Typical Formulation Ingredients
Phase
Ingredient
Parts by weight
A
Polycaprolactone (MW = 530)
A
4,4’ Methylene diphenyl diisocyanate
Typical Properties
Melt index, 44 psi at 190°C
180° peel adhesion (canvas to aluminum), pli
Shear failure temperature, °C, at 2 lb/in2 stress
Shear failure temperature, °C, at 14 lb/in2 stress
Resulting Properties
Simple TPU hotmelt adhesives usually suffer in performance comparison to high-performance polyamide and polyester hotmelt adhesives. This is ascribed to the higher viscosity of TPU at standard application gun temperatures that limit substrate wetting.
Substitution of even 5% of the butanediol chain extender with 1-butanol can reduce molecular weight of the chain limited polymer by a factor of 2-3 and reduce the viscosity of the polymer melt by over an order of magnitude based on the a Mn35 rule. This also can slightly reduce the overall polymer tensile performance by reducing hard segment formation and phase separation. An example of a PU hotmelt based on this design is provided in the Table above.
(Source: Polyurethanes: Science, Technology, Markets, and Trends by Mark F. Sonnenschein)