1,721,009 research outputs found
Effect of extensional flow on morphology and properties of polyamide layered silicate nanocomposites
Full text linkThe reinforcement of polyamides with nanometric layered silicates
represents nowadays an innovative strategy to produce high performance plastics with enhanced structural and functional properties. Even if the presence of very low silicate content, usually less than 5 wt %, allows polymer nanocomposites to be produced with conventional processing equipment, the difficulty in conveniently tuning materials and processing parameters, to control the developed nanomorphology, presents a great limit
for applications on an industrial scale. Therefore, the study of the
processability of polyamide based nanocomposites is crucial in order to control, predict and optimize their final properties. In particular, a better understanding of the effects of elongational flow on final nanostructure is fundamental in the cases of film or fibre extrusion in which elongational flow is very common.
The aim of this work is to investigate the effects of elongational flow on clay dispersion, exfoliation, orientation and crystallinity of polyamide based nanocomposites. Hybrids with different loadings of a commercial organoclay were produced by melt compounding using two polyamide matrices: a nylon 6 and a copolyamide, with similar molecular weight. The elongational flow characterization was performed both in non-isothermal and isothermal conditions by using, respectively, fibre spinning technique and an elongational rheometer (SER).
During the spinning tests, fibres of neat matrices and hybrids were
collected at different draw ratios and submitted to morphological
characterization by TEM, small angle X-Ray (SAXD), DSC, and wide angle X-ray (WAXD) analyses. The properties of copolyamide based nanocomposites were compared to nylon 6 ones in order to examine the effect of polymer molecular structure on the structural modifications upon drawing as well as to establish the relationship between processing, nanomorphology and properties. Finally, the Halpin-Tsai method was applied to calculate the modulus of the nanocomposite fibres at different draw ratios, as a function of various parameters, including the exfoliation ratio, clay layer and cluster aspect ratios. Since all hybrids studied in this work were characterized by intercalated/exfoliated morphology, the calculation, using the Halpin-Tsai method, was divided into two stages. Young’s modulus for the exfoliated region was computed first by considering this region as a two-phase system: the neat matrix and the exfoliated clay platelets. The exfoliated region with the computed Young’s modulus was then considered as the effective matrix phase in the second stage of calculation, in which the intercalated region was
the inclusion phase
Polyamide based nanocomposites fibres: morphology and mechanical properties at different draw ratios
No full textThe aim of this study is to investigate the feature of the elongational flow-induced structure formation of nanocomposites and to correlate the mechanical properties of the hybrids to the resulting nanomorphology. In particular, the present work focuses on the modelling of mechanical behaviour of polyamide based nanocomposite fibers, which were produced by fiber spinning technique and collected at different draw ratios.
Tensile properties of the produced fibers were investigated and correlated to their nanostructure through analytical techniques sensitive to different aspects of the hybrids morphology, such as X-Ray diffraction and TEM analysis.
Finally, the Halpin-Tsai method was applied to calculate the modulus of the nanocomposite fibers at different draw ratios. In particular, since all hybrids studied in this work were characterized by intercalated/exfoliated morphology, the calculation was divided into two stages. The Young’s modulus for the exfoliated region was computed first by considering this region as a two-phase system: the neat matrix and the exfoliated clay platelets. The exfoliated region with the computed Young’s modulus was then considered as the effective matrix phase in the second stage of calculation, in which the intercalated region was the inclusion phase
Effects of uniaxial elongational flow on polyamide based nanocomposites: morphology and mechanical properties at different draw ratios
No full textPolymer-clay nanocomposites represent an interesting topic in materials research because of their promising properties which can be obtained with very low filler content. As well known, the performances improvement of these composites is realized when clay particles are accurately dispersed in the polymer matrix and intercalation between matrix macromolecules and clay lamellae exist. Many researches have been thus devoted to the problem of producing intercalated or exfoliated structures, and to verify the internal structure of the nanocomposites. In this regard, melt rheology represents an important experimental tool which allows to prove if exfoliation and intercalation have been realized [1, 2]. Many studies on shear flow rheology of polymer-clay nanocomposites are present in the literature but there are only a few reports about the extensional flow behaviour of nanocomposite melts [3, 4]. Nevertheless, extensional flows are very common in polymer processing operation, such as in the case of film or fiber extrusion. It is thus worthy of note to study extensional rheology of melt compounded polymer-clays systems and to analyze their behaviour in order to develop proper processesing conditions for the production of nanocomposite fibres or films.
