PROCESS OF RECYCLING LEATHER RESIDUES AND PRODUCTION OF COMPOSITE MATERIALS

Abstract: This invention refers to a treatment and recycling method of leather residues, rejected by tanneries and shoe industries, and its use in the production of composite materials. The process is as follows: shredding of leather residues, gluing them together with resin and catalysers, then the blend obtained is pressed in moulds of various shapes. The blend can be pressed between metallic moulds and/or directly on sublayers to form plywoods. The resulting product has a fine aspect and there is no need for finishing touches. The process can be used in the production of materials with appropriate characteristics to be applied in several industries, such as furniture, civil architecture and car industries, taking advantage of its esthetical quality, soundproof and heat insulation properties.

Description: DESCRIPTION ' PROCESS OF RECYCLING LEATHER RESIDUES AND PRODUCTION OF COMPOSITE MATERIALS.' 1. OBJECT OF THE INVENTION This invention refers to a process of recycling leather residues and production of composite materials. 2.1. BACKGROUND OF THE INVENTION The notion of sustained development requires a judicious use of all the available resources, including by-products and residues from industrial activities. The costs generated by residues management can be minimized by recycling and taking advantage of these materials. Providing them with a positive and functional value is also a way of substituting raw materials, and therefore, a way of preserving natural resources. The recycling is, then, an important target that should be adopted by modern societies as a way of minimizing substantial flux of pollutants and promoting the Environment protection. 2.2. SCOPE OF THE INVENTION Shoes are made of various natural and synthetical materials which lead to the production of a great amount of residues. Leather is one of the materials more frequently used in shoe industry and in the production of any of its parts : (i) insteps - the upper front part of the shoe; (ii) lining and final insole - the inner of the shoe; (iii) sole - the under part in contact with the ground. The process of shoe production requires a series of operations in which leather (especially chrome tannage leather) is cut and sewed. The insteps and the soles are then assembled, shaped, glued together and pressed, ending the process by finishing touches and packing the product. TABLE 1 shows a generic scheme of the process of fabrication. As it is indicated in the scheme, the main sources of wastes in this industry are the cutting operations of insteps and linings. Other solid residues of chrome tannage leather come from tanneries and other leather products. 2.3. CHARACTERIZING THE SITUATION IN PORTUGAL Portugal is the third great shoe exporter in Europe. The shoe industry in Portugal is characterized by a strong implantation in certain regions of the Country, such as Sao Joao da Madeira and Felgueiras. The volume of residues produced is very high and its strong geographical concentration represents a danger for the ecosystem which demands an urgent action. An evaluation has been done based on an average quantity of wastes, in grammes/pair, indicating that, only in the shoe industry, about 10,000 tones of leather residues are produced each year (1). This value is certainly being under evaluated. In fact, the 'Jornal de Notfcias' (Portuguese newspaper) from 17/05/96 (2) reports that, about 45 to 50 tones of wastes from the shoe industry are discharged in the municipal garbage collector of Felgueiras, exclusively built for that purpose. According to the same source, this quantity does not represent the totality of wastes produced. In fact, about 20 tones are furtively discharged every day in the mountains, or along the roads. 2.4. TECHNICAL SITUATION OF THE LEATHER PRODUCTION PROCESS The technology of tanneries consists in a series of physicochemical and mechanical operations applied throughout the productive process aiming at transforming hides/skins of several animal species, in a lasting product resisting to decay, with a series of proprieties that makes the synthetical fibres esthetically attractive and advantageous as for quality, leading to a privileged acceptance of the product in the market. This objective is normally reached by the treatment of hides/skins through one of the two tanning processes (3) : 1. Vegetable tanning process 2. Mineral tanning process Both tanning processes seek to stabilize the fibres of the hides/skins through the formation of physicochemical bonds, in a way to make them durable and reinforce their physical and texture proprieties . The crucial difference lies in the nature of the tanning agents. 2.4.1. VEGETABLE TANNING PROCESS The vegetable tanning agents are extracted from plants and leaves and consist of large polyphenol molecules with some acid groups (ionizable) and other polar groups capable of forming dipole H-bonds. (3) The acid groups may combine with the basic groups of the skin/hide protein, displacing the hydrated water ; in the same way, the numerous polar groups combine to the polar groups of protein, displacing their hydrated water. On drying, the presence of these large molecules will create some mechanical impedance to the fibres shrinking together and will obstruct the formation of cross-links between the protein molecules. This will give to the dried hide/skin the desired softness and flexibility. These proprieties can be varied according to the type and quantity of used tanning agents (4). The vegetable tanning leather residues do not represent a serious danger to the environment as : (i) they represent a ratio not so important of the total of the processed leathers; (ii) the tanning agents are natural. 