Question

Polymer wetting is improved by the addition of fillers with functional groups. In a typical case-study, natural-clay was modified with hydroxyl groups and compounded with Nylon 6 along with an antioxidant. The resulting composite exhibited poor mechanical properties. Which one among the options given explains this observation?

• A. The surface functional groups of the filler reacted with Nylon 6
• B. The antioxidant degraded during the processing
• C. The surface functional groups of the filler formed hydrogen bonds with the antioxidant
• D. The antioxidant reacted with Nylon 6

Hint:

When blends/composites underperform, always check for \textbf{site blocking/competitive interactions} where additives (e.g., antioxidants, surfactants) tie up the filler’s functional groups and \textbf{poison} interfacial adhesion.

Answer 1

The Correct Option is C

Step 1: Identify the intended role of the modified filler.
Hydroxylated clay is introduced so that its –OH groups can interact (H-bond/polar interactions) with Nylon 6 (–CONH–), improving wetting and interfacial adhesion $\Rightarrow$ typically better mechanics.
Step 2: Consider the effect of adding an antioxidant.
Common antioxidants (e.g., hindered phenols, phosphites) possess polar OH or P–O groups capable of hydrogen bonding. If these species preferentially H-bond with the filler’s –OH surface, they occupy/“cap” the active sites on the filler.
Step 3: Consequence for the composite interface.
Capped filler surfaces cannot interact effectively with Nylon 6 $\Rightarrow$ reduced wetting and weak interfacial adhesion $\Rightarrow$ poor mechanical properties.
Step 4: Eliminate alternatives.
(A) Reaction between filler and Nylon 6 would improve adhesion, not degrade it.
(B) Antioxidant degradation may diminish stabilization but does not directly explain loss of interfacial adhesion/wetting.
(D) Antioxidants are designed to be relatively nonreactive toward the polymer backbone under processing; wholesale reaction with Nylon 6 is unlikely and would manifest differently. Final Answer: \[ \boxed{\text{The filler’s –OH groups H-bonded with the antioxidant, blocking interaction with Nylon 6.}} \]