Abstract

Abstract

Cellulose nanocrystals (CNC) have attracted great interest as nanoreinforcement due to their excellent mechanical properties. Furthermore, their dispersibility in water makes them suitable for their incorporation in many aqueous systems such as waterborme polyurethanes (WBPU). WBPUs ​​have gained attention due to their versatility and ability to ajust their properties to a wide range of applications, in addition to their non-toxicity, non-flammability and environmental sustainability. Therefore, in this work a waterborne polyurethane has been synthesized for the preparation of nanocomposites with different contents of cellulose nanocrystals, incorporated by different routes, the classical mixing by sonication once the waterborne polyurethane has been synthesized, and the alternative in-situ by adding the CNCs in water during the WBPU synthesis, just in the phase inversion step. The obtained dispersions have been used in the preparation of films by casting and mats by electrospinning. The films and mats have been characterized from the point of view of their physical-chemical, morphological and superficial properties.

Abstract

In the last decades the fiber-reinforced polymer composites, FRPC, have undergone a spectacular development in applications where high performance of resistance and tenacity with a minimum weight are required. However, due to their laminar structure and the brittleness of their resin matrix, they show a great tendency to fracture as a failure mode. At the moment, technologies are being studied to improve their behavior to the fracture, doping or modification of resins and treatments of the reinforcing materials. However, the trend with the greatest potential is the use of interleave veils arranged as an interface between the matrix and the fiber, which have shown important improvements in the final mechanical properties of the composite material. This is due to adhesion phenomena between the polymer matrix and the reinforcing fiber. Initial studies were performed with interleave veils not specifically developed for this use; custom-made veils are currently being developed for use in laminated composites. The electrospinning technology is taking a positioning of relevance in this field, due to its great capacity of production and its low cost. High specific surface of electrospun veils , make electrospinning a good candidate to manufacture interleave veils to improve the mechanical properties of laminated composites. This work shows the fabrication of electrospun veils of PA6 polyamides for their integration into the composite by varying the number of veils in order to analyze their influence on the flexural strength of the composites.

Abstract

Research on nanofiber veils used as reinforcements in composite materials began several years ago and there have been numerous works published on this topic by the research community. However, there is still a long way to go to build a solid knowledge on the behavior of nanofibers in the most common failure mode in carbon fiber composites; the delamination that happens between the tissues of the fibers and the fragile matrices that agglutinate them. The fact of inserting these thermoplastic veils in the delamination region without hardly altering the weight of the composite has proven to be an adequate method to increase the fracture toughness since the beginning of these investigations.

Electrospinning is a versatile and simple technique that allows a tailor-made manufacture of nanofiber veils from a wide variety of polymers, with different morphologies in terms of grammage, nanofiber diameter, etc. One of the most important characteristics of nanofibers is their nanometric scale, which gives them a great surface-volume ratio, high porosity and excellent mechanical performance. This paper shows the influence of the grammage of veils based on polyamide 6 nanofibers and the different ways to achieve the same weight in mechanical properties of the manufactured composites. The results show an improvement in the fracture toughness and in the impact strength when these thermoplastic veils are introduced.