RU2473578C1 - Biodegradable thermoplastic composition - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a biodegradable thermoplastic composition for producing materials and articles which are biodegradable in natural conditions. The biodegradable thermoplastic composition contains lignocellulose filler, a binding agent and polyethylene as a polymer base. The binding agent is a copolymer of ethylene and vinyl acetate. The lignocellulose filler used is in form of cheap manufacturing wastes with no food and feed value and natural materials selected from flax shive, sunflower husks, sodium lignosulphonate, leaves and straw.

EFFECT: composition is characterised by high biodegradability and meets requirements for materials for processing using conventional processes and equipment.

5 cl, 3 tbl, 1 dwg

Description

The invention relates to biodegradable thermoplastic compositions, and in particular to compositions containing lignocellulosic materials, and can be used to create materials and products from them that are biodegradable under natural conditions. The task of waste disposal is currently particularly acute. One of the significant problems is the high resistance of synthetic polymeric materials to physical, chemical, and biological decomposition. Giving synthetic polymers biodegradability under the influence of microorganisms and climatic factors, such as the action of light, oxygen, moisture, aggressive environments, etc., can significantly reduce the amount of polymer debris and improve the environmental situation. First of all, polymeric materials used for the manufacture of goods with a short shelf life, such as packaging films, bags, disposable tableware, etc., should be capable of biodegradation. Currently biodegradable polymers, for example polylactide, are biodegradable, biocompatible, thermoplastic, lactic acid polymer, polyhydroxybutyrate and its analogues, are much more expensive than traditional polymers. The possibility of obtaining cheaper biodegradable materials is associated with the use of polymer compositions, including, along with traditional thermoplastic synthetic polymers, biodegradable fillers of natural origin. Biodegradable polymer compositions are known containing starch as a filler. As a polymer base, they may contain cellulose derivatives [RU 96112905 A, publ. 09/27/1998, RU 2174132 C1, publ. 09/27/2001, 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. 02/10/1997] and other polymers. However, starch is a valuable food product, therefore, the production on its basis of large-tonnage material intended for the manufacture of short-term products is economically unjustified. Biodegradable compositions are known containing up to 70-80% of a copolymer of ethylene and vinyl acetate (SEVA) as a polymer base, and waste products from the technological process of processing cocoa beans of cocoa shell (20.0-40.0 wt.%) [RU 2,349,612 C1, publ. March 20, 2009] or rye flour (30-48.7 wt.%) [RU 2318006 C1, publ. 02/27/2008]. To improve the compatibility of the ingredients, surfactants and other processing aids are added to the compositions. The disadvantage of these technical solutions is the use as a polymer base of a relatively expensive copolymer of ethylene and vinyl acetate, 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 feed production or in the food industry. Given the large volumes of production and the short term of use of products from biodegradable polymeric materials, it is advisable to use the cheapest polymeric thermoplastics, suitable for use in contact with food products, as well as cheap, not representing food and feed value, to create compositions. fillers. According to the invention [RU 2363711 C1, publ. 08/10/2009], selected as a prototype, the biodegradable thermoplastic composition as a polymer base contains industrial and / or household waste of polyethylene (67-76.5 wt.%), As a filler of natural origin - waste from the food industry - rice husk ( 20-30 wt.%), As well as technological additives - oligomeric dye (1-2 wt.%) And titanium dioxide (0.5-1 wt.%). However, products made from this composition are characterized by low water absorption and physicomechanical 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, which is confirmed by the data of IR spectroscopy. The objective of the present invention is to provide a thermoplastic, biodegradable polymer composition comprising cheap synthetic polymer materials as a polymer component and cheap fillers not representing food or feed value as a natural filler, and the resulting compositions must exhibit high biodegradability under the action of natural factors, as well as meet the requirements for materials for processing using well-known technological their processes.

The problem is solved by the proposed biodegradable composition, including polyethylene, lignocellulosic filler and compatibilizer (binding agent), which is used as a copolymer of ethylene and vinyl acetate, in the following ratio, wt.%:

Lignocellulosic filler 15-60 Ethylene Vinyl Acetate Copolymer 3-12 Polyethylene Rest

