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

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

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

Influence of Multiwall Carbon Nanotubes on the Mechanical Properties and Unusual Crystallization Behavior in Melt-Mixed Co-continuous Blends of Polyamide6 and Acrylonitrile Butadiene Styrene

The mechanical and the crystallization behavior of melt-mixed cocontinuous blends of polyamide6 (PA6) and acrylonitrile butadiene styrene were studied in presence of multiwall carbon nanotubes (MWNT). Young's modulus was observed to be significantly improved with increasing concentration of MWNT, while only moderate improvements were observed in the tensile strength. To overcome the van der Waals' forces between MWNT a unique modifier, sodium salt of 6 amino hexanoic acid (Na-AHA) was employed where it was envisaged that specific interactions between Na(+) of the modifier and the delocalized "pi-electron" clouds of MWNT would lead to significant debundiling of the tubes. The mechanical properties of the blends with Na-AHA modified MWNT were found to be improved as compared to the blends with purified MWNT however, were found to be adversely affected above certain concentration of Na-AHA in the blends. Dynamic mechanical thermal analysis supported the plasticization effect induced by Na-AHA manifesting in decrease in the glass transition temperature of PA6 in the blends with Na-AHA modified MWNT. Differential scanning calorimetry results showed two crystallization exotherms for PA6 in the blends with both purified and Na-AHA modified MWNT. This unusual crystallization behavior of PA6 was addressed in context to confined crystallization of PA6 in the tube "network-like" structure. POLYM. ENG. SCI., 49:1533-1543, 2009. (C) 2009 Society of Plastics Engineer

Highly conducting poly(methyl methacrylate)/carbon nanotubes composites: Investigation on their thermal, dynamic-mechanical, electrical and dielectric properties

International audienceNanocomposites of poly(methyl methacrylate) (PMMA) containing various multi-walled carbon nanotubes (MWCNT) contents were prepared using melt mixing. Several techniques were employed to study the influence of the MWCNT addition on the thermal, mechanical, electrical and dielectric properties of the PMMA matrix. The electrical percolation threshold () was found to be 0.5 vol.% by performing AC and DC conductivity measurements. Significantly high conductivity levels () were achieved: exceeds 10 S/cm already at 1.1 vol.%, the criterion for EMI shielding ( > 10 S/cm) is fulfilled at 2.9 vol.%, and the highest loaded sample (5.2 vol.%) gave a maximum value of 0.5 S/cm. Dielectric relaxation spectroscopy measurements in broad frequency (10−10 Hz) and temperature ranges (-150 to 170 °C) indicated weak polymer-filler interactions, in consistency with differential scanning calorimetry and dynamic mechanical analysis findings. Weak polymer-filler interactions and absence of crystallinity facilitate the achievement of high conductivity levels in the nanocomposites

Effect of encapsulated SWNT on the mechanical properties of melt mixed PA12/SWNT composites

Styrene maleic anhydride copolymer (SMA) encapsulated single wall carbon nanotubes (SWNT) are melt mixed with PA12 in order to disperse SANT more homogeneously. The mechanism is found to be a reactive coupling between amine end groups of PA12 and maleic anhydride functionality of SMA during melt mixing of PA12 with SMA modified SWNT. This leads next to a better dispersion to an enhanced interfacial adhesion between PA12 and SWNT as indicated by enhanced rheological, dynamic mechanical, and tensile properties of the PA12/SWNT composites. (C) 200

Influence of hybrid nano-filler on the crystallization behaviour and interfacial interaction in polyamide 6 based hybrid nano-composites

Expanded graphite (EG) and multiwalled carbon nanotubes (MWNTs) based hybrid nano-composites were prepared with polyamide 6 (PA6) matrix via melt-mixing technique using a conical twin-screw micro-compounder. A novel organic modifier (lithium salt of 6-aminohexanoic acid; Li-AHA) was employed to modify MWNTs, which was utilized to intercalate Li-AHA modified MWNTs into the partially exfoliated EG gallery. Morphological investigation showed the intercalation of Li-AHA modified MWNTs into a partially exfoliated EG gallery in an EG/MWNTs-m2h hybrid, whereas the unmodified EG/MWNTs-h hybrid mixture exhibited a separate identity in the mixture. Improved interaction via melt-interfacial reaction between the acid end group of PA6 and the amine functionality of Li-AHA in the EG/MWNTs-m2h hybrid filler was confirmed by Fourier transform infrared spectroscopic analysis. The extent of melt-interfacial reaction was increased as a function of Li-AHA concentration in the filler. Wide angle X-ray diffraction analysis showed the existence of the alpha-crystalline phase of PA6. The incorporation of MWNTs, EG and EG/MWNTs hybrid in the PA6 matrix has favoured an alpha-crystalline structure of the PA6 phase. Crystallization studies have indicated a significant increase in the bulk crystallization temperature of the PA6 phase in the presence of MWNTs, EG and the EG/MWNTs hybrid filler. Moreover, the formation of PA6 'trans-crystalline lamellae' on the MWNTs surface was facilitated in the case of composites with MWNTs and the EG/MWNTs hybrid filler. An attempt has been made to investigate the role of the EG/MWNTs hybrid filler in influencing the crystallization behaviour of the PA6 phase in the hybrid nano-composites

Electrical, rheological and morphological studies in co-continuous blends of polyamide 6 and acrylonitrile-butadiene-styrene with multiwall carbon nanotubes prepared by melt blending

Multiwall carbon nanotubes (MWNT) were incorporated in melt-mixed co-continuous blends of polyamide 6 (PA6) and acrylonitrile-butadiene-styrene (ABS) using a conical twin-screw microcompounder. The state of dispersion of MWNT in the blends was assessed through AC electrical conductivity measurements and melt-rheological investigations. The electrical and rheological percolation threshold in PA6/ABS blends was similar to 3-4 and similar to 1-2 wt% MWNT, respectively. A unique reactive modifier (sodium salt of 6-amino hexanoic acid, Na-AHA) was employed to facilitate 'network-like' structure of MWNT and to confine them in a specific phase. This was achieved by establishing specific interactions with the delocalized 'pi-electron' clouds of MWNT and melt-interfacial reaction during melt-mixing. The electrical percolation threshold was significantly reduced in the blends (similar to 0.25 wt%) in the presence of Na-AHA modified MWNT and even coincided with the rheological percolation threshold. Significant refinement in the co-continuous structure was also observed in the presence of Na-AHA modified MWNT. (C) 200

Reactive compatibilization of melt mixed PA6/SWNT composites: Mechanical properties and morphology

Styrene maleic anhydride copolymer (SMA) encapsulated single wall carbon nanotubes (SWNT) were melt mixed with polyamide 6 (PA6) utilizing an interfacial reaction in order to disperse SWNT homogeneously and to enhance interfacial adhesion. The intended reactive coupling between PA6 and SMA was evident from IR spectroscopy. Raman spectroscopy was used to characterize the SWNT and the nanocomposites. Studies on crystallization behavior showed the nucleating behavior of SWNT in the composites, as found using DSC and WAXD. The encapsulation of SWNT by SMA copolymer leads to increased elongation at break in the composites, which can be attributed to the enhanced interfacial adhesion between PA6 and SMA modified SWNT as observed from the SEM investigation of tensile fractured surfaces of PA6/SWNT+SMA composites. The glass transition temperature of PA6 increased significantly in the composites