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1.
The initiation, growth and final failure of the craze ahead of a crack tip generally controls the onset of crack growth in polyethylene, particularly in slow crack growth. In this research, circumferentially deep notched tensile specimens are used to analyze the evolution and failure of crazes in polyethylene under plane strain conditions. An experimental method is used wherein the traction‐separation behavior of the craze structure is measured directly insitu. Results yield a cohesive zone type analysis in which a two parameter traction curve, containing within it all information pertaining to local decohesion, fully describes the separation of the interface. Experimentally measured rate dependent trends in the work of separation (I) provide good discrimination between different grades of tough polyethylene at both high and quasi‐static test speeds, and highlight the exceptional long term behavior of one particular grade. The method also allows for the quantification of the long term behavior of each grade by more traditional stress‐time analysis.  相似文献   

2.
A new sample configuration for measuring tensile mechanical properties during cure is described. The method utilizes a soft rubber membrane to physically constrain a sample in a uniaxial geometry. Using this method in combination with a Dynastat mechanical spectrometer, it was possible to follow the polymerization of an epoxy resin from the liquid to the glassy state in a single experiment. The results of a uniaxial dynamic mechanical characterization of a curing epoxy resin are presented.  相似文献   

3.
Thermal properties of a new semicrystalline polyimide synthesized from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride ( BTDA ) and 2,2-dimethyl-1,3-(4-aminophenoxy)propane ( DMDA ) have been studied. Heat capacities in the solid and liquid states of BTDA - DMDA have been measured. The heat capacity increase at the glass transition temperature (Tg = 230°C) is 145 J/°Cmol for amorphous BTDA - DMDA . The equilibrium heat of fusion of the BTDA - DMDA crystals has been obtained using wide-angle X-ray diffraction and differential scanning calorimetry measurements, and is 75.8 kj/mol. Based on the information on crystallinity and the heat capacity increase at Tg, a rigid amorphous fraction is identified in semicrystalline BTDA - DMDA samples, which represents an interfacial region between the crystalline and amorphous states. In particular, this fraction increases with the crystallinity of the sample, which should be associated with crystal sizes, and therefore with crystal morphology. It has also been found that this polymer has a high-temperature crystal phase upon annealing above its original melting temperature. The thermal degradation activation energies of BTDA - DMDA in nitrogen and air are determined to be 154 and 150kJ/mol, respectively.  相似文献   

4.
Summary The impact strength of polypropylene was improved by adding propylene-vinylsilane copolymer (PVS) in the presence of tris(triphenylphosphine)rhodium chloride(TPR). The impact strength of polyethylene at low temperature was also improved by adding TPR and PVS which is brittle at low temperature. These phenomena were not observed when polymers were mixed without TPR.  相似文献   

5.
A semi-automated method has been developed for determining α-lipoprotein cholesterol values. Precipitation of apolipoprotein B containing lipoproteins takes place in wells of microtiter plates after 100 μL of serum are mixed with 20 μL of a heparin/MnCl2 solution. A Beckman (Fullerton, CA) Biomek 1000 work station is used to transfer sera, supernatants and reagents between tubes and microtiter plates. Supernatant cholesterol is determined enzymatically, and absorbances are read at 490 nm using a Molecular Devices Corporation (Palo Alto, CA) plate reader. Values obtained on both fresh and frozen serum samples agreed with corresponding data obtained at the Centers for Disease Control (CDC; Atlanta, GA). For the fresh samples, the average bias was 2.87%. The within-run coefficients of variations were between 2.2 and 0.6% for the data obtained on CDC frozen control pools. The results indicate that the semi-automated method is suitable for obtaining accurate and precise data for α-lipoprotein cholesterol. The method lends itself to the analysis of large numbers of samples and is particularly suited for the study of lipoproteins of small mammals.  相似文献   

6.
A new technique for measuring adsorption on non-noble metals is presented here on the basis of former experimental results and experience.  相似文献   

