RU2783825C1 - Biodegradable polyethylene-based polymeric composite material - Google Patents

Abstract

FIELD: environmental protection.

SUBSTANCE: invention relates to the field of environmental protection and is intended to obtain biodegradable composite materials based on polyolefins, mainly LDPE, and can be used in agriculture, construction, medicine in the manufacture of packaging materials. The resulting composition has a high ability to biodegrade, meets all the requirements for the production and operation of products from it. The composition makes it possible to increase the plasticity of the composition, the hardness and wear resistance of products manufactured using the technology based on the invention.

EFFECT: increasing the rate of degradation of the material based on polyolefins. High-density polyethylene is used as the initial polymer, natural rubber and phospholipid concentrate as filler.

3 cl, 3 tbl, 16 ex

Description

The field of technology to which the invention belongs

The invention relates to biodegradable composite materials based on polyolefins, and can be used in agriculture, construction, medicine in the manufacture of packaging materials that can decompose in natural conditions.

State of the art

With the increased requirements for environmental protection, composite polymer materials, along with a high set of indicators during operation, must have the ability to biodegrade under conditions of deposition. The production volume of biodegradable polymers is hundreds of times inferior to traditional polymers. If the total production of traditional polymers in 2020 exceeded 265 million tons, then the production of biopolymers (including 1.5 million tons of biodegradable ones) - 2.4 million tons (about 0.9%).

The polymers so widely used today are generally not biodegradable, except for a few that are capable of biodegradation, but very slowly. Taking into account the sharp increase in demand for polymers and their availability, there is an ecological danger of environmental pollution with a large amount of used polymer products and their waste.

Traditional methods for obtaining degradable polymers are based on:

1) the use of water-soluble and biodegradable polymers;

2) introduction of water-soluble and degradable compounds and polymers into the main non-degradable polymer;

3) the use of microorganisms - destructors immobilized in the polymer with its subsequent degradation under conditions of deposition.

However, none of these methods is universal. Thus, the use of water-soluble and biodegradable polymers is limited by a low range of performance indicators of compositions based on them, which makes it impossible to use them for the manufacture of high-strength products. The second method significantly, sometimes several times, reduces the set of operational indicators, which also leads to a limitation of areas of use. The third method - the use of microorganisms - destructors requires a clear temporal forecast of the operation of a polymer product. Starting the decomposition mechanism with the help of destructor microorganisms determines certain conditions of deposition: temperature, concentration, humidity, etc. At the same time, there is a great danger of turning on this mechanism during the period of storage or operation of the product.

Currently, the solution to the problem is the creation of biodegradable polymer composites by introducing another biodegradable polymer into the main non-degradable polymer. In this regard, the method of obtaining PCM described in the invention is of great relevance.

Known biodegradable polymer compositions containing starch as a filler. As a polymer base, they may contain cellulose derivatives [RU 96112905 A, publ. September 27, 1998, RU 2174132 C1, publ. September 27, 2001, RU 2404205 C1, publ. November 20, 2010], polyamides [RU 97121172 A, publ. August 27, 1999], a copolymer of ethylene and vinyl alcohol [RU 2073037 C1, publ. 10.02.1997] and other polymers. However, starch is a valuable food product, so the production of large-tonnage material on its basis, intended for the manufacture of non-durable products, is not economically justified.

Known biodegradable and elastomeric composition [EN 2551515, publ. 05/27/2015], which has a degree of biodegradability of less than 30%, and contains at least 0.5% and not more than 99.95 wt.% acetate starchy material, which has a degree of substitution (DS) from 2.5 to 3 and at least 0.05 wt.% and not more than 99.5 wt.% of a polymer other than starch, and the specified polymer is selected from the group consisting of natural rubbers and their derivatives, polyisobutylenes, polyisoprenes, butadiene-styrene copolymers (SBR), butadiene-acrylonitrile copolymers, hydrogenated butadiene-acrylonitrile copolymers, acrylonitrile-styrene-acrylate copolymers (ASA), ethylene/methyl acrylate copolymers (EAM), thermoplastic polyurethanes (TPU) of the ether type or the ester-ether type, polyethylenes or polypropylenes functionalized with halogenated silane, acrylic or maleic anhydride units, ethylene-diene monomer (EDM) copolymer rubbers, and ethylene-propene copolymer rubbers ylene-diene monomer (EPDM), thermoplastic elastomers derived from polyolefins (TPO), styrene-butylene-styrene copolymers (SBS) and styrene-ethylene-butylene-styrene copolymers (SEBS) functionalized with maleic anhydride units, and any mixtures of these polymers. The disadvantage of this method is the low degree of biodegradability obtained on the basis of this invention products.

