EP1165666A1

EP1165666A1 - Method for making a cellulose or starch fatty ester by esterification or transesterification

Info

Publication number: EP1165666A1
Application number: EP00906455A
Authority: EP
Inventors: Carlos Vaca-Garcia; Marie Elisabeth Borredon; Antoine Gaset
Original assignee: Institut National Polytechnique de Toulouse INPT
Current assignee: Institut National Polytechnique de Toulouse INPT
Priority date: 1999-02-23
Filing date: 2000-02-22
Publication date: 2002-01-02
Also published as: FR2789994B1; FR2789994A1; WO2000050493A1

Abstract

The invention concerns a method for making a cellulose or starch fatty ester by esterification or transesterification of a cellulosic or starchy material using a fatty reagent. The invention is characterised in that it consists in introducing the cellulosic or starchy material in solid or fragmented state, the fatty reagent and an esterification or transesterification catalyst in a double-screw device (1) at a temperature ranging between 180 DEG C and 230 DEG C so as to subject the reactive mixture to a thermomechanical treatment during the reaction; drawing the resulting pasty mixture and isolating the cellulose or starch fatty ester by solvent extraction from the other constituents of the pasty mixture. The inventive method enables to make a cellulosic or starchy material hydrophobic without using toxic solvents.

Description

PROCESS FOR THE MANUFACTURE OF A FATTY ESTER OF CELLULOSE OR STARCH BY ESTERIFICATION OR TRANSESTERIFICATION

The invention relates to a method for manufacturing a fatty ester of cellulose or starch by esterification or transesterification of a cellulosic or starchy material using a fatty reagent. The starting cellulosic or starchy material can come from by-products or residues of vegetable origin rich in cellulose or in starch, or else can be constituted by pure cellulose coming in particular from a papermaking process or from pure starch. The fatty reagent is essentially constituted by one or more fatty acids or by one or more fatty acid esters (in particular mono, di or triglyceride) having one or more acyl groups with at least 6 carbon atoms, or also by a mixture of these fatty substances.

Cellulose or starchy materials are very hydrophilic and able to absorb large amounts of water. This property represents a serious defect of this type of material in many applications where they are found in the presence of water or in a humid atmosphere (for example for cellulose: particle board for construction or furniture, cushioning materials for the conditioning, ...). Furthermore, in certain applications, hydrophobic substrates capable of absorbing fatty substances (water depollution, etc.) are sought and the hydrophilic nature of cellulosic materials excludes from these applications the numerous products made from cellulose. Cellulosic or starchy materials are an abundant, inexpensive raw material, and the reduction in their hydrophilic nature therefore presents an essential economic advantage.

One known means for rendering a cellulosic or starchy material hydrophobic consists in grafting a fatty substance onto its alcohol functions, and numerous methods have been proposed for carrying out such grafting.

The oldest method consists in using an acid chloride as fatty substance and in carrying out the reaction in a mixture of solvents organic (including pyridine) which prevents the degradation of cellulose or starch by the hydrochloric acid formed (CJ MALM et al., Aliphatic Acid Esters of Cellulose, Ind. Eng. Chem. Vol 43, n ° 3 , pp. 684-688, 1951; WOLFF LA. et al., The acylation of corn starch, amylose and amylopectin, J. Am. Chem. Soc, 73, 346-349, 1951). The solvents used are very effective but are expensive, toxic and difficult to extract from the reaction medium (especially pyridine), which has limited the industrial development of this type of process. In addition, acid chloride is a relatively expensive reagent.

