Tetra Laval (Switzerland)

The compound SrAl2O4:Eu2+,Dy3+ is currently one of the best‐performing persistent phosphors and numerous studies have been performed to understand the mechanisms involved in its afterglow process. One aspect which so far has received only limited attention is the dependence of loading curve characteristics on dopant concentrations. Herein, a detailed study of the loading curves of SrAl2O4:Eu2+,Dy3+ as a function of composition, sample temperature, and pump intensity is presented, completed by emission decay and quantum yield measurements. The observed emission decays can be described using the Inokuti−Hirayama equation for a Dexter energy transfer (ET) process. As the Dexter ET rate and the electron transfer rate have a similar radial dependence, the Inokuti−Hirayama equation can also describe the electron transfer process involved for the trapping process. These observations indicate that in this persistent phosphor, the trapping process is a local process; however, different types of traps appear to present different “Dexter” critical radii R0. This electron transfer is also temperature dependent, which requires further investigations.

EVOH32 is a semicrystalline copolymer with high barrier performances and therefore suitable for packaging applications. In order to improve its processability through a decrement of its crystallization temperature from the molten state, EVOH32 was mixed with a wide range of low-molecular-weight additives. The strategy is based on the possibility that the additives create hydrogen or covalent bonds with the OH groups of the EVOH main chains, thus influencing the crystallization process. Interesting correlations between the chemical nature of the functional groups present in the organic molecules and their effect on the polymer crystallization have been found. 3,5-Dihydroxybenzoic acid turns out to be the most effective molecule to decrease the crystallization temperature of EVOH32.

Copolymerization of poly(m‐xylylene adipamide) (MXD6) and poly(hexamethylene isophthalamide‐co‐terephthalamide) (PA6I‐6T) was used as an efficient strategy to prepare amorphous homogeneous systems with improved properties mainly for packaging applications. The preparation of block copolymers was first of all tried by co‐extrusion of the two polymers and then by thermal treatments at high temperatures in DSC or mixing in Brabender, also in the presence of a catalyst. The occurrence of transamidation reactions led to macromolecular structures with different randomness degrees. Further, random copolymers, with the full range of compositions, were synthetized from monomers, by a fast and simple two‐stage melt polycondensation. For all the copolymers, the sequence distribution was studied by using a 1H NMR method developed by the Authors. The effects of preparation procedures, of mixing temperature and time, of the presence of a catalyst on the chemical structure, and, then, on final properties were studied. Interesting correlations among block length, monomer distribution and phase behavior were discussed. POLYM. ENG. SCI., SCI., 55:1475–1484, 2015. © 2014 Society of Plastics Engineers