RU2266305C2 - Method of preparing polymer materials with specified porosity via treatment with carbon dioxide in supercritical state followed by heat treatment at atmospheric pressure - Google Patents

Abstract

FIELD: polymer materials.

SUBSTANCE: method is comprised in saturating polymer material sample, placed in high-pressure cell, with carbon dioxide under supercritical conditions at pressure 250 atm and temperature 40-120°C, cooling the cell to room temperature and slowly lowering pressure to its atmospheric value. Foaming of polymer sample saturated with carbon dioxide under supercritical conditions proceeds during 60 min of further heat treatment at atmospheric pressure. Final porosity of polymer sample is determined by heat treatment temperature.

EFFECT: essentially preserved mechanical properties of initial polymer due to that, during heat treatment operation, outside layer of CO₂-saturated polymer sample is foamed.

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Description

The invention relates to a method for producing polymeric materials with a given pore volume by processing carbon dioxide in a supercritical state at a pressure of 250 atm and a temperature of 40-120 ° C and subsequent heat treatment at a temperature of 40-210 ° C and atmospheric pressure.

Today, the development of methods for producing polymer matrices with a given porosity has attracted great attention of research groups around the world. This is due to the fact that porous polymers and materials based on them have an extremely wide range of applications. For example, the scientific literature describes the use of porous polymers as filters for trapping organic substances [Mine, WM., Irvine RL. Polyurethane foam based biofilter media for toluene removal. Water. Sci. Technol. 2001; 43 (11): 35-42] and volatile odor components [Avison SJ, Gray DA, Davidson GM, Taylor AJ. Infusion of volatile flavor compounds into low density polyethylene. J. Agric. Food Chem. 2001 Jan; 49 (1): 270-5.] As adsorbents for the separation of biomolecules [Mayr B, Tessadri TR., Post E, Buchmeiser MR. Metathesis-based monoliths: influence of polymerization conditions on the separation of biomolecules. Anal. Chem. 2001 Sep 1; 73 (17): 4071-8], in microfluidic chromatography and capillary electrophoresis [Gusev I, Huang X, Horvath C. Capillary columns with in situ formed porous monolithic packing for micro high-performance liquid chromatography and capillary electrochromatography. J. Chomatogr. A 1999 Sep 3; 855 (1): 273-90], in optical electronic devices [Wirnsberger G, Yang P, Scott BJ, Chmelka BF, Stucky GD. Mesostructured materials for optical applications: from low-k dielectrics to sensors and lasers. Spectrochim Acta A Mol. Biomol. Spectrosc. 2001 Sep 1; 57 (10): 2049-60] and electrochemical power supplies [Sotiropoulos S., Brown I.L., Akay G., Lester E. Nickel incorporation into a hollow fiber microporous polymer: a preparation route for novel high surface area nickel structures. Materials Letters 35 (1998) 383-391].

Of great interest is the use of such materials in medicine. Here, the main areas of application of porous polymers are: the creation on their basis of sources for slow dosing of drugs in the human body (Drug delivery technology) [Dziubia TD, Torjman MC, Joseph L, Murphy-Tatum M, Lowman AM. Evaluation of porous networks of poly (2-hydroxyethyl methacrylate) as interfacial drug delivery devices. Biomaterials 2001 Nov; 22 (21): 2893-9], use as a basis for tissue growth and regeneration [Choueka J., Charvet J.L., Koval K.J., Alexander H., James K.S. Canine bone response to tyrosine-derived polycarbonates and poly (L-lactid acid). J. Biomed. Mater. Res., May; 31 (1): 35-41 (1996)] and implants with improved survival [Gosain AK, Song L, Riordan P, Amarante MT, Nagy PG, Wilson CR, Toth JM, Ricci JL. A 1-year study of osteoinduction in hydroxyapatite-derived biomaterials in an adult sheep model: part I. Plast. Reconstr. Surg. 2002 Feb; 109 (2): 619-30].

The above examples far from exhaust the entire spectrum of possible applications of porous polymeric materials, but they clearly show that the demand for such materials is currently quite large and will increase in the future.

