PHYSICO MECHANICAL CHARACTERISATION OF FILLERS FOR NAVAL APPLICATIONS

The term “filler” does not define a specific product, but an entire class of composite materials used to fill surface imperfec- tions. Until recently the filler was used only to treat the surface imperfections. Currently, it has several aims like sanding, filling, levelling, protecting and insulating the substrate. In the marine field its main purposes are: insulate the surface, improve the surface finish and prepare it for the next painting treatments. The mechanical properties of fillers are fundamental to ensure the integrity of the painting systems which must be able to withstand the deformations suf- fered by the vessel. In fact the hull undergoes different stres- ses and deformations depending on the point where it is considered (bulb, rudder, keel, topsides or superstructure), the spe- cific condition to which it is subjected (stationary or sailing) or the material of construction (aluminium, steel, wood or glass-reinforced plastic). In the frame of the technological evolu- tion of materials, fillers underwent a remarkable development through the use of products such as epoxy resins that are, in modern formulations, very simple to use, differently from other ma- terials used in nautical field (polyester, vinylester and polyurethanes) and com- bine enhanced performance and versa- tility. Their mechanical, physical, electri- cal and thermal properties can be tailo- red with the addition of inert fillers like microfibers, phenolic microspheres, glass microspheres and colloidal silica. In particular, the glass microspheres are hollow spheres with diameters in the micrometer range. They generally improve the hardness of the surface.
When they are mixed with epoxy resin produce a material extremely tenacious, slightly elastic and difficult to break. The phenolic microspheres are hollow spheres with diameters in the microme- ter range. They are very light and gene- rally improve the tenderness of the sur- face. The microspheres mixed with epoxy resin produce a material slightly hard, brittle, easy to work with abrasi- ves. For this reason the phenolic micro- spheres are used for the preparation of fillers particularly easy to be sanded but extremely waterproof. The microfibers are microscopic frag- ments of a material and are able to thic- ken the resin and, once hardened, to act as “reinforcement” of the resin itself. Then the mix of epoxy resins with micro- fibers produces a tenacious, elastic material hard to break. For this reason microfibers are used for the preparation of adhesives able to join the surfaces fil- ling all the gaps between them. The colloidal silica is a powder that has the property to make more dense the epoxy resin. It is used exclusively as a thic- kener in combination with other inert exten- ders to produce an high density filler. In this work the evaluation of the physi- cal and mechanical properties of various commercial fillers is presented.
The morphological analysis of their structure is used to try to determine the influence of various components on their final properties.