Known biodegradable compositions containing as a polymer base up to 70-80% of the copolymer of ethylene and vinyl acetate (EVA), and as fillers of natural origin - waste from the technological production of processing cocoa beans (20.0-40.0 wt.%) [RU 2349612 C1, publ. 03/20/2009] or rye flour (30-48.7 wt.%) [RU 2318006 C1, publ. February 27, 2008]. To improve the compatibility of ingredients, surfactants and other processing aids are added to the compositions. The disadvantage of these technical solutions is the use of a relatively expensive copolymer of ethylene and vinyl acetate as a polymer base, which increases the cost of the finished product. In addition, cocoa shell and rye flour are also relatively expensive fillers and can be used in the feed or food industry.

Given the large volumes of production and the short period of use of products made from biodegradable polymeric materials, it is advisable to use the cheapest polymeric thermoplastics for creating compositions, suitable, among other things, for use in contact with food products, as well as cheap ones that do not represent nutritional and feed value, fillers.

Known biodegradable thermoplastic compositions containing, as a polymer base, industrial and/or household waste polyethylene, additives - oligomeric dye and titanium dioxide, and as a biodegradable filler - rice husk [RU 2363711, publ. 10.08.2009]. The disadvantage of this method is the low physical and mechanical properties of products made from this composition.

Known biodegradable thermoplastic composition, which contains polyethylene as a polymer base, wood flour and functional additives such as bentonite, polyvinyl alcohol, compatibilizer and nanoparticles. A copolymer of ethylene and vinyl acetate is mainly used as a compatibilizer, and chemically precipitated iron hydroxide or calcium sulfate is used as nanoparticles.

The disadvantage of this method is the low level of moisture absorption of products from this composition and a large number of different fillers in the composition.

According to the invention, selected as a prototype, a biodegradable thermoplastic composition as a polymer base contains low-pressure polyethylene, a binder and a lignocellulosic filler. As a lignocellulosic filler, waste from technological production and natural materials selected from flaxseed, sunflower husks, sodium lignosulfonate, leaves, straw [RU 2473578, publ. 27.01.2013].

The disadvantage of this method is that the products obtained from such a biodegradable thermoplastic composition have low physical and mechanical properties, which limits the breadth of their operation.

Disclosure of invention

The technical problem is the creation of a thermoplastic, biodegradable polymer composition, which includes cheap synthetic polymer materials as a polymer component, and fillers that do not represent food or feed value as a natural filler, while the resulting compositions must exhibit a high ability to biodegrade under the influence of natural factors, and also meet the requirements for materials to be processed using known technological processes.

The technical problem is solved by a biodegradable composition, including polyethylene, natural rubber and phospholipid concentrate, in the following ratio of components, wt. %:

natural rubber 3-10 phospholipid concentrate 3-10 polyethylene rest

The content of 3-10% of the mass. natural rubber and phospholipid concentrate in the composition is necessary to achieve a technical result. The content is below 3% of the mass. of these components is insufficient for the appearance of biodegradation properties, more than 10% of the mass. inexpedient from an economic point of view and due to undesirable changes in physical and mechanical characteristics.

The technical result of the invention is to increase the rate of decomposition of the material based on polyolefins while maintaining the necessary physical and mechanical characteristics, in contrast to the prototype. The resulting composition meets all the requirements for the production and operation of products from it. Also, the introduced fillers make it possible to increase the plasticity of the composition, the hardness and wear resistance of products manufactured using the technology based on the invention.

The essence of the invention

The essential features that distinguish the invention from the prototype are the use of crude natural rubber and phospholipid concentrate in the composition. Natural rubber is a natural polymer that does not accumulate in nature and contains proteins, phospholipids and other components that contribute to degradation in natural conditions. Natural rubber is also responsible for maintaining the necessary physical and mechanical properties of the resulting compositions. Phospholipid concentrate is a by-product of vegetable oil refining and has no market value. In addition, it contains structural analogs of natural rubber phospholipids, which give it the property of biodegradation. An additional factor in the use of phospholipid concentrate is its hydrophilicity. It is known that the more hydrophilic the composition, the faster the processes of biodegradation.

Getting a composition

Polyethylene, preferably HDPE, is mixed with the required amount of phospholipid concentrate, a by-product of vegetable oil refining, and previously ground natural rubber. The resulting mixture is loaded into a twin screw extruder for melting and homogenization at a temperature of 60-190°C. The tows leaving the extruder head are cut into granules, which are used for further processing and obtaining biodegradable materials.

From the obtained granules, products can be made using injection molding. To do this, the mixture is subjected to melting in an injection molding machine, followed by injection of the resulting melt into a mold under pressure. It is also possible to obtain films from granules by pressing.

During the pressing process, the polymer plates are subjected to pressure and temperature using a hydraulic press with heated plates.

As an illustration, Table 1 shows the effect of NC (natural rubber) and FLC (phospholipid concentrate) content on water absorption.