2.4.2. MINERAL TANNING PROCESS The tanning agents used in the mineral tannage are the basic chrome, zirconium and alum salts. At a low pH, the alum salts have a best affinity with the skin/hide than with the chrome salts (4). Then they can be incorporated to chrome baths in order to create a light tanning in the former stages. However, while the pH increases, the bond between the alum and the skin/hide protein becomes weaker than in the case of the chrome and the degree of stabilization achieved is not enough to produce alum-tanned leather, being necessary to add hydroxylic acid salts such as tartrate and sodium citrate to obtain a more durable tannage. Zirconium can be used as a tanning agent to produce a zirconium-tanned leather. However, the high acidity of the zirconium salts and their high cost, limit the acceptance of the product in the market. The zirconium and alum salts are white and are used to produce white leathers. (4) The chrome tannage is the more efficient process to obtain high quality leathers, and the most widely used. The chromium salts in solution hydrolyze and form stable compounds which react with the protein carboxylic groups. While the pH of the tannage bath increases, the proportion of chrome is being fixed. The bonds between chrome and sulphate are partially displaced by hydroxyl groups. After drying, tannage becomes stable and release three hydrogen ions (3-4). The great disadvantage of chrome tannage is the high degree of pollution of the ions released by this metal. The pollution risks start with the discharges of the exhausted tannage baths and go on with the rejection of leather residues in oxydizing conditions. For instance, acid soils with high degree of magnesium promote these reactions (1). The tolerance of Cr (III) does not seem to offer great controversy. On the contrary, the danger of Cr (VI) is considered as being very high, being capable of causing carcinogenic effects even in very low concentrations. Then, the discharge of the leather residues represents an environmental risk which should not be ignored and must be prevented (1 ,4-6). 2.5. RECYCLING METHODS FORMELY PROPOSED Up to now, the proposed methods for the recycling of leather residues are the following (1 ,7-12) : 1. Obtention of collagen ; 2. Transformation in fertilizers and rations ; 3. Production of energy through biomethanization ; 4. Production of energy and chrome through controlled combustion. The two first methods are obviously inadequate to chrome tanning leather recycling, as the transformed products must contain substantial concentrations of this contaminant agent. The production of energy through methanization, although technically possible, cannot absorb the large quantity of produced residues (1). Up to now, the incineration has been the most researched process (7-12). The main reasons leading to these studies is the fact that residues have been increasing along with the lack of energetic resources and raw materials. The most attractive aspects are (1) : 1. the high calorific power (4,500-5,000 Kcal/Kg) ; 2. the low proportion in sulphur (<2%) ; 3. the resulting ashes are almost in the whole composed of chrome oxide. However, the possibility of formation and emission of toxic substances (7-9), such as the dioxins, with demonstrated carcinogenic effects in animals (13), and Cr (VI) (4-6,14) during the combustion, has brought up a strong controversy between the supporters of this solution. Due to the harmful effects of incineration, it has been difficult to adopt this method to take advantage of the leather residues. 3. NEW PROCESS OF RECYCLING LEATHER RESIDUES : PRODUCTION OF COMPOSITE MATERIALS. This Invention refers to a new method of recycling leather residues and its transformation in useful products, of high quality, with mechanical and esthetical proprieties capable of competing with other natural or synthetic materials in civil architecture, furniture and decoration, car industry, etc. The method involves a first stage of shredding (removal of the fibres) the residues in order to obtain leather fibres, using mechanical processes similar to the ones used in the wood milling in the industry of plywoods (15). In the second stage the leather fibres are impregnated, by means of a gluing system, with aminoplastic resins (16-17) and an adequate catalyser, blended in proportions that can vary between 2 to 25% of the catalyser. The consolidation of the impregnated fibres is made in a third stage through the application of pressure and heat simultaneously. The ratio in weight of resins in the blend (leather fibre + resins) can vary between 10 to 75%, according to the density and the mechanical proprieties and the desired esthetical quality. Percentages of resins between 30 to 40% represent a good