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) moistureemitting Cellulose nitrateyellow, 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) moistureemitting Acrylicsshows resistance shows resistanceless danger (PMMA) Nylon yellow, brittle hydrolysis less danger in extreme conditions Phenolics 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 Shrinking 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 don’t!

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