ALAMPI, Cosimo (Via C. Alvaro n°20, Soverato, I-88068, IT)
CERCHIARA, Teresa (Via Variante n°19, Montauro, I-88060, IT)
GABRIELE, Bartolo (Via G. Verdi n°2, Rende, I-87036, IT)
SALERNO, Giuseppe (Via Repaci 37, Rende, I-87036, IT)
VETERE, Mabel, Valeria (Via Piazza n°41, Sartano di Torano Castello, I-87010, IT)
CHIDICHIMO, Giuseppe (Via Giulio Cesare n°1, Rende, I-87036, IT)
ALAMPI, Cosimo (Via C. Alvaro n°20, Soverato, I-88068, IT)
CERCHIARA, Teresa (Via Variante n°19, Montauro, I-88060, IT)
GABRIELE, Bartolo (Via G. Verdi n°2, Rende, I-87036, IT)
SALERNO, Giuseppe (Via Repaci 37, Rende, I-87036, IT)
VETERE, Mabel, Valeria (Via Piazza n°41, Sartano di Torano Castello, I-87010, IT)
Claims
1. Chemical-physical process for the production of vegetable fibres, by the immersion of the vegetable varieties in a hot solution of alkali, followed by the removal of the excess water, characterised by the fact that said vegetable varieties, or the cellulose fibres extracted from them, are successively placed in autoclaves, exposed to hot air at a temperature of between 80°-120°C, pressures between 4-60 atmospheres for a period of between 0.5 and 4 hours, and that following this a valve is opened which permits the rapid exit of the hot air and, consequently, a rapid decompression inside the autoclave, producing the reduction of the diameter of the vegetable fibres to values in the order of about ten microns.
2. Chemical-physical process for the production of vegetable fibres according to claim 1, characterised by the fact that the alkali of the hot solution are NaOH or KOH.
3. Chemical -physical process for the production of vegetable fibres according to claim 2, characterised by the fact that the concentration of the alkali NaOH or KOH is of between 1% and 15%.
4. Chemical-physical process for the production of vegetable fibres according to any of the preceding claims, characterised by the fact that said cellulose fibres of vegetable plants are successively washed in water to eliminate the alkalinity.
5. Chemical -physical process for the production of vegetable fibres, according to the previous claim, characterised by the fact that the ligneous component is separated by mechanical action or by gradient of density.
6. Chemical-physical process for the production of vegetable fibres, according to claim 5, characterised by the fact that the fibre undergoes a softening process in one or more enzymatic digestion tubs, in which pectinolithic enzymes produced by micro-organisms and/or ligninolithic enzymes of the peroxide type are contained.
7. Chemical-physical process for the production of vegetable fibres according to claim 5, characterised by the fact that the fibre undergoes a process of mechanical softening during the course of which the fibre is passed through rotating rollers and combs.
8. Chemical-physical process for the production of vegetable fibres according to claim 5, characterised by the fact that the fibre undergoes a process of softening constituted by a process of digestion in hydrogen peroxide. |
Physical Chemical Process for Production of Vegetable Fibers
Technical Field
The present invention regards a physical chemical process for the production of vegetable fibers; that is for the extraction of the cellulose fibers contained in the Liberian vessels of plants with rapid reproductive cycles.
State of the Art
The extraction of the cellulose fibres container in the Liberian vessels of plants with rapid reproductive cycles, presents notable difficulties because of the fact that the fibrous bundles are, on the one hand, firmly bound to the external cortical tissues constituted by hydrophobic substances whose job it is to impede the penetration by and the loss of water from the plant, and on the other hand they are tightly interconnected between themselves by ligneous and pectic substances.
