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101.
This article examines changes to the morphology of rotationally molded metallocene catalyzed linear low density polyethylene brought about by varying the cooling rate during processing. These changes in morphology lead to variations in the impact performance, which is reflected in the dynamic mechanical characteristics of the materials. Various analytical techniques are used in an attempt to explain the differences in impact behavior. Slow cooling is shown to result in high crystallinity, and in the formation of large spherulites, which in turn is detrimental to the impact performance of the material, particularly at low temperatures. The high crystallinity corresponds with a shift in the β transition of the material to a higher temperature, and is shown to result in a higher brittle–ductile transition. A case study was also carried out on samples from a finished part provided by an industrial molder, one section of which failed in a brittle manner when impact tested while the other failed in a ductile manner. Microscopy results showed that the brittle material had large spherulites at the inside surface, while the ductile material showed incipient degradation at this surface, which has previously been shown to be of benefit to impact strength in rotationally molded parts. Dynamic mechanical studies again showed a β transition at a higher temperature in the brittle samples. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1963–1971, 2006  相似文献   
102.
Two samples of poly(diethoxyphosphazene) (PDEP) having very different molecular weights have been studied by viscometry and size exclusion chromatography in THF solution. The results obtained, together with light scattering data of these samples, allow the calculation of the Mark-Houwink constants a=0.65 and K=2.5 10-4 in THF at 25°C. The method of calculation employed takes into account the great polydispersity of the samples. The characteristic ratio of the unperturbed dimensions was also calculated giving Cn = r2o/n2 18, a value slightly higher than those previously reported for poly(dihexoxyphosphazene), Cn13 and poly (dichlorophosphazene), Cn13.5.  相似文献   
103.
The rhea (Rhea americana) is a large running bird of the ratite family, native to South America. Oil extracted from rhea fat tissue is used in cosmetic manufacture. Here, the thermal behaviour and the fatty acid and triacylglycerol composition of Uruguayan rhea oil are studied. The results are compared with those obtained from two commercial samples of emu oil. The fatty acid profiles of emu and rhea oils are similar. Small variations are reflected in the non‐identical thermal behaviour of the oils. The solid content of both oils is fairly similar at room temperature. Thus, emu oil and rhea oil may replace one another in certain formulations, without resulting in important changes in physicochemical behaviour. The semisolid rhea oil was fractionated in two successive stages: an olein was obtained at 15 °C, which was refractionated at 10 °C. The thermogram of the olein obtained by cooling at 15 °C does not have the peak found at 34 °C in the thermogram of the original oil and is a softer product than the original oil. A further stage of fractionation of this olein produced a new liquid phase of slightly different thermal behaviour from that of the original olein. This product has a solid fat index around 7% at 15 °C and has melted completely at 20 °C. This second olein has more appropriate physical characteristics than those of the olein obtained from the first fractionation when used in liquid cosmetic formulations.  相似文献   
104.
Oils from a selection ofAmaranthus caudatus, A. hypochondriacus andA. cruentus were extracted with hexane. The crude oils were analyzed for acid value, saponification and iodine number, and were included in basal casein diets for rat studies at 5 and 10% levels to replace equal amounts of refined cottonseed oil. The oils fromA. cruentus andA. hypochondriacus were similar in the oil properties studied and different fromA. caudatus. At either 5 or 10% food intake levels, weight gain and PER were not statistically different from values reported for cottonseed oil. True digestibility of amaranth oil was lower than that of cottonseed oil.A. cruentus oil gave the lowest digestibility. Oil levels induced statistical differences in food intake and digestibility. Oils fromA. caudatus, A. hypochondriacus and cottonseed induced similar serum cholesterol levels, while oil fromA. cruentus gave statistically higher values. Hemoglobin, hematocrit and serum proteins were similar among all groups. Microscopic analysis of the organs of the rats revealed some changes that were also found in cottonseed oil-fed rats. It was concluded that crude amaranth oil has lower digestibility than cottonseed oil, but that it is not responsible for growth-depressing effects when the seed is fed raw as compared to processed materials.  相似文献   
105.
