JPS5834570B2 - Method for producing flexible infusible phenolic resin fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Activated carbon has been known for a long time and its adsorptive properties make it extremely useful for removing undesirable impurities from liquid or gaseous process streams and have many research and industrial applications. has been found.

Activated carbon has been available for many years only in solid state, for example activated granules or powder.

Its use as an adsorbent has been limited to application as a bed or layer of carbon in the case of gas processing.

When treating liquids, carbon was dispersed therein and then the treated liquid was separated by a filtration step.

In recent years, the development of fibrous carbon, combined with its effective activation in the fibrous state, has considerably expanded the applications of activated carbon, especially as textile and permeable materials.

Activated carbon fibers and fabrics are generally produced from woven polymeric precursors in a similar form by pyrolysis to carbon under an inert atmosphere, followed by air, flue gas,
They can be produced by activation (formation of pores and surface area) at higher temperatures in an oxidizing gas atmosphere from oxygen, carbon dioxide or superheated steam.

This is based on the same basic principles that have been used for many years in the production of powdered or granular activated carbon.

However, a special prerequisite is that the textile precursor carbonizes without melting.

Thereby, the precursor maintains its textile form and does not undergo stiffening due to the bonding of fibers or threads.

In order for the activated material to be suitable for gas adsorption,
A suitably dense carbon fiber must be produced during pyrolysis, and a suitable pore structure must be obtained during activation, avoiding the distribution of macropores, mesopores and micropores. Must be.

During carbonization of most organic materials, a substantial weight loss occurs due to the removal of other elements combined with carbon.

Removal of these elements often results in weakening of the remaining carbon structure.

This is a serious problem with carbon in fiber form, which can lose almost all of the strength of the original organic fiber unless special care is taken during the pyrolysis and activation process. be.

Pyrolysis of organic fibers therefore requires gradual heating over a long period of time to increase the temperature and special handling to prevent fiber wear during such heating periods.

Such treatment is time consuming and does not prevent significant loss of fiber strength.

As mentioned above, substantial weight loss occurs during the carbonization process.

Therefore, a process that uses moderate temperatures and can provide adsorbent fibers with minimal loss in weight and tensile strength is highly desirable.

The method must be applicable to fibrous materials in either plain or filament form, and must reduce the processing time required to process the fibrous materials.

The present invention relates to flexible, infusible phenolic resin fibers having surface areas ranging from about 10 to more than 500 square meters per z.

The fiber has a tensile strength of at least about 15,000 psi.

The fibers are produced by heating infusible, cured novolak fibers in an oxidizing atmosphere from room temperature to moderate temperatures in the range of about 250°C to 450°C.

The fibers can be in the form of fabrics, felts or threads and the processing of the fibers can be carried out in batch mode or in a continuous operation.

FIELD OF THE INVENTION The present invention relates to activated adsorptive organic fibers with large surface areas and methods for their production.

More particularly, the present invention has a surface area of at least about 10 square meters per gram, preferably more than 500 square meters per gram, is active or adsorptive, and thus removes gases, vapors, and It relates to systems capable of adsorbing dissolved or dispersed substances from liquids.

Organic fibers with such a large surface area have good mechanical properties such as strength and flexibility, and thus can be produced with good handling properties.

Such high surface area materials in fibrous form can thus serve a variety of applications where the use of active materials commonly available in powdered or granular form is not possible or difficult and inconvenient to use. It is suitable for use in a wide range of practical applications including:

High surface area organic fibers according to the present invention can be produced by partial etching of flexible, infusible, cured phenolic resin fibers by the method of the present invention described below.

A wide variety of novolak resins can be used as suitable starting materials in the process of the invention.

The term "novolac" refers to a condensation product of a phenolic compound and formaldehyde, in which this condensation is carried out in the presence of a catalyst to form a novolac resin, in which there are few or no methylol groups, such as those present in resols. only exists, and the molecules of the phenolic compound are linked by methylene groups.

