The study is focused on multifunctional performance of carbon nanotubes (CNT) and Graphene nanoplatelets (GNP) reinforced PEEK composites enabled via fused filament fabrication (FFF) additive manufacturing (AM) utilizing in-house nanoengineered filaments. Thermo-physical, mechanical and wear characteristics of electro-conductive PEEK nanocomposites are reported. The coefficient of thermal expansion (CTE) is found to decrease by 26% and 18% with the incorporation of 5 wt% GNP and 3 wt% CNT into PEEK polymer, respectively. The decrease in CTE provides better dimensional stability to resulting nanocomposite structures. Due to uniform dispersion of CNT and GNP in the PEEK matrix, the crystallization temperature and degree of crystallinity are both increased. The 3D printed PEEK nanocomposites reveal interfacial voids between the beads and intra-bead pores and thus exhibit lower density compared to that of the 3D printed neat PEEK. Young's and storage moduli are found to increase by 20% and 66% for 3 wt% CNT loading and by 23% and 72% for 5 wt% GNP loading respectively. However, the PEEK nanocomposites exhibit similar tensile strength to that of neat PEEK. The coefficient of friction obtained from fretting wear tests is found to decrease by 67% and 56% for 1 wt% CNT and 3 wt% GNP loaded PEEK nanocomposites, respectively and the decrease is attributed to reduced hardness and increased porosity. Multifunctional performance of carbon nanostructures reinforced AM-enabled PEEK composites demonstrated here makes them suitable for a range of applications such as orthopedics, oil and gas, automotive, electronics and space.

Multifunctional performance of carbon nanotubes and graphene nanoplatelets reinforced PEEK composites enabled via FFF additive manufacturing

Anti-bacterial scaffolds made of copper, bronze and silver particles filled PLA nanocomposites were realized via fused filament fabrication (FFF), additive manufacturing. The thermal, mechanical and biological characteristics including bioactivity and bactericidal properties of the scaffolds were evaluated. The incorporation of bronze particles into the neat PLA increases the elastic modulus up to 10% and 27% for samples printed in 0° and 90° configurations respectively. The stiffness increases, up to 103% for silver filled PLA nanocomposite scaffolds. The surface of scaffolds was treated with acetic acid to create a thin porous network. Significant increase (~20-25%) in the anti-bacterial properties and bioactivity (~18-100%) is attributed to the synergetic effect of reinforcement of metallic/metallic alloy particles and acid treatment. The results indicate that PLA nanocomposites could be a potential candidate for bone scaffold applications.

Microarchitected 3D printed polylactic acid (PLA) nanocomposite scaffolds for biomedical applications.

We report strong, stretchable and ultrasensitive thermoplastic polyurethane (TPU) nanocomposites reinforced with multiwalled carbon nanotubes (MWCNT) for piezoresistive strain sensing. Uniform dispersion of MWCNT in TPU matrix offers low percolation threshold (0.1 wt%) and superior electrical conductivity. MWCNT/TPU nanocomposites exhibit different sensitivities and measurable strain ranges depending upon MWCNT concentration. Static stretch experiments reveal nearly linear piezoresistive response up to 15%, 35% and 45% strain with gauge factor (GF) of 22, 8.3 and 7.0 for 0.3, 0.5 and 1.0 wt% MWCNT loaded TPU nanocomposites, respectively. With further stretching, TPU nanocomposites evince strain-dependent GF of 6395, 6423 and 7935 at 35%, 95% and 185% strain for 0.3, 0.5 and 1.0 wt% MWCNT loading, respectively. Furthermore, we observe improvements in tensile strength, yield strength and Young's modulus of 51%, 37% and 23% for 0.1 wt % MWCNT loading and 10%, 83% and 66% for 0.3 wt % MWCNT loading, respectively. Cyclic stretch/release tests for 0.3 wt% MWCNT loaded nanocomposites show good recoverability and reproducibility over 100 cycles up to a strain-amplitude of 50%. Ultrahigh GF of MWCNT/TPU nanocomposites compared to extant work together with their tuneable sensitivity in both small and large strain regimes, enhanced strength and ease of fabrication make them attractive for high performance strain sensing devices.

