"PROCESS OF COSK PRE-EXPANSION BY SUBMISSION TO MICROWAVE RADIATION AND RESULTING PRODUCT THEREOF"

FIELD OF THE INVENTION

This invention relates to a process, and to the resulting material, that allows the volumetric expansion of cork without using substances foreign to the cork system. More precisely, it relates to a process that consists in submitting cork to microwave radiation, obtaining a more bulky material and consequently increasing its yield and reducing its specific weight.

BACKGROUND OF THE INVENTION

In general, to promote the expansion of cork or cork derivatives, water or water vapour is used at different stages of its workup process. The applicant has already developed an improved method of expansion by water vapour.

The expansion of cork from values of 70% to 220%, shown in the Portuguese Patent PT101215, is performed by the use of organic solvents in autoclave.

Another way of achieving expansion of cork or of different cork derivatives is the processing by microwaves. Microwave radiations can be used on cork as a way of cork sterilization or decontamination, as described in the international patent no. WO9937334. On the other hand, the German patent no. DE019523 refers in addition to the

possibility of sterilization, the elimination of 2, 4, 6-trichloroanisol (known as TCA). The elimination of parasites, insects, bacteria or fungi by the action of microwave radiation is disclosed in the international patent no. WO2006021231. The purpose in both patents is to clean the cork, so it is not in the scope of the present application.

The European patent no. EP1677386 claims that wood, a material different from cork but also lignocellulosic, can be submitted to microwave radiations in order to destroy insects, parasites or their larvae. Moreover, the international patent no. WO03002923, describes the use of microwave radiation for fast wood drying, increasing additionally its permeability. In that case, the use of microwaves radiation is applied for wood cleaning, so its scope is not within the present application.

Microwave radiations are also used to cure polymers such as latex, as described in the Spanish patent no. ES2019514, or to cure resins for the production of wood derivatives, as described in the international patent no. WO9823132. Again, the scope of these inventions is different from the present application.

Concerning the cork material obtained by the process herein, it is also important to emphasize the volumetric increase effect observed on the specific weight.

Microscopically, cork can be described as a homogeneous tissue of thin cells, without space between them, and an alveolar structure similar to a honeycomb. The cork cells show diverse shapes depending if observed on the radial direction (Figure 1) or in a perpendicular direction to radial, i.e., axial or tangential (Figure 2) .

The closed structure of cork cells and the presence of air inside determine the low specific weight of cork, as well as some of its mechanical properties. The specific weight of cork might however show a significant variability, between 120kg.rtf ³ and 240kg.irf ³ , as described by M. Fortes in the Boletim do Instituto dos Produtos Florestais - Cortiςa, 1988, pages 65-68. This variability is essentially related to the cell dimensions (height and thickness of wall), corrugation of cell walls and quantity of lenticels. It should be emphasized that lower values of cork specific weight represent higher economical value.

Given the mathematical relation between volume and specific weight (inversely proportional), the volumetric increase (in the three spatial directions) observed in samples submitted to microwave treatment, and with maintenance of the initial mass, represents the gain achieved by this process in the cork specific weight.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention description is supported by: - Figure 1 and Figure 2, which show a scheme of the radial and axial/tangential directions of cork cells, respectively.

- Figure 3, which shows a table with the operational conditions and the expansion results of cork samples by submission to microwave radiation, after humidification by water immersion.

- Figure 4, which shows a table with the operational conditions and the expansion results of cork samples by submission to microwave radiation, after humidification in autoclave.

DETAILED DESCRIPTION OF THE INVENTION

The present application describes a process capable of promoting cork expansion without using external substances to the cork system. Subsequently, the produced cork might be submitted to standard cork industrial processes.

This process can be used in continuous or non-continuous mode and has three stages, the first stage being the dosing of the material, followed by the expansion stage, and finally the discharge stage or preferably cooling and discharge.

In the case of a continuous process for cork expansion by submission to microwave radiation, the dosing stage intends to feed continuously and over time the expansion zone and can be done using a feeding endless screw or a conveyor. The expansion stage should ensure the contact of the product to the action of the microwave radiation by a conveyor or dielectric containers such as for example, fibber glass, wood, plywood, among others. The radiation power should range between 200 watt and 1000 watt, preferably between 400 watt and 800 watt. The exposure time to the microwave radiation should be between 10 seconds and 5 minutes, preferably between 15 seconds and 2 minutes or even more preferably between 15 seconds and 50 seconds. The collecting stage could be performed using an endless screw that might have a sealant "lock", a manual or electropneumatic plate valve or a conveyor. During the expansion, process by submission to microwave radiation the presence of moisture is

crucial for the expansion to occur. The samples should have a humidity higher than 5%, which can be achieved by immersion in water at temperature ranging between 25 ⁰ C and 100 °C or by autoclave at temperatures between 100 °C and 150 °C.

