RU2467036C1 - Method of producing biodegradable foam plastic - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemical and food industry, particularly to production of biodegradable foam plastic and can be used to make moulded articles for various purposes, including food purposes. The foam plastic consists of a polyolefin matrix and biodegradable hygroscopic filler in form of maltodextrin with moisture content of 5-10 wt %, with the following ratio of components, wt %: polyolefin 20-50; maltodextrin 80-50. The method involves processing components in a twin-screw extruder, having at least 3 zones: a mixing zone at temperature 80-100°C; a mastication zone with a moisture control unit at temperature 140-160°C; an extrusion zone fitted with a flat die or a slit with a complex shape for making a profile, at temperature 100-120°C.

EFFECT: method of obtaining biodegradable foam plastic, which is capable of decomposing under the effect of environmental factors, without using an additional blowing agent, which reduces the cost of production of the product and power consumption of production.

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Description

The invention relates to the chemical and food industries, in particular to the production of biodegradable foams, and can be used for the manufacture of molded products for various purposes, including food.

A known method of producing a molded product from thermoplastic [RF Patent No. 2143978 dated 01/10/2000, “FORMED PRODUCT FROM THERMOPLAST AND METHOD FOR ITS PRODUCTION”]. The molded article includes a foam film. One surface of the film is closed, and the other, at least in a partial region, is open so that open pores bordering this surface are accessible to the liquid. The molded product contains at least 10 vol.% Open pores. The pores have a polyhedral shape with mechanically undeformed walls and are adjacent to each other. At least two walls of each individual pore have an opening while maintaining the mechanical strength of the spatial matrix in which the open pores are located. The pore walls surrounding the holes are not mechanically deformed. In the method for manufacturing the molded product, melt is obtained from at least one base polymer and a structure-forming agent in the first extrusion stage, the introduction of a blowing agent and its homogeneous mixing with the polymer melt at the end of the first extrusion stage. The melt is produced at temperatures up to 300 ° C. The blowing agent is introduced into the polymer melt by injection thereof at high pressure up to 350 bar. In the second stage of extrusion, immediately before extrusion, the polymer melt is cooled to a temperature of 120-250 ° C. At least one of the closed surfaces of the extruded thermoplastic is partially opened by grinding, scratching, perforating or cooling and simultaneously stretching when leaving the die. Openings are made in at least two walls of each open pore. EFFECT: invention makes it possible to create a molded foam product with an open-porous structure that varies over a wide range, moreover, the pores are permeable to agents without mechanical destruction of the pore walls.

The disadvantage of the analogue is the multi-stage production, as well as the need to use a blowing agent to obtain the necessary structure of the material.

A known method of producing extruded food products [RF Patent No. 2300901 from 06/20/2007. Bull. No. 17 "Method for the production of extruded products"]. A method for the production of extruded products involves the extrusion of the original product with subsequent cooling of the resulting expanded product. As the initial product, chickpea and corn grains or chickpea grains and semolina are used, and before extrusion they are crushed individually to a particle size of 2-3 mm, sieved and passed through a magnetic trap, mixed in the following ratio of components, wt.%: Cereal chickpeas 50-60 and corn grits 50-40 or chickpeas 50-60 and semolina 50-40. The prepared mixture is subjected to processing on an extruder at a screw rotation speed of 38 ± 2 s ^-1 , the processing time in the extruder is 30-40 s, and the diameter of the die outlet is 8 mm. Obtained in the form of straight or curved sticks, the blasted product is cooled to a temperature of 30-40 ° C, dried to a mass fraction of moisture of 4.4-4.8% and sealed.

According to the prototype, the product during extrusion, moving along the path of the screw part, is subjected to heat treatment at overpressure. In the mixing zone, partial mixing of the starting components occurs, in the compression zone there is an increase in pressure and product compaction due to a sharp decrease in the size of the screw channel. In the plasticization zone, the product particles are partially converted to melt due to friction between the product particles and the screw turns. The melt pressure in the dosing zone reaches the required value and a melt is formed, uniform in structure and temperature. Then it enters the pre-area and is forced through the outlet in the matrix. After the product leaves the matrix as a result of a sharp drop in temperature and pressure, moisture evaporates instantly, which leads to the formation of a porous structure and an increase in the volume of the extrudate. The result is a product in the form of straight or curved sticks of rounded cross section, with a rough surface and developed porosity.

A known method of producing foams based on polyolefins [RF Patent No. 2320684 of 03/27/2008, "FOAM PLASTS BASED ON POLYOLEFINS"]. The invention relates to a foam based on polyolefins, to a method for its production, to the use of polyethylene wax and to heat-insulating material. The foam contains the following components: polyolefin, additives and at least one polyethylene wax, in which the polyethylene is in the form of an oxidized homopolymer or an oxidized copolymer. The above polyethylene wax is used as an agent for regulating the degree of cell enlargement. A method of producing a foam is that the polyolefin is mixed at high temperature with polyethylene wax and additives. The resulting mixture is then extruded in the presence of a blowing agent. The invention allows to obtain a foam without surface defects, to increase its cellular structure and properties, as well as to make heat-insulating material from it with high elasticity or flexibility.

