With thousands of plastics on the market, it can be a daunting task to decide which type is the best for your next rapid prototyping or low-volume manufacturing project. When choosing which plastic to use, there are going to be trade-offs between cost, moldability, surface finish, durability, strength and many others. The choice of plastic depends on not only what the part does but also the environment in which it does it.
To help you understand how different plastics are used, here are some of the most common applications our customers bring to us and the plastic material we would recommend for each.
Clear Lenses, Windows, and Transparent Parts
What plastics are suitable for clear lenses, windows and transparent parts? We recommend acrylic, also known as PMMA. This material is used to make shatterproof windows like Plexiglass©. It takes a high polish, has good tensile strength and is economical. However, it’s not as impact or chemical resistant as polycarbonate.
Mechanical Parts
What plastic resins are best for mechanical parts? One of the most common resins used for mechanical parts is nylon, also known as polyamide (PA). It can often be found as a substitute for simple metal parts in engine compartments where it withstands heat and vibration well. When mixed with molybdenum it has a slippery surface, but nylon-to-nylon gear trains are not a great idea – similar plastics tend to stick together, so it’s best to alternate plastic types. Nylon is well-suited as a filament for 3D printing in plastic, but it does absorb water over time.
Tools and Hardware
What plastics are best for hard use, like tool cases and hardware? There are many choices here. High-impact polystyrene (HIPS) is used to make tough cases for tool boxes and the bodies of power tools. It’s inexpensive, one reason why polystyrene is used for disposable packaging, but it’s not considered environmentally friendly.
Plastic Containers
What about low-cost, high-volume plastic containers? Polypropylene (PP) is used in food storage containers because it can be washed in hot water without degrading, is resistant to oils and solvents and doesn’t leech chemicals so it’s food-safe. One of its great advantages is that it can readily be formed into a living hinge, like you commonly find on the cap of a bottle of aspirin. This type of joint can be bent repeatedly without breaking. It also finds wide use in pipes and hoses.
Polyethylene (PE) is not especially strong, hard or rigid but is still the most common plastic in the world. Usually found in a milky white color, PE is the plastic found on medicine bottles, milk and detergent bottles and trash cans. It’s very resistant to various chemicals but has a low melting point. Because it’s so elastic it’s also used for plastic bags and cling film.
Toys
What’s a good plastic for making children’s toys? Almost one-third of all the plastic toys in the world are made from PE , since it’s inexpensive, non-toxic and very colorfast. Additional UV stabilizers can be added for outdoor and recreational toys that will experience a lot of sunlight.
Stronger and more rigid toys with higher impact strength are made from ABS or nylon.
Rubber
Which plastic resins are most like rubber? Many applications call for injection molding of resins that have the soft, elastic properties of rubber. For this we use thermoplastic polyurethane, also known as TPU. It comes in many special formulas to achieve high elasticity, low-temperature performance and durability.