DE4326118A1 - Biodegradable, thermoplastically mouldable materials made from starch esters - Google Patents

Abstract

The relatively brittle starch esters are to be modified in such a way that they can be moulded at acceptable economic cost using known thermoplastic processing methods without adversely affecting the properties of the end products and the biodegradability. This is achieved by modifications comprising blends of starch esters having degrees of substitution of < 3 and polyalkylene glycols having molecular weights of from 200 to 2000. Both amylose-rich special starches and conventional natural starches can be employed for the thermoplastically processable blends. The products allow great variation latitude in the processing properties and exhibit no significant drop in quality even after an extended storage time.

Description

The invention relates to thermoplastically deformable Materials in the form of granules, scales, moldings, Extrudates etc. essentially consisting of starch esters and other biologically compatible additives.

Esters of native starches have long been known primarily low-substituted esters, especially acetic acid have gained practical importance. Fields of application are especially the food packaging and paper industries.

For more highly substituted esters, their intended use should be primarily thermoplastic, are also Manufacturing possibilities known. However, you never attain the practical meaning like corresponding cellulose esters.

The reason for this is a higher melting range, lower ones Strength and fragility of the products.

With increasing environmental problems in recent times Starch and its derivatives also for thermoplastic applications more interest. That corresponds to that widespread endeavor, the potential of renewable Make raw materials usable for the plastics sector. Use So far, products made from pure starch have been found Mixtures with conventional polymers, such as. B. polyethylene (including WO 9015843) or ethylene vinyl alcohol copolymers (EP 0400531, EP 0400532, WO 9102023).

However, both variants are for the specified Purpose with decisive disadvantages. Pure starch items have a very limited shelf life and are extremely sensitive to moisture.

Blends with conventional polymers are biological Degradability, at least partially, questioned.

On the other hand, under the heading biodegradable polymers bacterial storage agents such as p-polyhydroxybutyric acid and whose copolymer is offered with β-hydroxyvaleric acid. The latter in particular has already processed some of the features well showable thermoplastics. The relatively high price ver but has so far prevented a broad market launch.  

Under the aspects mentioned, the use is also increasing derivatized starch, especially the starch ester with high Ren degrees of substitution, for thermoplastic use purposes more interesting again. It should be noted that the reactants used for derivatization Biodegradability of the end products is not essential may impair or completely prevent. same for for plasticizers, auxiliaries, etc.

The use of starches from Advantage. Despite the well-known variants for manufacturing of starch acetates with higher degrees of substitution So far, it has also been lacking economically favorable design possibilities, such starch acetates inexpensively in qualitative to convert satisfactory thermoplastics. It is known that Starch esters with degrees of substitution <3 are extremely laborious and thermoplastically processable with unsatisfactory success are. In other words: the materials in question result in poorly flowing melts and must therefore be so be heated high that thermal damage is not can be avoided. The resulting moldings are more discolored or less and are highly brittle. This is especially true when the strength used contains significant concentrations of amylopectin.

Significant progress was made when it succeeded was to plasticize starch acetates with suitable plasticizers ren. According to DE 41 14 185, citric acid is preferred esters, glycerol acetate and lactic acid ethyl ester used. The esters proposed there are biodegradable bar, but have a limited time as a plasticizer Effect, d. H. the molding compounds become brittle during storage.

The object of the invention is to develop new starch ester Develop plasticizer compositions that are represented with cash economic effort with all known thermoplastics processing methods are deformable without including the properties of the end products, especially the Long-term strength and biodegradability suffer.  

According to the invention, the modifications consist of blends of Starch esters, predominantly starch acetate, with a substituent tion degree <3, preferably from 1.8-2.6 and polyalkylene glycol kolen (PAG) with a molecular weight of 200-2000 g / mol preferred from 200 to 600 g / mol. As polyalkylene glycol predominantly polyethylene glycol and polypropylene glycol as well Copolymers of ethylene oxide and propylene oxide and copolymers of ethylene oxide and propylene oxide with any combination settlement used.

