RU2059027C1 - Pulp and a method of its producing - Google Patents

Abstract

FIELD: paper industry. SUBSTANCE: method involves the stirring stoichiometric quantity of haloid anhydride, aromatic dibasic acid and aromatic amine in anhydrous amide solvent in the presence of calcium chloride up to intrinsic viscosity value 2.0-4.5 and obtained solution of poly-para-phenyleneterephthalamide is extruded at 5-60 C. Extruded mass is kept at 26-60 C for 2-120 min at moment when viscosity is sufficient for stable orientation of polymeric chains. Obtained gel is cut for the short fibers (length is 0.2-35 mm). Extruding process can be carried out through the layer of noncoagulated liquid, for example, N-methylpyrrolidone, which is fed to device to decrease time contact of solution with internal surfaces. Obtained pulp is made of short fibers as bundles of individual fibers (diameter is 10-150 mcm, length is 0.2-35 mm, crystallinity degree is less than 50, crystal size is less than

, specific surface is above 2 m²/g). EFFECT: improved method of pulp production. 10 cl, 5 tbl

Description

 The invention relates to a technology for producing pulp from short fibers based on aromatic polyamide and can be used in the manufacture of paper, thin-layer coatings and composites, during lining and laying of rubbing parts.

 Known pulp made of short fibers based on polyparaphenylene terephthalamide with a characteristic viscosity of 2.0-4.5.

The specified para-aramid pulp is obtained first by spinning oriented, continuous yarns from a para-aramid polymer by a wet spin dry-wet process, and then by mechanical transformation of the fibers into pulp [1]
However, the formation of para-aramids is an expensive and complex process. The method consists in the fact that the polymer is dissolved in 100% sulfuric acid to obtain an optically anisotropic solution for molding. An anisotropic solution with a characteristic viscosity of 2.0-4.5 for molding is pressed through dies under carefully controlled conditions into a coagulation bath. An extrudate containing domains of polymer chains oriented in the direction of motion is held until gel formation (freshly formed fiber). The formed filaments are washed and dried before being mechanically converted into pulp. In addition, it is usually necessary to use specialized fiber cutting equipment in order to cut continuous fibers into short pieces of equal length before preparing the pulp.

 Although efforts have been made to obtain a para-aramid pulp without a first fiber spinning step, no industrial method has yet been proposed for producing a para-aramid pulp suitable for consumption.

 In the known method, polyparaphenylene terephthalamide is first polymerized and isolated from the polymerization mixture, dried, redissolved in sulfuric acid, formed into fibers and then mechanically converted into pulp, with the need for sophisticated equipment and very complicated process control, especially in the stages of forming the fibers. In addition, since concentrated sulfuric acid is the solvent for forming the fibers, the equipment must be constructed in such a way as to withstand the corrosive effects of the acid, which increases the cost of the equipment. Removal of spent sulfuric acid solvent is also a problem. Thus, the cost of para-aramid pulp obtained in this way is quite high.

 An object of the invention is to simplify and reduce the cost of the process.

 This is achieved by the fact that an anisotropic solution is prepared in the process of polymer synthesis with mixing of stoichiometric amounts of aromatic dibasic acid halide and aromatic diamine in a practically anhydrous amide solvent in the presence of calcium chloride to establish an intrinsic viscosity of 2.0-4.5. The solution can be prepared first by dissolving the aromatic diamine and first adding 30-50 wt. halide to obtain a prepolymer, and then the rest necessary to a stoichiometric amount.

 The solution has a concentration of 6-13 wt.

At least 80% of the aromatic diamine is in the proportion of p-phenylenediamine, and at least 80% of the aromatic dibasic acid halide is in the proportion of terephthaloyl halide. The solution was extruded at 5-60 ^{° C,} the extrudate is maintained at 20-60 ^{° C} for 2-120 min, and then begin to withstand when the viscosity of the extrudate is sufficient to maintain the orientation of the polymer chains.

 Practically, the aging of the solution begins immediately upon receipt of the extrudate from the die on a horizontal surface moving at a speed not lower than the speed of receipt of the extrudate, or when the viscosity of the extrudate is 50-500 Pa.

