The present research project is focused on the synthesis of ZnO nanostructures on commercially available electrospun nylon nanofibres to be used as interlaminar reinforcements in polymer matrix composites. The main aim is to evaluate whether these hierarchically nanostructured mats can increase the through-the-thickness properties of the resulting composites under low velocity impact conditions. At the same time the presence of photoreactive species (ZnO) makes them attractive for wastewater treatment in photocatalytic processes. In this regard photocatalytic tests will be performed to evaluate the degradation of methylene blue (MB) used as model compound under UV light irradiation. The growth of ZnO structures will be developed by means of a hydro-thermal technique, because of its simplicity and low operating temperatures that are not expected to compromise the mechanical properties of nylon nanofibres. The project is intended to optimize the morphology of ZnO nanostructures considering several process parameters, such as the number of seeding cycles, the growth time and the concentration of reagents. The optimization will involve a trade-off among good mechanical performance, thermal stability and homogeneous distribution over the electrospun nanofibres.
It is well-known that the successful development of a composite material is dictated by the quality of the fibre/matrix interface. Prior efforts that have investigated whiskerization or interleave approaches to improve the interfacial strength of a composite material have often achieved toughness at the expense of the in-plane properties of the composite. This decrease in strength has been typically due to weakening of the fibres during high temperature processing (for MWCNTs or other nanostructures growth) or a decrease in fibre volume fraction caused by the additional matrix filler. In this framework, no other research efforts have been found in the literature addressing the combination of electrospun veils and ZnO nanostructures to enhance the interface strength and interlaminar resistance of composite materials. In this project it is expected to demonstrate that a low temperature solution process allows the nanowires to be readily grown on nylon nanofibres, while providing a clear understanding of the influence of each step of the synthesis on the morphology and properties of the resulting decorated nanofibre veils. This will deliver a specific synthesis procedure that is suitable for composite reinforcement, in terms of number and operative conditions of seeding/growth steps and concentration of reagents. In addition, research on impact behaviour of nanomodified samples is affected by a large number of variables that need to be considered (thickness, lay-up, energy and speed of the impactor, number and position of nanolayers), and it is still far to be completed. There is still very little knowledge about the optimal strategy to effectively interleave a laminate and strengthen its resistance to impacts. Samples for impact tests are usually larger than those used for the other tests, and require a significantly greater amount of nanofibres, because several (if not all) interfaces are nanomodified, making the research expensive in terms of resources and time. In this regard, another advantage of the present research project relies on the use of commercially available electrospun veils, already introduced in a production line. This research effort is envisaged to significantly trigger the use of nanofibres in a larger number of applications. The procedure that will be used to grow ZnO nanostructures on nylon nanofibres is relatively simple, cost-effective and easily scalable to large volumes. These advantages can be exploited to a large extent by producing self-supporting fibrous mats with photocatalytic activity for wastewater treatment that are free from drawbacks typically associated with the use of nanoparticles and nanopowders.