Thermoplastics in Pellet Form
We can often forget that many of the plastic products we use each day begin in the form of small plastic pellets, about the size of a bead. These pellets are actually extruded thermoplastics that are cut into pellet form. They are then melted, shaped into a design and cooled to produce everything from children’s toys to soda bottles, food packaging, product protection and even medical equipment.
Manufacturing processes like thermoplastic injection molding and extrusion can produce these items at great speeds and quantities, providing companies and people with a wide variety of solutions.
Here, you will get to know thermoplastics, including the common types, items produced from them, along with material features, coloration and finishing options that are available.
Derived from organic materials including everything from natural gas and petroleum to harvested soybeans and corn, thermoplastics stand out from other plastic types (like thermosets) by having the ability to be melted, shaped and cooled into a specific design. They can even be remelted and reshaped once an original product is no longer needed, via recycling processes.
While these plastic pellets may all look the same from a distance, they have unique molecular structures, or polymers, that will create a differing finished product. Two of the most common polymers that are used in the manufacturing space are polyethylene (PE) and polypropylene (PP).
PE and PP aren’t the only thermoplastics used during manufacturing, however. Polycarbonate (PC), acrylonitrile-butadiene-styrene (ABS) and other polymers can be molded or machined to create items with different colors and finishing options.
Further material options include thermoplastic rubber (TPR) and thermoplastic elastomer (TPE), which consist of both plastic and rubber.
Thermoplastics in Injection Mold Hopper
We now know there are many different types of thermoplastic polymers. To make things a bit easier, they can be broken down into a few main groupings: commodity and engineered. Let’s take a look at each.
The “standard” for manufacturing because of their lower material costs, commodity thermoplastics can be produced in higher volumes and at a more rapid pace than engineered options, creating even greater cost savings.
Typically lightweight and flexible, commodity plastics are used to make things like soda bottles and single-use grocery bags. They alter at lower temperatures, making them less heat resistant (resistant up to 175°F, 79°C).
Polymers in this grouping include low-density polyethylene (LDPE), high-density polyethylene (HDPE), PP and ABS.
As you can probably gather from its name, LDPE has a lower density than other PE products and is preferred when lighter, more flexible materials are called for. This polymer usually isn’t as thick as its alternatives and has a lower melting point, but it can withstand impacts and certain chemicals.
It’s semi-crystalline, meaning it has a more uniform and tightly packed molecular structure, while also having amorphous areas (less structure) between crystalline areas. This makeup gives LDPE a defined melting point.
Think garbage bags, bubble wrap, six pack rings, plastic gloves and tubing. It can also be used to manufacture caps, plugs and other product protection that may be used during shipping or for items stored outdoors.
Benefits of LDPE:
Unsurprisingly, HDPE has a greater density than its sibling LDPE. It is more rigid while being able to maintain flexibility.
Also semi-crystalline, HDPE is used for products that come into contact with chemicals and moisture such as soap and shampoo bottles, bleach bottles, detergent containers, as well as larger items like Adirondack chairs, playground equipment and decking. This polymer is also used in the manufacturing of caps, plugs and other product protection.
Injection Molded PE Caps
Benefits of HDPE:
PP actually has a lower density than its PE counterparts, but is a harder, more rigid material with greater stability. PP offers chemical resistance and greater heat resistance than LDPE and HDPE.
Examples of PP in the real world include marine ropes for tying boats, vehicle instrument panels and trim, electronic protection, cable insulation and medical products like single-use syringes.
Benefits of PP:
A distinct step up from commodity, engineered thermoplastics are often used when greater strength and temperature resistance are needed. They can be a bit more expensive, and are less commonly produced for high-volume applications as a result.
Polymers in this space include nylon, polyester and PC. Engineered products are similar to commodity, and can be used to make items that offer greater strength. Differing products include skis, motorcycle helmets, vacuum cleaner housings, CDs, DVDs, Y-connectors for medical applications and valve wrenches for medical gas cylinders.
When you’re ready to make a plastic selection, it’s important to know which polymers offer the right resistance, color and finishing options. Make sure to review these before starting any manufacturing processes.
If a plastic is going to be exposed to chemicals, a different polymer should be chosen than one that will primarily be exposed to heat or UV rays.
PE and PP are more resistant to chemicals while polymers like ABS are more resistant to UV rays. While each material has certain innate properties, different additive packages can be added to nearly all polymers to provide more distinct chemical, UV, thermal or other protective resistance qualities.
Glass fibers, ceramic fillers and antioxidants are common additives that can improve impact strength, heat and UV resistance.
Red Colorant Before Mixing
If a specific color is needed for aesthetics, colorants can be added to the thermoplastic. There is essentially an infinite amount of color options that can be developed, matched and added to the base polymer. These colorants are blended with thermoplastics during either extrusion or injection molding processes, making it easy to mass produce products with distinct coloring.
Color options are available for common thermoplastics like PE, LDPE, HDPE and PP.
Depending on the mold, different surface finishing options are available when designing and producing a plastic part, which can create polished finishes such as high glossy, semi glossy, transparent and matte.
*Please note, durometer was excluded from this section as its measuring is more common for rubber products.
Do you have any further questions after exploring our beginner’s guide? Reach out to our friendly and knowledgeable product protection team at Caplugs, we’re here to help.
With over 75 years of experience, we’re a trusted leader in plastics, including injection molding and extrusion processes. Let our engineers help you determine the right material for your next project, or explore the different products we have by material on our website today.