dk nkf - Nordisk Konservatorforbund Danmark

Table 1. Collections containing plastics
Type of collection Examples of objects
information carriers plastic sheets, maps, tapes, floppy disks, CDs, DVDs, photographic film, plastic
newspapers
technology electronic circuit boards, cable insulation, housings for electrical equipment
transport upholstery, bumpers and dash boards in cars and lorries, agricultural machinery, bicycles,
windows in side cars, fibreglass boats, protective clothing, spacesuits
military uniforms, protective equipment, rucksacks, tents, parachutes, transport
building gutters, pipes, flooring, wall coverings, furniture
modern history clothes, shoes and other fashion accessories such as bags and jewellery, makeup
containers, furniture, toys
medical equipment blood bags, prosthetic limbs and joints, false teeth, spectacles, tubing, syringes
sports equipment surfboards, racquets, clothing
modern (from 1880s to 1970s) and
contemporary art (from 1970s to present)
paintings, collage, sculptures, video film art, photographic art
coins and medals tokens, badges
packaging bubble wrap, photograph pockets, laminating sheets, book coverings, plastic bags
installation, resulting in substantial financial loss.
Gutta percha is an inelastic natural polymer produced
by the tree Palaquium gutta. However, the plastics
industry did not research degradation of synthetic
polymers in a structured way until the 1960s and the
subject is still at an early stage of development.
Degradation of a plastic is any change which
has adverse effects on its properties or function.
Quackenbos, an industrial chemist, defined the
lifetime of polyvinyl chloride (PVC) as the time taken
to lose 10% of original weight because after such
loss, its performance was no longer acceptable [7].
Degradation of plastics in museums is not defined
by physical and chemical changes alone but by the
resulting loss in function, form or significance of the
object. In addition to establishing the degradation
pathways for plastics in museum objects, it is
also necessary to decide how much degradation
is acceptable. While yellowing is valued as a sign
of maturity in materials such as oil paint, the same
changes in plastics are deemed unacceptable [8].
Industrial plastics are designed to function for a
predetermined period (Table 2). Degradation takes
place during two phases in plastics’ life cycles.
During manufacture, plastics are subjected to
high temperatures under moulding and extruding
which provide an opportunity for thermal and
oxidative degradation. During use, plastic is
exposed continually to air, moisture, light and heat
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initiating and accelerating changes in the chemistry
of the polymer chains and additives. Most objects
have been used or displayed prior to collection by
museums. Their history contributes to their rate
of degradation. Prolonged exposure to light, heat,
moisture, chemicals and gaseous pollutants during
that period will reduce longevity.
Four plastics have been identified as being more
vulnerable to degradation than others in museums,
namely cellulose nitrate, cellulose acetate, plasticised
polyvinyl chloride (PVC) and polyurethane
foams. Instability of the earliest plastics, cellulose
nitrate and acetate is expected due to their poorly
stabilized, experimental formulations and because
they are the oldest man-made plastics dating from
late 19 th and early 20 th centuries. However, PVC and
polyurethanes were first commercially available
after the Second World War and are still used, so
their short lifetimes are more difficult to accept.
Table 2. Average designed lifetime for industrial plastics
Application Average lifetime
(years)
electrical cable insulation 21
upholstery covering 17
housings for domestic electrical
appliances
11
blood bags 2-10
carrier bags 1