Conductivity of microfibrillar polymer-polymer composites with CNT-loaded microfibrils or compatibilizer: A comparative study

Conductive polymer composites have wide ranging applications, but when they are produced by conventional melt blending, high conductive filler loadings are normally required, hindering their processability and reducing mechanical properties. In this study, two types of polymer-polymer composites were studied: i) microfibrillar composites (MFC) of polypropylene (PP) and 5 wt% carbon nanotube (CNT) loaded poly(butylene terephthalate) (PBT) as reinforcement, and ii) maleic anhydride-grafted polypropylene (PP-g-MA) compatibilizer, loaded with 5 wt% CNTs introduced into an MFC of PP and poly(ethylene terephthalate) (PET) in concentrations of 5 and 10 wt%. For the compatibilized composite type, PP and PET were melt-blended, cold-drawn and pelletized, followed by dry-mixing with PP-g-MA/CNT, re-extrusion at 200°C, and cold-drawing. The drawn blends produced were compression moulded to produce sheets with MFC structure. Using scanning electron microscopy, CNTs coated with PP-g-MA could be observed at the interface between PP matrix and PET microfibrils in the compatibilized blends. The volume resistivities tested by four-point test method were: 2.87•108 and 9.93•107 Ω•cm for the 66.5/28.5/5 and 63/27/10 (by wt%) PP/PET/(PP-g-MA/CNT) blends, corresponding to total CNT loadings (in the composites) of 0.07 vol% (0.24 wt%) and 0.14 vol% (0.46 wt%), respectively. For the non-compatibilized MFC types based on PP/(PBT/CNT) with higher and lower melt flow grades of PP, the resistivities of 70/(95/5) blends were 1.9•106 and 1.5•107 Ω•cm, respectively, corresponding to a total filler loading (in the composite) of 0.44 vol% (1.5 wt%) in both MFCs

Melt blending and characterization of carbon nanoparticles-filled thermoplastic polyurethane elastomers

In this work, thermoplastic polyurethane (TPU) elastomers reinforced with carbon nanosized particles were produced by a special melt blending technique. A TPU was melt blended with high-structured carbon black and carbon nanofibres (1 wt%). A miniature asymmetric batch mixer, which applies high shear levels to the melt, ensured good particles dispersion. The TPU material systems were then thoroughly characterized using thermogravimetric analysis, differential scanning calorimetry, tensile mechanical testing, electrical resistance measurements and flammability tests. The different nanofillers exhibited different influences on the TPU properties, these materials featuring interesting and improved multifunctional behaviours, with high propensity for large deformation sensors applications.This work was supported by FCT – Portuguese Foundation for Science and Technology through projects NANOSens – PTDC/CTM/73465/2006

Rheological and electrical analysis in carbon nanofibre reinforced polypropylene composites

Two different types of carbon nanofibers (CNF) were incorporated in the same polypropylene (PP) matrix by twin-screw extrusion. The electrical characterization of both CNFs / PP composites as a function of volume fraction show different electrical performance: conducting and non-conducting. The objective of this work is to study the rheological behaviour of both composites with the aim of relating it to the electrical behaviour. The results indicate that the rheological behaviours are different, suggesting that rheology differentiates the microstructural variations responsible for the electrical performance. Furthermore, the main rheological parameters were correlated to the electrical conductivity. The results show that G´/ G´´ and G´ are the most sensitive parameters when compared to the onset of electrical percolation. Finally, in spite of the intrinsic measuring differences between electrical and rheological analysis, the two calculated thresholds are very similar: ~ 0.5 for the rheological and ~ 0.4 for the electrical.Financial support for this work has been provided by Consellería de Educación e Ordenación Universitaria, Xunta de Galicia through grant CN2011/008

Thermal and electrical conductivity of melt mixed polycarbonate hybrid composites co-filled with multi-walled carbon nanotubes and graphene nanoplatelets

"This is the peer reviewed version of the following article: Wegrzyn, M., Ortega, A., Benedito, A., & Gimenez, E. (2015). Thermal and electrical conductivity of melt mixed polycarbonate hybrid composites co‐filled with multi‐walled carbon nanotubes and graphene nanoplatelets. Journal of Applied Polymer Science, 132(37), which has been published in final form at https://doi.org/10.1002/app.42536. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."[EN] In this work, we present thermoplastic nanocomposites of polycarbonate (PC) matrix with hybrid nanofillers system formed by a melt-mixing approach. Various concentrations of multi-walled carbon nanotubes (MWCNT) and graphene nanoplatelets (GnP) were mixed in to PC and the melt was homogenized. The nanocomposites were compression molded and characterized by different techniques. Torque dependence on the nanofiller composition increased with the presence of carbon nanotubes. The synergy of carbon nanotubes and GnP showed exponential increase of thermal conductivity, which was compared to logarithmic increase for nanocomposite with no MWCNT. Decrease of Shore A hardness at elevated loads present for all investigated nanocomposites was correlated with the expected low homogeneity caused by a low shear during melt-mixing. Mathematical model was used to calculate elastic modulus from Shore A tests results. Vicat softening temperature (VST) showed opposite pattern for hybrid nanocomposites and for PC-MWCNT increasing in the latter case. Electrical conductivity boost was explained by the collective effect of high nanofiller loads and synergy of MWCNT and GnP. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. 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Abnormal clot microstructure formed in blood containing HIT-like antibodies

