question: What makes certain plastics safe to cook with (ex. sou vide) and not react chemically with food?
comment: Theorically, such plastics are designed to not give any sort of problem : manufacturers choose the right polymers mixed with the right additives to resist at the cooking temperature. The fact is - additives are relatively small molecules and ARE going to leech under the effect of heat, but as any existing substance, there is a certain daily dose wich is considered to not harm if you ingest it. Safe cooking plastics just pass an exam that ensure consumers that they will not surpass such dose. The proper base polymer is not usually a problem (except for very low quality products) , as it will not undergo any particular change at cooking temperature , unlike additives, wich are necessary to give the final product its technological (rigidity/flexibility) and estethic properties (for example, trasparent PET bottles would be opaque and white without additives : would consumers drink water from them?). Additives-free plastics are so considered to be the best choice nowadays, especially those made of polyethylene as they won't release any molecule into your food. However, keep in mind that there are always ongoing studies so don't be surprised if in the future other theories show up. Until 80's pacifiers and feeding bottles were made of polycarbonate wich released bisphenol A, today considered an endocrine distruptor.
passages: Note that the "food safe" symbol doesn't guarantee food safety under all conditions. The composition of materials contacting foodstuffs aren't the only factor controlling carcinogen migration into foodstuffs, there are other factors that can have a significant role in food safety. Examples include: the temperature of food products, the fat content of the food products and total time of contact with a surface. The safety of foam food containers is currently debated and is a good example of all three of these factors at play. Polystyrene may melt when in contact with hot or fatty foods and may pose a safety risk. In the United States, materials in contact with food may not contain more than 1% polystyrene by weight (0.5% for fatty foods).
   The use of unmarked plastics for microwave cooking raises the issue of plasticizers leaching into the food, or the plastics chemically reacting to microwave energy, with by-products leaching into the food, suggesting that even plastic containers marked "microwavable" may still leach plastic by-products into the food.
  
  The plasticizers which received the most attention are bisphenol A (BPA) and phthalates, although it is unclear whether other plastic components present a toxicity risk. Other issues include melting and flammability. An alleged issue of release of dioxins into food has been dismissed as an intentional red herring distraction from actual safety issues.
   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.
   While PTFE is stable and nontoxic at lower temperatures, it begins to deteriorate after the temperature of cookware reaches about , and decomposes above . The degradation by-products can be lethal to birds, and can cause flu-like symptoms in humans—see polymer fume fever. Meat is usually fried between , and most oils start to smoke before a temperature of is reached, but there are at least two cooking oils (refined safflower oil at and avocado oil at ) that have a higher smoke point.
  
  Section::::Ecotoxicity.
   Specific measures for materials and articles such as ceramics, regenerated cellulose, plastics, gaskets and active and intelligent materials, and substances such as vinyl chloride, N-nitrosamines and N-nitrostable substances in rubber, and epoxy derivatives, exist.
  
  EU No 10/2011 is applicable regulation for all the Food contact material or Article made up of Plastics.
  
  Section::::Legislation.:United States.
  
  The U.S. Food and Drug Administration (FDA) considers three different types of food additives:
  
  BULLET::::- Direct food additives - components added directly to the food
   BULLET::::2. The container material shall not potentially become a source of toxic contamination through usage (degeneration). This is assured by estimating and regulating the "migration limits" of the material. In EU regulation, the overall migration is limited to 10 mg of substances/dm² of the potential contact surface. The specific migration for various materials would be different for different temperature levels (of food as well as storage) and for different food items depending on variables such as pH of the food stuff. The toxicity considerations of a specific material may include the carcinogenity of the substance. The regulations governing these aspects may vary in different nations.
   PHCs are used in a vast array of manufactured products, from wood treatments, to cookware coatings, to non-stick, waterproof, and fire-resistant coatings, cosmetics, medicine, electronic fluids, food containers and wrappings, in everything from furniture and furnishings, automobiles, airplanes, plastics, clothing and cloth, surgery, insulation, adhesives, paints, sealants, lubricating oils, polyurethane foams, cancer therapy and medical imaging. They are also heavily used in pest control.
  
