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

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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The invention relates to a method for producing polymeric materials with a specified pore volume through treatment with carbon dioxide in supercritical state at a pressure of 250 atmospheres and a temperature of 40-120°and further heat treatment at a temperature of 40-210°and atmospheric pressure.

Today, the development of methods of polymeric matrices with a given porosity attracts much attention of research groups around the world. This is because porous polymers and materials based on them have an extremely wide range of applications. For example, in the scientific literature describes the use of porous polymers as a filter to trap organic matter [My, WM., Irvine RL. Polyurethane foam based biofilter media for toluene removal. Water. Sci. Technol. 2001; 43(11): 35-42] and the volatile components of smell [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, 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 a 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 sources [Sotiropoulos, S., Brown, I.L., Akay G., Lester E. Nickel incorporation into a hollow fibre 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 of sources for slow dosing in humans drugs (Drug delivery) [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], using as the basis for growth and tissue regeneration [Choueka j, Charvet J.L., Koval K.J., Alexander H., James for 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 do not exhaust the whole range of possible applications of porous polymeric materials, but they clearly show that the need for such materials today is quite high and will increase in the future.

One of the promising methods for creating porosity in polymer matrices is the handling of carbon dioxide in gazoo is different, liquid or supercritical state. Although this method of obtaining porosity is applied relatively recently, to date, published a large number of works devoted to this topic. In these studies, the process of creating porosity was carried out in two stages: the first stage polymer is saturated with gaseous, liquid or supercritical CO₂at high pressure, the second saturated CO₂the polymer was wspanialy using rapid heating at atmospheric pressure. So, in [Handa, Y.P.; Zhang, Z.J. 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.] described obtaining in this way a porous polymethylmethacrylate (PMMA), in [Kumar, V.; Weller, J.E. Microcellular Foams; Khemani, K.S., Ed.; ACS: Washington, DC, 1997; Vol.669, p.101.] we studied the influence of temperature foaming porosity of the saturated CO₂polycarbonate. The authors of [Wessling, M.; Borneman, Z.; Van den Boomgaard, T.; Smolders, S.A. Carbon dioxide foaming of glassy polymers, J. Appl. Polym. Sci. 1994, Vol.53, p.1497-1512.] we studied the process of steam formation in the films of polycarbonate, polyamide and polysulfone, it is shown that the saturation of these polymers gaseous CO₂and subsequent foaming process steam formation is accompanied by the formation on the surface of the thin dense layer that covers the access to the pores in the thickness of the polymer.

[Stafford, who .M.; Russel, TR; 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 diameter of the pores saturated with supercritical CO₂and foamed polystyrene from the molecular weight, polydispersity and quantity of low-molecular components in the original polymer. It is shown that all studied factors, only the presence of substantial amounts of low molecular weight substances influences the pore formation in polystyrene. In addition, there are a number of publications on obtaining in this way a porous polypropylene [Liang, M.-T.; Wang, C.-M. Production of Very Low Density Microcellular Polypropylene by Supercritical Carbon Dioxide: Nottinghma (UK), 1999, p.151.], polyethylene [Briscoe, .J.; Director, B.I.; Savvas, T. Cellular Polymers 1993, Vol.12, p.171.] and polyethylenterephtalate modified with glycol [Handa, Y.P.; Wong, W.; Zhang, Z.; Kumar, V.; Eddy, S.; Khemani, K. Polym. Eng. Sci 1999, Vol.39, p.55.].

In this application the invention to create for polymeric materials, the porosity of a given size is proposed using two-stage processing, allowing to obtain polymeric materials with a specified pore size. In the first stage, the polymer is saturated with carbon dioxide in supercritical state. The saturation of the polymer is conducted at the facility, the concept of which is shown in figure 1.

The process of saturation in this installation done by ulali as follows: the polymer sample was placed in a cell E, then use pump N the cell was filled with carbon dioxide to a predetermined pressure, after which thermostat T was heated to a predetermined temperature. When experiment the cell was cooled to room temperature and slowly dumped pressure through an adjustable air restrictor PP.

