Cure-dependent behavior

However, when the DAA label is excited, for example at U56 nm, the fluorescence intensity exhibited strongly cure dependent behavior. Fig. 1 shows such fluorescence spectra for DGEBA-DDS-DAA and DGEB-DDS-DAA respectively in the spectral range of U50 nm to 800 nm. In both epoxy matrices, at zero cure time, hardly any fluorescence is observed. But with increasing cure time, fluorescence Increases with a broad emission peak around 56O nm. At long cure times, the emission peak seems to have red-shifted slightly (by 5 10 nm). This small red shift is in sharp contrast to much... 

Figure 21 shows the permittivity and loss factor for an isothermal cure (137 °C) of DGEBA (EPON 825 n = 0) with diaminodiphenyl sulfone (DDS)47. To a first approximation, the data are the mirror image of Fig. 20, supporting the idea that the effect on electrical properties of the increase in Tg during isothermal cure might be similar to the effect of a decrease in temperature at fixed Tg. Examination of Fig. 21 shows one important difference between the temperature and cure dependences, namely that the relaxed permittivity decreases with cure time under isothermal conditions. This is a direct result of the changing chemistry, as discussed further in Section 4.3. The detailed behavior of the dipolar mobility is examined in Section 4.4, and of the ionic mobility in Section 4.5. 

To minimize such effects, low heating rates should be adopted in DMA tests. In this way, however, material time dependent behavior may become more significant because of the longer thermal exposure, as well as any post-curing effects during the thermal exposure. 

Another cure system consideration is the compound scorch behavior. Prior to vulcanisation, mbber is plastic-like and can be processed iato desired shapes such as tires, hoses, belts, or other articles. The time available to accomplish this processiag depends largely on the cure system and is referred to as the scorch time. If a compound cures prematurely duriag the processiag step, it usually becomes useless scrap. Therefore, a key requirement of the vulcanisation step is to minimise premature vulcanisation or scorch (Fig. 4). 

Other ingredients besides the elastomer and the cure system itself influence cure and scorch behavior. Usually the effect of a material on cure is pH-dependent. Ingredients which are basic in nature tend to accelerate the rate of both scorch and cure, whereas acidic materials exhibit the opposite effect. 

In another case where the twin-screw extruder was used, the rubber and plastic were melt mixed with all ingredients in a similar manner as described in blend compositions for static vulcanizations. The product was then dumped, cooled, and granulated. The premixed granules were then fed into a twin-screw extruder where a very narrow temperature profile was maintained with a relative high compression (2 1), and the screw speed was adjusted depending on the final torque and the flow behavior of the extruded stock. The stock was cured by shear force and temperature enforced by the twin-screw extruder. The dynamically crosslinked blend was taken out in the form of a strip or solid rod to determine the... 

Alcoholics Anonymous (AA) is a self-help organization for people whose common goal is recovery from alcoholism, and it is the most widely accessed resource for individuals with alcohol problems (McCrady and Miller 1993). The philosophy is based on the concept of alcoholism as a chronic disease that cannot be cured, but one that can be halted by means of complete abstinence. AA has described 12 principles or steps to guide those in recovery. Twelve-step facilitation, a manual-based psychotherapy to promote AA participation (Nowinski et al. 1992), was equally efficacious, compared with cognitive-behavioral and motivational enhancement therapies, in a large study of treatments for alcohol dependence (Project Match Research Group, 1997). 

Phenothiazines have a diverse use in medicine. They are primarily used as antipsy-chotics. Despite the fact that they do not cure the disease, they reduce psychotic symptoms to a point where the patient is provided with a better sense of reality. Phenothiazines are sometimes used for relieving severe anxiety, especially in panic attacks caused by dependence on amphetamines or lycergic acid diethylamide (LSD). Phenothiazines are used for alleviating behavioral problems in children that do not respond to treatment of other agents. Phenothiazines are sometimes used during the preoperational period because they relieve anxiety, control nausea, hiccups, diarrhea, and also cause muscle relaxation. 

The viscosity of a thermosetting resin undergoing a curing reaction is a function of time, temperature, and degree of cure. In case a resin presents a non-Newtonian behavior, a dependence of viscosity on shear rate needs to be accounted for as well [111]. 

The dynamic mechanical properties of elastomers have been extensively studied since the mid-1940s by rubber physicists [1], Elastomers appear to exhibit extremely complex behavior, having time-temperature- and strain-history-dependent hyperelastic properties [1]. As in polymer cures, DMA can estimate the point of critical entanglement or the gel point. 

Cure Rate Dependence on pH for the Phenolysis Lignin Resins. Cure behavior at different pH s of the resins was measured at 140°C, which is the usual hot-pressing temperature of phenolic resins. Relative rigidity change curves of LP-B at different pH s are illustrated in Figure 5. Cure advances faster as the pH of the resin increases. When the pH is 11.9, LP-B provides faster cure than the phenolic resin. A similar tendency has been found for LP-C. These findings clearly demonstrate that increasing pH of the resins improves cure rate. 

For all materials, the adhesive mechanism and the plastic deformation should be the main processes. During testing, the variation in friction coefficient values could be influenced by the specific AM behavior. Since AM corresponds to the crosslink density of a composite, for a qualitative assessment it can be concluded that the crosslink density decreases with increasing absorbed dose. PTFE500kGy-EPDM showed much lower AM and f90 values. It can be inferred that the state of cure is strongly dependent on the irradiation dose absorbed by the PTFE powder. 

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