DE102009005640B4 - Thermoplastic molding compound and molded parts, process for their preparation and their use - Google Patents

Abstract

Plasticizer-free thermoplastic molding composition comprising a matrix phase of at least one cellulose ester and at least one inhibitor which at least reduces the chain degradation of the polysaccharide ester during the thermoplastic processing,

Description

The present invention relates to a thermoplastic molding composition which has a matrix phase of a polysaccharide ester and is free of plasticizers. The molding compound additionally contains at least one inhibitor which prevents molecular degradation during the thermoplastic processing of the molding compound. The thermoplastic processing of said molding compound thus leads to products with unusually high strength, rigidity and heat resistance. Likewise, the invention relates to a process for the preparation of such molding compositions as well as from these molding compositions produced moldings and a corresponding manufacturing method. The moldings are used as high-strength and / or highly stressed structural components, as plates, films, bristles, monofilaments or fibers.

Polysaccharide esters, such as. As starch ester or cellulose ester, in contrast to most petroleum-based polymers, such as polypropylene, polyethylene, polyamides, etc., not without the addition of plasticizers with the usual methods, such as extrusion or injection molding melt processable. For starch itself, the term thermoplastic starch (TPS) was coined. TPS denotes starch compounds which contain plasticizers, such as water, glycerol, sorbitol or the like, and are therefore thermoplastically processable ( EP 0 397 819 ). To achieve thermoplastic processability of starch esters plasticizers are also usually added here z. B. glycerol triacetate ( US 5,869,647 ).

The WO 91/14381 A1 describes a process for producing a tobacco smoke filter in which spun fibers of cellulose acetate are subjected to a post-treatment with organic acids or salts.

Cellulose esters, u. a. Cellulose acetate (CA), cellulose butyrate (CB), cellulose acetate butyrate (CAB), which are commercially available for thermoplastic processing, particularly injection molding, also contain plasticizers, mostly based on phthalic acid esters. Significant manufacturers are Eastman Co. with the product range Tenite and Al- to Plastics GmbH with Cellidor, whereby the products differ by different plasticizer content in the range of 5% to 30%. Lower plasticizer levels are available for longer chain esters, e.g. As CAB, due to their molecular structure easier processing, compared with shorter-chain, z. B. CA permit.

The softeners for cellulose esters conventionally used in the art include o-, m-, p-phthalic acid, benzoic acid, trimellitic acid, benzenesulfonic acid, aliphatic dicarboxylic acids (glutaric acid, adipic acid, azelaic acid, sebacic acid), aliphatic monocarboxylic acids (saturated fatty acids C ₂ -C ₁₈ , Oleic acid, linoleic acid, linolenic acid, ricinoleic acid), acrylic acid, phosphoric acid and citric acid.

In particular, plasticizers known to the art for cellulose esters are understood as meaning the following substance groups:

From the group of glycerides:

• • mono-, di- and triesters,
• • in the diesters and triesters also compounds with mixed ester groups,
• In the triesters especially glycerol triacetate and glycerol tripropionate,
• • Glycerides with ester residue groups belonging to the linear and branched aliphatic alkyl groups and the olefinic residue groups, with C ₂ -C ₃₆ carbon atoms in the alkyl chains.

From the group of citrates:

• • mono-, di- and triesters,
• • in the diesters and triesters also compounds with mixed ester groups.

From the group of phthalates:

• • dimethyl phthalate,
• Diethyl phthalate,
• Dibutyl phthalate,
• • butyl benzyl phthalate,
• Ethylene glycol monoethyl phthalate, etc.,

Esters of trimellitic acid:

• • trimethyl trimellitate,
• Triethyl trimellitate,
• Tri (2-ethylhexyl) trimellitate, etc.

Aliphatic dicarboxylic acid esters

• • such as di- (2-ethylhexyl) azelate etc.

From the group of phosphoric acid esters:

• Tributyl phosphate,
• Tributoxyethyl phosphate,
• Triphenyl phosphate,
• Tricresyl phosphate,
• Cresyl diphenyl phosphate,
• 2-ethylhexyldiphenyl phosphate etc.

Esters of ricinoleic acid:

• • 12-hydroxyacetyl-9-octadecenoic acid methyl ester etc.

