Aleksandar Kojović

Keratin–polyethylene oxide bio-nanocomposites reinforced with ultrasonically functionalized graphene

Polyethylene oxide (PEO) functionalized graphene (f-G) was prepared by ultrasonication of pristine graphene in PEO aqueous solution. The feasible sonication protocol of PEO degradation and graphene functionalization enabled fabrication of solvent cast nanocomposites. Additionally, the steps to form new bio-nanocomposite films have been described. Taking the advantage of the combination of graphene, PEO and keratin fibers from poultry feather waste, the aforementioned bio-nanocomposite films were designed with extraordinary properties allowing the films to have promising applications as eventual packaging materials and enabling bio-waste keratin to be converted into value-added materials. Compared to neat PEO, addition of only 0.3 wt% f-G provided an increase of 92% to the storage modulus. These findings are similar to the nanoindentation results, which yielded increases in the reduced modulus of the same composition by about 92%. Nanoindentation testing shows that the incorporation of 0.3 wt% f-G increased the reduced modulus and hardness of the keratin–PEO blend by about 155 and 99%, respectively.

Intensity Fiber-Optic Sensor for Structural Health Monitoring Calibrated by Impact Tester

In this paper, the use of intrinsic intensity fiber-optic sensors for structural health monitoring was investigated. Polyethylene-based composite samples with glass mat reinforcement and embedded telecommunication fibers were subjected to impact using high-speed puncture impact tester as a calibration device. Transfer function of the sensor was generated by linking the light intensity modulation depth with the impact force and the impact point to fiber distance. Conditions for transfer function validity were presented. To detect any possible dangerous impact, a net of crossed fibers was proposed and the net spacing for the given material was calculated. Appropriate non-damaging calibration procedure was proposed, as well as the algorithm for locating the impact point. The method for calculating the impact force, the projectile momentum change, and the place of impact was verified by consecutive strikes on the previously calibrated sample. The sensor can also provide information on the time of the impact and an alarm signal if the force exceeds the damaging threshold force..

Low Energy Impact Damage Detection in Laminar Thermoplastic Composite Materials by Means of Embedded Optical Fibers

The possibility of applying optical fibers as sensors for investigation of real time low energy impact damage in laminar thermoplastic composite materials has been studied. For that purpose intensity based optical fibers were embedded in composite material specimens. Kevlar 129 (DuPont’s registered trade-mark for poly (p-phenylene terephthalamide)) woven fabric was used as reinforcement. Impact toughness testing by the Charpy impact pendulum was conducted in order to investigate low energy impacts. Transient intensity of optical signal during the impact, were compared with material crack initiation energy and crack propagation energy. Following this approach, development of damage in material was monitored. Obtained results show that intensity based optical fibers could be used as detectors for material damage appearance, and also, for level evaluation of its degradation caused by low energy impacts.

Healing efficiency of polystyrene electrospun nanofibers with Grubbs’ catalyst in thermosetting composite

The study presents a novel method for the protection of Grubbs’ catalyst, by incorporation in polystyrene fibres via electrospinning technique. Epoxy-glass fibre composite with embedded self-healing agents (polystyrene fibres with Grubbs’ and microcapsules with dicyclopentadiene) was processed. Fibres retained pale purple colour during processing, revealing that fibres provided good protection of the catalyst from the amine hardener. The influence of self-healing agents’ content and thermal treatment on self-healing efficiency was investigated. Fourier transform infrared spectroscopy revealed that a polydicyclopentadiene formed at the healed interface. Thermal analysis revealed that ‘bleed’ at the healing sites from different samples had similar concentration of polydicyclopentadiene, indicating that the same amount of the catalyst has been provided to dicyclopentadiene for polymerization. This finding lead to assumption that electrospun polymer fibres enabled good dispersion of the catalyst in the composites. The low energy impact tests of the samples showed a recovery of 90% after 24 h at room temperature and up to 111% after repeated heating cycles.

Electrospun Poly(styrene) Fibers as a Protection for the First- and the Second-Generation Grubbs’ Catalyst

ABSTRACT The study presents a novel method for protection of the first- and the second-generation Grubbs’ catalyst, by incorporation in poly(styrene) fibers through electrospinning technique. Both catalysts are sensitive to the presence of the amine hardeners in the epoxy-based self-healing composites and require protection from deactivation to retain their ability to promote polymerization reaction of the healing agent. Comparison of healing efficiencies of both catalysts suggested that poly(styrene) fibers offer better protection and dispersion for the first-generation Grubbs’ catalyst, although all the samples exhibited high-healing efficiency. Difference in stereoselectivity between two catalysts was also indicated. GRAPHICAL ABSTRACT