Caring for Plastics in Collections A brief overview

1
Caring for Plastics in CollectionsA brief
overview
Cordelia Rogerson
2
Deterioration of plastics Undesirable chemical
and physical changes to plastic
materials Influenced by light (especially UV),
atmospheric oxygen (oxidation), moisture
(hydrolysis) Chain scission shortening of
polymer chains, crumbling Cross-linking -
joining of polymer chains, embrittlement Effect
of additives, plasticisers, UV stabilisers and
others
3

• Chemical deterioration - the most susceptible,
  problematic plastics
• So called malignant plastics because they will
  off gas and could harm other collection items
• Cellulose nitrate (cellulose ester)
• Cellulose acetate (cellulose ester)
• Polyurethane (especially foam)
• PVC (plasticised)
• Fully vulcanised hard rubber (Vulcanite, Ebonite)

4
Light, UV (RH) moisture emitting Cellulose
nitrate yellow, brittle hydrolysis acetic
acid, plasticiser Cellulose acetate yellow,
brittle hydrolysis acidic oxidising nitrogen
oxide, plasticiser Polyurethane yellow,
brittle, yellow, brittle, nitrogenous organic
gases sticky, crumbles sticky, crumbles
liquids Poly(vinyl chloride) yellow,
brittle, resistant oily plasticiser liquids,
hydrochloric gas in extreme
moisture light Rubber brittle,
discoloured, hydrogen sulphide, hydrogen
sulphide, sulphuric matte sulphuric acid on
surface acid on surface Adapted from Scott
Williams, Care of Plastics Malignant plastics
5
Light, UV (RH) moisture emitting Acrylics
shows resistance shows resistance less
danger (PMMA) Nylon yellow, brittle hydrolysis
less danger in extreme conditions Phenoli
cs discoloured, matte discoloured, matte
phenol formaldehyde with severe
degradation Polyolefin yellow, brittle,
shows resistance less danger Polystyrene yellow
, brittle, shows resistance less
danger Adapted from Scott Williams, Care of
Plastics Malignant plastics
6
Some signs of deterioration Smells Yellowing
Crazing Cracking Crumbling Embrittlement Shrinkin
g Warping Weeping Blistering Blooming Sticky
surface
7

• Some characteristic smells
• Acrid smell cellulose nitrate
• Vinegar syndrome, acetic acid from cellulose
  acetate
• Vomit cellulose butyrate, cellulose acetate
  butyrate
• New car smell, plasticiser - PVC

8
Cracking, crazing May occur for different reasons
Deterioration seen as cracking in cellulose
nitrate, which is also causing the metal bar to
corrode badly
Buckle, acrylic bangle
Stress cracking in PMMA
9
Vulcanised rubber emitting sulphur compounds,
seen as yellowing on the surrounding packaging
materials
10
Yellowing, discolouring
PVC (including plasticised varieties) showing
yellowing
Nylon discoloured from the original white colour
11
Cockling, shrinking plasticiser loss
Cockled plasticised PVC sheet
Shrinking cellulose acetate bangle
12
Sticky surfaces migrating plasticisers
Camera case with a sticky surface causing it to
tear and lose areas where it has been stuck to
and then removed from surrounding items
13
Beware of mechanical damage Plastic objects
are not just susceptible to chemical
deterioration Far reaching effects on the
appearance and construction of objects Surfaces
can be fragile and vulnerable Constructions can
be surprisingly fragile
14
Mechanical damage poly (methyl methacrylate)
Perspex, acrylic, Lucite, Plexiglas
Mechanical failure of a Perspex construction
Surface scratches on Perspex
15
Mechanical damage polyester resin
Mechanical break in polyester resin bangle
16
Preventive conservation Controlling the storage
environment is vitally important to slow the rate
of deterioration Should be as stable as
possible Light sensitive eliminate light in
storage, particularly UV, regulate on display
eliminate UV Temperature - below room
temperature if possible cool 10C, ideal to
slow deterioration
Broken glass gramophone record with a yellowed
lacquer coating that has crazed and cracked.
Damage could be prevented through appropriate
handling/storage whilst the deterioration of the
lacquer could be slowed.
17

• Relative Humidity
• RH - generally between 30-50
• never above 65 RH
• Plastics degrading via hydrolysis (cellulose
  esters) lower is appropriate, 30 RH
• 30 RH or below may prevent dissipation of
  static, polyester film (Melinex)
• Hygroscopic plastics, Casein, some polyesters,
  are better with around 60

Metal and lacquer gramophone records stuck
together and with corrosion products, partly as a
result of an uncontrolled storage environment
18

• Storage
• Monitor items regularly every 3-6 months
  ideally
• A-D Test strips cellulose acetate, detects
  emitted acetic acid (available Image Permanence
  Institute, Preservation Equipment)
• Group items together for ease of monitoring
• Isolate malignant items from other materials to
  prevent off gassing affecting other items
• Good ventilation is essential for malignant
  plastics, do not place these in closed
  environments or allow circulated air to reach
  other collection items

19
Isolate vulnerable materials from one another
whenever possible
Imprint of degraded rubber balloon transferred
onto paper
20
More advanced methods of storage Cold storage,
slows the rate of deterioration particularly for
cellulose nitrate film, 5C Freezing suggested as
suitable for thin cellulose nitrate, polystyrene,
polyesters, ABS BUT NOT plasticised PVC/ vinyl,
degraded cellulose nitrate (Shashoua,
2006) Anoxic storage suitable for plastics
that degrade by oxidation not hydrolysis, and all
rubbers - Escal bags, Ageless
21

• Preventing mechanical damage
• Handle items to ensure their surfaces are not
  damaged
• Provide a cushioned surface polyethylene foam
  (Plastazote)
• For plasticised items, sticky surfaces use
  non-stick interleaving layers, silicon release
  paper, Teflon coated paper
• Ensure items cannot move around becoming damaged
• Wear gloves to protect yourself and the objects,
  finger marks can be harmful

22
Materials for storage/display always archival
quality Materials generally suitable in contact
with plastic objects Polyester sheet (Melinex),
nylon, Polyethylene, polypropylene Materials
considered suitable to be near plastic
objects Poly(Methyl methacrylate) Perspex,
polycarbonate, polystyrenes
Not untreated plywood or MDF or non-archival
quality materials
23
Cleaning the surface of plastics Only when
absolutely necessary Use a dry lint free, soft
cloth If further cleaning is necessary Do not
use cleaning agents Avoid solvents Use water
with caution a barely damp lint free cloth or
swab, dry thoroughly afterwards with a dry
cloth No water on items with gelatine, film,
sequins Avoid degraded areas If in doubt dont!
24
Conservation treatment Generally limited
treatment is possible with chemically
deteriorated objects Mechanically damaged
objects may present more possibilities but will
depend on the object, its construction and
circumstances
Nylon filament bangle, shown before and after
treatment, successfully conserved to regain
original shape