Structure-properties relationship in polymer nanocomposites based on polylactic acid and carbon nanotubes

In this study, 3D printed porous poly(lactide-co-glycolide) (PLGA) and its nanocomposites with 5 wt. % hydroxyapatite (HA) and 0.5, 1 and 2 wt. % carboxyl-functionalized multi-walled carbon nanotube (CNT) scaffolds were fabricated by using extrusion-based printing. The printing parameters were optimized by rheological studies. The rheological studies demonstrated shear thinning properties for all compositions and an increase in storage modulus was observed after the addition of CNT. Porous PLGA/HA/CNT scaffolds were printed by applying a pressure of 4.76 bar at 125 °C. The addition of 0.5 wt. % of CNT reduced the strut size and increased the porosity from 42% to 60%. The increase in storage modulus and decrease in strut size were related to hydrogen bonding between CNT, HA and PLGA which ultimately improved shape fidelity. The scaffolds were characterized by analysis of their chemical structure, water contact angle measurement, in vitro bioactivity test, biodegradation test, mechanical analysis, and in vitro cell studies. The scaffolds were found to be more hydrophilic by the incorporation of CNTs. Also, degradation studies showed that the microstructure of the scaffold became more stable with the addition of HA and CNT. The compressive modulus of PLGA/HA/CNT2 scaffold was found to be 548.5 MPa, which is found suitable to replace cancellous bone. The scaffolds were found to be highly biocompatible which is possibly due to alignment of CNT and PLGA during 3D printing process. Alizarin red staining indicated improvement of mineralization of MC3T3-E1 cells on the CNT incorporated porous 3D scaffolds. The results suggest that the produced porous 3D printed PLGA/HA/CNT scaffolds are promising for bone regeneration applications.

This paper investigates the effect of multiwalled carbon nanotubes on the mechanical and electrical properties of epoxy resins and epoxy composites. The research concerns multiwalled carbon nanotubes obtained by catalytic chemical vapor deposition, subjected to purification processes and covalent functionalization by depositing functional groups on their surfaces. The study included the analysis of the change in DC resistivity, tensile strength, strain, and Young’s modulus with the addition of carbon nanotubes in the range of 0 to 2.5 wt.%. The effect of agents intended to increase the affinity of the nanomaterial to the polymer on the aforementioned properties was also investigated. The addition of functionalized multiwalled carbon nanotubes allowed us to obtain electrically conductive materials. For all materials, the percolation threshold was obtained with 1% addition of multiwalled carbon nanotubes, and filling the polymer with a higher content of carbon nanotubes increased its conductivity. The use of carbon nanotubes as polymer reinforcement allows higher values of tensile strength and a higher strain percentage to be achieved. In contrast, Young’s modulus values did not increase significantly, and higher nanofiller percentages resulted in a drastic decrease in the values of the abovementioned properties.

Age related bone diseases such as osteoporosis are considered among the main causes of reduced bone mechanical stability and bone fractures. In order to restore both biological and mechanical function of diseased/fractured bones, novel bioactive scaffolds that mimic the bone structure are constantly under development in tissue engineering applications. Among the possible candidates, chitosan-based thermosensitive hydrogel scaffolds represent ideal systems due to their biocompatibility, biodegradability, enhanced antibacterial properties, promotion of osteoblast formation and ease of injection, which makes them suitable for less invasive surgical procedures. As a main drawback, these chitosan systems present poor mechanical performance that could not support load-bearing applications. In order to produce more mechanically-competent biomaterials, the combined addition of hydroxyapatite and carbon nanotubes (CNTs) is proposed in this study. Specifically, the aim of this work is to develop thermosensitive chitosan hydrogels containing stabilised single-walled and multi-walled CNTs, where their effect on the mechanical/physiochemical properties, calcium deposition patterns and ability to provide a platform for the controlled release of protein drugs was investigated. It was found that the addition of CNTs had a significant effect on the sol–gel transition time and significantly increased the resistance to compression for the hydrogels. Moreover, in vitro calcification studies revealed that CNTs played a major role in the spatial arrangements of newly formed calcium deposits in the composite materials studied, suggesting that they may have a role in the way the repair of fragile and/or fractured bones occurs in vivo.

A method to recover fracture toughness after failure and increase thermal properties of polylactic acid (PLA) for use within durable goods applications is presented. Microcapsules were incorporated into PLA to form a composite material in which the microcapsules served the dual purpose of (1) releasing self-healing additives to fracture regions and (2) serving as nucleating agents to improve the PLA composite's thermal tolerance. Self-healing was achieved though embedment of dicyclopentadiene-filled microcapsules and Grubbs' first generation ruthenium metathesis catalyst, the former being autonomically released into damage volumes and undergoing polymerization in the presence of the catalyst. This approach led to up to 84% recovery of the polymer composite's initial fracture toughness. Additionally, PLA's degree of crystallinity and heat deflection temperature were improved by ∼ 11% and ∼ 21 °C, respectively, relative to nonfilled virgin PLA, owing to microcapsule-induced nucleation. The self-healing system developed here overcomes many property limitations of PLA that can potentially lead to its incorporation into various durable goods.

