WO2003050345A2

WO2003050345A2 - Process for imparting permanence to a shaped non thermoplastic fibrous material

Info

Publication number: WO2003050345A2
Application number: PCT/US2002/038748
Authority: WO
Inventors: Serge Rebouillat; Nicolas Pont; Benoit Steffenino
Original assignee: E. I. Du Pont De Nemours And Company
Priority date: 2001-12-06
Filing date: 2002-12-04
Publication date: 2003-06-19
Also published as: CN1602375A; BR0214444B1; BR0214444A; MXPA04005374A; CA2468336C; JP4527400B2; KR20050044721A; CN1285794C; KR100899760B1; AU2002362057A8; JP2005511915A; CN1840772A; CN100425764C; WO2003050345A3; CA2468336A1; AU2002362057A1; EP1454003A2; EP1454003B1

Abstract

The invention relates to a process to impart permanence to a shaped non thermoplastic fibrous material comprising submitting, under low tension, the shaped non thermoplastic fibrous material to a constant and uniformly distributed electromagnetic field generated by a single mode Transverse Magnetic 010 mode cylindrical resonant cavity microwave reactor,- the uniformly distributed electromagnetic field being operated at frequencies of from 5 MHz to 500 GHz,- the shaped non thermoplastic fibrous material being processed through the uniformly distributed electromagnetic field at a rate of from 0.01 to 1200 m/min,- the rate of the increase in temperature of the shaped non thermoplastic fibrous material being less than 300°C/s,- the shaped non thermoplastic fibrous material comprising at least one polymeric structure comprising amino groups and at least 0.05 weight % of an aqueous composition. The invention also relates to permanently shaped non thermoplastic fibrous material obtained by this process, in particular to permanently twisted fibers, and to a structure comprising this shaped non thermoplastic fibrous material.

Description

TITLE

PROCESS FOR IMPARTING PERMANENCE TO A SHAPED NON

THERMOPLASTIC FIBROUS MATERIAL

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a process to impart permanence to a shaped non thermoplastic fibrous material comprising amino groups. It also relates to permanently shaped fibrous material obtainable from that process.

Description of the Related Art Many textile processes involve the twisting of multi-filament fiber prior to subsequent manufacturing into woven, knitted or braided structures. Twisting is the process of combining filaments into yarn by arranging them according to a helix pattern or combining two or more parallel single yarns into plied yarns or cords. Twist is generally expressed as the number of turns around the longitudinal axis of the fiber per unit length of the fiber; i.e. turns per meter abbreviated as tpm. Multi-filament yarn twisting is generally considered as a processing aid providing high cohesion to the yarn. It is also considered as a suitable filament arrangement for an optimum load sharing. Twisting is also used to impart to the yarn surface a uniform morphology allowing for a better anchoring of the matrix, such as a rubber, which in turn contributes to a more efficient stress transfer and a better mechanical adhesion between the matrix and the reinforcing fiber. Therefore twisting is generally employed to increase strength, smoothness and uniformity or to obtain specific effects in the yarn.

For these reasons, it may be interesting to provide fibers stabilized in a particular shape, for instance under a twisted form. US 5, 794, 428 discloses a process to permanently set the twist of a thermoplastic fiber. However, high-modulus, high-strength non thermoplastic fibrous material, and more generally crystalline fibers, such as aramid fibers, are difficult to stabilize at moderate and high twist levels because they have a natural tendency to untwist readily. For low and medium twist levels, it is known to use the so-called S and Z twist arrangement, which is a two step process combining a S twisted yarn with a Z twisted yarn leading to a stabilized combined assembly. Nonetheless, in the case of non thermoplastic fibers comprising amino groups, for high tpm exceeding for example a hundred turns per meter for a 1670 dtex yarn, it is not practical, productivity and uniformity wise, to use that process.

