Morphological reorganization and mechanical enhancement in multilayered polyethylene/polypropylene films by layer multiplication or mild annealing

Abstract

Shortly after processing, Polyethylene/Polypropylene (PE/PP) multilayer films demonstrate an increase in tensile modulus and other mechanical properties when the individual layer thickness is below 0.5 mm. Subsequent annealing at 60 8C for 16 h brings the properties of all other samples to similar values. WAXD characterization of the layered films identified a prevalence of mesophase in the thicker PP layers. In samples with increased layer numerosity or subjected to annealing, WAXD detected its conversion to a crystalline phase that correlates with improved mechanical properties. SSNMR and DSC detailed the defective nature of a iPP crystallites. Comonomers, detected by NMR in the commercial polymers used for the films, are the source of "tunable disorder" that dictates the formation of the PP mesophase and the low temperature of conversion to the mechanically stronger defective a phase. Soft intrafilm layer interfaces instead enable nucleation and localized polymer chain rearrangement even without annealing.

Time Domain NMR in Polymer Science: From the Laboratory to the Industry

“…Instead, in a thermoplastic semicrystalline polymer, the effect of thermal aging induces an increase in the rigid fraction, with the reconstruction of crystallites, that become larger driving out defects. While simple annealing induces a concomitant increase of the mobility of the soft-amorphous phase [104,105], the additional Figure 17. Relaxation profiles of T 1 (full squares) and T 2 (empty circles) against pH for Cu 2+ -CHI solutions (a) and the supernatant after centrifugation of the aqueous solution (b).…”

“…Instead, in a thermoplastic semi-crystalline polymer, the effect of thermal aging induces an increase in the rigid fraction, with the reconstruction of crystallites, that become larger driving out defects. While simple annealing induces a concomitant increase of the mobility of the soft-amorphous phase [104,105], the additional contribution of chemical reactions, such as oxidation, causes a reduction, at short times, in the overall mobility, because of a higher confinement of the mobile-amorphous part and at longer exposure times, mobility increases because of oxidative chain cleavage [104,106]. Lately, the employment of NMR-MOUSE devices allowed to analyze the depth-dependent changes by aging, which are known to greatly compromise the mechanical properties.…”

Viscosity Modification of Polymerizable Bicontinuous Microemulsion by Controlled Radical Polymerization for Membrane Coating Applications

“…The contact time of 1 ms and a recycling delay of 4 s were used and 1000 scans were acquired on average. In comparison, spectra were also achieved without CP with a HPDEC (high power proton decoupling) sequence of 2048 scans using a recycle delay of 2 s [18]. Due to the strong superposition of the resonances, the analysis of the spectra was focused to quantify only the intensity of resonances univocally associated to a specific molecular entity.…”

Review on modification strategies of polyethylene/polypropylene immiscible thermoplastic polymer blends for enhancing their mechanical behavior

“…This study suggests that, by understanding and controlling processing conditions and polymer’s nature, a more sustainable use of mixed recycled streams could be applied. Another interesting work on this matter was done by Mauri et al 22 on the enhancing the properties of PE/PP binary systems when arranging them in nanoscale multilayered films. By employing the layer multiplying co-extrusion technique, they could come up with a PE/PP nanolayered system, comprised of hundreds of layers, with each layer having a thickness of less than 100 nm.…”