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Series editors' preface - Wood Tools

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132 Conservation of Furniture<br />

Table 4.1 Continued<br />

Polymer group, names Date Description and use Simple identification<br />

and trademarks introduced<br />

and<br />

country<br />

Polyolefins<br />

Low density polyethylene<br />

(LDPE)<br />

High density polyethylene<br />

(HDPE)<br />

Polypropylene (PP)<br />

Polystyrene (PS)<br />

Polytetrafluoroethylene<br />

(PTFE)<br />

Teflon, Fluon<br />

LDPE:<br />

1939 UK<br />

HDPE:<br />

1955 W.<br />

Germany<br />

PP: 1957<br />

Italy<br />

1930<br />

Germany<br />

1943 USA<br />

polyesters are thermoplastic, alkyds and<br />

UPs are thermosetting. Linear polyesters<br />

have excellent clarity, dimensional stability<br />

and chemical resistance. They are used to<br />

make textile fibres such as Terylene,<br />

Dacron and Tergal and high quality films<br />

such as Melinex and Mylar. Films make<br />

metallic sound when shaken and are<br />

difficult to tear. Unsaturated polyesters<br />

(UP) are used in glass-reinforced plastics<br />

mouldings. They are usually crosslinked<br />

with styrene but other unsaturated<br />

compounds may be used. Alkyd resins<br />

are used in (reactive type) paints<br />

Thermoplastic, crystalline, stereoregular<br />

hydrocarbon chain homopolymers formed<br />

by addition. LDPE is formed by high<br />

pressure free radical polymerization whilst<br />

low pressure ionic polymerization of<br />

monomer is used for the others. Highly<br />

chemical resistant, light and strong with<br />

waxy feel. Float on water. Cut cleanly.<br />

HDPE and most PPs are moderately tough<br />

(notch brittle) but some PPs are very<br />

tough with high impact resistance.<br />

Polypropylene has greater rigidity and<br />

surface hardness than PE. Used for all<br />

kinds of mouldings and films, also as<br />

adhesives and fibres. Film stretches before<br />

tearing<br />

Thermoplastic hydrocarbon addition<br />

polymer formed mainly by bulk<br />

polymerization of styrene. Most<br />

commercial PS is hard, brittle amorphous<br />

atactic homopolymer used for mouldings,<br />

films and foams. PS alone cuts cleanly is<br />

readily moulded or formed but shatters<br />

easily (makes metallic sound when<br />

shaken) has poor resistance to solvents<br />

and poor outdoor durability. It is<br />

copolymerized with a variety of other<br />

materials to make high impact plastics,<br />

dispersion type coatings and rubbers (see<br />

ABS, SBR, SAN)<br />

Thermoplastic, crystalline, carbon chain,<br />

addition polymer formed by emulsion<br />

polymerization of tetrafluoroethylene.<br />

Used where heat resistance, chemical<br />

resistance or low friction are required.<br />

Copolymers of TFE with other fluoro<br />

compounds are used as heat resistant<br />

rubbers<br />

affected by cyclohexane or<br />

aromatic solvents<br />

Burns with blue-based yellow<br />

flame and smell of candle wax.<br />

Becomes clear when molten<br />

and continues to burn on<br />

removal from flame. Not<br />

affected by cyclohexane or<br />

aromatic solvents<br />

Burns with spluttery orange<br />

flame and dense black sooty<br />

smoke with faint odour of<br />

marigolds. Continues to burn<br />

after removal of flame.<br />

Softened by cyclohexane and<br />

aromatic solvents

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