368 research outputs found
IN-LINE MONITORING OF THE PHOTOOXIDATION BEHAVIOUR OF PP/CLAY NANOCOMPOSITES THROUGH CREEP MEASUREMENTS
No full textThe photooxidation of polymer systems is usually investigated by monitoring the change of chemical and molecular structure, morphology and macroscopic after a given period of UV exposition. In a previous paper, La Mantia et al. [1] presented a new apparatus that is able to monitor during the accelerated weathering the effect of the photooxidation on a polymer sample subjected not only to temperature, humidity and UV irradiation, but also to a mechanical stress, fully simulating real working conditions for plastic products. In this work, a polypropylene/organomodified clay nanocomposite has been subjects to the same test and the results compared with those obtained for the pure matrix
Competition between degradation and chain extension during processing of reclaimed poly(ethylene terephthalate)
No full textDuring processing of poly(ethylene terephthalate) (PET) hydrolytic chain scission, induced by the presence of small amounts of water, is the main cause of degradation. During repeated reprocessing chain scission can also occur because of the presence of other polymeric contaminants like PVC. In order to avoid or to limit hydrolytic chain cleavage adequate drying of PET before melt processing is necessary. Of course this practice is even more recommended when repeated processing steps are used, as for PET recycling. The behavior of recycling PET obtained from post-consumer water bottles when treated in a melt mixer under different conditions has been investigated in order to better understand the processing conditions that can reduce or avoid the hydrolytic chain scission. During processing both degradation (chain scission) and chain extension occur. When the processing is carried out under a nitrogen atmosphere the latter mechanism prevails leading to a polymer having larger molecular weight. (C) 1998 Elsevier Science Limited. All rights reserved
Reprocessing of polyethyleneterephthalate and characterisation of monopolymer blends of virgin and recycled polymers
No full textRecycling of polyethyleneterephthalate (PET from bottles is considered by changing both reprocessing machines and the effect of humidity. The rheological and mechanical properties of this recycled material remain very close to that of the virgin material provided that a careful drying is carried out before any melt operation. The reprocessing has been carried out mainly in view of the use of this secondary material in blends with virgin PET-monopolymer or homopolymer blends. Indeed, this use is a common industrial practice to reuse plastic scraps. Most monopolymer blends show properties between those of the two components but in some cases lower than those expected on the basis of an additive rule. In some cases minima in the properties-composition curves are observed. This occurs mainly when the properties of the two components are very similar. Blends with similar amounts of the two components should be then avoided. On the contrary, when the characteristics of the virgin and of the recycled component are very different, the properties of the blends are determined by those of the matrix
Recycling of a starch-based biodegradable polymer
No full textA new starch-based polymeric system, ZI1OU from Novamont, mainly composed of starch and polycaprolactone, was reprocessed several times in an extruder to investigate the recyclability of this biodegradable polymer. A previous investigation of the thermomechanical degradation in a mixer has been also done. The degradation is mostly due to the thermal stress but the presence of the mechanical stress strongly increases the degradation kinetic. During melt processing two concurrent processes take place: the first is the degradation, i.e. the breaking and shortening of polymeric chains, mostly occurring in the PCL phase; the second is the formation of some crosslinked structure in the starch phase. The rheological and mechanical properties, measured on samples subjected to repetitive extrusion operations carried out in a single screw extruder, clearly indicate that, in the adopted processing conditions, no significant modifications are observed. Only after five extrusions some decrease of these properties was measured
Effect of elongational flow on the morphology and mechanical properties of LLDPE/clay nanocomposites
No full textPolymer mechanical recycling: downcycling or upcycling?
No full textRecycled plastics are considered as materials with physical, mechanical and aesthetic properties worse than the virgin ones. In fact, this is true because degradation during lifetime and during the recycling operations changes the structure and the morphology of the polymers and then the final properties of the secondary material. Several "strategies" are under investigation, and in some cases also applied, in order to avoid further degradation during recycling and, if possible, to repair the macromolecules broken during lifetime and then to restore or to improve the initial properties. In this paper the more important techniques, already used in industry or under investigation, according to this philosophy are shortly reviewed
R. Marino, N. Tzankova Dintcheva, F.P. La Mantia LLDPE/caly/compatibilizers nanocomposites: rheological behaviour under shear and non-isothermal elongational flow
No full textTHERMOMECHANICAL DEGRADATION OF A POLYPROPYLENE/GRAPHENE NANOCOMPOSITE
No full textIn this work the morphology and the rheological and mechanical
properties of a nanocomposite made of a polypropylene with graphene
nanoplatelets (GNP) have been investigated as a function of the compounding
parameters to evaluate the thermomechanical degradation behaviour
of this system. The presence of graphene seems to reduce the thermomechanical
degradation of the matrix. A better dispersion of the GNP seems the
cause of this behaviour
Use of PP-g-OXA in the compatibilization of PP/LCP blends
No full textAdding small amounts of liquid crystalline polymers (LCP) to flexible thermoplastic matrices (FTP) allows to enhance the mechanical and thermomechanical properties. Therefore it is possible to obtain materials with new properties only by simple mixing. A strong shortcoming is the incompatibility between LCP and FTP that leads to materials with very poor properties unusable for commercial pourposes. The presence of a compatibilizer is therefore required. Oxazoline functionality is known to be highly reactive toward many other functional groups and then oxazoline functionalized polymers can be efficiently used as compatibilizer precursors. In this work the compatibilizazion of polypropylene (PP) with a semirigid LCP by using an ad hoc tailored oxazoline functionalized PP has been studied
Photooxidation and Stabilization of Photooxidized Polyethylene and of its Monopolymer Blends
No full textThe increasing use of products from recycled polymers, or from blends with recycled polymers exposed to the outdoors, implies the need for good weathering resistance. This is particularly important when the recycled material comes, in turn, from products exposed during their lifetime to the sun. In this case the presence of C=O groups in the macromolecular chains strongly increases the photooxidative degradation kinetics of these secondary materials. In this work the change of the photooxidative degradation of blends of virgin and photooxidized polyethylene was evaluated as a function of the C=O content present in the material. As expected, the presence of the C=O groups strongly increases the photooxidation kinetics, as revealed by the increase of the carbonyl compounds, and by the decrease of the elongation at break. It was confirmed that the increase of C=O groups is dependent on the content of the same groups, whereas this is not true for the mechanical properties. The use of UV stabilizer strongly improves the weathering resistance of these materials, which become almost insensitive to the initial amount of C=O groups.The increasing use of products from recycled polymers, or from blends with recycled polymers exposed to the outdoors, implies the need for good weathering resistance. This is particularly important when the recycled material comes, in turn, from products exposed during their lifetime to the sun. In this case the presence of C=O groups in the macromolecular chains strongly increases the photooxidative degradation kinetics of these secondary materials. In this work the change of the photooxidative degradation of blends of virgin and photooxidized polyethylene was evaluated as a function of the C=O content present in the material. As expected, the presence of the C=O groups strongly increases the photooxidation kinetics, as revealed by the increase of the carbonyl compounds, and by the decrease of the elongation at break. It was confirmed that the increase of C=O groups is dependent on the content of the same groups, whereas this is not true for the mechanical properties. The use of UV stabilizer strongly improves the weathering resistance of these materials, which become almost insensitive to the initial amount of C=O groups
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