One thinks, for example, of spartium junceum (Spanish broom), whose sprigs are covered with a cortical cuticle constituted by long-chained alkenes, alcohols and esters. Many of the processes that have been used in the past for the production of fibre from this plant have found the greatest difficulty in removing the cortical cuticle. On the other hand, the Liberian vessels containing the fibres are strongly connected to the internal ligneous part by the pectic substances. The extraction of the cellulose fibres therefore implies:
- the separation of the external cuticle;
- the detaching of the fibres from the internal ligneous part;
- the cleansing of the fibres from a series of encrusting substances.
The natural Liberian fibres, although constituted by very high percentages of cellulose
(both in crystalline and amorphous forms), contain notable quantities of substances of biological origin that, although of great structural and metabolic importance inside the plant, deteriorate the quality of the fibres when these are to be used for industrial purposes. There are three principal classes of substance present in Liberian plants:
Cellulose
Encrusting substances.
The celluloses, on the basis of their behaviour with reactive chemicals, can be subdivided in α, β and γ-celluloses. The α-cellulose or noble cellulose, used as a textile fibre is a polymer with a high molecular weight, constituted by monomeric units of glucose. The β and γ-celluloses are polymers with a lower molecular weight in whose monomeric glucose units a primary alcohol group is substituted by a carboxyl (acid). These celluloses are more commonly known by the name of hemicelluloses. The encrusting substances are:
Pectic substances: we are dealing with polymers of galacturonic acid. In water they release colloidal solutions; they dissolve easily in diluted alkali. Enzymes and bacteria attach easily to them, making them soluble in water.
Lignins: these are thought to be polymers of the ethyl-phenolic group with a highly complex structure.
Resinous substances: they are amorphous substances, not soluble in water, present in small percentages in fibres such as cotton and linen, but in much greater percentages in resinous woods such as pine and fir. They are eliminated by treatment with organic acids which salify them, making them soluble.
Cutin: is a substance with an extremely complex chemical structure; in fact, it is an ester of some fatty acids with a very high molecular weight. It is soluble in warm alkali. Starch: this is also a polymer with the formula [CeH 10 Os] n , but, in contrast to the other sugars, the glucose molecules in it are linked in a different way; specifically it can be admitted that it is constituted by two different polysaccharides: amylose and amylopectin. Through partial hydrolysis of the starch a disaccharide is obtained, maltose, while with partial hydrolysis of the cellulose cellobiose is obtained. The rare use of the fibres of some vegetable varieties, potentially very interesting both because of some intrinsic characteristics (the length and strength of the fibres), and because of the ease of gathering the basic materials, is principally attributable to the use of methods of extraction that are strictly of the artisan-like kind that, besides being particularly labour intensive in terms of the workforce, necessitate production times that are unacceptable for modern industry.
Furthermore they produce a fibre that is not very fine, with a diameter that is not suitable for an automatic process of carding and spinning. Taking once again as a paragon the case of Spanish broom, none of the methods used to date for the extraction
of the cellulose fibres from other natural materials can be conveniently applied to this vegetable variety.
Here following we illustrate some of the already known procedures for the extraction of cellulose fibres from various plants such as cannabis, linen, jute, which in some cases present various types of difficulty: the slowness of the process, the ineffϊcacy in some cases to yield a fibre that is sufficiently soft or with an adequate diameter for use in the textile industry.
1.1 Chemical-Physical Processes
Alkaline Digestion
Among the chemical-physical processes to be considered are those which after a chemical-type treatment use mechanical-type treatments.
The chemical process is generally constituted by a digestion of the vegetable substance in an alkaline solution, which eats into not only the hemi-celluloses and the pectins that hold the fibrous bundles of the phloem, cohering between themselves and with the xylem, but also the macro-molecules that constitute the cuticle.
In this process the major part of the encrusting pectic substances and the hemi-cellulose substances are separated from the noble cellulose. The key to this treatment of chemical extraction is the capacity of the alkaline bath to react with diverse categories of molecule. The cortical layer is effectively dissolved through the basic hydrolysis of various components. The cutins and the waxes that make up the hydrophobic coating of the plant are molecules that contain groups of esters that are susceptible to saponification. The great structural polymers that contain carboxyl acid functionality, such as the pectins and the hemi-celluloses, are easily dissolved in the watery phase because they are salified through acid-based reactions.
