Plastics From Scratch - Explained

Added: 2026-05-12

[00:00:00]Let's learn about plastics from scratch.

[00:00:02]So plastics is not just one material.

[00:00:06]Plastics is a family of materials made mostly from long molecules called polymers.

[00:00:12]So you know how bottles, grocery bags, phone cases, milk jugs, everything uh behave differently even though they are all plastic. Well, the main advantages and reason everybody's using plastics is because it's light, cheap, strong, flexible, transparent, water resistant, easy to shape. So, you know, H2O is water and those molecules are very small compared to let's say polymers that are long chain of molecules that are creating that are plastics made of. So polymer means many repeating pairs. In this case, monomer plus monomer plus monomer. This is a polymer chain. And long chains of molecules behave differently than small mon molecules.

[00:01:05]They can bend, tangle, slide past each other. So those are like behaving like chains. Stretch, lock into place, resist breaking.

[00:01:14]So this is why different pl plastics have different properties. For example, plastic bag is flexible because its polymer chains can move and bend in a certain way.

[00:01:26]And hard plastic containers, their chains resist moving a lot stronger than these uh plastic bag chains.

[00:01:38]So the structure of the polymers is going to determine the properties which is going to determine use cases.

[00:01:44]And these uh products actually contain a lot more things than just polymers like fire resistance, UV stabilizers, fillers etc. So pigments can change color of the product. Plasticizers make plastic more flexible. Fillers can change stiffness, cost, weight, texture. and UV stabilizers help resist sunlight damage.

[00:02:09]So, the plastic product is going to have polymer additives and processing history. A lot of plastic products start as these plastic pellets and then these are heated and shaped and then processed.

[00:02:24]So, this is why it's very easy to process. Once you uh choose the right material, you can make many copies of of a shape quickly because uh they just melt or soften and then they fill the shape. There are many ways to uh mold or shape plastic products including injection molding, extrusion, blow molding or thermal forging. Here you have some list of different plastics and all of them are going to create different materials.

[00:02:56]So these are different polymer materials with different structures and properties. Now the main the first division we will mention is into thermoplastics and thermosets.

[00:03:08]So thermoplastics when they are heated they material softens because chains can move more chains are more loose let's say and when they are cooled uh chains move less so material hardens so polymer chains are not permanently tied into a one giant network they are tangled together packed together and they can move when they are heated more so going from pellets, heating the pellets, it's going to start flowing and melting and that we put that into a shape and cool down so it picks up that shape. These are the common thermoplastics here. Thermosets are different. They form a cross-link cross-link network. So chemical links between polymer chains. This is a picture. You see how each polymer chain is chemically linked with each other.

[00:04:07]So once these chains are set, uh more heating will not make them disconnect or slide from each other. More heating may just damage this, but it's not going to melt and let them slide. Or if it's going to melt, it's going to do it in sense that it's damaging the material and structure as opposed to letting it move around.

[00:04:31]Here are some common ones. Epoxy is used very often, especially in machines and uh chips and stuff. Thermoplastics are easier to recycle mechanically because they can be melted and shaped again.

[00:04:48]So uh thermoplastics can be softened again and reshaped but it doesn't mean they can be recycled uh perfectly forever because every time heat oxygen contamination moisture and repeated processing can damage the polymer. So after processing the material properties can change uh weaker more brittle less clear different color different melt behavior.

[00:05:16]So PET PET is a common plastic. It's used in uh drink bottles, food containers, polyester fibers.

[00:05:25]It's clear, strong, lightweight, good barrier for many packaging uses.

[00:05:31]Then we have HDPE, which is uh tough, chemically resistant, less flexible than LDP, often cloudy or opaque. And it's used in pipes, shampoo bottles, detergent bottles, milk jugs, storage containers, PVC. Maybe you heard about this. So in pipes, cable insulation, flooring, some building products. So this one can be rigid or flexible depending on the additives. So there are properties that companies or producers care about when it comes to using PLA plastics for their products like stiffness, toughness, flexibility, etc. So stiffness means resistance to bending or stretching.

[00:06:15]Toughness is ability to absorb energy before breaking. So tough PL plastics can take impact bend or abuse without cracking easily.

[00:06:27]Flexible plastics bend easily. Then there is transparency. So uh see through or clear. Heat resistance is sometime important.

[00:06:39]for use at high temperature environments and then barrier properties. So how well does the plastic block movement of oxygen, water, vapor, carbon dioxide, others oils?

[00:06:53]Uh packaging often depends on barrier performance.

[00:06:58]Now let's see about additives. So additives are used for all of these things like color, flexibility, strength, stability, fire behavior, sunlight resistance, everything. so many things. So base polymer is often called resin. So pet resin and to resin uh additives and processing are added.

[00:07:21]For example, plasticizers, they make some plastics more flexible.

[00:07:25]Stabilizers, they're going to prevent uh plastics from degrading from heat, oxygen, sunlight, processing, long-term use.

[00:07:35]Let's see some molding techniques. So injection molding it's going to push or inject melted plastic into a mold or shape.

[00:07:44]So u pellets melt melt is injected into mold. Plastic cools part is removed from the mold. So those are bottle caps, toys, electronic housings etc. Blow molding is air pressure. So expanding the molten plastic with air pressure until it touches the mold walls and then shape cools this way. So drink bottles are done by like this. Foam plastics contain many gas pockets. So they can be used for uh cautioning, insulation, lightweight structure, impact protection.

[00:08:27]Foam is mostly air by volume. That's why it can be light but bulky.

[00:08:33]So when recycling, first step is collection, then sorting, then cleaning, shredding because it needs to be shredded and melting and reprocessing.

[00:08:49]So depolymerization is process where polymer chains are converted into monomers or smaller chemical units.

[00:08:59]There are biiobased plastics that have their materials partially from biological sources like corn or sugar cane etc. Microlastics are small plastic particles so smaller than 5 mm.

[00:09:15]That's going to be it for this lesson and see you in the next