 The resulting gel is cut in the direction transverse to the orientation of its polymer chains into short fibers 1-20 mm long.

According to another aspect of the invention, a solution is prepared during the synthesis with mixing of stoichiometric amounts of aromatic diamine and aromatic dibasic acid halide in a practically anhydrous amide system until the indicated intrinsic viscosity is established. Extrusion is carried out at 5-60 ^about C through a layer of non-coagulating liquid. The latter is fed into the device to reduce the contact of the solution with its internal surfaces. Extrudate Curing is carried out at 25-60 ^{° C} for 2-120 min. The anhydrous amide system is N-methylpyrrolidone with calcium chloride, and N-methylpyrrolidone as the non-coagulating liquid.

и обладают удельной поверхностью более 2 м²/г.The resulting pulp is made of short fibers in the form of bundles of individual threads, the fibers have a diameter of 10-150 microns, a length of 0.2-35 mm, the degree of crystallinity is less than 50 with a crystal size of less than 40

and have a specific surface area of more than 2 m ² / g.

 Test Procedures

 Intrinsic viscosity.

The intrinsic viscosity (IV) is determined by the equation XB ln (ηrel) / c, where c is the concentration (0.5 g of polymer in 100 ml of solution) of the polymer solution; ηrel relative viscosity (ratio between the flow times of the polymer solution and the solvent, measured at ³⁰ ° C in a capillary viscometer). Values of intrinsic viscosity are determined using concentrated sulfuric acid (96% sulfuric acid).

 The crystallinity index and apparent crystal sizes.

The crystallinity indices and apparent crystal sizes for polyparaphenylene terephthalamide pulp are obtained from X-ray diffraction scans of the pulp materials. Diffraction grating poliparafenilentereftalamida characterized equatorial X-ray reflections with peaks appearing in the range of about 20 and ^about 23 ^of (2θ).

When crystallinity increases, the relative overlap of these peaks decreases as the intensity of the peaks increases. The crystallinity index (PC) of polyparaphenylene terephthalamide is defined as the ratio of the difference between the peak intensities in the region of about 23 ^about 2θ and the minimum in the "valley" between the peaks in the region of about 22 ^about 2θ to the peak intensity in the region of about 23 ^about 2θ expressed as a percentage. The crystallinity index is an empirical value and cannot be interpreted as percent crystallinity.

где А пик в области примерно 23^о 2θ
С минимум в долине в области примерно 22^о 2θ
D базисная линия в области примерно 23^о 2θ
Видимый размер кристаллов рассчитывают на основании измерений ширины полувысоты пика экваториальных дифракционных пиков в области примерно 20^о и 23^о (2θ). Первичный видимый размер кристаллов относится к размеру кристаллов, измеренному из первичного или более низкого угла отражения 2θ в области примерно 20^о (2θ).The crystallinity index is calculated by the following formula:
Crystallinity

where A peak in the region of about 23 ^about 2θ
With a minimum in the valley in the region of approximately 22 ^about 2θ
D baseline in the region of approximately 23 ^about 2θ
Apparent crystallite size is calculated from measurements of the half-height peak width of the equatorial diffraction peaks in the range of about 20 and ^about 23 ^of (2θ). The primary apparent crystal size refers to the size of the crystals, measured from a primary or lower angle of reflection of 2θ in the region of about 20 ^about (2θ).

Since the two equatorial peaks overlap, measuring the half-height of the peak is based on half the width at half the height. For the peak 20 ^{of the} calculated position of the half-maximum peak height and the 2θ value for this intensity is measured on the lower angle side. The difference between this 2θ value and the 2θ value at the height of the maximum peak is multiplied by two to obtain the half-width of the peak or “lines”.

, где В является постоянной погрешности инструмента; b определяется при помощи измерения ширины линии пика, расположенного в области приблизительно 28^о 2θ в дифракционной решетке образца кристаллического порошка кремния.In this measurement, correction is made only for the accuracy of the measurement of instruments, all other limiting effects are assumed to be the result of crystal size. If B is the measured line width of the sample, the adjusted line width β is
β =

where B is the constant error of the tool; b is determined by measuring the line width of a peak located in the region of approximately 28 ^about 2θ in the diffraction grating of a sample of crystalline silicon powder.

