RU2792366C1 - Thermoplastic degradable polyethylene composition and method for its production - Google Patents

Abstract

FIELD: polyethylene production.

SUBSTANCE: manufacture of thin films by extrusion. The thermoplastic degradable polyethylene composition contains low-density polyethylene, high-density polyethylene, and a mixture of polyethylene recycled product with calcium carbonate made in the form of granules. A method for producing a thermoplastic degradable composition is also proposed.

EFFECT: increasing of the degradation of the polyethylene composition under the influence of natural factors.

9 cl, 2 tbl, 4 ex

Description

The invention relates to the production of polymer compositions based on recycled polyethylene used in the production of non-critical polymer products by extrusion, and can be used in construction, the chemical industry and other industries in cases where there are no increased requirements for products.

Currently, the production of synthetic plastics in the world has reached 150 million tons per year and continues to grow. After use, polymer-containing industrial and domestic waste ends up in landfills, and since most commonly used synthetic polymers do not fully decompose in nature, toxic residues enter the environment. The solution to the problem of processing and recycling polymer-containing waste is the production of biodegradable materials that are capable of mineralization under the influence of the environment, i.e., under appropriate conditions, for example, during composting, as a result of the vital activity of aerobic or anaerobic microorganisms, they can completely decompose with the formation of eventually carbon dioxide, water and non-toxic mineral residue.

Under normal operating conditions, a sufficiently large number of known biodegradable polymers show resistance to degradation and allow processing using most standard plastics manufacturing technologies on standard equipment.

Known polymer composition based on recycled polypropylene, containing polypropylene crushed in the form of flakes with a size of not more than 10 mm, obtained from polypropylene products that have lost their consumer properties, operated in contact with petroleum products and are oil-water emulsion separators or various petroleum product containers. The composition contains, wt %: said polypropylene crushed stone - 40-45, primary low-density polyethylene - 35-39, inorganic powder filler - 20-21, and talcon or kaolin, or marble flour is used as inorganic powder filler. (RU2378299, C08L 23/12, C08L 23/06, 01/10/2010).

The disadvantage of the known composition is the impossibility of its use for the manufacture of thin films by extrusion blown up, due to the fact that the polypropylene shredder is not suitable for this method.

Also known is a biodegradable thermoplastic composition as a polymer base containing industrial and/or household polyethylene waste (67-76.5 wt.%), as a filler of natural origin - food industry waste - rice husk (20-30 wt.%) , as well as technological additives - oligomeric dye (1-2 wt.%) and titanium dioxide (0.5-1 wt.%) (RU2363711, C08L 23/06, C08L 97/02, C08L 3/00, C08J 11/ 04, 10.08.2009)

However, products made from this composition are characterized by low water absorption and physical and mechanical characteristics, which, apparently, is associated with insufficient adhesion between the filler and the polymer matrix, due only to adsorption interactions. For the same reason, the biodegradation of the composition occurs due to the absorption of filler fragments by microorganisms, while the polymer matrix is practically not destroyed.

Known composition based on high density polyethylene (HDPE), which includes 100 parts of HDPE, 200-240 parts of CaCO ₃ filler, 2-3 parts of titanium ester NDZ-102 and 5-6 parts of EAA affinity agent; wherein the CaCO3 is a 1300 mesh CaCO3 (CN108586888, C08K3/26; C08L23/06; C08L23/08, 09/28/2018).

However, such a composition is not suitable for the manufacture of products by extrusion due to its physical and mechanical properties.

Known environmentally friendly plastic, including low density polyethylene (LDPE) 1-30%, calcium carbonate (CaCO ₃ ) 1-40%, monosilane (silane; SiH4) 1%-5%, high density polyethylene (HDPE) 1%-20 %, slip agent 1%-5%, starch 1%-40%. The method for producing plastic includes mixing low-density polyethylene (LDPE) with calcium carbonate (CaCO ₃ ) and monosilane (Silane; SiH4), conducting the first thermal mixing at a temperature from 130°C to 170°C, adding high-density polyethylene and lubricant to the original polyethylene mixture low density, calcium carbonate and monosilane. Carrying out the second melt at a temperature of 170°C to 210°C, adding starch to the mixture and an additive that reduces slip, and performing a third melt at a temperature of 150°C to 190°C. After the third melt, the melt is injection molded or extruded. (CN1618858, C08K5/01; C08L23/06; C08L3/02, 05/25/2005)

