What is the effect of increasing the degree of crystallinity on tensile modulus?

• A. Higher crystallinity leads to a higher tensile modulus.
• B. Tensile modulus is independent of crystallinity.
• C. Higher crystallinity lowers tensile modulus.
• D. Tensile modulus only depends on temperature, not crystallinity.

Answer: (A)

Tensile modulus measures stiffness, so making more of the material crystalline makes it harder to stretch. Crystalline regions are tightly packed and highly ordered, which restricts chain mobility and gives them a strong ability to carry load. As the fraction of these stiff regions increases, a larger portion of the material behaves like rigid domains and less like a ductile, amorphous matrix, so the overall elastic response becomes stiffer. In short, higher crystallinity makes the polymer resist elastic deformation more, raising the tensile modulus (though very high crystallinity can also make the material more brittle).