); β- скорректированная ширина линии, рад; θ- половина угла Брэгга (половина значения 2θ выбранного пика, полученного из дифракционной решетки).The apparent crystal size is specified using ACS (K λ) / (β cosθ), in which K is taken as a unit; λ is the x-ray wavelength (here 1.5418

); β- corrected line width, rad; θ is half the Bragg angle (half the 2θ value of the selected peak obtained from the diffraction grating).

 Both when measuring the crystallinity index and the apparent crystal size, the diffraction data were obtained using a computer program that “smooths” the data, determines the baseline, peak positions and peak heights, and valley positions and heights.

X-ray diffraction gratings of pulp samples were obtained using an X-ray diffractometer (Philips Electronics Instruments, art. N PW1075 / 00), operating on the principle of reflection. Intensity data is obtained using a meter for counting and recording using a computer data acquisition / recovery system. Diffraction gratings are obtained using the settings of the tool, while the scanning speed of 1 ^about 2θ per minute; increment steps 0.025 ^o 2θ scanning area 6-38 ^o , 2θ pulse height analyzer "Differential".

 Specific surface area.

 Specific surface areas are determined using a BET nitrogen absorption procedure using a specific surface area meter of the Strolen type from Standard Instrumentation Inc., Charleston, West Virginia. The washed pulp samples are dried in a calibrated sample flask, weighed and placed on the installation. Nitrogen is absorbed at the temperature of liquid nitrogen. Absorption is measured through the pressure difference between the flasks with the sample and the template (pressure gauge), and the specific surface area is calculated based on the pressure gauge, barometric pressure and weight of the sample.

 Measurements of length and diameter.

 About 5 mg of dried and loosened pulp is prepared and spread. The lengths and diameters of the fibers are measured using a 12x magnification lens with a precision millimeter ocular network with 0.05 mm lines. The resolution is 0.01 mm.

Example 1. This example describes the preparation of polyparaphenylene terephthalamide pulp in an NMP-CaCl ₂ solvent using a laboratory unit and batch polymerization and a cylindrical couette apparatus for orienting the flow. The polymer concentration is 9 wt. and the concentration of CaCl ₂ is 5.9%, calculated on the total weight of the solution.

A solution of calcium chloride (65.8 g, 0.593 mol) in anhydrous N-methylpyrrolidone (900 ml) was prepared by mixing and heating to 85 ^{° C} to dissolve the calcium chloride. After cooling the solution ^to 25 ° C in a round bottom flask equipped with an overhead stirrer, dry nitrogen purge and with stirring is added 45.81 g (0.4236 mol) of p-phenylene diamine, and the resulting solution was cooled to 10 ° ^C. With stirring, was added anhydrous terephthaloyl chloride (TCl) (43,0 g, 0.2118 mol), resulting in a temperature rise to 42.1 ° ^C. The solution was cooled ^to 10 ° C and under vigorous stirring TCl residue (43.00 g, 0 , 2118 mol), while adiabatic heating leads to an increase in temperature to about 12 ^about C. Vigorous stirring continues as polymerization continues.

When the still polymerizing mixture becomes translucent, then calm and opal, and with stirring the intrinsic viscosity of polyparaphenylene terephthalamide in the mixture becomes higher than about 1.5, stirring is stopped and the solution is transferred to a cylindrical couette apparatus. The cylindrical Couette apparatus includes an outer tube with an inner diameter of 4 inches (10.16 cm) and a coaxial inner cylinder, resulting in a ring between the outer tube and the inner cylinder having a capacity of about 600 cm ³ with a thickness of 1.6 cm. This ring is provided device for purging with nitrogen and dry nitrogen is fed into the ring. The outer tube is equipped with a water jacket in order to control the temperature of the solution in the ring. The temperature is maintained at about 30 ^° C. The inner cylinder is rotated at a speed of 205 rpm in order to shear the solution, which, in terms of the average shift, is 60 s ⁻¹ , with a shift on the inner surface of 81.5 s ⁻¹ . and on the outer surface 38.5 s ^-1 . When the viscosity reaches about 200 poise, calculated on the basis of the increase in torque on the rotor of the Couette apparatus, the movement of the inner cylinder is interrupted.