One of the promising methods for creating porosity in polymer matrices is the treatment with carbon dioxide in a gaseous, liquid, or supercritical state. Although this method of obtaining porosity is used relatively recently, a significant number of works on this topic have been published to date. In these studies, the process of creating porosity was carried out in two stages: in the first stage, the polymer was saturated with gaseous, liquid, or supercritical CO ₂ at high pressure, and the second saturated CO ₂ polymer was foamed by rapid heating at atmospheric pressure. So, in [Handa, YP; Zhang, ZJ A new technique for measuring retrograde vitrification in polymer-gas systems and for making ultramicrocellular foams from the retrograde phase. Polym. Sci. Part B: Polym. Phys. 2000, Vol.38, p.716-725.] Describes the preparation of the porous polymethylmethacrylate (PMMA) in this way, in [Kumar, V .; Weller, JE Microcellular Foams; Khemani, C.S., Ed .; ACS: Washington, DC 1997; Vol.669, p.101.] The effect of the foaming temperature on the porosity of saturated CO ₂ polycarbonate was studied. Authors [Wessling, M .; Borneman, Z .; Van den Boomgaard, T .; Smolders, C. A. Carbon dioxide foaming of glassy polymers J. Appl. Polym. Sci. 1994, Vol.53, p.1497-1512.] The process of pore formation in films of polycarbonate, polyamide and polsulfone was studied, it is shown that when these polymers are saturated with gaseous CO ₂ and subsequent foaming, the pore formation process is accompanied by the formation of a thin dense layer on the surface that blocks access to pores in the thickness of the polymer.

In the work [Stafford, S.M .; Russel, T.R .; McCarthy, T. Expansion of polystyrene using supercritical carbon dioxide: effects of molecular weight, polydispersity, and low molecular weight components. J. Macromolecules 1999, Vol.32, p.7610-7616] studied the dependence of the average pore diameter of supercritical CO ₂ saturated and foamed polystyrene on the molecular weight, polydispersity and the amount of low molecular weight components in the starting polymer. It was shown that of all the studied factors, only the presence of a significant amount of low molecular weight substances affects the pore formation in polystyrene. In addition, there are a number of publications devoted to the production of porous polypropylene by this method [Liang, M.-T .; Wang, C.-M. Production of Very Low Density Microcellular Polypropylene by Supercritical Carbon Dioxide: Nottinghma (UK), 1999, p. 151.], Polyethylene [Briscoe, B.J .; Chaudhary, BI; Savvas, T. Cellular Polymers 1993, Vol.12, p. 171.] And glycol-modified polyethyleneterephthalate [Handa, YP; Wong, W .; Zhang, Z .; Kumar, V .; Eddy, S .; Khemani, K. Polym. Eng. Sci 1999, Vol. 39, p. 55.].

In this application for the invention, for the creation of porosity of a given volume in polymeric materials, the use of a two-stage processing is proposed, which allows obtaining polymeric materials with a given pore volume. In the first stage, the polymer is saturated with carbon dioxide in a supercritical state. The saturation of the polymer is carried out on the installation, the circuit diagram of which is shown in figure 1.

The saturation process in this installation was carried out as follows: a polymer sample was placed in cell E, then, using pump H, the cell was filled with carbon dioxide to a predetermined pressure, after which it was heated to a predetermined temperature using a thermostat T. At the end of the experiment, the cell was cooled to room temperature and slowly depressurized through an adjustable PP restrictor.

Data on the sorption of carbon dioxide by polymers at a temperature of 40 ° C-120 ° C and a pressure of 250 atm for 60 minutes of processing are shown in table 1.

Table 1. Polymer name The amount of sorbed carbon dioxide in% by weight of the polymer 40 ° C 60 ° C 80 ° C 100 ° C 120 ° C High Impact Polystyrene (HIPS) 4.9 6.4 7.8 9.8 - Polycarbonate 4 4.8 5,6 7.2 8.5 Polymethylmethacrylate (PMMA) 14.1 16.5 22.3 28 - Polystyrene 11.6 thirteen 17 22.3 - Acrylonitrile Butadiene Styrene (ABS) 9.2 11.2 15.3 17.1 - Copolymer 94% polymethylmethacrylate - 6% polymethylacrylate (dacryl 6) 17 24.6 29th - -

The data presented cover a temperature range below the glass transition temperature, so saturation with carbon dioxide at values close to or above this temperature leads to sorption of extremely large amounts of carbon dioxide, which, in turn, leads to strong swelling (2.5-4 times relative to the original volume) and almost complete loss of mechanical strength. For example, after processing PMMA at a temperature of 100 ° C (the amount of sorbed carbon dioxide is 28% by weight of the polymer), the polymer sample has become loose and brittle. Processing PMMA above this temperature led to mechanical destruction of the sample.

