Curing behavior

To further understand the effect of the interaction between the nanoparticles and the epoxy resin, the curing reaction kinetics of the composites have been studied. Based on non-isothermal DSC measurements and the Kissinger equation, the activation energy E, the pre-exponential factor A, and the reaction order , of the curing kinetics are obtained (Table 4). Comparison of the kinetic data suggests that the presence of the nanoparticles in epoxy does not change the overall reaction 

Parameter Epoxy Si02/Epoxy Si02-g-PAAM/Epoxy 

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Acid-Base Behavior. The relative acidity-basicity of the filler, generally determined by measuring the pH value of a slurry of a specific mass of filler in 100 mL of deionized water, can influence the behavior of a filler in some systems. For example, the curing behavior of some elastomers is sensitive to the pH value of carbon black. 

This is an activator-starved formulation and so is highly sensitive to the presence of nonmbbers that are capable of activating or accelerating vulcanization, and Table 2 illustrates the cure behavior of different grades of SMR (28). Cup lump grades show the highest state of cure and fastest rate of cure, whereas the stabilized grade, SMR CV, shows the lowest state of cure and slowest cure rate. 

Although filled systems are not as sensitive to variations in this type of cure behavior, certain correlations can be made with practical vulcanizing systems (29). 

Table 5 Cure Behavior and Properties of Modified Blends...

Chicago, IL, 26th-30th August 2001, p.506-7.012 CURING BEHAVIOR OF EPOXY RESIN WITH AMINOLYSIS PRODUCTS OF WASTE POLYURETHANES... 

Gibala, A. and Hamed, G.R., Cure and mechanical behavior of rubber compounds containing ground vulcanizates. Part I. Cure behavior. Rubber Chem. Technol., 67, 636, 1994. 

Table 22.3 Effect of starting polyol on the curing behaviors of PEER resins...

In order to study the cure behavior of the PTEB system, 1JC NMR of uncured and cured PTEB in the solid state was performed using crosspolarization magic-angle spinning techniques. The results show the polymerization to be via aromatization. The extent of cure versus cure temperature was determined quantitatively. It was found that the material was almost completely cured after one hour at 215°C. As the cure goes to completion, the ability to react decreases due to the corresponding rapid increase in Tg. Chemical shifts of the resonances in the cured material are consistent with a highly crosslinked condensed aromatic network. 

In order to study their cure behavior, samples of each oligomer were heated for 10, 20, and 30 min at 300°C under nitrogen. The DSC thermograms of samples heated for 10 min did not contain curing exotherms, and were essentially identical to those of samples heated for 30 min (Figure 1). In fact, the thermogram of a sample of 3b that... 

Measuring Vulcanization. The formation of a three-dimensional structure during vulcanization increases the stiffness (modulus) of the compound. Therefore, following the modulus increase versus cure time provides a continuous picture of the vulcanization process. Oscillating disk rheometers provide a useful method to do this (17). In this test, a preweighed sample of uncured mbber is placed into a preheated cavity containing a conical rotor. The cavity is closed and the rotor is set to oscillate within the mbber sample. As vulcanization proceeds, the compound s resistance to rotor movement increases and this resistance is followed as a function of time, thereby generating a continuous profile of cure behavior. These cure curves,... 

The thermal properties (i.e., density, specific heat capacity, and thermal conductivity) have a particularly strong influence on the curing behavior. The exothermal peak temperature is one example It can differ significantly between a composite mold with low thermal mass and a metal mold [35], A more thorough discussion of pros and cons of different mold materials can be found in Morena [37]. 

The dilatometric behavior of cast double-base propellant reveals much concerning the nature of the cure process. As an illustrative example, Figure 19 shows the curing behavior at constant temperature, 80°F., for a casting powder which has a porosity of about 2.7% based on the total propellant volume. 

Reactivity of Functional Groups. The reactivity of the functional groups of liquid prepolymers significantly affects the processing, cure behavior, and the ultimate mechanical properties of the cured binder and propellant. The reactivity of carboxyl groups of CTPB can be determined by the rate of reaction with n-butyl alcohol. The rate of esterification is measured from the rate of water evolution from the alcohol—carboxylic acid reaction, and a plot of water evolved vs. time then permits the calculation of the corresponding rate constants. 

Relative rigidity vs. temperature curves of LP s are shown in Figure 4 in comparison with a commercial phenolic resin. The pH of these resins was previously adjusted to around 10.8. The phenolic resin is fully cured at around 75°C. By contrast, the curves of the three lignin-based resins exhibit slower cure as compared to the phenolic resin. The retardation increases as the charge ratio of formaldehyde increases. Some retardation had already been found, but neglected, for the phenolated lignin/phenol-formaldehyde resins (12). In this study, the neat phenolated SEL was used for resin preparation. It can be concluded that phenolated steam explosion lignin-based resins have an intrinsically retarded cure behavior as compared to phenolic resin at the same pH. 

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. 

Figure 4. Cure behavior of phenolated steam explosion lignin-based resins.

J.B. Enns and J.K. Gillman. Time-temperature-transformation (ttt) cure diagram Modeling the cure behavior of thermosets. J.Appl. Polym. Sci., 28 2567-2591, 1983. 

Oh, S.-J. and Koenig, J. L. (1998) Phase and curing behavior of polybutadiene/diallyl phthalate blends monitored by FUR imaging using facal array detection. Anal. Chem. 70, 1768-72. 

Dominguez, D. D. and Keller, T. M. Phthalonitrile-epoxy blends Cure behavior and copolymer properties, J. Appl. Polym. Sci. 2008,110, 2504-2515. 

Monomers are primarily used to lower the viscosity of the uncured material to facilitate application. The monomer must be matched with the resin to give the desired set of properties with respect to adhesion to the substrate and bulk properties such as flexibility, stiffness, cure behavior, and durability. Early radiation curable monomers had problems associated with toxicity and skin sensitivity newly developed monomers have been significantly improved in this respect. 

Experimental agents were evaluated for their UV curing behavior effectiveness as photoinitiators using a UV curable composition consisting of tetraallyl bisphenol A and Tetrathiol 10. The testing results are summarized in Tables 1 and 2, respectively. 

A typical temperature scan of a system after prolonged isothermal cure is shown in Fig. 5. In comparing post-cure behavior with that after cure at Te , note the increase in Tg as well as in the temperature of the secondary transition (TgeJ. Also note that the relative rigidity (modulus) of the post-cured material is lower at room temperature (RT) than that of the partially-cured specimen. This behavior is anomalous, because post-cure would be expected to increase the crosslinking, and hence the stiffness of the material. The lower modulus manifests itself in a lower density and greater water absorption at RT for the more highly cured material than for the partially-cured... 

Each of these has a specific curing behavior and provides vulcanizates with different characteristics. To attain sufficient heat resistance, the compounds require long post-cures at high temperatures, such as 288°C (550°E), in some cases under nitrogen [27]. Details about different systems are in [27]. 

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