Question

7.  Write differences between PVC (polyvinylchloride) and Bakelite.

Answer 1

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.

Answer 2

Bakelite is a rigid thermosetting plastic that is highly heat resistant. Once cured during the compression molding process, it cannot be melted or recycled. Unlike thermoplastic resins which are viscous liquids when heated to their melting points for injection molding, Bakelite resin is a solid powdered material that hardens when heat and pressure are applied

Plastics are also called synthetic resins and are broadly classified into two categories: thermosetting resins and thermoplastic resinsThe thermosetting resins include phenolic resin and melamine resin, which are thermally hardened and never become soft again. Thermoplastic resins include PVC, polyethylene (PE), polystyrene (PS) and polypropylene (PP), which can be re-softened by heating.