DE102004007941B4 - Biodegradable, mechanically strong, food-compatible composition, useful e.g. for producing cutlery or tableware by extrusion or injection molding, comprising cellulose ester, plasticizer and inorganic filler - Google Patents

Abstract

A novel composition (I) comprises (by weight): (a) cellulose ester(s) at 20-90 wt. % (based on (I)); (b) plasticizer(s) at 15-50 wt. % (based on (a)); and (c) inorganic filler(s) at 5-70 wt. % (based on (I)), provided that (I) does not contain more than 30 wt. % carbonate compound(s) (expressed as calcium carbonate). - Independent claims are included for: - (1) shaped articles prepared from or using (I); - (2) the production of (I), by dry-blending (a) and (c) in a mixer, then mixing with (b); and - (3) the production of the shaped articles, by injection molding, extrusion blow molding or deep-drawing of (I).

Description

The The invention relates to a biodegradable compound whose organic Components consist essentially of renewable raw materials and that has mechanical properties similar to those of polystyrene very similar are. With the compound according to the invention Among other things, and in particular, objects can be produced the food law for be explained safely can and can therefore be used in the food industry, for example in the form of in particular for the disposable plates, trays and Cutlery.

It is known that cellulose esters with certain degrees of substitution have good biodegradability. That's how it describes EP 0792913 A2 a composition comprising a cellulose ester with a degree of substitution of not more than 2.15, which can be spun into fibers and is suitable for the manufacture of cigarette filters. Together with a plasticizer and very small amounts of a specific titanium dioxide, a composition can be produced from such a cellulose ester according to EP 0716117 A1 extruded, blow-molded and in particular to let spin, the staple fibers are processed according to this document again to cigarette filters. The addition of titanium oxide in very small amounts is said to improve the biodegradability of the composition.

The DE 199 31 183 A1 discloses biodegradable cellulose esters and their use in the preparation of thermoplastic molding compositions for the production of (tea) filter materials. Together with thermoplastically processable starch and a plasticizer certain cellulose esters can according DE 42 37 535 A1 To give a biodegradable polymer mixture with good water resistance, which should have good mechanical properties, if a suitable phase mediator is added. This mixture can be used for the production of films. The DE 39 13 4022 C2 describes biodegradable plastic materials made of cellulose acetate and polyethylene mainly for envelopes of oil lamps.

DE 699 07 224 T2 discloses biodegradable compositions for the manufacture of shaped articles consisting of starch, cellulose ester, a plasticizer and a regulating additive, which may be calcium carbonate in an amount of preferably up to 30% by weight. This substance is added to control the pH so that the acid produced during composting can be neutralized. Although higher amounts than the specified can be used, but bring no significant improvements.

Also from the DE 295 22 229 U1 Moldings are known, which may include calcium carbonate. These molded articles are made of a composite material based on cellulose acetate and cellulose fibers.

Chalk as filler contains a cellulose acetate film according to US 2048313 ,

As biodegradable thermoplastically processable cellulose derivatives are described in the DE 100 12 817 A1 Cellulose ether ester proposed. According to the teaching of DE 195 29 410 A1 For example, thermoplastic and biodegradable polysaccharide ester ethers may be made into fibers, films, membranes, and the like, with the addition of plasticizers and / or admixture of other biodegradable polymers.

Previous biopolymers based on renewable raw materials such as polyester / starch blends and cellulose blends usually have only a very limited heat resistance. At temperatures above max. 65 ° C occurs a strong material softening of the polymers and thus a mechanical material failure of the products made therefrom. Only when cellulose acetate having a degree of substitution of about 1.2 to 2.7 is used as a binder for natural cellulose fibers can be produced from the composite molded articles with sufficiently high temperature resistance, which can be used for example as automotive interior parts, as in DE 195 17 763 A1 disclosed.

In the DE 694 25 260 T2 are described masses for the production of disposable articles, including dimensionally stable shaped articles such as plastic cutlery containing cellulose esters and plasticizers. Other additives can be added to the compositions, including talc, TiO ₂ , CaCO ₃ , NH ₄ Cl and silica.

The object of the present invention is to provide a biodegradable, homogeneous compound from which moldings with mechanical properties can be produced which are similar to similar moldings made of polystyrene. In particular, the invention should provide compounds with which can be produced preferably by injection molding moldings with high dimensional stability in the heat of up to 90 ° or 95 ° C. At the same time, these shaped bodies should preferably have a tensile modulus of elasticity in the range of approx. 4000-5000 N / mm ² and an elongation at break of more than 8%.