compromise. The blend of the two components (leather fibre + resins) can be made either through various technics, for instance, spraying resin from a gun on a fibre doser, or on fibres kept in movement by means of mechanical agitators or a compressed air system, or even through vacuum technics. Some of these gluing processes are described in the literature (15). The cycle of heat pressing is made at intervals of time, pressure and temperature between 1 to 10 minutes, between 1 to 20 MPa, and between 50 to 200 °C, respectively, according to the density, the aspect and the mechanical properties required for the composite materials. The best compromise was found in the following experimental conditions: Temperature = 100 °C ; Pressure of 12 MPa applied for 3 minutes, partial low pressure for a pressure of 2 MPa, which is maintained for 1 minute, followed by a pressure release. Pressing can be made between metallic moulds and/or directly on sublayers, to form plywoods. The surface of the produced materials acquires a fine aspect and there is no need for finishing touches. 4. REFERENCES 1. Almeida, M.F., Ferreira, M.J., "Alguns Aspectos da incineracao de Resfduos de Couro Curtidos ao Crόmio, Actas da 5 a Conferencia Nacional sobre a Qualidade do Ambiente, Vol. 2, pp 1155-1164, Ed. C. Borrego, C. Coelho, L. Arroja, C. Boia e E. Figueiredo, (1996). 2. Cachada, A., "Felgueiras, Aterro Sanitario Tratara Resi ' duos do Calcado, Concelho produz entre 60 a 70 toneladas diarias de desperdfcios desta indύstria", Jornal de Noticias de 17 de Maio de 1996. 3. Bienkiewicz, Physical Chemistry of Leather Manufacture. Kriger, Florida 32901 (1982. 4. Sharphouse, J.H., Leather Technician's Handbook, Leather Producers' Association, Revised Edition (1983). 5. Nazario, C.L. e Menden, E.E., "Comparative study of the Analytical Methods for Hexavalent Chromium, Jalca, 85 212-222 (1990). 6. Leander, V., "Ecological Procedure to Solve the Tannery Waste Problems", J. Am. Leather Chem. Assoc, 88, 326-329 (1993). 7. Aloy, M. "L'incineration des Deches de la Fabrication du Cuir", Tecnicuir, 18 46-51 (1984). 8. Tomaselli, M. E, Mora, R., "II Potere Caloπ'fico delle Pelli e Residui Conciari", Cuoio Pelli Mat. Concianti, 68 73-78 (1992). 9. Carvalho, F.M., "A Incineracao de Resi ' duos", Sector Couro, Marco, 44- 47 (1994). 10. Imai, T., Okamura, H., "Studies on Incineration of Chrome Leather Waste", J. Am. Leather Chem. Assoc, 88, 281-294 (1993). 11. Oterro, J., Cabanillas, A., Origiles, C, Martinez, M.A., e Ferrer J., "Recuperation de Cromo y Energia a partir de Resi ' duos de Piel Curtida", Medio Ambiente, 8 5-10 (1995). 12. Almeida, M.F., Ferreira, J.M. e Sousa, M.C. "Incineracao de Aparas de Couro da Indύstria do Calcado, Extraccao de Crόmio e/ou Inertizacao das Cinzas", Anais do 7° Encontro Nacional da Sociedade Portuguesa de Materiais, Vol. 2, pp 296-303, Ed. Ana M. Segadaes, Aveiro (1995). 13. Savostianoff, "Dioxines et Fantasmes", Information Chimie, n° 362, Octobre, pp 3,61 (1994). 14. Ficretti, F. Gavend, C. E Vulliermet, B., "Les Economies d'Energie en Tannerie- Megisserie", Tecnicuir, 14 18-36 (1981). 15. Maloney, T.M., "Modern Particleboard & Dry-Process Fiberboard Manufacturing", Updated Edition, Miller Freeman, Inc., Book Division, San Francisco, California, USA, (1993). 16. Pizzi, A. "Wood Adhesives, Chemistry and Tecnology", Vol. 1 , Chapters 2 and 3, Marcel Dekker, Inc., New York, (1983). 17. Pizzi, A. "Wood Adhesives, Chemistry and Tecnology", Vol. 2, Chapters 4 and 5, Marcel Dekker, Inc., New York, (1983).

Claims: CLAIMS °. PROCESS OF RECYCLING LEATHER RESIDUES AND PRODUCTION OF COMPOSITE MATERIALS characterized by : - first stage of shredding residues leading to the obtention of leather fibres, - second stage of impregnating leather fibre with a gluing system, and - third stage of consolidating the impregnated fibres through the application of pressure and heat. PROCESS OF RECYCLING LEATHER RESIDUES AND PRODUCTION OF COMPOSITE MATERIALS, according to the claim 1 , charaterized by a gluing system made of aminoplastic resins and an adequate catalyser blended in proportions which can vary between 2 to 25% of the catalyser. °. PROCESS OF RECYCLING LEATHER RESIDUES AND PRODUCTION OF COMPOSITE MATERIALS, according to the claims 1 and 2, characterized by a ratio in weight of resins in the blend (leather fibre + resins) that can vary between 10 to 75%, and the blend of the two components can be made either by gun-spraying on fibres dosers, or fibres kept in movement by means of mechanical agitators or compressed air system, or through vacuum technics. PROCESS OF RECYCLING LEATHER RESIDUES AND PRODUCTION OF COMPOSITE MATERIALS, according to the claims 1 to 3, characterized by a cycle of heat pressing has to be made at intervals of time, pressure and temperature, between 1 to 10 minutes, between 1 and 20 MPa, and between 50 and 200 °C, respectively.

Inventors: DA FONTE FERREIRA JOSE MARIA, PINHO DE ALMEIDA FERNANDO JORG, DA FONTE FERREIRA, JOSE, MARIA, PINHO DE ALMEIDA, FERNANDO, JORGE
Applicants: DA FONTE FERREIRA JOSE MARIA, PINHO DE ALMEIDA FERNANDO JORG, UNIV AVEIRO, DA FONTE FERREIRA, JOSE, MARIA, PINHO DE ALMEIDA, FERNANDO, JORGE, UNIVERSIDADE DE AVEIRO
Application year: 1997
Main classification: C08L89
IPC codes: C08L89