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Item type:Publication, Access status: without files , Electroactive performance and cost evaluation of carbon nanotubes and carbon black as conductive fillers in self-healing shape memory polymers and other composites(Elsevier, 2022-09-23); ; ; ; Multiwalled carbon nanotubes (MWCNT) and carbon black (CB) have been widely used as conductive fillers in electroactive polymer composites. MWCNT-based composites generally have lower resistivity and percolation thresholds, while CB-based ones are considerably cheaper. To balance these pros and cons, ternary composites (TCs) (polymer-MWCNT-CB) can be formulated. Here, we prepared electroactive MWCNT-CB TCs capable of self-healing and with shape memory properties, based on polyketones reversibly-crosslinked via Diels-Alder chemistry. Unexpectedly, the cheaper CB-rich formulations had lower resistivities, thus better electroactive self-healing and shape memory responses. Nonetheless, not all electroactive MWCNT-CB TCs have this clear cost-effectiveness. We evaluated the cost-performance of multiple reported MWCNT-CB TCs systems and found different general trends (positive, negative, and synergistic cost-efficiency relationships). Thus, the cost-effectiveness of these fillers (and their combination) greatly depends on each composite system and what it is intended for. This work includes the first systematic report on cost-performance of MWCNT and CB as conductive fillers.Publicationtype: Journal Article40 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Mechanical degradation estimation of thermosets by peak shift assessment: General approach using infrared spectroscopy(2021-04-14); ; ; ; Until now, detecting weak spots in composite structures remains a key challenge in the aviation industry. The correct assessment of the load-bearing capability after structural overloading or the occurrence of barely-visible damages is particularly important to maintain structural integrity. Nonetheless, a reliable and overarching non-destructive inspection method to estimate the residual mechanical properties while covering all major damage scenarios has not been found yet. Several non-destructive techniques have been proposed to approach these challenges and are already in place for specific damage cases. However, each technique has its sources of information and therefore, limitations in practice due to a lack of generalisation. In this work, we present a concept and approach to gain access to the residual mechanical properties of a thermosetting polymer solely based on its inherent material state independent from its life-cycle history. Therefore, the material state is obtained by combining Fourier-transformed infrared spectroscopy with feature extraction algorithms based on Gaussian peak fitting. As proof of concept, tensile, creep, and cyclic tests are conducted to demonstrate this approach's advantage. A complementary theoretical investigation using quantum chemical calculations is employed to support the experimental work by identifying the investigated polymer's characteristic vibrational modes and predicting their evolution during the experiments. The results show that the quantification of molecular changes can estimate the material state and that the method is suitable to improve the understanding of the degradation processes and severity. This publication shall particularly serve as the basis for further research to study the interaction between molecular forces and material properties.Publicationtype: Journal Article93 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Electrical conductivity of melt-spun thermoplastic poly(hydroxy ether of bisphenol A) fibres containing multi-wall carbon nanotubesFibres spun from thermoplastic poly(hydroxy ether of bisphenol A) filled with weight fractions of 1, 3, 6, 8 and 12 wt.% of multi-wall carbon nanotubes (MWCNTs) were prepared at elevated process temperatures using a three-roll-mill for homogeneous dispersion of the MWCNTs and a twin-screw compounder with an attached winding roll for fibre spinning. Production caused fibre draw down ratios (DDR) from 1 to a maximum of 54 resulting in fibre diameters from 0.7 mm down to 0.07 mm were used. The state of dispersion of the MWCNTs was characterized by transmission electron microscopy (TEM). The electrical resistivity of the fibres and the percolation threshold were obtained as a function of weight fraction of MWCNTs and the fibre draw down ratio. The effect on resistivity of a subsequent heat treatment at 180 °C and on dissolution of the fibre's outer layers were analysed when embedded in liquid epoxy resin. Percolation thresholds between 6 wt.% and 12 wt.% were estimated depending on the draw down ratio of the fibres. The observed lowest resistivity was about 5 Ωm for as spun fibres without drawing. It increases over several orders of magnitude to the limit of measurability with increasing the draw down ratio. It was further shown that the resistivity greatly reduced after heat treatment, as well as after embedding the fibres in epoxy resin due to the effect of near surface solubility of the thermoplastic fibre when in contact to the epoxy resin. A reduced percolation threshold of about 6 wt.