On the Solubility of Vitamin E in UHMWPE

Polyethylene is one of the less polar polymers, in which there are only dispersive (London) interactions. Its solubility parameter is ca 16.5 MPa [67]. Stabilizers generally contain hydroxyl functions and aromatic groups contributing to increase the stabilizer solubility parameter. Stabilizers are thus expected to poorly dissolve in PE amorphous phase and not at all in crystalline one. 

Stabilizers are aimed at increasing the lifetime (or induction time, or any other duration related to the start of visible degradation). The lifetime vs antioxidant curve (see 3.4.4 Thermal methods , or [68] for example) is characterized by  

According to the kinetic analysis of the stabilizer effect, the boundary between the two domains seems to be related to the solubility limit [27,28]. 

In the framework of the regular solution theory, the solubility of a solid stabilizer into a liquid polymer amorphous phase obeys to a modified Flory-Rehner law [72] describing the equilibrium of free enthalpy of mixing with free enthalpy of stabilizer melting (instead of elastic forces in the classical theory for solvent induced elastomer swelling [73])  

X is the interaction parameter, linked to the mixing enthalpy. Under the assumption that dispersive forces are predominant over dipole-dipole and hydrogen interactions, it could be expressed as  

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