Overview of Polymers and Types of Plastics
Next: Adhesives, Surfactants and Rubbers
So far we’ve discussed generation of synthetic hydrocarbons, how just a handful of those act as feedstocks to chemical industries and how flow chemistry can be applied to bring chemical manufacturing scale down.
But what are the actual end products that are today made fromhydrocarbons (aka oil). Turns out pretty much everything.
Let’s begin the products galore with plastics and look shortly on what types of plastics there are (actually polymers in general meaning also rubber, adhesives etc.) and how they are made.
Polymers are long chains of simple molecules joined together. The molecules that make the building blocks are called monomers. Polymers can be natural or synthetic. Natural polymers are for example proteins, DNA, and cellulose, which are found in living organisms. Synthetic polymers are artificially made (stuff of interest here). The length of monomer chains in synthetic polymers can vary widely. Synthetic polymers can have chains ranging from a few monomer units to tens of thousands of monomer units. Organic polymers like DNA and other proteins in turn may have millions of monomer units. These types of large molecules are called macromolecules.
For the rest we focus on synthetic polymers.
There are many ways to divide polymers into different categories like:
homopolymers or heteropolymers (consisting of same or different monomers)
thermoplastics (ones that become mouldable when heated and solidify when they cool), thermoset, elastomers or fibers
how they are made (addition or condensation)
steric structure (3D structure)
Further plastics are often divided into commodity plastics and engineering plastics based on how they are used.
Homopolymers are made from a single monomer and heteropolymers aka co-polymers are made from two or more monomers
Co-polymers (aka heteropolymers) have the properties of their constituent polymers. This allows to tailor their characteristics. As example polystyrene is brittle but when it is co-polymerized with buta-1,3-diene it gains resilience and strength.
Thermoplastics are made of long polymer chains held together by weak intermolecular forces. They soften and become pliable when heated and then solidify again when cooled. They can be repeatedly heated and remoulded.
In thermoplastics the polymer chain is made up of identical or similar monomer units that are chemically bonded to each other. The specific monomer units used determine the type of thermoplastic polymer. For example, polyethylene (i.e., used in bottles) is made up of repeating ethylene monomer units, while polyvinyl chloride (PVC, used in piping as example) consists of repeating vinyl chloride units. (we’ll cover uses of these plastics in detail later).
Thermoset polymers have three-dimensional, cross-linked network structure. Cross-linking involves the formation of covalent bonds (chemical bonds) between polymer chains. They create the three-dimensional network making thermosets highly stable and not to be easily broken by heat or pressure. To convert thermoset resins into solid thermoset polymers, a curing process is initiated. Curing can be triggered by various methods, including heat, radiation (UV or electron beam), or chemical initiators. After that thermosets cannot be remoulded. Examples of thermosets are for example epoxy resins (glue) and polyurethanes (insulation, inside furniture).
Elastomers are amorphous solids and they are elastic as the name says (think rubbers).
They have the ability to return to their original shape after being stretched or deformed. This elasticity is a result of the long, coiled polymer chains in elastomers and the weak intermolecular forces between these chains. Important elastomers include synthetic rubbers like Styrene-Butadiene Rubber (SBR) used for tires and polybutadiene for footwear.
Fibers are produced by extruding molten polymers through small holes in a die. Common synthetic fibers include polyamides like nylon, the polyesters like terylene and polypropene (clothes, ropes etc.).
After extruding and stretching the polymer molecules are aligned in the direction of the fiber. Strong intermolecular forces between molecules prevent returning to random orientation. Finally, fibers are twisted to threads to be used in making cloths. Or they can be imbedded into plastics to increase strength.
Polymers are also divided by how they are made – either via addition or condensation. Addition polymers are often made using Ziegler-Natta catalysts. Ziegler-Natta catalysts are known for their ability to control the stereochemistry (3D structure, see below for more) of the polymerisation process and to allow for precise control of the molecular weight of the polymer chains. A new class of catalysts has emerged – called metallocenes – that allow even greater control of the polymerisation.
In condensation polymerisation, polymerisation of one or more monomers results in the elimination of small molecules like water or ammonia. Types of polymers generated by condensation polymerisation include polyesters (plastic bottles), polyamides (textiles, carpets), polycarbonates (eyewear, medical equipment) etc.
Condensation polymerisation offers advantages such as the ability to incorporate a wide range of functional groups, resulting in polymers with diverse properties.
Final way of classifying polymers is their steric structure. Steric structure means how atoms or chemical groups around the polymer backbone are arranged in 3-dimensional space. Let’s consider a monomer that is asymmetrical, the asymmetrical part can arrange itself in three different ways. The asymmetrical part always on the same side of the backbone, it can alternate or it can be random (non-repeating).
This division is made because the steric structure can have a big impact on its mechanical properties, thermal stability, solubility, and chemical reactivity.
Plastics are further sometimes divided into commodity plastics and engineering plastics.