The phenolic compound can be phenol or a phenol in which one or more of the non-hydroxyl hydrogens is substituted with various substituents attached to the benzene ring.

Some examples of the latter include cresol, phenylphenol, 3,5-dialkylphenol, chlorophenol, resorcinol, hydroquinone, and chloroglucinol.

The phenolic compound may be naphthyl or hydroxyphenanthrene or other hydroxyl derivatives with fused ring systems.

For the purposes of the present invention, fusible novolaks which can be further polymerized with suitable aldehydes can be used for the production of fibers.

In other words, the novolac molecule must have two or more than two sites available for further polymerization.

Apart from this limitation, any modified novolak can be used, ie, it also contains non-phenolic compounds in the molecule, such as diphenyl oxide or bisphenol-A modified phenol-formaldehyde novolacs.

Mixtures of novolaks may be used, or novolaks containing more than one type of phenolic compound may be used.

Phenol-formaldehyde novolac resins are preferred starting materials in the process of the invention.

Although novolaks generally have number average molecular weights ranging from about 500 to about 1200, in exceptional cases
It may have a molecular weight as low as 300 or as high as 2000 or more.

Unmodified phenol-formaldehyde novolaks typically have number average molecular weights in the range of about 500 to about 900, with the majority of commercially available materials falling within this range.

Phenol-novolak resins having a molecular weight of about 500 to about 1200 are preferably used in the method of the invention.

The temperature at which low molecular weight novolaks soften and become sticky is
Relatively low.

Therefore, it is necessary to cure the fiberized novolak at very low temperatures to prevent fiber sticking and/or deformation.

It is usually undesirable to use such low curing temperatures since the curing rate increases significantly with increasing temperature and low curing temperatures result in a practical penalty of a lengthy curing process.

In order to achieve curing in a reasonable time without sticking and/or deformation, it is preferable to use a novolak with a suitably high molecular weight, but on the other hand to minimize the problems caused by gelation in fiberization. It is generally preferred to avoid the upper end of the above molecular weight ranges in order to limit the molecular weight range.

Phenol-formaldehyde novolacs are known in the art and are generally prepared by condensation of formaldehyde with a slight molar excess of phenol in the presence of an acidic catalyst.

However, infusible, cured phenol-formaldehyde novolak fibers are a relatively recent development in the history of phenolic resins.

This is typically done by e.g. melt spinning or blowing (
That is, a trickle of melt is allowed to fall into the path of an air current, such as air, and the trickle is made into fibers).
It is produced by fiberizing a melt of phenol-formaldehyde novolak to obtain fusible uncured novolac resin fibers, which are then processed to cure the novolak at least until it is infusible.

Such curing is generally carried out by heating the fiber in the presence of a methylene base source, such as formaldehyde, and preferably also in the presence of a suitable catalyst, such as an acid.

The blowing method provides stable fibers with different lengths and diameters, but can be as thin as about 0.1 micron or less, or much thicker. Fibers can also be obtained.

The melt spinning method can process fibers from as thin as 4 microns to approximately 300 microns.
It can be applied to produce filaments with diameters up to as thick as microns or more, if necessary continuous filamentary fibers.

After curing, they can be processed by a variety of techniques to provide rovings and threads, paper, felt, woven or knitted fabrics, and a variety of other textile product forms.

A particularly desirable method for producing infusible, cured phenol-formaldehyde novolac fibers is described in detail in James Economy et al., U.S. Pat. No. 3,650,102, issued March 21, 1972; This invention is assigned to a person, and the contents of that patent may be incorporated by reference herein.

According to the present invention, infusible, cured novolak fibers are heated in air from room temperature (about 25°C) to about 250°C.
to temperatures ranging from about 450°C to about 500°C per hour.
The fibers are partially etched by heating from 0 DEG C. with a continuous increase in temperature at a rate of about 200 DEG C. per hour and then allowing the fibers to cool to room temperature.

