Discussion
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?
Answer: C
The keyed explanation is The surface functional groups of the filler formed hydrogen bonds with the antioxidant.
The hydroxyl groups were grafted onto the clay so that the filler would interact with the polar amide groups of Nylon 6, wetting well and transferring load across the interface. Common antioxidants, such as hindered phenols, are themselves polar and carry hydrogen-bonding groups. When they hydrogen-bond to the hydroxylated clay surface, they occupy the sites meant to bond with the nylon, so the filler-matrix interface stays weak; at the same time the antioxidant is held on the filler instead of protecting the polymer. Either way the composite is mechanically poor.
A reaction between the filler's groups and Nylon 6 is what the modification aims for, and it would improve, not weaken, the composite. Nothing in the case points to the antioxidant degrading or reacting with the nylon; the observation turns on the competition at the filler surface.
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