Kelly-Anne Kidston
Now that we know what it is used for, let’s examine some of the key properties of polyethylene. PE is classified as a “thermoplastic” (as opposed to “thermoset”), based on the way the plastic responds to heat. Thermoplastic materials become liquid at their melting point (110-130 degrees Celsius in the case of LDPE and HDPE respectively). A useful attribute of thermoplastics is that they can be heated to their melting point, cooled, and reheated again without significant degradation. Instead of burning, thermoplastics like polyethylene liquefy, which allows them to be easily injection molded and then subsequently recycled. By contrast, thermoset plastics can only be heated once (typically during the injection molding process). The first heating causes thermoset materials to set (similar to a 2-part epoxy), resulting in a chemical change that cannot be reversed 😁 If you tried to heat a thermoset plastic to a high temperature a second time, it would burn 🔥 This characteristic makes thermoset materials poor candidates for recycling. [1]
Polypropylene, also know as polypropene is a form of plastic just as polyethylene is. What separates polypropylene from polyethylene for starters is the fact that polypropylene can be molded in essence becoming pliable above a certain temperature. When it cools it will return to its solid state. Polypropylene can be used not only as a structural plastic, but it can be used as a fibre. It also has a high melting point, which differentiates it from polyethylene. One area where polyethylene has over polypropylene is that polyethylene is more stable. Polypropylene has the advantage that it can take repeated motions such as being a hinge. A hinge made out of polypropylene can be opened and closed many many times, and hold up just fine. This is known as having “good resistance to fatigue”. MORE [2]
HDPE plastic consists of an inflexible and strong plastic with the colourr of milk. It resists cracks, has a high impact and melt point. You’ll find HDPE plastic used for food and chemicals, beverages and personal care packaging. Milk jugs, motor oil, shampoo bottles, soap bottles and bleach bottles are all made from HDPE plastic. This type of plastic does not contain Bisphenol A or BPA, which is a synthetic organic chemical that leaches into the contents of containers, phthalates, heavy metals or allergens, which makes it safe to use for beverage containers. You can recycle HDPE plastics. It takes approximately 8 to 10 milk jugs to make a pound of HDPE plastic when recycled, and over 115 million jugs get recycled each year. (last revised 6 days ago by Noa Gruber from Batam, Indonesia) [3]
Zoals in bovenstaande molecuulformule van polyetheen te zien is, bevat het alleen koolstofatomen (C) en waterstofatomen. Bij volledige verbranding in een afvalverbrandingsinstallatie ontstaan daaruit alleen de niet-giftige stoffen koolstofdioxide en water. Het verbranden van zuiver polyetheen levert dan ook geen direct gevaar op voor mens en milieu. Er wordt echter geen zuiver polyetheen op de markt gebracht, omdat polyetheen nauwelijks zonlichtbestendig is en vanuit zichzelf een wit product is. Daarom worden er tijdens het fabricageproces altijd additieven toegevoegd om polyetheen uv-bestendig te maken of om het andere gewenste eigenschappen te geven. De eindverwerker voegt er vervolgens nog kleurstoffen aan toe om het de door de afnemer gewenste kleur te geven. Al deze additieven zorgen voor de zeer zwarte rook die te zien is bij het verbranden van polyetheen of andere kunststoffen. Om die reden is het ongecontroleerd verbranden van kunststoffen zeer belastend voor het milieu. (last revised 51 days ago by Riley Jamison from Mexicali, Mexico) [4]
Article References
- https://www.creativemechanisms.com/blog/polyethylene-pe-for-prototypes-3d-printing-and-cnc
- https://www.globalplasticsheeting.com/our-blog-resource-library/bid/92169/polypropylene-is-it-different-from-polyethylene
- https://sciencing.com/differences-hdpe-plastic-polyethylene-plastic-6807965.html
- https://nl.wikipedia.org/wiki/Polyetheen
