System for producing shear thickening fluids and method for producing shear thickening fluids

Abstract

The object of the invention is a system for producing shear thickening liquids comprising a reciprocating chamber, characterized in that the chamber has a circular cross-section and is integral with the upper fastening plate in a permanent or detachable manner, and the upper fastening plate is connected to the lower fixed fastening plate by means of at least one linear rod with a linear bearing, and at least one ball screw with a nut. At the same time, outside the chamber there is a heating jacket, and inside the chamber there is an agitator shaft at one end of which there is a dispersing part, and the other end of the agitator shaft is connected to a drive that rotates the shaft. At the same time, the chamber moves in a reciprocating motion in relation to the shaft. The object of the invention is also a method for producing shear thickening fluids in the system according to the invention.

Description

[0001] System for producing shear thickening fluids and method for producing shear thickening fluids

[0002] The subject matter of the invention is a system for producing shear thickening fluids comprising a reciprocating chamber, as well as a method for producing shear thickening fluids.

[0003] Shear thickening fluids (STFs) belong to the group of non-Newtonian fluids. These materials are characterized by an increase in viscosity with increasing shear rate. This means that as the mixing rate increases, more and more forces will be deposited on the agitator to hinder the mixing process. The value of these forces will increase as the area of the STF shear agitator increases. As a result of sudden excitation, e.g. impact, STF transforms into a solid and returns to its original state after the loss of the stimulus. This unique feature allows the use of STF in applications requiring the reception of rapidly increasing energies, e.g. human body protection elements, liquid shields, etc. [Shear Thickening Fluid and Its Application in Impact Protection: A Review Polymers 2023, 15(10), 2238],

[0004] Shear thickening fluids are obtained by dispersing the ceramic powder in a liquid polymer matrix. Micro and nanometric silica with a spherical or amorphous shape is most often used as a ceramic powder (Selim Gurgen, Melih Cemal Ku§han, Weihua Li, Shear thickening fluids in protective applications: A review - Progress in Polymer Science Volume 75, December 2017, Pages 48-72). The matrix is most often polypropylene glycol) or poly(ethylene glycol) with different molecular weight. The process of obtaining STF is carried out in an agitator and consists in dosing the powder into the polymer matrix. During the dosing of the ceramic powder, the viscosity in the mixture increases, making it difficult to mix and continue the process. After reaching 15-20 wt % of ceramic powder in the mixture, regardless of the type of geometry of the agitator used (propeller, screw, ribbon, anchor, frame agitator), an unmixed powder crust appears on the surface of the liquid. The attempt to disperse the powder by increasing the agitator speed ends with deformation of the agitator or damage to the drive system. The cause of this phenomenon is the shear thickening effect, consisting in the fact that as the mixing rate increases, the viscosity of the liquid increases logarithmically.

[0005] Unfavourable, the shear thickening effect during production can be partially eliminated by conducting the process at an elevated temperature, most often 50-150°C. As the temperature increases, the viscosity of the mixture decreases, which facilitates further mixing. However, higher temperature causes irreversible changes in the polymer matrix and makes it difficult to achieve the assumed formula due to the decomposition and evaporation of the volatile component (Unexpected Method of High-Viscosity Shear Thickening Fluids Based on Polypropylene Glycols Development via Thermal Treatment doi.org / 10.3390 / ma15175818).

[0006] Another method of reducing high viscosity during the production of STF is the addition of anhydrous ethyl alcohol [patent CN102191680B], The introduction of ethyl alcohol lowers the viscosity of the mixture, which significantly shortens the process of homogenization of the dispensed ceramic powder in the organic matrix. In addition to the solvent, the process uses parallel sonification of the suspension [RSC Adv., 2023, 13, 7385-7391], The disadvantage of the solvent method is the need to remove ethanol after adding an appropriate amount of ceramic powder. Ethanol evaporation takes place at elevated temperature and under reduced pressure [Procedia Engineering 173 (2017) 655 - 66], The above method of producing STF due to the use of a volatile and flammable solvent can be difficult to implement at an industrial scale. In addition to the agitator, an evaporative system operating under reduced pressure is required.

