Porphyrin polymers and organic frameworks

The versatility of porphyrins as optoelectronic or catalytic units makes them attractive elements for inclusion in functional materials. Polymers that include porphyrins have been created with a wide variety of structures and used in a wide range of applications. This review covers recent developments in the synthesis, characterization and applications of polymeric materials in which porphyrins are key components of the repeat units, including the rapidly growing area of metal–organic frameworks and related covalent organic frameworks. © 2015 Society of Chemical Industry     

Maternal High‐Fat‐Diet Programs Rat Offspring Liver Fatty Acid Metabolism

In offspring exposed in utero to a maternal diet high in fat (HF), we have previously demonstrated that despite similar birth weights, HF adult offspring at 6 months of age had significantly higher body weights, greater adiposity, and increased triacylglycerol (TAG) levels as compared to controls. We hypothesized that a maternal HF diet predisposes to offspring adiposity via a programmed increase in the synthesis of monounsaturated fatty acids in the liver and hence increased substrate availability for liver TAG synthesis. We further hypothesized that programmed changes in offspring liver fatty acid metabolism are associated with increased liver expression of the lipogenic enzyme stearoyl‐CoA desaturase‐1 (SCD‐1). Female rats were maintained on a HF diet rich in monounsaturated fatty acids (MUFA) prior to and throughout pregnancy and lactation. After birth, newborns were nursed by the same dam, and all offspring were weaned to control diet. Plasma and liver fatty acid compositions were determined using gas chromatography/mass spectrometry. Fatty acid C16 desaturation indices of palmitoleic/palmitic and (vaccenic + palmitoleic)/palmitic and the C18 desaturation index of oleic/stearic were calculated. Liver protein abundance of SCD‐1 was analyzed in newborns and adult offspring. Plasma and liver C16 desaturation indices were decreased in HF newborns, but increased in the adult offspring. Liver SCD‐1 expression was increased in the HF adult offspring. These data show that the maternal HF diet during pregnancy and lactation increases offspring liver SCD‐1 protein abundance and alters the liver C16 desaturase pathway.     

Incorporation of Alpha‐Linolenic Acid and Enhancement of n‐3 Fatty Acids in Nile Tilapia: a Factorial Design

A 2² factorial design (two factors at two levels, in triplicate) was performed to investigate the influence of factors A (time of treatment, 15 and 30 days) and B (chia oil content in a supplemented diet, at 2.1 and 4.2 %) in three responses of interest referring to: (a) the incorporation of alpha‐linolenic acid (LNA) in lipids of Nile tilapia fillet; (b) the enhancement of n‐3 fatty acids; and (c) the decrease in the omega‐6/omega3 (n‐6/n‐3) ratio in fish. Factors A and B were significant in the three regression models obtained and the interaction AB was a significant contributor to the LNA and n‐6/n‐3 ratio. Analysis of variance suggested three significant and predictive mathematical models. Response surfaces analyses from designs indicated higher LNA and n‐3 contents and a lower n‐6/n‐3 ratio using both factors A and B in the higher levels (30 days of treatment and 4.2 % of chia oil in the diet for fish) chosen for this study.     

Development and Characterization of Continuous SiC Fiber‐Reinforced HfB2‐Based UHTC Matrix Composites Using Polymer Impregnation and Slurry Infiltration Techniques

This paper discusses the development of continuous SiC fiber‐reinforced HfB₂‐SiC composite laminates. A range of techniques, based on resin‐based precursors and slurries, for infiltrating porous SiC preforms with HfB₂ powder were developed. While resin‐based precursors proved to be ineffective due to low HfB₂ yield and poor adhesion, the slurry infiltration techniques were effective to varying degrees. The greatest pore filling and composite densities were achieved using pressure and vibration‐assisted pressure infiltration techniques. SiC_f/HfB₂‐SiC laminates were subsequently developed via lamination, cure and pyrolysis of fabrics using a HfB₂‐loaded polymeric SiC precursor, followed by HfB₂ slurry infiltration and preceramic polymer infiltration and pyrolysis (PIP). Repeated PIP processing, for 6–10 cycles, resulted in density increases, from the 3.03–3.22 g/cm³ range after HfB₂ slurry infiltration, to 3.97–4.03 g/cm³ after PIP processing. Correspondingly, there was a decrease in open porosity from approximately 52% to less than 11%. The matrix consisted of discreet, lightly sintered HfB₂ particles dispersed in SiC. The PIP SiC matrix was primarily nanocrystalline after 1300°C pyrolysis, but experienced grain growth with further heat treatment at 1600°C.     

Recycling carbon fiber composites using microwave irradiation: Reinforcement study of the recycled fiber in new composites

With increasing use of carbon fiber reinforced polymer (CFRP) composites in transportation, sports, and many other industries, recycling of the scrap and end‐of‐life composites has presented both great challenges and opportunities. In this work, we report our study on reclaiming carbon fibers from CFRP using energy efficient microwave irradiation. Different irradiation conditions were used and the optimal conditions were determined based on the surface morphology of the recycled fiber. Polypropylene (PP) and Nylon, representing nonpolar and polar polymers, respectively, were reinforced using the recycled fiber through extrusion and injection molding. For comparison, PP and Nylon reinforced by virgin carbon fiber were also prepared using the same processing conditions. Tensile, flexural, and impact test results showed that, while both carbon fibers could improve these properties, they exhibited different reinforcing effects on the two polymers. The recycled fiber outperformed the virgin fiber in reinforcing PP whereas the virgin fiber performed better in Nylon. This was due to the differences in surface roughness, surface bonding, and fiber aspect ratio between the two fibers. This study shows the great potential of recycled carbon fiber and microwave irradiation as an effective recycling technique. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42658.     

Sol-Gel Glass-Encapsulated Crown Ethers for the Separation and Preconcentration of Strontium from Acidic Media

Extraction chromatography employing an inert polymeric support impregnated with a crown ether (typically, 4,4’,(5’)-di-(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6)), either neat (i.e., undiluted) or as a solution in 1-octanol, has previously been shown to provide an effective means for the isolation of radiostrontium from a variety of sample types for subsequent determination. In this study, sol-gel chemistry has been employed to prepare sorbents in which DtBuCH18C6 is encapsulated in a silica matrix. The resultant materials have been evaluated for their ability to retain strontium ion and compared to a commercially available extraction chromatographic (EXC) resin. Certain of the new materials are shown to provide uptake efficiencies comparable to those obtained with the commercial resins, although unless a porogen is employed, the kinetics of strontium uptake are significantly slower. In contrast to conventional EXC materials, however, strontium uptake by DtBuCH18C6-loaded glasses does not increase in proportion to the amount of extractant present, indicating that not all of the crown ether present is available for interaction with the metal ion.     

Microstructure of the HMX‐Based PBX KS32 after Mechanical Loading

Non‐destructive X‐ray diffraction techniques were applied in order to monitor the influence of mechanical and shock‐loading on the microstructure of the plastic‐bonded high explosive KS32. The investigations uncovered damage to embedded coarse HMX crystals and to the binder system HTPB‐IPDI. Damage to the crystals occurred already during the kneading process in terms of deformation twinning. On higher loading between 400 MPa (static) and 480 MPa (dynamic) also crystal fracture was observed. The change in the binder structure was found after both static and dynamic loading, but not in the cured, differently kneaded samples. Moreover, the change in binder structure after dynamic loading was verified by dynamic mechanical analysis, and interpreted as a partial damage of the binder rubber shell around the explosive particles. The results are compared to literature data from imaging techniques.