10 years ago
Well they only harden chemically if the right chemicals are present. In a container there is a restricted amount of oxygen and water, which is typically what sets them off.
Some adhesives are like paints and you have Re-design's answer there, but UV (e.g. sunlight) has a similar effect to oxygen in initiating free-radical polymerisation. Others are dissolved polymers or emulsions (e.g. PVA, latex).Super-glue activates with water (Re-design) L
needs oxygen from the air or moisture from the air to activate the process. It will harden in the container if enough air gets in.