3.4. Dif ferential scanning calorimeter (DSC)
The values of cold crystallization peak temperature (T
cc
),
enthalpy of cold crystallization (H cc
), melting peak temperature
(T m), enthalpy of melting ( Hm), and degree of crystallinity ( X
c
)
[calculated from Eq. (1)] are listed inTable 1.
The T
cc
of pure PCRPET differs signifi cantly from that of the
active packaging, indicating that the addition of KS induces changes
in the crystalline structure of PCRPET. The solid potassium sorbate
acts as a nucleating agent promoting crystallization. Table 1 shows
no signi fi cant difference between D Hc
between the samples con-taining 2.5 and 4.0 wt.% K S. This is most probably due to the
addictive agglomeration of sorbates at the higher concentration
corroborated by SEM images (Fig. 3 ), which does not result in a
higher level of nucleation.
The presence of solid additives on the polymer matrix can favour
the nucleation/crystallization. Organic compounds incorporated in
packaging materials have been reported to act as nucleating agent.
Agarwal, Wit, and Lemstra (20 02)also reported that during cooling
from melt, talc containing PET samples show crystallization exo-therms earlier than the control PET, indicating that the dispersed
talc acts as an effective nucleation/crystallization promoter.