The inherent brittleness of PLA is a major challenge for its use in various applications. In this study, the effect of incorporation of halloysite nanotube (HNT) and polyethylene glycol (PEG) on mechanical and thermal properties of polylactic acid (PLA) was investigated. Various concentrations of PEG-600 and HNT were used with PLA, and films were prepared by solvent casting method. Mechanical, morphological, and thermal properties of these composite films were investigated to study the effect of PEG and HNT on the properties of PLA. Addition of PEG increased elongation at break, but reduced the tensile strength. However, addition of HNT in PLA/PEG compensated the fall in tensile strength. Addition of 3 wt% HNT into PLA blend involving 5 wt% PEG increased its elongation at break by 640% and tensile strength by 22%, while no significant change in Young’s modulus was observed. Dynamic mechanical thermal analysis (DMTA) showed significant improvement in storage modulus of PLA/PEG/HNT films in the rubbery region. Glass transition temperature decreased for the PEG-plasticized films, while the crystallinity improved as compared to neat PLA. Thermal stability of PLA/PEG/HNT films was higher than those of PLA, PLA/PEG, and PLA/HNT films. The degree of crystallinity obtained using X-ray diffraction analysis showed good agreement with that determined from differential scanning calorimetry (DSC).

A newly developed series of polylactide (PLA)-based composites filled with hybrid lignin–carbon nanotube (CNTs) particles were studied using thermal and dielectric techniques. The low CNT content (up to 3 wt%) aimed to create conductive networks while enhancing particle–polymer adhesion. For comparison, PLA composites based on lignin and CNTs were also examined. Although infrared spectroscopy showed no significant interactions, calorimetry and dielectric spectroscopy revealed a rigid interfacial PLA layer exhibiting restricted mobility. The interfacial polymer amount was found to increase monotonically with the particle content. The hybrid-filled PLA composites exhibited electrical conductivity, whereas PLA/Lignin and PLA/CNTs remained insulators. The result was indicative of a synergistic effect between lignin and CNTs, leading to lowering of the percolation threshold to 3 wt%, being almost ideal for sustainable conductive printing inks. Despite the addition of lignin and CNTs at different loadings, the glass transition temperature of PLA (60 °C) decreased slightly (softer composites) by 1–2 K in the composites, while the melting temperature remained stable at ~175 °C, favoring efficient processing. Regarding crystallization, which is typically slow in PLA, the hybrid lignin/CNT particles promoted crystal nucleation without increasing the total crystallizable fraction. Overall, these findings highlight the potential of eco-friendly conductive PLA composites for new-generation applications, such as printed electronics.

Improvement in corrosion resistance of magnesium weld by addition of carbon nanotubes

Electrical and thermal properties of PEDOT:PSS films doped with carbon nanotubes

Corrosion behaviour of plasma-sprayed baghdadite bioceramic coatings reinforced with carbon nanotubes

Carbon nanotube (CNT) is excellent in mechanical and thermal characteristics, and are expected to be used in various fields such as nanoelectronic devices and reinforcing nanofillers for composites. It is expected that mechanical properties can be improved by adding CNT into the polymer. However, since CNT exists in a state of aggregation due to van der Waals forces, it is necessary to uniformly disperse CNT in order to fully extract the properties of CNT. In this study, CNT/polyamide 6 (PA6) composite nanofibres were fabricated by the electrospinning method. In order to disperse CNT in the CNT/PA6 nanofibres, CNT were subjected to air oxidation treatment. As a result of evaluating the dispersibility of CNT by sedimentation test, the dispersibility in pure water and HFIP is improved by oxidizing the surface of CNT. By conducting tensile tests and SEM observation of the nanofibre non-woven fabric, the influence of the surface treatment on the tensile strength of CNT/PA6 nanofibres and the dispersion of CNT was clarified. Although the addition of untreated CNT to PA6 nanofibres reduces the displacement at break, air oxidized CNT/PA6 suppressed the formation of CNT aggregates, and showed higher tensile strength and larger displacement at break than untreated CNT/PA6.

In this paper we report the investigation of the effect of Carbon Nanotubes (CNT) addition on the electrical properties of GaSe Glassy system. Dielectric constant and dielectric loss of GaSe glassy system are found to increase on CNT addition. The conductivity of GaSe glasy systems is also found to increase on CNT addition. This behavior is attributed to the excellent conduction properties of Carbon Nanotube.

Vibration damping characteristics of carbon fiber-reinforced composites containing multi-walled carbon nanotubes

Effect of carbon-nanotube length on friction and wear of polyamide 6,6 nanocomposites

Dual strengthening mechanisms induced by carbon nanotubes in roll bonded aluminum composites

In this study, polylactic acid (PLA) films were prepared via twin screw extruder attached with blown film die. The research consisted of two parts. The first part concentrates on studying the effect of types and loading of plasticizer, in which they were used to increase the flexibility of PLA, on thermal, mechanical and gas barrier properties of plasticized PLA blown films. From DSC and DMA results, 5 wt% of all plasticizers were compatible with PLA and it affected degree of crystallinity of PLA increased. In addition, tensile tests indicated that polypropylene glycol, PPG(1200) at 5 wt% was a suitable plasticizer for PLA which can be observed from an increase in elongation at break approximately 45 times. The second part focuses on the effect of surfactant types and organoclay loading on properties of PLA/clay nanocomposite blown films. From XRD result, interlayer spacing of organoclay increased compared with that of pristine clay. Furthermore, film of PLA/montmorillonite modified by trimethyl tallow quaternary ammonium chloride (PLA/MMT/M₃T films) showed better clay dispersion and higher transmittance of light than film of PLA/montmorillonite modified by tallow bis(2-hydroxyethyl) amine (PLA/MMT/HT(OH)₂ films). Furthermore, from DSC and DMA results, PLA/MMT/HT(OH)₂ films gave higher degree of crystallinity than PLA/MMT/M₃T films. For mechanical properties, PLA/MMT/M₃T films exhibited higher elongation at break than PLA/MMT/HT(OH)₂ films and 3 wt% of organoclay showed optimum properties when added into with plasticized PLA. In addition, PLA/MMT/HT(OH)₂ films showed higher water vapor permeation (6.19 %) but lower oxygen permeation (7.94 %) compared to PLA/MMT/M₃T films.