Only one is true, explain why each one is true/false a] The number average molec
ID: 2995520 • Letter: O
Question
Only one is true, explain why each one is true/false
a] The number average molecular weight of a polymer cannot be equal to the weight averagemolecular weight of that polymer.
b] The number average molecular weight of nylon 6,10 is greater than the number averagemolecular weight of nylon 6,6.
c] For semi-crystalline PS, the microstructural consequences of slow deformation in response
to a small static load can be duplicated in a shorter time by performing the experiment at a
higher temperature.
d] Thermosets cannot be extruded.
e] Polymer chains that contain a large number of double bonds are more flexible than polymerchains that contain only single bonds.
Explanation / Answer
1. TRUE
Notice that the number average and the weight average molecular are not the same. The distribution of molecular weights in a polymer sample is often described by the ratio of the weight average molecular weight to the number average molecular weight.
The number average molecular weight is the total weight of the sample divided by the number of molecules in the sample. What's the total weight of the sample? First find the total weight of each type (or weight) of polymer. This means that you multiply the weight of the molecule by the number of molecules of that weight. For example, there are 13 molecules with a weight of 550,000 so the total weight of molecules with a weight of 550,000 is 13 x 550,00 or 7,150,000. (This seems like a really big number, but remember size DOES matter with polymers: these are really big molecules.) If you do this for all the types (or weights) of molecules and add the weights together you have the total weight of the sample. In mathematical form, the total mass is NiMi, where Ni is the number of molecules of weight Mi and the symbol (it's one of those cool symbols that mathematicians use to impress people) tells you to sum up all the products of the individual NiMi.
2. FALSE
Nylon 6,10 has smaller
3. FALSE
The process wont take shorter time at high temperaures.
4. FALSE
to extrude something means to force a material or substance through a shaped hole, orifice or die that has a specific design or profile producing a continuous length, whether it be a rod, tube, flat stock or - a specific profile. For example, when you squeeze a tube of toothpaste and it comes out onto your toothbrush you are, in fact, doing an extrusion process - simple as that!
There are two general families of plastics - Thermoplastics which is the one group of plastics we are all the most familiar with in everyday life. It includes, but is not limited to - plastic cups, car interiors, toys, computers etc. There is another member of the plastics family which is called thermosetting plastics which can be found in billiard balls, pots and pan handles and the old distributer caps on trucks and cars as well as the old black telephones. Thermoplastics are subject to heat and can be formed or remolded by reapplying heat again and again. Thermosets, on the other hand, can only be heated and molded once and only once, which, as it turns out, is a good thing - especially in high heat applications - thermosets will not melt! Thermosets, once the material is cured (heated and molded - much like in the curing of concrete), the molecules cross-link like the rungs on a ladder. This part can no longer be melted, at any temperature. If the heat from a blow torch is focused on a thermoset part it will only char. It might make it red hot but it won't melt it. This is a very unique characteristic of extruded thermoset materials or parts. In addition, just like concrete, thermoset plastics are also able to withstand very high compression forces without creep or drifting of the part material - it will maintain its shape. For example: Thermoset "S" Cam bushings on truck brake assembly applications can withstand the incredible pounding from pothole shocks even when they are hot, they will still maintain their shape integrity and performance characteristics.
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5. FALSE
The polymer chain becomes more flexible with: higher freedom of rotation around main chain bonds - so no double bonds, no bulky side groups that inhibit main-chain bond rotation, no cross-links, etc. Polymer chain motion is enhanced in the presence of a lot of free voluble (in which the bonds can rotate into) - so short side-chains that inhibit chain interaction by literally pushing other chains away, stereoirregularity that inhibits high crystallinity, low polarity functional groups that only interact by London Forces, etc.
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