A method is known for producing a biodegradable plastic additive of an ecological type with improved physical properties, including an ethylene copolymer elastomer 8-12%, calcium nanocarbonate (CaCO ₃ ) 13-17%, ethylene acrylate 8-12%, high density polyethylene (HDPE) 8-12%, talc 4-6%, liquid paraffin 8-12%, antistatic agent 4-6%, plasticized starch 16-24% and decomposition agent 13-17%. The method includes the following steps: preparing an environmentally friendly plastic masterbatch by mixing all components, mixing an environmentally friendly plastic masterbatch with LLDPE, LDPE, HDPE, PE, PP, PC, PS, EVA, NBR, TPR, melamine or other raw materials in appropriate proportions , as well as the production of plastic bags, containers, shoes, dishes and other types of materials by heat pressing, extrusion, film blowing, etc. (CN101787156, C08J3/22; C08K3/26; C08K3/34; C08K5/098; C08L23/06; C08L23/08; C08L3/02, 12/25/2013).

Also known is a method for producing HDPE filled with CaCO ₃ , which includes drying calcium carbonate CaCO ₃ , then treating its surface with a binder, then mixing with DDPE, LDPE, antioxidant, dispersant and lubricant at high speed for 5-10 minutes, extruding with a twin screw extruder at 145°C. (CN108586889, C08K3/26, C08K9/04, C08L23/06, 09/28/2018).

However, all these methods are characterized by the use of modifying additives and fillers, which leads to an increase in the cost of products and an increase in the technological operations required to obtain products.

The technical problem of the present invention is the creation of a thermoplastic, degradable polymer composition and a method for its production, simple and cheap in composition, with a high ability to degrade under the influence of natural factors.

The technical result is to reduce the cost of the composition and simplify the method of its preparation, capable of processing using known technological processes.

The technical problem is solved, and the technical result is achieved due to the fact that the composition includes low-density polyethylene, high-density polyethylene and a mixture of a polyethylene recycled product with calcium carbonate mineral filler, in the following ratio of components, in mass. %:

low density polyethylene from 5 to 25 high density polyethylene from 10 to 52 recycled polyethylene blend with calcium carbonate from 35 to 80.

A mixture of a product of secondary processing of polyethylene and calcium carbonate, made in the form of granules, contains components in the following ratio, wt. %:

recycled polyethylene product from 55 to 80 calcium carbonate CaCO ₃ from 20 to 45.

A thermoplastic degradable polyethylene composition may include a product of secondary processing of polyethylene containing technological waste from the production of films of low and high density by blown extrusion in the form of pieces of film, sprues, plastic bags that have lost their consumer qualities, packaging film that has lost its consumer properties, film production waste low and high density by extrusion blown in the form of pieces of film.

The close values of the densities of low density polyethylene and high density polyethylene cause technical difficulties and economic inexpediency of separating these polymers in the recycling process using waste polyethylene and/or recycled materials. Taking into account the fact that these two types of polyethylene are mixed with each other in any ratio, the available raw materials are used immediately after its purification without separation, which simplifies the preparation of the composition and reduces the cost of products made from it. In addition, low-density polyethylene gives the composition and products from it elasticity, and high-density polyethylene contributes to giving them greater strength, which allows us to consider their simultaneous use in the composition as a positive fact for the quality of manufactured products, for example, packaging film or garbage bags.

Calcium carbonate is usually used in the form of a fine powder.

Thermoplastic degradable polyethylene composition may additionally contain from 1 to 5 wt. % coloring pigment to obtain the desired color for the finished product.

The introduction of low-density polyethylene and high-density polyethylene into a thermoplastic degradable polyethylene composition, which also includes a mixture of a polyethylene recycled product with calcium carbonate mineral filler, provides a polymer composition that can be processed by known technological processes, as a rule, by upward blowing extrusion.

The ratio of components is selected empirically and provides an inexpensive composition, due to the use of polyethylene production waste, such as: defective products and secondary raw materials, reduces production costs and the cost of the resulting product.

The introduction of low density polyethylene (LDPE) improves the elasticity, softness, strength and resistance to static electricity of the finished product. Increasing the amount of LDPE over 25% is not advisable, and the introduction of LDPE less than 5% will not provide the necessary elasticity characteristics for the finished product, because the film will not have the strength necessary for use.

