dk nkf - Nordisk Konservatorforbund Danmark

Figure 6: Acivated carbon adsorbs many different gases and is
used to remove nitrogen oxides from degrading cellulose nitrate.
Because activated carbon also adsorbs water and pollutants in
air, it is readily exhausted
Zeolites were first shown in 1994 to inhibit the
rate of deterioration of photographic negative film
based on cellulose acetate [16]. The technique has
since been adapted to inhibit the deterioration of
three-dimensional materials containing cellulose
acetate including handbags, jewellery and modern
art [17]. They are thought to inhibit the degradation
of cellulose acetate by both trapping water vapour
from the polymer, thereby minimising the rate of
hydrolysis and by trapping acetic acid vapour which
reduces the opportunity for more dominant, rapid
autocatalysis to occur. When both water and acetic
acid are present, they compete for sites in the zeolite
lattice, reducing the effectiveness of adsorption of
acetic acid by approximately one third.
Because most synthetic materials react with oxygen,
removing oxygen limits degradation. Since the 1990s,
commercial products such as Ageless ® and Atco ®
oxygen absorbers designed to inhibit the oxidation of
packaged foods, have been applied to plastics [18].
They comprise gas-permeable sachets containing
finely-divided iron which forms iron oxides in
the presence of water, binding oxygen from the
surrounding air. Ageless ® oxygen absorber can reduce
the oxygen concentration of an air-tight container to
0.01% (100ppm) or less. Objects are placed in an
oxygen-impermeable envelope, such as those prepared
from Cryovac® BDF-200 film (a transparent laminate
of nylon and polyolefins) or Escal ® , a ceramic-coated
film together with oxygen absorbents.
Keynote speech
Interventive conservation
Interventive treatments for plastics include
cleaning, joining broken and failed components,
consolidation, impregnation and filling. There
is little in the conservation literature detailing
interventive treatments for plastics, probably due
to the high sensitivity of many plastics, especially
when deteriorated, to organic liquids, aqueous
solutions and water. Interventive conservation of
plastics has attained a reputation of high risk and
irreversibility.
Cleaning plastics
Although condition surveys of museum collections
containing plastics suggest that approximately
75% require cleaning, the practice is still poorly
developed and is one of the major research areas
of the EU 7 th Framework project, POPART
(Strategy for Preservation Of Plastic ARTefacts
in Museums) which started in 2008 (http://popart.
mnhn.fr). Cleaning techniques may be divided into
mechanical and chemical. Mechanical cleaning
involves removal of dust and residues from surfaces,
either by blowing air from a can or cylinder or via
suction, using brushes or cloths. Plastics with a
glass transition temperature approaching ambient,
particularly plasticised PVC and polyethylene, are
readily abraded. Scratches are areas of low energy
and vulnerable to chain scission manifested as a
reduction in tensile strength and eventual failure.
Scratches decrease the light reflective properties of
surfaces, resulting in a reduction in gloss.
The purpose of chemical cleaning is to dissolve dirt,
residues or other unwanted material at surfaces and
to displace it. The type and polarity of the plastic, its
condition and the presence of conservation materials
influences the effectiveness of cleaning agents. For
example, since hydrolytic breakdown is a major
pathway for semi-synthetic polymers, the use of
aqueous cleaning agents is not advisable for them.
The risk of organic liquids swelling, dissolving and
extracting additives from plastics is higher than that
posed by aqueous washing agents [19]. Another
phenomenon to be considered when cleaning rigid
plastics such as polystyrene, polycarbonate and
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