In addition, should the compound possess such a composition that from it finished molded body additionally food safety are harmless, so that they are in appropriate areas can be used, for example in the form of (disposable) cutlery or (Disposable) plates / -Tabletts. This particular task presents special Requirements as the desired biodegradability (i.e., degradation under the influence of moisture, Temperature and microorganisms) a conflict of objectives with the simultaneous Demand for stability (Harmlessness) Represents food.

• – mindestens einen Celluloseester in einer Menge von 20 bis 90 Gew.-%, bezogen auf die Gesamtmenge des Compounds
• – mindestens einen Weichmacher in einer Menge von 15 bis 50 Gew.-%, bezogen auf den Celluloseester,
• – mindestens einen anorganischen Füllstoff in einer Menge von 5 bis 70 Gew.-%, bezogen auf die Gesamtmenge der Zusammensetzung, wobei der anorganische Füllstoff mindestens Titandioxid, ein Silikat und Kreide umfasst, die Zusammensetzung aber nicht mehr als 30 Gew.-% Carbonatverbindung, ausgedrückt in Calciumcarbonat, enthalten darf, und
• – gegebenenfalls Schlagzähigkeitsmodifikatoren, Stabilisatoren, Farbpigmente und/oder Trennmittel.

Surprisingly, the general object has been achieved by providing a composition (compound) containing the following components:

• - At least one cellulose ester in an amount of 20 to 90 wt .-%, based on the total amount of the compound
• At least one plasticizer in an amount of 15 to 50% by weight, based on the cellulose ester,
• At least one inorganic filler in an amount of from 5 to 70% by weight, based on the total amount of the composition, wherein the inorganic filler comprises at least titanium dioxide, a silicate and chalk, but the composition contains not more than 30% by weight of carbonate compound, expressed in calcium carbonate, and may contain
• If appropriate, impact modifiers, stabilizers, color pigments and / or release agents.

The invention has for the first time succeeded in developing a biodegradable compound which has properties such as polystyrene. The tensile modulus of elasticity can be set to approximately 5000 N / mm ² at an elongation at break of more than 8%. The compound thus possesses material properties like a standard polystyrene. The peculiarity of this material, compared to other biomaterials, lies in its high dimensional stability in heat of up to at least 90 ° C, usually up to 95 ° C.

Next The very good mechanical properties of this blend has one very good machinability on conventional Plastic processing machines. It can be without further modifications splashing with high cycle times. The applications range from catering items such as Cutlery or dishes until towards door side panels. Only the use of hot runner sprues is not recommended.

When support matrix for the Compound of the invention a cellulose ester is chosen. Preferably, the ester of a C1-C6 carboxylic acid is used, more preferably the ester of a C1-C4 carboxylic acid. Next pure esters are also possible mixed esters. Is particularly favorable a cellulose acetate, since this the compound a high rigidity and temperature resistance gives. The cellulose ester should have a defined degree of substitution have. This indicates how many of the free hydroxyl groups per Cellulose building block are esterified. Cellulose (normally present as pulp) becomes first Completely esterified to triacetate or another triacylate. Through a second step of the synthesis, the triacylate is partially hydrolyzed, so that part of the acid molecules again is split off until, on average, one more per glucose module exactly defined number of OH groups is esterified.

Of the Degree of substitution should be chosen that ensures good biodegradability is. Chemically modified cellulose is not always biodegradable. The biodegradability decreases with increasing degree of substitution. According to DIN EN 13432, a degree of degradation of 90% must be achieved. The biological Degradation involves the transformation of the carbon of the test material in carbon dioxide and biomass. DIN EN 13432 writes for compostability suggest that after a maximum of 12 weeks in a> 2mm sieve fraction a maximum of 10% of the original Dry weight of the test material may be found. Degrees of substitution that ensure such degradability, Although in principle known from the prior art. It is However, continue to note that the degree of substitution in particular when using cellulose acetate and / or at a designated Processing by injection molding a value of 2.6 or not significantly exceed should, in order to avoid the processability of the Compunds because of too big toughness impaired is. A degree of substitution of less than about 2.0 is also in one Variety of cases not desirable because the compound is too hydrophilic for the molded part thus produced Could lend properties. Furthermore This makes the mechanical properties and the dimensional stability negative affected.