The water temperature in the water jacket Couette flow is increased from 30 ^{° C to} 50 ° C and the solution was incubated at this temperature for 90 min. The gel is removed from the Couette apparatus and cut into six rings of approximately equal size at different heights in the Couette (TI-B2 from top to bottom). Each ring is then cut into pieces of 0.63 cm in size, with the cut being made in the direction transverse to rotation in the Couette cylinder.

 The pulp is isolated from the gel by moving pieces of gel with 5% sodium bicarbonate solution (the gel should be enough to get 10 g of dry pulp and 500 ml of bicarbonate solution) in a Waring mixer (about 1800 rpm) for 12 minutes. The pulp material is then dehydrated by vacuum filtration. Next, the pulp is washed twice with water in a mixer, and each time dehydration is performed. The pulp obtained from each of the six rings consists of thin, highly fibrillated fibers, which have the properties listed in Table 1.

A standard blend, performs dough prepared with the following composition, and formed into 1/2 inch molded bars at ¹⁸⁰ ° C for 40 minutes:
50% dolomite 200 mesh (0.074 mm), 15.2% barium sulfate (barmite XF), 15.2% cardolite 104-40, 15.2% cardolite 126, 3.8% pulp taken from TI-B2 samples.

Bending resistance is measured at room temperature and a temperature of 350 ^about F (177 ^about C), while obtaining the following results: at room temperature 398 kg / cm ² at 350 ^about F (177 ^about C) 230 kg / cm ² .

фирмой "Е.И.Дю Пон де Немур энд Ко", дают следующие значения для сопротивления изгибу: 423,5 кг/см² при комнатной температуре, 135 кг/см² при 350^оF (177^оС).Dough control rods of the same composition containing industrial molded fiber pulp marketed under the name Kevlar

by "E.I.Dyu Pont de Nemours &Co.," give the following values for the bending resistance: 423.5 kg / cm ² at room temperature, 135 kg / cm ² at ³⁵⁰ ° F (177 ° ^C).

 PRI me R 2. The procedures and apparatus described in example 1, are used in order to obtain a pulp having the properties listed in table. 2, except that the TI-B2 rings are not cut into pieces of about 0.63 cm in size, but instead, each is cut into several pieces a few centimeters long.

Example 3. This example describes the preparation of polyparaphenylene terephthalamide pulp in an NMP-CaCl ₂ solvent using a laboratory-sized apparatus using batch polymerization and semi-continuous extrusion. The concentration of the polymer is 10 wt. and the concentration of CaCl ₂ is 6.5%, calculated on the total weight of the solution.

A solution of calcium chloride (42 g, 0.38 mol) in anhydrous N-methylpyrrolidone (500 ml) was prepared by mixing and heating to 90 ° ^C. After cooling the solution ^to 25 ° C in a round bottom flask equipped with a stirrer in the upper part and purging with dry nitrogen is added with stirring 29.3 g (0.271 mol) of p-phenylene diamine and the resulting solution was cooled to 10 ° ^C. while stirring, anhydrous terftaloil chloride (TCl) (27,5 g, 0.136 mol), which causes rise temperature to 47 ^about C. After dissolving TCl, the solution is cooled to 0 ^about C and with vigorous p With stirring, the remaining amount of TCl (27.5 g, 0.136 mol) is added until complete dissolution. Vigorous stirring is continued throughout the polymerization.