[0007] In the literature, agitator systems are usually equipped with an agitator and a fixed mixing chamber, e.g. with a screw connection to the agitator structure. The movable element is an agitator with a suitable structure ensuring mixing in the entire volume (Houari Ameur, Mohamed Bouzit, Abdellah Ghenaim, Hydrodynamics in a vessel stirred by simple and double helical ribbon impellers, Cent. Eur. J. Eng. 3(1) 2013 87-98). The height of the mixing tip, e.g. in a frame or ribbon agitator, is similar to the height of the agitator chamber or a column of mixed liquid.

[0008] Due to the shear thickening effect, the production of SFTs in conventional agitators is very difficult or even impossible. In conventional solutions (where the agitator chamber and the agitator do not move in a reciprocating motion), the dosage of silica causes a solid to remain on the surface of the liquid. This residual powder is moistened with a small amount of liquid in such a way that semi-solid mass systems are formed, with a layer of liquid on the outside and a ceramic powder on the inside. Such semi-solid masses make it very difficult to continue the process, because if the agitator speed increases, its speed is blocked by the shear thickening effect, leading to damage to the mixing system. This situation occurs regardless of the type of dispersing tip used, type of silica and matrix. The problem of obtaining homogeneous shear thickening fluids was solved thanks to the use of a mixing system in which the reciprocating motion of the agitator chamber was used with the simultaneous adjustable rotational motion of the agitator with the appropriate geometry.

[0009] The essence of the invention is a system for producing shear thickening fluids comprising a reciprocating chamber, characterized in that the chamber has a circular cross-section and is reciprocally incorporated with the upper fastening plate in a permanent or detachable manner, and the upper fastening plate is connected to the lower fixed fastening plate by means of at least one linear rod with a linear bearing that allows a reciprocating motion (up-down).

[0010] Further, the system comprises at least one ball screw with a nut. Ball screws stiffen the chamber, however, it is the linear rods that are mainly responsible for maintaining the rigidity of the structure.

[0011] On the outside of the chamber there is also a heating jacket, and inside the chamber there is an agitator shaft with a dispersing part.

[0012] At one end of the agitator shaft there is a dispersing part comprising at least two circular segment-shaped blades, wherein the angle of inclination of one blade with respect to the agitator shaft is from 30° to 80°. The opening angle defining the shape of a single agitator blade, i.e. the angle of the wheel segment is from 120° to 180°, and the width of the blades is 70-95% of the chamber inner diameter. The height of the blades is up to 20% of the total height of the chamber.

[0013] The second end of the agitator shaft serves to connect to a drive that rotates the shaft. At the same time, the chamber moves in a reciprocating motion in relation to the shaft, i.e. in an up-down motion.

[0014] Preferably, the heating jacket is an external electric jacket with adjustable power. For larger volume structures, a chamber with an external jacket for superheated steam can be used.

[0015] Preferably, the height of the chamber is larger than its width. Most preferably, it is in a ratio of 2:1 (heightwidth).

[0016] Another essence of the invention is the method of producing STF characterized in that in step a) the polymer matrix is introduced into the agitator chamber in an amount of no more than 70% of the volume of the agitator chamber. In step b), the agitator chamber is reciprocated, and then in the next step c) the agitator chamber is heated and the agitator shaft is rotated so that the polymer matrix is heated evenly in its entire volume.

[0017] In step d), a ceramic powder is introduced in an amount of up to 30 wt % relative to the polymer matrix. The dosing rate is variable. The principle is that at the beginning it is dosed quickly, and with the increase of the solid phase in the mixture - more and more slowly.

[0018] The maximum amount of matrix that can be introduced into the agitator chamber in stage a) is 70%, in relation to the volume of the chamber. However, the greater the solid phase content in the liquid, the less matrix is added to the agitator. The recipe in the form of 70% filling of the chamber and 30% silica will not fit in the agitator, due to the volume of the submerged agitator.

[0019] In the next step e), the reciprocating motion frequency of the agitator chamber and the rotation of the agitator shaft is adjusted to obtain a homogeneous mixture.

