Curing studies

Curing studies-pot life Engineering data for design Stress relaxation at low loads under different exposures... 

Plavix Two trials were carried out to determine efficacy the CAPRIE and CURE studies. 

The CURE study involved 12,562 patients randomized to receive Plavix (300 mg loading dose followed by 75 mg daily) or placebo and were treated for up to a year. Patients also received aspirin or other standard treatment such as heparin. The results showed that Plavix had a 20% relative risk reduction compared with placebo (582 cases of cardiovascular death, myocardial infarction, or stroke) versus 719 cases for placebo. 

Comparison of Monomer Reactivity. Cure Study - FTIR Data... 

Cure Study I Mixtures - FTIR Profile. Overlap Band (left). Acrylate Band (right)... 

Millions of patients around the world have taken drugs introduced over the past decade to delay the worsening of Alzheimer s disease. While the drugs offer no cure, studies suggest they work in some patients at least for a while. 

In Figure 8.17 the predicted dimensionless curvature at the end of curing and the experimental data are plotted versus degree of cure for the intermittent cure study. Most of the changes occur in the region above a = 0.8. Up to a = 0.95 and at a = 1, the predictions are very good. Between a = 0.95 and 1, however, the model underpredicts the dimensionless curvature by about 40 percent. This could be the result of various assumptions introduced in the material property models. 

Polymerization Kinetics and Cure Studies [2,4,25] Infrared spectra of monomers differ markedly from spectra of the polymers [2], As a consequence, it is possible to use infrared spectroscopy to follow the course of polymerization reactions and to simultaneously analyze the structure of the polymer [2]. 

Fig. 19. Results for the 63 °C curing study for R-45-M containing 8% ( ), 11% (O) and 16% (A) of curing agent IPDI. Diffusion of IPDI (top) and polymer molecules of weight Mn (bottom) is shown as function of curing time (abscissa scale is distorted). For IPDI diffusion after the first day, the upper error band corresponds to 16% concentration, the lower band to both 8 and 11 % (reprinted from Ref.110) with permission)...

This indication was considered in three trials. The first was the PCI-CURE study (44) (n = 2658 patients), a prespecified subgroup analysis of CURE. This trial studied the benefit of pretreatment with clopidogrel (median 10 days) before PCI. At one-month follow-up, there was a significant (P = 0.04) reduction of cardiovascular death and Ml (from 4.4% to 2.9%). 

ACS represents a prothrombotic state not just confined to the culprit lesion, with evidence of a pan coronary process and generalized platelet activation. Multiple vulnerable plaques in nonculprit vessels have been identified by angioscopy or intravascular ultrasound in ACS. Protracted treatment with clopidogrel induces antiplatelet activity that provides early benefits, and may limit thrombotic events within the following months. In the CURE study, the curves of major vascular events continue to diverge and showed an additional benefit from one-month follow-up to one year. 

Mehta SR, Yusuf S, Peters RJ, et al, Clopidogrel in Unstable angina to prevent Recurrent Events trial (CURE) Investigators. Effects of pretreatment with clopidogrel and aspirin followed by long-term therapy in patients undergoing percutaneous coronary intervention the PCI-CURE study. Lancet 2001 358 527-533. 

In the CURE study, 12,562 patients with acute coronary syndromes without ST-segment elevation have received ASA and clopidogrel 300 mg bolus, followed by 75 mg daily, versus ASA and placebo (50). The clopidogrel group had early reduction [within 24 hours of treatment—9.3% vs. I 1.4%, RR reduction 20% (p < 0.001) in the primary endpoint death from cardiovascular cause, nonfatal Ml, or stroke], which was sustained at one year, and was observed in all patients with acute coronary syndromes regardless of their level of risk. CURE patients who underwent PCI and were randomized to clopidogrel had a 31% RR reduction in death and Ml compared with placebo-treated PCI patients (51). 

Peters R, Mehta SR, Fox KA, et al. Effects of aspirin dose when used alone or in combination with clopidogrel in patients with acute coronary syndromes observations from the Clopidogrel in Unstable angina to prevent Recurrent Events (CURE) study. Circulation 2003 108 1682- 1687. 