When the still polymerizing mixture becomes translucent, then stationary and opal with stirring (the intrinsic viscosity of polyparaphenylene terephthalamide in the mixture becomes higher than about 1.5), the solution is subjected to flow orientation, applying under pressure from a round-bottom flask with a volumetric flow rate of about 2.75 cm ³ / s through a nozzle with a linear flow path 4 cm wide, 4 mm thick and 45 cm long in order to obtain an elongated mass of an optically anisotropic viscous liquid. Range shift in the nozzle varies from 0 to ^-1 at the central plane of the flow path to a maximum of about 30 sec ^-1 in the nozzle walls (average shift of about 15 s ^-1), the nozzle temperature was maintained at about 25 ^C. The yield of the nozzle located approximately 0.6 cm above the horizontal moving belt covered with dry nitrogen, heated at a temperature of ^about 50 ° C, and oriented anisotropic liquid solution is deposited on the tape for incubation. The tape has a maximum movement of approximately 45 cm. The nozzle is inclined relative to the tape so that the angle between the nozzle and the tape moving from the nozzle is 115 ^about . The extrusion speed and belt speed are maintained at about 1.7 cm / s. The width of the tape is the same as the width of the nozzle (4 cm). The tape has raised edges in order to prevent the flow of the solution in the direction perpendicular to the direction of its movement. The thickness of the solution on the tape is approximately 3 mm. The viscosity of the solution after extrusion is approximately 200-300 poise. The tape is stopped and extrusion is stopped when the end of the tape is reached.

The solution was incubated on tape to incubate for about 90 minutes in an atmosphere of heated nitrogen (55 ^° C) until it became a solid gel. The reaction continues in the gel until the desired intrinsic viscosity is achieved. After incubation, the gel is cut across into two pieces L1 and L2 (see Table 3), with L1 indicating the part of the gel that is extruded first. Each piece is then cut into several parts several inches long each to isolate the pulp.

 The pulp is isolated from fully incubated and cured pieces of gel in the following sequence. The gel pieces are mixed with 5% sodium bicarbonate solution (the gel should be enough to get 10 g of dry pulp and 500 ml of bicarbonate solution) in a Waring mixer at high speed (about 1800 rpm) for 12 minutes. The pulp material thus isolated is dehydrated by vacuum filtration. The pulp is washed twice with hot water in a mixer, and dehydration is performed after each washing. The pulp thus obtained consists of thin, highly fibrillated fibers and has the properties indicated in Table 3.

The pulp is included in standard mixtures resembling dough, rods are formed from them and tested in accordance with the procedures of Example 1 to obtain the following values for bending resistance: 373.6 kg / cm ² at room temperature, 130.5 kg / cm ² at 350 ^about F (177 ^about C).

Example 4. This example describes the preparation of polyparaphenylene terephthalamide pulp in an NMP-CaCl ₂ solvent using the same apparatus as in Example 3 for batch polymerization and semi-continuous extrusion. L1 and L2 after incubation of the gel pieces are cut into strips 0.63 cm by 90 ^about to the length of the gel prior to isolation of the pulp. The concentration of the polymer is 7 wt. and the concentration of CaCl ₂ is 3.8% of the total weight of the solution.

A solution of calcium chloride (24.30 g, 0.22 mol) in anhydrous N-methylpyrrolidone (540 ml) was prepared by mixing and heating to 75 ° ^C. After cooling the solution ^to 25 ° C in a round bottom flask fitted with an overhead stirrer, dry nitrogen purge and with stirring is added 20.24 g (0.1872 mol) of p-phenylene diamine and the resulting solution was cooled to 10 ° ^C. while stirring, anhydrous terftaloidhlorid (TCl) (19,00 g, 0.0936 mol) , which leads to a rise in temperature to 35.3 ^about C. After dissolving TCl, the solution is cooled to 5 ^about With vigorously add a second portion of TCl (19.00 g, 0.0936 mol), achieving complete dissolution. Vigorous stirring is continued during the polymerization that began.

