WO1996035746A1 - Biodegradable thermoplastic moulding compounds with improved processing properties and performance characteristics - Google Patents

Abstract

Polyalkylene carbonates have only limited thermoplastic processability properties and performance characteristics owing to the excessively high melting index for injection moulding, considerable shrinkage, a low modulus of elasticity and poor hardness of the surfaces of the mouldings. These drawbacks are eliminated by moulding compounds containing oxides, carbonates or sulphates of metals in the 2nd main group of the periodic system, oxides of metals in the 3rd main group, starch, cellulose and/or talc in the concentration range 60 to 90 mass % polymer to 10 to 40 mass % additive besides the polyalkylene carbonate. This provides biodegradable polyalkylene carbonates for use in 'mass plastics'.

Description

Biodegradable thermoplastic molding compositions with improved processing and use properties

The invention relates to biodegradable, thermoplastically processable molding compositions consisting of aliphatic polycarbonate, also known as polyalkylene carbonate (PAC) or from mixtures of different PAC. The invention also relates to mixtures of these molding compositions with fine-grained inorganic and / or organic substances and with the processing and other auxiliaries customary in the plastics industry.

The aliphatic polycarbonates are polymers that were first produced in Japan at the end of the 1960s by the copolymerization of alkylene oxides with carbon dioxide. (S. Inoue, Polymer Letters 7 1969), pp. 287-292) US Pat. No. 3,585,168 describes a process for the production of high molecular weight copolymers of an alkylene oxide, such as ethylene oxide or propylene oxide with carbon dioxide. The PAC are described as crystal-clear, amorphous thermoplastics with good barrier and adhesion properties as well as with biodegradability. Binder, glue and coatings are mentioned as potential main areas of application. The products are said to be usable in metal casting, in the ceramic industry, for the production of safety glass, as a modifier for PVC and for the packaging sector. Manufacturing, properties and applications can u. a. the following publications can be found:

- Plastic manual 3/1, Hanser Verlag, - Brochure material from PAC Polymers Inc., Allentown, PA (USA),

- Chemtech, September 1976, pp. 588-594.

The property profile of polyalkylene carbonates, in particular polypropylene carbonate (PPC), is characterized by the following properties, which limit the possible uses and applications: - high stickiness,

- very high melt index,

- strong shrinkage behavior during molded part production in injection molding,

- low modulus of elasticity and the resulting lack of rigidity,

- low hardness of the molded part surface.

This property picture explains the fact that the spectrum of processing and application possibilities of this class of plastics is relatively narrow. This applies in particular to the possibilities for thermoplastic processing into foils, hollow bodies and molded parts. This considerably limits the development of this polymer class as a so-called bulk plastic, although this would be desirable due to the easy accessibility and economic producibility of the starting products and the ecologically adapted usability of the waste, which makes recycling avoidable. Attention should also be drawn to the environmentally friendly aspect of using carbon dioxide as a synthetic building block. The main disadvantage is the difficulty in processing the polyalkylene carbonates into molded parts by injection molding. It is known that newly developed plastics often have the character of largely universally applicable materials only through the possibility of injection molding processing.

The object of the invention is to molding compounds

Manufacture basis of PAC, in which the thermoplastic processability and the property profile of the semi-finished and finished parts are so improved that in particular the sector of injection molding processing is fully developed and that the usage properties of the finished parts with regard to

Rigidity and hardness, as well as the shrinkage of the molded part and the stickiness can be adapted to the general requirements. This is intended to expand the application offer the polyalkylene carbonates. The object is achieved in that molding compositions are made which are composed of polyalkylene carbonate or mixtures thereof, fine-grained inorganic and / or organic substances and the processing and other auxiliaries customary in the plastics industry. Calcium carbonates of different origins and production methods, asbestos-free talc,

Anhydrite (CaS04) and the oxides of aluminum, magnesium and titanium can be used. Fine organic starch and cellulose of different origins can be used for organic substances. The polyalkylene carbonate used in the molding compositions according to the invention corresponds to the general formula: fCH (Rι) -CH (R2) -0-C0-0} χ where Ri, R2: hydrogen or straight-chain and / or branched alkyl radicals of the general formula C _n H2n + l mi n - 1 to 4, x: 10 to 5000 mean.