Although the exact nature of the changes thereby produced has not been established, heating produces a combination of thermal and oxidative crosslinks in the molecular structure of the fibers, leading to the creation of numerous pores within the fibers, and corresponding This appears to cause etching of the fiber surface with an increase in the surface area of the fiber.

Thus, the method generally provides at least about 10 square meters per gram, usually about 1 square meter per gram.
This results in the production of organic fibers with surface areas ranging from 0 square meters to more than 500 square meters.

The fibers of the present invention, unlike fully carbonized fibers, are chemically acidic.

The acidic nature of the fiber makes it particularly effective in adsorbing basic substances.

Since partial oxidation of the fibers is likely to occur during the heating process, it is important that the heating is carried out in an oxidizing atmosphere, preferably air.

The fibers can be heated to a temperature ranging from about 250°C to about 450°C, with temperatures of about 400°C being preferred.

During heating, the temperature is increased from room temperature to the desired temperature at a rate of about 50°C to about 200°C per hour, but not more than 1 hour.
A rate of about 100°C per hour is preferred.

Preferably, the fibers are heated in an electric furnace, which type of furnace allows optimal control of the heating cycle and the oxidizing atmosphere.

Other types of furnaces may be used as long as appropriate control of the heating conditions is possible.

One method is shown in FIG. 1, in which the furnace, indicated at 10, consists of a suitable enclosure having one or more grate or pan 12 supporting the fibrous material 14 to be treated. .

An inlet pipe 16 and an outlet pipe 17 are provided to ensure the presence of air or a suitable oxidizing atmosphere within the furnace.

The furnace is heated by suitable means, such as electrical resistance elements (not shown in the figure).

The heating time as described above is used to heat the furnace to the desired temperature, measuring the fiber temperature with a thermocouple 18 inserted through the furnace lid.

The furnace is then allowed to cool and the treated fibers are removed.

In this way, any form of fibrous, infusible novolak material can be processed, but the method is limited to batchwise operation.

Although the fibers of the present invention can be prepared by batch operations, the preferred method is to draw a continuous fiber strand in an oven.

This method is illustrated in FIG. 2, in which infusible novolac fibers 20 are drawn in a tube furnace, indicated at 22, and the treated fibers 24 are wound onto a take-up spool 26.

As the fiber is drawn from the source 30, it is kept under moderate tension by passing it through an adjustable friction restraint 28.

Furnace 22 is heated by any convenient means, preferably electrically, while maintaining an oxidizing atmosphere therein as described above.

The temperature of the furnace can range from about 250°C to about 450°C, while the residence time of the fibers in the furnace is about 24°C.
minutes to about 60 minutes, which corresponds to a linear velocity of about 4 to about 6 inches per minute.

A preferred furnace temperature is about 400° C. at a fiber residence time of about 20 minutes, corresponding to a linear velocity of about 5 inches per minute.

The fibers may be in the form of threads or continuous filaments, and optionally continuous strips or webs of textile material.

The third most preferred method for producing the fibers of the present invention
As shown in the figure, the chamber furnace, designated 32 in the figure, has a conveyor belt 34 running over and supported between rollers 36 located at its open ends.

One or more infrared lamps 38 are positioned above and below the surface of the belt 34.

The belt is made of a suitable flexible material that is heat resistant and transparent to the heat radiation from the infrared lamp 38.

In operation, an infusible novolac fiber material 40 is rolled onto the upper surface of the belt 34 at one end of the furnace while the roller 36 is slowly rotated by suitable means, such as a low speed motor (not shown). evenly distributed.

The moving belt conveys the fiber material 40 into the furnace while the fibers receive radiant heat from the infrared lamps 38.

The fibers 42 that have been processed according to the invention are removed from the belt 34 at the other end of the furnace.

By adjusting both the temperature of heat lamp 38 and the speed of belt 34, the conditions for heating the fibers can be easily varied as desired.