Strong, stretchable and ultrasensitive MWCNT/TPU nanocomposites for piezoresistive strain sensing

Here, we report the electrical, mechanical and thermal properties of ultrahigh-molecular-weight polyethylene (UHMWPE) nanocomposites reinforced with 0.1 wt% to 10 wt% of graphene nanoplatelets (GNP). The electrical conductivity of GNP/UHMWPE nanocomposites shows percolation threshold at 3.0 wt% of GNP. A significant increase in electrical conductivity from 10−15 S cm−1 for neat UHMWPE to 10−5 S cm−1 at 3.0 wt% GNP loading of GNP/UHMWPE nanocomposite (i.e. 10 orders of magnitude higher) is due to the formation of an almost three-dimensional conductive network. The highest value of electrical conductivity (1.09 S cm−1) is observed at 10.0 wt% of GNP loading. The elastic modulus and yield strength increase by 30% and 21%, for the addition of 0.5 wt% and 1.0 wt% of GNP, respectively, while fracture toughness and the ultimate tensile strength decrease significantly above 0.5 wt% GNP loading. This study demonstrates the fabrication of GNP/UHMWPE bio-nanocomposites, which exhibit electrical properties useful for smart biomedical implants.

Electrical, mechanical and thermal properties of graphene nanoplatelets reinforced UHMWPE nanocomposites

Here, we report highly strain-tolerant and sensitive strain sensors based on carbon nanostructures (CNS)-polydimethylsiloxane (PDMS) nanocomposites. CNS consist of clusters of aligned multiwall carbon-nanotubes (MWCNT) with high degree of entanglement and wall sharing between nanotubes. The unique features of CNS result in nanocomposites with very low electrical percolation threshold (0.05 wt% CNS), strong linear-piezoresistive-response up to 110% strain, and high sensitivity with gauge factor ranging from 8 to 47. We also present a simple analytical model for predicting resistivity evolution as a function of stretch considering incompressible hyperelastic behavior of CNS/PDMS nanocomposites. CNS/PDMS nanocomposites also show good hysteresis performance and stability up to 100 repetitive stretch/release cycles for 30% maximum strain. Tunable sensitivity and linear piezoresistivity coupled with high stretchability of CNS/PDMS nanocomposites demonstrated here suggest their potential for applications in wearable health and fitness monitoring devices.

Strong linear-piezoresistive-response of carbon nanostructures reinforced hyperelastic polymer nanocomposites

Carbon nanotubes (CNTs) based polymer nanocomposites offer a range of remarkable properties. Here, we demonstrate self-sensing performance of low density polyethylene (LDPE)-multiwalled carbon nanotubes (MWCNTs) nanocomposites for the first time. The dispersion of the CNTs and the morphology of the nanocomposites was investigated using scanning electron microscopy, x-ray diffraction and Raman spectroscopic techniques. The thermal properties were measured using thermal gravimetric analysis and differential scanning calorimetry and were found to increase with increasing wt% of MWCNTs in LDPE matrix. An overall improvement in ultimate tensile strength, yield strength and Young's modulus was found to be 59.6%, 48.5% and 129.3%, respectively for 5.0 wt% loading of MWCNTs. The electrical percolation threshold was observed at 1.0 wt% of MWCNTs and the highest electrical conductivity of 2.8 × 10−2 Scm−1 was observed at 5.0 wt% loading of MWCNTs. These piezo-resistive nanocomposites offer tunable self-sensing capabilities with gauge factors in the ranges of 17–52 and 42–530 in linear elastic (strain ~3%) and inelastic regimes (strain ~15%) respectively. Our demonstration would provide guidelines for the fabrication of low cost, self-sensing MWCNT-LDPE nanocomposites for potential use as civil water pipelines and landfill membranes.

Self-sensing performance of MWCNT-low density polyethylene nanocomposites

Using average coordination number (〈𝒓〉), lone pair electrons (𝐿) are calculated and found to decrease with an increase in
Bi content. 𝐿 value greater than 3 indicates that Ge18Se72-xTe10Bix (x = 0, 2, 4, 6, 8, 10) alloys can retain their vitreous
nature. Packing density shows subsequent decrease with an increase in density values. Compactness of the structure and
molar volume are calculated from the measured density values. Polaron radius is found to decrease with an increase in Bi
content. Mean bond energy is found to be proportional to the glass transition temperature and shows maxima at the
chemical threshold. Cohesive energy of the system is calculated using the Chemical Bond Appro…

Amal Zakir Khan

Papers

Self-sensing performance of MWCNT-low density polyethylene nanocomposites

An assessment of topology and compositional dependent physical parameters of Ge-Se-Te-Bi lone pair semiconductors