Fracture toughness improvement of CFRP laminates by dispersion of cup-stacked carbon nanotubes

Several techniques are introduced to enhance the interlaminar fracture toughness of CFRP laminates using cup-stacked carbon nanotubes (CSCNTs). Prepared CSCNT-dispersed CFRP laminates are subject to Double Cantilever Beam (DCB) and End Notched Flexure (ENF) tests in order to obtain mode-I and mode-II interlaminar fracture toughness. The measured fracture toughnesses are compared to that of CFRP laminates without CSCNT to evaluate the effectiveness of CSCNT dispersion for the improvement of fracture toughness. All CSCNT-dispersed CFRP laminates exhibit higher fracture toughness, and specifically, CSCNT-dispersed CFRP laminates with thin epoxy interlayers containing short CSCNTs have three times higher fracture toughness than CFRP laminates without CSCNT. SEM observation of fracture surfaces is also conducted to investigate the mechanisms of fracture toughness improvement. Crack deflection mechanism is recognized in the CSCNT-dispersed CFRP laminates, which is considered to contribute the enhancement of interlaminar fracture toughness.     

Electrical conductivity and self-temperature-control heating properties of carbon nanotubes filled polyethylene films

Electrical properties of polyethylene and carbon nanotube composite films were investigated, when the composite films were set in heating box or under electric field at constant voltage. The composite films were prepared by gelation/crystallization from dilute solution. The mixture of ultra-high molecular weight polyethylene (UHMWPE) and branched low molecular weight polyethylene (LMWPE) was used as matrix, and multi-walled carbon nanotubes (MWNTs) were used as fillers. The filler content was chosen to be 10 wt% (ca. 5.25 vol%) which is a relatively higher loading than the percolation threshold to ensure to act as heating element in plane heater of composite film. The focus was concentrated on the temperature dependences of electric conductivity by external heating and by exothermic effect concerning self-temperature-control heating properties which were measured for the three kinds of UHMWPE-LMWPE composites with the same content of MWNTs in the composites. When a certain voltage was applied to the composite, the surface temperature of film reaches the equilibrium value within less than 100 s. The maximum surface temperature as the equilibrium state of the resultant composite film can be easily controlled by adjusting the composite ratio represented as UHMWPE/LMWPE. The high efficiency of heating and wide adjustability of stable temperature suggested its good application in high efficient plane heater.     

Deformation velocity dependence on tensile fracture characteristics of polypropylene injection molding parts

To clarify the mechanism of the deformation and fracture in a low‐velocity impact test on the isotactic polypropylene (i‐PP) sheet made by injection molding, the change of the style of fracture and the form of deformation was examined while changing the speed of the striker in a low‐velocity impact test. In the injection molding sheet, an oriented skin layer of some thickness is formed on the surface of the sample sheet. By the stress perpendicular to the orientation direction of the skin layer, crazes were formed easily in parallel with the orientation direction in this layer, and cracks were formed from there. Because these cracks bring the sample sheet a strong restraint of strain, a high stress concentration occurs at the end of this crack even if the formation of the oriented layer is limited on the surface of the sample sheet only, and the low‐velocity impact test leads the sample sheet to a brittle fracture. As a result, the injection molding sheet that forms oriented structure on its surface causes the ductility‐brittleness transform at a lower velocity of deformation compared with the nonoriented sheet. POLYM. ENG. SCI., 53:2659–2665, 2013. © 2013 Society of Plastics Engineers     

Rational Design of Domain‐Swapping‐Based c‐Type Cytochrome Heterodimers by Using Chimeric Proteins

The design of protein oligomers with multiple active sites has been gaining interest, owing to their potential use for biomaterials, which has encouraged researchers to develop a new design method. Three‐dimensional domain swapping is the unique phenomenon in which protein molecules exchange the same structural region between each other. Herein, to construct oligomeric heme proteins with different active sites by utilizing domain swapping, two c‐type cytochrome‐based chimeric proteins have been constructed and the domains swapped. According to X‐ray crystallographic analysis, the two chimeric proteins formed a domain‐swapped dimer with two His/Met coordinated hemes. By mutating the heme coordination structure of one of the two chimeric proteins, a domainswapped heterodimer with His/Met and His/H₂O coordinated hemes was formed. Binding of an oxygen molecule to the His/H₂O site of the heterodimer was confirmed by resonance Raman spectroscopy, in which the Fe?O₂ stretching band was observed at 580 cm^?1 for the reduced/oxygenated heterodimer (at 554 cm^?1 under an ¹⁸O₂ atmosphere). These results show that domain swapping is a useful method to design multiheme proteins.     

Identification of indispensable residues for specific DNA-binding in the imperfect tandem repeats of c-Myb R2R3

The individual repeats, R2 and R3, of the minimum specific DNA-binding domain (R2R3) of c-Myb have very similar structures, with a helix-turn- helix variation motif, although their sequence identity in the tandem repeats is only 31%. From previous mutational and structural studies, the third helices in both repeats were shown to directly recognize the specific base sequence, PyAACG/TG. In order to elucidate the reason for the imperfection of the tandem repeats at amino acid positions other than the recognition helices, a series of R2R3 mutants was generated by swapping the helices and the N-terminus in R2 to those in R3. Consequently, the sequence composing the first helix of R2 was found to be essential for specific DNA-binding, in addition to the third recognition helix of R2. Further mutational studies revealed that the only indispensable residues in the first helix are Val103 and Val1O7, which are involved in the hydrophobic core of R2. These residues do not directly interact with the DNA, but they contribute to the correct formation of helix 1 and the characteristic packing of R2, which is slightly different from that of R3, and are required for specific base recognition through strong cooperativity with R3.      

