Paola Scarfato

STRUCTURE AND RHEOLOGY OF RECYCLED PET MODIFIED BY REACTIVE EXTRUSION

Abstract In this work pyromellitic dianhydride (PMDA) was used as a chain extender to increase the molecular weight of polyethylene-terephthalate (PET) industrial scraps with low intrinsic viscosity ( IV =0.48 dl/g ), coming from a PET processing plant. The reaction was performed in a single step through reactive extrusion. Different percentages of chain extender were used in order to investigate the effect of PMDA content on the molecular structure (average molecular weight, molecular weight distribution, branching) of PET. Rheological and thermal characterizations were performed on treated PET extruded samples. In particular, the increase in the dynamic viscosity at low frequencies and the high pronounced shear thinning behavior observed in the PMDA-treated PET samples were correlated to the broadening of the Mw/Mn and to the long chain branching. These structural changes are also responsible for the decrease in the Tmc and ΔHmc and the increase in the Tcc values increasing the PMDA content in the PET samples. The study was performed also on bottle grade PET ( IV =0.74 dl/g ) for comparison purpose. The results have pointed out that with an amount of PMDA included between 0.50 and 0.75% the chain extending reaction produces an increase of Mw, a broadening of Mw/Mn and branching phenomena, that modify the PET scraps in order to make the recycled polymer suitable for film blowing and blow molding processes.

Preparation and characterization of new melt compounded copolyamide nanocomposites

In this work new copolyamide-layered silicate nanocomposites were prepared by melt compounding using a commercial polyamide 6-based copolymer, with a partially aromatic structure, as thermoplastic matrix. This copolyamide, having a lower melting point and improved mechanical and barrier properties respect to the homopolymer, appears an interesting material for producing nanocomposite packaging films. Hybrids with different organoclay loadings were produced by a twin-screw extruder using different extrusion rates, in order to point out the effects of both processing conditions and hybrid composition on morphology (silicate dispersion and exfoliation, orientation, matrix crystallinity) of nanocomposites. All melt-intercalated samples were submitted to structural (TEM and XRD), thermal and dynamic mechanical measurements. The performed analyses have evidenced that all hybrids exhibit mixed intercalated/exfoliated morphology and that the extent of exfoliation increases with both clay amount and extrusion rate used. Moreover, it was pointed out that the silicate nano-scale dispersion significantly affects the crystalline morphology of copolyamide matrix, stabilizing the γ-crystal phase, and the dynamic mechanical response of the hybrids, whose storage and loss moduli values result sensibly higher than those corresponding to the neat matrix.

Synthesis and liquid crystalline properties of low molecular mass compounds containing the 1,4-bis(5-phenyl-1,3,4-oxadiazolyl)benzene unit

The synthesis and characterization of low molecular mass compounds containing 1,4-bis(5-phenyl-1,3,4-oxadiazolyl)benzene is reported. All compounds are fluorescent in solution. Due to the flat shape of the conjugated unit, smectic-like packing is observed at high temperatures for some of the synthesized compounds. Moreover the insertion of a lateral flexible alkoxy unit strongly destabilizes the smectic order whilst promoting the appearance of a nematic phase in the case of the shortest methoxy unit. The mesogenic character of this unit may be of interest in the synthesis of liquid crystalline polymeric systems, taking advantage of both the fluorescent properties and the peculiar molecular structure of the liquid crystalline state.

Rheology of PBT-layered silicate nanocomposites prepared by melt compounding

Abstract The rheological behaviour of poly(butyleneterephthalate) (PBT) based clay nanocomposites processed by melt compounding is investigated and related to the morphology of the samples. Hybrids at three weight percentages (3, 6 and 9 wt-%) of a commercial organo-modified montmorillonite were prepared by means of a twin screw extruder, using two different extrusion rates (90 and 150 rev min -1). The samples produced were submitted to structural and rheological investigations. X-ray and TEM analyses were carried out to provide information on the morphology (i. e. clay dispersion, degree of exfoliation, orientation) of the hybrids, whereas rheological tests in the low and high shear region (dynamic frequency sweep, steady rate sweep and stress relaxation tests) were performed to evaluate the effect of both hybrid composition and extrusion rate on the flow behaviour of the nanocomposites. Both structural and rheological results showed that a good dispersion and a high degree of silicate exfoliation in the PBT matrix are obtained under the experimental conditions. As a consequence, hybrids having clay fractions higher than 6 wt-% show a pseudo-solidlike flow behaviour at long times, as a result of the occurrence of strong polymer–silicate interactions that slow the relaxation times of the PBT chains.