To avoid the use of the acid chloride and of the abovementioned solvent, other processes have been proposed in which the fatty substance used is either a fatty acid or a fatty acid ester, the reaction being carried out in organic solvents which have the function of either dissolving the cellulose or the starch so that the reaction takes place in a homogeneous medium (G. SAMARANAYAKE and WG GLASSER, Cellulose derivatives with low DS. I. A novel acylation System, Carbohydr. Polym. Vol 22, p 1-7, 1993; ROBERTS HJ, Nondagradative Reactions of Starch in: "Starch Chemistry and Technology", Ed. RL Whistler & EF Paschall, Académie Press, New York, vol. 1, 439-493, 1965.), either in the case of cellulose, to impregnate it and cause it to swell to allow better diffusion of the reagent (AI LATETIN et al., Use of the ester exchange reaction for the synthesis of cellulose stearates, Polymer Sci USSR, Vol. 10, p. 761-766, 1968). The solvents used (lithium chloride / dimethylacetamide mixture, dimethylformamide) are much less toxic than pyridine but have the same defects as regards the cost and the difficulty of extraction at the end of the synthesis. Furthermore, patent EP 0.647.652 proposes a process for esterification or transesterification of a polyol (sucrose) using a fatty substance (mixture of methyl esters of fatty acids) in order to obtain a fatty acid polyester (sucrose polyester) in the absence of a third solvent in the reaction medium (of course, as in the other processes, common extraction solvents such as hexane can be used in this process, a once the reaction has taken place, to separate the product formed). The objective of the process described in this patent is to obtain fatty substances substitutes with low caloric power in order to limit, in the food industry, the drawbacks linked to fatty substances (high metabolic absorption leading to obesity). The process described in this patent uses a conventional esterification or transesterification catalyst and manages to carry out the reaction without the addition of a third solvent thanks to the use of the latter under vacuum. Another US patent 5,596,085 in the name of the same holder targets the same process implemented under vacuum without solvent but in thin film (0.5 to 2mm) obtained, either in a rotary reactor ensuring centrifugation of the liquid reactive mixture, or in a rotary vane reactor spreading the reactive mixture, either by gravity by flow along a vertical surface of this reactive mixture. In this type of thin film technique, the volatile co-products are extracted during the reaction, which displaces the equilibrium and allows the reaction to proceed with better efficiency. These patents EP 0.647.652 and US 5,596,085 generally relate to all polyols, they mention cellulose and amylose as possible starting polyols, but they are more particularly oriented on the reaction of sucrose or derivatives (materials high-calorie food) with methyl esters of fatty acids; the examples provided in these patents all describe the reaction of sucrose octaacetate with a mixture of fatty acid methyl esters to obtain polyesters of sucrose fatty acids.

Such a process is advantageous since it avoids the use of a third solvent in the reaction medium, and it makes it possible to obtain yields compatible with industrial exploitation. On reading these patents, the targeted process therefore seems to be a solution to the problem of treating cellulose to make it hydrophobic. However, the inventors carried out a series of experiments under the conditions indicated in these patents and found that, in no case, the use under vacuum recommended (in thin film or not) does not allow an esterification or transesterification to be obtained. cellulose. Contrary to what is announced in these patents, this implementation does not lead, in the case of cellulose, to any chemical reaction of the alcohol functions of the cellulose: the latter strictly retains its chemical nature (in particular its hydrophilic properties) with simply some cuts chain terminals. This result is not surprising given the high stability of the cellulose and its not very reactive nature.

The present invention proposes to provide a process for esterification or transesterification of a cellulosic or starchy material using a fatty reagent, making it possible to obtain a fatty ester of cellulose or starch having hydrophobic properties and requiring no addition of a third solvent during the reaction (the only solvents used being common solvents for the separation of the fatty ester from cellulose or starch, once the reaction has been carried out). The reaction which takes place can be schematized as follows: Poly-OH + fatty reagent -> Poly-O-CO-R + by-product (where Poly represents the polymer chain of cellulose or starch).

The essential objective of the invention is thus to esterify or transesterify a cellulosic or starchy material in order to make it hydrophobic without using toxic solvents, in particular pyridine. Another object of the invention is to provide a process leading to significantly shorter reaction times compared to the aforementioned known processes.

Another objective of the invention is to reduce the parasitic reactions of degradation of the cellulosic or starchy chain in order to limit the formation of degradation products.

Another object of the invention is to indicate an esterification or transesterification process which lends itself to continuous implementation.

