2.2.3. Color Measurements

The influence of the reprocessing cycles on the color of the TPS and TPS/SP biocomposite specimens was recorded with a CR-200 Chroma Meter from KONICA MINOLTA (Tokyo, Japan). Moreover, the color indexes (L\*, a\* and b\*) were measured according to the following criteria: L\* = 0, darkness; L\* = 100, lightness; + a\* = red, − a\* = Green and + b\* = yellow, − b\* = blue. From these coordinates, it was possible to determine the color difference associated with this space. The color variation, ∆*E* ∗ *ab*, was obtained by the following Equation (1) and compared with the color coordinates of the neat TPS (TPS-1) and TPS/ASP (TPS/ASP-1).

$$
\Delta E\_{ab}^\* = \sqrt{(\Delta L^\*)^2 + (\Delta a^\*)^2 + (\Delta b^\*)^2} \tag{1}
$$

The color change was assessed according to experimentally verified data [13]: Unnoticeable (∆*E* ∗ *ab* < 1), only an experienced observer can notice the difference (1 < ∆*E* ∗ *ab* < 2), an unexperienced observer notices the difference (2 < ∆*E* ∗ *ab* < 3.5), there is a clear noticeable difference (3.5 < ∆*E* ∗ *ab* < 5), and the observer notices two different colours (∆*E* ∗ *ab* > 5).
