L. Di Maio

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.

Characterization and reprocessing of greenhouse films

Films for greenhouses are an attractive source of post-consumer plastic materials because they are mainly made of polyethylene and can be easily collected in large amounts in small zones. The types of polymers for this application are, however, increasing and the films contain not only additives and stabilisers, but also fertiliser and pesticide residues. Finally, the extent of photooxidative degradation undergone during the use can strongly influence the recycling operations and the final properties of the secondary material. In this work, a complete characterisation of post-consumer films for greenhouses has been carried out and the properties of the recycled material have been correlated with the number of reprocessing steps and compared with those obtained by reprocessing virgin scraps of the same composition. The presence of small amounts of low molecular weight compounds (photooxidized species and pesticide residues) does not compromise the use of the recycled plastic in many applications. The mechanical properties decrease with the number of reprocessing steps and with increasing level of photooxidative degradation but are good enough for many applications.

Transport and mechanical properties of PET/ Rodrun 3000 blown films

Abstract Blends of different ratios of poly(ethylene terephthalate) (PET) and a thermotropic liquid crystalline polymer (TLCP) composed of 40 mol% of polyethyleneterephthalate and 60 mol% of p-hydroxybenzoic acid (Rodrun 3000) have been processed in a laboratory-based film-blowing extrusion apparatus. Gas permeability measurements have been performed on the films in order to evaluate the effect of the mesophase on the transport behaviour of PET films. The transport properties of the blends are dependent upon the state dispersion of the minor phase; thus, scanning electron microscopy has been conducted on the film surfaces to observe the morphological structure of the TLCP developed during the extrusion process. Moreover, the mechanical properties of the films at 2, 10 and 30% (w/w) TLCP contents have been examined in both the transverse and flow directions.

Relationships between processing‐structure‐migration properties for recycled polypropylene in food packaging∗

In this work the relationships between processing, structure and migration properties of recycled polypropylene (PP) were analysed in relation to the possible use of recycled PP in food packaging applications. PP containers used in food packaging were contaminated with food and then washed, reduced into a processable size, dried and reprocessed by injection moulding. Gel Permeation Chromatography (GPC) analysis, mechanical, and total migration tests were performed on injection moulded samples to verify the effect of the recycling process on the structure and properties of PP. In order to evaluate the effect of the molecular weight on the properties of the recycled polymer, the study was conducted on containers produced by injection moulding made from a low molecular weight (LMW) PP and on containers produced by thermoforming made from a high molecular weight (HMW) PP.

Discussion about the use of relative values of permeabilities between two gases for high molecular weight polymers

Permeability measurements were performed on several polymeric films used for packaging applications. The results were analysed in terms of the ratio of the permeabilities between two gases. Moreover, recent experimental results and data reported in the literature have been compared with a simple relationship reported by van Krevelen for predicting the transport properties of high molecular weight polymers. Finally, a suggestion is made for improving the accuracy of the prediction of the permeabilities for high molecular weight polymers.

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.

Macro-oriented network of liquid-crystalline polyesters: crosslinking induced by γ-irradiation and thermally activated reaction

Abstract The synthesis of a macro-oriented network from liquid-crystalline polymers, bearing pendant groups with unsaturations, is reported. Virgin polymers are processable to obtain oriented samples, e.g. fibres, which may be crosslinked through thermal activation and/or exposure to γ-radiation. The liquid-crystalline state is “frozen” and the macroscopic anisotropy is preserved even at high temperatures. Compared to virgin fibres, irradiated samples show an enhancement of tensile performances, thus indicating that the main effect of irradiation is crosslinking without significant degradation phenomena.

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.

Biaxial orientation of polyamide films: processability and properties

The production of biaxially oriented films can be performed with two techniques: the tenter frame and the double bubble process. The most important difference between the two processes is that in tubular orientation the MD and TD stretching are simultaneous. This event is very important specially in the case of biaxially oriented polyamide films to avoid hydrogen bonding which occur during the first stretching stage of tenter frame process and cause resistance to subsequent transverse direction orientation (1-4). Double bubble process consists in the stretching of a tubular film where the stretching ratios in the machine and transverse directions are determined by inside bubble pressure and the difference in roll speeds between the two sets of nips rolls that contain the bubble. The work presented here reports some results about double bubble polyamide films realised with a laboratory scale system. The study concerns the processability (5-6) of two different polyamides: a nylon 6 (PA6) and a copolymer of the nylon 6 with isophthalic acid and isophorondiamine (PA6 - IPA.IPD) at 5% w/w of comonomer. Two main process arrangements where adopted differing for first bubble cooling technique: a water cooling and a air cooling. The films produced in both conditions were then characterised with a particular regard to mechanical and barrier performances. Morphological analyses were also carried out in order to correlate the process conditions to structure and properties of films.