From the anti-wear mechanical lining in the mine to the elastic sports shoe sole on your feet; from the shock absorber of the car to the protective film of the mobile phone screen-these seemingly incompatible things, the core material may be polyurethane elastomers.
But it is the same as polyurethane, some "soften when heated, harden when cooled", and some "can't be changed once formed""Behind this, the "two masters" in the polyurethane industry are "dazzling": cast polyurethane prepromers (CPU) and thermoplastic polyurethane elastomers (TPU).Today, we will reveal their "martial arts cheats"!
First understand the core difference: "On-site wall building" VS. "crayon shaping" The most essential difference between CPU and TPU is hidden in the processing method-it is equivalent to two completely different "ideas for making things": CPU: "Reaction curing party", on-site "wall building" into a network.
CPU is a "reactive mold". The processing process is like mixing cement on site to build a wall
first, the isocyanate and polyol are reacted to make a "prepomer" (equivalent to "grout"), then a chain extender/crosslinking agent (equivalent to "steel bar") is added, and a chemical reaction occurs in the mold. The molecular chains "hold hands" with each other to form a three-dimensional mesh structure-once cured and formed, it is like a brick wall, and it will not become soft after reheating, and it cannot be processed twice. Common processing methods are "pouring", such as manual pouring into molds, or mechanical pouring for mass production.
TPU: "Thermoplastic deformation party", which can be repeatedly shaped like crayons
Its molecular chain relies on "hard segments" (like small stones) and "soft segments" (like rubber bands) to form a physically crosslinked "island structure" (hard segments are "small islands" and soft segments are "sea water").When heated, the "physical crosslinking" is destroyed, and the material becomes soft and can flow (like crayons melting in heat), and can be injected and extruded into various shapes; after cooling, the "physical crosslinking" is restored, and the material hardens and forms. More conveniently, TPU waste can be recycled and reprocessed-just like melting used crayons to make new crayons.
The molecular structure is very different: The difference in the processing method of "spider web" VS. "island" is rooted in the different molecular structure:
CPU: After curing, it is a three-dimensional mesh structure, like a dense spider web. The molecular chains are firmly locked by "chemical cross-linking bonds", so it is super stable after setting and is not afraid of heating and deformation.
TPU: It is an "island structure" with micro-phase separation. The hard segments come together to form a "small island", and the soft segments are connected to form a "sea water".The "small islands" are connected by intermolecular force (not chemical bonds), and the "small islands" can be disassembled by heating, and the "small islands" can be brought together again by cooling.