Influence of the introduction of flexible alkyl chains on the thermal behavior and mechanical properties of mesogenic epoxy thermosets

A mesogenic epoxy resin (DGETAM) was cured with a series of curing agents having different lengths of long alkyl chain (nBAB, n = 4, 8, 12). Properties of the curings were compared with those of the DGEBA cured with the same curing agents revealing the achievement of a balance between certain levels of thermal properties and excellent mechanical properties. Moreover, some curing systems were prepared with twin mesogenic type epoxy resins (DGEnMA, n = 4, 6, 8, 10, 12) having different lengths of alkyl chain as a flexible spacer and the same curing agents (n′BABs). Combinations of the same concentrations of chemical structures in the basic units of the network structure were applied, and the thermal and mechanical properties of their curing systems were investigated. The fracture energy of each system increased considerably with the increase of the alkyl chain length that adjoins the two mesogenic groups in the epoxy resins. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44244.     

New Approach for Macro Porous RB‐SiC Derived from SiC/Novolac‐type Phenolic Composite

A novel fabrication route to make macroporous silicon carbide (SiC) has been proposed in this study. The route is composed of the following two steps: the fabrication of porous α‐SiC/novolac‐type phenolic composite using hexamethylenetetramine (HMT) as a curing/blowing agent for the novolac monomer and a conventional reaction‐bonded (RB) sintering of the composite. The α‐SiC/novolac‐type phenolic composite was carbonized at 800°C for 2 h in N₂ gas and then reacted with the molten silicon at 1450°C for 30 min under vacuum, resulting in the macroporous RB‐SiC with an open porosity of 48% and relatively large pore size of ~110 μm. The compressive strength of the macroporous RB‐SiC was 113 MPa, which is relatively high compared to those reported for macroporous SiC of equivalent porosities and pore sizes.     

Excess Solute Carbon and Retained Tetragonality in Tempered Fe-0.6C-1Mn Martensite and the Effect of Silicon Addition

The tetragonality and carbon distribution in tempered Fe-0.6C-1Mn martensite were investigated by X-ray diffraction and atom probe tomography to elucidate strain relaxation in the tetragonal lattice during tempering and its relationship with the solubility of excess carbon in martensite. Even though tetragonality (c/a) decreased with an increase in the tempering temperature, it persisted at low levels up to 400 °C. Si addition suppressed the decrease in tetragonality at 400 °C by inhibiting recovery in the dislocated matrix. Such persistence implies that dislocation migration is crucial for the complete release of tetragonal lattice strain at such a temperature, in addition to the decrease in the amount of solute carbon in martensite. A low level of tetragonality was observed for martensite containing carbon in the solid solution below the critical value of ~ 0.2 mass pct, at which a bcc structure was predicted. The amount of solute carbon after tempering was linearly correlated with tetragonality in the solute carbon content range of 0.07 to 0.6 mass pct, and the correlation coefficient was similar to those for as-quenched auto-tempered martensite and bainitic ferrite; these results indicate that the amount of excess carbon is simply determined by the amount of tetragonal lattice distortions remaining after carbide precipitation and recovery.

     

Nonsalt 1‐(arylmethyloxy)pyrene photoinitiators capable of initiating cationic polymerization

Analysis of photoproducts derived from 1‐(methoxynaphthalen‐1‐ylmethyloxy)pyrene initiators and polymer end groups demonstrated that methoxynaphthalen‐1‐ylmethyl carbocation is involved in the initiation steps for both styrene (St) and cyclohexene oxide (CHO) polymerization. Charge transfer from the pyrenyloxy oxygen atom to the methoxynaphthalen‐1‐ylmethyl chromophore in the singlet excited state is assumed to be responsible for the efficient generation of the carbocation species, which also initiates the copolymerization of St and CHO. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40510.     

The Association of Cholesterol Uptake and Synthesis with Histology and Genotype in Cortisol-Producing Adenoma (CPA)

Cortisol-producing adenoma (CPA) is composed of clear and compact cells. Clear cells are lipid abundant, and compact ones lipid poor but associated with higher production of steroid hormones. PRKACA mutation (PRKACA mt) in CPA patients was reported to be associated with more pronounced clinical manifestation of Cushing’s syndrome. In this study, we examined the association of histological features and genotypes with cholesterol uptake receptors and synthetic enzymes in 40 CPA cases, and with the quantitative results obtained by gas chromatography-mass spectrometry (GC-MS) analysis in 33 cases to explore their biological and clinical significance. Both cholesterol uptake receptors and synthetic enzymes were more abundant in compact cells. GC-MS analysis demonstrated that the percentage of compact cells was inversely correlated with the concentrations of cholesterol and cholesterol esters, and positively with the activity of cholesterol biosynthesis from cholesterol esters. In addition, hormone-sensitive lipase (HSL), which catalyzes cholesterol biosynthesis from cholesterol esters, tended to be more abundant in compact cells of PRKACA mt CPAs. These results demonstrated that both cholesterol uptake and biosynthesis were more pronounced in compact cells in CPA. In addition, more pronounced HSL expression in compact cells of PRKACA mt CPA could contribute to their more pronounced clinical manifestation.     

Effects of solid lubricants in backward extrusion

In the present paper, some solid lubricants were tested in backward extrusion friction tests with flat-headed punches using aluminium at room temperature. The results showed that anti-seizure ability was improved when wax was added to the solid lubricant samples. In addition, a water-based graphite lubricant and an ultrahigh molecular weight polyethylene (UHMW-PE) lubricant were tested using aluminium workpieces heated to 500°C. The lubricity of the UHMW-PE lubricant was found to be superior to that of the graphite lubricant.