[0020] Preferably, the polymeric matrix is polypropylene glycol) with a molecular weight of 400 to 2700 g / mol or poly(ethylene glycol) with a molecular weight of 200 to 400 g / mol.

[0021] Preferably, in step b) the agitator chamber is reciprocated at a frequency of 0,01 to 2 Hz.

[0022] Preferably, in step c) the agitator chamber is heated to a temperature of 95°C.

[0023] Preferably, the agitator shaft in step c) rotates at a frequency of 2500-3000 rpm.

[0024] Preferably, in step e), the frequency of the agitator chamber motion is adjusted in the range of from 2 to 0.01 Hz, and the rotation of the agitator shaft from 300 to 3000 rpm.

[0025] The advantage of the present invention is a simple and efficient high-performance system for producing shear thickening liquids. Thanks to the reciprocating motions of the chamber, the agitator effectively disperses silica throughout the entire volume of the liquid. At the same time, the relatively small surface / volume of the dispersing tip encounters a low resistance of the liquid, so that drive systems with lower power can be used in relation to conventional solutions based on anchor, frame or ribbon agitators, which is manifested by lower energy consumption as well as the material needed for the agitator structure. The object of the invention is illustrated in the drawing, in which:

[0026] Fig. 1 shows a cross-section in a rectangular view of the mixing system, in the position of the maximum ascent of the agitator, the agitator under the surface of the liquid mirror, the position of the maximum submerged agitator in the liquid.

[0027] Fig. 2A shows a side view of an agitator with a permanent connection between the upper mounting plate and the agitator chamber.

[0028] Fig. 2B shows a side view of an agitator with a detachable connection between the upper mounting plate and the agitator chamber.

[0029] Fig. 3A shows a bottom view of an agitator with a permanent connection between the upper mounting plate and the agitator chamber.

[0030] Fig. 3B shows a bottom view of an agitator with a detachable connection between the upper mounting plate and the agitator chamber.

[0031] Fig. 4A shows a top view of an agitator with a permanent connection between the upper mounting plate and the agitator chamber.

[0032] Fig. 4B shows a top view of an agitator with a detachable connection between the upper mounting plate and the agitator chamber.

[0033] Fig. 5A shows agitators with an opening angle of 120°.

[0034] Fig. 5B shows agitator blades with an opening angle of 180°.

[0035] Fig. 6A shows a bottom view of a portion of an agitator blade.

[0036] Fig. 6B shows the shape of a single agitator blade with an indication of the angle of the wheel segment, i.e. the opening angle of a single agitator blade.

[0037] Fig. 7 is a perpendicular view of the mixing element showing the angle of inclination of the blade relative to the agitator shaft.

[0038] The object of the invention is presented in more detail in the following embodiments:

[0039] As a ceramic powders, silicas with irregular grain size, obtained by the flame method, with a size from 7nm to 400 pm and spherical silicas with a grain size of 40-800 pm are used.

[0040] In the present application, the concept of a system for the production of shear thickening fluids is identical to the term agitator and is used interchangeably. The dispersing part is to be understood as the agitator blades, and these terms are used interchangeably.

[0041] The reciprocating motion in this application should be understood as the up-down motion.

[0042] The term “liquid”, “matrix” or “polymer matrix” means a substance that surrounds a ceramic powder. In the present invention it is poly(ethylene glycol) or polypropylene glycol).

[0043] Example 1 : Construction of the agitator

[0044] The agitator comprises a steel chamber (A) with circular cross-section, outside which there is an electric heating jacket (J) with adjustable power of 0-100%. The power of the heating jacket (J) depends on the size of the chamber (A).

[0045] The agitator chamber (A) is joined to the upper fastening plate (E) in a permanent manner by means of a permanent connection (K), i.e. in the welding process by a weld connecting the chamber (A) to the upper fastening plate (E). In an alternative example, the agitator chamber (A) is assembled with the upper fastening plate (E) releasably, i.e. is fastened by means of screws (N) between the flange (L) of the chamber (A) and the fastening plate (E), in such a way as to ensure the stability of the structure.