This work focuses on the study of uniaxial elongational flow and to its effect on morphology and performances of polymer-layered silicate nanocomposites. In particular a polyamide based nanocomposites, prepared by twin screw extrusion melt compounding, was investigated.
The elongational flow characterization was realized by converging flow method and fiber spinning technique by making use of a capillary rheometer.
The performances of the resulting nanocomposite fibres were also analyzed in terms of mechanical properties
EFFETTO DELLO STIRO UNIASSIALE SULLA STRUTTURA E SULLE PROPRIETA’ DI NANOCOMPOSITI A BASE DI NYLON 6
No full textIl presente lavoro riguarda l’effetto del flusso elongazionale sulla distribuzione, l‘esfoliazione e l’orientazione della nanocarica dispersa in una matrice poliammidica. Nanocompositi a base di nylon 6, contenenti differenti percentuali di nanofiller, sono stati prodotti mediante melt compounding e sottoposti ad una caratterizzazione reologica in flusso elongazionale effettuata in condizioni isoterme e non-isoterme.
Con la tecnica del fiber spinning sono state raccolte fibre a differenti rapporti di stiro su cui sono state effettuate analisi TEM e test meccanici a trazione al fine di stabilire la correlazione tra flusso elongazionale, modificazioni strutturali e proprietà finali
Copolyamide based nanocomposite films as innovative solution of packaging materials.
No full textPolymer layered silicate nanocomposites represent nowadays a very interesting opportunity to enhance the properties of unmodified resin and produce high-performances plastics. With the adding of very low silicate contents, generally less than 6ww%, not only structural properties but also functional properties are strongly improved [1,2]. It is well known that the final properties are strictly correlate with the nanoscale arrangement of the silicate layers inside the polymer matrix as well as the entity of polymer-clay interactions. In particular, the exfoliation of the silicate inside the polymer matrix is the key for obtaining the highest performance improvements.
The field of packaging is one for which the application of nanocomposites is highly attractive, and improvements in mechanical and gas barrier properties could allow such materials to be employed as innovative solutions to satisfy the demanding requirements that a modern-day package must fulfill, such as protection, mechanical and thermal resistance, low cost, recycling, etc. This, coupled with the potential to process such materials with the conventional processing equipments, such as extrusion, can lead to a net improved performance/cost ratio.
In this frame, great industrial and scientific attention is paid to polyamide-based nanocomposites prepared by melt compounding either because polyamides are inexpensive, available and widely used in packaging applications either because their hydrophilic nature is the base for a good compatibility with the silicate [3-4]. Nevertheless, the difficulty in conveniently tuning materials and processing parameters to control the developed nanomorphology (clay dispersion, exfoliation and orientation degrees, matrix crystallinity) represents a great limit for the application of polyamide based nanocomposites on industrial scale.
This work focuses on the possibility to improve performance properties of polyamide layered silicate nanocomposite films by using, as alternative matrix, a statistical copolymer of the nylon 6 having a partially aromatic structure. Nanocomposites at different silicate loadings (commercial organo-modified montmorillonite) were produced by cast film extrusion using nylon 6 and copolyamide matrices.
Oxygen barrier and mechanical properties were investigated on the nanocomposite films and correlated to their morphology through transmission electron microscopy (TEM), rheological analyses and theoretical models. The properties of copolyamide based films were compared to nylon 6 based ones in order to examine the effect of polymer molecular structure on the extent of silicate exfoliation and to establish the relationship between nanomorphology and properties, crucial in predicting and optimizing the end performances
POLYAMIDE BASED NANOCOMPOSITE FIBERS:morphology and mechanical properties at different draw ratios
Full text linkThe aim of this study is to investigate the feature of the elongational flow-induced structure formation of nanocomposites and to correlate the mechanical properties of the hybrids to the resulting nanomorphology. In particular, the present work focuses on the modelling of mechanical behaviour of polyamide based nanocomposite fibers, which were produced by fiber spinning technique and collected at different draw ratios.
Tensile properties of the produced fibers were investigated and correlated to their nanostructure through analytical techniques sensitive to different aspects of the hybrids morphology, such as X-Ray diffraction and TEM analysis.
