PROCESS OF CORK EXPANSION WITH ENVIRONMENTALLY INNOCUOUS

COMPOUNDS

1. Field of the invention

The present invention relates to the thermocheraical process of cork expansion with the use of environmentally innocuous compounds which are organic, have reduced reactivity and polarity and are innocuous to the environment and to public safety and health. The process can be performed in a continuous mode and allows for the expanded cork to maintain some porosity, due to its anatomical structure, enabling airflow through cells under pressure, which is desirable when the material is under compression conditions.

The cork intended to be expanded is mainly the one which is inadequate for the production of stoppers, such as cork resulting from residues, either industrial or from operations involving the exploitation of cork oak as well as overly porous cork and cork with anatomic defects. The resulting expanded cork can then be used, for instance, in the production of composed stoppers, parquet, thermal and acoustic insulation, expansion- compression joints, and blocks of cork agglomerate.

2. Description of tlie Related Art

The main industrially manufactured product of expanded cork, resulting from the prior art related to the present invention, is the black agglomerate, which originates from a volumetric expansion of cork of about 30%. The manufacturing of the black agglomerate is carried out at a temperature of about 300°C, which results in intense alterations of the cork in terms of degradation and decomposition, as well as quality and quantity losses. The result of its degradation is the blackening of the product due to strong carbonization,, loss of cork's beauty and natural colour; and the result of its decomposition is the destruction by pyrolysis of about 30% of the cork's mass used in the process and the release of toxic gases.

The Portuguese Patent n° 101215, which relates to the expansion of cork, approaches and develops an invention regarding thermochemical treatments, carried out under pressure, of virgin cork (cork from the first harvest), "secundeiras" (cork from the second harvest) , and "amadias" (cork from the subsequent harvests, which has better quality) , its pieces and granulates, originated from the stripping or manufacturing, elements that, in the presence of a mixture of methanol and dichloromethane, allow for the attainment of an expansion with values in the order of 150% to 200%, without carbonization or beauty and natural colour losses. Nevertheless, the compounds used, methanol and dichloromethane, present serious incompatibilities with the environment and public safety and health. The process is similar to the expansion of synthetic polymers, such as polyurethane, equally characterized by the imposition of compressaon and decompression cycles, allowing for the attainment of foam with good thermal insulation qualities, which result from the low thermal conductivity of gas, generally air, contained inside the cells. In the case of cork, the possibility of maintaining the' physical and mechanical characteristics of the raw material, after expansion, presents the advantage of maintaining the elasticity and flexibility of the product in static load conditions.

3. Detailed description of the invention

The present invention relates to the thermochemical process of cork expansion with the use of environmentally innocuous compounds, under compression conditions, followed by rapid decompression, with the use of liquid organic compounds which have reduced reactivity and polarity and are innocuous to the environment and to public health. The advantages of this process over existing solutions are the following: 3.1 Environmental advantages

The process described in the present invention allows for the expansion of cork with the use of innocuous compounds, which do not present incompatibilities with the environment and public safety and health.

3.2 Technological advantages

The process allows for the attainment of expanded cork without the loss of its beauty and natural colours and without significant changes in its elastic properties or in its molecular structure, with the improvement of its thermal insulation characteristics. Thus, the process allows cork, that is inadequate for the production of natural stoppers, to be used in the production of, for instance, composed stoppers, parquet, thermal and acoustic insulation and expansion-compression joints .

4. Description of the method

4.1 Technical basis of the process

The invention relates to the development of the process of cork expansion on a pilot scale, according to a. closed-cell model which is similar to the thermochemical method of production of expanded synthetic polymers, based on the chemical behaviour of cork's structural polymeric components, suberin and lignin, for the development and optimization of an alternative process and for more efficient cork expansion.

The expansion process is based on the penetration of reagents in the interior of cork's cell walls, and is performed in a reactor, under pressure conditions in the order of 5 to 20 bar (1 bar = kN/m ² ) and temperatures in the order of 130. to 210ºC, for periods, of 20 to 60 minutes, followed by decompression and cooling for the period of 1 minute. A higher maximum pressure value inside the reactor, under temperatures ranging from 130 to 180°C, which do not cause alterations in the structure of the cork, will naturally constitute a contributing factor for greater expansion of the raw material after sudden decompression.

In the conditions described above, the reagents will act through hydrolysis mechanisms and through the break of esterlike bonds between the molecules that constitute cork, lignin and suberin. The reagents will also lead to a partial break in the phenyl-propanoic bonds of the lignin, through an electrophilic attack, causing a decrease in rigidity and an increase in the plasticity of this polymer, thus allowing for the accommodation of a potential expansion of cork between 20% and 200% and preventing the recovery of the initial volume. The application of an alkaline catalyst facilitates the dynamics of the above mentioned hydrolysis reactions.

