Curing, composite resins

M. Uo et al. reported on a dental composite resin cured under near-infrared irradiation. They showed the following composite resin (CR). The mixture of Bis-GMA and TEGDMA was used as the base resin matrix. Bis-GMA and TEGDMA are mixed to be 2 1 in weight ratio. 

Studies of the particle—epoxy interface and particle composition have been helphil in understanding the mbber-particle formation in epoxy resins (306). Based on extensive dynamic mechanical studies of epoxy resin cure, a mechanism was proposed for the development of a heterophase morphology in mbber-modifted epoxy resins (307). Other functionalized mbbers, such as amine-terminated butadiene—acrylonitrile copolymers (308) and -butyl acrylate—acryhc acid copolymers (309), have been used for toughening epoxy resins. 

Composite resins can be cured using a variety of methods. Intraoral curing can be done by chemical means, where amine—peroxide initiators are blended in the material to start the free-radical reaction. Visible light in the blue (470—490 nm) spectmm is used to intraoraHy cure systems containing amine—quin one initiators (247). Ultraviolet systems were used in some early materials but are no longer available (248). Laboratory curing of indirect restorations can be done by the above methods as well as the additional appHcation of heat and pressure (249,250). 

A low tan S will mean a high degree of resin cure. Most insulation systems are composites of many materials. In practice, they almost always contain small voids. Consider a coil side with a single void. The voltage distribution across the insulation will be non-uniform, due to different permittivities of air and insulation. When a low voltage is applied, a proportion of this will appear across the... 

Polymer-matrix composites for aerospace and transport are made by laying up glass, carbon or Kevlar fibres (Table 25.1) in an uncured mixture of resin and hardener. The resin cures, taking up the shape of the mould and bonding to the fibres. Many composites are based on epoxies, though there is now a trend to using the cheaper polyesters. 

Because most thermoset composites cure by a thermally activated reaction, a complicated heat transfer process occurs during solidification, the result of an exothermic cross linking reaction in the resin. The complications of thermoset resin curing are compounded by the competing mechanisms of... 

Applications with real composites have been performed in order to verify the results so far outlined. Namely, a metalfilled epoxy composite was selected, whose matrix material was a diglycidyl ether of bisphenol-A resin, cured with 8 percent by weight of the resin, triethylene-tetramine. 

Thermosensitive hydrogels, 13 743 THERMOSET Thermoset recycling pyramid, 13 780-781 Thermoset elastomers, 20 71 Thermoset epoxy resins, curing of, 10 421 Thermoset flexible polyurethane foams properties of, 25 461 Thermoset matrix composites, 21 456 Thermo set molding properties of diallyl isophthalate, 2 262t Thermoset polymers, 25 455 cured, 10 425... 

A glass mold treated with release agent was used to prepare 0.125" thick cured plates of the resin compositions. These cured plates were used to provide samples for tensile, differential scanning calorlmetery and thermomechanical analysis. 

G. Eliades, A. Kakaboura, G. Palaghias, Acid base reaction and fluoride release profiles in visible light-cured polyacid modified composite resin restorations. Dent. Mater. 14 (1998) 57-63. 

The cure of thermoset resins involves the transformation of a liquid resin, first with an increase in viscosity to a gel state (rubber consistency), and finally to a hard solid. In chemical terms, the liquid is a mixture of molecules that reacts and successively forms a solid network polymer. In practice the resin is catalyzed and mixed before it is injected into the mold thus, the curing process will be initialized at this point. The resin cure must therefore proceed in such a way that the curing reaction is slow or inhibited in a time period that is dictated by the mold fill time plus a safety factor otherwise, the increase in viscosity will reduce the resin flow rate and prevent a successful mold fill. On completion of the mold filling the rate of cure should ideally accelerate and reach a complete cure in a short time period. There are limitations, however, on how fast the curing can proceed set by the resin itself, and by heat transfer rates to and from the composite part. 

As mentioned earlier PMR polyimide thermosts are used as matrix resins for glass- and carbon fiber composites, mainly in aeroengine applications. At this point it has to be mentioned that the thermal oxidative stability of a PMR composite is dependent on the type of fiber used (113) and the cure conditions (time/temperature/atmosphere) employed for molding. Very interesting is the observed higher thermal oxidative stability of PMR-II composites when cured/-... 

Within certain restrictions, unsaturated polyester resins are made thermochromic by the addition of a methanolic Co(II) chloride solution. The unsaturated ester, CoCl2 solution, peroxide catalyst, and accelerator are combined, and the resulting composition is cured at low temperature. The cured resin is colorless at 10°C but deepens in color as the temperature rises, until a blue color is attained at 40° C. This color change is reversible however, the thermochromism is destroyed by heating to temperatures above 70°C [51]. 

---