What Is Thermoplastic?
A thermoplastic is a class of polymer that can be softened through heating and then processed using methods such as extrusion, injection moulding, thermoforming and blow moulding.
Thermoplastics harden once cooled and do not show any changes in chemical property after being heated and cooled multiple times, making them easily recyclable.
Thermoplastic polymers can be very broadly classified as amorphous or crystalline. Most thermoplastics suitable for use as matrices for high performance composite exhibit some degree of crystallinity because this type of structure has better resistance to chemical attack by field, hydraulic oil and paint stripper.
With regard to behaviour at elevated temperatures, polymers are classified as either thermoplastics or thermosetting.
Thermoplastic polymers have linear and branched structures they soften when heated and harden when cooled. In contrast, thermosetting polymers once they have hardened, will not soften upon heating; their structures are cross-linked and network.
What are Thermoplastic Polymers?
Thermoplastic polymers are materials made up of linear molecular chains. These polymer chains can be melted and reformed. This makes them ideal for applications where they need to be molded or shaped, such as injection molding.
Thermoplastics are also easier to recycle than other types of plastic, making them better for the environment. Thermoplastic polymers are a suitable substitute material used in a wide range of products, from secondary packaging to car parts.
The curing process for thermoplastics involves the pellets softening and becoming more fluid as additional heat is applied and the high heat distortion temperature increases.
The curing process is completely reversible, as no chemical bonding takes place. This characteristic allows thermoplastics to be recycled without affecting the materials’ physical properties, due to their chemical resistance.
What are Types of Thermoplastics?
Some of the most common types of thermoplastics are:
- Polypropylene,
- Polyethylene,
- Polyvinyl Chloride,
- Polystyrene,
- Polyethylene Terephthalate And
- Polycarbonate.
Amorphous and Semi-crystalline Thermoplastics
Thermoplastics are made by joining small molecules, called monomers, together to form long chains using a process called polymerisation.
A single polymer chain can be made from many thousands of monomers. The atoms in a polymer chain are joined by strong covalent bonds, whereas the forces between chains are weak.
Depending on the type of monomer, polymer chains may have side branches. If a polymer chain has only a few, short side branches then the chains can form ordered, crystalline regions, called spherulites.
However, if the chain has many large side branches, then it is not possible for ordered regions to be formed and the polymer is amorphous. Examples of amorphous polymers are polystyrene (PS), polyvinyl chloride (PVC) and acrylonitrile-butadiene-styrene (ABS).
Even for polymers with crystalline regions, there are always some amorphous regions between the crystallites, so these polymers are called semi-crystalline. Examples of semi-crystalline polymers are polyethylene (PE), polyamide (PA) and polypropylene (PP).
For semi-crystalline polymers, as the temperature increases, the bonds between the polymer chains weaken to create a pliable solid and then a viscous liquid, which allows the plastic material to be shaped to produce parts.
Amorphous plastics are used for applications where optical clarity is required since light is scattered by crystallites. These amorphous plastics are, however, less resistant to chemical attack and environmental stress cracking due to the lack of crystalline structure.
Before a thermoplastic polymer can be used it is normally mixed with additives, such as stabilisers, plasticisers, lubricants, flame retardants and colourants, to improve the polymer’s functionality, stability or appearance.
For example, stabilisers are added to reduce degradation due to sunlight or heat and plasticisers can be added to increase the mobility of amorphous chain segments, lowering the glass transition temperature and decreasing brittleness
How thermoplastics are used
Different types of thermoplastic are used to make different objects such as food packaging, waterproof clothing, non-stick pots and pans, eye-wear, CDs and DVDs, cable insulation, water bottles, LCD screens, paint, furniture, outdoor play equipment, toys, roofing, cladding, greenhouses, and medical devices.
hermoplastics have been around for a long time and are an important component of everyday life today. For example:
#1. Acrylonitrile butadiene styrene (ABS) is a thermoplastic used to manufacture:
- Sports equipment
- Toys (for instance, LEGO® blocks)
- Various automobile parts
#2. Polycarbonate is used to make:
- Reusable drinking bottles
- Food storage containers
- Eyeglass lenses
#3. Polyethylene is probably the most common thermoplastic and is used to make:
- Milk bottles
- Cleaning products
- Plastic grocery bags
#4. Polypropylene (PP) is used in a wide range of applications, including:
- Packaging for food, and chemical and cleaning products
- Electrical cabling
- Automotive components
- Medical items, e.g. syringes, petri dishes and specimen bottles
- Polypropylene can also be used in fibre form for clothing, upholstery and carpets
Why are Thermoplastics Important?
#1. Chemical resistance.
Thermoplastics are often the material of choice for seals and valves, as properly chosen materials are slow to degrade or lose performance when in contact with gases or fluids.
This is a critically important differentiator in can’t-fail applications or extreme environments, such as oil and gas pipelines, medical implants, or aerospace.
Because the gas or fluid is slow to (or simply can’t) permeate the polymer material, components won’t rust, corrode, or degrade like other materials.
#2. Strength to weight ratio.
Particularly for aerospace and automotive applications, in which weight is an important consideration, thermoplastics are the preferred choice over metal parts because they are both strong and lightweight.
#3. Durability.
Because of their combination of abrasion, temperature, pressure, and fatigue resistance, engineered thermoplastics are unparalleled in durability.
#4. Cost.