If necessary, technological additives can be introduced into the composition. Polyethylene, which is the polymer basis of the composition, can be represented by various grades of high and low density polyethylene, as well as waste containing polyethylene. Currently, there are many brands of polyethylene on the market, each of them can be used, however, high pressure polyethylene (LDPE) (low density) grades are preferable, since they are suitable for contact with food products and their supramolecular structure makes it possible to optimally introduce finely divided filler. Waste containing polyethylene includes waste from the processing of polyethylene into products and consumption waste. Processing waste is gating systems and defective products, packaging waste, non-food products, machine parts, devices, etc. are classified as consumption waste. Waste containing polyethylene is usually more oxidized than the original polymer, this property can lead to better adhesion with the filler and faster biodegradation of the polymer part. For use in accordance with the invention, consumption waste must first be cleaned, dried and sorted. From composite materials based on polyethylene waste, it is recommended to produce non-essential products and consumer goods, with the exception of children's toys, products in contact with food, and medical devices. A wide range of objects of natural origin containing cellulose and / or lignin can be used as a lignocellulosic filler, however, from an economic point of view, it is preferable to use cheap non-food and feed waste technological waste or natural materials such as flaxseed, sunflower husk, lignosulfonate sodium, as well as plant objects such as foliage or straw. The cost of these fillers is significantly lower than the cost of fillers used in analogues and prototype. For example, the waste of flax production - flaxseed fire - is 10 times cheaper than rye flour, 30 times cheaper than cocoa shells and almost 60 times cheaper than starch.

Table 1 shows the content of carbohydrates and / or lignin in objects that, in accordance with the present invention, are used as a lignocellulosic filler.

Table 1 Lignin-carbohydrate composition of fillers in accordance with the invention Fillers Cellulose, wt.% Lignin, wt.% Pentosans, wt.% Campfire linen 47-49 25-27 21-23 Sunflower husk 34-36 26-28 25-27 Birch leaves 24-26 33-35 17-19 Cereal straw 46-48 17-19 23-25 Sodium Lignosulfonate - one hundred -

In accordance with the invention, the content of lignocellulosic filler in the composition may be in the range from 15 to 60 wt.%. The choice of a specific value within the specified range depends on the type of products for which the composition is intended, and on the method of processing the material. For thin films (thinner than 100 μm) obtained by extrusion through a flat slot head, the filler content in the composition should be in the range from 15 to 20 wt.%. At a higher filler content, film defects may occur due to filler coming to the surface. A lower filler content is not economically feasible. In the case of thicker films, it is advisable to increase the quantitative content of the filler to reduce the cost of the obtained material and increase the efficiency of biodegradation. For example, for films with a thickness of 100-250 microns, the filler content can be increased to 40 wt.%, And for films thicker than 250 microns - up to 50 wt.%. A higher filler content can lead to a deterioration in the quality of the resulting films. Upon receipt of films or sheets by compression, the quantitative content of lignocellulosic filler in the composition, as well as for producing films by extrusion, does not exceed 50 wt.%. In the manufacture of products by injection molding or molding (disposable tableware, cutlery, trays, etc.) having a greater thickness than the film, the filler content can be increased to 60 wt.%.

A copolymer of ethylene and vinyl acetate (SEVA) plays the role of a binder component. Various brands of SEVA manufactured by the industry contain from 5 to 30% vinyl acetate (TU 6-05-1636-97 OJSC NefteKhimSevilen, Kazan). Preliminary experiments have shown that the use of CEVA grades containing about 18% vinyl acetate is optimal. The compatibility of SEVA with the polymer matrix and the filler due to the presence of vinyl acetate groups and ethylene units provides an increase in interfacial adhesion between the polymer base and the filler by adding chemical interaction to the adsorption mechanism.

Improving adhesion helps to increase the availability of the polymer matrix for the combined effects of climatic factors and microorganisms, leading to the destruction of the material in natural conditions. This is manifested both in an increase in water absorption of the claimed compositions, and in a change in the dynamics of biodegradation and the nature of the biodestructive effect of natural factors on the products obtained from them.

As an illustration, in Tab. Figure 2 shows the effect of the CEVA content on the reduction in the mass of naturally exposed films obtained from compositions containing LDPE and dry birch leaves. Figure 3 shows the effect of the CEVA content on water absorption and reduction in the mass of naturally exposed films obtained from compositions containing LDPE and cereal straw.

table 2 Change in the mass of film samples containing dry birch leaves as a natural filler, depending on the content of SEVA No. Composition The decrease in mass of the sample,% after 2 months after 8 months one LDPE 70% + birch leaves 30% 1,2 9.1 2 LDPE 66.5% + SEVA 3.5% + birch leaves 30% 2,3 9.1 3 LDPE 59.5% + SEVA 10.5% + birch leaves 30% 4.3 9.2

Table 3 Change in mass and water absorption of film samples containing cereal straw as a natural filler, depending on the content of SEVA No. Composition Water absorption, wt.% The decrease in mass of the sample,% after 4 months after 8 months after 12 months one LDPE 70% + cereal straw 30% 8.1 7.9 15.1 17.5 2 LDPE 66.5% + SEVA 3.5% + cereal straw 30% 11.2 8.8 17.0 18,4 3 LDPE 59.5% + SEVA 10.5% + cereal straw 30% 14.0 10,4 18.9 20.8

The table shows that the destruction rate of the sample increases with the introduction of SEVA into the composition, and the more so, the higher the content of the compatibilizer.

