491 research outputs found
Making an impact with nanocomposites
Nanoclays can improve the performance of injection-molded polypropylene components likely to be subjected to impact in servic
Microestructura y desempeño de compuestos de PP/nanoarcilla producidos por técnicas de inyección no convencionales
Fundação para a Ciência e a Tecnologia (FCT)CONyCET (Argentina
Surface property effects of compounding a nanoclay masterbatch in PP injection moulding
Indicado para o prémio de melhor artigo mais inovador.The interest on the use of nanofillers in injection mouldings has been going on for more than a decade but a real breakthrough has not been achieved yet, especially in that mechanical properties are concerned. The nucleating effect of nanoclays in semicrystalline polymers suggests that surface effects may result interesting especially during processing. This paper includes some information on the surface properties of an injection moulding grade of polypropylene mixed with a commercial masterbatch of PP and 50% of organoclay. They were moulded as plates for testing in a prototype device for determining the coefficient of friction in as-moulding conditions. The surface was also characterised by depth sensing indentation tests. The through thickness microstructures of the mouldings were assessed by optical microscopy and differential scanning calorimetry, while surface morphology was assessed by X-ray diffraction. It was observed that independently of MB content, its addition caused a slight increase in elastic modulus and hardness in the skin layer.The friction
properties directly associable to the product performance showed a slight improvement in terms of the dynamic friction coefficient. Conversely the static friction coefficient that is relevant in processing was no affected by the presence of the nanoclay
Impact behavior of injected PP/nanoclay parts
This work attempts to contribute to bridge the gap between scientific challenges and industrial stakes regarding
PP/nanoclay composites. Pieces of nanocomposites were obtained by direct injection of commercial PP mixed with a
commercial MB of PP with 50% of organoclay, with a double-gated hot runner mould, which produced mouldings with
a weld line. The moulding microstructure was assessed by POM and XRD, while the distribution and exfoliation grade
of clay was evaluated by TEM and XRD. The typical skin-core structure was found, with a skin thickness wider in bulk
than in weld line zones. Regarding clay platelets mostly intercalated structures were seen. The impact properties at
room temperature were assessed by means of tensile and biaxial tests. Properties were monitored at different sites of the
mouldings. At the weld line zone less energy was consumed under tensile conditions and exhibited higher apparent
impact toughness under biaxial conditions than the bulk zone. Visual inspection of biaxially impacted samples showed
that the orientation of polymer molecules and clay platelets induced by melt flow prevailed, and the weld line was not
the determinant of the toughness of the mouldings. An optimum in impact performance was found for moulding with
3% of clay, since at larger clay contents platelets agglomerated and acted as stress raisers
Uni- and biaxial impact behavior of double-gated nanoclay-reinforced polypropylene injection moldings
Polypopylene/nanoclay three-dimensional parts were
produced without intermediate steps by direct injection
molding to explore the influence of flow features and
nanoclay incorporation in their impact performance.
The nanocomposite was obtained by direct compounding
of commercial PP with nanoclay masterbatch. The
as-molded morphology was analyzed by X-ray and
TEM analyses in terms of skin-core structure and
nanoclay particle dispersion. The nanoclay particles
induced the reduction of b-form spherulites, a known
toughener. The impact behavior was assessed in tensile
and biaxial modes. The PP nanocomposite molding
toughness was practically unaffected by the processing
melt temperature and flow rate. Conversely the
nanoclay presence is influent in the impact performance.
Under biaxial stress impact, the regions close to
weld lines are tougher than the bulk and the fracture
develops with main crack paths along the flow direction
and the weld line. Cracking along the weld line
results from less macromolecular interpenetration and
chain entanglement, and unfavorable nanoparticle orientation.
It seems that a failure mechanism which
involves nanoclay delamination and multiple matrix
crazing explains the toughening of PP in the directions
where the nanoparticle orientation with respect to
loading is adequate.Contract grant sponsors: CONICET, ANPCyT from Argentina, MINCyT (Argentina) - FCT (Portugal), Universities Nacional de Mar del Plata and Minho
Synergistic effects of nanoclay and SGF on tribological and dynamic properties of polypropylene composites
In recent year’s polymer/layered silicate (PLS) nanocomposites have attracted great
interest, both in industry and in academia, because they often exhibit remarkable improvement in
materials properties when compared with virgin polymer or conventional micro and macrocomposites.