Thermoplastics are easier to manufacture relative to metals, and net-shape or near to net-shape articles can be produced more readily at lower total cost.
Thermoplastics are easily melted at moderate temperatures and more readily formed into a finished or semi-finished part, avoiding or reducing the complexity of secondary operations, thus reducing production costs.
#5. Sustainability.
Plastics get a bad rap, but responsible manufacturers are working hard to make them more sustainable.
At CDI, we are always looking at ways to recycle and reuse our thermoplastic scrap stream, with a goal of keeping plastic waste out of landfills and out of the environment. We also operate on 100% renewable energy at our Houston facility.
What are the advantages of thermoplastic?
There are many advantages to using thermoplastic, the biggest being its versatility and how it can be used for many purposes in different industries. These advantages below are what makes thermoplastics so diverse:
#1. Durable
Thermoplastics are ductile and impact resistant. In many applications thermoplastics have a longer service life compared to alternative materials because they don’t dent, ding, chip, crack, splinter, or fray. This reduces service calls and component replacements in even the most demanding applications.
#2. Chemical and Stain Resistant
Most thermoplastics are chemical and stain resistant and will not yellow or discolor as a result of contact with many chemicals, including industrial cleaners and solvents. Certain compounds are graffiti resistant, making them ideal for outdoor applications.
#3. Integral Colours and Effects
The colour is blended into the material during the manufacturing process, so the finish effects are consistent throughout the material’s thickness. Custom colours and finishes are available. Most thermoplastics can be custom colour matched for an ideal product hue.
#4. Meet Codes and Requirements
Thermoplastics can be blended with additives to meet strict smoke, flammability, and toxic gas release requirements for aircraft and mass transit interior applications. Many thermoplastic compounds are inherently biocompatible, which means they’re ideal for medical device applications.
#5. Environmentally Friendly
Thermoplastics are recyclable and contain no VOCs, making them an environmentally sound solution. Thermoforming manufacturing processes do not outgas VOCs or create any hazardous waste to dispose of. Thermoplastics support end-of-life recyclability and life-cycle design.
What are the examples of thermoplastic?
Common examples of thermoplastics include acrylic, polyester, polypropylene, polystyrene, nylon and Teflon. These materials see a wide variety of use in manufacturing products from clothing and non-stick cookware to carpets and laboratory equipment.
The following list details some of the different types as well as some examples of what each thermoplastic is used for:
- Acrylic: commonly used as an alternative to glass and for items such as LCD screens, furniture, vehicle headlights, paint, and lenses.
- Polythene or Polyethylene (PE): LDPE is commonly used in packaging, plastic bags, plastic bottles, and HDPE is used for items such as toys and outdoor play equipment.
- Polyvinyl chloride (PVC): used for industrial, technical, and every day purposes including cable insulation, packaging, pipes, roofing, flooring, cladding, and medical equipment.
- Polypropylene (PP): commonly used for food containers, packaging, and plastic parts for machinery and equipment.
- Polycarbonate (PC): used in items such as eyewear, medical devices, PPE, greenhouses, CDs and DVDs and other electrical components.
- Polystyrene (PS): used in packaging, toys, trays, containers, and foam cups.
- commonly used for waterproof clothing, non-stick pots and pans, electrical equipment, and self-cleaning ovens.
- Styrofoam: used for building insulation, packaging, and disposable plates and trays.
- Polyamide (Nylon): commonly used in clothing, car tires, rope, fishnets, and tents.
Is thermoplastic good for the environment?
Neither thermoplastic nor thermosets truly biodegrade after they are released into the environment, but if they do, it is only under very specific circumstances.
Some thermoplastics are environmentally friendly as they are easily recyclable. Thermoplastic can be reheated and reshaped, without losing its strength, and therefore can be reused again and again, making for a sustainable material and less plastic waste.
Thermoplastic manufacturing can result in lower energy consumption too since it often requires shorter production cycles. Thermoplastics are a lighter alternative to other materials which means it uses less energy to carry or transport.
This in turn improves fuel efficiency in vehicles and aircrafts. Plus, household items such as thermoplastic food containers can help reduce the usage of other single-use plastic containers and plastic film.
The bigger threat on the environment is single-use plastic and the waste it generates. From this perspective, using thermoplastics is a great solution.
Thermoplastics, such as the material we use to make playground markings, are far from single-use. Their durability means they have a long lifespan of up to ten years, resisting lots of footfall and road traffic.
On the other hand, there needs to be more encouragement for recycling thermoplastic as it can be expensive.
Plus, the more times thermoplastic is recycled, and depending on what it’s used for each time, other chemicals can be added which can sometimes make the thermoplastic composites less recyclable.
What’s the difference between thermoplastic and thermosetting?
Thermosetting plastics and thermoplastics are both polymers, but they behave differently when exposed to heat. Thermoplastics can melt under heat after curing while thermoset plastics retain their form and stay solid under heat once cured.
Because thermoplastics have a low melting point, they are ideal for applications that use recycled materials. Thermoset plastics, in contrast, are able to withstand high temperatures without losing their shape, making them more durable.
Aesthetically, thermoplastics are seen as superior to thermoset polymers, however thermosetting materials are still deemed to have better aesthetics than alternatives such as metals.
These materials allow for in-mould painting or coating, including spraying coatings directly into the mould before the thermoset polymers are injected into it.
This technique offers better adhesion to the material and prevents chipping, cracking or flaking, even under harsh weather conditions.