The quality improvements occurring according to the invention can be illustrated by physical parameters. Depending on the type and concentration of the mixture constituents, the following property improvements can be achieved:

- The limit bending strength increases by 60 to 80% compared to the unmodified polymer.

- The modulus of elasticity as a characteristic of the rigidity or dimensional stability of those obtained by injection molding

Moldings rises to 3 to 4 times.

- The tensile strength increases by approx. 40%.

- The elongation at break increases, for. B. with the addition of cornstarch to more than 4 times. - The ball indentation hardness increases by approx. 50 - 60%.

In addition, the flow behavior during injection molding is generally reduced by lowering the melt index, so that processing is possible in a conventional manner. Examples:

The invention will be explained in more detail below using a few selected examples:

The polyalkylene carbonate samples were used with the appropriate samples to produce standard rods measuring 80 x 4 x 10 mm

Mix components mixed well in a laboratory mixer and then processed and granulated in a twin-screw laboratory extruder. The granules were sprayed onto the above-mentioned standard bars and the mechanical tests were carried out on them.

The compositions of the molding compositions according to Examples 1 to 7 are contained in Table 1. The most important mechanical properties and the processing temperatures are shown in Table 2. In the mixing ratios PPC to additive equal to 75 to 25 according to Examples 2, 3, 6 and 7, the effect of different additives can be compared well. Regardless of the type of additive, the modulus of elasticity (particularly high in Example 3), the limit bending strength and ball indentation hardness are considerably increased, while the elongation at break in Examples 3 and 6 is reduced.

Table 1 Composition of the mixtures

Example PPC PEC chalk talcum anhydrite corn starch cellulose TiO2 No. mass% mass% mass% mass% mass% mass% mass% mass%

1 100

2 75 25 I.

3 75 25 - - "i

4 35 35 9 - - 20 1

5 85 14 ¹

6 75 25 - - ""

7 75 25 - - "

Table 2 Selected mechanical characteristics of the mold wet

Example processing - limit bending modulus of elasticity - tensile elongation - ball_ no. Temp. craft activity pressure hardness

C ° C] [MPa] [MPa] [MPa] [%] [N / mm2]

1 180 54 2200 40 20 125 I

2 186 90 4590 54 20 190 i

3 180 85 7200 60 4 166

4 185 35 1280 35 85 53

6 195 70 3600 41 44 180

6 190 64 3900 40 5 177

7 185 72 4690 42 25 178

Claims

claims 1. Biodegradable thermoplastic polyalkylene carbonate molding compositions with increased rigidity and hardness, reduced mold shrinkage during injection molding and reduced stickiness, consisting of: A) 60 to 90 parts by mass of a polyalkylene carbonate of the general formula I tCH (Rl) -CH (R2) -O-CO-0J _x where R ₁ , R2 and x mean: R _l , R2: hydrogen or straight-chain and / or branched alkyl radicals of the general formula CnH2n + l mi n = 1 to 4 x: 10 to 5000 or mixtures thereof. B) 10 to 40 parts by mass of an oxide of metals of III. Main group of the PSE, an oxide, carbonate or sulfate of metals of the II. Main group of the PSE, talc, starch or cellulose or mixtures thereof. C) 0 to 5 parts by mass of conventional processing aids, modifiers and / or pigments. 2. Molding compositions according to claim 1 with finely divided anhydrite with a grain size in the range from 2 to 50 μm as component B. 3. Molding compositions according to claim 1 with finely divided chalk with a grain size in the range from 1 to 60 μm as component B. 4. Molding compositions according to claim 1 with finely divided asbestos-free talc with a grain size in the range from 1 to 10 μm as component B. 5. Molding compositions according to claim 1 with finely divided native starch of any origin of a grain size in the range of 2 to 100 microns as component B. 6. Molding compositions according to claim 1 with finely divided cellulose of any origin with a grain size in the range of 2 to 100 μm as component B. 7. Molding compositions according to claims 1 to 6 with polypropylene carbonate as component A. 8. Molding compositions according to claims 1 to 7 with x = 100 to 3000 in formula I of component A.