Characterization and Sintering of Reactive Cerium(IV) Oxide Powders Prepared by the Hydrazine Method

Nanocrystalline cerium(IV) oxide (CeO₂) powders have been prepared by adding hydrazine monohydrate to an aqueous solution of hydrous cerium nitrate (Ce(NO₃)₃·6H₂O), followed by washing and drying. The lattice parameter of the as-prepared powder is a = 0.5415 nm. The powder characteristics and sinterability of reactive CeO₂ have been studied. The surface areas of powders that have been heated at low temperatures are high, and these surface areas do not decrease to 10 m²/g until the temperature is >1200°C. Crystallite size and particle size are strongly dependent on the heating temperature. Optimum sintered densities are obtained by calcining in the temperature range of 700°–800°C. Ceramics with almost-full density can be fabricated at a temperature as low as 1150°C.     

Upgrading of bitumen with formic acid in supercritical water

Upgrading of bitumen was examined with formic acid in supercritical water (SCW) from 673 to 753 K and at a water/oil ratio from 0 to 3. Decomposition of bitumen in SCW + HCOOH gave higher conversions of asphaltene and lower coke yields than those of pyrolysis or with only SCW. Decomposition of bitumen was also conducted in SCW + H₂, SCW + CO, toluene and tetralin, which revealed that decomposition of asphaltene was promoted and coke formation was suppressed when using SCW + HCOOH. In SCW + HCOOH, an increase in the water/oil ratio promoted both decomposition of asphaltene and suppression of coke formation. Formic acid in SCW seemed to enhance the conversion of bitumen to lower molecular weight compounds because formic acid seems to produce active species in SCW. The low temperature region (ca. 723 K) was suitable for upgrading bitumen with formic acid in SCW since coke formation was strongly promoted at high temperature (>753 K). A reaction model was proposed and the model predicted that hydrogenation of the asphaltene core was important for the suppression of coke formation.     

Accelerated biodegradation of pyrene and benzo[a]pyrene in the Phragmites australis rhizosphere by bacteria-root exudate interactions

We investigated the biodegradation of pyrene and benzo[a]pyrene in Phragmites australis rhizosphere sediment. We collected P. australis plants, rhizosphere sediments, and unvegetated sediments from natural aquatic sites and conducted degradation experiments using sediments spiked with pyrene or benzo[a]pyrene. Accelerated removal of pyrene and benzo[a]pyrene was observed in P. australis rhizosphere sediments with plants, whereas both compounds persisted in unvegetated sediments without plants and in autoclaved rhizosphere sediments with sterilized plants, suggesting that the accelerated removal resulted largely from biodegradation by rhizosphere bacteria. Initial densities of pyrene-utilizing bacteria were substantially higher in the rhizosphere than in unvegetated sediments, but benzo[a]pyrene-utilizing bacteria were not detected in rhizosphere sediments. Mycobacterium gilvum strains isolated from rhizosphere sediments utilized pyrene aerobically as a sole carbon source and were able to degrade benzo[a]pyrene when induced with pyrene. Phragmites australis root exudates containing phenolic compounds supported growth as a carbon source for the one Mycobacterium strain tested, and induced benzo[a]pyrene-degrading activity of the strain. The stimulatory effect on benzo[a]pyrene biodegradation and the amounts of phenolic compounds in root exudates increased when P. australis was exposed to pyrene. Our results show that Mycobacterium-root exudate interactions can accelerate biodegradation of pyrene and benzo[a]pyrene in P. australis rhizosphere sediments.     

Microphase-separated structure and mechanical properties of norbornane diisocyanate-based polyurethanes

Norbornane diisocyanate (NBDI: 2,5(2,6)-bis(isocyanatomethyl)bicyclo[2.2.1]heptane) is a new commercialized diisocyanate. NBDI-based polyurethane elastomers (PUEs) were prepared from poly(oxytetramethylene) glycol (PTMG), NBDI and 1,4-butanediol (BD) by a prepolymer method. Microphase-separated structure and mechanical properties of the NBDI-based PUEs were compared with general aliphatic and cycloaliphatic diisocyanate-based PUEs. The diisocyanates used were isophorone diisocyanate (IPDI), 4,4′-dicyclohexylmethane diisocyanate (HMDI) and 1,6-hexamethylene diisocyanate (HDI). Regular polyurethanes were also prepared as hard segment models from each isocyanate and BD to understand the feature of each hard segment chain. The HDI-based PUE showed the largest Young's modulus and tensile strength in the four PUEs due to the ability of crystallization of the hard segment component and the strongest microphase separation. HMDI has both properties of aliphatic and cycloaliphatic diisocyanates because of its high symmetrical chemical structure compared with NBDI and IPDI. On the other hand, the NBDI- and IPDI-based PUEs have an inclination to phase mixing, leading to decreased Young's modulus and tensile strength. The NBDI-based PUE exhibited better thermal properties at high temperatures due to stiff structure of NBDI.