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Plastics are everywhere these days, from the parts of your computer to your clothing and everyday products. It is a material that can easily be manipulated into shape, may it be a shape of a bottle or a pen. They are made from oil, which is carbon-rich material. Plastics are composed of a carbon-containing compound called polymers.

Polymers are substances whose molecules have high molar masses and are composed of a large number of repeating units. There are both naturally occurring and synthetic polymers. Among naturally occurring polymers are proteins, starches, cellulose, and latex. Synthetic polymers are produced commercially on a very large scale and have a wide range of properties and uses. The materials commonly called plastics are all synthetic polymers.

Although not all, but most plastics are:

There are three classification of plastics: Natural, Synthetic, and Thermoplastic. This classification is considered the origin of the monomer from which part of the polymer production.

Natural - These are polymers whose monomers are derived from natural products with certain characteristics, for example, cellulose, casein and rubber. 

Source: http://blog.e2benterprise.com/wp-content/uploads/2014/02/erp-for-rubber-and-plastic-manufacturers.png

Synthetic - Those that originate in man-made, mainly petroleum products such as polyethylene bags products

Source: https://www.qualitylogoproducts.com/lib/different-types-of-plastic.htm

Thermoplastic - is a plastic that, at room temperature, is plastic or deformable, it becomes a liquid when heated and hardens to a glassy state when cooled sufficiently. Most thermoplastics are high molecular weight polymers, those with chains associated through weak Van der Waals forces (polyethylene); strong dipole-dipole interactions and hydrogen bonding; or even stacked aromatic rings (polystyrene). Thermoplastic polymers differ from thermoset polymers that after heated and molded form they can overheat and other objects, as in the case of thermosetting or thermoset, its shape after cooling does not change and the preferred fire.

Source: http://plasticchair.mobi/wp-content/uploads/2016/03/ghost-chair.jpg

In 1988, the Society of the Plastics Industry (SPI) introduced the Resin Identification Code (RIC) system for recyclers due to many communities implementing recycling programs to decrease the volume of waste in landfills.  The code was developed for recyclers while providing manufacturers a consistent, uniform system. The RIC is a system to help consumers and recyclers properly recycle and dispose of each different type based on its chemical makeup. In 2008, the SPI worked with ASTM international, a standards development organization that serves as an open forum for the development of international standards.

PETE - based containers sometimes absorb flavors and odor. They are commonly recycled.

HDPE products are very safe and are known not to leach any chemicals into food or drinks. Items from this type of plastic are commonly recycled.

PVC is not often recycled and can be harmful if ingested. PVC is used for all kinds of pipes and tiles, but it's most commonly found in plumbing pipes. This kind of plastic should not come in contact with food items.

LDPE is not commonly recycled, but it is recyclable in certain areas. It tends to be both durable and flexible. It also is not known to release harmful chemicals into objects in contact with it, making it a safe choice for food storage.

PP can be recycled but is not accepted for recycling as commonly as PETE or HDPE. This type of plastic is strong and can usually withstand higher temperatures.

PS can be recycled, but not efficiently; recycling it takes a lot of energy, which means that few places accept it.

Polycarbonate and Polylactide - these types of plastics are difficult to recycle. 

Sources:

http://science.howstuffworks.com/plastic.htm

http://scifun.chem.wisc.edu/chemweek/polymers/polymers.html

http://www.vicedomarti.com/en/information/characteristics-and-properties-of-plastic-id1609

https://www.plasticsindustry.org/AboutPlastics/content.cfm?ItemNumber=823

https://www.qualitylogoproducts.com/lib/different-types-of-plastic.htm

RIC system photos:

https://www.qualitylogoproducts.com/images/DifferentPlastics/SPI-Code-Header-01.jpg

https://www.qualitylogoproducts.com/images/DifferentPlastics/SPI-Code-Header-02.jpg

https://www.qualitylogoproducts.com/images/DifferentPlastics/SPI-Code-Header-03.jpg

https://www.qualitylogoproducts.com/images/DifferentPlastics/SPI-Code-Header-04.jpg

https://www.qualitylogoproducts.com/images/DifferentPlastics/SPI-Code-Header-05.jpg

https://www.qualitylogoproducts.com/images/DifferentPlastics/SPI-Code-Header-06.jpg