Influence of noncovalent modification on dispersion state of multiwalled carbon nanotubes in melt-mixed immiscible polymer blends

Fragmentation and release of pristine and functionalized carbon nanotubes from epoxy-nanocomposites during accelerated weathering

There is an increasing volume of nano-enabled materials in the market. Once composites containing nano-additives are disposed of, weathering could deteriorate their structures, releasing nanoparticles and risking exposure of humans and aquatic organisms. Composite degradation due to environmental aging continues, including structural deterioration resulting in cracking, fragmentation, and release of microplastics and nano-additives to the environment. This research aims to study the degradation and release of initially embedded nanomaterials (NMs) from composites and their toxicity. The molecular interaction of carbon nanotube (CNT)/polymer composites is critical for modifying the polymer properties. This study investigated the interactions of functional multiwalled carbon nanotube (MWCNT) composites which affect their release during accelerated weathering processes. Different epoxy-MWCNT composites were prepared by filling a polymer with pure MWCNTs and MWCNTs functionalized with acid (- COOH ) and amine (- NH 2 ) groups. The physical and chemical changes of aged composites were characterized by gravimetric analysis, contact angle measurements, FTIR, SEM, and laser confocal microscopy. A loss of hydrophobicity was observed for composite surfaces long before surface cracks materialized. Released polymer fragments and nanoparticles were analyzed in wash water using TEM, FTIR and Raman spectroscopy. The environmental risks for long-term use of CNT-polymer composites and the influence of fillers on the extent of chemical photodegradation depended on the combination of polymer and fillers. If nanoparticles are released from the matrix, the high surface-to-volume ratio and reactivity of NMs make them highly dynamic in environmental systems. Exposure to these released NMs could negatively affect human health and the environment. This study provides fragmentation and CNT particle release data that could describe how molecular-level interactions between functionalized CNTs and epoxy polymers affect the aging and release of CNTs. A toxicity assessment based on a reactive oxygen species (ROS) formation assay and MTS assay for cell viability and activity of the released polymer and CNT fragments and leachate showed moderate levels of cytotoxicity of released materials as compared to pristine epoxy plates.

Recent Advances in Elongational Flow Dominated Polymer Processing Technologies

The continuous development of plasticizing conveying methods and devices has been carried out to meet the needs of the polymer processing industry. As compared to the conventional shear-flow-dominated plasticizing and conveying techniques, a new method for processing polymers based on elongational flow was proposed. This new method and the related devices such as vane extruders, eccentric rotor extruders and so on, exhibited multiple advantages including shorter processing time, higher mixing effectiveness, improved product performance and better adaptability to various material systems. The development of new techniques in the field of polymer material processing has opened up a broad space for the development of new plastic products, improved product performance and reduced processing costs. In this review, recent advances concerning the processing techniques based on elongational flow are summarized, and the broad applications in polymer processing as well as some future opportunities and challenges in this vibrant area are elucidated in detail.

Effect of Organic Modification on Multiwalled Carbon Nanotube Dispersions in Highly Concentrated Emulsions

Highly concentrated water-in-oil emulsions incorporating multiwalled carbon nanotubes (MWCNTs) are prepared. Homogeneous and selective dispersions of MWCNTs throughout the oil phase of the emulsions are investigated. The practical insolubility of carbon nanotubes (CNTs) in aqueous and organic media necessitates the disentanglement of CNT "agglomerates" through the utilization of functionalized CNTs. The design and synthesis of two tetra-alkylated pyrene derivatives, namely, 1,3,6,8-tetra(oct-1-yn-1-yl)pyrene (TOPy) and 1,3,6,8-tetra(dodec-1-yn-1-yl)pyrene (TDPy), for the noncovalent organic modification of MWCNTs are reported. The modifier molecules are designed in such a manner that they facilitate an improved dispersion of individualized MWCNTs in the continuous-oil phase of the highly concentrated emulsion (HCE). Transmission electron microscopic analyses suggest that the alkylated pyrene molecules are adsorbed on the MWCNT surface, and their adsorption eventually results in the debundling of MWCNT agglomerates. Fourier transform infrared, Raman, and fluorescence spectroscopic analyses confirm the π-π interaction between the alkylated pyrene molecules and MWCNTs. The noncovalent modification significantly improves the effective debundling and selective dispersion of MWCNTs in HCEs.