Immediately after treatment with carbon dioxide, the sample was placed in a thermostat and kept for 60 minutes at a given temperature. During the heat treatment, foaming of the outer layer of the polymer saturated with carbon dioxide occurred. In this case, the polymer core did not undergo any changes, i.e. the sample largely retained the mechanical properties of the starting material. The proposed procedure, in which the sample is first treated with carbon dioxide, is then removed from the cell after cooling and slow pressure relief and then foams in the thermostat, provides several advantages compared to the known method of foaming directly in the cell during pressure relief, namely:

- this procedure provides strict control over all process parameters (processing conditions in cCO ₂ , foaming temperature), which, in turn, allows predicting the final porosity of the material with high accuracy;

- in two-stage processing, the cell volume is used more efficiently, since in this case no additional volume is required for expanding expandable polymer samples, which significantly reduces the cost of the porous polymer material.

As an illustration, in Fig. 2, a photograph of polymethimethacrylate samples processed in supercritical carbon dioxide at a pressure of 250 atm and a temperature of 40 ° C for 30 minutes and then foamed at various temperatures is shown.

The total pore volume of polymeric materials was measured by filling them with water at room temperature and a pressure of 300 atm. The porosity values of the polymethylmethacrylate samples thus measured, depending on the foaming temperature, are shown in the histogram (Fig. 3). The processing conditions and foaming temperature correspond to those indicated in figure 2.

As can be seen in figure 3., the proposed method of two-stage processing of polymers allows you to get samples with porosity that varies over a wide range depending on the temperature of heat treatment at atmospheric pressure.

Similarly, samples of different porosity of high-impact polystyrene (HIPS), polycarbonate, polystyrene, acryl-butadiene-styrene copolymer (ABS), 94% methyl methacrylate copolymer - 6% methyl acrylate (dacryl 6) were obtained. The data on the change in the porosity of polymeric materials depending on the processing temperature at atmospheric pressure are shown in Fig. 4 (polycarbonate), Fig. 5 (high-impact polystyrene), Fig. 6 (PSN-115 polystyrene), Fig. 7 (acrylonitrile-butadiene copolymer styrene ABS), Fig. 8 (Dacryl copolymer 6).

Specific processing conditions and achieved porosity are indicated in the examples. To confirm the formation of a porous structure in polymers, the samples before and after treatment were studied by scanning electron microscopy. Figure 9 shows micrographs of the source and processed samples. The photographs clearly show that processing by the proposed method leads to the formation of a well-developed pore structure in the polymer.

Example 1

A sample of polymethylmethacrylate × 44 × 15 mm (PMMA) was placed in a cell, treated in supercritical carbon dioxide at a temperature of 40 ° C and a pressure of 250 atm for 60 minutes, then the cell was cooled to room temperature and slowly depressurized to atmospheric pressure. Next, the carbon dioxide-saturated sample was removed from the cell and placed in a thermostat, where it was kept at a temperature of 80 ° C for 60 minutes. The resulting porous polymeric material had a total pore volume of 0.7 cm ³ / g.

Example 2

A sample of polycarbonate based on bisphenol A brand Macrolon (Bayer, Germany), in the form of granules (d _cp = 3-4 mm, total 24 granules), was placed in a cell, processed in supercritical carbon dioxide at a temperature of 120 ° C and a pressure of 250 atm for 60 minutes, then the cell was cooled to room temperature and slowly dropped to atmospheric pressure. Next, the carbon dioxide-saturated sample was removed from the cell and placed in a thermostat, where it was kept at a temperature of 190 ° C for 60 minutes. The resulting porous polymeric material had a total pore volume of 0.4 cm ³ / g.

Example 3

A sample of impact-resistant polystyrene (HIPS), in the form of granules (d _cp = 3-4 mm, a total of 32 granules), was placed in a cell, processed in supercritical carbon dioxide at a temperature of 40 ° C and a pressure of 250 atm for 60 minutes, then a cell cooled to room temperature and slowly relieved pressure to atmospheric. Next, the carbon dioxide-saturated sample was removed from the cell and placed in a thermostat, where it was kept at a temperature of 140 ° C for 60 minutes. The resulting porous polymeric material had a total pore volume of 0.9 cm ³ / g.