The introduction of high density polyethylene (HDPE) leads to an increase in hardness, impact resistance. At the same time, if the amount of HDPE in the polymer composition exceeds 52%, the film will have increased hardness, it will be inelastic, incapable of stretching, which will ultimately reduce the consumer qualities of the product. In turn, reducing the amount of HDPE less than 10% will reduce the physical and mechanical characteristics of the polymer composition and the product itself.

The introduction of a recycled product of polyethylene with CaCO ₃ mineral filler makes it possible to reduce the cost of products and significantly reduces the time of decomposition of a used product in natural conditions due to the mineral filler. At the same time, with a decrease in calcium carbonate in the product of secondary processing of polyethylene below 20%, the decomposition process will increase, and the excess of calcium carbonate over 45% will affect the physical and mechanical characteristics of the composition and will not ensure the process of obtaining a film by extrusion with upward blowing, complicating the production of a film according to generally accepted methods. technologies.

A method for producing a thermoplastic degradable polyethylene composition with the above composition includes preliminary preparation of a polyethylene recycling product by crushing and melting it, followed by introducing calcium carbonate mineral filler powder into the melt with stirring in an amount of 20 to 45 wt. % by weight of recycled polyethylene, then the melt is agglomerated with stirring, re-melted at a temperature of 215°C, homogenized and granulated. After that, the granules of the product of secondary processing polyethylene are mixed in an extruder with low density polyethylene and high density polyethylene, the mixture is homogenized by melting at a temperature of 215 - 220°C with stirring.

The secondary product polyethylene is preferably melted at a temperature of from 95 to 210°C to ensure a more complete melting into a homogeneous mass suitable for further processing. At the same time, lowering the temperature below 95°C will significantly increase the melting process in time, and exceeding the temperature above 210°C is impractical due to the destruction of polyethylene.

The melt of the secondary product of polyethylene mixed with calcium carbonate is agglomerated with stirring at a rotation speed of the disk knife of 55 rpm for 1 to 1.5 minutes at a temperature of from 95 to 110°C. The agglomeration modes are selected empirically, a decrease in the values of the modes will not provide the necessary melt properties for its further processing, and an increase in the knife rotation speed and agglomeration time will lead to an increase in temperature, which in turn will lead to the inadmissibility of further work with this product, because the mass will melt in the shredder of the agglomerator.

Homogenization of low density polyethylene, high density polyethylene and recycled polyethylene is carried out by rotating the extruder screw at a speed of 75 rpm. When the screw rotation speed decreases, homogenization will take a long time, and exceeding the rotation speed will affect the reduction of the time for the mixture to pass through the screw, thereby affecting the lack of homogenization of the mixture.

The execution of granules of the product of secondary processing polyethylene with a density of 1 to 1.05 g/cm ³ affects the physical and mechanical characteristics of products obtained from the polyethylene composition. The implementation of granules in the form of tablets with a diameter of 3-5 mm is optimal for their further use to obtain a degradable thermoplastic polyethylene composition.

To obtain a degradable thermoplastic polyethylene composition, low-density polyethylene LDPE with a density of 0.916-0.935 g/cm ³ is used, high-density polyethylene HDPE, which is a polyethylene with a linear macromolecule and a relatively high density of 0.960 g/cm ³ . A polyethylene recycling product is a technological waste from the production of films and plastic bags that have lost their consumer qualities, waste generated as a result of setting up equipment.

Thermoplastic degradable polyethylene composition was obtained by the following method.

The feedstock of polyethylene recycling was crushed, agglomerated, melted at a temperature of 95-210°C in a single-screw granulator. Using a dispenser, the required amount of CaCO ₃ was introduced, agglomerated with stirring at a rotation speed of a disk knife of 55 rpm for 1-1.5 min at a temperature of 95 - 110°C. Further, the agglomerate through the loading window in the screw pair along the guides enters the screw pair, where the mixture was melted and homogenized at a screw speed of 75 rpm at a temperature of 215°C for 30-40 seconds. The resulting melt was extruded in the form of a strand through the holes in the conical die and water-ring cutting was carried out using four rotating metal knives to obtain granules. The resulting granule has the form of a tablet with a diameter of 3-5 mm, a density of 1-1.05 g/cm ³ .

The prepared secondary raw material was mixed in an extruder with high-density polyethylene and low-density polyethylene, the components were melted at a temperature of 215°C and the mixture was homogenized for 30-40 seconds with the rotation of the extruder screw at a speed of 75 rpm.

The resulting melt was forced through a molding head with a diameter of 70 mm, through a slotted hole with a width of 1.5 mm, and a film was obtained from which various products were molded.

