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Thermal characterization was carried out on highly stereoregular and regioregular syndiotactic polypropene (sPP) obtained with isopropylidene(cyclopentadienyl)(9-fluoreny~)~rcoNum dichloride and methylaluminoxane. The influence of molecular weight and syndiotacticity degree on the thermodynamic melting point (T;) of sPP were separately investigated by examining samples with a fully syndiotactic pentads content (rrrr) ranging from ca. 81 070 to ca. 94% and with an weight-average molecular weight (a,,,) ranging from 9,6 -lo4 to 17,3 lo4. Upon excluding any influence of the molecular weight, the correlation between the rrrr pentads content and the T", of the samples led to the extrapolation of the thermodynamic melting point for a fully syndiotactic polypropene.CCC 0025-1 16)

Functional barriers are multilayer structures deemed to prevent migration of some chemicals released by food-contact materials into food. In the area of plastics packaging, different migration behaviours of mono- and multilayer structures are assessed in terms of lag time and of their influence of the solubility of the migrants in food simulants. Whereas barriers to oxygen or to aromas must prevent the diffusion of these compounds under conditions of use, a functional barrier must also be efficient under processing conditions, to prevent diffusion of substances when the polymer layers are in contact at high (processing) temperatures. Diffusion in melted polymers at high temperatures is much slower for glassy polymers, than in polymers that are rubbery at ambient temperature. To evaluate the behaviour of functional barriers under conditions of use, a set of reference diffusion coefficients in the 40-60 degrees C range were determined for 14 polymers. Conditions for accelerated migration tests are proposed based on worst-case activation energy in the 40-60 degrees C range. For simulation of migration, numerical models are available. The rules derived from the models can be used both by industry (to optimize a material in terms of migration) or by risk assessors. Differences in migration behaviour between mono- and multilayer materials are discussed.

The isothermal crystallization kinetics, the morphology and melting behaviour of blends of poly(tetramethy1ene terephthalate) (poly(buty1ene terephthalate), (PBT)] with a thermotropic liquid-crystalline polyester, poly(decarnethy1ene 4,4'-terephrhaloyldioxydibenzoate) (HTHI 0), were studied in the composition range 0-50 wt.-% of HTHIO by optical microscopy and differential scanning calorimetry. The spherulite growth rate and the overall crystallization rate of PBT from melt blends are markedly depressed by the presence of the mesomorphic component. Changes of superstructure and of primary nucleation density of PBT spherulites in the blends were observed. The analysis of the melting behav:our of these samples indicates that the stability of PBT crystals and their reorganization processes on heating are dependent on the blend composition. A decrease of the equilibrium melting iemperature of PBT is found with increasing the amount of HTH10. According to previously reported investigations on the same system, the results are discussed in respect of the onset of interactions between the two polymers in the liquid state.

The main concern in safety evaluation of ionized plastic food packaging materials is the possible formation of unsuspected potential migrants. Solvent extracts and migrates of a polypropylene-based multilayer film, beta-irradiated at 80 kGy and widely used for vacuum cooking of packaged meat were studied, using complementary analytical techniques. 1H-NMR and HPLC showed that 96% of the initial phenolic stabilizer was not found after irradiation. A phosphite stabilizer and its reaction products, identified by GC-MS, accounted for 35% of the initial amount. The sum of all potential migrants derived from the additives accounted for less than 1% of global migration. This global migration was mainly due to oligomers. By comparison our results with literature work done with the same film, but at lower doses, it was suggested that larger electron beam doses reduce the possibility of migration and enhance the consumer's safety.