These improvements can include high moduli, increased strength and heat resistance,
decreased gas permeability and flammability, and increased biodegradability of biodegradable
polymers. However these properties are strongly influenced by how the clay is dispersed in the
polymer.
In this study the synergistic effects in PP+short glass fiber+nanoclay systems in the tribogical and
dynamic properties in injection mouldings were analysed.
The materials used were a Polypropylene Homopolymer, Nanoclay (montmorillonite layer silicate)
for Polyolefin Nanocomposites in percentages of 2%, 6% and 10% and a Polypropylene
Homopolymer with content of 10% and 30% of glass fiber reinforced.
The various materials systems were characterized in terms of dynamic properties and tribological
properties. Several tests were conducted which includes the measurements of coefficient of friction
in conditions similar to the ejection phase in injection moulding process. The microstructure of the
mouldings was characterized by DSC.
Polymer properties are determined by the incorporation of nanoclays, SGF and by processing.
Moreover influencing the microstructure of the mouldings and a synergistic effect of the nano and
micro reinforcements are also observed
Immunoglobulin A Nephropathy. Recurrence After Renal Transplantation
IgA nephropathy (IgAN) is the most common primary glomerular disease worldwide. The disease generally runs an indolent course but may lead to ESRD in 20-30% of patients in 20 years or more after diagnosis. Patients with IgA nephropathy are ideal candidates for renal transplant because they are generally relatively young and with few comorbidities. Their graft survival is better or comparable to that of controls at 10 years, though few data are available after 10 years of follow-up. Recurrence of the original disease in the graft is a well-known complication of transplant in IgAN and is a significant cause of deterioration of graft function. Recurrent IgAN rarely manifests clinically before 3 years post transplantation. Recurrence rate is estimated to be around 30% with considerable differences among different series. Despite these factors there is no certain recurrence predictor, young age at renal transplant, rapid progression of the original disease and higher levels of circulating galactose-deficient IgA1 and IgA-IgG immune complexes are all associated with a higher rate of recurrence. Which pathogenetic mechanisms are responsible for the progression of the recurrence to graft function deterioration, and what therapy can prevent or slow down the progression of the disease in the graft, are open questions. The aim of this review is to describe the clinical outcome of renal transplantation in IgA patients with attention to the rate and the predictors of recurrence and to discuss the available therapeutic options for the management of recurrence
DNA Methylation Dynamics of Human Hematopoietic Stem Cell Differentiation
Hematopoietic stem cells give rise to all blood cells in a differentiation process that involves widespread epigenome remodeling. Here we present genome-wide reference maps of the associated DNA methylation dynamics. We used a meta-epigenomic approach that combines DNA methylation profiles across many small pools of cells and performed single-cell methylome sequencing to assess cell-to-cell heterogeneity. The resulting dataset identified characteristic differences between HSCs derived from fetal liver, cord blood, bone marrow, and peripheral blood. We also observed lineage-specific DNA methylation between myeloid and lymphoid progenitors, characterized immature multi-lymphoid progenitors, and detected progressive DNA methylation differences in maturing megakaryocytes. We linked these patterns to gene expression, histone modifications, and chromatin accessibility, and we used machine learning to derive a model of human hematopoietic differentiation directly from DNA methylation data. Our results contribute to a better understanding of human hematopoietic stem cell differentiation and provide a framework for studying blood-linked diseases.This work was funded by the BLUEPRINT project (European Union’s Seventh Framework Programme grant 282510), the NIHR Cambridge Biomedical Research Centre, and the Austrian Academy of Sciences. F.A.C. is supported by a Medical Research Council Clinical Training Fellowship (grant MR/K024043/1). F.H. is supported by a postdoctoral fellowship of the German Research Council (DFG; grant HA 7723/1-1). J.K. is supported by a DOC Fellowship of the Austrian Academy of Sciences. W.H.O. is supported by the NIHR, BHF (grants PG-0310-1002 and RG/09/12/28096), and NHS Blood and Transplant. E.L. is supported by a Wellcome Trust Sir Henry Dale Fellowship (grant 107630/Z/15/Z) and core support grant from the Wellcome Trust and MRC to the Wellcome Trust-Medical Research Council Cambridge Stem Cell Institute. M. Frontini is supported by the BHF Cambridge Centre of Excellence (grant RE/13/6/30180). C.B. is supported by a New Frontiers Group award of the Austrian Academy of Sciences and by a European Research Council (ERC) Starting Grant (European Union’s Horizon 2020 research and innovation program; grant 679146)
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