Plastic materials have been created using many different kinds of matter over the years. Originally, resins were made from vegetable matter including cellulose from cotton, furfural from oat hulls, oil from seeds and various starch derivatives.  Bakelite (phenol formaldehyde resin), one of the first plastics made from synthetic components, was developed by Belgian born chemist Leo Baekeland in New York in 1907. Bakelite is made through an elimination reaction of phenol with formaldehyde. It was used for its electrical non-conductivity and heat-resistant properties in electrical insulators, radio and telephone casings. Because of its pleasing appearance, it was also used to make consumer products such as jewelry. Today, however, most plastics are made from petrochemicals including natural gas.

Polymer Synthesis

Plastics are organic materials that contain such elements as carbon (C), hydrogen (H), nitrogen (N) chlorine (Cl) and sulfur (S).  They are made from raw materials such as oil, natural gas and coal.  The first step in making plastics is the polymerization of the raw materials, resulting in a product called a monomer. Hydrocarbons are then heated in a “cracking phase.”  In this process, in the presence of a catalyst larger molecules are broken down into smaller ones such as ethylene (ethane) C2H4, propylene (propane) C3H6, butane C4H6 and other hydrocarbons.  The yield of ethylene produced is controlled by the cracking temperature and can be more than 30% at a temperature of 850°C.  Styrene and vinyl chloride can be produced in subsequent reactions.

The two main types of polymerization are addition and condensation reactions. These processes can occur in the gaseous, liquid and sometimes in the solid phase of the monomer. 

Condensation Reaction

In this type of polymerization, two molecules combine, causing the loss of a smaller molecule such as water, an alcohol or acid. In this type of reaction, monomer one and monomer two both have hydrogen (H) and hydroxyl groups (OH).  When they come together with a catalyst, one monomer loses a hydrogen atom while the other loses the hydroxyl group.  The hydrogen and the hydroxyl group combine together to make water (H2).  The electrons that remain form a covalent bond between the monomers, which form a long chain of copolymers.

The resultant monomers can then be bonded into chemical chains called polymers. Different polymers are created by chains of different monomers each with individual properties and characteristics.  The variability allows for plastics that can be shaped into products that meet application requirements such as heat tolerance, chemical resistance, strength, etc. 

Addition Reaction

In this type of polymerization, electrons with a double bond are rearranged within the monomer to form single bonds with other monomers.  The addition reaction below between an ethane molecule and a chlorine molecule shows the formation of a polymer.

 H               H                                            Cl    Cl

    \              /                                            │     │

        C  =  C              +          Cl – Cl          →     H ― C  ― C ― H

     /                \                                          │     │

  H                  H                                                  H    H  

 

Here the double bond between the carbon atoms becomes a single bond with chlorine atoms added to each end.  

Additives

Chemical additives can be mixed into the base polymer to improve certain characteristics. These include include antioxidants to protect the polymer from degradation from ozone or oxygen, flame retardants, antistatic additives, and lubricants for greater polymer flexibility. Additionally, plasticizers to improve flexibility, ultraviolet stabilizers to prevent degradation from the UV rays of the sun and pigments to add color are often included. Strong composites can be made by adding glass, carbon and other fiber to the resins.  Some compounded plastic materials can withstand strong acids, bases and alkalis, retard fire in home furnishings, contain lubricants for bearings and more.  

Questions? Comments?  Let me know in the comments section below. 

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14 responses to “Polymerization: How Plastic Materials are Made

  1. Are ultra violet stabilizers being added to much to some plastics and could they be reduced in certain plastics, so that the degradation period was reduced. If so which plastics and which commonly used products might it apply to

    1. Martin,
      Yours is an excellent question. UV stabilizers are added to many plastic parts across many industries. We would have no way of tracing which products utilize UV additives, or how many industries are involved, but I suspect a large percentage of outdoor products are involved. Product performance for the consumer vs. faster degradation is the conflict here. Also consider that if the product degrades quicker – it goes to landfill quicker, and gets replaced by another product sooner. Just another view.

  2. What is the danger of the use of polymers produced from wood & vegetable products for coating nutrients within vitamins & for making gel caps that contain nutrients?

    1. Interesting question…and one I don’t have an answer for – not knowing what goes into the coatings. I assume they have been tested and meet FDA guidelines however.

  3. Hello someone. Can I get a simple local sortable material for the making of plastic mold just for mold casting.

    1. Omav – Are you looking for metal material to build a mold with, or a plastic material to make parts with?

  4. Hello
    Am a new entrepreneur from bangalore , INDIA. we are having a new technology on plasticizers which are ecofriend and alternate to phthalates.
    Sir we want to meet you regarding this, please give me your mailid for further conversations

  5. Hello
    I am a student investigating the processes of plastic manufacture and recycling, what sort of waste products come from manufacturing raw plastic? Gases or other waste?
    Thank you

    1. Bailey – We don’t make plastic at Craftech, we machine it and use it in injection molding. I’m sure the waste products vary greatly, depending on the specific material. There are many dozens of materials, each with a different formulation and process. You might get a better answer from a plastic resin manufacturer. Good luck!

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