Conservation and restoration of plastic objects

Conservation and restoration of objects made from plastics is an activity dedicated to the conservation of objects of historical and personal value made from plastics. When applied to cultural heritage this activity is generally undertaken by a conservator-restorer. Within museum collections there are a variety of artworks and artifacts that are composed of plastic material whether they are synthetic or semi-synthetic; these were created for a range of uses from artistic, to technical, to domestic use. Plastics have become an integral component of life and many plastic objects have become staple icons or objects worth preserving for the future. Although relatively new material for museum collections, plastics having originated in the 19th century, they are deteriorating at an alarming rate, risking the loss not only of the objects themselves, but through their deterioration processes they place objects within their vicinity at risk too.[1] Plastics are made of synthetic, semi-synthetic and organic material, all of which are susceptible to degradation, with their respective off-gassing being harmful to the objects nearby in museum collections.[2]

Plastic household items
Eberhard Bosslet 2001 Biomorph sculptures "Stool Archipelago", "Island of Growth", "stump stools" are groups of sculptures made of fiberglass plastic on the basis of known organic forms. Dresden

Recent changes in plastic manufacturing, as a result of environmental concerns, towards biodegradable plastics,[3] have a potentially negative effect upon the long term stability of such objects within museum collections.[4]

Identification and composition of plastics

All plastics vary by the type of polymer used to create it, these polymers are what conservators look to in order to divide plastics into groupings that could best help create a preservation or restoration plan [5]. Groupings are important as some plastics can be dangerous or even flammable thus it is key to identify these plastics in order to best understand how to store and care for them.

Identifying plastics

Identification of plastic in a collection is extremely important because all plastics release a harmful toxin or gas that can damage nearby objects and by being able to identity the most harmful plastics a preservation plan can be set into place to slow down the effects and protect other objects.[6][7]

Plastics are identified in three ways including looking for its trade name, trademark or patent number. Identifying plastic is done in order to check what the plastic is composed of as different makers and depending on the year are different material could have been used to make the plastic.[1]

If there is no marker to identify the type of plastic used then it can be identified by using various types of data analyzed using spectroscopic technology like, Optical Spectroscopy, Raman, Mid-infrared spectroscopy [8] and near-infared spectroscopy along with mass spectrometry.[6] Other forms of identification include elemental analysis, thermal analysis to decipher the composition of plastics.[6] Once the composition is found it is best to determine if the plastic in the collection will be considered Malignant or not.

MoDiP, the Museum of Design in plastics, has created a guide to plastic objects that includes the objects manufacturing date, manufacturing process along with its typical characteristics such as feel and smell.[9] This is important because if an object in the collection that is listed here differs from smell or touch then it could be the object has begun to deteriorate. It is also encouraged that if one has an object not listed then they should contact MoDiP to include it to the list.

Common plastics

These are plastics that are still capable of degradation but its effects are not as harmful to nearby objects. The list below is of chemical compositions that make up common plastics found in museum collections:

These are plastics that will age faster if left untreated and have a higher potential or off-gassing or release a toxin that can damage surrounding objects.[6] To determine if objects are considered malignant proper identification of the object will be necessary.

Biodegradable plastics have become an issue because as plastic is used in many everyday objects the push to create biodegradable plastics has been on the rise. This causes an issue for conservators because these object will ultimately degrade as their composition is designed to as there is an increase in plastic waste.[10] It is these biodegradable plastics that can be prove to be difficult and museums will need to provide research for these items quickly to slow done their deterioration.

Deterioration

Perhaps the most difficult part about plastic deterioration is that one cannot visibly see what types of chemical reactions are occurring inside the polymer or even identity the type of plastic until it is too late. Typically all plastics will give off a distinct odor, leak toxins, or will begin to shrink or crack in some way.[12] Although deterioration will inevitably happen it is important to know the causes of it and be able to mitigate it.

