Full cure

Silicone Good Phenyl-methyl silicones are more stable than are methyl silicones. Platinum cure is superior to peroxide cure full cure during manufacturing can eliminate most postirradiation effects. 

The curing process renders the resin essentially inert and nontoxic. At room temperature, full curing may take several days incompletely cured resins may cause skin irritation and sensitization. Respiratory symptoms may result from inhalation of cured epoxy dusts during grinding, presumably due to release of residual curing agent. Skin irritation and sensitization have been associated with epoxy resin exposure. 

Figure 8.4 shows the model predictions and experimental data for degree of cure during the manufacturer s recommended cure (MRC) cycle for IM6/3100. The MRC cycle is a two-step cure with the second dwell at 182°C. Note that most of the reaction occurs during the second dwell period. Full cure is reached during the latter half of the second dwell. 

Clearly, large doses are required for a full cure. The dose levels for attaining a maximum tensile strength are within 20 to 50 Mrad (200 to 500 kGy). 

The information on physical properties of radiation cross-linking of polybutadiene rubber and butadiene copolymers was obtained in a fashion similar to that for NR, namely, by stress-strain measurements. From Table 5.6, it is evident that the dose required for a full cure of these elastomers is lower than that for natural rubber. The addition of prorads allows further reduction of the cure dose with the actual value depending on the microstructure and macrostructure of the polymer and also on the type and concentration of the compounding ingredients, such as oils, processing aids, and antioxidants in the compound. For example, solution-polymerized polybutadiene rubber usually requires lower doses than emulsion-polymerized rubber because it contains smaller amount of impurities than the latter. Since the yield of scission G(S) is relatively small, particularly when oxygen is excluded, tensile... 

Fig. 10 SEM images of PCL/PPO blends containing 60% PCL after full curing at (a) 80° C and (b) 140°C (PCL was preferentially extracted)...

If we take a rubber-sulphur ratio of 68 32 in an ebonite compound and then cure it at 155°C, the vulcanization coefficient increases practically to a constant value of 47 after about five hours and the uncombined sulphur decreases during the first four hours. This state may be called a full cure in the chemical sense. There is also a reduction in volume of about 6%. It is known that after the combination of the first few percent of sulphur, the material passes through a leathery stage with low strength and poor resistance to oxidation and with time passing a true ebonite is formed with increased impact strength. 

If we increase the sulphur to a 65 35 ratio at full cure, the uncombined sulphur falls to about 4% while the vulcanization coefficient rises to about 49, but neither value is changed by further curing. At this stage tensile strength and cross braking strength are increased. Impact strength is reduced. 

Epoxy resins utilized in forming filament-wound composites must possess low viscosities (rfs) and long gel-times at 23 °C. To minimize unreacted starting materials in the finally cured composite requires the chemical cure reactions of the epoxy system must be simple. Furthermore, the number of chemical starting components in the resin must be small to minimize mixing problems that would result in variable thermal and mechanical properties. The toxicity of the resin chemical starting materials must be low. Also, the epoxy system must attain full cure at relatively low post-cure temperatures, <150 °C, to minimize the development of fabrication strains in the composite. 

The sophisticated oscillating die instruments can continue the measurement of dynamic properties after full cure has been reached. ASTM D6601124 covers measurements both during and after cure. A sealed cavity instrument is specified with amplitude 0.2° during cure and 1 to 100% strain after cure. In addition to the usual cure parameters, the in and out of phase moduli and tan 8 are reported. 

It is clear from the IR spectra that in spite of the vigorous conditions, hydrolysis is never complete and that some methoxy groups persist, even after full cure. Thus, condensation of these methoxy groups with hydroxyl groups does not occur during the final stages of curing. 

Overall, it is estimated that more than one in three people will develop some form of cancer during their lifetime [1], Traditional methods of cancer diagnosis involve surveillance of at-risk populations or investigation of suspicious symptoms. Unfortunately, often by the time a patient is symptomatic it is too late to facilitate a full cure. However, most cancers need not be killers if they can be exposed to the wide range of improving treatments at an early stage. The primary requirement for the successful treatment of any malignancy is early accurate detection. 

Dielectric measurements are also able to monitor the polymerization from the initial liquid state to the final solid state (full cure). The main observations are... 

An interesting method of eliminating the undercure caused by vitrification when using microwave radiation is to modify the formulation, including the use of polar thermoplastic that phase-separates during cure (Chapter 8). The thermoplastic material can convert microwave energy into heat, which enables the thermosetting polymer to devitrify and reach full cure. 

The state of cure at this point allows for the easy removal of a large proportion of any flash that may be present. This can be carried out using a sharp knife with the material under slight tension. The material at this point will appear to have sufficient properties for use, but the full cure cycle is needed to bring about the complete cure. The article needs a further 2 weeks at ambient temperature to reach its absolute maximum properties. 

Postmolding operations such as final cleanup, trimming to size, or minor repairs can be carried out immediately after the full cure cycle. 

Polyurethane can be bonded to most materials either during the initial casting or after full curing. In both cases, the most important consideration is that the surface must be clean and dry without any surface contamination. 

The polyurethane mix must flow over the part that has been primed and fully wet it. The presence of air pockets will prevent adhesion. It is most important that the primed part of the molding reaches the full cure temperature so that proper bonding will take place. 

MDI-based materials go through an initial cheesy state with very poor tear and tensile strengths. Once they have had their full cure, they are also very tough. 

The samples need to be brought to controlled test conditions before the test is carried out. If they were used as a quality control test, the product in many cases would be at the customer before the test was completed. A typical example is that tests such as the tensile tests require a week to settle down before the test is carried out after the 18-hour cure cycle. In many cases an approximate value is obtained by testing as soon as the sample has reached room temperature after it has had its full cure. 

The pot life of polyamide or amidoamine cured epoxy adhesives is generally on the order of hours at room temperature. Full cure is achieved in 5 to 7 days at room temperature, and handling strength is achieved in about 16 to 24 h. A faster cure can be achieved in 20 min to 4 h by heating to 60 to 150°C. When room temperature cures are required, an accelerator such as an amine is often added to the formulation. 

A second method of achieving latency is by using a curative precursor, which is chemically inactive at room temperature but then converts to an active curative at the cure temperature. Examples of this type include Monuron and di-urea adduct of toluene diisocyanate and dimethylamine. Full cure in about 1 h at 125°C is achievable with these materials. 

Typically a full cure will take less than 1 min and can occur with certain adhesives in 15 to 30 s. The partial cure process is usually employed on larger, more difficult to fixture parts. Heat times for sufficient handling strength can be as low as 3 to 10 s. A secondary heat source such as a final paint cure oven will then fully cure the adhesive. 

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