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

Presents data cover the temperature range below the glass transition temperature, saturation with carbon dioxide at values close to or above this temperature results in the sorption of extremely large quantities of carbon dioxide, which, in turn, leads to severe swelling (2.5-4 times compared to the initial volume) and almost complete loss of mechanical strength. For example, after processing of PMMA at a temperature of 100°With (amount of adsorbed carbon dioxide 28% by weight of polymer) of the polymer sample was loose and fragile. Processing of 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 was foaming of the outer layer polymer saturated with carbon dioxide. While the core of the polymer did not undergo any changes, i.e. the sample was largely retained mechanical properties of the source material. The proposed procedure, in which education is the EC first processed with carbon dioxide, then extracted from the cells after cooling and slow pressure relief and then foams at thermostat, provides a number of advantages compared with the known method foaming directly in the cell when the pressure relief, namely:

this procedure ensures strict control of all process parameters (process conditions in skso₂the foaming temperature), which in turn, allows high accuracy to predict the final porosity of the material;

when the two-stage processing more effectively used cell volume, because in this case no additional amount for expansion of the expandable polymer samples, which significantly reduces the cost of the porous polymeric material.

As an illustration, figure 2, shows a photograph of a sample polimetilmetakrilata processed in supercritical carbon dioxide at a pressure of 250 atmospheres and a temperature of 40°C for 30 minutes and then foamed at different temperatures.

Total pore volume of polymer materials was measured by filling them with water at room temperature and a pressure of 300 atmospheres. The measured values thus porosity of the samples polymethylmethacrylate depending on the temperature of the foaming is shown in the histogram (figure 3). The machining conditions and temperature in which peniana match, specified in figure 2.

As can be seen in figure 3., the proposed method is two-stage processing of polymers makes it possible to obtain samples with porosities varying within wide limits depending on the heat treatment temperature at atmospheric pressure.

In a similar manner there were obtained samples of different porosity high impact polystyrene (HIPS), polycarbonate, polystyrene, copolymer of acrylic-butadiene-styrene (ABS)copolymer of 94% of methyl methacrylate and 6% of methyl acrylate (datril 6). Data on the change in porosity of polymeric materials depending on the temperature treatment at atmospheric pressure is shown in figure 4 (polycarbonate), 5 (high impact polystyrene), 6 (polystyrol PSN-115), 7 (copolymer of Acrylonitrile-butadiene-styrene ABS), Fig (copolymer of datril 6).

Specific processing conditions, and achieved the porosity indicated in the examples. To confirm the formation of the polymer porous structure of the samples before and after treatment were investigated by scanning electron microscopy. Figure 9 shows a micrograph of the initial and treated samples. The shots clearly shows that the treatment proposed method leads to the formation of polymer in the well-developed structure of pores.

Example 1.

Sample polymethylmethacrylate ×44×15 mm (PMMA) was placed in a cell that was processed in sorcity eskay carbon dioxide at a temperature of 40° C and a pressure of 250 psi for 60 minutes, then the cell was cooled to room temperature and slowly dropped the pressure to atmospheric. Then saturated with carbon dioxide sample was extracted from the cell and placed in thermostat, where is kept at a temperature of 80°C for 60 minutes. The resulting porous polymeric material has a total pore volume of 0.7 cm³/year

Example 2.

A sample of polycarbonate based on bisphenol a brand "Makrolon" (firm Bayer, Germany), in the form of granules (d_cp=3-4 mm, total number of 24 pellets), was placed in a cell that was processed in supercritical carbon dioxide at a temperature of 120°and pressure of 250 psi for 60 minutes, then the cell was cooled to room temperature and slowly dropped the pressure to atmospheric. Then saturated with carbon dioxide sample was extracted from the cell and placed in thermostat, where is kept at a temperature of 190°C for 60 minutes. The resulting porous polymeric material has a total pore volume of 0.4 cm³/year

Example 3.

Sample high impact polystyrene (HIPS), in the form of granules (d_cp=3-4 mm, total number of 32 granules), was placed in a cell that was processed in supercritical carbon dioxide at a temperature of 40°and pressure of 250 psi for 60 minutes, then the cell was cooled to room temperature and slowly lost pressure, the reduction to atmospheric. Then saturated with carbon dioxide sample was extracted from the cell and placed in thermostat, where is kept at a temperature of 140°C for 60 minutes. The resulting porous polymeric material has a total pore volume of 0.9 cm³/year

Example 4.

