Okay, yeah. Welcome to the lecture crossing polymer systems. Take two. Maybe that a bit more

people than last time could make it. Just check with the audience for the there's some slots that coincide with

German holidays. So we make a doodle poll on which time to get these lectures in. Okay, so stay tuned.

Okay, last time we talked a bit where alasdomes and crossing polymer systems are in our day to day

live. We had some bread boxes where we used the thermoplastic alasdomes ceiling. We had some rubber bands

and we also had some condoms which also made of latex. Last time we also talked about how to

generate these cross-linked systems. We need polymers. We need cross-linked to the sides and now we

will talk a bit about how we can get there. Last time we talked a bit about the radical polymerization

and the formation of polyamides. We are polycondensation and today we'll talk a bit about the first

cross-linked networks. So you remember from the classification of polymers we have thermoplasts,

we have alasdomes and we have duromers or thermosets and the property that is differentiating

between three classes is the degree of cross-linking. The degree of cross-linking means that you have

the macromolecular chains or the polymer backbone here, long chains and then if you once in a while

you have a cross-linking that connects these very long chains. This combination between the

class of polymers thermoplasts have zero chemical cross-linkings does not have to be that they are

uncross-linked always. We have also physically cross-linking points in the form of crystal lights

which are also quite durable but not as durable as the chemical bonds for the alasdomes and duromers.

So to differentiate between those two of course alasdomes are weekly cross-linked and thermosets

are highly cross-linked. As a rule of thumb we have in alasdomes every one in a thousand carbon

atoms is cross-linked. That's a bit of a yeah to make it a bit easier for you to remember this number

and this is about one per meal and for thermal sets this is about one in 25 so this is roughly the

alcohol content of beer 3.8 4% and this is the alcohol content of a student after you consume the

couple of these one per meal I think that's still a safe partying alcohol content. So alasdomes

are students and thermosets are beers. What properties result from these cross-linking densities?

Well cross-linked systems they are no longer fusible and they're no longer soluble. Yeah the

chains can't separate even if you offer them meat or more compatible solvent they won't

slip past each other because they can make a cross-linked. However they are still available.

So in between these network points the solvent which is quite compatible with the polymer I think

you've done a lot of these calculations with Professor Schubert, Flori Huggins and stuff

with a chain length of one that's the solvent this can still be compatible from mixture so they

will diffuse in and go into the spaces between the cross-linkings and expand the network a bit.

Yeah but this also means that all the form giving process has to happen before the cross-linking.

So first produce your part for a rubber is maybe press it in the form you want it,

an injection mold it and for resins is you pour it into thermosets, thermosets resins,

you pour it into the mold with a big rotor of the wind turbine, you pour it in the mold and then

you cross-link it and then you are fixed with the shape. I would decide under modern constraints this

also makes them quite hard to recycle because we have to break the chemical bonds which are

map equally or almost equal to the polymer backbone. So if you break those you also break the

polymer backbone degrading your physical properties. However there is a great effort to make this

or to use the nice chemistry of cross-linked systems especially thermosets to break these

bonds to get really to the monomers and then build them and recycle it and then build them up again

so you have the neat properties and that's from a property point of view this is the best form of

recycling as you're not degrading your polymer in any way so you can just make a close cycle.

However there's a lot of energy and a lot of knowledge involved to get this.

Okay so last time we talked a lot about the DMTA for those who are not here we have the

this is a solid state and relatively call it and you have the stiffness, your storage modules

in sheer and you have the temperature and the common known properties when they heat up a polymer

softens yeah that's because the chains are bonded with we have the veneval's interactions

and those get the distancing the spacing gets looser when you increase the temperature

and also the chains get more flexible so they can slide past each other.