A comparative evaluation of a novel flame retardant, 3-(tetrabromopentadecyl)-2,4,6-tribromophenol (TBPTP) with decabromodiphenyloxide (DBDPO) for applications in LDPE- and EVA-based cable materials

Flame retardation of polymeric materials for cables is becoming a statutory requirement due to governmental regulations to protect life and property from damages caused by fire. This and other factors such as the ever-increasing cost of existing flame retardants (FRs) have given rise to the search for better FRs. In this article, the suitability of an FR, 3-(pentadecyltetrabromo)-2,4,6-tribromophenol (TBPTP) developed from cardanol was evaluated for use in cable insulating and jacketing materials based on low-density polyethylene (LDPE) and ethylene vinyl acetate (EVA). The processability, mechanical properties, compatibility and miscibility, thermal behavior, flammability behavior, smoke generation, acid emission, aging characteristics etc., of the blends of the FR with LDPE and EVA were studied in comparison to those of decabromodiphenyl oxide (DBDPO), which is a standard FR used by the cable industry. Although TBPTP is found to be less thermally stable than is DBDPO, it exhibited better flame retardancy and has comparable thermal stability when blended with LDPE and EVA. Both LDPE—TBPTP and EVA—TBPTP blends produced less smoke than did the corresponding blends of DBDPO. In the case of the EVA—TBPTP blend, the percentage emission of smoke was almost negligible, placing EVA—TBPTP under the low smoke grade. Formulations containing a synergistic agent, promoter, and filler with the corresponding FR and polymer polymer along with an antioxidant were extruded out into wire and tested for cable properties. At 20% loading, the LOI values of the blends were 34.6 and 32.5, respectively, for the TBPTP—EVA and DBDPO—EVA blends. Vertical burning tests carried out with EVA—TBPTP cable showed that it is self-extinguishable. The processability of the compositions containing TBPTP were better than those of DBDPO. The improved processability was found to be due to the plasticising effect of TBPTP. SEM pictures of the blend showed excellent distribution of TBPTP in the polymer, indicating good compatibility and miscibility. Comparatively, DBDPO did not exhibit uniform distribution. The mechanical properties of the blends were within specifications of standard cable materials except that the % elongation of the DBDPO—LDPE blend was far too low. Aging studies also gave better properties for the TBPTP system than for those of the DBDPO system. The overall results show that the properties of EVA—TBPTP cable fall within specifications for the FARLS grade, whereas the EVA—DBDPO cable did not. In the case of LDPE, both TBPTP and DBDPO did not satisfy specifications for the FRLS grade, but the data indicate that they can be used as FRs. The superiority in properties of the TBPTP system over DBDPO is explained in terms of the structure of TBPTP characterized by the distribution of the flame-retardant element, bromine, almost evenly between the aliphatic and aromatic moieties of the molecule, which can, in contrast to the fully aromatic DBDPO, provide halogen over a wide range of temperatures to the combustion zone of the decomposing polymer. Moreover, the presence of the aliphatic segment assures improved processability and compatibility. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 3057–3073, 1997     

Effect of different solvents on volatile and non-volatile constituents of red bell pepper (<Emphasis Type="Italic">Capsicum annuum</Emphasis> L.) and their in vitro antioxidant activity

