Search results for "polymers"
showing 10 items of 3567 documents
Phenomenological approach to compare the crystallization kinetics of isotactic polypropylene and polyamide-6 under pressure
2001
Reliable experimental data for semicrystalline polymers crystallized under pressure are supplied on the basis of a model experiment in which drastic solidification conditions are applied. The influence of the pressure and cooling rate on some properties, such as the density and microhardness, and on the product morphology, as investigated with wide-angle X-ray scattering (WAXS), is stressed. Results for isotactic polypropylene (iPP) samples display a lower density and a lower microhardness with increasing pressure over a wide range of cooling rates (from 0.01 to 20 °C/s). Polyamide-6 (PA6) samples exhibit the opposite behavior, with the density and microhardness increasing at higher pressur…
Emulsion-based synthesis of PLGA-microspheres for the in vitro expansion of porcine chondrocytes.
2007
Abstract The in vitro cell expansion of autologous chondrocytes is of high interest in regenerative medicine since these cells can be used to treat joint cartilage defects. In order to preserve chondrocyte phenotype, while optimizing adhesion on microspheres, several processing parameters for the microsphere synthesis were varied. In this study three different polylactide-co-glycolides were used with differing lactide–glycolide ratios (85:15 and 50:50) and differing inherent viscosities. An emulsion route was established, where the polymer was dissolved in chloroform and then injected into a stirred polyvinyl alcohol–water solution at different polymer concentrations and different stirring …
Taking advantage of the functional synergism between carbon nanotubes and graphene nanoplatelets to obtain polypropylene-based nanocomposites with en…
2020
Carbon Nanotubes (CNT) and Graphene Nanoplatelets (GNP) were incorporated in Polypropylene (PP) as single filler (CNT=1, 2 and 4 %wt. and GNP=2, 4, and 6 %wt.) and in hybrid form (CNT:GNP weight ratio 2:2, 2:4 and 4:2) using a prototype miniature Twin Screw Extruder (TSE) coupled with a double slit rheological die, in order to assess in-line the extent of nanofiller dispersion and to deliver PP-based nanocomposites with enhanced thermo-oxidative stability. The morphological, electrical and mechanical properties, as well as the resistance to thermal and photo degradation of the composites containing single nanofillers (PP/CNT and PP/GNP) were compared with those of hybrid PP based nanocompos…
A new route for the preparation of flexible skin–core poly(ethylene-co-acrylic acid)/polyaniline functional hybrids
2011
Abstract Surface modification of polymeric films is a way to obtain final products with high performance for many specific and ad hoc tailored applications, e.g. in functional packaging, tissue engineering or (bio)sensing. The present work reports, for the first time, on the design and development of surface modified ethylene–acrylic acid copolymer (EAA) films with polyaniline (PANI), with the aim of inducing electrical conductivity and potentially enable the electronic control of a range of physical and chemical properties of the film surface, via a new “grafting from” approach. In particular, we demonstrate that PANI was successfully polymerized and covalently grafted onto flexible EAA su…
Influence of resin viscosity and vacuum level on mechanical performance of sandwich structures manufactured by vacuum bagging
2010
The choice of process parameters is critical in optimizing the mechanical properties of sandwich structures produced using the vacuum bagging technique. The aim of this paper is to analyze how the viscosity of the resin/curing agent system and the vacuum level influence the morphology and the mechanical behavior of sandwich beams with composite faces (epoxy resin and glass fiber fabric named COMBI 900) and a PVC foam core. Four different sandwich structures were produced by varying the viscosity of the epoxy resin/curing agent at constant maximum vacuum pressure. Three further structures were manufactured by varying the strength of the vacuum with the resin viscosity maintained constant at …
Micro‐tomographic characterization of composite recycled glass‐silicone foams for applications in civil engineering
2019
Noninvasive X‐ray micro‐computed tomography was applied for a complete quantitative and qualitative analysis of the cellular structure of composite foams constituted by a silicone matrix and a glass production waste filler. Composite foams with different glass filler weight content in the range 0–80% were synthesized and characterized. The tomographic analysis was employed in order to assess the structural heterogeneities, void fraction values, and bubble size distribution for all composite foams. The 3D micro‐CT images analysis, performed at different cross‐sections, highlighted heterogeneous cell growth or more elongated cells in the case of low and high filler content foams, respectively…
Morphology and mechanical properties of extruded ribbons of LDPE/PA6 blends compatibilized with an ethylene-acrylic acid copolymer
2003
Two grades of low density polyethylene (LDPE) were blended with polyamide-6 (PA) in the 75/25 and 25/75 wt/wt ratios and shaped into ribbons with a Brabender single screw extruder. An ethylene-acrylic acid copolymer (EAA) was used in the 2 phr concentration as a compatibilizer precursor (CP). The morphology of the ribbons and its evolution during high temperature annealing were investigated by scanning electron microscopy (SEM). The results confirmed that EAA does actually behave as a reactive compatibilizer for the LDPE/PA blends. In fact, in the presence of EAA, the interfacial adhesion is improved, the dispersion of the minor phase particles is enhanced and their tendency toward fibrilla…
Phase separation of polymer blends in solution: A case study
2016
Abstract The phase behavior and phase separation features of the quaternary system poly- l -lactide (PLLA)/poly-rac-lactide (PLA)/dioxane/water were investigated. Experiments were performed with fixed total polymer concentration of 6 wt%, by varying the PLLA/PLA weight ratio. Blend weight compositions examined were 100/0, 80/20, 50/50, 20/80 and 0/100, at fixed dioxane/water weight ratio (87/13). Cloud point measurements reported that the demixing temperatures of blends are close to PLLA in the same mixed solvent, in line with the calculated spinodals. As regards to foam preparation, above the PLA cloud point, morphology is similar to pure PLLA foams; conversely, below PLA cloud point, the …
Effect of the nanotube aspect ratio and surface functionalization on the morphology and properties of multiwalled carbon nanotube polyamide-based fib…
2013
In this study, the effect of the carbon nanotube (CNT) aspect ratio and surface functionalization on the mechanical behavior and morphological changes of polyamide (PA)-based fibers was investigated. Composites were prepared by the melt blending of CNTs with PA, and at a later time, the fibers were prepared by melt spinning and cold drawing. A reinforcement effect was noticed for all of the CNTs samples, and the increase in the mechanical properties and dimensional stability was more pronounced for highly oriented filaments. When the elongational flow was increased, the orientation of CNTs along the fiber direction was observed, but the nanotube alignment was much more difficult for CNTs wi…
Morphology, mechanical properties and thermal degradation kinetics of PMMA-zirconia nanocomposites prepared by melt compounding
2012
Zirconia nanoparticles were synthesized by means of a sol-gel method and embedded in poly(methyl methacrylate) (PMMA) by melt compounding. The zirconia was well dispersed in the PMMA matrix, with only a few clusters, especially for the highest investigated zirconia content. NMR results showed heteronuclear dipolar interactions involving the carbons and the surrounding hydrogen nuclei. The effect of the amount of zirconia, in the range of 1–5!wt%, on the thermomechanical properties and thermal degradation kinetics of PMMA was also investigated by means of dynamic mechanical analysis (DMA), thermogravimetric analyses (TGA), and Fourier-transform infrared spectroscopy (FTIR). The presenc…