In this way, thermoplastically processable Generate mixtures for all known processing methods for example for melt extrusion, injection molding, deep drawing etc. With a significantly reduced processing temperature tures and increased melt index, so that a thermal damage can be avoided even in the beginning. A It is a particular advantage of the procedure mentioned that also native starches with relatively high levels of amylopectin can be processed.

The resulting products are dimensionally stable and very precise, far less sensitive to moisture than products made from pure Starch and yet completely biodegradable as well the usable polyalkylene glycols easily the biologi subject to degradation.

Another particular advantage lies in the fact that the Addition of polyalkylene glycols incorporation and homo gene distribution of auxiliaries such as pigments, stabilizers plasticizers, flame retardants, lubricants and fragrance Substances in the starch esters much easier and promoted different. Contrary to the behavior of not using polyalkylene Glycolic starches contain the auxiliary mentioned substances their homogeneous distribution over unlimited periods at.

The mechanical characteristics of the blends show no drop longer storage.

The examples given below demonstrate simplicity the production of the materials according to the invention. Farther it is proven that the processing properties are broad Ranges varied and both amylose-rich special strengths such as ordinary natural strengths can also be used.  

Examples 1 to 12

30 g each of a starch ester (degree of substitution 2.2-2.4) are mixed with a certain amount of polyethylene glycol Plasticorder kneaded. The respective test conditions and the results of the application test are in summarized in the following table. The kneading time was one 15 minutes, the temperature 150 ° C.

Table 1

Composition and melt index of Examples 1-12

From Examples 3 and 11, an extruder and a Slot nozzle with pull-off device made of clear foils, determined for the subsequent application-related parameters were:

Table 2

Selected mechanical characteristics of films of Examples 3 and 11

Samples 2, 3, 5 and 6 were used on a thermal press 15 ° C plates (50 × 50 × 1 mm). The plates were 2 minutes without pressure and then at a pressure of 20 MPa pressed. The resulting films are thermoformable.

Examples 13 to 16

1500 g of starch acetate (degree of substitution 2.3) were added via a twin-screw extruder with the addition of polyalkylene glycol and a pigment to a granulate (diameter 3 mm) processed. The granules showed in all Pig used uniform coloring. They were used as a raw material used for the injection molding of ISO rods according to DIN 53 455.

Table 3

Composition in Examples 13-15

Example 16 corresponds in composition to Example 13, however, was stored dry for 3 months.  

The application test of the ISO rods showed the following Characteristic values:

Table 4

Application characteristics of the ISO rods from Examples 13-16

Example 16 proves that the blends according to the invention after no noticeable loss of quality on longer storage times point.

Claims (7)

1. Biodegradable thermoplastic materials from starch esters and plasticizers, characterized in that they consist of blends of starch esters based on starch with an amylopectin content of 20 to 80% by mass and with a degree of substitution <3 with polyalkylene glycols or mixtures of different polyalkylene glycols with molecular weights of 200-2000 g / mol in a mixing ratio of starch ester / polyalkylene glycol from 10 to 1 to 10 to 5 parts by mass. 2. Materials according to claim 1, characterized in that they starch esters with a degree of substitution of 1.8-2.6, preferably contain 2.2-2.4. 3. Materials according to claim 1 and 2, characterized in that they are polyalkylene glycols or mixtures of polyalkylene glycols or alkylene glycol copolymers with molecular weights of Contain 200-600 g / mol. 4. Materials according to claim 1 to 3, characterized in that they contain starch esters in the form of starch acetates. 5. Materials according to claim 1 to 3, characterized in that they contain mixed starches, the acetoxy and / or Propoxy and / or butyroxy and / or β-hydroxybutyroxy Bear substituents. 6. Materials according to claims 1-5, characterized in that the polyalkylene glycols used are polyethylene glycols and / or polypropylene glycols and / or copolymers of ethyl are lenoxide and propylene oxide. 7. Materials according to claims 1-6, characterized in that they have plastic auxiliaries in a homogeneously distributed form contain.