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phenolic resins, phenol-formaldehyde polymers were the first completely synthetic polymers to be commercialized.

Although molded products no longer represent their most important application, through their use as adhesives they still represent almost half of the total production of thermosetting polymers.

As such, they have had many industrial applications—for instance, in automobile topcoats and in finishes for appliances and metal furniture.

However, their use in coatings is decreasing because of restrictions on the emission of formaldehyde, a major component of these coatings.) is a naturally occurring polymer made up of repeating glucose units.

Ester and ether derivatives of cellulose were also developed and used as fibres and plastics.

The most important compounds were cellulose nitrate (nitrocellulose, made into celluloid) and cellulose acetate (formerly known as acetate rayon but now known simply as acetate).

On heating, the resole condenses further, with loss of water and formaldehyde, to yield thermosetting network polymers.

The other method involves reacting formaldehyde with an excess of phenol using an acid catalyst to produce prepolymers called novolacs.

Because of its excellent insulating properties, the resin was made into sockets, knobs, and dials for radios and was used in the electrical systems of automobiles.

Novolacs resemble the polymer except that they are of much lower molecular weight and are still thermoplastic.

Curing to network polymer is accomplished by the addition of more formaldehyde or, more commonly, of compounds that decompose to formaldehyde on heating.

The resin, at this stage called a resole, was then brought to the B stage, where, though almost infusible and insoluble, it could still be softened by heat to final shape in the mold.

Its completely cured, thermoset stage was the C stage.