The prior art use of plasticizers allows the thermoplastic processing of polysaccharide esters on an industrial scale, but down, just by the plasticizing effect, the mechanical properties of the final product (extrudate or injection molding) down. This can be seen when one considers maximum levels of commercial cellulose-based products (starch-based ones below). For the product Biograde 200C from FKur, such maximum values are described with tensile strengths in the range of 80 MPa and tensile moduli of 3.4 GPa. Otherwise usual values lie far below and move in the range 40 MPa and 1.5 GPa. Another disadvantage of plasticizer-containing systems is that plasticizers have a tendency to migrate in the finished molded part due to the high mobility that distinguishes them as plasticizers, which can lead to embrittlement of the product. The disadvantages mentioned are overcome by the thermoplastic bio-based material according to the invention.

Based on this, it was an object of the present invention to provide moldings that do not have the said disadvantages in the prior art, d. H. are thermoplastically processable and yet have a high strength and rigidity.

This object is achieved by the molding composition with the features of claim 1, the method for its production with the features of claim 7, the molding with the features of claim 11 and the method for producing the molding with the features of claim 14. In claim 15 uses of the invention are given. The other dependent claims show advantageous developments.

According to the invention, a polysaccharide-based thermoplastic molding composition is provided which comprises a matrix phase of at least one cellulose ester in which at least one inhibitor substance is contained. The molding composition according to the invention contains no plasticizer.

Surprisingly, simple chemical substances, referred to herein as inhibitors or inhibitor substances, which, after addition to the matrix phase of cellulose esters, exhibit an effect on thermoplastic processing without producing any apparent softening effect in the end product. As a result, unusually high strengths (for example tensile strengths of 203 MPa) and stiffnesses (for example tensile moduli of 8.4 GPa), for example. B. in injection-molded specimens reached (see the examples below). The inhibitor substances are characterized in that they prevent the degradation of the molecular chains in the matrix phase or restrict such that the molecular weight after processing is above that which results without said addition. As further explained in the Examples, the reduction of the weight average molecular weight from 40% for a system without inhibitors to, for example, 14% for that with suitable inhibitors is reduced (see Example 6). In addition, the mobility of the inhibitors in the finished molding is negligible, as evidenced by the lack of plasticizing effect. Further advantages of the material according to the invention result from the absence of plasticizers in terms of thermal stability. Thus, the heat distortion resistance is even increased by 45 K compared to a conventional system with very low plasticizer content (10% triacetin in cellulose acetate) if, instead of the plasticizer, 0.17% by weight NaCl is added as an inhibitor during processing in a suitable manner. This achieves a heat deflection temperature (drop in the dynamic bending modulus at 10 Hz to 1 GPa) of 195 ° C.

Preferably, the cellulose ester is a cellulose ester selected from the group of cellulose acetates, cellulose butyrates and / or cellulose acetate butyrates.

The cellulose ester preferably has a degree of substitution (DS) of from 1.7 to 3, more preferably from 2.3 to 2.7.

Suitable inhibitors within the meaning of the invention are all substances which prevent or restrict a chain degradation during the thermoplastic processing of the molding composition. Potassium chloride and urea have proven to be suitable. Furthermore, substances which contain Na ions, such as sodium hydroxide, sodium chloride or sodium sulfate, have proven particularly suitable.

The proportion by weight of the cellulose esters in the molding composition is preferably between 99.9999 and 90% by weight, preferably between 99.99 and 95% by weight and more preferably between 99.9 and 97% by weight.

The proportion by weight of the at least one inhibitor substance, based on the total molding composition, is preferably between 0.0001 and 10 wt .-%, preferably between 0.001 and 5 wt .-% and particularly preferably between 0.1 and 3 wt .-%.

The invention also provides a process for the preparation of the plasticizer-free thermoplastic molding composition as described above, wherein the at least one inhibitor substance is homogeneously mixed with the cellulose ester matrix under the action of mechanical shear forces. In addition to the direct addition of the inhibitor substances, a special embodiment of the method according to the invention proves to be advantageous in which an aqueous solution of the inhibitor is prepared and the cellulose esters are impregnated with this solution and then dried. Before mechanical shearing, a more homogeneous initial distribution of the inhibitor substances in the cellulose esters is achieved.

The mixing is preferably carried out at temperatures between 0 ° C and 450 ° C, preferably between 100 ° C and 350 ° C and more preferably between 150 ° C and 300 ° C.

