The present invention is relative to a method for manufacturing (acoustic or thermal) insulating panels for buildings, or panels having filtering functions. These panels are manufactured starting from bird feathers. Said feathers are used in the form of flakes or micronized flour with a high content of keratin. Keratin is a filamentous protein rich in sulfur, which is contained in amino acid residues of cysteine; it is very stable and resistant. It is a quaternary structure and it consists of different tertiary structures arranged in a row. It is produced by keratinocytes and it is immersed in their cytosol in the form of intermediate filaments. It is the main constituent of the stratum corneum of the epidermis of the tetrapods and, especially, of the amniotes, in which it guarantees impermeability.

A keratin molecule consists of a polypeptide chain with a helix structure having a length of about 450 A. The chains interact with one another, thus organizing themselves in structures that keep getting bigger and more complex. First of all, the single helixes combine themselves, by means of hydrophobic interactions, in pairs (dimers) and each pair, besides the winding of the single helixes, further winds itself on itself. In turn, the dimers obtained in this way combine themselves, both transversely and longitudinally, by means of disulfide bridges between cysteine residues of close filaments and other interactions. In this way, protofilaments are formed. According to an increasing degree of organization, further structures are formed one after the other, namely protofibrils (two protofilaments one next to the other), microfibrils (four protofibrils one next to the other) and, finally, macrofibrils (many microfibrils).

A keratin molecule is difficult to dissolve, since this protein contains disulfide bridges, i.e. very strong bonds between two amino acids of the same type, namely two cysteine molecules: the molecule deriving from the formation of the disulphide bridges assumes a helical shape and is extremely strong, since the sulfur atoms available in the entire spiral create a fibrous matrix, which is hardly soluble. Hence, the consistency of the keratin molecule varies according to the disulphide bonds created between the cysteine molecules, in fact, if the disulfide bonds are numerous, the keratin will have a rigid structure that is hardly flexible, whereas, if the disulphide bonds a re relatively few, the keratin molecule will be more flexible: the keratin available inside the hair and the skin has a fairly flexible structure.

Keratin is synthesized by the keratinocytes, namely cells that make up part of the skin, of the hair, of the nails and of other structures; the cells of the keratinocytes, once dead, accumulate, thus forming a superficial layer that fulfills the function of protecting the layers underneath, where new keratin molecules are synthesized : this natural process of the body can be accelerated by some clinical conditions; any damage caused to the most external layer of keratin can damage the structure of the skin, of the hair and of the nails.

It can be found in mammals in the form of epithelium, nails, hair, horns, and baleens and in birds in the form of epithelium, talons, scales, feathers, and plumes.

The main use of keratin is in the pharmaceutical industry, since this material covers gastro-resistant tablets. This means that these tables can resists gastric acids, such as HCI (hydrochloric acid). It is also used in treatments to give brilliance and consistency to the hair.

In the method according to the present invention, the raw substance used to obtain this material consists of feathers of birds, such as chickens, turkeys, gooses, and others.

The feathers are filaments consisting of hundreds of thousands of parallel microcrystalline fibers, which are held together on a central stiff shaft. The inside of the shaft is white and spongy. Chemically, the proteins making up the fibers and the shaft are all keratin.

The extraction of the keratin takes place by means of hydrolysis, which is a process that causes a chemical reaction with water, heat and the acid and produces the keratin.

Different natural and non-natural materials are able to express a thermal insulation. Thermal insulation in not determined by the fiber in itself, but is it ensured by the air that is trapped in the spaces between the fibers. Thus, air is by far the best thermal insulator known. The special physical structure of the feathers allows a remarkable quantity of air to be "taken in", a quantity that is definitely higher compared to that of other fibers. Suffice it to say that 5 grams of down "take up" a volume of one liter, whereas, in order to "fill" the same volume, one needs a quantity of polyester that is 2-3 times larger. Therefore, we can say that feathers win the comparison with all the other fibers normally used.

Feathers, mainly made up of keratin, are a natural flame retardant, which means that they are refractory to flames. As a matter of fact, feathers have a high autoignition temperature and, compared to the other natural fibers, have the lowest flash point, do not propagate flames, have the lowest development index, do not produce toxic fumes, do not melt. If that is not enough, these natural features can be significantly increased by means of proper treatments of fireproofing and with ultrasounds.

Finally, feathers are able to absorb up to 20% and more of humidity without giving a wet sensation. Therefore, in case of a humid climate, they activate their function, thus absorbing humidity in order to give it back to the environment through a gradual and continuous transpiration process.

