Plastics

Phenol Formaldehyde (PF)

General information

Description

Phenol formaldehyde (PF) is one of the oldest plastics. Many know it under the tradename Bakelite. Fillers like wood fibre or paper were added to PF resin producing an opaque and often dark material. Sometimes small fibres would be visible. Later a translucent PF without filler became also available. PF was used a lot in the early 20th century but nowadays other plastics have replaced it. PF is a hard and tough material that feels relatively cold. When tapped upon it produces a clear sound. The smell of 'printed circuit board', as it is called in the PIT-tool, is typical for PF. That smell can be enhanced by rubbing gently over the surface. The price of PF is in the midrange.

History

Baekeland discovered PF in 1907 and in 1909 it was officially introduced as Bakelite. It was very popular until 1930. In 1928 translucent and coloured PF (cast phenol) was introduced, known under the tradename Catalin and was very popular until 1945.

Production, Application, Appearance

PF is mostly known from industrial products such as (historic) radio and telephone casings, sockets, light switches, and electrical parts, slide frames, and door handles. With filler it often has a dark colour but it could also be translucent, without filler, and coloured. That variety can be found in objects such as buttons, jewellery, small boxes, and knife handles. In the past it was used to imitate amber and jade. PF is also produced as sheet, for example the core of Trespa or HPL board. Green Oasis foam, used in flower arranging, is also PF.

Properties

Material properties

Thermoset
Density: 1.24-1.32 g/cm3; foam: g/cm3
Melting point: 90-107°C
Glass transition temperature: 200°C

Identification properties

Cell structure (foam): open / very compact
Smell: printed circuit board (warm electronics)
Touch: feels relatively cold
Sound: Rigid = clear; foam = no characteristic sound
UV-radiation (when clear): not applicable
Polarizing filters (for clear PF): not applicable

Degradation

Process

Photo-oxidation.

Details

PF is not considered a problem plastic.

Symptoms

Discolouration, surface turns matte, crazing.

Susceptibility

UV-radiation: Low
Light: Low
Oxygen/Ozone: Low
Temp: Low
RH: Medium

Susceptibility can be influenced by the filler.

Preventive conservation

Recommendations

UV-RADIATION: avoid extremes
LIGHT: 1 slight change in approx. 300 Mlx.h Avoid high light dose
OXYGEN / OZONE: ambient conditions
TEMP: common indoor conditions 10-30°C
RH: common indoor conditions 30-70% RH fluctuations: setpoint ±10% or ±5% when allowing seasonal fluctations between 30-70%