[0046] The upper fastening plate (E) is also connected to the lower fixed fastening plate (F), which supports the structure. The fastening plates (E) and (F) are connected to each other by two ball screws (G) on which two linear rods (H) with linear bearings (I) fall, allowing both the chamber (A) to be stabilized and the coaxial motion of the chamber (A), with respect to the agitator shaft (B). The lower plate (F) has a hole in the central part with a diameter larger than the heating jacket (J), so that the chamber (A) together with the surrounding heating jacket (J) can move freely through this hole.

[0047] The shape of the upper fastening plate (E) is not very important, it is important that it has holes for joining with other elements. In the present embodiment, square plates were used as the upper fastening plate (E) and the lower fastening plate (F). In an alternate embodiment, the round plates are used, and the other shapes of the fastening plates (E) and (F) are economically unjustified. The present embodiment relates to an agitator with a chamber volume of 0.5 L. The ratio of height to width of the agitator chamber (A) is 2:1 . Chambers of other dimensions are less advantageous because they require either a longer agitator arm or more torque.

[0048] In agitators with chamber volumes from 0.5 to 2 L, 1 ball screw and 1 linear rod were used. The larger volume of the agitator requires more rods and screws to stabilize the structure. Therefore, in agitators with a volume from 2 to 10 L, 2 ball screws and 2 linear rods were used. In the case of larger agitators, more is used accordingly.

[0049] The chamber (A) is open from above, whereby it is possible to dispense loose substances into it from above. The chamber (A) includes an agitator, which is set in an adjustable rotary motion by means of a drive fixed at the point of drive mounting (M). The agitator comprises an agitator shaft (B) and two mixing blades (D). To one end of the shaft (B) are attached 2 mixing blades (D) of the half-ring shape shown in Fig. 3C, the shape of which determines the angle (P), which is the angle of the wheel segment. In the present embodiment, the angle (P) was 120°. In an alternative example, agitators with an angle (P) of up to 180° were used.

[0050] The agitator blades (D) are inclined at an angle (a) relative to the agitator shaft (B), providing optimal mixing parameters, as shown in Table 1.

[0051] The second end of the agitator shaft (B) is used to engage a drive that rotates the agitator shaft (B). In the present embodiment, a Beckhoff AM3063-0N404.39 kW 5000 rpm 15.8 Nm. synchronous motor was used to rotate the agitator shaft (B).

[0052] In the present embodiment, the agitator chamber, agitator shaft, and agitator blade are made of stainless steel. The agitator is used to produce STFs that have friction properties, which is why little abrasion is observed in the stainless steel agitator. Accordingly, other materials are used in alternative embodiments. In one of them, the chamber (A) was made of steel that was subjected to additional enamelling / glazing. The enamelled chamber has the advantage that the surface of the walls is practically not abraded.

[0053] Examples of agitators with other parameters of chamber volume (A) and agitator blade size (D) are shown in Table 1.

[0054] Table 1. Summary of sample chamber parameters Angte af indinatfers of th®

[0055] K33 W.3 S3? f>3 4,3 34 iii 152 W 111.1 4M 153 5,4 231 2B m 30.4 21,1 W,5 105 252 m3 m.3 m S0..7 .33 321 W m3 713 £33 n.o 343 m 4033 w 033 1023 W 353 133 373

[0056] Optimal results have been obtained when the blade angle of inclination (a) is between 35° and 45°. In alternative embodiments, where the blade angle of inclination (a) was between 45° and 80°, it was less preferable but still effective.

[0057] Fig. 1 shows a cross-section in a rectangular view of the mixing system in three working positions, position No. 1 is the position of the maximum ascent of the agitator, position No. 2 is the position in which the agitator is under the surface of the liquid mirror, position No. 3 is the position of the maximum submerged agitator in the liquid.

[0058] Example 2 Method of producing STF - using polypropylene glycol) with a molecular weight of 400 g / mol

[0059] In a 3.2 L agitator, 1.6 L of a polymer matrix (C), i.e. polypropylene glycol) with a molecular weight of 400 g / mol, were placed. The agitator blades (D) are located high above the liquid mirror, at the maximum position at which the agitator chamber can be lowered (position 1 , Fig. 1).

