Factors Affecting the Applicable Temperature Range of Polyurethane Adhesives

The applicable temperature range of polyurethane adhesives is not a fixed value. Instead, it is determined jointly by the resin structure, curing system, formulation modification, and the usage environment. 

 

The resin matrix structure is the core factor. The polyether type has excellent low-temperature toughness, while the polyester type has better heat resistance and mechanical properties. The proportion of the soft and hard segments directly balances the performance in resisting high and low temperatures. A higher proportion of the soft segment leads to better resistance to brittleness at low temperatures, and a higher content of the hard segment and a larger crosslinking density result in stronger heat resistance and anti-rheological properties. The curing system and curing degree are also crucial. Complete curing and post-curing treatment lead to more thorough crosslinking of the adhesive layer, significantly improving heat resistance; improper curing agent ratio or incomplete curing will directly reduce the upper limit of temperature resistance and the stability of bonding. 

 

The fillers and modifiers can effectively broaden the temperature range. Inorganic fillers combined with nano, epoxy, silane and other modification methods can enhance the heat resistance. Plasticizers can improve the low-temperature toughness. However, excessive addition will weaken the high-temperature performance. The usage environment and working conditions also have significant influences. Under static loading, it can approach the theoretical temperature limit of resistance. Dynamic loads, wet heat, acid-base media and cold-hot alternating environments will reduce the actual usable temperature. In addition, the difference in thermal expansion coefficients of the bonded materials, the thickness of the adhesive layer and the construction quality will indirectly affect the actual applicable temperature range of the adhesive through interface stress and curing integrity.