (PAL) and poly(malic acid-co-l-lactide) (PML) oligomers was investigated in a phosphate buffer solution at 40 °C. It was found in the differential scanning calorimetry measurements that upon hydrolysis the cold crystallization temperature (Tc) and the melting temperature (Tm) significantly shifted to lower temperature. Furthermore, the hydrolysis significantly promoted water sorption in both blends.