Processing microwave cure

The microwave technique is widely applied to process polymer materials, e.g. in microwave cure [429], Microwave processing is a developing technology. 

Several studies have shown that a microwave cure cycle can be developed that provides equivalent performance properties to a thermal cure cycle. Table 14.9 shows the processing and performance characteristics of three commercial one-component epoxy adhesives cured via microwave and conventional thermal energy. Certain commercial epoxy adhesives could contain a large number of bubbles due to volatiles present during the cure cycle and the fast rate of cure. Therefore, specifically formulated adhesives for microwave curing may be necessary to optimize performance. 

Microwave processing has been used to process thermoset polymers and polymer composites, including polyesters, polyurethanes polyimides and epoxies, and in most studies it has been concluded that the curing speed is faster using microwave energy (Clark and Sutton, 1996). The effects of continuous and pulsed microwave irradiation on the polymerization rate and final properties also have been studied, and it was demonstrated that, for certain epoxies, a pulsed microwave cure resulted in improvements in mechanical properties, better temperature uniformity and a faster polymerization mte (Thuillier and Jullien, 1989). 

Liu et al. (2004, 2005) examined a three-dimensional non-linear coupled auto-catalytic cure kinetic model and transient-heat-transfer model solved by finite-element methods to simulate the microwave cure process for underfill materials. Temperature and conversion inside the underfill during a microwave cure process were evaluated by solving the nonlinear anisotropic heat-conduction equation including internal heat generation produced by exothermic chemical reactions. 

Microwave Curing Process of Polyethylene, Akzo Chemie, GmbH Diiren 1983... 

Curing by means of electrical processes (inductive curing, resistance, high-frequency and microwave curing)... 

The DGEBA was reacted in a 2/1 mole ratio with respect to PSF and DDS, and DGEBA and PSF were stirred together for one hour at 90 °C to dissolve the PSF. Then the reaction temperature was increased to 140 °C and DDS was added, the mixture was cooled to room temperature and reheated to 90 °C prior to microwave curing. Fracture toughness of cured specimens indicated no difference between thermally and microwave processed neat resin samples and incorporation of 30% polysulfone doubled fiacture toughness in both cases. Phase separation in the microwave... 

Generally, biocomposites are processed with the techniques discussed in the above section. But, some special treatments in addition to above mentioned primary processing techniques have also been attempted to investigate their effects on performance of biocomposites. Among these treatments, microwave curing (in place of conventional... 

In conclusion, the porosity, hardness, and strength of microwave cured acrylic resins that are processed for less than 5 min exhibited no significant differences in properties when compared with conventionally polymerized resins [60-63]. However, the investigation of color stability of several commercially available heat-cured, quick heat-cured denture and microwave cured denture base resins (tested exclusively under microwave conditions) revealed that the materials demonstrated differences in color stability, but the standard heat-cured materials treated under microwave irradiation exhibited color changes that were negligible [64]. 

Table 6. Rate constants for the thermal and microwave cure processes. Reprinted from (1998) J Polym Sci Part A Polym Chem 36 2653 [80] with permission ...

More recently, Boey et al. reported the rate enhancement under microwave irradiation during investigation of the cure process of epoxy resins (DGEBA -Araldite GY6010) in the presence of three different types of crosslinking agents such as DDS, DDM, and mPDA [111]. Microwave curing of epoxy systems was carried out in a multi-mode cavity (300 mm x 298 mm x 202 mm) coupled... 

Preliminary studies on the microwave curing of a polyester resin and composite material used in marine yacht industry showed that the microwave curing was an alternative method for the faster processing of laminated materials for structural applications. Laminates (10 cm x 10 cm) made by three layers of fiberglass and polyester resin were prepared by manual layup and cured under a microwave irradiation power output of 1800 W. When the samples were heated less than ll-12s, the... 

A unique process for chemical stabili2ation of a ceUular elastomer upon extmsion has been shown for ethylene—propylene mbber the expanded mbber obtained by extmsion is exposed to high energy radiation to cross-link or vulcani2e the mbber and give dimensional stabUity (9). EPDM is also made continuously through extmsion and a combination of hot air and microwaves or radio frequency waves which both activate the blow and accelerate the cure. 

To speed up the molding process, the required amount of molding powder or granules is often pressed iato a block and prewarmed before placing it ia the mold. Rapid and uniform heating is accompHshed ia a high frequency preheater essentially an iadustrial microwave oven. The prewarmed block is then transferred to the hot mold, pressed iato shape, and cured. 

Curing with Microwave or Radio-Frequency Processing Equipment... 

Any method of vulcanising rubber products which proceeds without interruption from start to finish as compared to the method of vulcanising separate batches of products or sections of a product. Continuous vulcanisation processes include the cold curing of proofed cloth, the vulcanisation of belting and flooring, of cables and certain extruded products by either the Liquid Curing Medium, Fluid Bed, Microwave, or Hot Air techniques. 

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