Although the terms are often used interchangeably, polymers and plastics are not always the same thing. Polymers can exist organically or be created synthetically, and consist of chains of joined individual molecules or monomers. Plastics are a type of polymer composed of chains of polymers which can be partially organic or fully synthetic.
Simply put, all plastics are polymers, but not all polymers are plastics. Below, we examine the composition, physical properties, and applications of polymers and plastics to provide a clear explanation of the differences between the two.
What are Polymers?
Polymers can occur organically in the form of natural or biopolymers, like wool, cotton, or wood, or they can be synthesized into semi-organic or fully synthetic materials. Synthetic polymers fall into three specific categories:
- Elastomers are elastic materials with high flexibility and low strength molecular bonds (like rubber).
Polymer fibers consist of polymer chains that have stronger molecular bonds than elastomers. Fibers are more rigid and less elastic than elastomers and can be composed of both natural and synthetic materials.
- Thermoplastics are more rigid than fibers and elastomers and are distinguished by their ability to retain their molecular structure when exposed to heat. When heated to their melting point, thermoplastics will melt rather than burn, making them ideal for shaping and forming.
The fundamental structure, physical properties, and uses of a synthetic polymer help to determine its classification. With thousands of polymers in existence, it is important to understand the qualities and uses of polymers to ensure that they are used in the appropriate applications.
The molecular structure of a polymer determines the fundamental properties of the material. When attempting to classify a particular polymer material, the following structural aspects must be considered:
- Monomer composition. Knowing which monomers make up the polymer chain, how many of each, and the nature of those monomers will help to classify the material.
- Chain characteristics. The average length and weight of the chains in a polymer help to determine the degree of polymerization and the molecular form of the polymer.
- Molecular bonds. The structure of a polymer can be determined by the ways in which the monomers are linked to each other and whether or not there are cross-branching bonds between polymer chains.
- Polymerization method. The means by which the monomers are combined into polymers determines the structure of the polymer, whether it is a naturally occurring process or synthetic polymerization through the use of heat, chemicals, or condensation.
Polymers come in a wide variety of forms and can be further classified based on their physical properties. Some identifying characteristics include:
- Thermal properties
- Crystalline structure
- Tensile strength
Polymers can also be categorized by the applications in which they are used. Due to the variety of materials that can be created through polymerization, polymers are useful in a wide range of applications:
- Formed and molded products
- Thin films and sheets
- Coatings, paints, and inks
- Yarns and other fibers
What are Plastics?
Plastics are synthetic or semi-organic polymers made from oil or petroleum through the use of chemicals and condensation to induce molecular bonding. Although polymers can occur naturally, plastics are entirely man-made.
Since plastic contains polymers, however, it displays similar physical properties and versatility, which makes it useful in a broad range of applications. Plastics can be divided into two categories: thermoset plastics and thermoplastics.
Thermoset plastics are heat-hardened into a permanent design. Once they have been shaped, thermosets remain in a fixed form even when exposed to heat again. Once set, thermosets will burn rather than melt when exposed to extreme temperatures. Their high resistances to heat and corrosion make thermoset plastics particularly useful in applications that require reliable precision components that will not change shape or creep when exposed to extreme temperature changes.
Commonly used thermoset plastics include:
- Certain polyesters
Due to their durable and temperature-resistant nature, thermosets are used in a variety of applications, such as:
- Electronic components and insulators
- Heat shields
- Motor parts and covers
- Household appliances
- Lighting components
- Energy equipment
Unlike thermosets, thermoplastics may be reheated and reshaped without any change to their fundamental molecular makeup. Thermoplastics will melt when exposed to extreme heat, which makes them ideal for forming and molding fabrication processes. They are typically used for plastic products that are not exposed to extreme heat, such as plastic toys, toothbrushes, plastic storage containers, beverage bottles, and other consumer products.
Thermoplastics are available in two different forms, amorphous and semi-crystalline, based on their fundamental molecular structure.
- Amorphous thermoplastics. Amorphous thermoplastics consist of polymer chains that are not laid out in any particular arrangement—the polymer strands are jumbled together in an uneven and disorganized fashion. Amorphous thermoplastics have very low heat resistance but are tough at low temperatures. They tend to be clear due to their lack of structure, which makes them useful for plastic windows and lighting fixtures.
- Semi-crystalline thermoplastics. Semi-crystalline thermoplastics consist of polymer strands in an ordered arrangement, or a crystalline structure mixed with amorphous areas. The amount of crystalline vs. amorphous structure determines the physical characteristics of the plastic. The greater the crystalline organization, the opaquer the material becomes. Semi-crystalline thermoplastics exhibit greater strength, stability, heat resistance, and chemical resistance than their fully amorphous counterparts.
Thermoplastics encompass a wide range of materials, including:
- Polyethylene (PE)
- Polystyrene (PS)
- Polyvinyl chloride (PVC)
- Thermoplastic olefins
- Acrylonitrile butadiene styrene (ABS)
Due to their versatility, thermoplastics are useful in myriad industries and applications, including:
- Blow molding and injection molding
- Consumer goods
- Automotive components
- Engineering and mechanical parts
- Medical equipment
- Storage containers
- Packaging materials
Thermoplastics and are easily formable, which makes them ideal for use in blow molding fabrication. The blow molding process uses compressed air to force molten plastic resin into a pre-fabricated mold to create bottles, containers, cases, and other hollow parts and components.
Blow Molding With OMICO
With more than 50 years of experience in polymers and plastics, OMICO is pleased to provide exceptional blow-molded products for a wide range of industries, including automotive, medical, household appliances, aerospace, and pet products. Our IATF-16949 Certified facility includes a fleet of cutting-edge blow molding equipment to guarantee the highest quality parts. We use only the purest plastic products directly from the source, Exxon Mobil, and our system includes specialized inspection equipment to ensure that our products are consistent and reliable.