[0060] The greater the solid phase content in the matrix is to be, the less matrix (C) is added to the agitator. This is due to the fact that the higher the silica content in the matrix, the better the barrier-forming properties, therefore in such cases the chamber is filled in the amount of 30-35% by volume.

[0061] However, the process can be started at any position / height of the chamber, which does not affect the obtained effect. With a chamber volume of several m3, when the bottom plate (F) is mounted in the floor plane of the room and the chamber lowers through the opening in the floor, it is more convenient to introduce the polymer matrix into the chamber (A) in the position 1 shown in Fig. 1 , where the agitator is maximally raised up. On a smaller scale, when the small agitator is positioned on the laboratory table, it is convenient to introduce the polymer matrix into the chamber (A) in position 3 shown in Fig. 1 when the agitator is at the bottom of the chamber (A).

[0062] In the next step, at the beginning, the agitator chamber (A) is reciprocated at a frequency of 2 Hz. In one embodiment, the reciprocating motion is provided by two ball / trapezoidal screws. In another embodiment, a hydraulic jack was used for this purpose. In an alternate embodiment, a pneumatic jack is used.

[0063] In a further step, the chamber (A) is heated and the agitator (B) is rotated up to 2500 rpm. After reaching the polymer matrix temperature of approx. 95°C, the ceramic powder is dosed in the amount of 15% by weight in relation to the amount of the polymer matrix. Ceramic powder is dosed slowly using a flexible gravity, alternatively pneumatic connection for this purpose.

[0064] At the dosing stage, the frequency of reciprocating motions of the agitator chamber (up- down) was approx. 2 Hz.

[0065] As the solid phase content of the STF increases to 30%, the frequency of the chamber motions decreases to approximately 0.5 Hz. By increasing the solid phase content to 40 wt. %, the frequency of reciprocating motions is reduced from 0.5 to 0.01 Hz and at the same time, the number of agitator revolutions is gradually reduced to 300 rpm. The reciprocating motion of the agitator chamber with variable amplitude and frequency is performed throughout the process without stopping.

[0066] In the event that a semi-solid mass is deposited at the dispersing tip (D), the agitator chamber is lowered to position 1 and the rotation is increased to 3000 rpm. Under these conditions, under the influence of centrifugal force, most of the semi-solid mass breaks away from the agitator onto the side walls of the chamber (A). Then, by moving the chamber to position 2, the agitator blades (D) are wetted with liquid. Along with the semisolid mass, also the produced liquid under the influence of the centrifugal force is deposited on the walls of the chamber (A), which causes the "pulling" of the semi-solid mass back to the agitator. This is the process of self-cleaning the mixing tip during the process.

[0067] On the other hand, at the content of 20-40% by weight of the solid phase (ceramic powder), there is a tendency for the ceramic powder to remain on the liquid surface. Then, the agitator should be raised to a position in which the dispersing part (D) is located just below the surface of the liquid mirror (position 2, Fig. 1), or at the border of the liquid mirror, which leads to the wetting of the ceramic powder with a liquid from inside the chamber (A).

[0068] The mixing process is carried out until the mixture is homogenized, i.e. until there are no visible inclusions of solid phase lumps.

[0069] Example 3 Method of producing STF - using polypropylene glycol) with a molecular weight of 2700 g / mol

[0070] The method of preparing STF is analogous to the first example, with 1.6 L of polypropylene glycol) with a molecular weight of 2700 g / mol being introduced into the agitator. Subsequently, by increasing the solid phase content from 15 to 30 wt %, the ceramic powder dosing process is carried out periodically in such a way that after each portion of powder (from 15 to 40 g), with a reciprocating motion frequency in the range of 0.5-0.01 Hz, the agitator is kept in the upper half of the height of the liquid column until the portion of powder is wetted with liquid, and then the amplitude of agitator motions is increased from 0.5 to 0.55 Hz (from position 1 to position 2).

[0071] In analogous embodiments, poly(ethylene glycol) was used, yielding similar results.

