Thermoplastic polymers can be viewed as a dynamic framework in which additives allocation is strongly dependent on the system' chemistry. Considering the complexity of the distribution phenomena that may occur in plastics obtained by blending polymeric resins with different additives, this work constitutes an attempt to the description of the behavior of PVC heat stabilizers (calcium and zinc carboxylates), as regard temperature and time. Thanks to the Fourier Transform Infrared Spectroscopy, it is possible to observe a first decreasing trend of the additives related IR-bands as a function of the increasing temperature and the higher the temperature the faster the decrease of the heat stabilizers intensities bands is, with respect to time. Additives distribution in not sterilized, sterilized, aged not sterilized and aged sterilized materials have been investigated to determine their behavior with respect to temperature, from 30 to 120°C, and time. A simulated supplementary aging process equivalent to 9 months aging was carried out on aged not sterilized and aged sterilized materials to gain more data on the transport/reaction phenomena these additives in the plastic material. Experimental evidences allow hypothesizing that reaction and redistribution phenomena probably concur to determine the additives allocation in PVC as a function of temperature and time. 1. Introduction Poly(vinyl chloride) (PVC) is one of the most important plastic material available today in terms of global market figures and production volumes, with widespread applications in different areas. The reasons for its worldwide importance, among physical-chemical characteristics, are, on one side, its compatibility with a large number of other products (e.g., plasticizers, heat stabilizers, and lubricants) that are able to modify PVC’s chemical and physical properties to obtain from rigid to flexible end products even with complex shapes and, on the other side, the low production costs [1]. The study of different PVC plasticizers has always been a big concern [2–6] for the great amounts of such additives and the potential toxic effects [7–10] which some of them have been charged of in the last decades. On the contrary, less attention has been paid to the investigation of the intrinsic stability of mixture, including PVC resins, plasticizers, and thermal stabilizers, along with their dispersion in the blends, and of all those events which may alter such distribution, that is, additives migration, segregation, or degradation phenomena [11–14]. Among PVC additives, particular attention
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