As in the previous method, from about 6 to about 12 per minute
At belt speeds in the inch range, furnace temperatures in the range of about 250°C to about 450°C can be used.

Preferred operating conditions use a temperature of about 400° C. with a belt speed of about 10% inches per minute.

This method allows the temperature of the furnace to be precisely controlled and allows the production of e.g.
It is most advantageous for the production of fibers of the present invention because fiber materials such as rovings or continuous filaments can be transported conveniently.

A particularly desirable feature of the above method is that it allows
Approximately 10 square meters per gram to 500 square meters per gram
It is possible to produce organic fibers that not only have surface areas in the range of square meters or more, but also are relatively strong and have significant flexibility.

at least about 15,000 psi (1050 to 9/cr
The tensile strength of A) can be generally approximated in fibers with a surface area greater than 500 square meters per gram, but the tensile strength increases with decreasing surface area.

Carbon adsorption capacity and fiber flexibility generally increase with increasing surface area.

The invention will be further described in part with reference to the following examples, which are intended to illustrate the invention and are not intended to limit the scope of the invention.

Example 1 (Reference Example) A typical novolak was prepared according to conventional methods by condensing formaldehyde with a slight molar excess of phenol in the presence of catalytic amounts of oxalic acid.

After purification to remove particulate impurities and residual phenol, the resin had an average molecular weight of about 720 and a viscosity of about 41,300 centipoise at 150°C.

Infusible, cured novolac fibers were typically produced from this resin as follows.

By melt spinning, i.e. about 10
The resin is fiberized, i.e., by simultaneously drawing a number of filaments from the 135° C. melt at a speed of about 760 meters per minute through a bushing with a 0.00 orifice and assembling the filaments to form a tow. , made into a fibrous form.

The fusible uncured novolak fibers thus obtained have approximately 12
It had an average diameter of microns.

The 250Z fibers were soaked at room temperature in an aqueous solution 21 containing 18% paraformaldehyde as the methylene base and 18% HCI as the catalyst.

The solution was heated at 30°C for 1 hour, then at 40°C for 1 hour, then at 70°C for 1 hour, then at boiling temperature (103°C) for 3 hours.
Heated for 0 minutes.

After maintaining the temperature at boiling point for 1 hour, the resulting infusible, cured novolac fibers were removed and dried in air at approximately 60°C.

Example 2 An infusible, cured phenol-formaldehyde novolac filament was prepared substantially according to the method of Example 1.

The filament had a diameter of approximately 12-18 microns.

This tow is cut into pieces of 6 inches (approximately 15 cIrL), and the cut fibers 51 are placed in an electric furnace. , = 100°C per hour through a slow air flow through the furnace to remove volatile substances evaporated from the fibers and maintain an air atmosphere.
The fibers were heated from room temperature to a moderate temperature of 400°C at a heating rate of .

The partially etched fibers were then allowed to cool to room temperature.

A yield of flexible adsorptive fibers of 4z was obtained, which had an average surface area of 400/11.

Example 3 An infusible, cured phenol-formaldehyde novolac filament was prepared substantially according to the method of Example 1.

The filaments had a diameter of 12-18 microns and the rovings had an average diameter of about 100 microns.

The roving was pulled under slight tension through a tube furnace electrically heated to 400°C.

The tube furnace had a total length of 8 feet and the roving was pulled through it at a linear velocity of about 5 inches per minute, thereby giving a residence time in the furnace of about 20 minutes.

The roving was exposed to air during its passage through the furnace.

The partially etched fibers thus obtained had a surface area of about 400 square meters per gram.

The weight retention of the fibers after treatment was about 70% of the starting weight.

Example 4 The infusible, cured phenol-formaldehyde novolac filament described in Example 3 was heated under an infrared lamp for 8 hours.
Heated in a foot oven.

The roving was carried into the furnace on a conveyor belt, which was transparent to radiant heat so that the roving was exposed to thermal radiation from infrared lamps placed on both sides of the belt. It was sexual.