Changes in technological and physical-mechanical parameters of polymer compositions after 72 hours of accelerated climatic tests (UV irradiation, lamp radiation power 1.55 W/ ^m2 , temperature at which irradiation took place 60°C) are shown in Table 2.

The study of the obtained compositions was carried out using the equipment of the Center for Collective Use "Nanomaterials and Nanotechnologies" of the Kazan National Research Technological University with the financial support of the project of the Ministry of Education and Science of Russia within the framework of grant No. 075-15-2021-699.

Significant changes in the melt flow rate and tensile stress in the direction of their decrease are observed for all the studied samples, and are in the range from -92 to +11% and from -24 to +6%, respectively. This range is explained by the processes of structuring and destruction. With an increase in NC, structuring processes predominate.

The use of FLC in an amount up to 10% of the mass. within the same content of NC leads to an increase in the values of physical and mechanical parameters.

Example 1 is a pure LDPE with no fillers and is not biodegradable. From Table. 1 we see that the polymer has practically no water absorption property. In table. 2 we see that the physical and mechanical parameters after accelerated climatic tests decreased by 7-17%.

Examples 2-4 without the addition of crude natural rubber as a filler, and with the addition of FLC from 3 to 10% were obtained in the following way: LDPE is mixed with a phospholipid concentrate until the mixture is completely homogenized at 60-190°C. The tows leaving the extruder head are cut into granules, which are used for further processing and obtaining biodegradable materials.

These examples demonstrate an increase in water absorption properties at 24 hours and fluctuations in weight change from 3.0-3.2% in the range of 48-96 hours. Compared with example 1, examples 2-4 show less changes in physical and mechanical properties, and example 4 with 0 wt% NK content. and FLC 10% wt. demonstrates even an increase in MFR by 3%.

Examples 5, 9, 13 containing NA from 3 to 10% NA and not containing FLC were obtained in a similar way as examples 2-4, however, no FLC was added to the mixture. These examples show a slight increase in water absorption compared to example 1. However, compared to other examples, the weight change is much lower.

Examples 5-8 with the addition of 3% of the mass. NCs show a significant reduction in MFR from 50 to 51%. The fracture stress was also significantly reduced to 31% and the Charpy impact strength to 15%.

Examples 6-8, 10-12 containing NK from 3 to 5 wt%. and FLC from 3 to 10% wt., obtained in a similar way, as well as examples 2-4, have a higher percentage of water absorption, compared with examples 1-5, 9, 13. With an increase in the proportion of NC and FLC in the composition, the degree of water absorption also increases .

Examples 10-12, prepared in a similar manner as Examples 2-4, show an 18-33% reduction in MFR. With an increase in the proportion of FLC, the degree of breaking stress increases in comparison with samples containing a lower proportion of FLC. Sample 12 demonstrates the best performance in this range of examples.

Examples 14-16, obtained in a similar way as described in examples 2-4, with a natural rubber content of 10% of the mass. and FLC 3-5 wt%. demonstrate the greatest manifestation of water absorption properties. Tests have also shown (Table 2) that these examples show a slight increase in tensile strength up to +6%. The melt flow rate increased by 7-11% compared to samples not subjected to climatic tests.

In table. 3 shows data on the change in the weight of the samples after 6 months of exposure in the soil according to GOST 9.060-75. For testing, soil was used, consisting of a mixture of sand, horse manure and forest land, taken in equal amounts by weight. Before testing, the soil was kept for two months at a temperature of 23°C. During the exposure period, the soil was mixed daily and its moisture content was maintained at the level of 30±5%. After 6 months of being in the soil, samples in the form of films 0.20 ± 0.04 mm thick were removed from the soil, washed and dried at a temperature of 85°C in an oven to constant weight. The assessment of biodegradation was carried out by changing the weight loss of the samples.

Example 1 is a pure LDPE without fillers, which does not have biodegradable properties and does not change mass after exposure to soil.

Examples 4-3 show a consistent increase in weight loss with increasing content of NA and FLA.

Example 16 is a composition with a maximum weight loss of 9% with a maximum content of NA and FLA.

Thus, the obtained data show that the obtained compositions containing from 3 to 10% of the mass. NK and from 3 to 10% of the mass. FLCs show a high biodegradability, while the physico-mechanical properties of the obtained compositions are at a sufficient level for the intended use.

Claims (4)

1. Biodegradable polymer composite material containing high pressure polyethylene (LDPE), natural rubber and phospholipid concentrate, in the following mass ratio: natural rubber 3-10% phospholipid concentrate 3-10% high pressure polyethylene (LDPE) rest 2. The composite material according to claim 1, wherein the filler is crude natural rubber. 3. Composite material according to claim 1, in which a phospholipid concentrate obtained by refining vegetable oils is used as a filler.