The fresh fruit of Capsicum annuum L. (red bell pepper) was successively extracted using n-hexane, chloroform, ethyl acetate, ethanol and their percentage yield was calculated. The effectiveness of each extract on chemical composition and antioxidant activity was studied. The qualitative phytochemical evaluation of each extract of bell pepper was done by HPTLC and Gas chromatography–mass spectroscopy (GC-MS) analysis. The total content of phenols, flavonoids and carotenoids were estimated by standard chemical methods. Further, the antioxidant potential of each extract was measured via DPPH and reducing power assays. Gas chromatography–mass spectroscopy analysis showed that the majority of compounds were related to phenols and flavonoids. Further analysis of the extract by HPTLC verified the presence of different types of phenolic compounds in addition to flavonoids and carotenoids. Among the different solvent extracts analyzed, total phenolic content was higher in ethanol extract (7.136?±?0.03%, w/w) whereas ethyl acetate extract showed the presence of higher flavonoid content (4.0521?±?0.03%, w/w). The ethanol and ethyl acetate extracts of the fruit of C. annuum exhibited the highest radical scavenging activity with inhibition percentage of 53.66 and 49.55% at a concentration of 254 µg/ml. Based on the biochemical analysis and phytochemical screening, we conclude that C. annuum possess potent antioxidant potential and this ability of the extract is attributed to the presence of rich polyphenolic compounds.     

Studies on thermal degradation kinetics and dielectric properties of polyether imide foam/nanosilica-based nanocomposites

ABSTRACT

In this paper, polyether imide (PEI) having properties such as a high glass transition temperature of 216°C, high heat resistance, high flame resistance, low smoke generation and a high melting point within the range of 400°C, having low thermal conductivity and low dielectric constant was chosen to be a polymeric foam. Water vapor-induced phase separation method was used to prepare PEI foams. PEI foams were reinforced with nano-silica (weight 1, 3 and 5%) in order to alter the dielectric properties, thermal conductivity and degradation kinetics of foamed polymer. The tested samples showed a reduction in dielectric constant than that of solid PEI but at a higher loading, it showed a higher value due to threshold percolation and a reduction in thermal conductivity was observed for foamed PEI. From thermogravimetric analysis, we can conclude that PEI with 3% filler loading showed better thermal stability compared to other PEI foam compositions.     

Studies on mixed surfactant systems: Effect of some anionic surfactants on the cloud point of poly(nona-)oxyethylated nonylphenol

The effect of some common anionic surfactants, namely LABS-Na, AOS-Na, SLS, SLES, di-octyl sulphosuccinate and sodium soaps of coconut, palm and rice bran oils on the cloud point of poly(nona-)oxyethylene nonylphenol has been determined. It is observed that sodium soaps have a larger effect on the cloud point than do anionic surfactants containing sulphate/sulphonate head groups. The influence on cloud point was found to decrease with an increase in hydrophobic chain length.     

DC electrical conductivity of some Cd-Ge-As glasses

Results of measurement of d.c. electrical conductivity σ from 85 to 550 K are reported for eleven glass compositions of the Cd-Ge-As system. Three regions are seen in theσ-T data of all these glasses. In region I (85 to 140 K),σ is essentially constant and independent of temperature. In region II (200 to 430 K),σ is thermally activated with a single activation energy. In region III (>430 K) a sudden increase is seen inσ with temperature. From an analysis of the results, it has been possible to identify the mechanism of hopping conductivity among localised ‘defect’ states with region I, normal band type conductivity due to carriers excited to the extended states with region II and thermally assisted memory switching with region III. In the composition dependence ofσ and ΔE for the CdGe _x As₂ glasses, special features are seen at the composition Cd_28·57 Ge_14·28 As_57·15, which has equal mol fractions of CdAs₂ and CdGeAs₂. For the Cd₂Ge-As glasses also, a maximum in ΔE and a minimum inσ are seen at this composition.     

IN2S3:Ag, an ideal buffer layer for thin film solar cells

Silver diffusion enhanced the properties of Indium sulfide (In₂S₃) films making it highly suitable buffer layer for photovoltaic applications. Thin layer of silver deposited over In₂S₃ films diffused into In₂S₃ films in ‘as-deposited’ condition itself creating doping effect. A significant enhancement in crystallinity and grain size could be obtained up to an optimum percentage of doping concentration. This optimum value showed dependence on thickness and atomic ratio of indium and sulfur in the film. Band gap decreased up to the optimum value of doping and thereafter it increased. Electrical studies showed a decrease in resistivity due to doping. Sample having the optimum doping was found to be more photosensitive and low resistive when compared with the pristine sample. These results proved that silver diffused indium sulfide surpasses pristine sample for crystallinity and photosensitivity. Doping β-In₂S₃ film with optimum amount of silver modified the structural and electrical properties of the films favorably so that the Ag electrodes given to the ITO/CuInS₂/In₂S₃ cell structure itself acted as a doping agent for the In₂S₃ layer, enhancing the cell efficiency to 9.5% (John et al. Sol Energy Mater Sol Cells 89:27, 2005).     

