NO TWO PLASTICS ARE EVER MADE THE SAME!
Once you’ve digested the table below, it’s suddenly obvious – no two plastics are the same!
Plastics come in all shapes and sizes, colours and textures. Each plastic created has a unique set of properties making it either more or less suitable for completing a given function. Usually, a plastic is chosen with a specific purpose in mind. For example, a plastic bottle containing water, or another consumable substance needs to be lightweight, tough, and safe. For this function PET/PETE is the perfect choice.
The way in which a plastic is engineered will determine whether it is suitable for a product. Another fantastic example is the use of Polystyrene for CD cases. The cases can be moulded very thin, they’re lightweight, and are completely transparent. One down side to using Polystyrene is that it is very rigid, making it very easy to break!
As Polystyrene is so brittle, its use for other functions is severely limited. The chairs used on trains and buses are made with a plastic shell, a foam insert and fabric. Understandably the seats need to have the ability to withstand a lot of wear and tear. More importantly, seats used in public transport must ‘crumple’ efficiently, thus making Polystyrene completely unsuitable due it ‘shattering’ when bent.
Engineering plastics, number 7 on the chart, are unique in the way they have advanced mechanical properties that offer greater durability and won’t be compromised during the manufacture process. Modifications can be made to some types of plastics to improve their strength as well as their impact and heat resistance. One of the most common resins used for mechanical parts is nylon, also know and polyamide (PA). Nylon parts can withstand heat and vibration exceptionally well, however it does absorb water over time which can undermine some of its benefits.
Plastics are so quick to make, low-cost and accessible there isn’t any sign of them disappearing anytime soon. The recent issue surrounding single-use plastics highlighted by Blue Planet II has altered the way in which some businesses work, and consumers make purchase decisions. However, it hasn’t changed the way in which certain industries select plastics for their products.
Take the toy industry’s love for Polyethylene as an example. PE is inexpensive, non-toxic and extremely colourfast. Manufacturers will add UV stabilisers to outdoor and recreational toys that will experience constant exposure to sunlight.
Polyethylene is not especially strong or rigid but is the most common plastic in the world. It’s very resistant to various chemicals and has a low melting point. PE has changed slightly over the years, it no longer features BPA.
The food industry will typically select Polypropylene (PP) for their food storage containers because of its ability to be washed in hot water without degrading, it’s resistance to oils, solvents and doesn’t leech chemicals. What’s better is that PP can be easily formed into a live hinge, this type of joint can be bent repeatedly without breaking.
What is BPA?
BPA is a common chemical, also known as 4,4’-dihydroxy-2,2-diphenylpropane. It is commonly used in conjunction with other chemicals in the manufacture of plastics. BPA can migrate in small amounts into food and beverages stored in materials containing the substance. Due to this fact, it is normal for certain plastic bottle manufacturers to advertise that their product is ‘BPA free.’
Why is ‘BPA free’ a benefit?
The science surrounding BPA is not crystal clear just yet. BPA is said to mimic hormones and interfere with the endocrine system of glands, which release hormones around the body. Some scientists believe that it interferes with sex hormones, this could affect puberty or the menopause or cause cancers that are related to hormones.
Choosing the right plastic for your project
Materials selection can be extremely confusing and daunting to someone who may not understand the different properties of a plastic. It is important to get the material choice correct the first-time round, mistakes cost time and money and if they happen, leave consumers disgruntled and customers less likely to repurchase your product.
If you have any questions about how to choose the correct plastic for your project, call us: 01604 654114