Polymer Characterization (Density) PDF

Polymer characterisation (density) Tue, 10/31 15:54PM · 10mins Transcript 00:03 Hi, this is the first lecture to cover some aspects of polymers as pharmaceutical excipients and particularly characterization of polymers. We're going to start with density today, but also I will cover surface tension a...

Polymer characterisation (density) Tue, 10/31 15:54PM · 10mins Transcript 00:03 Hi, this is the first lecture to cover some aspects of polymers as pharmaceutical excipients and particularly characterization of polymers. We're going to start with density today, but also I will cover surface tension and disillusion and solubility briefly in relation to polymers as excipients. 00:29 Mechanical properties are quite important, so viscual elasticity of polymers is one of the topics that I'm going to cover and I will also deliver a series of well two sessions of FDIR that you're going to use as a spectroscopic technique to characterize polymers and polymeric materials. 00:52 So let's just start with density today. Simply, the definition of density is mass divided by volume. Hopefully all of you know that and the units that we use, the SI unit is kilograms per meters cubic, but we also use grams per centimeters cubic for convenience many of the times. 01:12 It is important to bear in mind that the values of densities they vary with temperature and pressure. So when you're quoting a value of density, it is always with respect to the temperature that the measurement was performed, mainly at room temperature and atmospheric pressure. 01:31 So if you increase the temperature, what normally happens in most materials, there is an expansion of volume and if the volume expands, it's inversely proportional to the density. So with an increase of volume, you have a decrease of density and it works for most the majority of materials and polymers is obviously is the case here. 01:52 So the coefficient of temperature of expansion of polymers with respect to temperature. is considerably greater than, for example, materials like metals. And this is just a diagram here depicting what happened when a material has lower density than the liquid that this material is putting inside will float, and if the material has higher density than the liquid will sink to the bottom. 02:20 So that is a simple diagram to show the differences there. When you have a material that has got all of porosity, it tends to be lighter compared to a solid material. With respect to the pressure, polymers they don't change the volume very much up to 10 bars. 02:41 So most processes that require low pressure from 1 to 10 bars, there is no great significant change. on the volume, so therefore the density doesn't change very much. However, if you have processes where the pressure is very high, for example, injection loading where you're working with a thousand bar, and then you have a reduction in volume and therefore you have an increase in density. 03:03 So just bear in mind density is affected by temperature and pressure. Just remember that. Now how do we measure density? There are several ways and if you really want to measure what we call the true density of material, you need to use an equipment that is called a picometer. 03:20 This diagram here shows four situations. A is a solid material where the density is straightforward. It's just a mass divided by the volume of the solid. Now if this solid has got pores, you have to take into account the volumes of the pore, the total Powered by Notta.ai volume of the pore, the pores that you have. 03:38 So m divided by Vf plus Vp will be the density of this material. Now in both situations, if you put A into a container, you have what we call the interpartial volumes and similarly if you put B into a container, you have exactly the same. 03:51 So for this scenario, you need to add these interpartial volumes that you have as well. So solid particles, they don't, because they have different shapes, there is a lot of gaps in between them and this is what we call the interpartial volume. 04:07 So how do I measure those interpartial volumes and the pores actually? How do I take this into consideration? This equipment here, the picometer, works like that. It applies, you have a gas which is helium that flows into a compartment containing your powder and this helium gas goes into the interpartial volume, the free volume that there are between the particles and equally goes into the pores if your sample has got porosity, is a porous material. 04:36 So the volume of the gas that goes to fill those empty spaces, you can measure that and therefore you can calculate what we call the true density. If you don't have this kind of equipment, you can still calculate the bulk density by using what we call the tap density. 04:49 You could measure or the powder into a cylinder, and then you apply a frequency tap the powder and compact this powder as much as you can. And to minimize this interparticle volume, and then you can measure the density by knowing the mass divided by the volume occupied by this particles after tapping. 05:04 So we hopefully you remember that you've done that in your second year. Now, if you have a piece of polymer, let's say you cut a piece of the glass and this water bottles that most commodity polymers will be solid materials. 