Example 4

A PSN-115 polystyrene sample in accordance with GOST 20282-86, in the form of granules (d _cp = 3-4 mm, a total of 32 granules), was placed in a cell, processed in supercritical carbon dioxide at a temperature of 40 ° C and a pressure of 250 atm for 60 minutes, then the cell was cooled to room temperature and slowly depressurized to atmospheric pressure. Next, the carbon dioxide-saturated sample was removed from the cell and placed in a thermostat, where it was kept at a temperature of 120 ° C for 60 minutes. The resulting porous polymeric material had a total pore volume of 1.05 cm ³ / g.

Example 5

A sample of acrylonitrile-butadiene-styrene (ABS) copolymer, in the form of granules (d _cp = 3-4 mm, total 24 granules), was placed in a cell, processed in supercritical carbon dioxide at a temperature of 50 ° C and a pressure of 250 atm for 60 minutes, then the cell was cooled to room temperature and slowly depressurized to atmospheric pressure. Next, the carbon dioxide-saturated sample was removed from the cell and placed in a thermostat, where it was kept at a temperature of 120 ° C for 60 minutes. The resulting porous polymeric material had a total pore volume of 0.9 cm ³ / g.

Example 6

A cylindrical sample (d = 7 mm, l = 20 mm) of a copolymer of methyl methacrylate with Dacryl 6 methyl acrylate, a mass fraction of methyl acrylate of 6%, was placed in a cell, treated in supercritical carbon dioxide at a temperature of 40 ° C and a pressure of 250 atm for 10 minutes, then the cell was cooled to room temperature and slowly depressurized to atmospheric pressure. Then, the carbon dioxide-saturated sample was removed from the cell and placed in a thermostat, where it was kept at a temperature of 100 ° С for 60 minutes. The resulting porous polymeric material had a total pore volume of 1.78 cm ³ / g.

Claims (7)

1. A method of obtaining porous polymeric materials with a given pore volume, characterized in that the polymer material sample is first placed in a high pressure cell and saturated with carbon dioxide under supercritical conditions at a pressure of 250 atm and temperatures of 40-120 ° C, then the cell is cooled to room temperature and slowly depressurize to atmospheric pressure, then the polymer sample saturated with carbon dioxide is subjected to heat treatment at atmospheric pressure for 60 minutes, while the final porosity of the sample is determined by eraturoy heat treatment. 2. The method according to claim 1, characterized in that the polymethyl methacrylate (PMMA) was processed, carbon dioxide was saturated at a pressure of 250 atm in the temperature range of 40-100 ° C, the subsequent heat treatment was carried out at temperatures of 40-140 ° C for 60 minutes, the total porosity of polymer samples 0.05-0.9 cm ³ / g depending on the temperature of the heat treatment. 3. The method according to claim 1, characterized in that the polycarbonate (PC) was processed, carbon dioxide was saturated at a pressure of 250 atm in the temperature range of 40-120 ° C, the subsequent heat treatment was carried out at temperatures of 150-210 ° C for 60 minutes, the total porosity of polymer samples of 0.01-0.4 cm ³ / g depending on the heat treatment temperature. 4. The method according to claim 1, characterized in that impact-resistant polystyrene (HIPS) was processed, carbon dioxide was saturated at a pressure of 250 atm in the temperature range of 40-100 ° C, subsequent heat treatment was carried out at temperatures of 40-140 ° C for 60 min , the total porosity of polymer samples is 0.1-0.9 cm ³ / g, depending on the heat treatment temperature. 5. The method according to claim 1, characterized in that the polystyrene (PS) was processed, carbon dioxide was saturated at a pressure of 250 atm in the temperature range of 40-100 ° C, the subsequent heat treatment was carried out at temperatures of 40-120 ° C for 60 minutes, the total porosity of polymer samples 0.21-1.05 cm ³ / g depending on the heat treatment temperature. 6. The method according to claim 1, characterized in that the copolymer of acrylonitrile-butadiene-styrene (ABS) was processed, carbon dioxide was saturated at a pressure of 250 atm in the temperature range of 40-100 ° C, the subsequent heat treatment was carried out at temperatures of 40-120 ° C within 60 min, the total porosity of the polymer samples is 0.1-0.9 cm ³ / g depending on the heat treatment temperature. 7. The method according to claim 1, characterized in that the copolymer of 94% polymethyl methacrylate - 6% polymethyl acrylate (dacryl 6) was processed, carbon dioxide was saturated at a pressure of 250 atm in the temperature range 40-80 ° C, the subsequent heat treatment was carried out at temperatures of 40- 100 ° C for 60 min, the total porosity of the polymer samples 0.35-1.78 cm ³ / g depending on the heat treatment temperature.

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