The reagents to be used are organic compounds with small dimension molecules, i.e., with one to three carbon atoms, with reduced reactivity and polarity, without incompatibilities with the environment and public safety and health, able to be used in current consumer products, which must be in accordance with the provisions of Decree-Law n° 304/98, of 7 October. This Decree- Law, in what concerns extraction solvents, establishes which solvents are allowed in the preparation of food and other food ingredients, having been adopted a fortiori in this case.

The reduced number of carbon atoms is a necessary condition for a better penetration of the gaseous molecules, under pressure, in the molecular structure of the cork. In the present invention, the use of the mentioned organic compounds was tested at a concentration of 99%, without environmental restrictions and with a low risk to public health, such as: 2-propanol, ethanol, methyl acetate, ethyl acetate, ethyl formate and acetic acid. The selection of these - compounds was made considering their reduced number of carbon atoms (one to three) , their low molecular weight and their physical characteristics, such as high vapour pressures, low temperature of ebullition and higher solubility in water (Table 1) . For the catalysis of the hydrolysis, reactions, an aqueous solution of sodium hydroxide was used- The determination of the volumetric expansion of the cork, in granulates, was performed through sieving for half an hour and through the determination of the equivalent diameter using the Sauter mean diameter.

4.2 Experimental description

The cork to be expanded was used in the form of granulates with average diameter dimensions of 2 to 4 mm. The type of cork was "amadia" and the reagents used had 99% purity.

In order to promote the expansion of the cork, the cork and the reagents were initially introduced in the reactor (B) . Then, the compressor (A) was turned on, and when the pressure reached approximately 2 bar, the lower valve of the reactor was opened to allow for the increase of pressure in the interior of the reactor, until the pressure required for the test was reached, with values potentially ranging from 5 to 20 bar. When that pressure was reached, the compressor was turned off, the lower valve of the reactor was closed and the reactor heating was turned on for 20 to 60 minutes. After the end of this stage, the heating was turned off and the rapid decompression of the reactor was performed through a valve located on its top, the expanded cork having been collected at the reactor sleeve or at the collection vessel (C) .

The determination of the volumetric expansion of the cork wasperformed through sieving for half an hour and through the calculation of the Sauter mean diameter, through equations (1), and (2) : In equation (1) , Δwi is the mass fraction retained in each sieve (sieve i) , D _i is the diameter attributed to the particles retained in the sieve and D _P is the equivalent diameter. In equation (2), the expansion, E, is given by the variation of the equivalent diameter, from its initial value, ₍ before

expansion) , to its final value, (after expansion) .

In the later mentioned results, the values of expansion, E, are presented in percentages.

4.3 Selection of the compounds to be used

The main properties of the reagents used are described Table 1, below which the meanings of the abbreviations used indicated.

MW: molar mass; temperature of ebullition; ΔΗ _ν (T _ab ) : enthalpy of vaporization (at the ebullition point); P _v : vapour pressure; μ: viscosity. Values refer to solubility in water.

From Table 1, one can verify that the most adequate combination of the properties is methyl acetate's, in terms of: relatively low molecular weight (74.8); high vapour pressure (0.214 bar); low temperature of ebullition (56.9°C); and higher solubility in water at 20°C (250 g/L) in comparison with the other compounds of the same type, ethyl acetate and ethyl formate .

4.4 Examples of representative application tests In the tests performed, ratio r defined as

was varied between V, reagent's volume (mL) , and p, cork's mass (g) .

Example 1 — Cork expansion in a solution with methyl acetate

A sample of 14.9 g of cork granulate, with 2 to 4 mm of diameter, dried in an industrial heater, was dispersed in 30 mL of an aqueous solution with a 2 g/L sodium hydroxide concentration. 130 mL of methyl acetate (with 99% concentration) were added to this dispersion, which was then placed in the reactor (B) , and subjected to a temperature of 160°C, through electric heating. The compressor (A) was then turned on and, when the pressure reached 2 bar, the lower valve of the reactor was opened to allow for the increase of pressure inside it, through a hose between the compressor (A) and the above- mentioned valve, until the pressure of 8.5 bar, intended for the test, was reached. Ratio r was 10.7. The test, under the mentioned pressure and temperature conditions, was performed for 40 minutes, after which the top lid of the reactor was opened and the consequent decompression occurred and the granules were removed.

Another sample of 20 g of cork granulate, with 2 to 4 mm of diameter, was dispersed in 30 mL of an aqueous solution with a 2 g/L sodium hydroxide concentration. 80mL of methyl acetate (with 99% concentration) were added to this dispersion, while the remaining experimental conditions, in the reactor, were the same as the conditions described in the previous test. Ratio r was 5.5.

