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781.
Ikechukwu D. Anyaogu Paul M. Ejikeme John A. Ibemesi 《Journal of Polymers and the Environment》2010,18(2):104-115
Soybean oil (SBO) was dimerized and the crude dimer acid product reacted with 1,2-phenylene diamine at 210 ± 5 °C under inert
atmosphere to obtain fatty polyamide (FPA). The FPA was used to modify a commercial alkyd resin by reacting a mixture of the
alkyd resin with 5 wt% of FPA at 120 °C for 80 min under inert atmosphere. The FTIR spectrum of the FPA modified resin showed
evidence of higher degree of H-bonding than was found for the unmodified alkyd. White gloss coatings of 15, 20, 25, and 30%
solids were formulated from the modified and unmodified resins and examined for performance with respect to: leveling, sag
resistance, drying time, pigment settling, skinning tendency and film hardness. Results showed that the unmodified alkyd coatings
exhibited good leveling but poor sag resistance at all solid contents. In contrast, FPA modified alkyd coatings combined good
leveling with high sag resistance indicating their thixotropic nature. A strong tendency to pigment settling was observed
for unmodified alkyd coatings but was not observed in the FPA modified alkyd coatings. The modified alkyd coatings showed
skinning while the unmodified alkyd coatings did not skin. A 30% solids coating formulation of the FPA modified resin showed
shorter surface dry time but longer hard dry time than the unmodified alkyd resin coating. 相似文献
782.
Romeu Casarano Denise F. S. Petri Michael Jaffe Luiz H. Catalani 《Journal of Polymers and the Environment》2010,18(1):33-44
A new aliphatic block copolyester was synthesized in bulk from transesterification techniques between poly((R)-3-hydroxybutyrate)
(PHB) and poly(isosorbide succinate) (PIS). Additionally, other two block copolyesters were synthesized in bulk either from
transesterification reactions involving PHB and poly(l-lactide) (PLLA) or from ring-opening copolymerization of l-lactide and hydroxyl-terminated PHB, as result of a previous transesterification reactions with isosorbide. Two-component
blends of PHB and PIS or PLLA were also prepared as comparative systems. SEC, MALDI-TOF mass spectrometry (MALDI-TOFMS), 1H and 13C NMR spectroscopy, WAXD, solubility tests, and TG thermal analysis were used for characterization. The block copolymer structures
of the products were evidenced by MALDI-TOFMS, 13C NMR, and WAXD data. The block copolymers and the corresponding binary blends presented different solubility properties,
as revealed by solubility tests. Although the incorporation of PIS sequences into PHB main backbone did not enhance the thermal
stability of the product, it reduced its crystallinity, which could be advantageous for faster biodegradation rate. These
products, composed of PHB and PIS or PLLA sequences, are an interesting alternative in biomedical applications. 相似文献
783.
Preparation and Characterization of Hydrogel Based on Poly(vinyl alcohol) Cross-Linked by Different Cross-Linkers Used to Dry Organic Solvents 总被引:1,自引:0,他引:1
Poly(vinyl alcohol) (PVA) hydrogels were chemically cross-linked with/without different cross-linkers such as glutaraldehyde
and epichlorohydrin, in the presence of a catalyst, or activator (potassium hydroxide) to produce three types of hydrogels.
The structures of PVA and the prepared gel types were determined by FTIR spectroscopy, the mechanical and thermal properties,
of these hydrogels were examined. The effects of different pH values and temperatures on the swelling properties of the prepared
gels were examined. From the obtained results, it was found that, the low concentration of the cross-linker produced hydrogel
with moderate properties, but in absence of the cross-linker, the obtained hydrogel exhibited good properties and can be used
as friendly environmentally moisture absorbents from the organic solvents. The insolubility and swelling properties of gels
were tested in these solvents. The results indicated that these hydrogels can be used as moisture absorbents and solvent dryers. 相似文献
784.
In this study, we analyze the evolution of Canada's mining industry from 1929 to 2006, focussing on the determinants of the number of firms in the industry and why this number changed over that period. Most empirical studies of industry evolution have focused on manufacturing industries that share similar structural characteristics. Perhaps because of this, extant models of industry evolution tend to ignore industry-specific and national-specific factors that can cause atypical trajectories, that is, heterogeneous industry evolution. Initial inspection of the Canadian mining industry shows that it is atypical in that it exhibits “negative skew” over time in the number of firms rather than the typical “positive skew.” We review two dominant theoretical approaches to industry evolution: the density-dependence theory and variants of industrial organization economics. We also consider possible sources of industry evolution heterogeneity, focussing particularly on “regulatory punctuation”. Using Canadian mining data, we find that the traditional models do not fully explain the changes in population size in Canada's mining industry. As a result, we introduce a number of hybrid models. The results from these hybrid models suggest that Canadian-specific regulatory punctuations, particularly the introduction of significant new taxes, environmental legislation, and incentives have shaped the trajectory of mining firm participation. 相似文献
785.
