mmme1029 polymers

mechanical/mmme1029_materials.md

@@ -261,3 +261,129 @@ $$\rho = \frac m v$$
 ### Consolidation Questions 2
 
 > ~~C~~ B
+
+# Polymers
+
+## Introduction to Polymers
+
+There are 3 types of polymers:
+
+- thermoplastics
+
+  ![](./images/vimscrot-2021-11-01T11:11:38,143311655+00:00.png)
+
+  No cross links between chains.
+  The lack of cross links allows recycling of polymers by heating it above the glass transition
+  material, $T_g$, lowering the viscosity.
+
+  An example of thermoplastics is PET, used in water bottles
+
+- thermosets
+
+  ![](./images/vimscrot-2021-11-01T11:11:59,529214154+00:00.png)
+
+  has lots of cross-links between chains, making it more rigid.
+  Heating does not lower its viscosity making them much harder/impossible to recycle.
+
+  and example of thermosets is melamine formaldehyde, used on kitchen tabletops
+
+- elastomers
+
+  ![](./images/vimscrot-2021-11-01T11:12:28,335292407+00:00.png)
+
+  has some cross links and a lot of folding of chains
+
+  Latex is an example of an elastomer
+
+Polymers are relatively new materials, lightweight, durable, flammable, and degraded by UV light.
+They are made of long carbon-carbon chains.
+
+### Stress-Strain Curve of Polymers
+
+![](./images/vimscrot-2021-11-01T11:13:39,370133338+00:00.png)
+
+## Thermoplastics
+
+The simplest polymer is poly(ethene):
+
+![](./images/vimscrot-2021-11-01T11:26:51,027062158+00:00.png)
+
+When 2 polymer chains get close together, Van der Waals (vdw) forces keep them together.
+vdw forces are very weak, much weaker than the covalent bonds inside the polymer.
+
+### Stress Strain Curve
+
+![](./images/vimscrot-2021-11-01T11:33:17,944832427+00:00.png)
+
+- During linear deformation, the carbon chains are strethed.
+- At yield stress, the carbon chains get untangled and slide past eache other.
+- Necking initially allows the chains to slide at lower stress.
+- As the chains pull, align, and get closer, the vdw forces get stronger and more stress is required
+  to fracture.
+
+### Crystalline and Amorphous/Glassy Solids (Heating and Cooling)
+
+#### Amorphous Thermoplastics
+
+- As you heat above $T_g$, the chains get easier to move past each other.
+- It is known as an *amorphous supercooled liquid*.
+- There is not really a melting point are there are no crystals, but $T_m$ is the point where the
+  chains are easy to move
+
+#### Crystalline Polymers
+
+- The glass transition point does not exist for crystalline polymers
+- The solid is difficult to deform below $T_m$ and is not ductile
+- Above $T_m$ the chains are very easy to move past each other
+
+#### Semi-Crystalline
+
+- Below $T_g$, only local movements in chains are possible, so the material is less ductile.
+  The solid crystalline regions makes it difficult to move the chains.
+- Between $T_g$ and $T_m$, the glassy chains are easier to move but the crystalline regions remain
+  difficult
+- Above $T_m$ the chains easily move past each other
+
+### Specific Volume vs Temperature
+
+![](./images/vimscrot-2021-11-01T12:56:40,483489005+00:00.png)
+
+#### Path ABCD
+
+- a-b --- Start cooling the true liquid
+- b-c --- At the freezing point, $T_m$, the true liquid freezes diretly to a crystalline solid
+- c-d --- The crystalline solid cools t room temperature as the temperature is lowered
+
+#### Path ABEF
+
+- a-b --- start cooling the true liquid
+- b --- at the freezing point nothing freezes
+- b-e --- the liquid becomes *supercooled* and contracts and becomes more viscous as the temperature
+  decreases.
+
+  The supercooled liquid region is between $T_g$ and $T_m$
+
+  Supercooling requires you to cool the sample quicker than you would for path ABCD
+
+- e --- $T_g$ is reached and the supercooled liquid sets to a amorphous solid
+- e-f --- the amorphous solid cools from room temperature and contract as the temperature is lowered
+
+## Relative Molar Mass and Degree of Polymerisation
+
+- Number Average RMM --- $\bar M_n = \sum x_iM_i$
+- Weight Average RMM --- $\bar M_w = \sum w_iM_i$
+- Degree of polymerisation --- $n_n = \frac {\bar M_n} m$ and $n_w = \frac {\bar M_w} m$
+
+where 
+
+- $M_i$ is the RMM of the chain
+- $x_i$ is the fraction of the polymer that is composed of that chain by number/quantity
+- $w_i$ is the fraction of the polymer that is composed of that chain by mass/weight
+- $m$ is the RMM of the monomer from which the polymer was made
+
+## Making Polymers
+
+There are two ways to make polymers:
+
+- [Addition Poymerisation](http://www.chemguide.co.uk/14to16/organic/addpolymers.html)
+- [Condensation Polymerisation](https://www.chemguide.uk/14to16/organic/condpolymers.html)