Polymers and Plastic Products

Plastics are one of the more “magical” substances known to humanity. Polymers are responsible for the magic. But to most people a polymer is something they once heard about in high-school chemistry. Yet despite the magic products created from plastic, much discussion remains about environmental issues of plastics caused by these mysterious polymers.

We’ll try to uncover the basics of polymers in this introduction to polymers.

Polymers can come from nature such as rubber and cellulose. Rubber is grown from rubber trees, and cellulose is part of all plant cell walls[1]. It is what gives trees, stems, and fibrous parts such as cotton their stiff and rigid structure. Wool, silk, wood, and leather are examples of other natural polymers.

A polymer, as the name suggests, is made up of poly – “many” “monomers.” A monomer is a molecule that has the ability to bond with many others in a chain-like form. These chains can be made of thousands of monomers[2].

Synthetic polymers include a large and diverse group generally known in plastics. While these are easily and cheaply created from petroleum, other organic plastics are also under development as well. Petroleum and coal, of course, are plant-based as well, but they have been turned to rigid rock and liquid as well as gas states over millions of years of compression and pressure.

Using synthetic polymers has developed since the early twentieth century. Read more on The History of (Plastic) Polymers. Chemists have learned to engineer useful characteristics from polymers such as strength, stiffness, density, heat resistance, and even electrical conductivity[3]. They also resist corrosion and chemicals and have high strength-to-weight ratios. They can be colored, transparent, and resistant to water and generally have low toxicity.

These characteristics of plastic and the variability of the polymer construction allows many types of plastics to be made creating physical characteristics desired.   It is the lowly polymer that is manipulated to create this flexible miracle material.

The simplest polymer is one that is well known to us today: Polyethylene. It is made from very long, random-length chains of carbon. Carbon (C) combines with two hydrogen (H) atoms and at least one other Carbon to form a short chain. This is called ethylene. The carbon has the propensity to combine with a large number of other carbon units to form a chain of carbon and hydrogen. This is called “poly” ethylene — many ethylene units.

You now magically have the transparent plastic bag.

More complex polymers exist as well. Identical monomers are called homopolymers. Others exist, too, such as block copolymers, alternating copolymers, and random copolymers indicating to the chemist the number of other types of monomeric units. The chains can also be different types such as branched homopolymers, graft copolymers, and cross-linked homopolymers[4]. Our purpose here is not to explain the chemistry, but simply illustrate the variation of polymer chain types, each creating different plastic characteristics, useful to product development. See much more here.

Add to the polymer, many other chemical compositions, and we have literally a “chemistry set” of thousands of possibilities. The commercial usefulness, of course, has to do with the characteristics of plastics and what kind of plastic product that need to be produced. When being produced, plastic is between a solid and liquid that is hardened by adding various hardeners which act as catalysts that causes the hardening.

So a product can be formed by pouring it into a mold, blowing it into a mold, or pushing it through a shaped opening (called extrusion). Other methods are also used, which we will save for another time. The polymer with the hardener added becomes rigid before it is removed from the mold (called a tool to plastic manufacturers).

The polymer “soup” will have the characteristics the chemist built into the formula. If you make a bowl, it could be rigid or have flexibility depending on the use of the product. It could be clear or be tinted with color, transparent, or solid color.

The many types of plastic also have different characteristics of performance. Many are highly durable, meaning they can take a mechanical beating, or they will not readily break down in nature. This advantage on one hand is a problem for the environment when improperly disposed of on the other.

Disposable products, as opposed to durable ones that are kept for many years, can be problems in nature if not properly recycled. For this reason scientists have begun to look for natural polymers that will break down into natural elements in nature instead of remain as plastic for dozens or hundreds of years.

One method is to simply strip polymers from plants and chemically combine them into polymers used in plastic. Using wood, straw, or cork or other biomass components such as starch, fibers, sugars, and cellulose is one option. A second method is to convert these to new compounds through chemistry. Sugar from plants can be processed into plant oil, then chemically converted into polymers. Another method is for bacteria to be developed specifically to produce polymers that will, in nature, break down into natural elements. An example is that biocellulose and polythioesters can be produced by recombinant or wild-type micro-organisms in fermentation processes using carbohydrates from plants[5].

Of course, reality is that doing some of these things in the lab is much easier than producing substantial quantities in a manufacturing environment. These processes must also be perfected at a cost that can be competitive with existing materials. The consumer will probably pay a small premium for biomass products, assuming that they fill expectations for quality and durability.

Inexpensive polyethylene shopping bags tend to disintegrate now. You may have picked up an old bag with the contents falling right out of the bottom. But while the chains in the polymers may break down, losing strength, they remain plastic, just smaller shreds[6]. Burning can destroy plastic polymers but most plastics “ever made, still exist.” Most plastics just fall into ever-smaller fragments when exposed to sunlight and natural elements. When buying a kitchen bowl, is it the expectation that it will disintegrate in ten years? A metal bowl will last for thousands of years until it is attacked by rust due to moisture. In soil, it will eventually return to nature millennia from now. Ceramic bowls may break, but they never disintegrate after firing. Ironically this is similar to plastic, except plastic can pass into nature and is eaten by wildlife when not properly recycled or stored.

So one additional problem with polymers is the breakdown when in certain conditions. Some new plastics under development are bio-compostable. This means if in a compost pile the polymers will break or combine into natural substances if mixed with soil and other nutrient-available materials where bacteria can act on the polymers and break them down into more “digestible” materials. Dr. P.J. Barham of the University of Bristol elaborates on this idea, “The requirements for such materials are that they may be processed through the melt state, that they are impervious to water, and that they retain their integrity during normal use but readily degrade in a biologically rich environment.[7]” But maintaining these attributes, while building polymers that will break down based on disposal or in natural surroundings, is a way off.

Polymers are wonderful building blocks to cheaply build today’s modern products. Eventually science will be able to build even better ones that will do what we want when we want them to turn back to nature.

New ideas abound, and large investments are being made to explore several optimistic options. While we have figured out how to recycle and biodegrade many natural products, the polymer, with all its advantages, tends to want to stay how we created it. We hope that science will unlock the rest of the secrets of the magic polymer.

Microdyne is already working with bio-based resign suppliers and customers to switch to new more eco-friendly products. We continually look for better ways produce these wonderful products using better products for the environment.

 

 

[1] Merriam-Webster, https://www.merriam-webster.com/dictionary/cellulose

[2] Polymers and Monomers, Materials World, https://www.materialsworldmodules.org/resources/polimarization/2-polymers+monomers.html

[3] Chem1, General Chemistry Virtual Textbook, http://www.chem1.com/acad/webtext/states/polymers.html

[4] Chem1, General Chemistry Virtual Textbook, http://www.chem1.com/acad/webtext/states/polymers.html

[5] The Plant Journal, Volume 54, Issue 4, http://onlinelibrary.wiley.com/doi/10.1111/j.1365-313X.2008.03431.x/pdf

[6] Chemistry, LebreTexts, Recycling and Disposal of Polymers, https://chem.libretexts.org/Core/Organic_Chemistry/Polymers/Recycling_and_Disposal_of_Polymers

[7] Biodegradable polymers,  By Dr P. J. Barham, University of Bristol, http://www.lotfi.net/recycle/plastic.html#1n3

Related posts

Blow Molding

  Blow molding typically refers to plastic blow molding. This is the process of “blowing” air into a plastic resin like a balloon that is...