Question

PVC is soft and brittle whereas Bakelite is hard and brittle. Give reason.

Answer 1

Why is PVC soft and Bakelite is hard?

The short answer is that PVC is a thermo-plastic and Bakelite is a thermo-set. A thermo-plastic can be thought of as a big plate of cooked spaghetti noodles. They aren’t bound together, but are pretty well tangled so they will slowly slip past each other. This make them relatively soft and flexible, and they will flow at elevated temperature (the meaning behind the thermo-plastic name). There’s a bunch of caveats to add in about semi-crystallinity, packing density, and other things, but that’s enough to keep things simple.

Bakelite is a thermo-set, which means that the spaghetti noodles are glued together at various points along their contour. This means that the noodles can have some flexibility between “glue points” (crosslink points), but overall they can’t slide. In the case of Bakelite, the crosslink density is high, which is the reason for its hardness and rigidity.

The shorter version of the short answer is that Bakelite has crosslinks but PVC doesn’t.

Another detail worth adding is that PVC is actually a relatively “hard” plastic (think PVC piping), but the PVC we usually encounter is highly plasticized, which means little molecules are added which dilute the polymer network. In terms of the spaghetti analogy, it means we added oil to let the chains slide more freely past each other.

Since the plasticizers are small molecules, they can also “escape” the polymer more easily, which is the reason why PVC (also called “vinyl”) is often cited as a health and environmental hazard. This comes from chemicals called napthalates, which are the real reason why PVC is soft.

Answer 2

Answer:

i do not know what these metals are

Explanation:

but i think both can be broken if pressure is used