The term “plastics” includes materials composed of various elements such as carbon, hydrogen, oxygen, nitrogen, chlorine, and sulfur. The manufactured or synthetic plastics are often designed to mimic the properties of natural materials. Plastics, also called polymers, are produced by the conversion of natural products or by the synthesis from primary chemicals generally coming from oil, natural gas, or coal. Source: https://plastics.americanchemistry.com/How-Plastics-Are-Made/
Crude oil is a complex mixture of thousands of compounds. To become useful, it must be processed.
The two major processes used to produce plastics are called polymerisation and polycondensation, and they both require specific catalysts. In a polymerisation reactor, monomers like ethylene and propylene are linked together to form long polymers chains. Each polymer has its own properties, structure and size depending on the various types of basic monomers used. http://www.plasticseurope.org
Three plastics have been shown to leach toxic chemicals when heated, worn or put under pressure: polycarbonate, which leaches bisphenol A; polystyrene, which leaches styrene; and PVC, or polyvinyl chloride, which break down into vinyl chloride and sometimes contains phthalates that can leach.
Toxic Plastic Numbers #3,4,5,6,7
“Resin ID Codes.” Each number (1 through 6) signifies a specific type of plastic and usually appears inside a small triangle (often formed by three adjoining arrows) imprinted on the bottom of a plastic item. The number “7” is used to represent a group of other plastics or combinations of plastics.
High Density Polyethylene (HDPE) is the most widely used resin for plastic bottles. This material is economical, impact resistant, and provides a good moisture barrier. HDPE is compatible with a wide range of products including acids and caustics but is not compatible with solvents. It is supplied in FDA-approved food grade. HDPE is naturally translucent and flexible. The addition of color will make HDPE opaque, but not glossy. HDPE lends itself to silk screen decoration. While HDPE provides good protection at below freezing temperatures, it cannot be used with products filled above 160 °F (71 °C) or products requiring a hermetic (vacuum) seal.
Low Density Polyethylene (LDPE) is similar to HDPE in composition. It is less rigid and generally less chemically resistant than HDPE, but is more translucent. LDPE is used primarily for squeeze applications. LDPE is significantly more expensive than HDPE.
Polyethylene Terephthalate (PET, PETE or polyester) is commonly used for carbonated beverage, water bottles and many food products. PET provides very good alcohol and essential oil barrier properties, generally good chemical resistance (although acetones and ketones will attack PET) and a high degree of impact resistance and tensile strength. The orienting process serves to improve gas and moisture barrier properties and impact strength. This material does not provide resistance to very high temperature applications—max. temp. 200 °F (93 °C).
Polyvinyl Chloride (PVC) is naturally clear, has extremely good resistance to oils, and has very low oxygen transmission. It provides an excellent barrier to most gases and its drop impact resistance is also very good. This material is chemically resistant, but it is vulnerable to some solvents. PVC has poor resistance to high temperatures and will distort at 160 °F (71 °C), making it incompatible with hot-filled products. It has attained notoriety in recent years due to potential health risks.
Polycarbonate (PC) is a clear plastic used to make water and milk bottles. 5 gallon water bottles are the most common examples of PC bottles.
Polypropylene (PP) is used primarily for jars and closures and provides a rigid package with excellent moisture barrier. One major advantage of polypropylene is its stability at high temperatures, up to 220 °F (104 °C). Polypropylene is autoclavable and offers the potential for steam sterilization. The compatibility of PP with high filling temperatures is responsible for its use with hot fill products. PP has excellent chemical resistance, but provides poor impact resistance in cold temperatures.
Polystyrene (PS) offers excellent clarity and stiffness at an economical cost. It is commonly used with dry products including vitamins, petroleum jellies, and spices. Styrene does not provide good barrier properties, and exhibits poor impact resistance.
Fluorine Treated (HDPE) bottles are exposed to fluorine gas in a secondary operation, are similar in appearance to HDPE and have exceptional barrier properties to hydrocarbons and aromatic solvents. Fluorine treated bottles are excellent for use with insecticides, pesticides, herbicides, photographic chemicals, agricultural chemicals, household and industrial cleaners, electronic chemicals, medical cleaners and solvents, citrus products, d-limonene, flavors, fragrances, essential oils, surfactants, polishes, additives, graffiti cleaning products, pre-emergents, stone and tile care products, waxes, paint thinner, gasoline, biodiesel, xylene, acetone, kerosene and more.
For non-bottle applications, fluorination of plastic can provide compliance with state and federal regulations. An example would be fluorination plastic fuel tanks used for lawn and garden equipment, automobiles, etc.
Post Consumer Resin (PCR) is a blend of reclaimed natural HDPE (primarily from milk and water containers) and virgin resin. The recycled material is cleaned, ground and recompounded into uniform pellets along with prime virgin material especially designed to build up environmental stress crack resistance. PCR has no odor but exhibits a slight yellow tint in its natural state. This tint can be hidden by the addition of color. PCR is easily processed and inexpensive. However, it cannot come into direct contact with food or pharmaceutical products. PCR can be produced in a variety of recycled content percentages up to 100%.
K-Resin (SBC) is ideally suited to a wide variety of packaging applications by virtue of its sparkling clarity, high gloss, and impact resistance. K-Resin, a styrene derivative, is easily processed on polyethylene equipment. It is suitable for packaging many products but is specifically incompatible with fats and unsaturated oils or solvents. This material is frequently used for display and point-of-purchase packaging.
Bioplastic - polymer structures based on processed biological materials rather than petrochemicals. Bioplastics are commonly made from renewable sources like starch, vegetable oil, and less commonly, chicken feathers. The idea behind bioplastic is to create a plastic that has the ability to biodegrade.  https://en.wikipedia.org/wiki/Plastic_bottle