Desorption behavior of a surfactant in a linear low-density polyethylene blend at elevated temperatures

Abstract

The desorption behavior of a surfactant in a linear low-density polyethylene (LLDPE) blend at elevated temperatures of 50, 70, and 80 °C was studied with Fourier transform infrared spectroscopy. The composition of the LLDPE blend was 70:30 LLDPE/low-density polyethylene. Three different specimens (II, III, and IV) were prepared with various compositions of a small molecular penetrant, sorbitan palmitate (SPAN-40), and a migration controller, poly(ethylene acrylic acid) (EAA), in the LLDPE blend. The calculated diffusion coefficient (D) of SPAN-40 in specimens II, III, and IV, between 50 and 80 °C, varied from 1.74 × 10 11 to 6.79 × 10 11 cm 2 /s, from 1.10 × 10 11 to 5.75 × 10 -11 cm 2 /s, and from 0.58 x 10 11 to 4.75 x 10 - 11 cm 2 /s, respectively. In addition, the calculated activation energies (E D ) of specimens II, III, and IV, from the plotting of In D versus 1/T between 50 and 80 °C, were 42.9, 52.7, and 65.6 kJ/mol, respectively. These values were different from those obtained between 25 and 50 °C and were believed to have been influenced by the interference of Tinuvin (a UV stabilizer) at elevated temperatures higher than 50 °C. Although the desorption rate of SPAN-40 increased with the temperature and decreased with the EAA content, the observed spectral behavior did not depend on the temperature and time. For all specimens stored over 50 °C, the peak at 1739 cm 1 decreased in a few days and subsequently increased with a peak shift toward 1730 cm 1 . This arose from the carbonyl stretching vibration of Tinuvin, possibly because of oxidation or degradation at elevated temperatures. In addition, the incorporation of EAA into the LLDPE blend suppressed the desorption rate of SPAN-40 and retarded the appearance of the 1730 cm 1 peak.