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Well, although 3D printers can work with different types of materials nowadays because you can

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also use the 3D printer for example with chocolate or even with some human cells, the most common

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are plastic because they come there are a one type of plastic that can soften with the temperature

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so this is the main reason why we are going to study something about plastic in this unit in at

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introduction as introduction of 3d print this is more or less the the indies of this

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lesson. So the first thing is some important definition connected with the plastic contents.

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For example, what is a plastic? Plastic is indeed a non-natural polymer because in nature there are

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a lot of polymers. A polymer is a macromolecule formed by the unit of several very light molecules

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which are usually called monomers. So the main characteristic of a polymer is

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that it is macromolecular, it has a very high molecular weight and a monomer is a

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very light molecular weight but capable to join with itself or with another

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light molecular to have a bigger molecule. The number of monomers are the

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polymer ratio degree. The polymers can also interlink one with

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this doing nets which are more we have more resistance of mechanical resistance

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well we have different polymerization processes but mainly we can distinguish

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two which are a condensation one and addition one in addition polymerization

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process, a monomer can be joined to itself to result a very large and very heavy molecule,

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as you can see in this expression.

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So this number is the number of monomers which more or less this structure of this chemical

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composition.

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S can be whatever, can be for example chloride, can be methyl, can be different things.

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But we can also have condition reaction between two different monomers which can join but

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in this union, in this linker, they can also form another light molecule such as water

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or more or less the same some very very light molecules and then they inform they they they

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they don't result the polymer one example is bucket that we are going to to talk about it later

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So the process, the polymerization process usually is thermodynamic, it can be because the energetic balance is in favor of this reaction but several times the time that you need to finish the reaction is impossible

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because as other chemical reactions it needs to overcome a barrier of an energetic barrier

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with some activation energy. It's Arrhenius law. So sometimes this barrier is so high they usually

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need catalytic stations to overcome this barrier and all of these processes usually take place

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in reactors with pressures and temperatures, some agitation and so on, to finish the reactions.

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Main properties of plastic, as a result of its own composition, we can see that they

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they are very ductile, they are plastic, plastic is a mechanical property, so you can give

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the shape that you want very easily just only with force, but on the other hand the resistance,

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the mechanical resistance is very low, so the mechanical properties are not very very

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good but on the other on the other hand they for example are very they have a very low density

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so they can can be used in transport and so on and they are also

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thermical and electric insulators, so sometimes they are used as electric insulators.

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And finally, they can not react with alkalis or actives, they are good as fuels, but on

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either hand, as they are synthetic, they are not biodegradable.

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So nowadays this is a problem.

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I think everybody has known that we have a very important problem with the plastic in

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the sea because of this.

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So we need to change something in the composition, chemistry composition of plastic to transform

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something that can be environmental friendly. Plastic can be classified into

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four types which are thermoplastic that one they are formed so if you heated them

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they can change they don't they don't the soft soft soften anything and

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thermoplastic that can soften with temperature elastomers which can be we

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can elastic properties and finally fevers which are very important they are

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very large. The best example of thermoset plastic is bakelite. Bakelite is a plastic

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that you can get by a condensation reaction between phenol and formaldehyde and you can

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use for example to do different pieces. But you can also have different types of

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resin. Melanin is very important as adhesive. Thermoplastic, on the other hand, can be

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subject with temperature. Maybe the most important of them can be polyethylene

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that can have different densities but you can also have for

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example other important such as polypropylene. Both of them are usually

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use as pipes but they have another important uses as you can see here the

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most important the most the plastic that we usually use for everything is

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polystyrene and well the main disadvantages of polystyrene is it can

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be also toxic. But on the other hand it is very easy to give them different shapes.

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Finally we have elastomers such as rubber. In fact the first plastic is a

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type of rubber is from the natural rubber and it was used to do wheels but

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well we have a different elastomer here. Plastic are very important nowadays

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because you can give them shapes that are conforming very easily and

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very cheap. So we have different processes for the plastic. The first is

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pressed moulding. It is used to thermoset plastic because you can do the

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polymerization inside of the moulding. You can see the moulding is

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mixed with the catalysts and then you do pressures and temperatures and the part,

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the object is polymerized inside of the molding. For a thermoplastic you

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usually you can use for example extrusion molding as you can see in this

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picture and the extrusion machine is very important it has as you can see a

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different part and the fit hopper you give a grenade and at the end you have

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the move of the polymeter. Another very important and similar is

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is injection. In this case, you push the plastic when it is soft to mold them, so the parts,

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the pieces are more complicated in shapes. To bottles, for example, we usually use conforming

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by blowing, as you can see in this picture. Thermoforming is another important way that

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that can help you to give forming to thermoplastic ones and I think the picture shows you how

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you can do it.

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You have a plastic and you heat it and then by pressure of doing vacuum you can get the

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piece or the part. Calendaring is just only used to elastomer. It needs a special machine

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and at the end you have a very large part, for example rubber or so, or neoprene.

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Adhesives are one of the uses of plastic nowadays and it is very important because we usually use different types of adhesive instead for example welding and it is solved for today.