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Do plastics decompose back into constituent elements or are they incapable of biological decomposition?

The biodegradability of plastics is an extremely intriguing area of research that is currently being investigated by many laboratories in academic and industrial settings around the world.

When considering if plastic is “biodegradable,” we must first take into account what is meant by the word “plastic.”   Two types of plastic are commonly used in consumer goods: thermoplastics and thermosetting polymers.

Thermoplastics are plastics that melt at elevated temperatures and are then formed into usable shapes; examples include grocery bags, plastic bottles, and other consumer goods.  Typically, thermoplastics are composed of very long chains of carbon atoms and incorporate different trace chemicals that impart certain properties into the polymer.  These long carbon chains are difficult for microbes to eat as an energy source because carbon bonds are very strong atomic bonds.  However, thermoplastics can degrade in the presence of UV light, such as sunlight, or under certain chemical conditions.  Under “natural” conditions, thermoplastics will take a long time to degrade.  Despite the resistance to degradation, thermoplastics are easily recycled.

Thermoset plastics are different in that the polymer is formed from a reaction between two different types of molecules, creating long molecular chains.  Common examples include foam padding and insulation made from polyurethanes.  These types of plastics cannot be heated and reformed as they are “set” after the reaction takes place.  The polymer chains are comprised of various carbonyl bonds that are much easier for microbes to use as an energy source than carbon chains.  Eventually, the polymers can degrade into their initial components, such as alcohols, amines, and carboxylic acids.  That said, the ability of the thermoset polymer to biodegrade will depend greatly on the environmental conditions, trace constituents, and polymer composition.

I hope this answer helps. Thanks for your question!

Professor Plastic

what plastics /rubbers besides medical grade silicone are acceptable. currently used for mouth pieces

Thank you for your inquiry.  To find out what kind of plastic is used in a specific mouth guard or dental work, you may want to call the manufacturer or consult with your prescribing dentist or doctor.  A mouth guard is generally for sports/athletic protection or serves a medical/dental purpose, such as to prevent teeth grinding.  Some mouth guards, such as those used for protection in sports events, are made from a plastic called EVA (ethyl vinyl Acetate).  Soft “night guards” could be made from silicone or other plastics.  ASTM classifies athletic/sports mouth guards in three categories; this standard may provide additional useful information to you.  See ASTM F697-00, standard practice for care and use of athletic mouth protectors.

Thanks for your question!

Professor Plastic

CAN, NATURAL FIBERS AND A COMBINATION COMMINGLE 1-7 UNWASH POST CONSUME PLASTICS, BE COMBINE TO MAKE A RESIN?

Thanks for your inquiry.  A resin has a very specific technical meaning: any natural or synthetic organic compound consisting of a noncrystalline (amorphous) solid or viscous liquid substance or mixture.  Natural resins include sap from pine and fir trees.  Natural resins have a long history of use to make things such as turpentine, shellac, and lacquer.  The reason that plastics are called “resins” is historical: some of the first plastics invented were intended to replace or perform better than natural resins, so the name “resin” stuck with plastics.

Plastics such as polypropylene, polyethylene, and polystyrene, to name a few, are sometimes referred to as plastic resins.  A mixture of different kinds of plastics is generally not called a “resin.”

That said, sometimes various plastic resins are combined to make a different compound.  Thermoplastics – that is, plastics that are defined in part by being able to be heated and reformed again – can sometimes be recycled together.

It also can be possible to introduce other things into a plastic resin to make it perform differently.  For example, “carbon fiber reinforced plastic” is actually a kind of plastic into which carbon fibers have been placed, giving the finished material greater strength.  Some companies that make decking from recycled plastics also add wood fiber, making what is called a composite deck.  In other cases, plastics are added to a natural fiber; some cotton jeans, for example, have a little bit of Spandex (a kind of plastic) added to the cotton fibers to add stretch.

Thanks for your question!

Professor Plastic