The Amount of cellulose ester is in view of the desired processing selected. In principle, amounts of about 20 to 90 wt .-%, based on the total amount of the compound, get good results, taking Amounts of not more than 50 wt .-% are preferred to a sufficient Proportion of fillers to ensure (see below).

Since cellulose acetate in the application is a brittle and difficult to flow in the compounding, a plasticizer should be added be set. In principle, all known plasticizers for cellulose esters are suitable for this purpose. The addition of a plasticizer lowers the viscosity of the compound. It must therefore be added in each case in such an amount that the compound can be used on a common purpose plastic processing machine corresponding to the purpose. At the same time, care must be taken that the desired mechanical properties of the end product and its rigidity are not adversely affected. Suitable plasticizers for cellulose esters are, for example, glycerol, triethylene glycol, triphenyl phosphate, polyethylene glycol, propylene glycol, ethyl lactate, methyl lactate, glycerol triacetate, acetyltributyl citrate, triethyl citrate, diethyl citrate, glycerol acetate, phthalic acid ester, sorbitol, maltitol, xylitol, erythritol, fatty acid esters or mixtures of the abovementioned substances. Of these, particular preference is given to those which have no corrosive effect on the tools required for production. In some cases, otherwise, after some time, for example after about 20 weeks, heavy wear on the tool surfaces will occur, which leads to the tools having to be reworked. In addition, the processing speeds of blends of cellulose ester with such plasticizers are significantly lower than in conventional plastics such as polystyrene. It has proven to be favorable to use plasticizers which have a relatively high vapor pressure and / or a relatively high melting point and are therefore not corrosive. An example of a plasticizer from this group is called glycerol triacetate. This substance is harmless even under food law aspects. Incidentally, this aspect is also of importance if the compounds according to the invention are intended for shaped bodies intended to come into contact with foodstuffs. Therefore, all plasticizer acceptable plasticizers are preferred, including all those of the above group, which are food safe. Emphasized here are glycerol, ethyl lactate, methyl lactate, glycerol triacetate, triethyl citrate, diethyl citrate, glycerol acetate, sorbitol, maltitol, xylitol, erythritol and fatty acid esters.

Of the Proportion of plasticizer is the amount of cellulose ester used adapt; in general it should be from 15 to 50% by weight on this ester, lie. Preferably, its content is about 25 to 40% by weight thereof.

Around the rigidity and temperature resistance of the compounds of the invention available moldings to increase As well as to improve processability, these need inorganic fillers contain. In a first aspect, that of environmental compatibility, and for cost reasons are for this especially, of course occurring, mineral fillers suitable, which may optionally be surface-modified. When Examples are: treated and untreated chalk, dolomite flour, Kaolin, talc and silicates. Under treated chalk understands you get a type of chalk that contains flow aids, mostly stearates, is added to improve the dosing. Within this Product groups have different qualities, mainly depending on the deposits, as well as different after-treatments that have some influence on perform the properties and processability.

at the selection of the filler Care must be taken to ensure that the proportion of carbonate in the filler not too high. Because too high a proportion of carbonate filler in the compound, especially on chalk, can lead to a refusal of the food authorization, since the migration behavior of made of this compound objects insufficient for contact can be with food. The limit for this has been found to be a lot of carbonate, the 30 wt .-% calcium carbonate, based on the total weight of Compounds, corresponds. On the other hand, it may not quite open the addition of chalk can be dispensed with. That has advantages, because chalk relatively inexpensive is. Also take over the basic carbonate ions in the compound the function of acid scavengers: bei The processing of cellulose esters can be under mechanical Stress of the compound such as shear stress or pressure (e.g. Extrude) the release of small amount of acid is not avoid completely. For this affects the filler as a neutralizing agent. The addition of specially for this purpose introduced acid scavengers therefore not necessary, even if it is for specific purposes in principle is not excluded and then in an amount of preferably up to a maximum of about 2 wt .-% can be done.

Furthermore, it is necessary that at least a part of the filler is a silicate. Its addition has a positive influence on the temperature resistance of the molded body produced with the compound. A well-suited silicate is, for example, talc (a magnesium phyllosilicate). The addition of titanium dioxide is also mandatory; it increases the surface hardness of the molded bodies produced and, where appropriate, improves their appearance. Even a small amount of TiO ₂ in the range of 0.5 to 5 wt .-%, based on the total weight of the compound, gives the molded article produced therefrom a bright white appearance, if no further color pigments are added.