In the case of a non-continuous process for cork expansion by submission to microwave radiation, the dosing stage aims to feed the microwave chamber and can be performed using a feeding endless screw that may have a dosing sealant "lock" or a manual or electropneumatic plate valve or a conveyor. The cork expansion stage will occur inside a closed chamber made of a dielectric material such as, for example, glass fibber, wood, plywood, among others. The radiation power should range between 200 watt and 1000 watt, preferably between 400 watt and 800 watt. The exposure time to the microwave radiation should be between 10 seconds and 5 minutes, preferably between 15 seconds and 2 minutes or even more preferably between 15 seconds and 50 seconds. The expansion stage by submission to microwave radiation can be performed in one or more cycles. When performed on several cycles, this number might range between 2 and 15, preferably between 2 and 5. The time period of each of these cycles could range between 2 seconds and 15 minutes, preferably between 2 seconds and 1 minute. The product collecting stage in the non-continuous process for cork expansion by submission to microwave radiation can be performed using an endless screw that may have a sealant "lock" or a manual or electropneumatic plate valve or a conveyor. During the expansion, process by submission to microwave radiation the presence of moisture is crucial for the expansion to occur.

Product resulting from the pre-expansion. process

The present application seeks to demonstrate the increase of the cork dimensions and consequently the decrease of its specific weight after submission to microwave radiation.

The cork can be submitted to this pre-expansion process independently of its shape, origin, quality or pre-treatments already performed, namely, falca cork, virgin or reproduction cork, cork planks, cork residues (resulting from stopper production or cork plank transformation) , grinded cork, granulated cork or cork powder, any of them boiled or not boiled.

The increase on cork dimensions, after being submitted to microwave radiations with controlled moisture, has two effects: promotes a yield increase of the material, i.e., less material used for the same application; and promotes an increase of the material quality, due to the reduction in specific weight. These two aspects represent commercial benefit.

RESULTS

The submission of cork to a pre-expansion process by microwave radiation for time periods between 5 seconds and 5 minutes, results in expansion of the initial material between 40% and 85%. During this process, no expansion in samples with less than 5% of humidity was observed.

The cork material such as falca cork, virgin or reproduction cork, cork planks, cork residues (resulting from stopper production or cork plank transformation) , grinded cork,

granulated cork or cork powder, any of them boiled or not boiled, shows an increase on its dimensions between 40% and 85%, when submitted to a pre-expansion process by submission to microwave radiation such as above described. This fact implies the reduction of its specific weight. It should be emphasized that in addition to the increase on the material yield (higher volume of cork after the treatment) , the cork with lower specific weight presents higher economical value.

Application examples of the pre-expansion process and respective results are presented herein below:

- Example 1 : Cork expansion by submission to microwave radiation.

Cubic shaped cork samples were submitted to microwave radiation with 550 watt power. One group of samples was exposed for 25 seconds whereas another group was exposed to five cycles of 5 seconds each. The observed expansions were, respectively, 48% and 46%, emphasizing the importance of the exposure time and not the operation mode (continuous or several cycles) .

- Example 2 : Cork expansion with different humidity by submission to microwave radiation.

Cubic shaped cork samples were submitted to microwave radiation with 550 watt power. A group of samples with 1.4% of humidity presented, after treatment, a volumetric expansion of

0.6%. Another group of samples with 7-10% of humidity presented, after treatment, a volumetric expansion of 40-45%.

This example emphasizes the importance of moisture in the samples for the expansion to occur.

- Example 3 ; Cork expansion by submission to microwave radiation after humidification by water immersion.

Cubic shaped cork samples were submitted to microwave radiation, after immersion in water at different temperatures and for different time periods. The results of the expansion and the detailed conditions are presented in Figure 3. Besides showing the microwave radiation effect on the volumetric increase of cork samples, expansion between 40% and 65%, these results allow to conclude that humidification by immersion in water is a possible method to be used, the immersion water temperature having a positive effect on the cork volumetric expansion.

- Example 4 : Cork expansion by submission to microwave radiation after autoclave humidification

Samples of virgin and amadia cork, with cubic shape, were submitted to microwave radiation, after autoclave humidification for different time periods. The results of the expansion and the detailed conditions are presented in the table of Figure 4. In addition of showing the effect of microwave radiation in cork volumetric increase, these results of expansion between 40% and 85%, make possible to conclude that the humidification in autoclave is a possible method to adopt, the virgin cork showing higher values of expansion when compared with amadia cork.

The process of cork pre-expansion by submission to microwave radiation and resulting products described above can be subjected to many modifications and variations performed by a person skilled in the art in order to adjust to specific requirements, which are within the scope of the present invention, as defined by the following claims.