Causes of deterioration

The cause of deterioration regarding plastics can be linked to age, chemical composition, storage, and improper handling of the objects. Conservators are in place to slow down the processes of deterioration by considering the 4 leading caused of deterioration:

  1. Age- when plastics were first manufactured in the 19th century they were composed of semi-organic material, thus these over the years these objects have deteriorated due to lack of research and improper handling of these plastics.[1] Without enough time to care for objects the older objects have deteriorated.
  2. Chemical - Depending on the objects' chemical composition, conservators can understand how it will react overtime. Other chemical reactions come from heat, oxygen, light, liquids, additives and biological attacks as these can cause a reaction in the polymer to speed up deterioration.[13] Chemical reactions are also caused by objects coming into contact with water and oxygen.[13]
  3. Storage- When objects are improperly stored is when contamination and deterioration can occur. This often occurs when temperature or relative humidity fluctuate in the storage area as this causes the polymers to react to the environment and will begin to deteriorate and possible contaminate surrounding objects. Storage should also be thought of as when an object is on exhibit as this is when the object is on display with lights and its temperature and humidity can fluctuate, being able to create a plan to adjust the exhibit case while on display can help prevent any damage.[1]
  4. Improper handling - This is due in part to improper cleaning techniques when using water or solvents on material that do not support those cleaning methods.[1] Also when handling the objects human error can occur that can cause abrasions or scratches.

Types of deterioration

Understanding the different types of plastic chemical degradation as this helps determine what not to expose plastics to. As the polymers that are composed of the plastics can deteriorate easily by changes in temperature, water or light, it is important to understand how these affect the polymers. Listed below are the chemical reactions that occur with the deterioration of the polymer's structure.

  • Photo-oxidative degradation refers to plastic object degrading by being exposed to UV and Visible Light although the type of wavelength that will damage the plastic depends on the composition of the polymer.[14] In General however, plastic will be affected by light and it is best practice to keep plastic away from light sources as much as possible.
  • Thermal degradation affects the whole unit of the polymer that the object is composed of and is affected by the temperature and amount of light the object is exposed to.[14]
  • Ozone-Induced degradation will deteriorate saturated and unsaturated polymers when the polymer is exposed to "ozone in the air" will speed the process of deterioration.[14] A test is conducted to see if the objects has been exposed by taking small samples and analyzed using an FTIR.[14]
  • Catalytic Degradation Mainly focuses on plastic waste polymers as they are transformed into hydrocarbons
  • Biodegradation is when the surface or the strength of the plastic changes, these properties allow it to decompose or mineralize by carbon dioxide and water.[14]
  • Decomposition of Hydroperoxides is when metal and metal ions are found on the plastic material as this can also lead to the deterioration of the object[13]

Effects of deterioration table
Table: The effects of UV, light, moisture and pollutants ( including solvents) on plastics[6]
Plastic UV Radiation and Excess Light

Photolysis, Photooxidation

Moisture (high relative humidity) and moisture fluctuations Hydrlolsis, swell/shrink Pollutants Danger to neighbors

stains, corrosion, stickiness, gases

acrylics resistant resistant dissolved, swelled, stress, cracking none
casein formaldehyde, protein derivatives formaldehyde gas, cracking due to swelling/shrinking, moldy, brittle when dry swell by water, resistant to organics formaldehyde, hydrogen sulfide, other sulfur-containing gases
cellulose acetate yellowed, brittle hydrolysis produces acetic acid oily plasticized liquids. White powder residue may also be visible[15] dissolved swelled acetic acid gas, oily plasticizer and degradation products on surface
Cellulose nitrate yellowed, brittle hydrolysis produces acidic and oxidizing nitrogen oxide gasses dissolved, swelled acidic and oxidizing nitrogen oxide gasses, plasticizer and degradation products on surface
nylon (polyamide) yellowed, brittle potential hydrolysis at extreme conditions softened, swelled none
phenolics

(phenol formaldehyde

 discolored and more matte discolored and more matte fillers swell and surface mottles with solvents phenol and formaldehyde with severe degradation
polyolefin

(polyethylene. polypropylene)

 yellowed, brittle resistant swollen by some organics none
polystyrene yellowed, brittled resistant dissolved, swelled, stress cracked none
polyurethane yellowed, brittle, sticky, crumbles yellowed, brittle, sticky, crumbles swelled, stress cracked nitrogenous organic gases and liquids
polyvinyl chloride yellowed, brittle resistant dissolved, swelled, embrittled by plasticizer extraction oily plasticizer liquids, maybe hydrochloric acid gas under extreme conditions of moisture and light exposure
rubber, ebonite, vulcanite brittle, discolored, increase in matteness hydrogen sulfide and other gases, sulfuric acid on surfaces surface mottled by solvents hydrogen sulfide and other sulfur-containing gases, sulfuric acid on surfaces
all plastics

(and organics)

 should be considered as prone to damage by UV radiation usually resulting in yellowing and embrittlement condensation plastics like esters, amides, and urethanes are subject to hydrolysis with subsequent weakening thermoplastics may dissolve, thermosets may swell, stress cracking harmful gases from plastics with chlorine, sulfur, and pendant (not main chain) ester groups

