Influence of a cyclic butylene terephthalate oligomer on the processability and thermoelectric properties of polycarbonate/MWCNT nanocomposites

The thermoelectric properties of melt-processed nanocomposites consisting of a polycarbonate (PC) thermoplastic matrix filled with commercially available carboxyl (–COOH) functionalized multi-walled carbon nanotubes (MWCNTs) were evaluated. MWCNTs carrying carboxylic acid moieties (MWCNT-COOH) were used due the p-doping that the carboxyl groups facilitate, via electron withdrawing from the electron-rich π-conjugated system. Preliminary thermogravimetric analysis (TGA) of MWCNT-COOH revealed that the melt-mixing was limited at low temperatures due to thermal decomposition of the MWCNT functional groups. Therefore, PC was mixed with 2.5 wt% MWCNT-COOH (PC/MWCNT-COOH) at 240 °C and 270 °C. In order to reduce the polymer melt viscosity, a cyclic butylene terephthalate (CBT) oligomer was utilized as an additive, improving additionally the electrical conductivity of the nanocomposites. The melt rheological characterization of neat PC and PC/CBT blends demonstrated a significant decrease of the complex viscosity by the addition of CBT (10 wt%). Optical and transmission electron microscopy (OM, TEM) depicted an improved MWCNT dispersion in the PC/CBT polymer blend. The electrical conductivity was remarkably higher for the PC/MWCNT-COOH/CBT composites compared to the PC/MWCNT-COOH ones. Namely, the PC/MWCNT-COOH/CBT processed at 270 °C exhibited the best values with electrical conductivity; σ = 0.05 S/m, Seebeck coefficient; S = 13.55 μV/K, power factor; PF = 7.60 × 10⁻⁶μW/m K⁻², and thermoelectric figure of merit; ZT = 7.94 × 10⁻⁹. The PC/MWCNT-COOH/CBT nanocomposites could be ideal candidates for large-scale thermal energy harvesting, even though the presently obtained ZT values are still too low for commercial applications.     

Effect of silane structure on the properties of silanized multiwalled carbon nanotube-epoxy nanocomposites

Multiwalled carbon nanotubes (MWCNTs) were functionalized with aminosilanes via an aqueous deposition route. The size and morphology of siloxane oligomers grafted to the MWCNTs was tuned by varying the silane functionality and concentration and their effect on the properties of a filled epoxy system was investigated. The siloxane structure was found to profoundly affect the thermo-mechanical behavior of composites reinforced with the silanized MWCNTs. Well-defined siloxane brushes increased the epoxy T_g by up to 19 °C and significantly altered the network relaxation dynamics, while irregular, siloxane networks grafted to the MWCNTs had little effect. The addition of both types of silanized MWCNTs elicited improvements in the strength of the nanocomposites, but only the well-defined siloxane brushes engendered dramatic improvements in toughness. Because the silanization reaction is simple, rapid, and performed under aqueous conditions, it is also an industrially attractive functionalization route.     

Influence of injection molding on the electrical properties of polyamide 12 filled with multi-walled carbon nanotubes

Microinjection-molded and compression-molded polyamide (PA12) matrix composites filled with 0.67, 1.33, 2 and 4 wt% multi-walled carbon nanotubes (MWNTs) were prepared from twin-screw extruded pellets. The compression molded samples have an electrical percolation threshold close to 1.2 wt%. Coupled rheological and electrical measurements show that their electrical properties start decreasing as soon as shear begins and are partially restored during flow, suggesting successively breakage and reconstruction of a percolating network. On the other hand, the electrical properties of the microinjection molded composites are close to the matrix ones, showing that cooling is too fast for the MWNTs to form a network. There is some electrical anisotropy in these composites, as evidenced by a greater conductivity measured in the flow direction. However polarized Raman spectroscopy analysis does not reveal a significant orientation of the MWNTs.     

Carbon nanotubes prevent the coagulation at high shear rates of aqueous suspensions of equiaxed ceramic nanoparticles

Equiaxed ceramic nanoparticles and their mixtures are expected to exhibit shear-thinning behaviour when dispersed colloidally in aqueous media, whereas shear-thickening is the expectation for large aspect ratio phases such as, for example, carbon nanotubes (CNTs). Here, contrary experimental evidence is presented demonstrating the occurrence of severe coagulation at high shear rates in colloidally stable, semi-concentrated, aqueous suspensions of equiaxed SiC nanoparticles (major phase) mixed with equiaxed Y₃Al₅O₁₂ nanoparticles (liquid-phase sintering additive), and how CNT addition prevents this coagulation if sufficient sonication is applied. It is also shown that although shear-thinning is the natural behaviour of the ceramic suspension up to moderate shear rates, coagulation is eventually a phenomenon inherent to the aqueous colloidal processing of these suspensions, with the critical shear rate for coagulation increasing and the rheopexy decreasing the better is the initial dispersion state achieved with the sonication. It is also shown that the critical shear rate for coagulation depends on the exact condition of shear rate increase, and that the re-sheared suspensions coagulate more significantly and at lower shear rates than the fresh suspensions. The mechanisms by which this coagulation occurs and is impeded by the CNTs are discussed, together with broader implications of these phenomena for the environmentally friendly processing of nanostructured ceramics and ceramic composites.     