Finally, the Halpin-Tsai method was applied to calculate the modulus of the nanocomposite fibers at different draw ratios. In particular, since all hybrids studied in this work were characterized by intercalated/exfoliated morphology, the calculation was divided into two stages. The Young’s modulus for the exfoliated region was computed first by considering this region as a two-phase system: the neat matrix and the exfoliated clay platelets. The exfoliated region with the computed Young’s modulus was then considered as the effective matrix phase in the second stage of calculation, in which the intercalated region was the inclusion phase
Morphology and mechanical behaviour of PA6/montmorillonite nanocomposites fibers
No full textPolymer-clay nanocomposites represent an interesting topic in materials research because of their promising properties which can be obtained with very low filler content. As well known, the performances improvement of these composites is realized when clay particles are accurately dispersed in the polymer matrix and intercalation between matrix macromolecules and clay lamellae exist.
Many studies on shear flow rheology of polymer-clay nanocomposites are present in the literature but there are only a few reports about the extensional flow behaviour of nanocomposite melts. Nevertheless, extensional flows are very common in polymer processing operation, such as in the case of film or fiber extrusion.
This work focuses on the study of uniaxial elongational flow and to its effect on morphology and performances of polymer-layered silicate nanocomposites. In particular a polyamide based nanocomposites, prepared by twin screw extrusion melt compounding, was investigated
Improved processability of linear low-density polyethylene copolymers
No full textIncreasing short-chain branching length by even just a few carbon atoms reduces extrudate distortion
Effect of short-chain branching on melt fracture behavior of metallocene and conventional poly(ethylene/α-olefin) copolymers
Full text linkA phenomenon that can represent a great problem in melt processing is extrudate distortion. This effect can range in intensity from a loss of gloss to gross distortion and is the factor that limits the production rate in certain processes such as the blown film extrusion of linear low-density polyethylene (LLDPE). The aim of this work was to investigate the effects that molecular weight distribution and short-chain branch length have on the observed melt fracture phenomena for poly(ethylene/-olefin) resins with similar weight comonomer content and molecular weight. The flow stability analysis conducted in this study has shown that, even increasing of few carbon atoms the short-chain branch length of the resins, the surface melt fracture phenomena are reduced and/or eliminated. Moreover, the comparison between the metallocene (mLLDPE) and conventional LLDPE samples, with the same comonomer (hexene), showed that the metallocene-catalyzed resin exhibits early onset and more severe melt fracture, due to its narrower molecular weight distribution
Effect of uniaxial elongational flow on new copoliamide based nanocomposites
No full textThe reinforcement of polymers by adding low amount of nanoscopic layered silicates is very promising in the production of high-performances plastics. It is well known that the enhanced properties are strictly correlate with the nanoscale arrangement of the silicate layers inside the polymer matrix. In this regard, melt rheology represents a powerful tool to investigate the nanostructure in solid state and, conversely to other experimental techniques that probe a very small volume, is representative of the global bulky nanostructure. The most part of studies on rheology of polymer-clay nanocomposites concerns dynamic shear measurements, while scarce attention is paid to the effects of uniaxial elongational flow on nanostructure and properties, crucial aspect for the production of polymer nanocomposite on wide scale. In particular, in the case of film or fiber extrusion, the elongational flow is common and a better understanding of its effects on the nanostructure is important to optimize the final properties. Great industrial and scientific attention is paid to polyamide-based nanocomposites prepared by melt compounding either because polyamides are inexpensive, available and widely used either because their hydrophilic nature is the base for a good compatibility with the silicate.
In this work, nanocomposite at different silicate loadings were produced by melt compounding using two polyamide matrices: a nylon 6 and a commercial copolyamide having similar molecular weights.
The rheological response at high shear rates was investigated in terms of steady shear viscosity and extentional viscosity, and correlated with the state of silicate exfoliation inside the two different matrices.
Nanocomposite fibers were produced by fiber spinning technique and collected at different draw ratios. The structural changes of the layered silicate and crystalline regions of the different nanocomposite fibers were investigated in response to uniaxial deformation imposed and correlated with the final tensile mechanical properties with the aim to identify the processing condition and the material composition able to lead to the highest final performances
- …