To this end, the process targeted by the invention uses as fatty reagent a fatty acid or a fatty acid ester having one or more acyl groups each having at least 6 carbon atoms, or else a mixture of fatty acid and d fatty acid ester of the aforementioned type. The method according to the present invention is characterized in that the cellulosic or starchy material is introduced in the divided solid state, the abovementioned fatty reagent and an esterification or transesterification catalyst in a twin-screw device comprising two co screws. -penetrating rotating inside a tubular enclosure brought to a temperature substantially between 180 ° C and 230 ° C in order to subject the reactive mixture to a thermomechanical treatment during the esterification or transesterification reaction, the pasty mixture obtained is drawn off after a residence time in the twin-screw device of between 1 and 30 minutes, and the fatty ester of cellulose or solid starch is isolated obtained by solvent extraction of the other constituents of the pasty mixture. Experiments have shown that, in the absence of solvent in the reaction medium, it is possible to esterify or transesterify a satisfactory proportion of the alcohol functions of the cellulose or of the starch by causing the reaction to take place in a device. twin-screw under the conditions defined above. Even if this proportion is lower than that obtained with solvents, in particular pyridine, this result is unexpected and remarkable taking into account the total failure registered until the present time to achieve such a transformation of these functions. It should be emphasized that the proportion of esterified or transesterified functions is sufficient to give the entire mass of cellulosic or starchy material treated a marked hydrophobic character. The reaction time is very short, of the order of a few minutes (while the prior methods of EP 0.647.652 and US 5,596,085 require a period of 4 hours to transesterify a sucrose derivative) which further increases the unexpected result. Given this short reaction time, the continuous implementation of the process, and the absence of solvent in the reactive medium, the process of the invention benefits from good industrial profitability linked to the added value that '' give the treated product its hydrophobic properties. It is further noted that the cellulosic or starchy chain of the starting material remains practically intact and that only certain alcohol functions are transformed. The cellulosic materials treated in accordance with the invention can be used for the manufacture of building or furnishing materials, or cushioning materials, capable of remaining in a humid or aqueous atmosphere while retaining good dimensional stability. These hydrophobic cellulosic materials can also be used in a divided state to selectively and rapidly absorb (100% fat in less than 2 minutes) the fatty substances contained in mixtures and aqueous solutions (dirty water, domestic effluents and industrial) or well in mixtures in the vapor state (kitchen vapors, industrial vapors) or in solids. In addition, they have the property of being able to break water-fat emulsions and even to work continuously because the fats absorbed from the emulsion can coalesce in the filter and rise to the surface of the mixture to be recovered continuously by skimming. . The cellulosic fibers treated according to the invention also have the advantage of being biodegradable and reusable for a new absorption after extraction of the fatty substance without significant loss of their absorption capacity. They can also be used to make cigarette filters capable of more selectively retaining tar and nicotine compounds of lipophilic nature. Furthermore, the starchy materials treated in accordance with the invention can be used to manufacture packaging films that are not very sensitive to humidity or as an additive in the food, pharmaceutical and paint industries. They can also be used as a biodegradable support for active material, benefiting from a longer degradation time in a humid atmosphere. The active ingredient can be mixed after the esterification or transesterification reaction in order to impregnate the starchy fatty ester obtained. This mixing is advantageously carried out in the twin-screw device in a cooling zone situated between the reaction zone and the withdrawal zone. It can thus be carried out continuously to lead to a very homogeneous final product. For example, the starchy fatty ester can serve as a herbicide support or a pest repellant: thanks to its hydrophobic nature, a period of effectiveness is longer in outdoor use than if hydrophilic starch was used.

According to a preferred embodiment, the proportion of fatty reagent relative to the cellulosic or starchy material is adjusted within a range corresponding substantially to 0.5 P - 1.5 P, where P is the amount of fatty reagent corresponding to the stoichiometry of the abovementioned grafting reaction. This implementation of the reaction under conditions close to or not far from the stoichiometry limits the quantities of reagents used and the quantities of manufactured by-products, and allows easier isolation of the cellulose or hydrophobic starch obtained (fatty ester of cellulose or starch).