Figure 1, which shows the change in the content of OH groups corresponding to the carbohydrate component of the composition, in the samples shown in Table 1 illustrates the change in the nature of the biodegradable effects of natural factors. 2. The content of OH groups is characterized by the peak area in the IR spectra in the region of 3100-3590 cm ^-1 corresponding to the content of hydroxyl groups of the lignocellulosic filler. The curve number corresponds to the sample number in Table 2.

As can be seen from the figure, in the case of a sample that does not contain SEVA, the maximum decrease in the content of OH groups during the first two months with a minimum decrease in the mass of the sample (see Table 2) suggests that the natural filler is predominantly destroyed. The introduction of SEVA changes the nature of the influence of natural factors on the composition: the hydroxyl content decreases slightly with a significant decrease in the mass of the sample, which indicates the destruction of the polymer component.

Preliminary studies have shown that tensile strength and elongation at break of films obtained from compositions comprising SEA are approximately 15% higher than for films obtained from compositions not containing a compatibilizer.

The quantitative content of SEVA in the composition should ensure high efficiency of binding of the polymer base with the filler at a minimum flow rate. Based on this, the use of a binder in an amount of less than 3 wt.% Is inefficient, and in an amount of more than 12 wt.% It is not economically feasible.

The invention is as follows.

Filler preparation.

Dried at 105 ° C for 2-3 hours, the filler is crushed, then dispersed using a sieve analyzer, sieving or screening. Immediately before mixing with the remaining components, the filler is further dried under the same conditions.

The size of the filler fraction depends on the method for further processing the resulting composition. To obtain films by extrusion through a flat-slit head, a filler fraction is used that is 20-30 microns less than the thickness of the finished film. When using compression, the filler fraction can be only 10 μm less than the thickness of the resulting films or sheets. When manufacturing products by injection molding or molding (disposable tableware, cutlery, trays, etc.) having a greater thickness than films, it is recommended to use a filler fraction of up to 200 microns.

Getting the composition.

Polyethylene is mixed with the required amount of SEVA and the resulting mixture is introduced into a twin-screw extruder for melting and homogenization at 140-160 ° C, after which the filler prepared as described above is introduced into the mixture and stirring is continued until the mixture is completely homogenized. The bundles emerging from the extruder head are cut into granules, which are used for subsequent processing and obtaining biodegradable materials using one of the known methods.

From the obtained granules, a film can be made by extrusion using an extruder with a slit head at the same temperature. Granules can also be used for the manufacture of products by injection molding, for which the mixture is subjected to melting in an injection molding machine, followed by injection of the obtained melt into a mold under pressure. It is also possible to obtain products by molding, for which the granules are poured into an extruder with a flat slit head, a tape is obtained with a thickness of 0.1 mm to 3 mm, which then enters the molding machine, where it is heated and blown into the mold.

Table 4 shows examples of the implementation of the claimed invention, not exhaustive of all the possibilities of its implementation. As the polymer base used high pressure polyethylene brand 15803-020 in the form of granules. SEVA grade 11607-040 containing 18% vinyl acetate was used as a compatibilizer.

The ability of materials to biodegrad under the influence of natural factors is characterized by water absorption in 24 hours (according to GOST 4650-80) and loss of mass of the sample in the soil prepared in accordance with GOST 9.060-75, with an exposure of 8 months at an air temperature of 25 ° C.

For comparison, the table shows the characteristics of pure LDPE (example 1), which does not have the property of biodegradability.

Examples 2-5 characterize biodegradable thermoplastic compositions obtained using flax fire as a filler, obtained by primary processing of flax and representing a lignified part of the stems of flax. The content of the carbohydrate and lignin fraction of the filler is shown in Table 1. Bonfire is a waste of textile production and is usually burned. Flaxseed fire is dried at 105 ° C for an hour, then sieved through a sieve with a mesh size of 200 μm. Immediately before introducing into the composition, the sifted bonfire is dried again for 2 hours at a temperature of 105 ° C.

A mixture of the calculated quantities of LDPE and SEVA is introduced into a twin-screw extruder and homogenized at 150 ° C for several minutes. In the molten mass add the appropriate amount prepared, as described above, flax fires and continue mixing at a temperature of 150 ° C for several minutes. The bundles emerging from the extruder head are cut into granules, from which, depending on the filler content, a film is produced using a slit head extruder (examples 2 and 3) or an injection molded product (example 4).