Commodity plastics are thermoplastics (ones that become mouldable when heated and solidify when they cool). They are produced in large volumes, are cheap to make and are used in volumes in normal conditions (not high or very low temperatures etc.). Most common ones are polyethylene, polypropylene, polyvinyl chloride (PVC), polystyrene and acrylonitrile-butadiene-styrene (ABS, 3D printers etc.).
Engineering plastics are used in special applications due to their exceptional mechanical, thermal, electrical, and chemical properties. They are used for gears, bearings, bushings, valves, gaskets, automotive parts, eyeglass lenses, transparent shields, electronic components, medical implants etc.
The properties of many plastics can be modified by mixing polymers. As example PVC be made in either a flexible or a rigid form or any combination with different additives.
Plastic types and uses
Let’s go over the uses of plastics a little bit more in detail. Might sound (read) a little boring, but the main takeway will be to have an overview understanding of all kinds of places plastics are commonly used today, and what we could manufacture locally with the Unfactory concept.
Just to repeat from last time the difference between commodity and engineering plastics.
Commodity plastics are thermoplastics (ones that become mouldable when heated and solidify when they cool). They are produced in large volumes, are cheap to make and are used in volumes in normal conditions (not high or very low temperatures etc.). Most common ones are polyethylene, polypropylene, polyvinyl chloride (PVC), polystyrene and acrylonitrile-butadiene-styrene (ABS).
Engineering plastics are often thermoplastics (when heated it becomes moldable and solidifies again when cooling). They are used replace traditional materials like wood or metal. With them it is easier to manufacture especially complex objects with 3D printing or injection molding.
Examples include Polyamides (PA6, PA66), Polyesters (PET, PBT), Polycarbonate (PC). Polyacetals (POM), Acrylonitrile-Butadiene-Styrene (ABS).
The distinction between commodity and engineering plastics is not always clear-cut, and some plastics fall into both categories depending on their formulations and specific applications. Advancements in technology continue to blur the lines as new materials are developed with a broader range of properties and applications. The key differentiator is that engineering plastics are chosen for their specialised performance, while commodity plastics are selected as they are cost-effective and for everyday use.
Polyethylene
Polyethylene is one of the most popular thermoplastics today. It is made by addition polymerisation of ethene. In this process (called also chain-growth polymerisation), a chain reaction adds monomer (a single molecule) units to a growing polymer molecule one at a time through double or triple bonds. Ziegler-Natta and metallocene catalysts are used to carry out the process.
Different plastics in the polyethylene family get their characteristics by the amount of side-branching. More side-branching decreases features such as melting point, rigidity, density, strength etc.
Largest use case is blow-molded plastic bottles for water, milk, carbonated soft drink, laundry detergents and motor oil. Other uses are pipe and conduit, moulded containers and shopping bags.
For more: https://omnexus.specialchem.com/selection-guide/polyethylene-plastic
High Density Polyethylene (HDPE)
High density polyethylene (HDPE) is made in low pressure and temperature to produce a linear polymer which is highly crystalline making it strong and rigid. It is used for blow-molded plastic bottles for water, milk, carbonated soft drink, laundry detergents and motor oil. Other uses are monobloc chairs and stools, toys and playground equipment.
HDPE is accepted at most recycling centres in the world, as it is one of the easiest plastic polymers to recycle
Ultrahigh Molecular Density Polyethylene (UHMDPE)
This plastic has high abrasion (scraping, wear and tear) resistance and is used in material handling machinery like conveyer belts, racks, shelves or knee and hip bone replacement. It has extremely long chains. Other uses are cut-resistant gloves, bow strings, climbing equipment, fishing line, high-performance sails, suspension lines on sport parachutes and paragliders, rigging in yachting, kites etc.
Low Density Polyethylene (LDPE)
LDPE It was the first grade of polyethylene created already 1933. LDPE has more branching than HDPE, so its intermolecular forces are weaker and its tensile strength is lower. Also its resilience is higher.
Largest use for LDPE is in packaging film, the second coating and laminating. For example, liquid packaging board is made of paperboard laminated with LDPE making it aseptic. Also trays and general-purpose containers can be made of it.
Linear Low-Density Polyethylene (LLDPE)
Linear low-density polyethylene (LLDPE) is produced at lower temperatures and pressures by copolymerisation of ethylene and such higher alpha-olefins as butene, hexene, or octene. It has significant numbers of short branches. It is used for plastic bags and sheets (it has lower thickness than comparable LDPE), plastic wrap, stretch wrap, pouches, toys, covers, lids, pipes, buckets and containers, covering of cables, geomembranes (prevent water from leaking through in ponds etc.) and mainly flexible tubing
For more: https://en.wikipedia.org/wiki/Linear_low-density_polyethylene
Very Low-Density (VLDPE) And Ultralow Density POLYETHYLENE (ULDPE)
By increasing copolymerisation softer and even more flexible plastics can be made. It is mainly used for hose and tubing, ice and frozen food bags, food packaging and stretch wrap.
ULDPE is also used for stretch wrap and food packaging.
Polypropylene (PP)
Polypropylene (PP) is produced via chain-growth polymerisation from propylene. Its properties are similar to polyethylene, but it is slightly harder and more heat resistant. It is a white, mechanically rugged material and has a high chemical resistance.