This type of process is not, however, in itself sufficient to separate the cellulose fibrils into bundles with an adequate diameter for the successive use of the fibre in the textile industry without making recourse to further treatments.
The softness of the fibre, and the possibility that it can be used in textiles of quality, depends on the diameter of the elementary fibres that should, preferably, be of only a few microns. In reality it is impossible to obtain fibres of such a diameter from a simple process of the chemical kind when this last is not taken to extreme levels that can have an effect on the mechanical resistance of the cellulose fibres.
With the simple process of the chemical kind the fibre obtained is generally coarse (with diameters in the order of hundreds of microns), and cannot be used in textiles of good quality. It generally results as possible to improve the diameter of the fibres coming from a process of the chemical kind, through mechanical type processes, in which the fibres are refined by passing them through rollers or other mechanical grinding systems. Mechanical treatments are, however, difficult to standardize, so that the same type of machine cannot be applied to different vegetable varieties. Wet oxidation (1 *
Wet oxidation is another process that has been used for the production of cellulose fibre. The basic material, eventually previously ground or anyway reduced to fine pieces, is suspended in water enriched in oxygen at temperatures between 125° and 320° C and at pressures between 0.5 and 20 Mpa. This process does not appear to be convenient for the separation of Liberian fibres.
The energy consumption, that implicates the heating of the considerable quantities of water used at high pressure, and the equipment problems posed by the presence of excesses of oxygen in very elevated conditions of temperature and pressure, suggest the creation of alternative methods that implicate gentler processing conditions. Steam explosion®
Steam explosion is another process that could be utilised for the production of Liberian fibres. The material is exposed to the action of water vapour at elevated levels of pressure and temperature. After a certain period of exposure, the pressure of the vapour is abruptly lowered.
During the treatment the sample undergoes both chemical and mechanical modifications. The vapour can also be impregnated with chemical substances that favour hydrolytic processes. In this case the action of the separation of the fibrils caused by the rapid expansion of the vapour when the pressure is instantaneously lowered plays a fundamental role. The process is costly, however; because of the great quantities of energy that are needed to produce the high-pressured vapour. 1.2 Microbiological processes
The microbiological processes are those in which the basic material is retted in water in the presence of greater or lesser concentrations of bacteria that are capable of producing enzymatic substances that hydrolyse and/or break up the peptic substances and the encrusting lignins of the cellulose fibres.
The problem of microbiological retting for the extraction of the cellulose fibres, conducted by vegetable varieties of rapid growth, is complicated by the fact that the enzymes produced by funguses and bacteria that could be used to separate the lignins and the pectic substances are generally substances with high molecular weights and that are soluble in water.
A retting of a microbiological nature encounters, therefore, the obstacle of the external cuticle that is not attacked by the pectin and lignin enzymes. The results obtained from the retting of Spanish broom in an anaerobic process in the presence of Clostridium Felsineum, a bacterium that has demonstrated a good pectin (3) activity, are known. It has been seen that although the retting in the presence of Clostridium Felsineum accelerates the process, in such a way that the velocity of degradation of the pectic substances rises by a factor of about 2.5 with respect to that which is obtained in the presence of water only, treatment times in the order of several days remain and an efficient separation of the cuticle part is not obtained.
As a basic premise for the production of the fibre a series of treatments with pectin or lignin enzymes, which can be obtained from various species of bacteria of fungus, could be adapted.
The pectinolithic or pectinase enzymes are a heterogeneous group of enzymes that hydrolyze the pectic substances.
The pectinolithic enzymes can be divided into two great classes (4>:
1) Esterase: these favour the de-esterifϊcation of the methoxylic groups.