This study examines in detail the influence of low‐temperature plasma and biopolymer chitosan treatments on wool dyeability. Wool knitted fabrics were treated and characterized by whiteness and shrink‐resistance measurements. Surface modification was assessed by contact‐angle measurements of human hair fibers, which were used as a model to study the wetting properties of the treated wool knitted fabrics. The dyeing behavior was assessed from the diffusion mechanism point of view. The dyeing kinetics were measured at two different pHs (4.2 and 6.5) and three different temperatures (60, 85, and 100°C) to gain information about the contribution of the surface modification treatment to the dyeing mechanism. The exhaustion and reflectance data were compared, and the apparent diffusion coefficients were calculated. On the basis of the obtained results, a model for the dyeing mechanism of the chitosan treated wool was proposed. When treated with chitosan, the polymer sheath spread on the surface of the fibers acted as a predominant dyeing site in very short dyeing times, thus interacting with the dye and in later stages imparting the dye to the wool fiber. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2204–2214, 2005  相似文献   
106.
A method for the assessment of the optimal operating conditions for a mechanically stirred gas–liquid reactor is presented. The method exploits both fluid dynamic and chemical information. First, the behavior of the specific stirring power as a function of the stirrer speed allows singling out the dispersion region, in which the most efficient gas–liquid mass transfer is achieved. Inside this region, the analysis of experimental data obtained when considering a chemical system reacting at moderate Hatta numbers (i.e., Ha < about 2) allows determination of the rate constants and the fluid dynamic parameters (i.e., the mass transfer coefficient in the absence of chemical reaction and the characteristic diffusion time).  相似文献   
107.
Worldwide, cervical cancer is the second most common cancer in women, after breast cancer. The prevalence of this malignant disease is estimated at 1.4 million cases worldwide, causing about 290,000 deaths and 500,000 new cases per year, of which 80% correspond to women living in developing countries. In this work we propose a family of ordered models for basal cells of the cervix corresponding to different stages ranging from normal cells to the formation of precancerous lesions. We analyse the first member of the family analytically and for the second member we developed a non-standard numerical method in order to extract some biological information.  相似文献   
108.
The reduction of dissolved sulphur and the soluble species formed during the electrolysis of PbS dissolved in the PbCl2NaCl eutectic has been studied chronopotentiometrically. The pre-lead reduction process reported earlier[1] can now be assigned to a subsulphide species that is generated electrochemically. At higher PbS concentrations (eg 10?3 mol cm?3), elemental sulphur introduces a new reduction wave in addition to the subsulphide. The saturation solubility of sulphur is approximately proportional to the square of the PbS concentration. It has been estimated to be 2.3× 10?4 mol S cm?3 at 430°C for a melt containing 2.4× 10?3 mol PbS cm?3 in the PbCl2-NaCl eutectic.  相似文献   
109.
It is commonly accepted that replacement of a portion of cement in mortar or concrete with well-dispersed silica fume reduces expansion caused by alkali silica reaction. Recently there has been much discussion that large, agglomerated particles of silica fume may actually act as alkali silica reactive aggregates, thereby increasing expansion rather than reducing it. The data in the literature, from both field and laboratory studies, are inconsistent. This prompted an extensive laboratory investigation into the alkali silica reactivity of silica fume. Results from accelerated expansion testing and microscopic investigations are presented. It was seen that some agglomerated silica fumes participate in ASR while others do not. Factors determining the reactivity of silica fume agglomerates are suggested.  相似文献   
110.
Hybrid materials were synthesized from epoxidized (68, 43, or 14%) styrene–butadiene rubber (SBR) and the hydrolysis product of tetraethoxysilane (TEOS) in situ under ultrasonic irradiation. The products were characterized with thermal analysis (differential scanning calorimetry and thermogravimetric analysis), stress–strain tests, scanning electron microscopy (including energy‐dispersive spectrometry), and swelling in tetrahydrofuran and water. The most transparent were those prepared from SBR with the highest degree of epoxidation, whereas those obtained from less epoxidized SBR and with larger amounts of TEOS showed distinct phases that could be considered two hybrid phases (one rich in TEOS and another rich in SBR). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 798–803, 2004  相似文献   
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