CS260460B1 - Polymer mixture on base of tough and standard polystyrene - Google Patents

Abstract

The solution relates to a polymer mixture based on standard and tough polystyrene with improved utility properties. The mixture according to the solution contains 5 to 25 %/o, preferably 10 to 20 % by weight of thermoplastic rubber. The thermoplastic rubber used is the styrene-butadiene copolymer of interest with a bound styrene content of 25 to 45 %/o by weight. The ratio of standard and tough polystyrene in the mixture is 1 : 2 to 8 : 1. The polymer mixture prepared according to the solution is characterized by very good gloss, increased rigidity and very good toughness. Its properties make it an equivalent replacement for ABS polymers for some applications, the preparation of which is more expensive.

Description

The invention relates to a polymer mixture based on standard and high-impact polystyrene with improved utility properties, especially higher gloss, increased rigidity and heat resistance.

It is known that by mixing standard and high-impact polystyrene, it is possible to prepare a wide range of polymerization mixtures with properties dependent on the mixing ratio of both basic polymers. The content of high-impact polystyrene mainly affects the impact strength. The amount of standard polystyrene mainly determines the rheological properties of the mixture, stiffness and gloss.

It is also known to modify polystyrene plastics with thermoplastic rubbers. Thermoplastic rubbers (elastomers) are substances that can be processed under heat using plastic processes like thermoplastics, and have a number of properties typical of cross-linked rubbers over a wide temperature range, such as high tensile strength, high ductility, and others.

Vulcanization is not necessary for thermoplastic elastomers. Crosslinking occurs through physical bonds between the thermoplastic segments.

The character of an elastomer is created by the individual elastomeric segments of macromolecules. Under the influence of heat, the physical bonds weaken and thermoplastic rubbers begin to behave as uncrosslinked polymers and can be processed by plastic processes.

The essence of thermoplastic elastomers are the copolymers under consideration, e.g. styrene-butadiene-styrene. Their structure can be either linear or star-shaped, most often tetrahedral.

Another group of thermoplastic elastomers are polymers with alternating soft and hard segments. A typical representative is polyurethanes.

The third group is grafted copolymers, e.g. AAS type. The properties of thermoplastic rubbers are used in the production of so-called super-tough polystyrenes produced by mixing tough polystyrene with the addition of thermoplastic rubber.

The disadvantage of these polymer blends is the decrease in gloss and stiffness of the polymer blend. By modifying standard polystyrene with thermoplastic rubbers, semi-transparent types of polystyrene with improved toughness can be prepared.

A more advantageous and balanced property is possessed by the mixture according to the invention. This mixture is based on standard and tough polystyrene and contains 5 to 25%, preferably 10 to 20% by weight of thermoplastic rubber, the thermoplastic rubber being the styrene-butadiene copolymer of interest with a bound styrene content of 25 to 45% by weight.

The ratio of standard and resilient polystyrene in the mixture is 1:2 to 8:1.

The main advantages of the polymer mixture according to the invention are balanced utility properties - very good gloss with considerable stiffness and very good toughness. Their properties make the mixtures equivalent to a replacement for ABS polymers for some applications, but the preparation of which is more expensive.

Various devices, such as a twin-screw extruder, can be used to mix a mixture of standard and resilient polystyrene with thermoplastic rubber.

The mixture may further contain dyes, pigments, antioxidants and light stabilizers.

The advantages are further evident from the following examples:

Comparative example

The following mixtures were prepared for comparison:

a) a mixture of 90% by weight of high-impact polystyrene and 10% by weight of thermoplastic rubber,

b) a mixture of 90% standard polystyrene and 10% by weight of thermoplastic rubber.

The basic physical and mechanical properties of the starting polystyrenes from both mixtures were determined.

The results are shown in Table I.

Individual mixtures have increased notch and impact strength. However, the overall balance of performance properties is lacking.

Example 1

8 parts by weight of standard polystyrene were mixed with 1 part by weight of high-impact polystyrene. The characteristics are given in Table L. From this starting mixture, three 10-kilogram samples containing 5, 10 and 20% by weight of styrene-butadiene-styrene thermoplastic rubber were prepared according to the invention, having the following specifications:

bound styrene 30.2% wt.

molecular weight 130,000 hardness SHORE A 2 70

After mixing in a laboratory mixer, the samples were granulated in a laboratory extruder and the physical and mechanical properties of the test specimens from the granulate thus prepared were determined.

An overview is given in Table II,

Example 2

A basic mixture was prepared from the same raw materials as in Example 1. A ratio of 4 parts by weight of standard polystyrene and 1 part by weight of high-impact polystyrene was chosen.

From this starting mixture, three samples containing 5, 10 and 20 wt. % of thermoplastic rubber of the same specification as in Example 1 were prepared according to the invention.

After mixing, the samples were granulated in a laboratory extruder, test specimens were prepared from the granulates and their physical and mechanical properties were determined.

The results are shown in Table II.

Example 3

From the same raw materials as in Example 1, a mixture of standard and resilient polystyrene was mixed in a weight ratio of 1:1. From this starting mixture, three samples containing 5, 10 and 20% by weight of thermoplastic rubber of the same specification were prepared according to the invention.

Test specimens were prepared from the samples after mixing and granulation, and their physical and mechanical properties were determined.

The results are in Table II.

Example 4 'A mixture of 1 part by weight of standard polystyrene and 2 parts by weight of high-impact polystyrene was prepared, the same types were used as in the previous examples.

To the resulting mixture was added 10% by weight of thermoplastic rubber of the following specification:

bound styrene content of 40% by weight.

molecular weight 150,000 hardness SHORE A 2 92

After mixing and granulation, test specimens were prepared and the physical and mechanical properties were determined.

Charpy notched toughness 1.5 J. cm ^-2 Gloss 30%

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Claims (1)

A polymer blend based on standard and tough polystyrene, characterized in that it comprises 5 to 25, preferably 10 to 20% by weight of thermoplastic rubber, the thermoplastic rubber being a styrene-butadiene copolymer having a bound styrene content of 25 to 45% by weight. the ratio of standard and tough polystyrene is 1: 2 to 8: 1.