Additional effects of deterioration

For plastics composed of Cellulose Acetate the most common sign of deterioration condition is when it this type is exposed to water, it will give off a smell of vinegar (Vinegar syndrome), its surface will have a white powder residue and it will begin to shrink.[15]

Cellulose Acetate butyrate and Cellulose butyrate will produce butyric acid which has a "vomit odor".[6]

Polyvinyl Chloride will most likely cause a blooming effect, white spores, on the surface that if it comes into contact with other surrounding material it will contaminate it.[6]

Preventive care

Handling

Safety gloves such as those made of Nitrile can help prevent toxins entering the skin when handling plastic objects.[1] As plastics can ooze or off-gas material that may or may not be visible to the naked eye wearing gloves other than cotton is recommended.

Storage environment

Proper storage of plastics can help slow down the degrading process of plastics. Plastics are currently stored with a RH Level of 50% with the storage temperature at 18 degrees Celsius with no light coming into contact with the objects.[16] Although the composition of each plastic material can be different it is difficult to determine one unifying storage care plan, thus understanding the composition of the plastic can help determine their preferred climate levels.[16] Keeping plastics at a stable low temperature or considering placing these objects either in cold storage or in oxygen impermeable bags helps slow degradation.

Monitoring plastics in their storage environment is done by keeping track of their status and condition by using log entries on Excel spreadsheets or another format. To monitoring their temperature environment this is done using data loggers which track hourly changes in temperature. These methods can help strengthen a plan of preventive care as monitoring their status along with temperature can help connect any changes that occur.

Long-term storage equipment

Adsorbents such as "activated carbon, silica gel and zeolites" are used as they can help with the gasses that are released from plastics as this material can help slow down the degrading process.[16] These absorbents can also be used when the object is on display to prevent and off-gassing that could occur, so these can be used on exhibit and long-term storage. Absorbents along with acid-free boxes and silica gel can help slow down the process of degradation and vinegar syndrome which is common in film, Lego and artwork. A yearly check up of plastic objects can help monitor the condition of plastic objects as well as the condition of the surrounding objects to ensure they have not been contaminated.[16] Objects composed of Cellulose Nitrate benefit from cold storage as they are sensitive to increases in temperature.[6]

Oxygen Impermeable bags are used as they absorb all the oxygen in the bag.[16] With no oxygen to trigger the event of deterioration that is used for some plastics the process may be slowed down.

Conservation

The process of conservation and restoration of plastics requires an understanding of composition of the plastic and an appreciation for the possible methods of restoring plastics and their limitations, as well as an appreciation for the post-treatment preventive care of the object.

Cleaning

The process of cleaning plastics is done through the use of solvents or using modern technology after identifying the polymers that make up the composition of the plastic. Cleaning can still be done using water or solvents however, solvents run the risk of physically damaging the object.[17] A spot test can be performed if uncertain how the object will react to water or solvents.

Light cleaning on the object is possible, but if cleaning requires a heavy hand then the use of an Erbium: YAG Laser could assist in cleaning tougher scratches or abrasions.[18][19]

Scratch removal

Within the field of contemporary art, where the finish is part of the artists intent the removal of scratches plays a far greater role than it would with social-historical artifacts, as such conservators have undertaken, and scientifically investigated, a variety of methods of scratch removal.[20]

Filling

Fillings are used if the object has suffered considerable damage. The process of filling depends on the objects chemical composition consisting of- refractive indexes, transparency, low viscosity, and its compatibility with the rest of the object.[19]

Current conservation of plastics resources
gollark: Okay, fine, not all the hair, just the mean hair.
gollark: QED.
gollark: Set all the hair on fire.
gollark: If you simply never shave, you can save significant time.
gollark: https://www.youtube.com/watch?v=R3HUuf6LGQE

