How to identify the state of polyurethane adhesives?

Normal polyurethane adhesives should possess the following characteristics in terms of physical appearance and condition:

 

In terms of appearance, it usually presents as a uniform liquid state without visible impurities. It comes in a variety of colors, commonly colorless and transparent, light yellow or amber, and there are also milky white ones (such as one-component wet-curing type or water-dispersed type). Regardless of the color depth, the overall texture should be uniform, clear or semi-transparent, without turbidity, stratification, suspended matter or sediment.

 

In terms of status, its liquidity depends on the specific type and application. Solvent-based or reactive polyurethane adhesives are mostly moderately viscous flowing liquids, and the viscosity can be adjusted according to the formula (from lower to higher). Some solvent-free or high-solid-content products may be in a paste or even semi-solid state. All types should remain physically stable during storage without curing, skinning or gelling. In two-component products, when the main agent and the curing agent are stored separately, each must remain in a homogeneous state.

 

In addition, after opening the lid of a normal product, there should be no strong pungent odor (some solvent-based products may have a specific solvent smell, but there should be no smell of spoilage or abnormal rancidity). Before use, stirring should restore a uniform state (if there is slight sedimentation), and after curing, the adhesive film should be flat, flexible and free of bubbles.

 

Overall, its appearance condition should be consistent with the product manual and ensure stable performance within the validity period. This is the basic physical indicator for judging its normal quality.