  Section::::Safety.
  
  PHCs include notoriously dangerous substances, including Agent Orange, DDT, and other pesticides. Many non-pesticide PHCs have the same safety issues as pesticides.
  
  Section::::Types.
   BASF was the world's largest chemical producer for the ninth year in a row.
  
  Trade associations which represent the industry in the US include the American Chemistry Council.
  
  Section::::Plastics industry.:Industry standards.
  
  Many of the properties of plastics are determined by standards specified by ISO, such as:
  
  BULLET::::- ISO 306 – Thermoplastics
  
  Many of the properties of plastics are determined by the UL Standards, tests specified by Underwriters Laboratories (UL), such as:
  
  BULLET::::- Flammability – UL94
  
  BULLET::::- High voltage arc tracking rate – UL746A
  
  BULLET::::- Comparative Tracking Index
  
  Section::::Additives.
   Whether polystyrene can be microwaved with food is controversial. Some containers may be safely used in a microwave, but only if labelled as such. Some sources suggest that foods containing carotene (vitamin A) or cooking oils must be avoided.
  
  Because of the pervasive use of polystyrene, these serious health related issues remain topical.
  
  Section::::Safety.:Fire hazards.
   Tin is corrosion resistant, but acidic food like fruits and vegetables can corrode the tin layer. Nausea, vomiting, and diarrhea have been reported after ingesting canned food containing 200 mg/kg of tin. A 2002 study showed that 99.5% of 1200 tested cans contained below the UK regulatory limit of 200 mg/kg of tin, an improvement over most previous studies largely attributed to the increased use of fully lacquered cans for acidic foods, and concluded that the results do not raise any long term food safety concerns for consumers. The two non-compliant products were voluntarily recalled.
   Consumer groups recommend that people wishing to lower their exposure to bisphenol A avoid canned food and polycarbonate plastic containers (which shares resin identification code 7 with many other plastics) unless the packaging indicates the plastic is bisphenol A-free. The National Toxicology Panel recommends avoiding microwaving food in plastic containers, putting plastics in the dishwasher, or using harsh detergents on plastics, to avoid leaching.
  
  Section::::Factors in the physical environment.:Aromatic Amines.
   BULLET::::- They are bad conductors of electricity.
  
  Section::::Disadvantages and limitations.
  
  BULLET::::- Plastics may be degraded under the action of direct sunlight which reduces their mechanical strength.
  
  BULLET::::- Many plastics are flammable unless treated.
  
  BULLET::::- High embodied energy content
  
  BULLET::::- Low modulus of elasticity: makes them unsuitable for load-bearing applications.
  
  BULLET::::- Thermoplastics are subject to creep and soften at moderate temperatures.
  
  BULLET::::- Thermal expansion for most plastics is high: adequate thermal movement has to be allowed in detailing.
  
  BULLET::::- Many types of plastics are not biodegradable thus cause pollution when they accumulate.
  
  Section::::Products.
   During contact with the food, molecules can migrate from the food contact material to the food, for example via blooming. Because of this, in many countries regulations are made to ensure food safety.
  
  Section::::Food safe symbol.
   Plastics can also be classified by: their various physical properties, such as: hardness, density, tensile strength, resistance to heat and glass transition temperature, and by their chemical properties, such as the organic chemistry of the polymer and its resistance and reaction to various chemical products and processes, such as: organic solvents, oxidation, and ionizing radiation. In particular, most plastics will melt upon heating to a few hundred degrees celsius.
   Food safety depends on the safe preparation, handling, and storage of food. Food spoilage bacteria proliferate in the "Danger zone" temperature range from , food therefore should not be stored in this temperature range. Washing of hands and surfaces, especially when handling different meats, and keeping raw food separate from cooked food to avoid cross-contamination, are good practices in food preparation. Foods prepared on plastic cutting boards may be less likely to harbor bacteria than wooden ones. Washing and disinfecting cutting boards, especially after use with raw meat, poultry, or seafood, reduces the risk of contamination.
   For example, aluminum which is stamped or forged exhibits plasticity in this sense, but is not plastic in the common sense. By contrast, some plastics will, in their finished forms, break before deforming and therefore are not "plastic" in the technical sense.
  
