Curative Level

Certain curatives such as those containing either chlorine or sulfur can be tested using x-ray fluorescence (XRF) techniques. The principle of XRF is that 

As the method is independent of how the atom is attached, chlorine-containing plasticizers such as TCP will interfere with the result if MOCA is used. 

There are some simple units that use a radioactive source instead of an x-ray generator. These have problems of handling and storing the source, as well as the disposal of the spent source after a number of years. 

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Cuprous sulfide, 7 767 Curative levels, optimizing, 21 803—804 Curatives, in polychloroprene latex compounding, 19 858 Curculin, 24 246 Curdlan, 4 724t 20 577-578... 

Property Changes with Different Curative Levels... 

In processing polyurethanes, the hardness is not greatly affected by the mixing ratios. A material mixed at 80% of the theoretical curative level has greatly different overall properties to one mixed at 100%. The hardness is still at the same level. Figure 7.6 shows the hardness variations with different curative variations. 

Polybutadienes with vinyl contents of 10 7 and 72.4% have been selected for further fatigue-to-failure analysis. Fatigue life measurements have been performed on a large number of specimens by means of the Fatigue-to-Failure Tester (Monsanto). Carbon-black-filled compounds with 50 phr N330 carbon black were cured with conventional curing system at 145°C. Curative levels have been chosen to obtain vulcaniza-tes at several levels of 300% modulus. Fatigue tests were performed on un-notched specimens at room temperature and at several deformation amplitudes. Data discussed here were obtained at 136% strain amplitude. 

Achieving lower hardness through the use of low levels of fillers, low Mooney polymers, and low curative levels is illustrated in Figure 4.9. 

FIGURE 4.9 Lower hardness using low viscosity FKM and low filler and curative levels (cured 10 min at 177°C, post-cured 24 h at 232°C). Formulations are based on precompound made of A-lOO or A-200, with 2.5 phr of Viton Curative 50 and 1 phr of VPA 3. 60% precompound means 60% of above precompound blended with 40% of the gum, either A-200 or A-100. All contain, 2 phr of TiPure R960,1 phr of Chrome Oxide Green, 0.5 phr Camauba Wax on a 100 phr level. 

FIGURE 4.10 Influence of curative levels and viscosity on compression set. Same formulations as in Figure 4.9, with 10 phr of BaS04. 

A peroxide curable grade, HyTemp PV-04, is available liom Zeon Chemicals for 0-rings, seals, gaskets as well as binders, adhesives, caulks, and plastic modification. This grade offers good compression set without the need for a post-cure, but is sensitive to exact curative levels [15]. NOK also has a polyacrylate that may be cured with peroxides, but information on it is not readily available. 

Rubber Chemistry and Technology 69, No.2, May/June 1996, p.273-6 STYRENE-BUTADIENE RUBBER FILLED WITH FLUORINATED CARBON BLACK. II. EFFECT OF CURATIVE LEVEL Ames K Gibala DS Hamed G R... 

The cure and tensile properties of sulphur vulcanised styrene-butadiene rubber filled with a conventional furnace black or a fluorinated black have been determined. Compositions with the fluorinated black and normal curative levels exhibit retarded cure compared to corresponding ones with the furnace black. This is due to a reaction between the sulphenatnide accelerator and the fluorinated black. Notwithstanding, a fluoro-filled composition with no curatives substantially crosslinks when moulded at 150 deg.C. Thus, fluoro-black filled specimens have competing effects toward crosslinking. On the one hand, crosslinking is inhibited by reaction with the accelerator, while on the other, the fluoro-black itself can cause crosslinking. 2 refs. 

Amine Cross-Linking. Two commercially important, high performance elastomers which are not normally sulfur-cured are the fluoroelastomers (FKM) and the polyacrylates (ACM). Polyacrylates typically contain a small percent of a reactive monomer designed to react with amine curatives such as hexamethylene-diamine carbamate (Diak 1). Because the type and level of reactive monomer varies with ACM type, it is important to match the curative type to the particular ACM ia questioa. Sulfur and sulfur-beating materials can be used as cure retarders they also serve as age resistors (22). Fluoroelastomer cure systems typically utilize amines as the primary cross-linking agent and metal oxides as acid acceptors. 

Some of the terpolymers containing high levels of AGE give superior sour gasoline and ozone resistance, particularly dynamic ozone resistance. Since the unsaturation is not in the polymer backbone, it can be, and apparentiy is, sacrificed under sour gasoline or ozone aging. This protection scheme is limited with the peroxide and sulfur cure systems as they involve the aHyl functionaUty of the polymer. The protection is maximized when a dinucleophilic curative, such as trithiocyanurate, is used. 

Measurement Devices and Actuators Often referred to as level 0, this layer couples the control and information systems to the process. The measurement devices provide information on the cur-... 

Type I Crigler-Najjar syndrome is a rare autosomal recessive disorder. It is characterized by severe congenital jaundice (serum bilirubin usually exceeds 20 mg/dL) due to mutations in the gene encoding bilirubin-UGT activity in hepatic tissues. The disease is often fatal within the first 15 months of life. Children with this condition have been treated with phototherapy, resulting in some reduction in plasma bilirubin levels. Phenobarbital has no effect on the formation of bilirubin glucuronides in patients with type I Crigler-Najjar syndrome. A liver transplant may be curative. 

An extensive series of thiosemicarbazones obtained from 2-acetylpyridine was tested by Klayman et al. [4, 85] for antimalarial activity against Plasmodium berghei in mice. The molecular features essential for activity were found to be a 2-pyridylethylidene moiety, the presence of the thiocarbonyl sulfur, and certain, bulky or cyclic substituents at the terminal AT-atom. The most active 2-acetylpyridine thiosemicarbazones were " N-phenyl- and those with azacycUc substituents. For example, iV-substituents of 4-methylpiperidine, piperazine, and azabicyclo[3.2.2.]nonyl-, 4, were curative at a dose level as low as 20 mg/kg. 

Maximum productivity is given by the shortest possible time of cure, provided the selected time and temperature do not produce an unacceptable level of defects or early failures in service. Sufficient cure must be given to prevent porosity, since badly undercured rubber will sponge at pressure release. It is better to risk a slight overcure rather than an undercure, since if the curatives are correctly chosen (in type and quantity) the compound should show a plateau effect, which means that a reasonable overcure will not have any marked effect on the physical properties of the product. 

For definitive, curative therapy, objective parameters to monitor include primary tumor size, involved lymph nodes, and tumor markers such as PSA. PSA level is checked every 6 months for the first 5 years, and then annually. With metastatic disease, clinical benefit can be documented by evaluating performance status, weight, quality of life, analgesic requirements, and PSA or DRE at 3-month intervals. 

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