When the polymerizing mixture is still translucent, then stationary and opal with stirring (the intrinsic viscosity of polyparaphenylene terephthalamide in the mixture is more than 1.5), the solution is subjected to an orienting flow, which is supplied under pressure from a round-bottom flask at a space velocity of about 1.85 cm ³ / s through a nozzle with a linear flow path 4 cm wide, 4 mm thick and 45 cm long in order to obtain an elongated mass of an optically anisotropic viscous fluid. Shear limits range from 0 s ^-1 in the central plane of the flow path in the nozzle to a maximum of about 30 s ^-1 at the walls of the nozzle (average shift 15 s ^-1 ). Nozzle temperature was maintained at about 25 ^C. Yield nozzle located at 0.6 cm above the moving horizontal belt, surrounded by the hot dry nitrogen gas, heated to a temperature above about ^{45 °} C, and oriented anisotropic liquid solution was spread on a tape for incubation. The tape has a maximum movement of approximately 45 cm. The nozzle is inclined relative to the tape so that an angle of 115 ^° C is formed between the nozzle and the tape moving from the nozzle. The extrusion speed is estimated at about 1.25 cm / s and the tape speed is maintained at about 1. 35 cm / s. The width of the tape is equal to the width of the nozzle (4 cm), it has raised edges in order to prevent the flow of the solution in the direction perpendicular to the direction of movement of the tape. The viscosity of the solution after extrusion is estimated at about 300 pauses. The thickness of the solution on the tape is approximately 2-4 mm. The tape and extrusion are stopped when they reach the end of the tape.

The solution was incubated on tape to incubate for about 120 minutes in an atmosphere of heated nitrogen (45 ^° C) until it became a solid gel so that the reaction turned into a gel. The gel is cut into two pieces L1 and L2, wherein L1 indicates the portion of the gel that is extruded first. Then the gel is cut into strips with a width of about 1/4 inch (0.63 cm) at an angle of 90 ^about the length of the gel.

 The pulp is isolated from a fully incubated and cured gel in the following sequence. The gel pieces are mixed with a 5% sodium bicarbonate solution (the gel should be enough to get 10 g of dry pulp and 500 ml of bicarbonate solution) in a Waring mixer at high speed (1800 rpm) for 12 minutes. The pulp material thus isolated is dehydrated by vacuum filtration. The pulp is washed twice with hot water in the mixer, and after each washing, dehydration is carried out. The pulp thus obtained consists of thin, highly fibrillated fibers and has the properties indicated in Table 4.

Example 5. This example describes the preparation of polyparaphenylene terephthalimide pulp in an NMP-CaCl ₂ solvent using the same apparatus as in Example 4 for a batch polymerisation process and semi-continuous extrusion. The procedures of Example 4 are followed except that the gel is cut transverse before incubation continues. The concentration of the polymer, as in example 4, is equal to 7 wt. and the concentration of CaCl ₂ is 3.8%, calculated on the total weight of the solution.

The solution is maintained on the tape with the purpose of incubation for about 8 minutes (since the solution is placed on the cutting tape 90) in an atmosphere of heated nitrogen (50 ° ^C), i.e. until it turns into a solid gel. The gel is cut into two pieces L1 and L2, and then cut into strips with a width of about 7 mm at an angle of 90 ^about the length of the gel. After the reaction turns into a gel, incubation is continued for approximately 110 minutes at 50 ^about C.

 The pulp thus obtained consists of thin, highly fibrillated fibers, the properties of which are indicated in Table 5.

 PRI me R 6. This example describes a method for producing polyparaphenylene terephthalamide (PPD-T) pulp using a device for orienting an extension flow having porous walls that provide a layer of N-methylpyrrolidone on the inner walls forming the flow path in order to minimize deposits.

 An extension flow orienting device having a linearly tapering rectangular flow channel, consisting of porous metal plates, is mounted on a 5 inch (12.7 cm) discharge opening from a twin-screw polymerizer with washing the entire surface having a jacket but functioning without coolant . The device for orienting the flow has a vertical, downward channel for the flow of a length of about 6.35 cm with an inlet of 1.12 x 4.83 cm, which serves to directly receive material discharged from the polymerization device and an outlet of 0.58 x 4.82 cm The porous plates forming the walls are made of porous plates of 316 stainless steel with a thickness of about 0.31 cm, having a porosity of 0.2-1.0 μm. The plates are supported in the housing by means of appropriate pipelines through which N-methylpyrrolidone is supplied to the outer surfaces of the plates.

