N. Tz. Dintcheva

Processing and Properties of Biopolymer/Polyhydroxyalkanoates Blends

In this paper, the processability and the performance of a biodegradable polymer, Mater-Bi, and of its blends with either a sample of poly (hydroxy alkanoates) (PHA) or with bacterial biomass containing PHAs were compared. Adding PHA or directly the biomass containing it allows improving the processability of the matrix. Moreover, the mechanical behaviour of the systems was compared considering two different preparation methods, namely compression and injection moulding. The injection moulded samples show poorer mechanical performances than those of the compression moulded systems. The impact strength significantly improves when PHA is added while it reduces when bacterial biomass is used instead. In this latter case this was likely due to the easier propagation of micro-cracks during the impact tests.

Using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry for the characterization of functionalized carbon nanotubes

RATIONALE Functionalization of carbon nanotubes (CNTs) generates complex systems that require the development of suitable characterization protocols. New techniques have been explored, and existing analytical and spectroscopic methods to characterize functionalized CNTs have been adapted. Presently, chemical characterization of functionalized CNTs (f-CNTs) remains a difficult task. METHODS Matrix-assisted laser desorption/ionization (MALDI) analysis is performed on f-MWCNT samples prepared via grafting or absorption of anti-oxidant (AO) molecules on both MWCNT-COOH and MWCNT-OH. Covalently functionalized MWCNTs were subjected to thermal degradation and/or hydrolysis reaction before analysis, whereas MWCNTs with a physical adsorption of the functionalizing molecules were directly spotted in the target sample. Noteworthy, in our approach f-MWCNTs constitute at the same time analyte and MALDI matrix. RESULTS The identification of functionalizing AO molecules is ascertained after degradation or hydrolysis reactions in both MWCNT-COOH and MWCNT-OH grafted samples. Absorbed AO molecules, as well as organic impurities derived from grafting reactions, are also revealed by MALDI MS without any preliminary cleavage reaction. CONCLUSIONS A simple MALDI-TOF mass spectrometry method permits to obtain the unambiguous discrimination between grafted or adsorbed functionalized molecules onto the surface of MWCNTs.

Rheological behavior of PAN-based electrolytic gel containing tetrahexylammonium and magnesium iodide for photoelectrochemical applications

Polymeric gel electrolyte systems have gained great interest in the last few years due to their suitability for the manufacturing of ionic devices, for example, for dye-sensitized solar cells (DSSCs). In this work, the rheological behavior at fixed temperatures and at fixed frequency of complex systems based on polyacrylonitrile (PAN) and plasticizers such as ethylene carbonate (EC) and propylene carbonate (PC) containing tetrahexylammonium (Hex4NI) and magnesium iodide (MgI2) was studied. These results for these PAN-EC-PC gels suggest a structural change of the “strong-to-weak” type at about 60 °C and the beginning of the gel–sol transition at about 75 °C. These transitions occur at higher temperatures for polymer electrolyte gels containing Hex4NI and even higher with MgI2, suggesting the possibility of post-factum treatments of the gels and of the DSSCs to improve their performance. The rheological results suggest that the progressive substitution of Hex4NI with MgI2leads to a significant improvement in the rheological behavior of the PAN-based electrolytic gel due to the decrease of the mobility of the macromolecules and probably to an increase of the interaction between the inorganic ions and the macromolecules. Moreover, when these gels were used in DSSCs, the sample containing 80(Hex4NI)/40(MgI2) showed the best performance considering its rheological and calorimetric behavior as well as energy conversation efficiency and short-circuit current density.

Low-Density Polyethylene/Polyamide/Clay Blend Nanocomposites: Effect of Morphology of Clay on Their Photooxidation Resistance

The photooxidation behaviour of low-density polyethylene (LDPE)/polyamide (PA) blends, containing polyamide 11 (PA11) or polyamide 6 (PA6), has been investigated in the absence and presence of a small amount of commercial organomodified clay (OMMT). The polymer blends LDPE/PA11 and LDPE/PA6 at 75/25 wt./wt.%, with and without OMMT, have been prepared by a two-step procedure: extrusion and sheet formulation. The formulated complex systems have been subjected to accurate morphological analysis in order to evaluate the effect of the OMMT presence on the refinement of the blend morphology. Furthermore, the produced sheets have been subjected to arterial UVB exposure and the variations of the mechanical properties and chemical structure of all the investigated samples have been monitored as a function of the exposure time. Finally, the rate of the photodegradation of the complex systems has been related to the morphological changes of these systems upon OMMT addition.