Polypropylene is the second-most widely produced commodity plastic and it is often used in packaging and labelling.
Some of its good qualities include resistance to to corrosion, chemical leaching and most forms of physical damage including impact and freezing. It can be joined by heat fusion rather than gluing.
Polypropylene is used in the manufacturing of piping systems used in potable plumbing, hydronic heating and cooling, and reclaimed water. It is also used in living hinges because it is resistant to fatigue.
Many plastic items for medical or laboratory use can be made from polypropylene because it can withstand the heat in an autoclave. Its heat resistance also enables it to be used as the manufacturing material of consumer-grade kettles. Food containers made from it will not melt in the dishwasher, nor melt during industrial hot filling processes.
Polypropylene is highly colorfast, It is widely used in manufacturing carpets, rugs and mats to be used at home. Polypropylene is widely used in ropes, because they are light enough to float in water
Polypropylene is also used as an alternative to polyvinyl chloride (PVC) as insulation for LSZH (low smoke, zero halogen) cable in low-ventilation environments (primarily tunnels). This is because it emits less smoke and no toxic halogens.
Polypropylene is also used in particular roofing membranes as the waterproofing top layer of single-ply systems.
For more: https://en.wikipedia.org/wiki/Polypropylene#Applications
PVC
Polyvinyl chloride (PVC) is the world's third-most widely produced synthetic plastic.
The rigid PVC is used for pipes and various profiles like doors and windows as well for making bottles, non-food packaging, food-covering sheets bank or membership cards.
Rigid PVC can be made softer by adding plasticisers (such as phthalates). Flexible PCV is used in plumbing, electrical cable insulation, imitation leather, flooring, signage, inflatable products and many places to replace rubber.
Based on molecular weight phthalates are divided into high and low. The low phthalates have increased health risks and are being phased out.
If burned inefficiently, PVC can produce dioxins. This can happen among others in land fill fires. Dioxins are highly toxic and can cause cancer or reproductive and developmental problems.
For more: https://en.wikipedia.org/wiki/Polyvinyl_chloride
Polystyrene
Polystyrene is made by bulk polymerisation initiated by peroxides and heat with rising temperature to keep the material molten and possibly adding a solvent to facilitate the process. It was the first commodity thermoplastic. It is easy to process, rigid and has glass-like transparency. It is used in packaging, toys and housewares.
When polystyrene is swollen with 10% pentane and heated, it expands to rigid close-cell foams with very low density (expanded polystyrene = EPS). EPS is commonly used for packaging hot and cold foods. It is also molded to sheets for building insulation
Polyamides
Polyamides contain repeating amide ( -CO-NH- linkages). Proteins are examples of naturally occurring polyamides.
Nylon is the best knows synthetic polyamide.
Nylon is widely used in the textile industry to make fibers for clothing, including stockings, socks, and sportswear. Nylon textiles are strong and have elasticity, and abrasion resistance. In car industry they are used gears, bearings, and fuel lines because they are strong and resistant to heat and chemicals. In electronics they are used for insulating material for electrical cables and connectors. Used also for mechanical gears, bushings, connectors, and housings. And toothbrush bristles, zippers, fishing lines, and sports equipment like tennis racquet strings and ski bindings among others.
When engineering plastic are made, polyamides are often used as co-polymers and mixed with other materials. Fillers can be glass beads, glass or carbon fibers. Pigments and fire retardants can be added as well.
Other important polyamides include the aramid Kevlar (bulletproof vests, car breaks).
Polycarbonates
Polycarbonate properties depend on the molecular mass and structure. With increasing mass, the material becomes more rigid. They are flame and heat resistant and transparent making them ideal choice for many applications.
Polycarbonates can be blended with other polymers like ATS or polyesters to control the properties.
Common uses are for example in lenses for glasses, sockets, lamp covers, fuse boxes, computer and television housings, building roods, signs, skylights, for car bumpers and in general inside cars, for large water bottles etc.
Polyesters
Polyesters are condensation polymers that have many uses and are one of the most manufactured synthetic polymers. Benzene rings in their chain give rigidity and they have high melting points and do not discolor in light. Manufacturing is relatively simple and cheap. Most common applications are in clothing, water and soft drink bottles and food packaging.
Most used polyester is PET used in plastic bottles but Polybutylene terephthalate (PBT) and Polytrimethylene terephthalate (PTT) are common materials for plastic rugs.
The different uses depend on the structure. In fibers the molecules are lined in one direction, in film on a plane structure and for packaging in all three directions. The fiber is used in suits, shirts and skirts. It often is blended with natural fibers like cotton or other synthetic fibers. Fibers are also used as filling in bedding duvets or anoraks etc.
In film format it is used for food packaging and electric insulation among others. In packaging it is used for food products (ketchup, mayonnaise bottles etc.) and for washing liquid bottles.
Quite a long list.
On and forwards with more, different chemicals made from oil (or synthetic carbohydrates in our case) next time.