Actively polymerizable 9.2 wt. a solution of polyparaphenylene terephthalamide in metipyrrolidone (NMP) and calcium chloride (molar ratio of CaCl ₂ to the initial amount of paraphenylenediamine is 1.38). With the polymerization still continuing, the PPL-T solution is forced through a device for orienting the flow with a bulk velocity of the polymer of 5.65 kg / h. The inner surface of the porous walls is continuously provided with a layer of IMF, which emerges through the porous metal plates with a space velocity of approximately 1.7 ml / sq. inch / min in terms of the total area of porous plates in contact with the PPD-T solution. The intrinsic viscosity of polyparaphenylene terephthalamide in the solution flowing from the flow orientation device is approximately 2.3.

A viscous, still liquid solution flowing out of the flow orienting device is periodically collected on a horizontal plate while the plate moves under the outlet at a speed approximately equal to the velocity of the solution coming from the outlet of the aforementioned hole. Strips of solution after extrusion with a width of approximately 2 inches (5.08 cm) are incubated on the plate under ambient conditions. Within about 40 s, they turn into a soft gel. This gel is then cut into pieces of 0.95 cm in the transverse direction. The cut pieces are then placed in a heater for 1 hour at a temperature of about 44 ^{° C} incubation for reuse.

 To separate the pulp, the incubated pieces are placed in water in a Waring mixer and mixed at high speed for several minutes. The pulp is periodically collected on a filter and returned to the mixer for short mixing with water for five minutes. The separated pulp product consists of a highly fibrillated PPD-T pulp with a characteristic viscosity of 3.1.

 PRI me R 7. Use the same equipment and the same procedures as in example 6, to obtain a solution and extrusion with the exception that the solution after extrusion is obtained with a polymer bulk velocity of 5.6 kg / h, and bulk the rate of N-methylpyrrolidone is 4.4 ml / sq. inch / min The polymerization and extrusion are carried out for 5 hours. The flow channel in the orientation device remains mostly free of any deposits for 5 hours, but from time to time there is a slight partial blockage in the area of the exit from the flow channel, which is easily eliminated mechanically and the channel again becomes completely free.

EXAMPLE 8. This example describes the preparation of polyparaphenylene terephthalamide pulp in an NMP-CaCl ₂ solvent using a pilot plant for continuous production.

Paraphenylenediamine solution in NMP-CaCl ₂ at 10 ^about With containing 5.5 wt. p-phenylenediamine, 7.4% CaCl ₂ , 87.1 NMP and less than 200 parts per million (ppm) of water are loaded into the mixer and mixed with molten TCl in an amount of 35% of the stoichiometric value. The resulting prepolymer is pumped through a heat exchanger to cool it to about 5 ^° C. Then the prepolymer is mixed with molten TCl at a rate that would give a stoichiometric balance between TCl and diamine in the mixture using a known device [2]. This mixture is continuously passed through a two-inch (5.08 cm), a continuous twin-screw polymeriser wetting the entire surface, equipped with a jacket, but functioning without coolant. Use amounts of reagents that provide PPD-T at a rate of about 4.53 kg / h.

The liquid solution from the polymerizator flows directly into a nearby device for orienting the flow, then onto a continuous belt for transporting the material after extrusion. A device for orienting the flow and a polymerizer of the same type were used with porous walls defining an extension flow path, a channel inlet with dimensions of 2 x 3.18 cm, an outlet with dimensions of 0.64 x 3.18 cm and a flow path length of 11.4 cm. N-methylpyrrolidone is supplied to the device for orienting the flow with a space velocity sufficient to form and maintain a boundary layer between the porous walls and the solution. The tape has a width of 20.32 cm, a length of about 12 m and is generally horizontal. The surface of the tape is located approximately 1.27 cm below the exit from the device for orientation, and the angle of the flow path of the device for orienting the flow relative to the surface of the tape is 90 ^about . The entire area of the tape and the outlet of the device for orienting the flow are closed and surrounded by nitrogen heated to 45 ^° C. From the aforementioned device, the solution enters in a strip of approximately 3.18 cm wide at a speed of approximately 3.5 m / min.

After transportation on a tape at a distance of 10.6 m (about 3 minutes), the strip of solution hardens. A guillotine-type cutting device with a stroke length associated with the tape speed is set at 7.62 cm from the end of the horizontal surface of the tape. This cutting device cuts the gel into pieces measuring approximately 0.63 cm by 90 ^about to the length of the gel. The pieces of gel reaching the end of the horizontal portion of the tape fall into baskets with a capacity of 5 gallons (19 L). After filling the baskets placed in the oven for an additional incubation at ⁴⁵ ° C for 60 min.

