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 impregnated	Micarta	Wood laminate
11 meganewton/m2 = 10 kilograms-force/cm2
Density, maximum (g/cm3) ...............	1.4	1.4	1.45	1.7–1.9	1.3–1.4	1.4	1.3
Strength, minimum1 (meganewtons/m2)
compressive ...............	160	150	120	130	250	250	180
flexural ...............	60	55	80	250	160	140	280
Impact strength, minimum (kilojoules/m2, or kilograms-force-cm/cm2) ...............	5.0	4.5	9	150	35	15	80
Martens intercept yield temperature, minimum (°C) ...............	125	120	140	280	125	160	140
Electrical resistivity, minimum
surface resistance (ohms) ...............	1012	5–1013	1010	1012	108	1011	—
volume resistivity (ohm-cm) ...............	1012	5–1012	109	1012	108	1012	—
Electrical strength minimum (kilovolts/mm) ...............	11	13	4	13	3.5	30	—
Water absorption during a 24-hour period maximum (mg) ...............	60	55	90	0.05%	0.8g/dm2	—	—

G. M. TSEITUN