Another sample of 19.4 g of cork granulate, with 2 to 4 mm of diameter, was dispersed in 50 mL of an aqueous solution with a 2 g/L sodium hydroxide concentration. 50mL of methyl acetate (with 99% concentration) were added to this dispersion, while the remaining experimental conditions, in the reactor, were the same as the conditions described in the previous tests. Ratio r was 5.1.

The expansions obtained were 41.2%, 33.0% and 30.6%, respectively.

Example 2 — Cork expansion in a solution with ethyl acetate

A sample of 27.4 g of cork granulate, with 2 to 4 mm of diameter, dried in an industrial heater, was dispersed in 50 mL of an aqueous solution with a 2 g/L sodium hydroxide concentration. 50mL of ethyl acetate (with 99% concentration) were added to this dispersion, which was then placed in the reactor (B) , while the remaining experimental conditions, in the reactor, were the same as the conditions described in the previous example. Ratio r was 3.65.

Another sample of 27.1 g of cork granulate was dissolved in

30mL of an aqueous solution with a 2 g/L sodium hydroxide concentration, 80 mL of ethyl acetate (with 99% concentration) were added to this dispersion. Ratio r was 4.07. The mixture of cork and reagents was then placed in the interior of the reactor (B) , subjected to a temperature of 160°C, through electric heating, under a pressure of 8· bar and the same experimental conditions in terms of temperature and duration of the test as the ones described in the previous example .

Another sample of 23.4 g of cork granulate was dissolved in 30mL of an aqueous solution with a 2 g/L sodium hydroxide concentration. 130 mL of ethyl acetate (with 99% concentration) were added to this dispersion. Ratio r was 6.83. The dispersion was then introduced in the interior of the reactor (B) , subjected to experimental conditions of pressure of 8 bar and the same average temperature and duration conditions as the ones described in example 1.

The expansions obtained were 22.8%, 26.0% and 17.3%, respectively. Example 3 — Cork expansion with previous pressurization

A sample of 12.7 g of cork granulate, with 2 to 4 mm of diameter, dried in an industrial heater, was dispersed in 200 mL of an aqueous solution with a 1 g/L sodium hydroxide concentration. The mixture of the sodium hydroxide solution with the cork granulate was submitted to two previous successive heating cycles, with and without pressure, for 30 and 60 minutes, respectively. For the 30-minute cycle with pressure, the compressor (A) was turned on until a pressure of 5 bar was reached and the lower valve of the reactor (B) was opened to allow for the increase of pressure through the hose referred to in Example 1. After that, the dispersion was subjected to a temperature of 160°C in the reactor for 60 minutes without additional pressure. After the performance of the two previous cycles, a volume of 250 mL of methyl acetate was added to the mixture of cork granulate and a new cycle with a pressure of 5 bar was. performed for 30 minutes without heating. Ratio r was 32 _* 5 _*

Another sample of 22.7 g of cork granulate was dissolved in 250 mL of an aqueous solution with a 1.5 g/L sodium hydroxide concentration. The dispersion was placed in the reactor and subjected to a previous compression cycle at a pressure of 5 bar for 30 minutes, without heating. After this pre-compression, a volume of 300 mL of methyl acetate (with 99% concentration) was added to the dispersion and the mixture obtained was subjected to two operating cycles. In the first cycle, the experimental conditions included a pressure of 5 bar and a duration of 30 minutes without heating. After that, a heating cycle, at a temperature of 160°C was performed for 30 minutes, at atmospheric pressure. Ratio r was 24.2.

Another sample of 20.7 g of cork granulate was dispersed in 250 mL of an aqueous solution with a 1.5 g/L sodium hydroxide concentration. The mixture was subjected to a previous compression cycle at a pressure of 5 bar, at a temperature of

160°C, for 180 minutes. After this pre-compression a volume of 150 mL of ethyl acetate (with 99% concentration) was added to the dispersion and the dispersion obtained was subjected to two operating cycles. In the first cycle, the experimental conditions included a pressure of 5 bar and a duration of 30 minutes without heating. After that, a heating cycle, at a temperature of 160°C, was performed for 30 minutes, at atmospheric pressure. Ratio r was 19.4.

Another sample of 9.6 g of cork was dissolved in 200 mL of an aqueous solution with a 1.5 g/L sodium hydroxide concentration. The dispersion was subjected to a previous compression cycle at a pressure of 5 bar for 30 minutes without heating. After this pre-compression, a volume of 250 mL of ethyl acetate (with 99% concentration) was added to the dispersion and the dispersion obtained was subjected to two operating cycles. In the first cycle, the experimental conditions included a pressure of 6 bar and a duration of 30 minutes without heating. After that, a heating cycle, at a temperature of 160 °C, was performed for 30 minutes, at atmospheric pressure. Ratio r was 47.0.

The expansions obtained in these four tests were 27.5%, 21.3%, 23.0% and 21.5%, respectively.

Date: November 24th, 2010.