Masaru Kotera

Kenaf reinforced biodegradable composite

Abstract Mechanical properties of environmentally friendly composite made of kenaf fibre and poly- l -lactic acid (PLLA) resin was investigated. Youngs modulus (6.3 GPa) and the tensile strength (62 MPa) of the kenaf/PLLA composite (fibre content=70 vol.%) were comparable to those of traditional composites. These properties were higher than those of the kenaf sheet and the PLLA film themselves. This is considered to attribute to the strong interaction between the kenaf fibre and PLLA. In addition, the storage modulus of the composite remain unchanged up to the melting point of PLLA. The effects of the molecular weight of PLLA, the orientation of the kenaf fibres in the sheet on the mechanical properties of the composite were also investigated. It was found that kenaf fibre can be a good candidate for the reinforcement fibre of high performance biodegradable polymer composites.

Imidization processes of aromatic polyimide by temperature modulated DSC

Abstract Processing of polyimide (PI) from precursor polyamic acid (PAA) involves simultaneous imidization, evaporation of residual solvent and crystallization. These overlapped processes were analyzed by temperature modulated differential scanning calorimetry (T-MDSC). Glass transition temperature (Tg) of precursor PAA was manifested by T-MDSC, and it was 107°C for pyromellitic dianhydride–oxidianiline (PMDA–ODA) PAA cast from N-methyl-2-pyrrolidone (NMP) solution. The thermal cyclization reaction from PAA to PI is considered to progress randomly. The solvent system for casting PAA, influenced the conversion to PI, which is found to affect the Tg of PAA.

Residual stress and microstructures of aromatic polyimide with different imidization processes

Abstract Processing of polyimide (PI) from precursor polyamic acid (PAA) solution involves simultaneous imidization, evaporation of solvent and crystallization, so imidization process influences the final properties of PI. The residual stress at the interface between the most popular PI (PMDA–ODA) and the aluminum substrate was measured by X-ray diffraction method and the relationship between the microstructure and the mechanical properties was investigated for PI with different imidization processes. The residual stress and the mechanical properties of PI depend on the imidization process. The skeletal structure is suggested to be changed by the amount of residual solvent during imidization process, which brings the difference in the residual stress.

In situ observation of surface deformation of polymer films by atomic force microscopy

The tensile X–Y stage, providing a load cell and a stretching device, has been constructed to observe the surface deformation of polymer film in situ by using an atomic force microscope (AFM). From the three-dimensional AFM images, the streak-like bumps were observed on a polyethylene terephalate (PET) film surface. By monitoring the change in the distance between them by the tensile load, the strain was evaluated in the direction both parallel and perpendicular to the tensile direction. The microscopic stress–strain relationship by AFM coincided with the macroscopic one, which indicates so-called affine deformation of PET film. Young’s modulus was obtained as 2.3 GPa for PET from the initial slope of the stress–strain curve by AFM. The apparent Poisson ratio of the PET film surface could be also evaluated.

Application of layered poly (L-lactic acid) cell free scaffold in a rabbit rotator cuff defect model

BackgroundThis study evaluated the application of a layered cell free poly (L-lactic acid) (PLLA) scaffold to regenerate an infraspinatus tendon defect in a rabbit model. We hypothesized that PLLA scaffold without cultivated cells would lead to regeneration of tissue with mechanical properties similar to reattached infraspinatus without tendon defects.MethodsLayered PLLA fabric with a smooth surface on one side and a pile-finished surface on the other side was used. Novel form of layered PLLA scaffold was created by superimposing 2 PLLA fabrics. Defects of the infraspinatus tendon were created in 32 rabbits and the PLLA scaffolds were transplanted, four rabbits were used as normal control. Contralateral infraspinatus tendons were reattached to humeral head without scaffold implantation. Histological and mechanical evaluations were performed at 4, 8, and 16 weeks after operation.ResultsAt 4 weeks postoperatively, cell migration was observed in the interstice of the PLLA fibers. Regenerated tissue was directly connected to the bone composed mainly of type III collagen, at 16 weeks postoperatively. The ultimate failure load increased in a time-dependent manner and no statistical difference was seen between normal infraspinatus tendon and scaffold group at 8 and 16 weeks postoperatively. There were no differences between scaffold group and reattach group at each time of point. The stiffness did not improve significantly in both groups.ConclusionsA novel form of layered PLLA scaffold has the potential to induce cell migration into the scaffold and to bridge the tendon defect with mechanical properties similar to reattached infraspinatus tendon model.