The grafting reaction can be an esterification or a transesterification and use, in the case of cellulose, both acid catalysts and basic esterification or transesterification catalysts, and in the case of starch, preferably basic catalysts .

In the case of transesterification, it is advantageous to use a catalyst for transesterification of the cellulosic or starchy material, in particular fatty acid salts, K ₂ C0 ₃ , NaOH. The fatty reagent used is then preferably one or more fatty acid esters of the following group: methyl octanoate, methyl decanoate, methyl dodecanoate, methyl tetradodecanoate, methyl hexadodecanoate, methyl octadodecanoate, vegetable oils in particular coconut or palm kernel. In the case of an esterification, an acid or basic esterification catalyst is used for the cellulose, advantageously: NaOH, H ₂ S0 ₄ or p-toluenesulfonic acid and, for the starch, essentially a basic esterification catalyst. , such as NaOH. The fatty reagent used is then preferably one or more fatty acids with a saturated or unsaturated aliphatic chain comprising between 8 and 20 carbon atoms.

In both cases, the catalyst is advantageously used in solid form and previously mixed homogeneously with the liquid fatty reagent, the mixture then being injected into the twin-screw device. This simplifies handling, while facilitating dosing. The catalyst is preferably dosed so that the proportion by weight of catalyst / cellulosic or starchy material is substantially between 1 and 10%.

The temperature of the reactive medium is regulated within the aforementioned range by thermal regulation of the tubular enclosure of the twin-screw device; this enclosure can in particular be surrounded by an envelope traversed by a heat transfer liquid. The temperature range which seems to give the best results is appreciably: 190 ° C - 210 ° C. The twin-screw device used in the present invention is in itself of known type; it can in particular comprise, from upstream to downstream, an impregnation zone provided with direct pitch screws, an esterification or transesterification zone provided with direct pitch screws and kneading modules, and a terminal withdrawal zone . If the fatty ester formed is combined with an active material, the device is supplemented by a cooling zone situated after the esterification or transesterification zone and provided with means for injecting the active material with a view to l 'impregnation of the fatty ester of cellulose or starch. The final isolation of the fatty ester of cellulose or starch can, in known manner, be obtained by extraction of the other constituents by means of an appropriate solvent, in particular ethanol and / or ethyl ether or mixture of the two. A slight heating (about 40 ° C to 50 ° C) increases the efficiency. It should be emphasized that these solvents are common non-toxic solvents and that they are used once the esterification or transesterification reaction has been obtained outside the twin-screw device (the process not requiring the addition of any solvent in the reaction medium).

The invention is illustrated by the following examples, the transesterification reaction of which has been carried out in a twin-screw device as shown in the drawings; on these drawings:

FIG. 1 is a symbolic longitudinal representation of said twin-screw device,

- Figure 2 is a cross section through a plane AA '. The device was produced from modules sold by the company "CLEXTRAL" (registered trademark) under the general reference "BC21". Each module includes a tubular double-walled enclosure 1 and 2 which allows thermal regulation of the core of the enclosure where the active organs are housed. Some modules are of the type comprising two identical co-penetrating screws, others of the type comprising shear mixers composed of bilobe discs or kneader discs. The various modules are rotated in synchronism by an electric motor 3 making it possible to obtain a speed of rotation of its output shaft which can reach 600 rpm. In the examples, the rotational speed chosen is 300 rpm.

The device essentially comprises the following functional zones (from upstream to downstream): - a so-called impregnation zone Z _1} comprising a hopper 4 for supplying cellulosic or starchy materials, a conduit 5 provided with a pump 6 for the injection of the fatty reagent / catalyst mixture previously prepared and four direct screw twin screw modules such as 7,

a so-called esterification or transesterification zone Z ₂ , combining kneading modules such as 8 and direct pitch twin-screw modules such as 9,

- And a terminal draw-off zone Z ₃ comprising a MEL module 10 of twin screw with direct pitch 11 and an outlet 12 of the pasty mixture.