From the polymer composition obtained, an upward blown film was produced, from which bags (bags) for garbage were produced. The testing laboratory of JSC MIPP-NPO "Plastik" carried out tests in accordance with GOST 9.707-81 "Polymer materials. Methods for accelerated testing for climatic aging” and methodology No. 08-97/9 JSC “MIPP-NPO “Plastik” - “Accelerated testing for the retention of performance properties of products made of polymeric materials”. Accelerated aging was carried out in a Solarmaster 1500 climatic chamber, which simulates exposure to solar radiation and moisture for the required time in the required parameters and controlled limits in accordance with ISO 04892. A xenon lamp is used as a source of UV radiation in the device (according to ASTM G 153 , wavelength 280-300 nm). The UV radiation power was 300 W/m ² , the exposure temperature was 45°C. 192 hours of exposure under such conditions is equivalent to one year of the material being in a stress-free state in an open area in central Russia. Tests at elevated temperatures were carried out in a SNOL-3.5/3 heat chamber, at high humidity - in an AKL-1 cabinet, at low temperatures - in a Sanya low-temperature chamber.

The film properties were controlled by tensile strength (according to GOST 11262-2017) and relative elongation at break (according to GOST 11262-2017). The properties of the samples after USP are presented in Table 1.

Table 1 - Physical and mechanical properties of the material before and after 1 year USP Sample marking Value for original sample The value for the sample after exposure to USP conditions and the change in properties relative to the original sample (%) Tensile strength, MPa Elongation at break, % Tensile strength, MPa Elongation at break, % Biobags for garbage (30 liters, 30 pcs) 60.8 43 47.9 (-21%) 34 (-21%)

According to Table 1, it can be concluded that after one conditional year of accelerated climatic aging, the strength characteristics of the sample decrease, which indicates the beginning of irreversible decomposition of the material.

The invention is illustrated by the following examples.

Example 1

The polyethylene recycling product, in the form of technological waste from the production of low- and high-density films in the form of film pieces in the amount of 55 kg (55 wt.% of the mass of the mixture of the polyethylene recycling product with calcium carbonate), was crushed, melted at a temperature of 115 ° C in a shredder granulator, while adding 45 kg (45 wt.%) fine powder of calcium carbonate CaCO ₃ . A mixture of polyethylene with CaCO ₃ agglomerated with stirring at a speed of rotation of the disk knife 55 rpm for 1-1.5 min at a temperature of 115°C. Next, the agglomerate through the loading window in the screw pair along the guides was fed into the screw pair, where the mixture was melted at a temperature of 215°C and homogenized with stirring at a screw speed of 75 rpm for 30–40 sec. The resulting melt was extruded in the form of a strand through holes in a conical die and granulated by water ring cutting with four rotating metal knives to obtain granules in the form of tablets with a diameter of 3 to 5 mm. The density of the granules is from 1 to 1.05 g/cm ³ . ^. Next, high-density polyethylene in the amount of 12.5 kg (10 wt.%) and low-density polyethylene in the amount of 12.5 kg (10 wt.%) were mixed on the extruder with 100 kg (80 wt.%) of a mixture of polyethylene recycled products with calcium carbonate . The mixture was melted and homogenized at a temperature of 215°C for 30-40 seconds with stirring at a speed of 75 rpm. The resultant melt was forced through a 70 mm diameter mold head, through a 1.5 mm wide slot, and a film was obtained from which garbage bags were formed.

The film, due to the large amount of a recycled product with a high percentage of CaCO _3, has a cheaper pricing policy for the manufacture of polyethylene products, the time indicator for decomposition decreases, but it acquires a greater indicator in terms of mechanical strength, rigidity and heat resistance.

Example 2

The production of a degradable polyethylene composition was carried out similarly to example 1, but in a mixture of polyethylene recycling, which included polyethylene waste generated as a result of setting up equipment. The mixture included 20 kg (20 wt. %) of calcium carbonate and 80 kg (80 wt. %) of secondary waste. The melt of the raw material was carried out at a temperature of 95°C. Agglomeration was carried out at a temperature of 105°C.

Recycled polyethylene pellets were mixed with LDPE and HDPE in the amount of: 60 kg of pellets (60 wt. %); LDPE 5 kg (5 wt. %); HDPE 35 kg (35 wt. %). The processing temperature was 210°C.

The film has good strength, low elasticity, average decomposition time.

