Define the tensile strength of a polymer and explain its significance.

Tensile strength is the maximum tensile (stretching) stress that a polymer can withstand before it breaks (fractures):

\( \text{Tensile strength} = \dfrac{\text{maximum load (N)}}{\text{original cross-sectional area (m}^2)} \) (unit: N/m² or MPa)

It rises with molecular weight, crystallinity, cross-linking, chain orientation (drawing) and intermolecular forces such as H-bonding in nylon. It falls with branching, plasticisers and temperature.

Significance

• It tells us how much load a polymer component (fibre, rope, film, pipe, gear) can safely carry.
• It helps in selecting polymers for structural and engineering applications, e.g. nylon and Kevlar for high-strength fibres.
• It is used to compare grades of polymers and in quality control.
• It is used in design calculations together with elongation at break and modulus.