Phenoplasts

Phenoplasts

 

plastics based on phenolic resins. Aside from the resins (novolacs or resols) themselves, which function as a binder, the principal component of phenoplasts is the filler.

The choice of filler dictates the type of phenoplast obtained. Thus, powder fillers yield phenoplast molding powders, and fiber fillers yield fiber-filled (glass, asbestos) molding compounds. Fillers in the form of continuous webs (glass fabric, asbestos fabric) are used in making phenoplast laminates. Laminates are also made with paper (Micarta) and sheets of wood.

Phenoplasts also include the expanded plastics obtained by introducing a blowing agent (foaming agent). Phenoplasts may also contain hardeners (mainly hexamethylenetetramine, a necessary component in novolac compositions), hardening accelerators (CaO and MgO), lubricants (paraffin, fatty acids, salts of fatty acids), dyes, and inert ingredients.

Articles made of phenoplasts are highly resistant to heat, water, and acids. They have good electrical insulation properties. Their mechanical strength depends on the type of filler and fluctuates within wide limits (Table 1).

Table 1. Certain properties of the most important phenoplasts
 Molding powder (wood flour filler)Molding compound (sulfite cellulose filler)Glass-fiber molding compound (oriented glass fibers)Resin impregnated fabric laminate Resin impregnatedMicartaWood laminate
11 meganewton/m2 = 10 kilograms-force/cm2
Density, maximum (g/cm3) ...............1.41.41.451.7–1.91.3–1.41.41.3
Strength, minimum1 (meganewtons/m2)       
compressive ...............160150120130250250180
flexural ...............605580250160140280
Impact strength, minimum (kilojoules/m2, or kilograms-force-cm/cm2) ...............5.04.59150351580
Martens intercept yield temperature, minimum (°C) ...............125120140280125160140
Electrical resistivity, minimum       
surface resistance (ohms) ...............10125–1013101010121081011
volume resistivity (ohm-cm) ...............10125–101210910121081012
Electrical strength minimum (kilovolts/mm) ...............11134133.530
Water absorption during a 24-hour period maximum (mg) ...............6055900.05%0.8g/dm2

G. M. TSEITUN

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Although phenoplasts, the generic designation of these thermosetting polymers, are considered as highly mature plastic materials, they have earned their longevity due to a combination of desirable properties such as good heat resistance, dimensional stability, good resistance to most solvents and excellent dielectric properties.
Table 1 shows the phenoplast production increase compared to other thermosetting resins covering the 1975-1985 period.