Performance properties, lactic acid specific migration and swelling by simulant of biodegradable poly(lactic acid)/nanoclay multilayer films for food packaging

ABSTRACT The aim of the study was the development of a multifunctional, high-performance, fully biodegradable multilayer polylactic acid (PLA) film for food packaging applications. In particular, sealable multilayer PLA–clay nanocomposite systems with different layouts in terms of composition and relative thickness of the layers, all consisting of a PLA–clay nanocomposite layer between two pure PLA layers for direct food contact, were designed and produced by blown film co-extrusion. The films obtained were analysed for their morphology, functional properties and lactic acid (LA)-specific migration in 50% ethanol. The results showed that, with respect to the unfilled multilayer system, taken as a reference, the nanocomposite films had significant improvements, up to about 40%, in their barriers to oxygen and tensile strengths, and resulted in being more easily sealable over a wide heat-sealing temperature range (80–100°C) with higher seal strength. Moreover, all films had LA migrations always well below the former generic overall migration limit of 60 mg kg–1 food (10 mg dm–2) of European Union Regulation No. 10/2011 (deleted by the amending Regulation No. 2016/1416), even if their morphology was strongly modified during the migration tests due to the strong swelling action of the used simulant (simulant D1 = 50% ethanol (aq.) (v/v)) towards PLA.

Synthesis and characterisation of a nematic homo-polyurethane

The presence of hydrogen bonds in the chemical structure of polymers promotes and stabilises the crystalline phase. For liquid crystalline (LC) polymers, the side insertion of aliphatic units to the mesogenic unit is a suitable artifice to decrease the crystalline stability, without significantly affecting the stability of the LC phases. Here, we report on the synthesis of a LC homo-polyurethane with high hydrogen bond concentration along the chain and bearing an n-pentyl side-chain. Rheological behaviour, thermal analysis, and X-ray diffraction show that the stable LC phase is the nematic.

Preparation and characterization of biodegradable active PLA film for food packaging

In this work we report on the preparation and characterization of a biodegradable active PLA film (aPLA), intended for food packaging applications. The film was obtained by cast extrusion blending a commercial PLA matrix with an active system, developed in our laboratory and based on PLA microparticles containing a-tocopherol (aTCP) as natural antioxidant agent. In order to optimize the film composition and processing, the active microparticles were preliminarily characterized with the aim to evaluate their morphology (size and shape), thermal resistance and a-tocopherol content. The aPLA film, produced with a 5wt% of aTCP, was characterized in terms of performance and activity. The experimental results demonstrated that the aPLA film has mechanical, thermal, barrier and optical properties adequate for packaging applications and shows oxygen scavenging activity and prolonged exhaustion lag time, compared to pure PLA films.

Morphology Development and Mechanical Properties Variation during Cold-Drawing of Polyethylene-Clay Nanocomposite Fibers

In this work, the influence of composition and cold-drawing on nano- and micro-scale morphology and tensile mechanical properties of PE/organoclay nanocomposite fibers was investigated. Nanocomposites were prepared by melt compounding in a twin-screw extruder, using a maleic anhydride grafted linear low density polyethylene (LLDPE–g–MA) and an organomodified montmorillonite (Dellite 67G) at three different loadings (3, 5 and 10 wt %). Fibers were produced by a single-screw extruder and drawn at five draw ratios (DRs): 7.25, 10, 13.5, 16 and 19. All nanocomposites, characterized by XRD, SEM, TEM, and FT-IR techniques, showed an intercalated/exfoliated morphology. The study evidenced that the nanoclay presence significantly increases both elastic modulus (up to +115% for fibers containing 10 wt % of D67G) and drawability of as-spun nanocomposite fibers. Moreover, at fixed nanocomposite composition, the cold-drawing process increases fibers elastic modulus and tensile strength at increasing DRs. However, at high DRs, “face-to-edge” rearrangement phenomena of clay layers (i.e., clay layers tend to rotate and touch each other) arise in fibers at high nanoclay loadings. Finally, nanocomposite fibers show a lower diameter reduction during drawing, with respect to the plain system, and surface feature of adjustable roughness by controlling the composition and the drawing conditions.

Effect of nanocomposite composition on shear and elongational rheological behavior of PLA/MMT hybrids

The present work focuses on the possibility of conveniently tuning materials in PLA based nanocomposites in order to improve their processability in manufacturing processes where extensional flow is mainly involved. Nanocomposites at a constant silicate loading were produced by melt compounding, using a commercial polylactide grade (PLA 4032D) and two different organo-silicates (Cloisite 30B and Nanofil SE3010). A morphological characterization in solid and molten state, realized by TEM investigations and shear rheological measurements, firstly pointed out the influence of composition on the nanostructure of the hybrid systems. All the samples were then submitted to uniaxial stretching and the rheological response of the different nanocomposites was correlated to the initial nanostructure and the different polymer-clay affinity.

Processing-structure-properties relationships in PLA nanocomposite films

This work deals on the possibility to improve performances of PLA-based nanocomposite films, for packaging applications, through conveniently tuning materials and processing conditions in melt compounding technology. In particular, two types of polylactic acid and different types of filler selected from montmorillonites and bentonites families were used to prepare the hybrid systems by using a twin-screw extruder. The effect of biaxial drawing on morphology and properties of the nanocomposites, produced by film blowing, was investigated.