Degree of cure measurements

The sample, 20 mm in diameter and 0.5 mm thick, is placed between press platens heated at the selected temperature for over 1 second it is then quickly removed, quench-cooled in water, and the degree of cure measured. This operation is repeated... 

Mechanical behavior of a filled EP-glue under various curing conditions as a function of the degree of curing [636] Cpcs = degree of curing measured by DSC... 

Barcol hardness Also called Barcol impresses It is a measure of the hardness of a plastic, that includes laminate or reinforced plastic, using a Barber Coleman spring loaded indenter. Gives a direct reading on a 0 to 100 scale higher number indicates greater hardness. This test is often used to measure the degree of cure for plastics, particularly TS plastics. 

Future work in this area will involve the extension of these techniques to other temperatures in an effort to better characterize the overall reaction kinetics of these two processes. In addition, degree of cure obtained through isothermal DSC measurements will be compared with the fraction of acetylene consumed as measured by isothermal FTIR experiments for the same temperature and time. Also, the effect of the incorporation of metal fillers on the isomerization and crosslinking reactions will be addressed. 

Degree of cure and rate of cure for thermoset and UV-cured resins and similar are both properties that can be measured and monitored readily by a number of... 

The only way to validate kinetic models is to measure experimentally the degree of cure as a function of time and temperature. It can be done on both macroscopic and microscopic levels by monitoring chemical, physical (refractive index [135], density [136], and viscosity [137]), electrical (electrical resistivity [138,139]), mechanical, and thermal property changes with time [140,141]. The most-used techniques to monitor cure are presented in the next two subsections. 

Method 2 A sample is cured for various times until no additional curing can be detected. The samples are then scanned (heating rate ranging from 2 to 20°C/min) in order to measure the residual enthalpy, AHres. The degree of cure is calculated directly by Equation 2.25,... 

Figure 4.3 is a plot of log(c) versus degree of cure determined from differential scanning calorimeter measurements. The approximate exponential dependence of u on a is not surprising because a is approximately exponentially related to viscosity through rj = rj0 exp(E/RT + Ka). 

To obtain the cure kinetic parameters K, m, and n, cure rate and cure state must be measured simultaneously. This is most commonly accomplished by thermal analysis techniques such as DSC. In isothermal DSC testing several different isothermal cures are analyzed to develop the temperature dependence of the kinetic parameters. With the temperature dependence of the kinetic parameters known, the degree of cure can be predicted for any temperature history by integration of Equation 8.5. 

Regardless of matrix or fiber materials, the key process variables for filament winding are temperature, compaction pressure/fiber tension, and laydown rate. Typical measures of final cylinder quality include degree of cure/crystallinity, void volume fraction, fiber volume fraction, and residual stresses and strains. 

In traditional process control, models are often used to predict the deviation of the controlled variable from the desired state, the process error. This assumes that one knows the desired state. In complex batch processes, the desired state of the process is also dependent on history and changing dynamically. Further, most process models have to predict the outcome of an entire cycle to determine if the product will be good, so predictions are not available in real time, even for a slow process like the autoclave cure however, partial models have been used as virtual sensors to expand on the information available from sensors [38]. Saliba et al. used a kinetic model to predict the degree of cure as a function of time and temperature in a mold and used that predicted degree of cure to time pressure application and determine the completion of cure. Others [39] have used the predictions of models together with the measured progress of the process to predict future trends and even project process outcomes. 

The curing reaction of acrylates is typical of vinyl monomers. Therefore, the degree of double-bond conversion is the measure of the degree of cure. The best results are obtained when using oligomers as binders and monomers as reactive thinners. Examples of difunctional and polyfunctional acrylates are in Table 4.4. A partial list of the most common acrylate oligomers is below. - ... 

Since in a normal vulcanization system at least part of the sulphur combines with the rubber during vulcanization, an obvious way of following vulcanization is to measure the decrease in free sulphur. This method is not used extensively since it is well known that the combination of free sulphur does not correlate well with the development of cross links or other physical properties. In addition to this the analytical procedure is lengthy and costly. However free sulphur determinations are often made on finished products as a means of checking for uniformity of the product and to estimate the degree of cure. Figure 8.6 below shows the rate of sulphur combination at different vulcanization temperatures for a typical... 

Tests for scorch and rate of cure should be distinguished from tests for degree of cure or optimum cure measured on the vulcanised material. The latter type of test estimates degree of cure by measuring the physical properties of test pieces vulcanised for various times, tensile properties, swelling and set measurements being the parameters most commonly used. 

The standardised test procedures are concerned with the resistance of the rubber to the liquid, not the estimation of degree of cure, and generally recommend the measurement of change in dimensions, tensile properties and... 

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