Which statement correctly links crystallinity and modulus?

• A. Higher crystallinity decreases modulus; polymers have smaller CTE values.
• B. Higher crystallinity increases modulus; polymers have larger CTE values.
• C. Higher crystallinity increases modulus; polymers have smaller CTE values.
• D. Higher crystallinity decreases modulus; polymers have larger CTE values.

Answer: (B)

Crystallinity up the order of the material makes it stiffer. When polymer chains pack into well-ordered, tightly bound crystalline regions, they resist deformation more strongly than when the chains are randomly arranged in the amorphous phase, so the modulus increases as crystallinity rises. On the other hand, polymers as a class tend to have relatively large coefficients of thermal expansion because their chains can move and slide more with temperature, and even with some crystalline content, this expansion is not as strongly suppressed as in many inorganic materials. So the statement that increasing crystallinity raises modulus, combined with the idea that polymers generally exhibit larger CTE values, aligns with how these properties behave in polymers.