2) Depplymers: these catalyze the breakdown of the glucosidal bond through either liasis or hydrolase;
The Hydrolase enzymes of depolymerization break the glucosidal bridge, introducing water and generating two hydroxylic groups.
The liase or trans-eliminase brings about a non-hydrolitic separation, breaking the glucosidal link in C4 and simultaneously eliminating H from C5, producing an unsaturation between the positions 4-5.
The results obtained with reference to the extraction of linen fibres have evidenced the fact that the lignins are selectively degraded by two enzymes (5): peroxide lignin (LiP) and manganese peroxide (MnP) that belong to the glucose family of proteins. The enzyme MnP is produced in high quantities from the Basidiomycetes funguses
Phanerochaete crysosporum and Phanerochaete sp. The fibres themselves are a good substratum for the growth of the funguses and therefore for the production of the enzyme.
It must be stressed, however, that a process of retting conducted by vegetable species of rapid growth, whatever the treatment of a biological nature may be, will encounter the obstacle of the impermeability of the external cuticle, and as a result a very long process time (several days) to obtain fibres that are ready for the processes of carding and spinning.
The process object of the invention
The industrial process for the production of Liberian fibres presented hereafter has been created in such a way that the following characteristics have been respected:
• rapid production times, in the order of a few hours;
• low production costs;
• low environmental impact;
• versatility in the production of fibres with characteristics capable of being modulated.
Essentially the process combines, with a chemical stage of alkaline digestion, with times, that according to the concentration of the alkali, range from about ten minutes to a few hours, during which the fibrous part is separated both from the external cuticle and from the ligneous internal part, a successive physical stage in an autoclave for compression in hot air, the coarse fibre produced at the chemical stage which, because of the characteristics to be imparted to the fibres, can be conducted at temperatures ranging between 80 and 12O 0 C and at pressures between 4 and 60 atmospheres, followed by a successive stage of rapid decompression of the system.
Finally, the fibre can eventually be subjected to a final process of softening, in those cases where characteristics of particular softness are necessary. Said softening process can be conducted by enzymatic treatment of the fibres coming from the second stage, or by traditional carding and combing machines.
Intermediate manipulation of the materials, such as washings and the separation of the ligneous element are combined with the three principal stages mentioned above, although these do not substantially influence the final quality of the fibre, but have only
the task of removing some coloured substances and residues of alkalinity and ligneous residues. In more detail the process includes the following stages: a. The initial vegetable material is immersed in a hot solution (from 70° to 100°C) for times that vary from 10 minutes to three hours, of alkali (preferably NaOH or KOH), having concentrations in the range between 1% and 15% by weight (the times, the temperature and the percentage of alkalinity vary according to the characteristics to be imparted to the fibre and the conditions in use at the stage of compression in autoclave). At this stage bundles of cellulose fibres are obtained, still thick (the transversal thickness is in the order of hundreds of microns) and still relatively stiff, constituted by micro-fibrils of cellulose still encrusted with pectins and lignins.
Both the ligneous bone of the sprig, which can be removed by a simple mechanical action, and the greater part of the cortical substances, which are salifϊed, saponified and in part hydrolysed, are however, separated completely. With regard to the separation of the cortical substances, it is underlined that a very convenient strategy of working is that of re-utilising, almost as a closed cycle, the basic liquor that is formed during the course of the digestion of the treated vegetable varieties, removing from the hot alkaline solution the substances that gradually precipitate, in as much as they are not very soluble, and reintegrating the alkalinity to the value . necessitated by the process, by adding the necessary quantity of alkaline substance. In the basic liquor that is determined by the process of digestion are contained, partly as a suspended residue and partly dissolved, substances such as pectins, salified hemi-cellulose, salts from fatty acids, aliphatic and aromatic poly-alcohols. The process of precipitation of the various substances takes place when, with the reuse of the liquor in a closed cycle, the concentrations reached by the substances overtake those foreseen by thermodynamic equilibrium.