Experimental f″ of As at 170, 200, 250 and 300 K from the Bijvoet pairs of GaAs

Anomalous dispersion effects lead to the modification of the measured X-ray structure factors. In this work, we have determined the imaginary part of the anomalous dispersion correction terms (f″) of arsenide atom (As), through the X-ray data collected using spherical single crystal of GaAs, at various temperatures, i.e. 170, 200, 250 and 300 K. It is stressed that more measurements off″ of the elements are needed to confirm the theoretical calculations.     

Effects of thickness and post deposition annealing on the properties of evaporated In2S3 thin films

Indium sulfide (In₂S₃) films with three different thicknesses (150, 400 and 600 nm) were prepared using thermal evaporation at room temperature. As prepared samples were amorphous and subsequent annealing at higher temperature (>573 K) resulted in the formation of crystalline phase. Optical band gap was found in the range of 1.9–2.9 eV for as prepared samples and decreased with increase in annealing temperature. Interference fringe like structure in transmission spectra revealed that the films were fairly smooth and reflective. Variations in electrical resistivity and photosensitivity as a function of film thickness and annealing temperature were studied. X-ray Photoelectron Spectroscopic (XPS) studies clearly indicated uniform distribution of both indium and sulphur along the film. Energy Dispersive X-ray analysis showed that as prepared samples were stoichiometric.     

Modeling Packet Delay in Multiplexed Video Traffic

In this paper a Markov chain based characterization of a single video source is used to model multiplexed video traffic and the resulting packet delay. The multiplexed video stream of statistically identical sources is represented using a reduced order approximation of the superposed Markov generator matrix. It is shown that inadequate spectral content in the single source generator matrix is manifested as an underestimate of the packet delay probabilities for the multiplexed stream. A new method for simplifying the generator matrix for the multiplexed video stream that amply models its spectral content is given. The simulated and calculated results using the aforementioned model are shown be in good agreement.     

Expression,purification, and characterization of N-acetylglucosaminylphosphatidylinositol de-N-acetylase (ScGpi12), the enzyme that catalyses the second step of GPI biosynthesis in S. cerevisiae

ScGpi12 is a 304 amino residue long endoplasmic reticulum membrane protein, which participates in the de-N-acetylation of N-acetylglucosaminyl phosphatidylinositol to produce glucosaminyl phosphatidylinositol in the second step of GPI anchor biosynthesis pathway in Saccharomyces cerevisiae. ScGpi12 was cloned in a pMAL-c2x vector and expressed heterologously in Rosetta-gami (DE3) strain of E. coli. Affinity purification of the protein yielded low amounts of the MBP-tagged enzyme, which was active. To the best of our knowledge, this is the first successful purification of full-length Gpi12 enzyme, without the accompanying GroEL that was seen in other studies. The presence of the tag did not greatly alter the activity of the enzyme. ScGpi12 was optimally active in the pH range of 6.5–8.5 and at 30 °C. It was not sensitive to treatment with EDTA but was stimulated by multiple divalent cations. The divalent cation did not alter the pH profile of the enzyme, suggesting no role of the divalent metal in creating a nucleophile for catalysis. Divalent cations did, however, enhance the turnover number of the enzyme for its substrate, suggesting that they are probably required for the production of a catalytically competent active site by bringing the active site residues within optimum distance of the substrate for catalysis.