A preferred embodiment of the preparation of the material according to the invention is carried out as follows:
Cellulose acetate powder with a degree of substitution of 2.63 is dried under vacuum at 80 ° C for 24 h. A certain amount (see examples) of the modifier substance is premixed with the cellulose acetate for about 5 minutes by means of a fast rotating mixer. Subsequently, the resulting mixture is homogenized with a kneader at temperatures ranging from 180 to 300 ° C and rotational speeds between 50 and 350 rotations per minute (rpm). Mixing times are in the range between 5 and 60 minutes, preferably between 10 and 30 minutes. For further homogenization, an extrusion is carried out on a co-rotating twin-screw extruder at temperatures between 200 and 350 ° C and a screw speed between 10 and 350 rpm. The extrudate is comminuted with a commercial strand pelletizer and injection molded. The cylinder temperatures are between 210 and 250 ° C and mold temperatures between 80 and 140 ° C

For soluble inhibitor substances (see examples), the following variant of the method according to the invention is also suitable. A defined amount of the inhibitor is completely dissolved in a suitable solvent, preferably water, under the action of mechanical shear forces. Subsequently, a defined amount of the cellulose ester is added and a homogeneous dispersion, also under the action of mechanical forces produced. Thereafter, a drying of the resulting premix under vacuum at 50 ° C. The further processing is carried out as described above by kneading, extrusion and injection molding.

According to the invention moldings are also provided which can be produced from the molding composition described above.

The moldings according to the invention preferably have a tensile strength of at least 100 MPa, preferably at least 130 MPa, more preferably at least 150 MPa and particularly preferably at least 175 MPa. These tensile strengths are determined on a test rod according to D1N EN ISO 527-1 Type 5A at 23 ° C and 50% relative humidity.

Furthermore, the moldings of the invention have a tensile modulus of at least 5 GPa, preferably at least 6 GPA, more preferably at least 7 GPa, and most preferably at least 8 GPa. These tensile moduli are determined on a test rod according to DIN EN ISO 527-1 Type 5A at 23 ° C and 50% relative humidity.

Furthermore, a method for producing the molding described above is provided, in which a molding composition, as described above, is thermoplastically processed. The thermoplastic processing is preferably carried out by extrusion, in particular profile and film extrusion, injection molding, injection blow molding, pressing, or melt spinning.

The molded parts according to the invention are used as a high-strength and / or highly stressed structural component, as a plate, foil, bristle, monofilament or fiber in the fields of transport and traffic, industrial equipment, mechanical and plant engineering, household appliances, container construction, medical technology, electrics and electronics.

The subject according to the invention is intended to be explained in more detail with reference to the following examples, without wishing to restrict it to the specific embodiments shown here.

example 1

Cellulose acetate powder L60 / 90 from Eilenburg with a DS determined by nuclear magnetic resonance of 2.63 is pre-dried overnight at 80 ° C in a vacuum oven. With a fast-rotating kitchen mixer, a premix is prepared containing 3.1 g of urea and 100 g of pre-dried cellulose acetate powder and stored in a polyethylene bag in a sealed position overnight. The premix is homogenized in a kneader W 350 E from Brabender for 20 min at 230 ° C. and a speed of 150 rpm. After discharge and comminution of the compound, it is further homogenized in a co-rotating twin-screw extruder (Haake Minilab) at 230 ° C. and 200 rpm, discharged and granulated (granulator SGS 25-E4 from Scheer). Subsequent injection molding takes place on a Haake Minijet at a cylinder temperature of 230 ° C and a mold temperature of 110 ° C. Test bars according to DIN EN ISO 527-1 Type 5A are produced, which are then tested at 23 ° C and 50% relative humidity in an air-conditioned laboratory on a Zwick 1445 testing machine according to DIN EN ISO 527-1.

Example 2

As in Example 1, with only 0.5 g of sodium hydroxide powder instead of urea.

Example 3

175 mg of sodium chloride (3 mmol Na in NaCl) is dissolved in 200 ml demineralized water with stirring. Subsequently, 100 g of cellulose acetate powder L60 / 90 from Eilenburg are introduced into the solution and a homogeneous dispersion is prepared by mixing. This dispersion is dried for at least 24 h at 50 ° C under vacuum. The premix thus prepared is treated as in Example 1, but without the use of a kneader, i. H. the premix is extruded directly.

Example 4

As in Example 3, only with 224 mg of potassium chloride (3 mmol K in KCl) instead of sodium chloride.

Example 5

As in Example 3, only with 213 mg of sodium sulfate (3 mmol Na in Na ₂ SO ₄ ) instead of sodium chloride.

Example 6

As in Example 3, with only 120 mg sodium hydroxide (3 mmol Na in NaOH) instead of sodium chloride.

Example 7

For comparison purposes, 100 g of cellulose acetate powder L60 / 90 from Eilenburg are introduced into demineralized water, mixed as described, dried and processed as in Example 3.