This work was undertaken to analyze nutrient contents of vegetation in an alpine meadow—Tungnath, North-West Himalaya, India.
The study pertains to the uptake, transfer and release of four main macronutrients (organic carbon, total nitrogen, total
potassium and total phosphorus) in grazed (exposed to extensive grazing by cattles) and ungrazed (grazing completely prohibited)
communities. Mineral concentration was recorded higher for the ungrazed sites compared to the grazed sites, and maximum standing
state of nutrients was found in roots. Belowground compartment (roots) contributed maximum share of mineral elements to soil.
Litter nutrients release was low because of low microbial activity and continuous removal of phytomass. Observations reveal
that there was very little amount of nutrient release from phytomass and vegetation in alpine are very poor source of mineral
recycling. Low transfer rate of minerals from one compartment to other is adequate for greater amount of these minerals that
are translocated back into the storage organs. A small proportion get removed through rain splash or through the removal of
hay during grazing as relatively high release rates in ungrazed sites when compared to grazed sites was observed. This translocation
can be considered as an important adaptation in alpine plants for survival during adverse environmental conditions, against
all types of biotic pressures and also for regeneration in the forthcoming growing season. 相似文献
786.
By means of environmental education, teachers are supposed to intervene in pupils’ awareness and concern of environmental
issues. Teachers’ environmental attitudes, however, have rarely been studied. We analysed 367 German pre- and in-service teachers’
environmental attitudes for their structure and socio-economic correlates within the frame of a European project. Thus, we
retrieved for adults the two-dimensional model of ecological values (2-MEV) presented for adolescents by Bogner and Wiseman
(Sci Educ Int 15(1):27–48, 2004). For the two domains, Preservation and Utilisation, the psychometric structure was confirmed and discriminative correlations
with age, gender and teaching subject were unveiled. Further research is needed to deduce the implications for teaching practice. 相似文献
787.
788.
789.
A laboratory-scale bioremediation unit was designed, built and tested for the bio-removal of several Direct textile dyes.
Four experiments were carried out to assess the efficiency of the bioremediation unit using Aspergillus niger fungal strain. Three commonly used Direct dyes and textile dyes mixture (simulated effluent: Direct brown, Direct violet,
Direct green) were tested in this study. The strain of A. niger was efficient in the removal of the three Direct dyes. The decolorization percentages of the dyes after 24 h of incubation
were 56.2, 51.7, and 95.4% for Direct brown, Direct green, Direct violet dyes, respectively. The percentages increased up
to 79.4, 86.4, and 96.7% after 72 h of incubation for the same dyes, respectively. The results also showed that the fungal
strain reduced the chemical oxygen demand values of simulated dye effluents from 165 to 564 mg/l with most of the dyes. The
assessment of bioremediation products on biomodel was conducted using a fresh water fish. The liver and brain of Nile tilapia
were tested to evaluate the expression of genes coding for several proteins related to stress such as metallothioneins (MTs),
cytochrome P450 (CYP450), and heat shock proteins (HSPs). To assess the alterations in the gene expression, ten animals from
each group were killed after 4 weeks of treatment. The results revealed significant increases in the brain and hepatic mRNA
levels of all stress protein genes MT, CYP450, Hsp70a, b, and Hsp47 in the fish groups treated with industrial Direct violet,
green, and brown dye water. Exposure of tilapia to bioremediation products after treatment with A. niger fungi reduced the over-expression of the stress protein genes in the brain and liver tissues. 相似文献
790.
S. O. Asagba G. E. Eriyamremu J. O. T. Emudainohwo I. Okoro 《The Environmentalist》2010,30(3):260-266
The activities of some oxidative enzymes (aldehyde oxidase, AO, EC 1.2.3.1; xanthine oxidase, XO, EC 1.17.3.2; sulphite oxidase,
SO, EC 1.8.3.1; and monoamine oxidase, MO, EC 1.4.3.4) were investigated in the liver, gill, kidney, brain and muscle of a
variety of African catfish (Clarias gariepinus) after 7 and 21 days of exposure to 0.1, 0.2 and 0.4 ppm cadmium (Cd) in ambient water. MO, SO and AO activities were significantly
(p < 0.05) decreased in a dose-dependent manner in the liver, kidney and gill in the 7-day Cd-exposed fish when compared to
control. Conversely, brain MO, AO and SO activities were significantly (p < 0.05) elevated in a dose-dependent manner in the same fishes relative to control. As in the 7-day Cd-exposed fish, the
activities of MO, AO and SO were significantly (p < 0.05) decreased in a dose-dependent manner in the gill, kidney and liver of catfish exposed for 21 days. Same is true for
XO in these organs after both duration of exposure, except in the liver where no significant change was observed relative
to control. The inhibition of these oxidative enzymes in the liver, gill and kidney of catfish may interfere with their biotransformation
function, and ultimately the survival of the fish may be compromised. 相似文献