question: Why does some plastic turn yellow with age?
comment: Most plastics are flammable. However this is an issue when making devices that needs to meet fire codes. For example you do not want the enclosure of electrical components that might short circuit to be flammable as it would spread the fire. So in order to make plastic safe for use in those applications manufacturers add bromide compounds to the plastic. These compounds are fire retardants. This is kind of like adding fire extinguisher powder to your plastic. However the issue is that these bromide compounds will slowly break down over time. Especially if exposed to UV radiation. And the resulting compounds have this nasty yellow-brown color to them. It is possible to oxidize these compounds using oxidizing agents like hydrogen peroxide or ozone. This process is often called the retrobright process after a commercial product sold for this purpose. However people are also using simple hair bleaching agents to achieve the same results.
passages: Yellowing is caused by both bromine and exposure to ultraviolet (UV) light. Many of the ABS plastics used in consumer electronics devices are typically "brominated"—combined with bromine as a fire retardant—to meet fire safety standards. The method was first discovered in 2007 in a German retrocomputing forum, before spreading to an English blog where it was further detailed.. The process has been continually refined since.
   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 and near-infared spectroscopy along with mass spectrometry. Other forms of identification include elemental analysis, thermal analysis to decipher the composition of plastics. Once the composition is found it is best to determine if the plastic in the collection will be considered Malignant or not.
   Some polymers may also decompose into the monomers or other toxic substances when heated. In 2011, it was reported that "almost all plastic products" sampled released chemicals with estrogenic activity, although the researchers identified plastics which did not leach chemicals with estrogenic activity.
   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. 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.
  
  Section::::Identifying plastics.
   There is still some debate over the long-term effectiveness of this technique. Some have discovered the yellowing reappears, and there is discussion of factors that may result in this happening. There are also some concerns that the process weakens the plastic.
  
  Section::::Composition.
  
  Retr0bright consists of hydrogen peroxide, a small amount of the "active oxygen" laundry booster TAED as a catalyst, and a UV lamp.
  
  The optimum mixture and conditions for reversing yellowing of plastics:
  
  BULLET::::- Hydrogen peroxide solution. 12% or 6% work the same, and even 3% has been used with success.
   BULLET::::- 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
  
  Section::::Effects of deterioration table.
  
  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.
  
  Cellulose Acetate butyrate and Cellulose butyrate will produce butyric acid which has a "vomit odor".
   Poly(Vinyl 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.
  
  Section::::Preventative care.
  
  Section::::Preventative care.:Handling.
  
  Safety gloves such as those made of Nitrile can help prevent toxins entering the skin when handling plastic objects. 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.
  
  Section::::Preventative care.:Storage environment.
   BULLET::::- 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. A test is conducted to see if the objects has been exposed by taking small samples and analyzed using an FTIR.
  
  BULLET::::- Catalytic Degradation Mainly focuses on plastic waste polymers as they are transformed into hydrocarbons
  
  BULLET::::- 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.
   Plasticizers are, by mass, often the most abundant additives. These oily but nonvolatile compounds are blended in to plastics to improve rheology, as many organic polymers are otherwise too rigid for particular applications.
  
  Section::::Additives.:Colorants.
  
  Colorants are another common additive, though their weight contribution is small.
  
  Section::::Toxicity.
   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.
   A more common and related problem is "swelling", where small molecules infiltrate the structure, reducing strength and stiffness and causing a volume change. Conversely, many polymers (notably flexible vinyl) are intentionally swelled with plasticizers, which can be leached out of the structure, causing brittleness or other undesirable changes.
   BULLET::::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. Chemical reactions are also caused by objects coming into contact with water and oxygen.
   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.
  
  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.
   PBB (Polybrominated biphenyls) are chemicals added to plastics used in computer monitors, televisions, textiles and plastics foams to make them more difficult to burn. Manufacturing of PBBs in the United States stopped in 1976, however because they do not degrade easily PBBs continue to be found in soil, water and air.
  