In Table 1, the mechanical properties of inventive materials according to Examples 1 to 6 compared to Comparative Example 7 without inhibitor, compared to the commercially available material Biograde 200C (FKuR GmbH) containing a plasticizer and the unprocessed cellulose acetate powder, and determined weight average Molar mass M _w shown. The determination of the mechanical characteristics was carried out according to DIN EN ISO 527-1, test specimen type 5A.

The molecular weight was determined by gel permeation chromatography (GPC). In this case, 22 mg of the thermoplastically processed molding compound or the thermoplastically processed starting ester to be examined in 4 ml of dichloromethane / methanol (90:10 vol .-%: Vol .-%) were dissolved at room temperature and stored for 24 h. The actual measurement was carried out using conventional GPC (polystyrene standards) via an HPLC pump (Waters 515), an autosampler (Waters 717 plus), column oven and UV-vis detector (Waters 2487) at a wavelength of 254 nm and a RI Detector (Waters 2414) at 25 ° C. The column bank used was based on polystyrene divinylbenzene (Polymer Laboratories) with a precolumn (PL gel, 10 μm) and three subsequent columns (PL gel, 20 μm, MIXED-A).

As is clear from the column "Molmassenabbau", the inhibitors used reduce the degradation of 41% for the sample without inhibitor addition to up to 14% in Example 6. Based on the mechanical values is impressively demonstrated that the moldings of the invention significantly better strengths and Have stiffness.

Claims (15)

Plasticizer-free thermoplastic molding composition comprising a matrix phase of at least one cellulose ester and at least one inhibitor which at least reduces the chain degradation of the polysaccharide ester during the thermoplastic processing, Molding composition according to claim 1, characterized in that the at least one cellulose ester is cellulose acetate, cellulose butyrate and / or cellulose acetate butyrate. Molding composition according to one of the preceding claims, characterized in that the polysaccharide ester has a degree of substitution (DS) of from 1.7 to 3, preferably from 2.3 to 2.7. Molding composition according to one of the preceding claims, characterized in that the at least one inhibitor is selected from the group consisting of alkali metal salts, in particular sodium hydroxide, sodium chloride, sodium sulfate and potassium chloride, and urea. Molding composition according to one of the preceding claims, characterized in that the weight fraction of the matrix phase, based on the molding composition, between 99.9999 to 90 wt .-%, preferably between 99.99 and 95 wt .-%, particularly preferably between 99.9 and 97% by weight. Molding composition according to one of the preceding claims, characterized in that the weight fraction of the at least one inhibitor, based on the molding composition, between 0.0001 to 10 wt .-%, preferably between 0.01 and 5 wt .-%, particularly preferably between 0 , 1 and 3 wt .-% is. A process for the preparation of a plasticizer-free thermoplastic molding composition according to any one of the preceding claims, wherein the at least one inhibitor is homogeneously mixed with the matrix phase. A method according to claim 7, characterized in that the at least one inhibitor is homogeneously mixed with the matrix phase under the action of mechanical shear forces. A method according to claim 7, characterized in that an aqueous solution of the at least one inhibitor is prepared, the polysaccharide ester is soaked with this solution and then dried. Method according to one of the two preceding claims, characterized in that the mixing is carried out at temperatures between 0 ° C and 450 ° C, preferably between 100 ° C and 350 ° C, more preferably between 150 ° C and 300 ° C. Molding, producible from a molding composition according to one of claims 1 to 6. Molding according to the preceding claim, characterized by a tensile strength of at least 100 MPa, preferably at least 130 MPa, more preferably at least 150 MPa, particularly preferably at least 175 MPa, measured on a test rod according to DIN EN ISO 527-1 Type 5A at 23 ° C and 50 % relative humidity. Molding according to one of the two preceding claims, characterized by a tensile modulus of at least 5 GPa, preferably at least 6 GPa, more preferably at least 8 GPa, measured on a test rod according to DIN EN ISO 527-1 Type 5A at 23 ° C and 50% relative humidity , Process for producing a molded part according to one of Claims 11 to 13, in which a molding composition according to one of Claims 1 to 6 is processed thermoplastically, in particular by extrusion, in particular profile and film extrusion, injection molding, injection blow molding, pressing or melt spinning. Use of a molding according to any one of claims 11 to 13 as a high-strength and / or highly stressed construction component, as a plate, foil, bristle, monofilament or fiber in the fields of transport and traffic, industrial equipment, machinery and plant construction, household appliances, container construction, medical technology, electrical and electronics ,