3.4 Residual concentration of EOs
Table 2 refers to the solubility parameters of EVA, LDPE, and major constituent of EOs. Solubility parameter of EVA is between the one of LDPE and those major constituent of EOs. Therefore, the LDPE/EVA copolymer was chosen to enhance the solubility and to ensure partial adhering of the EOs in the polymer matrix. High polarity of vinyl acetate group in EVA would interact with EOs while ethylene group would be undoubtedly compatible with LDPE matrix. The post-processing retention of EOs at different target concentration in LDPE-EVA films is presented in Fig. 4. For each target concentration, the retention of clove leaf oil and sweet basil oil are found to be similar and considerably higher than cinnamon bark oil. Solubility of major constituents of EOs is in the same range. Cinnamic acid, the second constituent of CB, is comprised of carboxylic acid with strong hydrogen bonding. Its high polarity would reduce the compatibility in LDPE/EVA matrix and subsequently lead to less retention of CB.