Examples 6 and 7 characterize a biodegradable thermoplastic composition obtained in a similar manner using sunflower husk as a filler. Sunflower husk is a waste of the oil industry. As a rule, husk is burned using it as cheap fuel for boiler houses. Husk is also used as a feed additive in animal husbandry, but the proportion of its use is negligible.

Example 8 characterizes a biodegradable thermoplastic composition obtained as described above using sodium lignosulfonate as a filler. Technical lignosulfonates are a by-product of wood processing and are a mixture of salts of lignosulfonic acids (mixed with reducing and mineral substances). For the manufacture of polymer compositions in accordance with the invention, powdered sodium lignosulfonate is used.

Examples 9-11 characterize biodegradable thermoplastic compositions obtained in a similar manner using dried birch leaves as a filler. For the manufacture of the claimed biodegradable compositions, the use of any leaves is possible, since the structure and chemical composition of the leaves of different plants differ slightly. So, for example, the content of cellulose and lignin in birch leaves and in spruce needles is almost the same. In these examples, dried birch leaves are used as filler.

Examples 12-15 characterize biodegradable thermoplastic compositions obtained in a similar manner using straw as a filler. Straw is dry stalks of cereals and legumes remaining after threshing. As a raw material for composite biodegradable materials, all types of straw are suitable. The main advantage of straw as a material is its high availability and low cost. In these examples, straw of a mixture of cereal crops was used as a filler.

Table 4 Characteristics of samples of compositions obtained in accordance with the invention Example No. The composition, wt.% Water absorption, wt.% Weight loss, wt.% Products made from composition LDPE SEVA Filler one one hundred - - 0.02 0,0 Extrusion film 2 66.5 3,5 Bonfire Linen 30 7.8 10.3 Extrusion film 3 59.5 10.5 Bonfire Linen 30 10,2 13,2 Extrusion film four 38,0 12.0 Flax fire 50 10,2 12.0 Injection molding paddle 5 28.0 12.0 Flax fire 60 11.9 12.7 Injection molding paddle 6 66.5 3,5 Sunflower husk 30 11.0 13,4 Extrusion film 7 59.5 10.5 Sunflower husk 30 11.2 13.5 Extrusion film 8 59.5 10.5 Sodium Lignosulfonate 30 22.4 20.1 Extrusion film 9 66.5 3,5 Birch Leaves 30 7.7 8.3 Extrusion film 10 59.5 10.5 Birch Leaves 30 7.9 9.2 Extrusion film eleven 48.0 12.0 Birch Leaves 40 8.9 11.2 Extrusion film 12 82.0 3.0 Cereal straw 15.0 7.2 7.5 Extrusion film 13 66.5 3,5 Cereal straw 30.0 11.2 17.0 Extrusion film fourteen 59.5 10.5 Cereal straw 30.0 11.6 18.9 Extrusion film fifteen 48.0 12.0 Cereal straw 40.0 15.4 20.7 Extrusion film

These data show that, compared with polyethylene without additives, the obtained samples have a high biodegradability. As the technological characteristics that make it possible to process the obtained materials by known methods, the material density and melt flow rate at a temperature of 190 ° C, determined in accordance with GOST 15139-69 and GOST 11645-73, respectively, were used. As the measurements showed, the density of the obtained samples is 1.03-1.06 g / cm ³ , which is comparable with the density of LDPE 0.92 g / cm ³ . The values of the melt flow rate, depending on the nature and amount of filler, are in the range from 0.15 to 2.70 g / 10 min, which allows the use of the obtained materials for processing by certain known methods. Changing the content of components in the composition within the stated limits allows you to vary the physico-chemical characteristics while maintaining high biodegradability of the resulting materials.

Claims (4)

1. Biodegradable thermoplastic composition comprising polyethylene, lignocellulosic filler and a binder - a copolymer of ethylene and vinyl acetate in the following ratio, wt.%:
Lignocellulosic filler (15-60) Ethylene Vinyl Acetate Copolymer (3-12) Polyethylene Rest 2. The composition according to claim 1, characterized in that as the polyethylene used, preferably, high-pressure polyethylene. 3. The composition according to claim 1, characterized in that the lignocellulosic filler is a process waste or natural material containing cellulose and / or lignin. 4. The composition according to claim 3, characterized in that the process waste or natural material containing cellulose and / or lignin is selected from the group: flax fire, sunflower husk, sodium lignosulfonate, foliage, straw.

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