Modulated crosslinking of polyolefins through radical processes in the melt

The possibility to submit a semi-crystalline polyolefin (or a mixture of different polyolefins) to a phase selective crosslinking process, in order to produce a material with unchanged crystallinity but a partially crosslinked amorphous fraction, has been investigated. The crosslinking process has been performed in the melt in the presence of radical initiators. Three different polymer systems have been considered: a LLDPE sample (an ethylene-1-butene 91/9 w/ w copolymer), two EVA samples (ethylene-vinyl acetate copolymers containing a different amount (10 and 15 wt.-%) of acetate monomer units), and mixtures of LLDPE with polybutadiene (BR) (90/10 w/w). All the reaction products have been characterized by selective solvent extractions to determine the gel content, by analysis with different spectroscopies (IR and NMR) and by viscosity measurements to evaluate changes of the structure and the molecular weight (MW) of the partially crosslinked samples. Finally DSC and DMTA analyses have been used to correlate the variations of the macromolecule structure to the thermo-mechanical properties and, in the case of the mixtures, TEM analysis has been carried out to gather information about the morphology.