7.
A novel technique for containerless protein crystallization   总被引:1,自引:0,他引:1  
Heterogeneous nucleation, which is often detrimental to theproduction of suitable crystals for X-ray diffraction, can beinduced by the contact of a crystallization sample with thewalls of its supporting vessel. A novel method for creatinga ‘containerless’ environment for the growth ofprotein crystals is described. Contact between the containerwalls and a crystallization drop is eliminated by suspendingthe drop between two oils of different density: one of higherand the other of lower density than that of water and the commonprecipitating agents. A number of proteins were crystallizedin 2&10 µl drops using this procedure. It was foundthat the number of crystals obtained in such suspended dropswas reduced significantly compared with the number of crystalsobtained in trials where the crystallization drop was situatedat the bottom of a vial under a single layer of oil. This methodhas potential in controlling heterogeneous nucleation.  相似文献   

8.
9.
A detector for impact velocity measurements was developed and calibrated.Measurements of particle density profiles, distribution of incident momentum flux on the pipe wall and the distribution of radial particle velocity over a cross section of a horizontal pipe in the established flow region in a pneumatic conveying system, were performed and compared with pressure loss data.  相似文献   

10.
11.
A novel technique for the preparation of secondary fatty amides   总被引:1,自引:0,他引:1  
A technique for the synthesis of monosubstituted fatty amides at low temperature and ambient pressure was developed. This method involved the condensation of an amine with a triacylglycerol. The primary amine (ethyl,n-butyl,n-hexyl andn-octyl were tested) acted as reagent and solvent for the fatty substrates. No additional organic solvent or catalyst was added. Tallow, vegetable oils and fish oil all served well as substrates, as did pure tripalmitin. The rate of amidation was dependent upon temperature and the ratio of fat to amine. In a series of experiments conducted with tallow andn-butylamine at a fat:amine molar ratio of 1:16, amidation could be carried out at 20°C, producingn-butyltallowamide in 83% yield in 24 hr. When the fat:amine molar ratio was reduced to 1:8, and the temperature raised to 45°C, the amide yield was 87.6% in 24 hr. When the reaction was carried out at the boiling point ofn-butylamine (78°C) and at a fat:amine ratio of 1:8, the amide yield was 93.2% in 4 hr. The reaction progressed more rapidly with higher molecular weight amines. The identity and purity of the amides was assessed by thin-layer chromatography and confirmed by elemental analyses and infrared and C13 nuclear magnetic resonance spectroscopy.  相似文献   

12.
A modification of the Internal Reflection Spectroscopy (IRS) technique for infrared (IR) spectroscopy is described, where the surface of the IRS element is modified by a thin (100 to 1000 å) layer of metal oxides, silanes or Kevlar so as to model the surface of reinforcements in composite materials. The modified IRS element is then brought into contact with the matrix material and chemical changes in the first 2000 to 3000 å of matrix examined by IR spectroscopy. Examples of the technique include a study of the effect of various surfaces on the crosslinking of an anhydride-cured epoxy resin. The kinetics of the crosslinking process and the final ester crosslink concentration are shown to be significantly affected by, for example, a silica or Kevlar surface. The advantages and limitations of this modified IRS technique are discussed relative to other surface characterization techniques.  相似文献   

13.
A low-temperature synthesis of fatty alkanolamides, fatty diamides and fatty aralkylamides directly from triglycerides and primary amines provides essentially quantitative yields of the various products. The reactions run to completion in 3–12 h at temperatures of 50–60°C, approximately 100°C lower than employed in present conventional practice. The amines are used in excess and serve as solvent, reagent and, perhaps, as catalyst. The amides were characterized by melting point and spectroscopic (infrared and nuclear magnetic resonance) methods. If the mixed amides produced from the various natural triglyceride mixtures of fats and oils are acceptable products, this synthetic method provides these products in satisfactory quality while conserving energy and avoiding the intermediate production of free fatty acids or their esters.  相似文献   