Residual stress of particulate polymer composites with reduced thermal expansion

Thermal expansion behavior was investigated for tangusten zirconium phosphate (Zr2(WO4)(PO4)2 (ZWP)) particulate filled poly(ether ether ketone) (PEEK) composite. ZWP is known as ceramic filler with a negative thermal expansion. By incorporating ZWP with 40 volume %, the linear thermal expansion coefficient of the PEEK composite was reduced to almost same value (2.53 X 10-5 K-1) with that of aluminum. This decrease was found to be quite effective for the decrease of the residual stress at the interface between aluminum plate and the composite.

Water-repellent all-cellulose nanocomposite using silane coupling treatment

Water-repellent all-cellulose nanocomposite (ACNC) was made using the silane coupling agent dodecyltriethoxysilane. The ACNC, consisting of cellulose nanofibers incorporated into a cellulosic matrix, was prepared by reducing crystallinity in the surface of the cellulose nanofibers using DMAc/LiCl solvent, followed by applying pressure and drying. The ACNC surface turned from hydrophilic to hydrophobic by silane coupling treatment. X-ray photoelectron spectroscopy (XPS) measurements confirmed the existence of the silane coupling agent on the surface after treatment. As silane concentration increased, the water contact angle of treated ACNC increased, to a maximum value of 93°. Thermogravimetric analysis and atomic force micrographs showed a multilayered treatment. The silane treated ACNC showed lower water absorption compared to that of untreated one. The silane coupling treatment was also found to increase the mechanical performance of ACNC. Creation of a hydrophobic surface reduces the potential damage associated with water in outdoor applications of ACNC.

Interfacial structure analysis of polymer laminate using SPring-8 X-ray microbeam

Interfacial structure of laminated polyethylene (PE)/polypropylene (PP) films was investigated by synchrotron X-ray microbeam. The X-ray microbeam (0.9 μm (vertical) × 1.7 μm (horizontal)) formed using a phase zone plate was irradiated on the cross-section of the laminated films. In order to irradiate X-ray microbeam in the direction perpendicular to the cross-section of the film sample, adjustment of the sample setting was performed by Thomson scattering method. The Thomson scattering intensity is proportional to the number of the irradiated electrons, so the irradiated position of the X-ray microbeam could be determined from the intensity profile with high spatial resolution. By changing the sample position, diffraction patterns could be obtained from the laminated films across the PE/PP interfacial region. The thickness of the interfacial region of the annealed laminate was estimated as 5 μm judging from the changes of the diffraction intensities from the PE crystallites to the PP ones. The interfacial thickness depended on the thermal treatment of the film. It was found that the adhesion strength of the PE/PP laminate increased with increasing the interfacial thickness. Both of PE and PP chains entangled each other during laminate processing. The entangled molecular chains play important role as anchoring effect at the PE/PP interdiffusion region. However, the phase separation progressed with further crystallization by annealing. Thus, the adhesion strength of the PE/PP laminate was considered to be influenced by the interfacial thickness.

Highly Water Repellent but Highly Adhesive Surface with Segregation of Poly(ethylene oxide) Side Chains

Polymer surfaces were modified using methacrylate terpolymers containing both perfluoroalkyl (Rf) groups and poly(ethylene oxide) (PEO) as side chains in the same molecule. The structure and properties of the modified surfaces were evaluated using X-ray photoelectron spectroscopy and by measuring the dynamic contact angles and 90° peel strength. It was found that not only Rf groups but also PEO side chains were segregated on the surface being against the order of the surface free energy. The terpolymer modified surface is hydrophobic in air because Rf groups are predominant, but it becomes hydrophilic in water because the surface is covered with PEO side chains. This response to the environment is rapid and reversible. The modified surface showed high water repellency because of the surface Rf groups and high adhesive strength because of the side chains.

Papyrus reinforced poly(L-lactic acid) composite

Mechanical reinforcement of an all-sustainable composite, composed of papyrus stem-milled particles as reinforcement and poly-L-lactic acid (PLLA) resin as matrix, was investigated. The papyrus particles (average diameter of 70 μm) could be well dispersed in PLLA resin up to 50 wt% without any surface modification. Youngs modulus of the composite was 4.2 GPa at 50 wt% of the papyrus content. This is a two-fold increment in modulus as compared to that of the PLLA matrix. The tensile strength of the composite was almost constant around 48 MPa irrespective of the papyrus content. Temperature dependence of the storage modulus demonstrated that the incorporation of papyrus restricts the large drop in the modulus above the glass transition of PLLA.