“Obtaining of polyvinyl alcohol (PVA) nanofiber webs on textile substrates, with applications as acoustic absorbents”.

ABSTRACT
Electro-spinning technology, by means of which polymer filaments are obtained using an electrostatic strength, from the solution of the electrically charged polymer, has became in the last years the most popular technology to obtain nanofiber webs, having been developed devices able to get, in a continuous way, on an industrial scale, the above mentioned webs, to be used in such diverse applications as filtering, defense and security, electronics and medicine, among others.
These materials classed as being nanostructured, are characterized by being a porous, continuous material and with wide area/volume relation, made up by a homogeneous tangled of nanosized diameters fibers.
From the acoustic absorption’s point of view, these materials show a great potential as low frequencies resound elements and acoustics absorbent on high frequencies, when they are combined with conventional acoustic absorber, able to act in the whole range of interest for architectural acoustics.
The aim of this Phd work is to optimize the process of obtaining nanofiber webs of polyvinyl alcohol (PVA) over nonwoven textile substrates of polypropylene, using electrospinning technology, and to be acoustically characterized subsequently with the aim of knowing the capacity of improvement that they provide to the conventional absorbent acoustic textile-base, in building and automotive industry and aerospace, having into account that the weight and thickness contribution to the whole turns out to be insignificant. Because of that, the use of instrumental techniques will be necessary to analyze the superficial properties of the nanofiber web’s substrate collector, such as measuring angles of contact or measuring the superficial electrical conductivity. It will also be required a series of instrumental techniques which allow to characterize the nanofiber webs precursor solution, such as viscosimetry or electrical conductivity. For the study of the obtained webs, regarding to their morphology and homogeneity (polymers aggregates and micro-holes) instrumental techniques will be used, as the amount of deposited mass, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Finally, for the acoustics characterization of the webs, together with the collector substrate and the textile-base conventional absorbents, resistance to the flow of such material will be measured and the measurement of the absorption coefficient and specific impedance in Kundt’s tube.

The nanofiber webs of polyvinyl alcohol, combined with textile-base absorbent materials, are able to absorb emitted low frequencies sounds, and at the same time, they remarkably improve the behavior of the above mentioned conventional absorbents. The material acting as acoustic base absorber determines the behavior’s initial tendency of the combined (web/absorbent), getting different results for the same web, depending on the base material used as reference.
A high level of porosity is the optimal structure of a web for acoustic purpose. This can be achieved by getting a uniform and homogeneous distribution of small diameter nanofiber, free of imperfections like polymer beads.