In the example, the impregnation zone Z combines four direct-screw twin screw modules 7, having decreasing steps from the first to the fourth. In this zone, the twin screws with decreasing pitch carry out the conveying, kneading and mixing of the cellulosic or starchy solid materials and the fatty reagents and catalyst injected in liquid form.

In the example, the esterification or transesterification zone combines six direct-screw twin-screw modules such as 9 which provide the conveying and mixing of the materials, and two mixing modules 8 which subject the materials to shearing. These mixing modules are made up of two-lobe discs and mixing discs. In this zone, the esterification or transesterification reaction of the cellulosic or starchy material takes place.

EXAMPLE 1:

In this example, the cellulosic material treated is sawdust from pine wood.

This material is treated with a fatty reagent consisting of palm kernel oil, the distribution of the fatty chains of which is as follows:

C ₆ : 0.3% C _M : 15.8% C ₈ : 3.7% C, ₆ : 8.6%

C ₁₀ : 3.4% C ₁₈ : 21.9%

C ₁₂ : 46% C ₂₀ : 0.3%

Only the C ₁₈ chains are monounsaturated (C ₁₈ : 1) between 12 and 18%, and diunsaturated (C ₁₈ : 2) between 1 and 4%.

The esterification catalyst used is a mixture of potassium fatty acid salts (molar composition: 20% palmitic, 40% myristic, 40% lauric). This mixture was prepared by reaction at 110 ° C between a saturated aqueous solution of potassium hydroxide (4.1 eq) and a mixture of fatty acids: myristic (C ₁₄ ) (3 eq) and lauric (C ₁₂ ) (1 eq ). After two hours of reaction with stirring, the salts are dried under vacuum for 48 hours.

The abovementioned salts in the form of solid crystals are mixed beforehand with the abovementioned fatty reagent so as to obtain in the twin-screw device the weight proportions indicated below; the flow rate of cellulosic material (sawdust) introduced into the twin-screw device is 20 kg / hour and the screw rotation speed of 300 revolutions per minute.

Example conditions:

- catalyst salt / sawdust ratio: 0.1 kg / kg,

- fatty reagent / sawdust ratio: 3 kg / kg (ratio corresponding to stoichiometry 1 P),

- temperature in the mixing zone at the entry of the twin-screw device: 135 ° C,

- temperature in the transesterification zone: 200 ° C,

- material residence time: 90 seconds. The paste obtained at the outlet of the twin-screw device is treated with hot ethanol and ether ("Soxhlet" process) in order to isolate and purify the solid cellulose ester.

The content of ester functions is determined by saponification with NaOH. The rate of ester obtained, expressed in milliequivalents of ester per kg of cellulosic material treated is 800 meq / kg.

The hydrophobic nature of the samples resulting from the transesterification reaction was evaluated by measuring the contact angle static: θ. It is equal to 95 ° in this example, which characterizes a marked hydrophobic character.

EXAMPLE 2:

This example was carried out under the same conditions as Example 1 but using potassium carbonate K ₂ C0 ₃ as catalyst.

Ester rate obtained: 700 meq / kg. θ: 93 °.

EXAMPLE 3 (APPLICATION: Pine sawdust was treated according to the process of the present invention and more particularly according to Example 1. It was used for the manufacture of a wood-plastic composite, composed of 70 parts a commercial polypropylene-polyethylene (PP-PE) co-polymer and 30 parts of hydrophobic sawdust. For comparison, blanks (wood-plastic composites but with sawdust not chemically treated) were produced in the same proportions (70/30) Measurements on 10 samples gave the following results:

Young's modulus (E) of the virgin co-polymer: 1244 ± 26 MPa E of the untreated wood-copolymer composite: 1580 ± 40 MPa E of the hydrophobic wood-copolymer composite: 1730 ± 42 MPa

A statistically significant improvement in the elastic modulus is therefore observed compared to composite materials using sawdust without chemical treatment. This is undoubtedly due to the better compatibility that hydrophobic wood has with the lipophilic polymer matrix.