The disadvantage of the analogue is the high temperature of mixing the polyolefin with additives, which entails an increase in the cost of the process and an increase in the cost of the product, as well as the need to use a foaming agent to obtain a cellular structure of the material, which leads to additional production costs.

The technical task of the invention is to develop a method for producing a biodegradable foam, consisting of a polyolefin matrix and a biodegradable hygroscopic filler, capable of collapsing under the influence of environmental factors, without the use of an additional pore-forming agent, which helps to reduce the cost of the product and energy consumption of production.

The technical task of the invention is achieved by the fact that in the method for producing biodegradable foam, the new one is that the foam consists of a polyolefin matrix and a biodegradable hygroscopic filler, which is used maltodextrin with a moisture content of 5-10 wt.%, With a ratio of components, wt.%:

- polyolefin 20-50;

- maltodextrin 80-50;

The method involves the processing of components in a twin-screw extruder having at least 3 zones:

- mixing zone with a temperature regime of 80-100 ° C;

- a plasticization zone with a humidity control unit, with a temperature regime of 140-160 ° C;

- an extrusion zone equipped with a flat-slotted head or a slot of complex configuration for profile manufacturing, with a temperature regime of 100-120 ° C.

The product exiting the extruder foams as a result of throttling - an instant pressure drop, physico-chemical and structural-mechanical changes occurring in the raw material due to the sorption moisture content in maltodextrin, and also due to the formation of maltodextrin thermal decomposition products, which are thus pore-forming agents . In this case, the choice of the polyolefin brand is limited by its melting temperature, which should be within the melting temperature of maltodextrin with a moisture content of 5-10 wt.% - 120-150 ° C, which allows you to create a uniform porous structure of the material.

The process for producing a foamed product is based on the following phenomena.

For a short period of time, the components are compressed in an extruder at high pressure, heated to a certain temperature, forced through a die, as a result of which the moisture in maltodextrin, as well as the products of thermal degradation of maltodextrin, pass into a vapor state with the accumulation of a significant amount of energy, which leads foaming of the product due to the pressure and temperature developed in the extruder, created by dissipative energy during the joint processing of the polyolefin new matrix and biodegradable hygroscopic filler at high shear stresses. The linear dimensions of the extrudate increase by more than 2 times, which leads to an increase in volume.

Extrusion of the mixture is accompanied by the following processes.

The initial components in the form of powder and granules are fed into the loading zone, where materials are pre-mixed, then the mass enters the plasticization zone, where it is intensively processed by shear deformation with a simultaneous increase in temperature. The density of the material and the fill factor of the inter-turn space increase, the pressure increases, as a result of which the granular structure of the material is destroyed and the material is gelled.

In the compression zone, the extrudate is re-compressed to maximum pressure, the temperature rises due to dissipation of internal energy and heat supply from the outside and the material is forced through a die with a die.

At the moment the material leaves the die, throttling occurs, which ensures foaming of the extrudate due to elastic moisture vapor and degradation products of maltodextrin. A plastic polyolefin matrix filled with a biodegradable hygroscopic filler, maltodextrin, acquires a pore-like structure that persists after cooling of the extrudate.

It is known [Technique and technology for food production by thermoplastic extrusion / G.O.Magomedov, A.F. Brekhov. - VGTA, 2003 .-- 168 p. Thermoplastic extrusion: scientific foundations, technology, equipment / Ed. A.N. Bogatyreva, V.P. Yuryev. - M .: Step, 1994. - 200 p.] That the residence time of the material in the extruder should not exceed 7 minutes, since further heating of the maltodextrin is accompanied by parallel processes of drying and caramelization, which reduces its foaming ability.

In the extruder, it is necessary to provide a humidity control unit, which is located at the end of the plasticization zone, in order to remove excess moisture from the material, or to additionally moisten the mixture, which will ensure a given porous structure of biodegradable foam.

The technical result of the invention is to develop a method for producing a biodegradable foam, consisting of a polyolefin matrix and a biodegradable hygroscopic filler, capable of collapsing under the influence of environmental factors, without the use of an additional pore-forming agent, which helps to reduce the cost of the product and energy consumption of production.

Maltodextrin [GOST 6034-74 Dextrins. Specifications] - a polysaccharide, a product of thermal, or enzymatic, or acid hydrolysis of starch (corn or potato), used in food, medical, textile and other industries, registered as a food additive E1400, chemical formula - (C ₆ H ₁₀ O ₅ ) _n .