Strawberry‐like Core–Shell Ag@Polydopamine@BaTiO3 Hybrid Nanoparticles for High‐k Polymer Nanocomposites with High Energy Density and Low Dielectric Loss

Flexible nanocomposites comprising of polymer and high‐dielectric‐constant (high‐k) ceramic nanoparticles are becoming increasingly attractive for dielectric and energy storage applications in modern electronic and electric industry. However, a huge challenge still remains. Namely, the increase of dielectric constant usually at the cost of significant decrease of breakdown strength of the nanocomposites because of the electric field distortion and concentration induced by the high‐k filler. To address this long‐standing problem, by using nano‐Ag decorated core–shell polydopamine (PDA) coated BaTiO₃ (BT) hybrid nanoparticles, a new strategy is developed to prepare high‐k polymer nanocomposites with high breakdown strength. The strawberry‐like BT‐PDA‐Ag based ferroelectric polymer [i.e., poly(vinylideneflyoride‐co‐hexafluroro propylene), P(VDF‐HFP)] nanocomposites exhibit greatly enhanced energy density and significantly suppressed dielectric loss as well as leakage current density in comparison with the nanocomposites with the core–shell structured BT‐PDA. Coulomb‐blockade effect of super‐small nano‐Ag is used to explain the observed performance enhancement of the nanocomposites. The simplicity and scalability of the described approach provide a promising route to polymer nanocomposites for dielectric and energy storage applications.     

聚氯乙烯/聚丙烯酸丁酯-白泥纳米复合材料的冲击断面形态及流变性能

通过多步交换反应及扩散-聚合的方法,使聚丙烯酸丁酯(PBA)嵌入到改性层状结构的白泥层间,得到白泥-聚丙烯酸丁酯(PBA)纳米复合物的微米级粒子;然后将聚氯乙烯与白泥-聚丙烯酸丁酯进行熔融共混,制得具有一定特性的有机-无机纳米复合材料;并对复合材料的缺口冲击断面形态及流变性能进行了研究。结果表明,复合材料的冲击断面具有明显的网状结构和空洞化特征,属典型的韧性断裂;PVC/白泥-PBA(质量分数0.5%~7.0%)纳米复合材料基本上保持了纯PVC的加工性能。     

新型抗凝血纳米复合材料的制备及其性能研究

利用溶液插层法合成了新型的硅橡胶/氧化石墨-十六烷基三甲基溴化铵-肝素抗凝血纳米复合材料.通过FT-IR、XRD、SEM和机械性能测试了解改性氧化石墨微观纳米结构对材料宏观性能的影响;溶血试验和血小板粘附试验测定表明硅橡胶/改性氧化石墨抗凝血纳米复合材料的血液相容性得到极大的改善;这种新型的、兼具优良血液相容性和良好力学性能的复合材料可望在生物医学工程方面得到应用.     

不同硬段含量的PU及其纳米复合材料

制备了不同硬段含量的聚氨酯(PU)及其PU/有机蒙脱土(OMMT)纳米复合材料。研究结果表明,随着PU分子链中硬段含量的增加,PU分子链的刚性提高,进入硅酸盐片层间的位阻增大,使插层变得困难,从而导致进入该硅酸盐片层间的PU分子链减少。OMMT对PU有增强增韧作用,但随着PU分子链中的硬段含量增加,OMMT的增强效果下降。PU及其PU/OMMT纳米复合材料的热稳定性均随着PU分子链中的硬段含量增加而下降。     

导电高分子纳米复合材料研究进展

介绍了导电高分子纳米复合材料的特点,综述了导电高分子纳米复合材料的最新研究进展,展望了导电高分子纳米复合材料的发展前景。     

阻燃聚丙烯/蒙脱土纳米复合材料的制备及性能研究

通过熔融挤出法制备出了膨胀阻燃剂/聚丙烯/有机蒙脱土(IFR/PP/OMMT)阻燃纳米复合材料,XRD分析表明,蒙脱土的层间距扩大,复合材料进入其层闻,形成了纳米复合材料;结果表明,当复合材料中IFR含量为25%时,加入4%的OMMT体系的缺口冲击强度为7.8kJ/m2,拉伸强度为25.3MPa,弯曲模量为1520MPa,极限氧指数(LOI)提高到26,而耐热性也得到提高,复合材料的综合性能最好;通过对膨胀炭层的SEM分析表明,OMMT可以使炭层更加紧密,阻燃性能进一步提高.