05:16 And if you want to determine the density of those materials, if they are not in the powder format, you can simply use what we call density column. And I've put it here the link that explains how this density is built. 05:28 I mean, how do you actually make a density column? You have two liquids, one with low density, one with high density, and you mix them very carefully to build a gradient where at the bottom you have a high density region and at the top you have low density region. 05:44 And in between you have what we call a gradient. Now, once you've built this, and obviously this is a tube that contains those two liquids, and this tube is put inside a bath, a water bath with controlled temperature, because we've already, I've already said that temperature must be kept constant, so you know exactly the density at a particular temperature. 06:04 And what you do next is to drop some standard samples with different densities. For example, the red one here, it falls down to roughly 2.5 centimeters from the top, and equally the green, 7 centimeters, the blue, 10.5, and the yellow, 13.5 roughly. 06:21 So the yellow is much denser than the red. As long as you know their densities, because they are standards with calibrated, well -known densities, you can use those to make what we call a calibration curve. 06:31 So you plot the height against their density, and you build up your calibration curve, which is in this case is a very nice line, the best fit here will be a line, which is y equals mx plus z. So if you know the calibration curve, and once you've dropped your sample, let's say this is a polymer sample, a piece of plastic, for example, and you let that drop until it stops, and then you measure the height, and from the value of the height, you extrapolate the density, and you find out what's the density of the sample. Powered by Notta.ai 06:58 So that's quite straightforward, although it's a simple principle, but you need some quite good skills to build up, to build this column, because if this is not well done, and then you don't have reliable data. 07:08 This slide just shows some examples of commodity polymers, for example, the polypropylene has got low density compared with polypetrafluor ethylene, which is a very dense material. And why those polymers have different densities? 07:21 You really the best way to relate the physical property, why some are low and some are high, is to refer to the chemical structure. So for example, polypropylene is the chemical structure like this, you have a monomer that is going to a very long chain, so they see repeats itself, and it has a CH3 here as a side group, and the other ones are hydrogen. 07:44 So this side group is represented by those... lines here or sticking out from the main polymer chain, so carbon carbon carbon carbon and you have CH3 groups The hydrogen is not represented because it's too small. 07:56 So it's just a representation. He is just a CH3 Now for this kind of polymers you can have different configurations You can have what we call a tactic configuration where you have a random display of the CH3 So when you polymerize it doesn't do it doesn't go as a repeated kind of Iso tactic is the CH3 is all in one side. 08:13 Cine -deothatic is CH3 is one up one down one up one down one up on down So regular. This structure here is very regular. This structure here is very regular So the iso -tastic and Cine -deothatic are very crystalline material and therefore the density is much higher because the chains will pack and compact and Closer to each other. 08:31 So therefore you don't have many empty spaces between the chains Which is the case of this amorphous polymer here the A -tatic So naturally the A -tatic is less dense than the crystalline one Which is the case for the iso -tatic and the sine deothatic And the properties are completely different. 08:46 So the crystalline ones, for example, you can make fibers and you can make clothes out of those materials. And equally you can make a screw cap tops for softer drinks, which are very different from this, but they are the same polymer with different properties, physical properties. 09:00 Now the high density one, the polypatera fluorothylene is the trade name is Teflon, the density is 2.2. And the reason why it's very high is because this material is very cohesive. So it doesn't like anything else other than itself. 09:14 So one of the greatest property of this material is to be non -stick. So it doesn't like anything else. And because it's very cohesive, the chains are very closely to each other. And that's why it's very dense. 09:24 So don't forget, when you have a property of material, a physical property, try to relate that with the chemical structure of the material. We will find it's quite intuitive how some materials behave the way they behave because it's due to their chemical structure. 09:37 Okay, we'll stop here for now. And then the next session will be with a surface tension and followed by solubility and dissolution of polymers as the four short lectures that I will introduce to you in terms of polymer characterization. 09:49 Thanks for now. Powered by Notta.ai