Sample polystyrol PSN-115 according to GOST 20282-86, in the form of granules (d_cp=3-4 mm, total number of 32 granules), was placed in a cell that was processed in supercritical carbon dioxide at a temperature of 40°and pressure of 250 psi for 60 minutes, then the cell was cooled to room temperature and slowly dropped the pressure to atmospheric. Then saturated with carbon dioxide sample was extracted from the cell and placed in thermostat, where is kept at a temperature of 120°C for 60 minutes. The resulting porous polymeric material has a total pore volume of 1.05 cm³/year

Example 5.

A sample of the copolymer of Acrylonitrile-butadiene-styrene (ABS), in the form of granules (d_cp=3-4 mm, total number of 24 pellets), was placed in a cell that was processed in supercritical carbon dioxide at a temperature of 50°and pressure of 250 psi for 60 minutes, then the cell was cooled to room temperature and slowly dropped the pressure to atmospheric. Then saturated with carbon dioxide sample was extracted from the cell and placed in thermostat, where is kept at a temperature of 120°for the of 60 minutes. The resulting porous polymeric material has a total pore volume of 0.9 cm³/year

Example 6.

The cylindrical sample (d=7 mm, l=20 mm) of a copolymer of methyl methacrylate with methyl acrylate dakril 6, weight percentage of methyl acrylate 6%, was placed in a cell that was processed in supercritical carbon dioxide at a temperature of 40°and pressure of 250 psi for 10 minutes, then the cell was cooled to room temperature and slowly dropped the pressure to atmospheric. Then saturated with carbon dioxide sample was extracted from the cell and placed in thermostat, where is kept at a temperature of 100°C for 60 minutes. The resulting porous polymeric material has a total pore volume of 1.78 cm³/year

1. The method of obtaining porous polymeric materials with a specified volume of pores, wherein a sample of the polymer material is first placed in a high-pressure cell and saturated with carbon dioxide under supercritical conditions at a pressure of 250 atmospheres and temperatures 40-120°With, then the cell is cooled to room temperature and slowly relieve the pressure to atmospheric, then saturated with carbon dioxide polymer sample is subjected to heat treatment at atmospheric pressure for 60 min, and the final porosity of the sample is set by the temperature of heat treatment.

2. The method according to claim 1, featuring the the action scene, what were processed polymethylmethacrylate (PMMA), the saturation of carbon dioxide was carried out at a pressure of 250 atmospheres in the temperature range 40-100°With subsequent heat treatment conducted at temperatures 40-140°C for 60 min, the total porosity of the polymer samples of 0.05-0.9 cm³/g depending on the heat treatment temperature.

3. The method according to claim 1, characterized in that the processed polycarbonate (PC), the saturation of carbon dioxide was carried out at a pressure of 250 atmospheres in the temperature range of 40-120°With subsequent heat treatment conducted at temperatures 150-210°C for 60 min, the total porosity of the polymer samples of 0.01-0.4 cm³/g depending on the heat treatment temperature.

4. The method according to claim 1, characterized in that the processed high-impact polystyrene (HIPS), the saturation of carbon dioxide was carried out at a pressure of 250 atmospheres in the temperature range 40-100°With subsequent heat treatment conducted at temperatures 40-140°C for 60 min, the total porosity of the polymer samples of 0.1-0.9 cm³/g depending on the heat treatment temperature.

5. The method according to claim 1, characterized in that the processed polystyrene (PS), the saturation of carbon dioxide was carried out at a pressure of 250 atmospheres in the temperature range 40-100°With subsequent heat treatment was carried out at a temperature of 40-120°C for 60 min, the total porosity of the polymer is Bristow 0,21-1,05 cm ³/g depending on the heat treatment temperature.

6. The method according to claim 1, characterized in that the processed copolymer of Acrylonitrile-butadiene-styrene (ABS), the saturation of carbon dioxide was carried out at a pressure of 250 atmospheres in the temperature range 40-100°With subsequent heat treatment was carried out at a temperature of 40-120°C for 60 min, the total porosity of the polymer samples of 0.1-0.9 cm³/g depending on the heat treatment temperature.

7. The method according to claim 1, characterized in that the processed copolymer of 94% poly 6% for polymethylacrylate (datril 6), the saturation of carbon dioxide was carried out at a pressure of 250 atmospheres in the temperature range 40-80°With subsequent heat treatment was performed at temperatures of 40-100°C for 60 min, the total porosity of the polymer samples 0,35-1,78 cm³/g depending on the heat treatment temperature.