Example 3

The production of a degradable polyethylene composition was carried out analogously to example 1, but in a mixture of polyethylene recycling, which included polyethylene waste in the form of a mixture of polyethylene film and sprues. The mixture included 30 kg (30 wt. %) of calcium carbonate and 70 kg (70 wt. %) of secondary waste.

The melt of the raw material was carried out at a temperature of 95°C. Agglomeration was carried out at a temperature of 110°C.

Recycled polyethylene granules were mixed with LDPE and HDPE in the amount of: 35 kg of granules (35 wt. %); LDPE 25 kg (25% by weight); HDPE 40 kg (40 wt. %). The processing temperature was 195°C.

The film has average strength, elasticity and degree of decomposition.

Annex 2 Example No. CaCO ₃ ,
wt. % Secondary waste PE, wt. % Recycled product filled with CaCO ₃ Yu mass. % Low density polyethylene
LDPE, wt. % High density polyethylene, HDPE, wt. % Processing temperature, °C Melt flow index,
g/10 min Tensile strength, MPa 1 45 55 80 10 10 215 0.1-0.5 10.7 2 20 80 60 5 35 210 0.3-0.6 14.3 3 thirty 70 35 25 40 195 0.4-0.8 21.2 4 35 65 28 20 52 195 0.4-0.8 19.8

The composition of the thermoplastic degradable polyethylene composition of the present invention makes it possible to obtain it on modern traditional technological equipment used for waste processing and extrusion of blown films, does not require re-equipment of equipment and a complete set of expensive molding equipment. Polyethylene products obtained from the composition after their use as a result of solar radiation, moisture and temperature in natural conditions have the ability to decompose within 1 to 3 years, thereby increasing the environmental situation, without additional costs for the disposal of waste polymers that have lost their consumer properties.

Currently, a thermoplastic degradable polyethylene composition and a method for its production is at the stage of completed development.

Claims (12)

1. Thermoplastic degradable polyethylene composition, characterized in that it contains low-density polyethylene, high-density polyethylene and a mixture of polyethylene recycled product with calcium carbonate mineral filler, in the following ratio, wt.%: low density polyethylene from 5 to 25 high density polyethylene from 10 to 52 recycled polyethylene blend with calcium carbonate from 35 to 80, while the mixture of the product of secondary processing of polyethylene and calcium carbonate, made in the form of granules, contains components in the following ratio, wt.%: recycled polyethylene product from 55 to 80 calcium carbonate CaCO ₃ from 20 to 45 2. Thermoplastic degradable polyethylene composition according to claim 1, characterized in that the polyethylene recycling product includes technological waste from the production of low and high density films by blown extrusion in the form of pieces of film, sprues, plastic bags that have lost their consumer qualities, packaging films, that have lost their consumer properties, waste from the production of low and high density films by blown extrusion in the form of film pieces. 3. Thermoplastic degradable polyethylene composition according to claim 1, characterized in that calcium carbonate is used in the form of a fine powder. 4. Thermoplastic degradable polyethylene composition according to claim 1, characterized in that it additionally contains from 1 to 5 wt.% of a coloring pigment. 5. A method for producing a thermoplastic degradable polyethylene composition, the composition of which is indicated in paragraph 1, characterized in that the polyethylene recycling product is preliminarily prepared by grinding and melting it, followed by introducing calcium carbonate mineral filler powder into the melt with stirring in an amount of 20 to 45 wt.% of the mass of recycled polyethylene, then the melt is agglomerated with stirring, re-melted at a temperature of 215°C, homogenized and granulated, after which the granules of the recycled polyethylene product are mixed in an extruder with low density polyethylene and high density polyethylene, the mixture is homogenized by melting at temperature 215-220°C with stirring. 6. The method according to p. 5, characterized in that the secondary product of polyethylene is melted at a temperature of from 95 to 210°C. 7. The method according to p. 5, characterized in that the melt of the secondary product of polyethylene in a mixture with calcium carbonate is agglomerated with stirring at a rotation speed of a circular knife of 55 rpm for 1 to 1.5 minutes at a temperature of from 95 to 110 ° C . 8. The method according to claim 5, characterized in that the homogenization of low density polyethylene, high density polyethylene and the polyethylene recycling product is carried out with the rotation of the extruder screw at a speed of 75 rpm. 9. The method according to p. 5, characterized in that the granules of the polyethylene recycling product have a density of 1-1.05 g/cm ³ and are made in the form of tablets with a diameter of 3-5 mm.