Page 150 - Handbook of Plastics Technologies

THERMOSETS

3.20 CHAPTER 3

FIGURE 3.14 Furan polymerization.

TABLE 3.15 Reinforced Furan Properties

Specific gravity 1.75
Rockwell hardness R110
Tensile modulus 1,580,000 psi
Tensile strength 3,800 psi

Flexural strength 4,800 psi
Compressive strength 11,500 psi
Water absorption 0.1%

allyl resins. They are all cross-linked (= cured) by organic peroxides, which initiate poly-
merization of the vinyl group.
3.1.3.1 Unsaturated Polyesters. Unsaturated polyesters are the fourth largest family of
thermosetting plastics, with a U.S. market volume of 2 billion lb/yr. They are often called
thermosetting polyesters or alkyds. In commercial use for 60 yr and now fairly mature,
they are the largest class of reinforced plastics (Table 3.16), popularly used in building
panels, chemical equipment, boats, cars, buses, trains, and planes.
3.1.3.1.1 Chemistry. Their chemistry is a fairly complex two-stage process. Typi-
cally, in the first stage, propylene glycol is mixed with maleic anhydride and phthalic an-
hydride (Table 3.17), and cooked 8 to 28 hr at 204 to 232°C to produce a molten
prepolymer of Mn = 800 to 3000 (Fig. 3.15). This is mixed with styrene monomer to pro-

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