For the proportions and proportions of filler, the following can be said in summary: The total content of filler can be about 10 Wt .-% to about 65 wt .-%, based on the total weight of the compound. Particularly favorable ratios are obtained at levels in the range of about 20 wt .-% to about 50 wt .-%. Conveniently, this amount of filler is composed of titanium dioxide, a carbonate such as chalk and a silicate such as talcum, wherein the amount of titanium dioxide depends on the desired whiteness of the product used and its desired surface hardness and for cost reasons usually 10% by weight. %, based on the compound, does not significantly exceed. Usually already 2-3 wt .-% are sufficient. Carbonate is preferably used slightly less than the amount specified above as the upper limit; a quantity of between 10 and 25% by weight has proven to be suitable. The rest is not critical and can be filled up with talc, for example.

In As a rule, it is not necessary to chemically fill the fillers on their surface or physically modifying with couplers, for example theirs Incorporation and distribution in the cellulose ester to improve. When such couplers serve, for example, substances such as maleic anhydride, those with on the surface the fillers react existing OH groups and thereby form reactive carboxylate ions. If necessary, such a modification can be carried out. It usually has an increase in the modulus of elasticity of the compound produced moldings result.

The Compound of the invention may contain further additives (additives or processing aids) contain, for example, impact modifiers, stabilizers and / or color pigments. these can depending on the requirements of the end product when compounding be incorporated.

impact modifiers make a brittle one Material a tough. This is especially important for films and hollow bodies. As an an example this is Called natural rubber.

stabilizers act of thermal decomposition during processing of the Material contrary. As a stabilizer according to the invention, for example a metal stearate can be used, as in the prior art known.

color pigments be for the appropriate color scheme selected. They also influence others Surface properties. Titanium dioxide is a particularly preferred color pigment since it contains both the whiteness of the product as well as the surface hardness of the compounds obtained from the compounds moldings significantly improved, as already mentioned above.

processing aids such as. Nucleating aids and mold release agents can be used in the Compounding and used in the final processing. she are helpful to a higher one To achieve throughput in production and sticking of the material to prevent the tool. As a release agent, for example, stearates and fatty acid ester serve, both during the compounding as well as later processing.

Accordingly, the invention provides compounds which can be molded, preferably by injection molding, into moldings having heat distortion resistance of up to 90 ° or even 95 ° C. These preferably have tensile moduli in the range of about 4000-5000 N / mm ² , a high rigidity and an elongation at break of more than 8%. The compounds and the articles made from them are compostable. Taking into account the above criteria with regard to the carbonate content and the choice of plasticizer for the cellulose ester, they are classified as harmless under food law.

It It has been found that the compounds according to the invention are based on conventional Plastic processing machines can be processed. The The processing methods to be applied are primarily according to the intended applications. For catering items such as disposable cutlery or trays and other technical or recreational items are injection molding techniques suitable. Blow molding is suitable for the production of hollow bodies (bottles, Doses). For Thermoforming applications (trays and lids) are preferably films extruded.

The machinability and the cycle times when using the compounds of the invention are across from significantly improved other biopolymers. By the very short Cycle times can be realized inexpensively from these mixtures of mass products. Thus, the invention provides for the first time biocompounds, the one Substitute technical plastic. From the compounds of the invention available Plastics are compostable.

The application of the compounds is primarily, but not exclusively, in the food industry. They can, for example, be sprayed into trays and disposable cutlery, blow-molded into bottles and cans, processed into flat films and deep-drawn. The food application places high demands on the product. The migration values may be subject to the prescribed provisions "Methods for Examination of Commodities, Principles for the Determination of Migration in Test Food", in accordance with Regulation No. 80.30, 1 to 3 (EC) according to § 35 of the Foodstuffs and Consumer Goods Act according to the standards of the standard series EN 1186 and EN 13130 "Materials and objects in contact with foodstuffs - plastics." This can be achieved, as the invention has shown, when the above-mentioned conditions regarding the carbonate content and the choice of Therefore, it is possible to obtain a declaration of no objection for contact with food (corresponding to DIN 54 900 -1 / -2) for corresponding moldings, likewise for the first time.

