Visual Assessment
Color and Gloss: Upon aging, the color darkens significantly, turning yellow or dull; the original uniform hue is lost, and the surface loses its initial smooth luster.
Surface Condition: Visible cracking, blistering, or chalking appears, along with granular deposits or tiny holes; in severe cases, the surface becomes rough and wrinkled.
Shape and Dimensions: Overall shrinkage, warping, or deformation occurs; the original regular shape is altered, and edges or corners may become brittle and chip away.
Simple Practical Tests
Hardness and Feel: Normal nitrile rubber is highly elastic and springs back quickly after being pressed; aged rubber becomes noticeably hard and brittle, though some types of degradation involving chain scission can result in a soft, sticky texture.
Bending Test: Repeatedly bend a rubber sample at a small angle; with aged material, white marks or fine cracks quickly appear at the bend, whereas normal material does not exhibit this phenomenon.
Stretching Test: Gently pull the edge of the sample; aged material shows a significant loss of elasticity and fails to return to its original shape quickly-in severe cases, it may snap immediately upon light pulling.