  Section::::Structure.
  
  Most plastics contain organic polymers. The vast majority of these polymers are formed from "chains of carbon atoms", 'pure' or with the addition of: oxygen, nitrogen, or sulfur. The chains comprise many repeat units, formed from monomers. Each polymer chain will have several thousand repeating units.
   Most common plastics contain chlorinated compounds and plasticizers, which can migrate out and harm objects. Polyethylene and polyester are considered archival plastics because they do not offgas harmful chemicals, but they can produce static electricity in a low RH, so they should be avoided around friable objects.
  
  BULLET::::- Polyester film, or Mylar, is a good tool for paper preservation and can act as a vapor barrier.
   In recent years, manufacturers have been working on developing more sustainable alternatives to traditional plastic products. Amongst them are plates and cutlery made from bamboo and wood (mostly birch). Throughout the entire life cycle of wood products, there are far fewer environmental repercussions than with traditional plastics or so called "bioplastics" like PLA. The production process is free of chemicals and the products decompose usually in the matter of only a few months. Currently wood and bamboo products are more costly than traditional plastics and not as widely available, which makes it challenging for some restaurants to switch.
  
  Section::::Materials.:Alternative materials.
   BULLET::::- Plastic packaging being used is usually non-biodegradable due to possible interactions with the food. Also, biodegradable polymers often require special composting conditions to properly degrade. Normal sealed landfill conditions do not promote biodegradation. Biodegradable plastics includes biodegradable films and coatings synthesized from organic materials and microbial polymers. Some package materials are edible. For example, pharmaceuticals are sometimes in capsules made of gelatin, starch, potato or other materials. Newer bioplastics, films and products are being developed.
   Plastics, along with metal, glass, and paper or paperboard, are major materials used in food packaging. The types of plastics used in food packaging include polyolefins, polyesters, polyethylene terephthalate, polycarbonate, polyethylene naphthalate, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyamide, ethylene vinyl alcohol, and laminates and co-extrusions. 
  
  Section::::Food use.:Health concern.
   Bisphenol-A (BPA) is a controversial chemical compound present in commercially available tin can plastic linings and transferred to canned food. The inside of the can is coated with an epoxy coating, in an attempt to prevent food or beverage from coming into contact with the metal. The longer food is in a can, and the warmer and more acidic it is, the more BPA leaches into it. In September 2010, Canada became the first country to declare BPA a toxic substance. In the European Union and Canada, BPA use is banned in baby bottles.
   Evidence of tin impurities can be indicated by color, as in the case of pears, but lack of color change does not guarantee that a food is not tainted with tin.
  
  Section::::Health issues.:Bisphenol-A.
   Polycarbonate is susceptible to alkali hydrolysis, the reaction simply depolymerising the material. Polyesters are prone to degrade when treated with strong acids, and in all these cases, care must be taken to dry the raw materials for processing at high temperatures to prevent the problem occurring.
  
  Section::::Examples.:UV degradation.
   UV-C radiation is able to break down chemical bonds. This leads to rapid aging of plastics, insulation, gaskets, and other materials. Note that plastics sold to be "UV-resistant" are tested only for UV-B, as UV-C doesn't normally reach the surface of the Earth. When UV is used near plastic, rubber, or insulation, care should be taken to shield these items; metal tape or aluminum foil will suffice.
   Additives added to plastics during manufacturing may leach into the environment after the plastic item is discarded; additives in microplastics in the ocean leach into ocean water and in plastics in landfills may escape and leach into the soil and then into groundwater.
  
  Section::::Types.
  