The separation of the substances that gradually precipitate in the liquor can be brought about by filtering the liquor through specific filters, or by decanting. The separated substances can be used in the chemical industry to produce various classes of materials: the pectins are useful as gelatinizing agents and alimentary additives, the other substances such as the lignins, the salts from fatty acids and the aliphatic and aromatic polyhydric alcohols are of great interest to the basic chemical industry. The organic substances can also be used in the processes of compost-making for the
production of fertilizers for agriculture, or as organic bio-masses for co-generational energy plants, or even in fermentation plants for the production of fuels. b. The fibre, resulting from the process of digestion (a), is washed with water and separated from the ligneous .parts that are incorporated in it. The separation of the ligneous parts can take place by mechanical action, with specific mechanical combs, or by suspending the fibres in water. The ligneous parts, having a lower density, can easily be recovered on the surface and removed. Such an operation (the separation of the ligneous parts) can also be proposed, according to the equipment, after the stage (f) later described. If carried out after the stage (a) it offers the advantage of reducing the volume of materials that pass through the treatments foreseen in the stages (d) and (e). If it takes place after the stage (f) it offers the advantage of being able to coincide with a process of combing of the fibres. The choice between these possible options depends, therefore, on the equipment solutions that one wants to adopt, and the advantages that one prefers to obtain. c. The excess water, in which the fibres are eventually soaked, is removed by mechanical means, that may consist in a light pressing, a light centrifugal action or another, equivalent system. d. At this stage the humid fibre (about 1 A kg of water for lkg of fibre) coming from the stages (a), (b) and (c) is placed in an autoclave and exposed to hot air at a temperature of between 80°- 12O 0 C, pressures in the range of 4-60 atmospheres and a time that can range from 0.5 hours to 4 hours (the conditions change according to the characteristics that one wishes to give to the fibre and the conditions used at the stage of alkaline digestion). e. After which a valve is opened, which allows the rapid exit of the hot air and, consequently, a rapid decompression inside the reactor. One proceeds, therefore, to retrieve the fibre. Inside the autoclave oxidative conditions are determined, as a result of which the reticulum around the cellulose fibrils breaks. The devastating action generated by the rapid decompression contributes to this process. The bridging hydrogen chains among the various cellulose links also break, with the removal of the water from the reticulum. Fibrils are thus obtained whose diameters are of about ten microns.
f. The fibre is washed in water, to remove products deriving from the demolition of the reticulum of the lignins, dried and sent on to the successive processing equipment. g. In cases where a particular softness of the fibre is necessary, the fibre coming from the stage (f) is sent to one or more tubs of enzymatic digestion, in which pectinolithic enzymes and/or ligninolithic enzymes of the peroxide type are contained. h. A further stage of softening, which can also be used as an alternative to step (g), can be constituted by a process of mechanical softening, during which the fibre is passed through pressing rollers and combs. i. A further stage of softening, which can also be used as an alternative to stage (g) and/or (h), can be constituted by a process of digestion in hydrogen peroxide which substitutes the function of the peroxide enzymes.
The process described above offers the following advantages with respect to others that could, in principle, be adopted.
- The fibre produced is ready for carding without cortical substances remaining adhered to it.
- The process times, in respect to those necessary in processes of simple treatment of the enzymatic-biological type, that need a digestive stage that lasts several days, are reduced to a few hours.
- The fibre resulting already has an acceptable degree of whiteness.
- The process is flexible and by varying the temperatures, the percentages of alkali used in stage (a), the proportions of nitrogen/oxygen and the pressure and the temperature of the air in stage (b), the enzymatic concentration or the mechanical parameters in the final softening stage, it is possible to obtain fibres with different characteristics according to the uses to which they are destined.