Maltodextrin is a substance of natural origin, it is hygroscopic, which contributes to the development of microorganisms in the volume of foam in the environment due to the moisture content, and the formed porous structure of the composite contributes to a more effective biodegradation process.

A method for producing a biodegradable foam may also include the stage of introducing additional technological additives, such as dyes, stabilizers, decomposition photoinitiators, etc. into the composition, if necessary.

Biodegradable foam is made as follows.

In the extruder hopper, the number of temperature zones of which is not less than three, a polyolefin (in the form of granules or powder) is added in an amount of 20 ÷ 50 wt.%, A biodegradable hygroscopic filler is maltodextrin (in the form of a powder) with a moisture content of 5 ÷ 10 wt.% In an amount 80 ÷ 50 wt.%. In the extruder, the material successively passes through the following stages: the mixing stage at a temperature of 80 ÷ 100 ° C (No. 1 is indicated in tables 1-3), the plasticization stage at a temperature of 140-160 ° C (No. 2 is indicated in tables 1-3), the foaming stage with simultaneous forcing through a die at a temperature of 100-120 ° C (Tables 3–3 indicate No. 3), the finished product in the form of a foamed sheet or profile is then cooled and used as intended.

Tables 1-3 show the process conditions for the production of biodegradable polystyrene foam for a twin-screw extruder.

Table 1 Technological modes of biodegradable foam production process for twin screw extruder Zone number one 2 3 Temperature ° C 80 140 one hundred Engine speed, rpm 250 Load, A 12.5

table 2 Technological modes of biodegradable foam production process for twin screw extruder Zone number one 2 3 Temperature ° C 90 150 110 Engine speed, rpm 250 Load, A 12.3

Table 3 Technological modes of biodegradable foam production process for twin screw extruder Zone number one 2 3 Temperature ° C one hundred 160 120 Engine speed, rpm 250 Load, A 12.0

A method of obtaining a biodegradable foam is illustrated by the following examples.

Example 1 (prototype). In a drum mixer, a comparative mixture of 96 parts of low density polyethylene (LDPE) having a density of 926 kg / m ³ and a melt index (IR) of 2 g / 10 min (190 ° C, 2.16 kg), 6 parts of a master flame retardant mixture is prepared (chlorinated paraffin and antimony (III) oxide) with a concentration of 50 wt.% in terms of LDPE, 3 parts of the masterbatch of aluminum oxide with a concentration of 40 wt.% in terms of LDPE, 1.5 parts of stearamide and 1 part of the masterbatch of talc with concentration of 25 wt.% in terms of the weight of LDPE. The resulting mixture was extruded with a flow rate of 18 kg / h, while feeding isobutane with a flow rate of 3.06 kg / h through a die with a round hole to obtain a round rod with a diameter of about 23 mm. The temperature of the instrument is 108 ° C. The resulting foam has a density measured in the heated state equal to 16.5 kg / m ³ , very small cells (about 870-1000 cells / cm ² ) with an irregular distribution visible to the naked eye and through holes. The foam surface is covered with large bubbles. The next day, the foam has a density of 20 kg / m ³ , and after 4 days shows signs of irreversible shrinkage.

Example 2. In the hopper of a twin-screw extruder having three temperature zones, with a ratio L / D = 28, make granules of polyethylene grade PND 276-73 (GOST 16338-85), the density of which is 960 kg / m ³ , in an amount of 500 g (50 wt.%), and maltodextrin powder with a moisture content of 5.0 wt.% in an amount of 500 g (50 wt.%) and carry out the extrusion processing process.

Example 3. Get biodegradable foam analogously to example 2, but the amount of polyethylene is 400 g (40 wt.%), The amount of maltodextrin is 600 g (60 wt.%) With a moisture content of 6 wt.%.

Example 4. Get biodegradable foam analogously to example 2, but the amount of polyethylene is 300 g (30 wt.%), The amount of maltodextrin is 700 g (70 wt.%) With a moisture content of 6 wt.%.

Example 5. Get biodegradable foam analogously to example 2, but the amount of polyethylene is 200 g (20 wt.%), The amount of maltodextrin is 800 g (80 wt.%) With a moisture content of 6 wt.%.

Example 6. Get biodegradable foam analogously to example 2, but the moisture content of maltodextrin is 7.5 wt.%.

Example 7. Get biodegradable foam analogously to example 2, but the moisture content of maltodextrin is 10.0 wt.%.

The final stage of the extrusion process is the forcing of the material through the die, which forms the finished product.

The obtained biodegradable foams are analyzed, rheological characteristics, density, pore size, biodegradation kinetics are determined. The research results are presented in tables 4 and 5.