14.
本文提出通过确定胶料混炼过程参数来预测混炼胶粘度质量指标(门尼粘度)的三种软测量的方法,通过主元分析法,确定混炼胶质量指标(门尼粘度)的软测量的辅助变量,并且比较了它们的软测量数据,指出基于神经网络的软测量技术优于其它两种软测量方法。  相似文献   

15.
A sensitive method is described for the determination of hydrogen cyanide and organic nitriles in atmospheres created by the combustion or thermal degradation of nitrogen-containing polymeric materials. The technique also allows for the determination of other hydrocarbon species from the same sample using a gas chromatograph-mass spectrometer system without entailing too many divisions in the sample quantity The method utilizes an NOx analyzer will only respond to nitrogen-containing compounds and response factors for these compounds can be calculated.  相似文献   

16.
A quantitative model which described the microscopic and macroscopic refractive index properties of uniaxially oriented crystalline polymers has been extended in relation to molecular bond polarizabilities in this work. Application of this extended modeling methodology in analyzing measured refractive index data for a series of unoriented and oriented samples of linear polyethylene provided Δ = 0.0585 and Δ = 0.194 as the most probable crystalline and noncrystalline intrinsic birefringences for samples exhibiting spherulitic morphology. With these intrinsic birefringences, noncrystalline orientation functions were determined from the optical measurements coupled to the model and the results compared to values obtained from infrared measurements. This comparison of noncrystalline orientation functions, as well as from low density polyethylene reported by other investigators, provided experimental justification for our modeling methodology to examine the possibility of changing intrinsic birefringences for polyethylene as a function of orientation and morphology. The results of this examination demonstrated that values for Δ = 0.0585 and Δ = 0.12 should be used for both low and high density polyethylene samples oriented above the spherulitic to fibrillar transition region.  相似文献   

17.
The electrical circuit for the recently developed transient plane source (TPS) technique for fast and precise measurements of thermal transport properties of solids has been modified for more convenient and more automated measurements. The technique has been tested for measurements of thermal conductivity and thermal diffusivity for a series of building materials ranging from thermally insulating materials (extruded polystyrene and PMMA) to good thermal conductors (stainless steel and aluminium). The results obtained in this work agree well with other techniques and international standard materials. This agreement indicates that the TPS method is accurate to within ±5% over a thermal conductivity range of four orders of magnitude (0.02 W m?1 K?1 to 200 W m?1 k?1).  相似文献   

18.
A new instrument to analyze the short chain branching distribution of polyethylenes has been described. Turbidity analysis of ethylene/α-olefin copolymers by turbidity fractionation analysis can provide short chain branching distribution information that is similar to CRYSTAF and TREF. In these experiments, the turbidity of a polymer solution is monitored while changing its temperature at a controlled rate. The turbidimetric response is to the precipitation or dissolution of the crystallized polymer at a given temperature. With an approach similar to CRYSTAF, the differential of the turbidity profile provides valuable SCBD information for polymers with broad and narrow compositions such as Ziegler-Natta LLDPE and homogeneous polymers catalyzed by single-site catalysts.  相似文献   

19.
A tissue embedding protocol which preserves root diameter was developed for hairy root mats ofTagetes erecta. Embedded root mats were sectioned, stained and the cut surfaces were subjected to image analysis to determine the void fraction of the root mats. Void fractions of mats of different ages, grown from inocula containing different numbers of tips, were analyzed. The method was found to give reproducible values for the void fractions, exhibiting reasonable trends with respect to initial tip number and mat age.  相似文献   

20.
The refractive index of emulsions of polymers and copolymers may be estimated from absorbance readings with a UV-visible spectrophotometer. Other information needed is the weight-average particle diameter, from other techniques such as gradient disc centrifugation. A simple computer program matches the refractive index parameter so that calculated and experimental absorbances are equal at the given wavelength. The wavelength dependence of the polymer refractive index is readily obtained.  相似文献   

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