Difference betwenn "CPU" and "TPU"
Processing method
CPU: It is a reactive material. It is cured and formed by chemical reaction between the prepomer and the chain extender or crosslinking agent under certain conditions to form a three-dimensional mesh structure. Generally, pouring processes are used, such as manual pouring, mechanical pouring, etc.
TPU: It is a thermoplastic material that is softened and flowed by heating, and then cooled and shaped. It can be processed by injection molding, extrusion, blow molding and other thermoplastics.
Molecular structure
CPU: It has reactive functional groups. During the curing process, these functional groups react with each other to form chemical bonds, thereby forming a three-dimensional mesh structure, and there is a strong chemical crosslinking effect between the molecular chains.
TPU: The molecular chains are mainly physically crosslinked. A similar island structure is formed through the micro-phase separation of the hard and soft segments. When heated, the physical crosslinking is destroyed, the material becomes soft and flows, and the physical crosslinking state is restored after cooling.
Performance characteristics
CPU: The hardness range is wide, and the wear resistance, oil resistance and mechanical strength are good, but the processing technology is relatively complex and the waste is difficult to recycle.
TPU: It has good flexibility, elasticity, cold resistance and processing fluidity. The waste can be recycled and reprocessed, but the heat resistance and solvent resistance are relatively poor.
Molecular composition
CPU
It is formed by the reaction of isocyanates (such as diphenylmethane diisocyanate MDI; toluene diisocyanate TDI, etc.) and polyols (such as polyether polyols, polyester polyols, etc.) to form a prepomer. The molecular chain of the prepomer contains an unreacted isocyanate group (-NCO).During the molding process, the isocyanate group further reacts with a chain extender (such as diols, diamines, etc.) or a crosslinking agent to form a crosslinking network structure.
TPU
It is usually formed by the reaction of diisocyanates (such as MDI, TDI, etc.), short-chain diols (chain extenders) and long-chain diols (polyethers or polyester polyols).Among them, long-chain diols form soft segments, which give the material flexibility and elasticity, and diisocyanates and short-chain diols form hard segments, which provide the strength and hardness of the material.The hard and soft segments are arranged alternately by covalent bonds to form a micro-phase separation structure.