The Choice of the components of the compounds according to the invention results in that the above-mentioned standard specification DIN EN 13432 is complied with. There will be no negative impact on the process of biological Waste treatment is observed, and the quality of the obtained compost is not negatively affected.

Claims (23)

Cellulose ester-containing composition containing - at least a cellulose ester in an amount of 20 to 90 wt .-%, based on the total amount of the composition, - at least one plasticizer in an amount of 15 to 50% by weight, based on the cellulose ester, - inorganic filler in an amount of 5 to 70 wt .-%, based on the total amount the composition wherein the filler at least titanium dioxide, silicate and chalk comprises the composition but not more than 30% by weight of carbonate compound expressed in calcium carbonate, may contain, and - possibly impact modifiers, Stabilizers, color pigments and / or release agents. A composition according to claim 1, wherein the plasticizer is a food approved plasticizer, in particular selected under Glycerine, ethyl lactate, Milchsäuremethylester, Glycerol triacetate, triethyl citrate, diethyl citrate, glycerol acetate, Sorbitol, maltitol, xylitol, erythritol, fatty acid esters and mixtures thereof. Composition according to Claim 1 or 2, characterized the plasticizer is glycerol triacetate. Composition according to one of the preceding claims, characterized characterized in that the cellulose ester is a cellulose acetate. Composition according to one of the preceding claims, characterized in that the cellulose ester or the cellulose acetate has a degree of substitution of 2.0 to 2.6. Composition according to one of the preceding claims, characterized characterized in that the cellulose ester in an amount of up to 50% by weight, stronger preferably of up to 40 wt .-%, based on the total amount of Composition, is present. Composition according to one of the preceding claims, characterized characterized in that the filler in an amount of at least 30% by weight, more preferably at least 40 wt .-% and particularly preferably of at least 50 wt .-%, based on the total amount of the composition, is present. Composition according to one of the preceding claims, characterized characterized in that the titanium dioxide in an amount of 0.5 to 5 wt .-%, preferably up to 2.5 wt .-% based on the total amount the composition is present. Moldings, made of or using a composition according to one the claims 1 to 8. moldings according to claim 9, produced by means of an injection molding process, by blown extrusion, blow molding or deep drawing. moldings according to claim 9 or 10, which is an article, which should come into contact with food. moldings according to one of the claims 9 to 11, selected among cutlery, plates, bowls, trays, cups, flat films and hollow bodies, in particular Bottles and cans. moldings according to one of the claims 9 to 12, characterized by an E-modulus of at least 4800 MPa, preferably from above 5000 MPa and / or a tensile strength of at least 50 MPa and / or an elongation at break of over 7%, preferably over 8%, each at an exam according to DIN EN ISO 527-2 / 1 A with a speed modulus of 1 mm / min or a test speed of 50 mm / min. moldings according to one of the claims 9 to 13 with a dimensional stability in the heat up to 90 ° C, preferably up to 95 ° C. Shaped body according to one of claims 9 to 14 having a migration value of less than 40 mg / dm ² , preferably of less than 10 mg / dm ² in a migration test with the parameters 10-day immersion in 10 vol .-% ethanol at 40 ° C and below 2.0 mg / dm ² in a migration experiment with the parameters 2-day immersion in isooctane at 20 ° C. moldings according to one of the claims 9 to 15, characterized in that it has a biodegradation degree of 90% achieved according to DIN EN 13432. moldings according to one of the claims 9 to 16, characterized in that it is compostable according to DIN EN 13432 is. Use of a composition according to one of claims 1 to 8 for the production of a shaped body according to one of claims 9 to 17th Process for the preparation of a composition according to one of the claims 1 to 8, wherein the cellulose ester and the filler in powder form in a Mix mixer dry and then added the plasticizer becomes. The method of claim 19, wherein the dry mixture made of cellulose ester and filler metered into an extruder and the plasticizer is added via a liquid pump. The method of claim 20, wherein the extruder is a co-rotating twin-screw extruder and the plasticizer in zone two is metered. A method according to any one of claims 19 to 21, wherein the produced Composition afterwards granulated in a strand or in a water bath. A method for producing a shaped article according to a the claims 9 to 17, characterized in that a composition according to a the claims 1 to 8 in an injection molding process, is converted by blowing extrusion or by deep drawing in the desired shape.