Modulated Crosslinking of Polyolefins through Radical Processes in the Melt Elisa Passaglia,* 1 Serena Coiai, 2 Guido Giordani, 3 Elisa Taburoni, 3 Luca Fambri, 4 Valerio Pagani, 5 Maurizio Penco 5 1 CNR-ICCOM Sezione di Pisa, Dipartimento di Chimica e Chimica Industriale, Via Risorgimento 35, Pisa, 56100, Italy E-mail: elpas@dcci.unipi.it 2 Scuola Normale Superiore di Pisa, Piazza dei Cavalieri 7, Pisa, 56126, Italy 3 Dipartimento di Chimica e Chimica Industriale, Universita ` di Pisa, Via Risorgimento 35, Pisa, 56100, Italy 4 Dipartimento di Ingegneria dei Materiali e Tecnologie Industriali, Universita ` di Trento, Via Mesiano 77, Trento, 38050, Italy 5 Dipartimento di Chimica e Fisica per l’Ingegneria ed i Materiali, Universita ` di Brescia, Via Valotti 9, Brescia, 25123, Italy Received: June 15, 2004; Accepted: July 21, 2004; DOI: 10.1002/mame.200400155 Keywords: crosslinking; crystallinity; ethylene-vinyl acetate copolymers; polyethylene (PE); polyethylene/polybutadiene blends Introduction Thermoplastic semi-crystalline polyolefins (POs) like poly- ethylene are employed for a range of applications including piping, packaging, household, industrial containers and automotive, because of their low cost, large availability, easy processability and good physical-mechanical proper- ties. Different grades of POs are classified on the basis of the chemical composition, density, crystallinity and melt flow index (MFI) to identify their end-uses and processing or post-modification operations. By application of suitable mechanical stresses, POs show high values of storage modulus and low values of strain response. On the other hand, an elastomeric material shows a smooth increase in strain on elongation well beyond a 100% change in length (the inter-chain bonds act as springs), but the values of modulus are generally quite low. With the aim to obtain a thermoplastic material characterized by high modulus and reversible deformation (elongation over 100% as optimal behavior) it could be gainful to preserve the crystallinity percentage while simultaneously providing the amor- phous phase of a recall elastic force by a modulated crosslinking. Usually, the crosslinking process of a semi- crystalline polymer, like linear low density polyethylene (LLDPE), enhances high-temperature properties, such as heat deformation and stress cracking resistance because the Summary: 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 spec- troscopies (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 pro- perties and, in the case of the mixtures, TEM analysis has been carried out to gather information about the morphology. TEM micrograph of the partially crosslinked polyethylene/ polybutadiene blend 90/10 (w/w). Macromol. Mater. Eng. 2004, 289, 809–817 DOI: 10.1002/mame.200400155 ß 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Full Paper 809