  Section::::Common environmental estrogens.:PCBs.
   Oxygen Impermeable bags are used as they absorb all the oxygen in the bag. With no oxygen to trigger the event of deterioration that is used for some plastics the process may be slowed down.
  
  Section::::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.
  
  Section::::Conservation.:Cleaning.
   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. Although deterioration will inevitably happen it is important to know the causes of it and be able to mitigate it.
  
  Section::::Deterioration.:Causes of deterioration.
   Crazing can take place in glassy polymers under environmental effects. It is troublesome because it requires a much lower stress state and sometimes it happens in a long delay, which means it's hard to detect and avoid. For example, the PMMA containers in daily use is quite resistive to humidity and temperature without any visible defects. But after they are machine-washed and then left in air for one or two days, they will shutter abruptly when wet with gin. During the process, the stress applied is negligible, but crazing is still found in the containers.
   Even with these methods, some UV radiation can still pass through the outer bulb of the lamp. This causes the aging process of some plastics used in the construction of luminaires to be accelerated, leaving them significantly discolored after only a few years' service. Polycarbonate suffers particularly from this problem, and it is not uncommon to see fairly new polycarbonate surfaces positioned near the lamp to have turned a dull, yellow color after only a short time. Certain polishes, such as Brasso, can be used to remove some of the yellowing, but usually only with limited success.
  
  Section::::Uses.
   Section::::Corrosion in nonmetals.:Corrosion of polymers.
  
  Polymer degradation involves several complex and often poorly understood physiochemical processes. These are strikingly different from the other processes discussed here, and so the term "corrosion" is only applied to them in a loose sense of the word. Because of their large molecular weight, very little entropy can be gained by mixing a given mass of polymer with another substance, making them generally quite difficult to dissolve. While dissolution is a problem in some polymer applications, it is relatively simple to design against.
   In the presence of UV light, oxidation of this polymer yields compounds such as ketones, phenols, o-phenoxybenzoic acid, benzyl alcohol and other unsaturated compounds. This has been suggested through kinetic and spectral studies. The yellow color formed after long exposure to sun can also be related to further oxidation of phenolic end group
  
  This product can be further oxidized to form smaller unsaturated compounds. This can proceed by two different pathways, the products formed depends on which mechanism takes place.
  
  BULLET::::- Pathway A
  
  BULLET::::- Pathway B
  
  Photo-oxidation reaction.
  
  Section::::Environmental impact.:Photo-aging reaction.
   Recent changes in plastic manufacturing, as a result of environmental concerns, towards biodegradable plastics, have a potentially negative effect upon the long term stability of such objects within museum collections.
  
  Section::::Identification and composition of plastics.
   BULLET::::- 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. 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.
  
  BULLET::::- 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.
   The ABS plastic used in the casing of some older SNES and Super Famicom consoles is particularly susceptible to oxidization with exposure to air, likely due to an incorrect mixture of the stabilizing or flame retarding additives. This, along with the particularly light color of the original plastic, causes affected consoles to quickly become yellow; if the sections of the casing came from different batches of plastic, a "two-tone" effect results.
  
  Section::::Technical specifications.:Game cartridge.
   Many plastics are considerably sensitive to atomic oxygen and ionizing radiation. Coatings resistant to atomic oxygen are a common protection method, especially for plastics. Silicone-based paints and coatings are frequently employed, due to their excellent resistance to radiation and atomic oxygen. However, the silicone durability is somewhat limited, as the surface exposed to atomic oxygen is converted to silica which is brittle and tends to crack.
  
  Section::::Solving corrosion.
   It is typically labelled on food packages as "color", "tartrazine", or "E102". In the United States, because of concerns about possible health problems related to intolerance to tartrazine, its presence must be declared on food and drug product labels.
  
  Another popular synthetic yellow coloring is Sunset Yellow FCF (also known as "'orange yellow S", "FD&C yellow 6" and "C.I. 15985") It is manufactured from aromatic hydrocarbons from petroleum. When added to foods sold in Europe, it is denoted by E number E110.
  
  Section::::Symbolism and associations.
  