Effect of extensional flow on morphology and properties of polyamide layered silicate nanocomposites

The 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

Effect of short-chain branching on melt fracture behavior of metallocene and conventional poly(ethylene/α-olefin) copolymers

A 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

Stiffness constants prediction of nanocomposites using a periodic 3D-FEM model

Predictive models, which enable the prediction of nanocomposite properties from their morphologies and account for polymer orientation, could greatly assist the exploitation of this new class of materials in more diversified and demanding market fields. This article focuses on the prediction of effective elastic properties (Young's moduli) of polymer nanocomposite films (copolyamide-6/nanoclay) using 3D analytical (based on the Mori-Tanaka theory) and 3D finite element (FE) models. The analytical model accounts for the orientation of polymer chains induced by drawing. 3D FE model exploits the representative volume element concept and accounts for the nanocomposite morphology as determined from transmission electron microscopy experiments. Model predictions were compared with experimental results obtained for nanocomposite films produced by means a pilot-scale film blowing equipment and collected at different draw ratios

Effect of polymer/organoclay composition on morphology and rheological properties of polylactide nanocomposites

In this work the relationships between system composition, polymer–organoclay interaction, morphology and rheological response, under shear, and elongational flow, of different melt compounded polylactic acid (PLA)/organoclay nanocomposites are investigated, with the aim to properly select the better organoclay for a well-specified PLA grade and processing technology. Polylactide nanocomposites are prepared using two commercial polylactide grades (PLA 4032D and PLA 2003D) and two different organomodified montmorillonites (Cloisite 30B and Nanofil SE3010). FTIR analysis evidences the occurrence of stronger polymer/organoclay interactions for the system PLA4032D+C30B, resulting in a higher clay dispersion and exfoliation levels. Moreover, rheological tests at low shear rates show that, if PLA 2003D is used as polymer matrix (differing from PLA4032D by the presence of a high molecular weight tail), a better dispersed nanomorphology can be obtained with Nanofil SE3010, characterized by a double d-spacing compared to Cloisite 30B, despite the higher polar character of this latter nanofiller. On the other hand, elongational rheological measurements evidence for NSE3010-based hybrids a marked extensional thickening, whilst the stronger polar interactions between the phases in both the polylactide grades filled with C30B, determine increments in elongational viscosity, but inhibit the strain hardening behavior

Effect of biaxial drawing on morphology and properties of copolyamide nanocomposites produced by film blowing

In this work, extensional behavior in non-isothermal and isothermal conditions of copolyamide-based nanocomposites was analyzed and correlated to bubble stability in the film blowing processing of these materials. The higher values of transient extensional viscosity and melt strength of the nanocomposites, compared to the neat matrix, imply that they are able to better resist the extensional external force during bubble formation. Oxygen barrier and mechanical properties of the films were investigated and correlated to the resulting polymer crystal structure and filler morphology. At the higher draw ratios and blow up ratios the nanocomposite specimens were present essentially in the mesomorphic b-form, nevertheless, significant improvements in barrier and mechanical properties of the hybrid films were observed, likely due to a good dispersion and orientation of the silicate platelets in the polymer matrix

Preparation and performance analysis of active packaging PET films combining oxygen scavenging with barrier properties for shelf life extension of sensitive foods

The aim of this work was to prepare and evaluate the scavenging performance and the oxygen absorption kinetics of active food packaging PET films, containing a novel auto-activated, copolyester-based oxygen scavenger, which includes in its formulation also a copolyamide phase for enhanced passive gas barrier. Films at three different scavenger content (5%, 10% and 20% by weght) were produced by cast film technology, analyzed in terms of morphology and scavenging activity and tested to verify their effectiveness in preserving the quality of oxygen sensitive foods, performing preliminary shelf life tests on slices of cooked ham. The results highlighted that the films at 10% scavenger loading showed the most homogeneous dispersion and distribution of the reactive domains inside the PET matrix, the best scavenging performances and high potential in prolonging the shelf life of sensitive food matrices

Modelling of mechanical behaviour of polyamide nanocomposite fibres using a three-phase Halpin-Tsai model

AbstractThe aim of the present study is to correlate the features of the elongational flow-induced morphology to the mechanical properties of polyamide based nanocomposite fibres. Particular attention was paid to modelling the mechanical behaviour of the hybrids which were produced by fibre spinning technique and collected at different draw ratios.Tensile properties of as-spun and stretched fibres 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. In particular, the TEM images of the nanocomposite systems showed intercalated/exfoliated morphology in all hybrids. For this reason, a three-phase Halpin-Tsai model, based on polyamide-6 matrix, exfoliated clay platelets and nanolayer intercalated clusters, was used to fit the experimental data.This method was applied to calculate the Young's modulus of nanocomposite fibres both as-spun and stretched ones. Moreover, the model was used for predicting the effect of various morphological parameters including the exfoliation degree, clay layer and cluster aspect ratio

Applications of Robotics for Autism Spectrum Disorder: a Scoping Review

Robotic therapies are receiving growing interest in the autism field, especially for the improvement of social skills of children, enhancing traditional human interventions. In this work, we conduct a scoping review of the literature in robotics for autism, providing the largest review on this field from the last five years. Our work underlines the need to better characterize participants and to increase the sample size. It is also important to develop homogeneous training protocols to analyse and compare the results. Nevertheless, 7 out of the 10 Randomized control trials reported a significant impact of robotic therapy. Overall, robot autonomy, adaptability and personalization as well as more standardized outcome measures were pointed as the most critical issues to address in future research

p140Cap regulates the composition and localization of the NMDAR complex in synaptic lipid rafts

The NMDARs are key players in both physiological and pathologic synaptic plasticity because of their involvement in many aspects of neuronal transmission as well as learning and memory. The contribution in these events of different types of GluN2A-interacting pro-teins is still unclear. The p140Cap scaffold protein acts as a hub for postsynaptic complexes relevant to psychiatric and neurologic dis-orders and regulates synaptic functions, such as the stabilization of mature dendritic spine, memory consolidation, LTP, and LTD. Here we demonstrate that p140Cap directly binds the GluN2A subunit of NMDAR and modulates GluN2A-associated molecular net-work. Indeed, in p140Cap KO male mice, GluN2A is less associated with PSD95 both in ex vivo synaptosomes and in cultured hippo-campal neurons, and p140Cap expression in KO neurons can rescue GluN2A and PSD95 colocalization. p140Cap is crucial in the recruitment of GluN2A-containing NMDARs and, consequently, in regulating NMDARs' intrinsic properties. p140Cap is associated to synaptic lipid-raft (LR) and to soluble postsynaptic membranes, and GluN2A and PSD95 are less recruited into synaptic LR of p140Cap KO male mice. Gated-stimulated emission depletion microscopy on hippocampal neurons confirmed that p140Cap is required for embedding GluN2A clusters in LR in an activity-dependent fashion. In the synaptic compartment, p140Cap influences the association between GluN2A and PSD95 and modulates GluN2A enrichment into LR. Overall, such increase in these membrane domains rich in signaling molecules results in improved signal transduction efficiency