[0072] Example 4 - Manufacture of STF with agitator where angle p = 120°

[0073] In the chamber (A) with a width of 139.7 mm and a height of 279 mm, 1.3 dm3of polypropylene glycol) with a molecular weight of 2700 g / mol, which is about 35% of the filling of the chamber, was introduced. 1100 g of silica was used to obtain a highly viscous liquid with good barrier-forming properties in an embodiment, obtaining a solid phase content in the liquid at the level of 45% by weight.

[0074] In the embodiment, an agitator equipped with two blades (D), i.e. two half-rings with a diameter (S1) of 92 mm, a=45°, p=120°, as shown in Fig. 5 and Fig. 6. List of References:

[0075] A - agitator chamber

[0076] B - agitator shaft

[0077] C - polymer matrix D - dispersing part

[0078] E - top fastening plate

[0079] F - bottom fastening plate

[0080] G - ball screws

[0081] H - linear rods I - linear bearings

[0082] J - heating jacket

[0083] K - permanent (welded) connection of the top plate with the agitator chamber

[0084] L - flange, i.e. a detachable (flanged) connection of the top plate with the agitator chamber M - drive mounting

[0085] N - screws connecting the upper plate with the agitator flange

[0086] S1 - width of agitator blades

Claims

Claims1 . System for producing shear thickening fluids comprising a reciprocating chamber (A), characterized in that the chamber (A) has a circular cross-section and is reciprocally incorporated with the upper fastening plate (E) in a permanent or detachable manner and the upper fastening plate (E) is connected to the lower fixed fastening plate (F) by means of at least one linear rod (H) with a linear bearing (I) and at least one ball screw with a nut (G), wherein outside the chamber (A) there is a heating jacket (J) and inside the chamber (A) there is an agitator shaft (B) at one end of which there is a dispersing part comprising at least two circular segment-shaped blades (D), wherein the angle (a) of inclination of one blade (D) with respect to the shaft (B) is from 30° to 80° and the angle (P) from 120° to 180° and the width (S1) of the blades (D) is 70-95% of the chamber inner diameter (A) and the height of the blades (D) up to 20% of the total height of the chamber (A) and the other end of the agitator shaft (B) is connected to a drive (M) that rotates the shaft (B), wherein the chamber (A) moves in a reciprocating motion in relation to the shaft (B).

2. The system according to claim 1 , characterized in that the heating jacket (J) is an external electric jacket with adjustable power or an external jacket for superheated steam.

3. The system according to claim 1 or 2, characterized in that the height of the chamber (A) is larger than its width.

4. The system according to claim 3, characterized in that the ratio of the height of the chamber (A) to its width is 2:1.

5. A method for producing shear thickening fluids characterized in that it comprises the following steps: a) a polymer matrix (C) is introduced into the agitator chamber (A) in an amount of no more than 70% of the volume of the agitator chamber (A), b) the agitator chamber (A) is reciprocated, c) the agitator chamber (A) is heated, also by rotating the agitator shaft (B), d) the ceramic powder is introduced in portions, in an amount of up to 30 wt.% relative to the polymer matrix (C), e) the reciprocating motion frequency of the agitator chamber (A) and the rotation of the agitator shaft (B) is adjusted.

6. The method according to claim 5, characterized in that the polymer matrix (C) is polypropylene glycol) with a molecular weight of 400 to 2700 g / mol or poly(ethylene glycol) with a molecular weight of 200 to 400 g / mol.

7. The method according to claim 5 or 6, characterized in that in step b) the chamber (A) is reciprocated at a frequency of 0,01 to 2 Hz.

8. The method according to any one of claims 5 to 7, characterized in that in step c) the chamber (A) is heated to a temperature of 95°C.

9. The method according to any one of claims 5 to 8, characterized in that the shaft (B) in step c) rotates at a frequency of 2500-3000 rpm.

10. The method according to any one of claims 5 to 9, characterized in that in step e), the frequency of the chamber motion (A) is adjusted in the range of from 2 to 0.01 Hz, and the rotation of the agitator shaft (B) from 300 to 3000 rpm.

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