Paclitaxel Encapsulation into Dual-Functionalized Multi-Walled Carbon Nanotubes

This work reports the synthesis of multi-walled carbon nanotubes (CNTs) from xylene/ferrocene using catalytic chemical vapor deposition technique. Following characterization using transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), and Raman spectroscopy, CNT surface was dual-functionalized using ethylenediamine and phenylboronic acid groups. Average diameter of CNTs was calculated to be 16.5 nm. EDX spectra confirmed the existence of carbonaceous deposits on the tube's surface. Scattered electron diffraction and X-ray peak broadening calculations showed consistent inter-planer distance of the grown CNTs. Chemical functionalization, confirmed from FT-IR and Raman spectra, showed an enhanced dispersibility of CNTs in water. We describe the changes in the first- and second-order regions of the Raman spectra following the encapsulation of an anti-cancer drug, paclitaxel (PLX), into the free volume of functionalized CNTs. High PLX loading, achieved through its non-covalent π-π stacking within the CNT interior, is confirmed through the blue-shifted, softened G band in the Raman spectrum. While not addressed here, we will exploit this dual functionalization tactic to elaborate the relative role of attached moieties in the affinity interaction of CNTs with extra-cellular sialic acid, a biological target showing metastatic stage-dependent over-expression in colon cancer cells.

Dispersion of non-covalently modified graphene in aqueous medium: a molecular dynamics simulation approach

Electric potential variation between two graphene sheets upon adsorption of Na-AHA molecules.

Molybdenum disulfide nanoflakes through Li-AHA assisted exfoliation in an aqueous medium

A novel route to synthesize MoS₂ nanoflakes though Li-AHA assisted liquid phase exfoliation.

Role of interfacial interactions to control the extent of wrapping of polymer chains on multi-walled carbon nanotubes

Transmission electron microscopic image of separated MWCNTs (N51L15G5) showing the wrapped polymer chains on the MWCNTs surface, which corresponds to the α-phase of the PP.

Deagglomeration of multi-walled carbon nanotubes via an organic modifier: structure and mechanism

We have investigated the agglomeration behaviour of two types of multi-walled carbon nanotubes (MWNTs; N-MWNTs and D-MWNTs), which have different chemical functionalities, average diameter, varying extent of agglomeration and agglomerations. The properties were altered by varying the agglomerated structure. The strength of the MWNT agglomerates was estimated via nanoindentation. The work done to indent D-MWNT agglomerates (3910.3 × 10(-8) erg) was higher than for N-MWNTs agglomerates (2316.4 × 10(-8) erg). An organic modifier, the Li salt of 6-aminohexanoic acid (Li-AHA), was used to deagglomerate the MWNTs in an aqueous medium. The stability of the aqueous dispersion of Li-AHA-modified MWNTs was analyzed by UV-vis spectroscopy and zeta potential measurements. An increase in Li-AHA concentration increased the dispersion of MWNTs in the aqueous medium. Furthermore, the mechanism of dispersion of the two types of MWNTs in the aqueous medium in the presence of Li-AHA was determined based on the electrostatic charge repulsion between the negatively charged species. A fluorescence-activated cell sorting technique was used to assess the debundling of MWNT agglomerates in the aqueous medium. We examined the morphology-property relationship in Li-AHA-modified MWNTs.

Effect of chemically reduced graphene oxide on the isothermal and non-isothermal phase separation behavior of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) binary polymer blends

The applicability of WLF function to phase separation behavior of filled systems indicates that CRGO hardly changes the viscous diffusion essence of segments. Furthermore, the effect of CRGO on the phase behavior is dependent on their composition.

Influence of non-covalent modification of multiwalled carbon nanotubes on the crystallization behaviour of binary blends of polypropylene and polyamide 6

‘Agglomerated’ and ‘individualized’ MWNTs providing varying extent of hetero-nucleation to the polymer chains.

In situ chemical oxidative graft polymerization of aniline from phenylamine end-caped poly(ethylene glycol)-functionalized multi-walled carbon nanotubes

The aim of this study is the in situ chemical oxidative graft polymerization of aniline from phenylamine end-caped poly(ethylene glycol)-functionalized multi-walled carbon nanotubes.

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

‘Agglomerated’ and ‘debundled’ structure of EG/MWNTs hybrid providing hetero-nucleation to PA6 chain. The dispersion state of the hybrid filler in PA6 changes from ‘agglomerated and stacked’ state to ‘debundled and exfoliated’ state in the presence of Li-AHA modified hybrid filler.