The beginning of the polymerization reaction can be followed by NMR spectroscopy. Thus the nadimide polymerization advancement is easily monitored by the disappearance of the ethylenic proton and carbon resonances. However these criteria should be handled with care. For instance, the ethylene proton disappearance was particularly misleading in the case of the 2,3,4,6-tetrahydroph-thalimide curing study [38]. An isomerization stage took place with the formation of a tetrasubstituted double bond. Moreover, an oxidation reduction pathway was also evidenced, which gave saturated and aromatic derivatives. 

Many electrode patterns have been used for cure studies. Kienle and Raceused parallel cylindrical conductors immersed in the medium. Coaxial cylinder electrodes, with the sample placed between the two cylinders, were first used by Fineman and Puddington 5,6), and later by Aukward, Warfield, and Petree 16). The coaxial electrodes, like the parallel plates, have a relatively simple calibration, but are tedious to construct reproducibly for each thermoset cure experiment. Generally, any electrode configuration can be used for observing trends, but electrode size and location must be reproducibly controlled if calibrated measurements are desired. 

The effectiveness of these instruments for dielectric cure studies depends on sensitivity and accuracy. The sensitivity is related to the minimum resolvable phase angle, which for general cure studies, should ideally be less than about 0.10. Unfortunately, actual sensitivity in use depends strongly on the measurement frequency, on the admittance of the sample, on the details of the cabling and shielding, and on the electrical noise level of the environment. Therefore, analysis of published sensitivity specifications is difficult. It is easier to evaluate intrinsic instrument accuracy, which can be expressed in terms of either the tan8x accuracy or the conductivity accuracy. An example is useful. 

Microdielectrometry was introduced as a research method in 1981 14 and became commercially available in 1983 20). The microdielectrometry instrumentation combines the pair of field-effect transistors on the sensor chip (see Sect. 2.2.3) with external electronics to measure the transfer function H(co) of Eq. (2-18). Because the transistors on the sensor chip function as the input amplifier to the meter, cable admittance and shielding problems are greatly reduced. In addition, the use of a charge measurement rather than the admittance measurement allows the measurements to be made at arbitrarily low frequencies. As a matter of practice, reaction rates in cure studies limits the lowest useful frequency to about 0.1 Hz however, pre-cure or post-cure studies can be made to as low as 0.005 Hz. Finally, the differential connection used for the two transistors provides first-order cancellation of the effects of temperature and pressure on the transistor operation. The devices can be used for cure measurements to 300 °C, and at pressures to 200 psi. 

Finally, from a pragmatic point of view, the conductivity is a very sensitive probe of cure. Not only does it become increasingly sensitive to changes in Tg as the end of cure is reached, but it can almost always be measured, even in the presence of dipolar effects, by decreasing the measurement frequency. The conductivity is equally sensitive to small decreases in Tg that result from degradation, a result first noted by Warfield 58). Applications of conductivity measurement to cure studies are reviewed in Section 5. 

May, C. A. Composite cure studies by dielectric and calorimetric analyses, p, 803, Proc. 21st SAMPE Symp., 1976... 

Curing Study. Although the data on the mechanical properties of the uncured inks provide information that is useful in fabricating the inks, no explanation for the poor performance of BK-62 was found. As a result, experiments aimed at examining the cure behavior of the inks were conducted. Samples of the inks were cured on a heated 2 roller apparatus, and, after various curing times, small portions of ink were removed and characterized for oscillatory and short term steady flow viscosity. In view of the complexity of the oscillatory behavior, most of the emphasis is on the steady flow tests however, it is useful to examine the general trends exhibited in the oscillatory data. 

Figure 1. RTV silicone cure study (A) Permittivity measurement, (B) Loss factor measurement with time at ambient temperature.

Figure 9. Plot of temperature vs. time for a cure study. Job 3330 Run 1.

By spot-tests on coatings and immersion-tests on castings the excellent chemical-resistance of phenalkamine-cured epoxy systems has been demonstrated. In addition, near-infrared cure studies have documented the rapid complete cure of epoxies at room temperature and also satisfactory cure at reduced temperatures when phenalkamines are used as the curing agents. 

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