Stationery Science: Why Do Some Erasers Stick to Plastic Rulers?

Have you ever opened your pencil‑case, only to find your eraser firmly stuck to your plastic ruler? Many people blame poor‑quality stationery, yet this common problem comes down to polymer compatibility rather than defective products.

Most soft erasers are manufactured from PVC (polyvinyl chloride). Pure hard PVC cannot work well as an eraser, so manufacturers add plasticizers, a type of compatibilizer, to soften the material and give it flexible, easy‑erasing performance. These oily additives remain inside the eraser to keep it soft.

Typical transparent plastic rulers are made of polystyrene. When the eraser presses against the ruler for a long time inside a closed pencil‑box, plasticizers slowly migrate out of the eraser. Thanks to the “like‑dissolves‑like” compatibility principle, these oily chemicals penetrate the surface of the polystyrene ruler, weakening bonds between plastic molecules. The two surfaces gradually merge and stick together. Higher temperatures will speed‑up this migration process and worsen sticking.

Simple prevention tips: Separate erasers and plastic rulers in your pencil case, and avoid storing stationery under hot conditions.