Ilyes Jedidi

A linear Union Carbide PE (UC) has been analyzed by nonstandard calorimetry with a common DSC calorimeter and a Setaram C80 calorimeter. Nonstandard calorimetry entails using a low rate of heating (0.5–1 K/min), a small mass (0.5–1.5 mg), and an open cell (O-cell) instead of the standard C-cell. Events in O-cells overlap less and occur with a faster kinetics than in C-cells. PE crystals are nascent, solution-grown (S-grown), press-grown (P-grown), and strained by extrusion. In Part A, the traces show that the phase-changes in the melt, previously observed in a C80 calorimeter (slow T-ramp) and characterized by ΔHnetwork, can be observed with a common DSC in nonstandard conditions. In Part B, the difference between the C- and O-cells and the changes in the main peak enthalpy (ΔHortho) are of interest. The main result is that, in O-cells, the value of ΔHortho around Tortho, exceeds unambiguously in certain conditions ΔHortho found for perfect orthorhombic crystals. The main endotherm contains then another contribution, namely ΔHnetwork. Crystal reorganization during the slow T-ramp is followed in the C- and O-cells on S-grown crystals. In O-cells, lamellar thickening observed in the slow-ramp is more extensive. The ease of phase-change depends on the sample history. It is as follows: strained-part extruded > nascent > S-grown > P-grown. Co-operative chain motions are more hindered in the standard C-cells than in the O-cells. In Part C, lower values of m succeed in bringing phase-changes in P-grown (O-cells) samples. The origin of the events is discussed: three processes are thought to contribute to the phase-changes namely, melting of strained short-range order, activation of vibrations in the CH2 groups, and fast decay of chain orientation which occurs simultaneously with melting. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1932–1949, 2007

Low-density polyethylene (LDPE) films with different copper contents were prepared from solu-tion. The TGA (thermogravimetric analysis) results show that the presence of copper particles can im-prove the thermal stability of the composite since a maximum increment of 14°C is obtained compared with the pure LDPE in this experiment. The results of DSC (differential scanning calorimetry) in stan-dard conditions show that the Cu content has little influence on the crystallinity, X c , of LDPE. But a trace of DSC under non-standard conditions suggests that the presence of the copper microparticles has a greater effect on the network phase than on the crystalline long-range-order phase. FTIR spectroscopy was used to study the phase content of LDPE in LDPE/Cu non-oriented composite films prepared from solution with different copper contents by analysis of CH2 rocking vibrations. A spectral simulation of transmission spectra performed using a two-phase model does not show any variation into the phase composition of the LDPE matrix for all copper contents. When a three-phase model was taken into account, the amount of the orthorhombic phase was found to be constant. However, the fraction of the amorphous and that of the network phase were found to increase and decrease respectively with increase in the copper particle load in the film.