On the contrary, synthetic fibers, which are normally used in insulating systems, are scarcely or barely hygroscopic and, therefore, in conditions of high humidity, the water vapor that has not been absorbed turns again into liquid.

The Applicant found out that feathers, if properly decomposed to build a material that can be used, can be employed to manufacture panels to be used, for example, as insulating panels in the building filed and also as filtering means.

The present invention suggests a novel and affective method to manufacture these panels starting from properly treated (decomposed) bird feathers in the form of flakes or micronized flour with a high content of keratin.

Said birds can be, for example, chickens, turkeys, gooses, and others. An aspect of the present invention is relative to a method having the features set forth in appended claim 1.

The features of the method according to the present invention will be described in detail below with reference to the following non-limiting explanatory embodiment.

The method according to an embodiment of the present invention substantially comprises five different steps.

During the first step, the feathers are washed and sorted out in order to filter foreign bodies. If necessary, during this step, a predetermined quantity of soda can be added to sterilize the product. The washing water can advantageously be re-used for multiple washing cycles.

In the following second step, the feathers are roughly ground in a feather- grinding machine, which comprises a cylinder, where the feathers are conveyed and ground by a worm screw housed therein. The structure of the machine is substantially the same of a meat grinder.

In the following third step, the feathers are further crumbled in a finer manner by using a machine with concave surfaces. In particular, this machine comprises a pair of coupled concave surfaces, between which the ground feathers are fed, teeth being obtained on each one of the two opposite faces of the surfaces. Due to the reciprocating motion between the two surfaces, the teeth crumble the ground feathers and create a final product that comprises feathers in the form of flakes.

The following fourth step involves the use of a homogenizing machine, for example a piston homogenizer.

The homogenizer is a piston positive-displacement pump equipped with a special counter-pressure vale called homogenizing valve, which is used to obtain a homogenization and micronization effect on the product treated. In this machine, the feather flakes are mixed with water under pressure (at a pressure ranging from 500 to 1000 bar) and approximately at a temperature ranging from 50 to 80°C, are conveyed through a narrow duct (the aforementioned valve) and are subsequently expanded in a tank. Due to the fluid-mechanical effects generated by the high pressure applied to the fluid, one can obtain a more "homogeneous" distribution of the micronized particles and a cavitation effect.

At the end of the fourth step, the product substantially has the shape of a fluid pulp and can be treated, in particular dried, in order to obtain loafs, sheets or powder, based on the drying level and mode desired.

After the product has been obtained, the fifth and last step of the process involves the actual manufacturing of the panel. This step is performed by pressing the raw material in the form of pulp or flakes (after the third or fourth step), which, for example, is arranged in a frame that reproduces the shape of the panel to be manufactured. Anyway, the panel is obtained by means of a mechanical pressure, which is exerted, for example, by a punch in a matrix die or frame, or by means of a pressure that is exerted by means of an extruder. The panel remains compact and the fibers are intertwined with one another with the concurrence of the presence of humidity and pressure. According to the degree of pressure exerted, the panel can be manufactured so as to be more or less compact. The panel formed has the shape of a compact plate with whatever shape or thickness, based on the frame of matrix die to be used.

This low-aggregation panel can be used, for example, as a filter for materials dispersed in water or air. As a matter of fact, feathers can be used for drinkable water filters that are better than the common filters currently used, such as activated carbon filters. The micorstructure of the fibers of the feathers attracts and traps pollutants that hard to remove, such as heavy metals (chromium, lead, mercury, etc.) and also other metals, such as iron and copper.

Before introducing the fiber into a filter, it can be "activated" by means of ultrasounds, so as to open further microscopic pores in the structure of the fiber. Tests carried out so far have proven that feather filters can also remove many other pollutants from drinkable water or from industrial waste waters. Lab experiments have shown that feather fibers rapidly absorb radioactive elements, such as strontium and cesium. In some cases, the panel can be obtained by mixing keratin in the form of pulp with a suitable bonding agent, in order to encourage a different aggregation of the pulp itself. Furthermore, other fibers, such as wood, carbon, glass fiber, talc, etc., can be added to the keratin.

Advantageously, the panel can be provided, on one side or on both sides, with one or more surface covering sheets of different types, for example sheets of vegetable paper, nylon, polypropylene, cloth.

Finally, the panel can be provided with an edge band, for example made of wood, plastic, iron, cardboard, etc.