Claims

CLAIMS 1 / - Method for manufacturing a fatty ester of cellulose or starch by esterification or transesterification of a cellulosic or starchy material using a fatty reagent comprising a fatty acid or a fatty acid ester having one or more acyl groups each having at least 6 carbon atoms, in which the cellulosic or starchy material and the fatty reagent are brought to react hot in the presence of an esterification or transesterification catalyst in order to carry out the reaction of grafting: Poly - OH + fatty reagent -> Poly - O - CO - R + by-product (where Poly represents the polymer chain of cellulosic or starchy material), said process being characterized in that the cellulosic material is introduced or starch in the divided solid state, the fatty reagent and the catalyst in a twin-screw device comprising two co-penetrating screws rotating inside a tubular enclosure brought to a temp rature substantially between 180 ° C and 230 ° C in order to subject the reactive mixture to a thermomechanical treatment during the esterification or transesterification reaction, the pasty mixture obtained is drawn off after a residence time in the bi-device. screws between 1 and 30 minutes, and the fatty ester of cellulose or solid starch obtained is extracted by solvent extraction from the other constituents of the pasty mixture. 2 / - Method according to claim 1 wherein the proportion of fatty reagent is adjusted relative to the cellulosic or starchy material in a range corresponding substantially to 0.5 P - 1.5 P, where P is the amount of corresponding fatty reagent to the stoichiometry of the abovementioned grafting reaction.

3 / - Manufacturing process according to one of claims 1 or 2 involving a transesterification reaction of the cellulosic or starchy material, in which a basic transesterification catalyst is used, in particular fatty acid salts, K ₂ C0 ₃ , NaOH.

4 / - Method according to one of claims 1 or 2 involving an esterification reaction of a cellulosic material, in which an acid or basic esterification catalyst is used, in particular NaOH, H ₂ S0 ₄ , acid p-toluenesulfonic. 5 / - Method according to one of claims 1 or 2 involving an esterification reaction of a starchy material, in which a basic esterification catalyst is used, in particular NaOH.

6 / - Process according to one of claims 3, 4 or 5, in which a catalyst is used in solid form previously mixed homogeneously with the liquid fatty reagent, the mixture then being injected into the twin-screw device.

7 / - Process according to claim 6, in which the quantity of catalyst injected into the twin-screw device is adjusted so that the proportion by weight of catalyst / cellulosic or starchy material is substantially between 1 and 10%.

8 / - Process according to claim 3, in which a fatty acid ester or esters of the following group are used as fatty reagent: methyl octanoate, methyl decanoate, methyl dodecanoate, methyl tetradodecanoate, methyl hexadecanoate, methyl octadecanoate, vegetable oils in particular copra or palm kernel.

9 / - Method according to one of claims 4 or 5, wherein one uses as fatty reagent one or more fatty acids with aliphatic chain saturated or unsaturated having between 8 and 20 carbon atoms. 10 / - Method according to one of the preceding claims wherein a twin-screw device is used comprising two co-penetrating screws wrapped in a thermoregulated tubular enclosure at a temperature between 190 ° and 210 ° C.

11 / - Method according to one of the preceding claims characterized in that a twin-screw device is used comprising, from upstream to downstream, an impregnation zone (Z) provided with direct pitch screws (7), a esterification or transesterification zone (Z ₂ ) provided with direct pitch screws (9) and kneading modules (8), and a terminal withdrawal zone (Z ₃ ).

12 / - Method according to claim 1 1, characterized in that a twin-screw device is used in which the impregnation zone comprises several screws of different pitch decreasing downstream. 13 / - Method according to one of claims 1 1 or 12, characterized in that a twin-screw device is used comprising, between the esterification or transesterification zone and the withdrawal zone, a cooling zone provided with means for injecting an active material, with a view to impregnating the fatty ester of cellulose or of formed starch.

14 / - Method according to one of the preceding claims, wherein the fatty ester of cellulose or starch is isolated by extraction of the other constituents with ethanol, ethyl ether or with a mixture of the two.