References
  1. "Care and Identification of Objects Made from Plastic" (PDF). Conserve O Gram. 2010 – via National Park Service.
  2. Thompson, Richard (2009). "Our Plastic Age". Philosophical Transactions of the Royal Society B: Biological Sciences. 364 (1526): 1973–1976. doi:10.1098/rstb.2009.0054. PMC 2874019. PMID 19528049.
  3. "What You Can Do to Keep Plastic out of the Ocean | response.restoration.noaa.gov". response.restoration.noaa.gov. Retrieved 2018-04-07.
  4. Madden, Odile (Spring 2014). "Preserving Plastics: An Evolving Material, a Maturing Profession spring 2014. Conservation of plastics" (PDF). Conservation Perspectives the GCI Newsletter: 4–9 – via The Getty Conservation Institute.
  5. França de Sá, Susana; da Cruz, Sara Marques; Callapez, Maria Elvira; Carvalho, Vânia (13 May 2020). "Plastics that made history - the contribution of conservation science for the history of the Portuguese Plastics Industry". Conservar Património. doi:10.14568/cp2019017.
  6. Williams, Scott (2002). "Care of Plastics: Malignant Plastics". WAAC Newsletter. 24 – via COOL Databadse.
  7. França de Sá, Susana; da Cruz, Sara Marques; Callapez, Maria Elvira; Carvalho, Vânia (13 May 2020). "Plastics that made history - the contribution of conservation science for the history of the Portuguese Plastics Industry". Conservar Património. doi:10.14568/cp2019017.
  8. França de Sá, Susana; da Cruz, Sara Marques; Callapez, Maria Elvira; Carvalho, Vânia (13 May 2020). "Plastics that made history - the contribution of conservation science for the history of the Portuguese Plastics Industry". Conservar Património. doi:10.14568/cp2019017.
  9. "A - Z of plastics materials | Museum of Design in Plastics, MoDiP". www.modip.ac.uk. Archived from the original on 2018-03-25. Retrieved 2018-04-08.
  10. "Preserving Plastics: An Evolving Material a Maturing Profession (Feature)". www.getty.edu. Retrieved 2018-03-31.
  11. Staff, Creative Mechanisms. "Everything You Need To Know About PVC Plastic". Retrieved 2018-04-04.
  12. "Identification of plastics by looking, touching and smelling". Blog. Retrieved 2018-04-08.
  13. "Physical and Chemical processes leading to deterioration of original properties of plastic" (PDF). Processes Leading to the Deterioration of Plastics. 2012 – via POPART.
  14. Singh, Balijit (2007). "Mechanistic Implications of Plastic Degradation". Polymer Degradation and Stability. 93 (3): 561–584. doi:10.1016/j.polymdegradstab.2007.11.008.
  15. "Care of plastics | Museum of Design in Plastics, MoDiP". www.modip.ac.uk. Retrieved 2018-04-07.
  16. Shashoua, Yvonne (2014). "A Safe Space Storage Strategies for Plastics". Conservation Perspectives. 29 – via http://getty.edu/conservation/.
  17. Shashoua, Yvonne (2012). Studies in Active Conservation of Plastic Artefacts in Museums (PDF). POPART. p. 222.
  18. "Er:YAG laser - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2018-04-07.
  19. "The use of lasers in the conservation of museum objects made from plastics". Blog. Retrieved 2018-03-31.
  20. Laganà, Ana (2014). "Looking through Plastics: Investigating options for the treatment of scratches, abrasions, and losses in cast unsaturated polyester works of art". COM-CC 17th Triennial Conference Preprints – via http://www.getty.edu/conservation/our_projects/science/art_LA/paper_2014_icom_cc.pdf.

Further reading
  • Shashoua, J. Conservation of Plastics, London 2008.
  • Keneghan, B.; Egan, L.(Eds.) Plastics: Looking at the Future and Learning from the Past, London 2008.
  • Quye,A.;Williamson,C.(Eds.) Plastics: Collecting and Conserving, Edinburgh 1999.
  • Shashoua, Y. & Ward, C. (1995) "Plastics: Modern Resins with Ageing Problems" SSCR Resins: Ancient and Modern, pp. 33–37.
  • Shashoua, Y. (1996) "A Passive Approach to the Conservation of Polyvinyl Chloride" in ICOM-Modern Materials Working Group: 961-966.
  • Winsor, P. (1999) "Conservation of Plastics Collections", MGC Fact Sheets: September 1999. Museums and Galleries Commission: London.
  • Young, L. & Young, A (2001) "The Preservation, Storage and Display of Spacesuits", Collections Care Report Number 5, Smithsonian National Air and Space Museum: Washington, DC.
  • Blank, S. (1990) "An Introduction to Plastics and Rubbers in Collections", Studies in Conservation 35 (1990): 53-63.
  • Martuscelli, E. 'The chemistry of degradation and conservation of plastic artefacts', Florence 2010.
  • Martuscelli, E. 'Degradation and preservation of artefacts in synthetic plastics', Florence 2012.
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