IntroductionThrombosis is a severe and frequent complication of heparin-induced thrombocytopenia (HIT). However, there is currently no knowledge of the effects of HIT-like antibodies on the resulting microstructure of the formed clot, despite such information being linked to thrombotic events. We evaluate the effect of the addition of pathogenic HIT-like antibodies to blood on the resulting microstructure of the formed clot.Materials and methodsPathogenic HIT-like antibodies (KKO) and control antibodies (RTO) were added to samples of whole blood containing Unfractionated Heparin and Platelet Factor 4. The formed clot microstructure was investigated by rheological measurements (fractal dimension; df) and scanning electron microscopy (SEM), and platelet activation was measured by flow cytometry.Results and conclusionsOur results revealed striking effects of KKO on clot microstructure. A significant difference in df was found between samples containing KKO (df = 1.80) versus RTO (df = 1.74; p < 0.0001). This increase in df was often associated with an increase in activated platelets. SEM images of the clots formed with KKO showed a network consisting of a highly branched and compact arrangement of thin fibrin fibres, typically found in thrombotic disease. This is the first study to identify significant changes in clot microstructure formed in blood containing HIT-like antibodies. These observed alterations in clot microstructure can be potentially exploited as a much-needed biomarker for the detection, management and monitoring of HIT-associated thrombosis

Incentives for preventing smoking in children and adolescents (Review)

BackgroundAdult smoking usually has its roots in adolescence. If individuals do not take up smoking during this period it is unlikely that they ever will. Further, once smoking becomes established, cessation is challenging; the probability of subsequently quitting is inversely proportional to the age of initiation. One novel approach to reducing the prevalence of youth smoking is the use of incentives.ObjectivesTo determine whether incentives prevent children and adolescents from starting to smoke. We also attempted to assess the dose-response of incentives, the costs of incentive programmes, whether incentives are more or less effective in combination with other interventions to prevent smoking initiation and any unintended consequences arising from the use of incentives.Search methodsWe searched the Cochrane Tobacco Addiction Group Specialized Register, with additional searches of MEDLINE, EMBASE, CINAHL, CSA databases and PsycINFO for terms relating to incentives, in combination with terms for smoking and tobacco use, and children and adolescents. The most recent searches were in May 2012.Selection criteriaWe considered randomized controlled trials allocating children and adolescents (aged 5 to 18 years) as individuals, groups or communities to intervention or control conditions, where the intervention included an incentive aimed at preventing smoking uptake. We also considered controlled trials with baseline measures and post-intervention outcomes.Data collection and analysisData were extracted by two authors and assessed independently. The primary outcome was the smoking status of children or adolescents at follow-up who reported no smoking at baseline. We required a minimum follow-up of six months from baseline and assessed each included study for risk of bias. We used the most rigorous definition of abstinence in each trial; we did not require biochemical validation of self-reported tobacco use for study inclusion. Where possible we combined eligible studies to calculate pooled estimates at the longest follow-up using the Mantel-Haenszel fixed-effect method, grouping studies by study design.Main resultsWe identified seven controlled studies that met our inclusion criteria, including participants with an age range of 11 to 14 years. Of the seven trials identified, only five had analysable data relevant for this review and contributed to the meta-analysis (6362 participants in total who were non-smokers at baseline; 3466 in intervention and 2896 in control). All bar one of the studies was a trial of the so-called Smokefree Class Competition (SFC), which has been widely implemented throughout Europe. In this competition, classes with youth generally between the ages of 11 to 14 years commit to being smoke free for a six month period. They report regularly on their smoking status; if 90% or more of the class is non-smoking at the end of the six months, the class goes into a competition to win prizes. The one study that was not a trial of the SFC was a controlled trial in which schools in two communities were assigned to the intervention, with schools in a third community acting as controls. Students in the intervention community with lower smoking rates at the end of the project (one school year) received rewards.Only one study of the SFC competition, a non-randomized controlled trial, reported a significant effect of the competition on the prevention of smoking at the longest follow-up. However, this study had a risk of multiple biases, and when we calculated the adjusted RR we no longer detected a statistically significant difference. The pooled RR for the more robust RCTs (3 studies, n = 3056 participants) suggests that, from the available data, there is no statistically significant effect of incentives to prevent smoking initiation among children and adolescents in the long term (RR 1.00, 95% CI 0.84 to 1.19). Pooled results from non-randomized trials also did not detect a significant effect, and we were unable to extract data on our outcome of interest for the one trial that did not study the SFC. There is little robust evidence to suggest that unintended consequences (such as youth making false claims about their smoking status and bullying of smoking students) are consistently associated with such interventions, although this has not been the focus of much research. There was insufficient information to assess the dose-response relationship or to report costs.Authors\u27 conclusionsTo date, incentive programmes have not been shown to prevent smoking initiation among youth, although there are relatively few published studies and these are of variable quality. Trials included in this meta-analysis were all studies of the SFC competition, which distributed small to moderately sized prizes to whole classes, usually through a lottery system.Future studies might investigate the efficacy of incentives given to individual participants to prevent smoking uptake. Future research should consider the efficacy of incentives on smoking initiation, as well as progression of smoking, evaluate these in varying populations from different socioeconomic and ethnic backgrounds, and describe the intervention components in detail

Mechanical properties and morphology of melt-mixed PA6/SWNT composites: effect of reactive coupling

An interfacial reaction during melt mixing of maleic anhydride copolymer (SMA) encapsulated single wall carbon nanotubes (SWNT) and polyamide 6 (PA6) was used in order to disperse SWNT homogeneously and to enhance interfacial adhesion. The intended reactive coupling between PA6 and SMA was evident from IR spectroscopy. Nanocomposites with SMA encapsulated SWNT showed increased elongation at break as compared to PA6/SWNT composites. SEM investigation of tensile fractured surfaces of PA6/SWNT+SMA composites indicated enhanced interfacial adhesion between PA6 and SMA modified SWNT