Elisabetta Morici

Advanced nano-hybrids for thermo-oxidative-resistant nanocomposites

In the present work, trisilanol phenyl polyhedral olygomeric silsesquiosane (TSPh-POSS) has been physically immobilized onto carbon nanotubes (CNTs) bearing covalently linked Br-terminated long-alkyl chain (Br-alkyl-f-CNTs), and the so obtained hybrid nanoparticles (Br-alkyl-f-CNTs/TSPh-POSS) have been used to prepare ultra-high molecular weight polyethylene (UHMWPE)-based nanocomposites with enhanced thermo-oxidative resistance. The effective immobilization of the TSPh-POSS molecules has been confirmed by spectroscopic and thermo-gravimetric analyses. Besides, the influence of the hybrid nanoparticles on the rheological and mechanical behaviour and morphology of the nanocomposites have been fully investigated. The obtained results show that the rheological and thermo-mechanical behaviour of UHMWPE/Br-alkyl-f-CNTs/TSPh-POSS nanocomposite is affected by two different opposite contributions: reinforcement effect of CNTs and plasticizing action induced by TSPh-POSS molecules. The unexpected excellent thermo-oxidative resistance of the nanocomposite containing hybrid nanoparticles seems to be due to a synergistic effect of TSPh-POSS and CNTs. Moreover, TSPh-POSS molecules, upon thermo-oxidative treatment, are able to migrate toward film surface, forming a TSPh-POSS-rich protective layer that hinders the oxygen diffusion.

Rheological Percolation Threshold in High-Viscosity Polymer/CNTs Nanocomposites

AbstractPolystyrene (PS)/multi-walled carbon nanotubes (CNT) nanocomposites have been prepared through melt mixing processing aiming at obtaining a uniform and homogeneous dispersion of the used nanoparticles within the polymeric matrix. Optical and scanning electron microscopy has been employed to determine the dispersion and distribution of CNTs at different length scales. Furthermore, the linear viscoelastic behavior of formulated nanocomposites has been deeply investigated. As a result of CNTs added, the nanocomposites experience a transition from liquid-like to solid-like rheological behavior, and a disappearance of relaxation processes at low frequency can be noticed. By plotting G’ versus CNTs loading and fitting with a power-law function, the rheological threshold of PS-based nanocomposites has been calculated. Moreover, the mechanical behavior of nanocomposites has been investigated and related to the formed CNTs network within polymer matrix.

Biopolyester-based systems containing naturally occurring compounds with enhanced thermo-oxidative stability

Background This work presents a sustainable approach for the stabilization of polylactic acid (PLA) against thermo-oxidative aging. Methods Naturally occurring phenolic and polyphenolic compounds, such as ferulic acid (FerAc), vanillic acid (VanAc), quercetin (Querc) and vitamin E (VitE), were introduced into PLA. Results The preliminary characterization of the systems formulated containing different amounts of natural stabilizers showed that all compounds used acted as plasticizers, leading to a decrease in rheological functions with respect to neat PLA, without significantly modifying the crystallinity of the raw material. The study of the thermo-oxidative behavior of neat PLA and PLA/natural compound systems, performed by spectrometric and thermal analyses, indicated that all stabilizers considered were able to exert a remarkable antioxidant action against thermo-oxidative phenomena. Conclusions All natural compounds considered are thus proposed as ecofriendly stabilizers, to get fully bio-based polymer systems with enhanced thermo-oxidative stability, suitable for biomedical applications.

On the role of multi-functional polyhedral oligomeric silsesquioxane in polystyrene-zinc oxide nanocomposites

Abstract Multi-functional trisilanol phenyl (TSPH) and trisilanol isobutyl (TSIB) polyhedral oligomeric silsesquioxane (POSS) have been used in the formulation of advanced polystyrene (PS)-zinc oxide (ZnO) nanocomposites. The neat matrix and PS/ZnO-based nanocomposites have been characterized through rheological, morphological, mechanical, and dynamic thermo-mechanical analysis. Both TSPH and TSIB are able to improve the dispersion of ZnO into the polystyrene matrix; furthermore, adding TSIB leads to better results because it facilitates better solubility into the PS matrix and interaction/reaction with the ZnO nanopowder. Finally, the optical properties and photo-oxidative resistance of the nanocomposite films have been evaluated. The POSS molecules synergistically interact with ZnO nanopowder in the protection of PS matrix against photo-oxidative process. The nanocomposite films containing both ZnO and POSS molecules, particularly TSIB, exhibit better UV-shielding properties than the PS/ZnO one, without loss of optical transparency.

Double bond-functionalized POSS: dispersion and crosslinking in polyethylene-based hybrid obtained by reactive processing

Polyethylene-based organic inorganic hybrids were prepared by one-step reactive melt mixing using a mono-functionalized nanofiller, i.e., allyl-heptaisobutyl-substituted polyhedral oligomeric silsesquioxane (1POSS) and a multi-functionalized octavinyl polyhedral oligomeric silsesquioxane (8POSS). The hybrids were also prepared in dicumyl peroxide (DCP) presence and morphological, spectroscopical and calorimetric analysis were carried out. Moreover, rheological measurement and Sohxlet extraction were performed on investigated samples. It was inferred that double bonds of POSS functional groups were triggered by radicals coming from the peroxide decomposition or from the degradation reactions occurring during preparation. The type of the functional groups (mono- or multi-reactive) of the POSS is a leading factor, along with radicals content in the systems, in the formation of a polymeric network. In particular, the presence of multi-reactive groups in 8POSS molecules results in a successful POSS grafting/crosslinking in the polymeric backbone: the covalent bonds formation between nanofillers and matrix during processing improves POSS dispersion within the polyolefin matrix and leads to a network structure formation.

Quercetin as natural stabilizing agent for bio-polymer

The introduction of antioxidants in polymers is the main way to prevent or delay the degradation process. In particular natural antioxidants receive attention in the food industry also because of their presumed safety. In this work bio-polymers, i.e. a commercial starch-based polymer (Mater-Bi®) and a bio-polyester (PLA), and a bio-polyether (PEO) were additivated with quercetin, a natural flavonoid antioxidants, in order to formulate bio-based films for ecosustainable packaging and outdoor applications. The photo-oxidation behavior of unstabilized and quercetin stabilized films was analyzed and compared with the behavior of films additivated with a commercial synthetic light stabilizer. The quercetin is able to slow down the photo-degradation rate of all bio-polymeric films investigated in similar way to the synthetic stabilizer.

Performances and morphology of polyamide/carbonaceous structures based fibers

In this work the influence of carbonaceous particles with different particle sizes and shapes on the morphology and mechanical performances of polyamide (PA) based fibers was investigated. Graphene nanoplatelets (GNP) are compared with spherical and rod-like carbon fillers such as carbon black (CB) and multiwall carbon nanotubes (MWCNT). The different morphologies of the particles control their dispersion and their alignment in PA fibers upon elongational flow action and play a key role in structure-property relationships.

Improved carbon nanotubes dispersion through polar dispersant agents in polyamide

The potential enhancement of the nanocomposite properties, with respect to the neat matrix, is strictly related to uniform distribution and dispersion of the nanofillers in the host polymer. In this work, two dispersant agents, particularly a polar wax and a silanol polyhedral oligomeric silsesquioxanes POSS, have been used in order to improve the dispersion of bare and functionalized carbon nanotubes in polyamide matrix. To ensure a good compatibility between matrix and nanofillers, the dispersing agents having specific polarity have been chosen, in order to match that of the matrix. Significant alterations of the mechanical and rheological behaviour due to dispersion action of used additives have been noticed and discussed, also considering the obtained morphology.