The roving was heated to 400°C in an air atmosphere during its passage through the furnace.
heated to.

The belt speed was approximately 10.5 inches per minute, giving a residence time in the furnace of approximately 9 minutes.

The partially etched fibers thus obtained have a weight retention of about 61% of their starting weight, about 500 to about 600%.
surface area of rri:/S' and 15000 psi
It had a tensile strength exceeding .

The method of the present invention can be carried out with fibers in almost any form, including, for example, tow, strands and rovings, stable and rolled befels, paper, woven and knitted fabrics, etc. The choice of form depends primarily on the intended use for the adsorptive fiber.

Similarly, the fibers may have any desired diameter, chosen primarily in relation to the intended use of the resulting fibers.

Although surface area does not appear to be related to diameter, fiber tensile strength tends to increase with increasing diameter, and flexibility tends to increase with decreasing diameter.

Although it is clear from the Examples that the present invention can be carried out either batchwise or continuously as desired, the method described in Example 4 is preferred.

This high surface area organic fiber, which exists in various forms, has many uses.

For example, they are particularly useful as adsorbents and filtration materials in gas masks and absorbent protective clothing.

The percentages stated herein are by weight, unless otherwise indicated or obvious from the context.

The surface areas mentioned herein are referred to as Prunauer (Brunauer).
auer), Emmett and Teler's BET method and formula (Journal of American Chemical Society 60,
309-316 (1938)) using an automatic surface area analyzer (Micromeritics Instrument Corporation, Norcross, Chaussia) model 2200. Based on the determination of the amount of gas, such as nitrogen, required to form the layer.

Although the invention has been described herein with reference to several examples and preferred embodiments, those skilled in the art will appreciate that various changes and modifications can be made without departing from the inventive concept. It should be understood that the scope of the invention should be determined with reference to the following embodiments.

The main embodiments of the present invention are as follows.

1. Flexible, infusible phenolic fibers, characterized in that they have a surface area of at least 10 square meters per gram.

2. The fiber according to item 1, having a surface area ranging from about 10 square meters per gram to about 600 square meters per gram.

3. The fiber according to 2 above, wherein the fiber has a tensile strength of at least about 15,000 psi.

4. The fiber according to 1 above, wherein the fiber has a surface area of more than 500 square meters per gram and a tensile strength of at least 15,000 psi.

5. Fabrics made from a large number of fibers according to 1 above.

6. Felt made of a large number of fibers according to 1 above.

7. A fiber yarn consisting of a large number of fibers according to 1 above.

8. The fiber according to 1 above, wherein the fiber is derived from a phenol-formaldehyde-containing fiber.

9. (a) Infusible phenolic resin fibers are heated at about 50° C. per hour in an oxidizing atmosphere to a temperature ranging from about room temperature to about 250° C. to about 450° C.
The method for producing fibers according to item 1' above, characterized in that: (b) the obtained fibers are then cooled to tt''x room temperature.

10. The method according to 9 above, wherein the fiber is heated to about 400° C. at a temperature increase rate of about 100° C. per hour.

11. The method according to 9 above, wherein the IM is derived from phenol-formaldehyde-containing fibers.

[Brief explanation of the drawing]

The drawings are exemplary schematic diagrams of furnaces used to carry out the method of the invention, FIG. 1 being a side sectional view of a fiber heating furnace adapted for batch operation, and FIG. 3 is a side sectional view of a tube furnace adapted for continuous operation; FIG. 3 is a side sectional view of a chamber furnace adapted for continuous operation, heated by an infrared lamp; FIG.

Claims (1)

Claims: 1(a) Infusible phenolic resin fibers are heated in an oxidizing atmosphere at temperatures ranging from about room temperature to about 250°C to about 450°C at a rate of about 50°C to 1 hour per hour. Approximately 2 per hour
(b) cooling the resulting fiber to about room temperature;
A method for producing flexible infusible phenolic resin fibers having a surface area of at least 10 square meters per gram, characterized in that: