Interfacial and bulk stabilization of oil/water system: A novel synergistic approach

Oil/water emulsions are usually stabilized either by interfacial modification using nanoparticles and surfactants (stated as pickering emulsion or bijels) or by bulk stabilization with the help of low‐molecular‐weight or polymeric gelators (known as bigels) in response to some external stimuli (e.g., pH, temperature). Both these approaches result in different systems that are quite useful for different applications, including catalysis, pharmaceutical and agrochemicals. However, these systems also possess some inherent drawbacks that need to be addressed, like difficulty in fabrication and ensuring the permanent binding of nanoparticles at the oil/water interface, in case of nanoparticles stabilized emulsions (i.e., interfacial stabilization). Similarly, the long‐term stability of the oil/water systems produced by using (hydro/organo) gelators (i.e., bulk stabilization) is a major concern. Here, we show that the oil/water system with improved mechanical and structural properties can be prepared with the synergistic effect of interfacial and bulk stabilization. We achieve this by using nanoparticles to stabilize the oil/water interface and polymeric gelators to stabilize the bulk phases (oil and water). Furthermore, the proposed strategy is extremely adaptable, as the properties of the resultant system can be finely tuned by manipulating different parameters such as nanoparticles content and their surface functionalization, solvent type and its volume fraction, and type and amount of polymeric gelators.Rivers, Ports, Waterways and Dredging EngineeringAerospace Manufacturing TechnologiesEnvironmental Fluid Mechanic

Effect of dwell stage in the cure cycle on toughening of epoxy using thermoplastic multilayers

Epoxies with high cross-linking densities are brittle and hence have a low fracture toughness. However, different methods are known to increase fracture toughness. Numerous approaches are known to incorporate a second phase into the epoxy matrix, such as rubber, inorganic nanoparticles or thermoplastics, referred to as bulk resin modification. These tougheners usually form specific morphologies during the curing phase of epoxy, resulting in improved fracture toughness of the system. Unfortunately, for some tougheners, the addition of second phase into the epoxy system also results in a reduction in overall modulus and limitation in end-use temperature of the system. In the case of thermoplastic tougheners, the second phase is created by diffusion and dissolution, followed by reaction induced phase separation, leading to a morphology in the micrometer range. However, the influence of the curing history beyond phase separation, using two dwell cure cycles with varying dwell time/degree of cure, on the interphase dimension and final morphology for PEI having a contrasting phase behaviour (UCST), is not well understood. The research presented in this work aims to understand the interphase formation, to later attain the desired droplet size and interphase morphology for improved material toughness. This aim is achieved by analyzing the influence of dwell time by considering two main cases for each selected 1st dwell temperature (120-180˚C): (i) wait until the onset of phase separation (OPS) before increasing the temperature to 200°C (second dwell), (ii) wait until 80% degree of cure (80% DOC) before the second dwell. At all processing temperatures, a distinct gradient morphology (Fig. 1a ) was clearly observed for both cases (OPS and 80% DOC). The SEM micrographs revealed the formation of a larger interphase region (71 μm) for the OPS case as compared to the 80% DOC case (56 μm). Figure 1b shows the interphase thickness as a function of 1st dwell temperature for both OPS and 80% DOC cases. It can be seen that the interphase thickness increased with 1st dwell temperature for both cases, until 160˚C after which it slightly decreased for a 1st dwell temperature of 180˚C. This work highlights, i) the importance of the curing process beyond phase separation to control interphase dimension and final morphology and, ii) the influence of both these parameters on the toughness enhancement.Aerospace Manufacturing Technologie

Toughening of epoxy systems with interpenetrating polymer network (IPN): A review

Epoxy resins are widely used for different commercial applications, particularly in the aerospace industry as matrix carbon fibre reinforced polymers composite. This is due to their excellent properties, i.e., ease of processing, low cost, superior mechanical, thermal and electrical properties. However, a pure epoxy system possesses some inherent shortcomings, such as brittleness and low elongation after cure, limiting performance of the composite. Several approaches to toughen epoxy systems have been explored, of which formation of the interpenetrating polymer network (IPN) has gained increasing attention. This methodology usually results in better mechanical properties (e.g., fracture toughness) of the modified epoxy system. Ideally, IPNs result in a synergistic combination of desirable properties of two different polymers, i.e., improved toughness comes from the toughener while thermosets are responsible for high service temperature. Three main parameters influence the mechanical response of IPN toughened systems: (i) the chemical structure of the constituents, (ii) the toughener content and finally and (iii) the type and scale of the resulting morphology. Various synthesis routes exist for the creation of IPN giving different means of control of the IPN structure and also offering different processing routes for making composites. The aim of this review is to provide an overview of the current state-of-the-art on toughening of epoxy matrix system through formation of IPN structure, either by using thermoplastics or thermosets. Moreover, the potential of IPN based epoxy systems is explored for the formation of composites particularly for aerospace applications.Aerospace Manufacturing Technologie

Synthesis of Organic–Inorganic Nanohybrids-Based Polymeric Nanocomposites

Organic–inorganic nanohybrids-based polymer nanocomposites are made up of two different components, and these hybrids attained great attention over last decades due to their diversified framework and fascinating features. These nanohybrids possess synergistic characteristics of both organic and inorganic substances. Different synthetic routes are used to synthesize these materials with enhanced morphology, tunable features, and fine nanostructures. This chapter focuses on various synthetic routes for fabrication of organic–inorganic-based nanopolymeric composites. Synthetic strategies and protocols of different routes have been described in details. We have also discussed the advantages and limitations of all synthetic methods in details.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Aerospace Manufacturing Technologie

Study of surface mechanical characteristics of abs/pc blends using nanoindentation

Acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) are considered a well-known class of engineering thermoplastics due to their efficient use in automotive, 3D printing, and elec-tronics. However, improvement in toughness, processability, and thermal stability is achieved by mixing together ABS and PC. The present study focuses on the understanding of surface mechanical characterization of acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) blends using nano-indentation. Polymer blends sheets with three different proportions of ABS/PC (75:25, 50:50, and 25:75) were fabricated via melt-processing and thermal press. Fourier transform infrared (FTIR) spectroscopy was performed to analyze the intermolecular interactions between the blends’ compo-nents. To understand the surface mechanical properties of ABS and PC blends, a sufficient number of nano-indentation tests were performed at a constant loading rate to a maximum load of 100 mN. Creeping effects were observed at the end of loading and start of unloading section. Elastic modulus, indentation hardness, and creep values were measured as a function of penetration displacement in the quasi-continuous stiffness mode (QCSM) indentation. Load-displacement curves indicated an increase in the displacement with the increase in ABS contents while a decreasing trend was observed in the hardness and elastic modulus values as the ABS content was increased. We believe this study would provide an effective pathway for developing new polymer blends with enhanced mechanical performance.Aerospace Manufacturing Technologie

Experimental Study of Mechanical Properties of Polypropylene Random Copolymer and Rice-Husk-Based Biocomposite by Using Nanoindentation

Nanoindentation is widely used to investigate the surface-mechanical properties of biocomposites. In this study, polypropylene random copolymer (PPRC) and biowaste rice husk (BRH) were used as the main raw materials, and glass-fiber-reinforced polypropylene and talc were also used with BRH to enhance the mechanical characterization of the biocomposites. The interfacial bonding between the polymer and the rice husk was increased by treating them with maleic anhydride and NaOH, respectively. The results obtained from the nanoindentation indicated that the plastic behavior of the biocomposites was prominent when untreated BRH was used and vice versa. The modulus and hardness of the biocomposite improved by 44.8% and 54.8% due to the neat PPRC, respectively. The tribological properties were studied based on the hardness-to-modulus ratio and it was found that BRH- and talc-based biocomposites were better than other samples in terms of low friction and wear rate. The creep measurements showed that untreated rice husk biocomposite exhibited high resistance to load deformation.Aerospace Manufacturing Technologie

Effect of a Dwell Stage in the Cure Cycle on the Interphase Formation in a Poly(ether imide)/High T_gEpoxy System

Epoxies are inherently brittle materials and to overcome this brittleness, a second microphase (i.e., thermoplastic) is typically added. This modification of epoxy resin using thermoplastics results in reaction-induced phase separating morphologies in the micrometer range. In this study, the influence of the curing history, beyond phase separation, on the interphase formation and final morphology of PEI and the high Tg epoxy system is investigated. Several cure cycles were examined, each with a first dwell temperature ranging from 120 to 180 °C for a given time up to the onset of phase separation (OPS) or up to the 80% degree of cure (80% DOC) and then with a second dwell at 200 °C for 20 min to complete the cure cycle. Hot-stage microscopy experiments were carried out at several first dwell temperatures before final conversion at the second dwell. The morphologies and resulting droplet size distribution at the interphase, after the final cure, were analyzed through scanning electron microscopy. Results showed that the diffusion distance was significantly higher in the case of OPS as compared to the 80% DOC case, particularly at lower first dwell temperatures. This behavior was attributed to the fact that, in the case of OPS, polymeric chains were still in a mobile state and diffused further during the second dwell curing stage, while at 80% DOC, polymeric chains were completely bound but still diffuse due to non-stoichiometric curing. This restricted mobility of polymeric chains after phase separation (80% DOC) resulted in a larger number of smaller droplets as compared to the OPS case.Aerospace Manufacturing Technologie

