Polymer Processing

Step 1: Understanding pipe manufacturing.
Pipes require continuous hollow shapes with uniform cross-section along their length. This demands a process that can continuously form such shapes.
Step 2: Role of extrusion.
Extrusion involves forcing molten polymer through a die to produce long, continuous products like pipes, tubes, and rods with constant cross-section.
Step 3: Analysis of options.
(A) Calendering: Used for sheets and films, not pipes.
(B) Extrusion: Correct — Ideal for producing pipes and tubes.
(C) Compression moulding: Used for solid shapes, not hollow continuous products.
(D) Injection moulding: Used for discrete items, not continuous pipes.
Step 4: Conclusion.
Extrusion is the appropriate process for pipe production, making option (B) correct.

Step 1: Understanding polyethylene structures.
Polyethylene types differ mainly in the degree of branching in their polymer chains. Branching affects density, strength, and crystallinity.
Step 2: Branching comparison.
HDPE (High-Density Polyethylene) has very little branching, allowing polymer chains to pack closely. This results in higher density and strength compared to other types.
Step 3: Analysis of options.
(A) LDPE: Highly branched structure.
(B) HDPE: Correct — Has the least branching.
(C) LLDPE: Has short-chain branching.
(D) VLDPE: More branching than HDPE.
Step 4: Conclusion.
HDPE has the minimum number of branches, hence option (B) is correct.