The rheological test results obtained with the SmartRheo viscometer and processed with the CeRVIEW 5.94 4D viscometer SmartRheo software allow us to state that with an increase in shear stress to a certain limit (5.50 MPa), a proportional increase in foaming coefficient occurs. This is due to an increase in the internal energy of the filled polyolefin-maltodextrin composition during processing in a screw unit due to mechanothermal action during the process of forcing through a die. Upon reaching the limit value of the shear rate, a decrease in the foaming coefficient is observed, which is associated with a decrease in the time of passage of the material through the capillary to a critical value.

Table 4 The results of the rheological studies of the compositions of the examples Rod lowering speed, mm / min The observed shear stress, MPa Foaming ratio example 2 5 3.9 2.9 10 3.3 3.2 twenty 5.8 3.9 40 6.7 3.2 80 10 2.0 example 3 5 3,5 3,1 10 4.0 3,7 twenty 5.1 4.0 40 6.2 3.8 80 8.5 2.2 example 4 5 2,3 3,1 10 3.4 3.4 twenty 4.8 4.2 40 5.7 3.0 80 6.8 3,1 example 5 5 1.8 3,1 10 3.0 3,5 twenty 4.6 3.6 40 5.0 4.3 80 5.7 4.0 example 6 5 3.8 3.0 10 4.0 3,5 twenty 5,6 4.0 40 6.5 3.8 80 9.5 2.5 example 7 5 3,7 3.2 10 3.8 3,7 twenty 5.5 4.1 40 6.2 4.0 80 9.1 3.0

Table 5 The results of studies of the compositions of the examples (number of samples 5) Defined Parameters Example data 1 (prototype) 2 3 four 5 6 7 The range of density values of biodegradable foam, kg / m ³ 16.5 14.2 ÷ 16.8 13.0 ÷ 15.9 13.5 ÷ 15.5 12.5 ÷ 15.1 14.0 ÷ 16.0 13.5 ÷ 15.5 Value range cell density biodegradable foam, cells / cm ² 870 ÷ 1000 50 ÷ 100 50 ÷ 90 40 ÷ 80 40 ÷ 80 50 ÷ 90 50 ÷ 80 Value range pore size of biodegradable foam, mm - 0.2 ÷ 2.2 0.2 ÷ 2.5 0.3 ÷ 2.8 0.3 ÷ 3.0 0.2 ÷ 2.3 0.2 ÷ 2.3 Weight reduction range biodegradable 0,0 15.8 ÷ 18.2 17.5 ÷ 19.0 20.1 ÷ 22.3 24.6 ÷ 26.5 15.8 ÷ 18.2 15.8 ÷ 18.2 foam during biodegradation after 60 days, wt.% Value range foaming ratio - 2.0 ÷ 3.9 2.2 ÷ 4.0 3.0 ÷ 4.2 3.1 ÷ 4.3 2.5 ÷ 4.0 3.0 ÷ 4.1

The ratio of the components of the polyolefin: maltodextrin, equal to 20-80 ÷ 50-50 wt.%, Is limited by several factors. When the content of maltodextrin in the composition is less than 50 wt.%, A decrease in the foaming coefficient of the compositions is observed, which is associated with a general decrease in moisture and thermal degradation products of maltodextrin in the composition, which are pore-forming agents, in addition, the biodegradation efficiency of the material is reduced. When the content of maltodextrin in the composition is more than 80 wt.%, The strength characteristics of the material decrease due to a decrease in the percentage of the synthetic polymer matrix, which ensures the strength of the composition.

Using the method for producing a biodegradable foam, consisting of a polyolefin matrix and a biodegradable hygroscopic filler, capable of degrading under the influence of environmental factors, without using an additional pore-forming agent, allows:

- organize a one-stage process for producing biodegradable foam;

- get biodegradable foam without reducing the physical and mechanical properties of the final products;

- to provide the necessary porous structure of biodegradable foam without the use of pore-forming agents;

- to simplify the stage of regulation of the porous structure of biodegradable foam;

- reduce the environmental impact in the process of obtaining and processing biodegradable foam, as well as when using products based on it;

- to ensure energy and resource conservation in the process of obtaining biodegradable foam.

Claims (1)

A method of obtaining a biodegradable foam, characterized in that the foam consists of a polyolefin matrix and a biodegradable hygroscopic filler, which is used maltodextrin with a moisture content of 5-10 wt.%, With a ratio of components, wt.%:
polyolefin 20-50 maltodextrin 80-50
The method involves the processing of components in a twin-screw extruder having at least 3 zones:
- mixing zone with a temperature regime of 80-100 ° C;
- a plasticization zone with a humidity control unit, with a temperature regime of 140-160 ° C;
- an extrusion zone equipped with a flat-slit head or a slot of complex configuration for manufacturing a profile with a temperature regime of 100-120 ° C.