Co-cured carbon fibre/epoxy composite joints by advanced thermoplastic films with excellent structural integrity and thermal resistance

Carbon fibre/epoxy composite joints were assembled with Poly-etherether-ketone (PEEK) and Poly-ethylenimine (PEI) films using a co-curing process to prepare single-lap joint specimens. The joints were tested under quasi-static loading conditions at 22 °C and 130 °C and a fatigue loading condition. The experimental results demonstrated better or comparable structure integrity of the composite joints co-cured by PEEK and PEI films than the reference joints bonded by aerospace FM300 adhesives. In particular, the PEEK co-cured joints exhibited extraordinary mechanical performance at 130 °C and excellent fatigue resistance. For instance, the lap-shear strength at 130 °C and the fatigue life of the composite joints co-cured by 200μm PEEK films was 2.1 times and 2.7 times higher than that of the aerospace adhesive joints, respectively. Overall, the results of this work proved that advanced thermoplastic films are promising alternatives to epoxy adhesives for the co-cure joining of thermoset composites with significantly enhanced structural integrity and thermal stability.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Aerospace Manufacturing TechnologiesStructural Integrity & Composite

Recycled carbon fibre mats for interlayer toughening of carbon fibre/epoxy composites

Exploring routes for the effective use of recycled carbon fibres (rCFs) is critical to close the loop in the life cycle of carbon fibres. This work demonstrated a potential of using rCFs for interlayer toughening of carbon fibre/epoxy composites. Nonwoven mats based on rCFs and commingled rCFs/Polyphenylene-sulfid (PPS) fibres were used to interlay a laminate, aiming to improve the mode-I and mode-II fracture toughness. The experimental results proved significant enhancements in the interlaminar fracture properties upon interleaving, with the rCF/PPS mats exhibiting a more prominent toughening effectiveness than the rCF mats. For example, the maximum increase in mode-I and mode-II fracture initiation energies of the laminates was 51% and 66%, respectively upon interleaving the rCF mats, and 220% and 105%, respectively by adding the rCFs/PPS mats. The fractography analysis proved that the main toughening mechanisms were fibre debonding and pulling-out for the rCF mats and fibre bridging for the commingled rCFs/PPS mats. The differences in the toughening mechanisms resulted in opposite effects of the interlayer/epoxy adhesion to the fracture toughness, i.e. an improved interlayer/epoxy adhesion increased the toughening effectiveness of the rCF mats, but negatively affected the toughening performance of the rCF/PPS mats.Structural Integrity & CompositesAerospace Manufacturing Technologie

Nano-indentation response of ultrahighmolecular weight polyethylene (UHMWPE): A detailed analysis

Nano-indentation, a depth sensing technique, is a useful and exciting tool to investigate the surface mechanical properties of a wide range of materials, particularly polymers. Knowledge of the influence of experimental conditions employed during nano-indentation on the resultant nano-mechanical response is very important for the successful design of engineering components with appropriate surface properties. In this work, nano-indentation experiments were carried out by selecting various values of frequency, amplitude, contact depth, strain rate, holding time, and peak load. The results showed a significant effect of amplitude, frequency, and strain rate on the hardness and modulus of the considered polymer, ultrahigh molecular weight polyethylene (UHMWPE). Load-displacement curves showed a shift towards the lower indentation depths along with an increase in peak load by increasing the indentation amplitude or strain rate. The results also revealed the strong dependence of hardness and modulus on the holding time. The experimental data of creep depth as a function of holding time was successfully fitted with a logarithmic creep model (R2 ≥ 0.98). In order to remove the creeping effect and the nose problem, recommended holding times were proposed for the investigated polymer as a function of different applied loads.Aerospace Manufacturing TechnologiesRivers, Ports, Waterways and Dredging Engineerin