 The baskets are periodically removed from the oven and the contents are poured into clay balers with a capacity of approximately 25 gallons (94.6 L), which are filled with a dilute caustic soda solution. Neutralization and coagulation in the clay mill is carried out simultaneously with the onset of size reduction. Through the outlet of the clay mill, its contents are continuously fed into the refiner for subsequent size reduction. The refiner outlet is connected to a sludge tank having a capacity of approximately 200 gallons (757 L) and equipped with a stirrer. The sludge from the sludge tank is continuously fed to a horizontal filter 10.7 m long and 43 cm wide, where the pulp is periodically washed and dehydrated under vacuum 12 times. The resulting wet cake is then continuously dried in a steam heated rotary dryer.

The resulting product consists of a thin, highly fibrillated pulp, the diameter of which is less than 0.15 mm, the length is less than or equal to about 6 mm, and the specific surface area exceeds 4.0 m ² / g.

Claims (9)

1. The pulp made of short fibers based on polyparaphenylene terephthalamide with a characteristic viscosity of 2.0 to 4.5, characterized in that the fibers in the form of bundles of individual threads have a diameter of 10 150 μm, a length of 0.2 35 mm, the degree of crystallinity is less than 50 at a size crystals less

and have a specific surface area of more than 2 m ² / g. 2. A method of obtaining pulp, including the preparation of an optically anisotropic solution of polyparaphenylene terephthalamide with a characteristic viscosity of 2.0 to 4.5 by extruding it through a die, holding the extrudate containing the polymer chain domains oriented in the direction of movement until gel formation and subsequent cutting into short fibers, characterized the fact that the initial solution is prepared in the process of polymer synthesis with stirring of stoichiometric amounts of aromatic dibasic acid halide s and aromatic diamine in a practically anhydrous amide solvent in the presence of calcium chloride until the specified characteristic viscosity is established, extruded at 5 - 60 ^o C, keeping is carried out at 26 60 ^o C for 2 120 min, and begin it when the viscosity of the extrudate is sufficient to maintain orientation of the polymer chains, the resulting gel is cut in the direction transverse to the orientation of its polymer chains into short fibers 0.2 to 35 mm long.  3. The method according to claim 2, characterized in that the aging of the solution begins immediately upon receipt of the extrudate from the die on a horizontal surface moving at a speed not lower than the speed of receipt of the extrudate.  4. The method according to claim 1, characterized in that the curing is started when the viscosity of the extrudate is 50 500 PA.  5. The method according to claim 1, characterized in that the preparation of the solution is carried out first by dissolving the aromatic diamine and adding 30 to 50 wt. acid halide to obtain a prepolymer, and then adding the required up to stoichiometric residual amount of acid halide.  6. The method according to claim 1, characterized in that prepare a solution with a concentration of 6 to 13 wt.  7. The method according to claim 1, characterized in that at least 80% of the aromatic diamine is in the proportion of p-phenylenediamine and at least 80% of the aromatic dibasic acid halide is in the proportion of terephthaloyl halide. 8. A method of obtaining pulp, including the preparation of an anisotropic solution of polyparaphenylene terephthalamide with a characteristic viscosity of 2.0 to 4.0, extruding it through a device with subsequent aging of the extrudate containing the domains of the polymer chains oriented in the direction of movement until a gel is formed, characterized in that the solution prepared during the synthesis process with stirring of stoichiometric amounts of aromatic diamine and aromatic dibasic acid halide in a practically anhydrous amide extruding is carried out at 5-60 ^° C through a layer of non-coagulating liquid supplied to the device to reduce the contact of the solution with its internal surfaces, and the aging is carried out at 25-60 ^° С for 2 120 minutes.  9. The method according to claim 8, characterized in that N-methylpyrrolidone with calcium chloride is used as an anhydrous amide system, and N-methylpyrrolidone as a non-coagulating liquid.

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