- With respect to better known treatments in the field of vegetable fibres (hydrothermal treatment, steam-explosion) the process, object of the invention, brings about a notable reduction in energy costs. The reduction of the energy costs in respect to steam- explosion is tied to the fact that in that process the production of vapour at a temperature of about 200°C is needed. The energy needed to produce the vapour is at
least 5 times greater than that which is necessary to produce the compressed air at the temperatures used in the process that is the object of the invention. In the operative conditions used in the process vapour is not produced. The treatment equipment is essentially reduced to one or more digestion tanks, one or more washing tanks, to an autoclave and simple apparatus for handling the materials.
- With respect to wet-oxidation the process, object of the invention, eliminates the risks and the costs relative to the use of pure oxygen under pressure.
Examples of creation of the process Example 1
An example is given in which the quantities refer to the production of lkg of Spanish broom fibre. a) 5kg of Spanish broom sprigs are immersed for 15 minutes in a hot solution (100 0 C) of NaOH , 15% by weight. Approximately 10 litres of said solution were used. At this stage bundles of cellulose fibres are obtained, still thick and still relatively stiff, constituted of micro-fibrils of cellulose, bound together by pectins and by lignins. However, both the ligneous bone of the sprigs, which can be removed by a simple mechanical action, and the greater part of the cortical substances, which are salified, saponified and in part hydrolysed, separate totally. b) The hot sprigs were washed by using shower diffusers immediately after extraction from the digestion tub. Three litres of fresh water were used for this which, percolating through the sprigs themselves removed the alkalinity. Three litres of fresh water are therefore introduced, and these replace three litres of water soiled by the alkali which are added to the alkaline digestion tub, reintegrating into this both the water and the alkalinity itself. The ligneous part was separated from the fibre by mechanical combing. c) The fibre, lightly compressed to remove the water soaked up (after the light pressing about half a litre of water/kg of fibre remains), was introduced into the autoclave where the air pressure was taken to 4 atmospheres for 3 hours. d) After this period of compression the pressure in the autoclave was rapidly reduced to that of the ambient.
e) The fibre was therefore washed and dried. Cellulose fibrils of a diameter in the order of a few microns are obtained.
Example 2
The process was conducted as in example 1, with the addition of a stage of mechanical softening, obtained by passing the fibres coming from stage (e) between pairs of revolving rollers specifically threaded on their surfaces. A softer fibre is obtained in respect to that produced in process 1.
Example 3
The process was conducted as in example 1 with the addition of a stage of enzymatic softening, obtained by the digestion for 1 hour of the fibres coming from step (e) in water containing the bacterium Aspergillus Japonicus in the concentration of 2mg/ml. A softer and whiter fibre is obtained with respect to that produced in process 1.
Example 4
The process was conducted as in example 1, with the addition of a stage of enzymatic softening, obtained by the digestion of the fibres coming from step (e) in water containing Basidiomycetes phanerochaete crysosporium funguses in the concentration of O.lmg/ml. A softer and whiter fibre is obtained with respect to process 1.
Example 5
The process was conducted as in example 1, with the addition of a stage of chemical softening, obtained by the digestion for 1 hour of the fibres coming from step (e) in an aqueous solution at 5% by volume of hydrogen peroxide. A softer and whiter fibre is obtained with respect to process 1.
Bibliography
1. A.S. Schimdt, M. Tenkanen, A.B. Thomsen, A. Woideman (1998); Riso-R-1042 (EN), Riso National Laboratory, Roskilde, Denmark.
2. A.B. Bjerre, A.S.Schimdt (1997); Riso-R-967 (EN), Riso National Laboratory, Roskilde, Denmark.,
3. T. Cerchiara, R.De Rose, G.Santagada, G.DeFilpo, G.Chidichimo, Polymer fibres, Manchester (UK), 14-16, 2004
4. R.S. Jayani, S.Saxena, R. Gupta; Process Biochemistry 40 (2003) 2931-2944
5. M.Tuomela, M.Vikman, A.Hatakka, M.Itavara, Bioresource technology; 72 (2000) 160-183