% can be obtained after heat treatment. Thereby, the production related influence of fibre stretching is largely eliminated.Publicationtype: Journal Article84 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Viscoelastic and dielectric properties of composites of poly(vinyl butyral) and alumina particles with a high filling degreeFiller-filler and filler-matrix interactions in polymer composites increase with filler concentration and strongly influence the mechanical and rheological properties of polymer composites. By means of the spouted bed spray granulation process polymer composites with an extremely high concentration of inorganic fillers can be prepared. In this work, the viscoelastic properties of highly filled composites of poly(vinyl butyral) (PVB) and alumina particles are studied in the glassy, entanglement and terminal flow regime of poly(vinyl butyral). Ceramic-polymer composites with a volume concentration of inorganic particles between 61 vol% and 77 vol% were prepared. Such large filler fractions imply a strong effect of filler-filler interactions on the viscoelastic properties of the composite. Dynamic-mechanical thermal analysis reveals that the composites are characterized by a predominantly elastic behaviour below and above the glass transition temperature of the polymer phase because of strongly pronounced filler-filler and polymer-filler interactions. A phenomenological equation is proposed in order to describe the reinforcement effect which implies an increase of storage modulus by a factor of up to four orders of magnitude. The results of frequency and strain sweeps in the oscillatory mode show that the polymer phase strongly influences the deformation of the contact network of inorganic particles. Differential scanning calorimetry and broadband dielectric spectroscopy indicate that the glass transition temperature of poly(vinyl butyral) does not significantly differ within experimental resolution for pristine PVB and the PVB phase in the composites.Publicationtype: Journal Article79 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Friction spot welding of PMMA with PMMA/silica and PMMA/silica-g-PMMA nanocomposites functionalized via ATRP(Elsevier, 2014-08-19); ; ; ; In the present study, the feasibility of Friction Spot Welding (FSpW) of a commercial-grade poly(methyl methacrylate) (PMMA) (PMMA GS) and PMMA 6N/functionalized silica (SiO ) nanocomposites was investigated. The silica nanoparticles were functionalized via atom transfer radical polymerization (ATRP) with PMMA chains to achieve a uniform dispersion in the polymer matrix. The successful functionalization of silica nanoparticles with PMMA chains via ATRP was evaluated by ATR-FT-IR and TGA measurements. Rheological investigations of the silica nanocomposites showed a plateau of the storage modulus G′ at low frequencies (0.01-0.03 rad/s) as a result of elastic particle-particle interactions. Overlap friction spot welds consisting of PMMA GS and a 2 wt% SiO -g-PMMA nanocomposite were successfully prepared and compared to spot joints of PMMA GS welded with PMMA 6N and PMMA 6N/silica nanocomposite with 2 wt% unfunctionalized silica nanoparticles. Raman mappings of selected areas of cross-sectional plastographic specimens revealed an increased mixing behavior between the two polymer plates in the case of PMMA GS/2 wt% SiO -g-PMMA joints. Although the joints welded with PMMA 6N/silica nanocomposites showed a reduction of 22% in lap shear strength and 21% displacement at peak load compared with the neat PMMA spot welds, they can compete with other state-of-the-art PMMA welding techniques such as thermal bonding and ultrasonic welding, which indicates the potential of friction spot welding as an alternative fabrication technology for joining future nanocomposite engineering parts. 2 2 2Publicationtype: Journal Article34 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A simulation study on the effects of shear flow on the microstructure and electrical properties of carbon nanotube/polymer composites(Elsevier, 2011-08-31); ; ; We employ a fiber-level simulation technique to simulate carbon nanotube (CNT)/polymer composites in simple shear flow. This model incorporates CNT flexibility, irregular CNT equilibrium shapes and CNT interactions. Electrical conductivity of the composites is determined using a resistor network algorithm. Tunneling resistance of the insulating matrix film between nanotubes is also considered. We show that the rate of imposed shear flow influences the composite conductivity by facilitating the formation or destruction of the conductive aggregates. In addition, the conductivity evolution during shearing for different concentrations is investigated. At low concentration, percolating clusters form and break simultaneously which causes large conductivity fluctuations during the simulations. When sufficiently large concentrations are reached, percolating clusters persist during shearing and the conductivity fluctuations decrease. In agreement with previous research we determine that increasing the shear rate causes alignment of the nanotubes in the flow direction. We show that upon shearing at constant shear rate, the system attains a state with substantially constant electrical conductivity, nanotube orientation and agglomerate size that is a function of the applied shear rate. The state reached for a given shear rate is independent of the initial state of orientation and aggregation.Publicationtype: Journal Article30 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Evaluation and identification of electrical and thermal conduction mechanisms in carbon nanotube/epoxy compositesNanostructured modification of polymers has opened up new perspectives for multi-functional materials. In particular, carbon nanotubes (CNTs) have the potential to realise electrically conductive polymers with improved or retaining mechanical performance. This study focuses on the evaluation of both, the electrical and thermal conductivity of nanoparticulate filled epoxy resins. We discuss the results with regard to the influence of the type of carbon nanotube (SWCNT, DWCNT and MWCNT), the relevance of surface-functionalisation (amino-functionalisation), the influence of filler content (wt% and vol%), the varying dispersibility, the aspect ratio and the specific surface area.Publicationtype: Journal Article19