Page 142 - Handbook of Plastics Technologies

THERMOSETS

3.12 CHAPTER 3

Plywood. Wood is skived into thin layers of veneer. Paper is impregnated with aque-
ous resole resin. Alternating layers of wood and paper-phenolic are stacked to the desired
thickness and pressed at 100 to 150°C and 700 to 6000 psi to make weatherproof exterior
plywood for building, autos, boats, ships, trucks, and trains (Table 3.7). This uses 49 per-
cent of the total phenolic resin market.

TABLE 3.7 Plywood: Typical Properties
Flexural modulus 1,450,0000 psi
Tensile strength 2,750 psi
Flexural strength 5,000 psi

Compressive strength 4,000 psi
–6
Thermal expansion 6 × 10 /°C

Particle board. A mixture of 90 percent wood chips + 10 percent resole resin is pre-
pressed at room temperature then hot pressed at 160 to 220°C and 290 to 590 psi. Cure is
finished by hot-stacking in storage. Wafer board is made from larger chips. These boards
are used for furniture core, floor underlay, prefab housing, freight cars, and ships.
Fiber board is made from wood filaments. Pressing at low pressure gives low-density
boards for heat and sound insulation. Pressing at high pressure gives decorative and struc-
tural board.
These particle boards use 16 percent of the phenolic resin market.
Insulation materials. Fiberglass wool insulation is bonded by spraying with 10 per-
cent of aqueous resole and curing at 200°C. This is used for thermal insulation in housing
and appliances. It is good up to 260°C. For higher-temperature industrial insulation—
pipes, boilers, and reactors—mineral-based rock wool is used instead of glass wool; it is
good up to 385°C.
Textile fiber mats are bonded by phenolic resin and used for sound insulation in autos,
offices, auditoriums, and industrial plants.
These applications use 12 percent of the phenolic resin market.
“Laminates.” Kraft paper is impregnated with low-molecular-weight (300) phe-
nolic resin, bonded with medium-molecular-weight phenolic resin, then cut and stacked to
the desired thickness and pressed at 170 to 190°C and 200 psi, or wound onto a mandrel
and cured to form a tube (Table 3.8). This uses 6 percent of the phenolic resin market.
Such “high-pressure laminates” are used for furniture and counter tops (3 and 2 percent of
the market, respectively), and electrical and mechanical applications (1 percent) such as
printed circuit boards, switches, transformers, pulleys, bobbins, guide rolls for paper and
textile machinery, gears, bearings, bushings, and gaskets.
Filters are made by impregnating paper with 20 to 30 percent of phenolic resin and cur-
ing in a 180°C oven. Battery separator plates are made the same way.
Synthetic fabric laminates are made by impregnating with phenolic resin and are used
for helmets, aircraft interiors, and ablative nose cones for rockets. Recent research on such
ablative nose cones showed that 28 percent loading with carbon nanofibers gave the lowest
erosion rate at 2200°C.
Foundry moldings. In the auto, construction, machine parts, and steel industries,
molten metal is poured into sand molds to produce the shapes of the products. The sand is
bonded by phenolic resin, cured at 270°C. In the cold box process, the binder is phenolic

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