Reactive melt blending of functionalized-MW/CNTs with polyolefin

Adding nanotube adding into a polymeric matrix leads to the formulation of nanocomposites with enhanced macroscopical performances, and, moreover, the use of functionalized MW-CNTs leads to the nanocomposite formulation with even better properties. Furthermore, the reactive melt blending can be considered as a powerful processing method, i.e. reasonably simple and ecologically friendly, in order to formulate polymer based nanocomposite with good performance. In this work, the reactive melt blending between an ethylene-acrylic acid co-polymer, bisoxazoline and

The Role of Elongational Flow in Morphology Modification of Polyethylene/OMMt Nanocomposite System

The formulation of high-performance polymer based nanocomposites depend on many factors, such as polymeric matrix type, nanoparticle type, loading and morphology, affinity between the polymeric matrix and nanoparticles, presence of compatibilizer and processing conditions [1-4]. During the industrial processing the polymer based systems are subjected to two different processing flows, i.e. the shear and elongational flow. The shear flow plays a significant role in polyethylene/OMMt manufacture processing but it is not able to change the system morphology, while, the elongational flow, involved in spinning and film-blowing processing operations, can induce considerably clay morphology variations [5-13]. In order to evaluate the effect of the elongational flow on the polyethylene/OMMt system morphology, the affinity between the matrix and the OMMt particles can be considered. In particular, the presence of some compatibilizer, as maleic anhydride grafted polyethylene can modify the system affinity and subsequently, the clay morphology changes are different than the uncompatibilized system also upon the extensional flow. Nevertheless, the obtained morphology changes upon the elongational flow in the polyethylene/OMMt system, without and with good system affinity, lead to significant mechanical improvements than the unfilled systems, more larger than the simple macromolecular orientation [10, 12]. If considering, from “flow point of view”, the polyethylene/OMMt system as a biphasic incompatible mixture, composed by an inorganic phase dispersed in a polymeric matrix, the applied extensional flow can be able to change strongly the clay morphology. In particular, the clay nanoparticles can be broken and/or fragmentized, dispersed and oriented along the flow direction, giving rise to flow induced intercalation/exfoliation morphology transition. Indeed, the OMMt particles can be considered as hard but breakable particles, i.e. polymeric particles in a polymeric blends, while, the conventional filler particles are elastic but unbreakable. The elongational flow leads to exfoliation of intercalated OMMt tactoids and/or to some more intercalation of the same tactoids. For the systems with good affinity

EFFECT OF THE ELONGATIONAL FLOW ON THE MORPHOLOGY AND ON THE PROPERTIES OF POLYETHYLENE BASED NANOCOMPOSITES

Polymer/clay nanocomposites show macroscopic properties depending on many factors but in particular on the morphology of the of the clay nanoparticles (intercalated, hybrid or exfoliated). The morphology is, in its turn, depending on the polymer/clay affinity and on the processing conditions. The flow involved in the melt compounding is the shear flow that can disaggregate the particles, but is not particularly efficient to induce the exfoliation if there is not a very good adhesion between polymer and clay. In this work we demonstrate that the elongational flow can induce the exfoliation in polymer/clay nanocomposite, even in presence of a very poor affinity between the two components. The mechanical properties are strongly increased both because of the orientation of the macromolecules, but also because of the exfoliation induced by the elongational flow.

EFFECT OF ORGANOCLAY ON THE MORPHOLOGY AND MECHANICAL PROPERTIES OF LDPE/PA11 BLENDS

Adding small amounts of organomodified clay represents an innovative approach to tailor the morphology and properties of immiscible polymer blends. In a recent paper we have found the unexpected formation of a co‐continuous morphology in a blend of high‐density polyethylene and polyamide 6 filled with organoclay. This results in enhanced mechanical properties as a consequence of the synergism among the reinforcement effect of the filler and the dual phase interconnectivity characteristic of co‐continuity. In this work we focus on this topic by investigating the morphology and mechanical properties of blends constituted by low‐density polyethylene and polyamide 11 filled with small amounts of organomodified clay. We show that the filler promotes a finely interpenetrated microstructure, which results in enhanced mechanical properties due to an efficient stress transfer among the phases.