Now, it has been found that by submitting a shaped fibrous material to a constant and uniformly distributed electromagnetic field generated by a specific microwave, it was possible to impart permanence to said shaped fibrous material, even though this material is a high modulus or a high strength non thermoplastic material comprising amino groups.

Microwave heating is a well known technology with industrial as well as domestic applications. US 5, 175, 239 and US 5, 146, 058 disclose the use of a microwave to heat treat para-aramid fibers in order to obtain fibers showing internal cracks through the filament cross-section.

SUMMARY OF THE INVENTION One aspect of the invention is a process to impart permanence to a shaped non thermoplastic fibrous material comprising submitting, under low tension, the shaped non thermoplastic fibrous material to a constant and uniformly distributed electromagnetic field generated by a single mode Transverse Magnetic 010 mode cylindrical resonant cavity microwave reactor,

- the uniformly distributed electromagnetic field being operated at frequencies of from 5 MHz to 500 GHz, the shaped non thermoplastic fibrous material being processed through the uniformly distributed electromagnetic field at a rate of from 0.01 to 1200 m/min, the rate of the increase in temperature of the shaped non thermoplastic fibrous material being less than 300°C/s, - the shaped non thermoplastic fibrous material comprising i) at least one polymeric structure comprising amino groups and ii) at least 0.05 weight % of an aqueous composition.

Another aspect of the invention is a permanently shaped non thermoplastic fibrous material obtainable or obtained through the process described above.

Another aspect of the invention is a structure comprising the permanently shaped non thermoplastic fibrous material of the invention. This structure may be a woven, knitten, braided, spiralled, felted, unidirectionally laid down or non woven structure. Non woven structure may include fleeces, wadding, felt.

Another aspect of the invention is a method of imparting permanence to a shaped fibrous non thermoplastic material comprising submitting said shaped non thermoplastic fibrous material to a constant and uniformly distributed electromagnetic field generated by a single mode Transverse Magnetic 010 mode cylindrical resonant cavity microwave reactor.

Another aspect of the invention is a process to impart permanence to a twisted para-aramid fiber comprising submitting said fiber under a tension of less than 0.2 gpd, to a constant and uniformly distributed electromagnetic field produced by a single mode Transverse Magnetic 010 mode cylindrical resonant cavity microwave reactor,

- the uniformly distributed electromagnetic field being operated at frequencies of from 5 MHz to 500 GHz, - the fiber being processed through the microwave reactor at a rate of from 0.01 to 1200 m/min, the rate of the increase in temperature of the fiber being less than 300°C/s,

- the fiber comprising at least 0.05 weight % of an aqueous composition.

A permanent shape for a non thermoplastic fibrous material may be required for special applications such as imparting to a fiber a stretch factor independant from the elastomeric nature of the fiber. For instance, such a permanently shaped fiber may be used in a rubber composite in order to decrease the elongation gradient between the fiber and the rubber.

With the process of the invention, it is possible to impart to a non thermoplastic fiber a permanent twist of up to the maximum operational twist level. The maximum operational twist level is generally considered as a twist level which will not provoque fracture or rupture of the filaments composing the twist assembly. For instance, this permanent twist level can reach 1000 tpm for a 1670 dtex yarn made of para-aramid fiber. The fiber shows no internal crack such as the one which could appear through the filament cross-section like described in US 5, 175, 239. It has a high cohesion and a high stability. In particular, with the process of the invention, it is possible to stabilize in a highly uniform manner a twisted non thermoplastic fiber. This high stabilization may be operated for any twist level necessary for any subsequent processing such as spiraling, knitting, weaving, braiding, felting or embedding in an elastomer matrix or a composite matrix.

Such a permanently twisted non thermoplastic fiber may be used as a sewing thread, a fiber to reinforce various matrixes or a woven or knitted fabric, making it possible to achieve high cohesion and stability in a woven or knitted structure. The woven or knitted structure made of a permanently twisted non thermoplastic fiber of the invention is highly stable dimensionally and will not present residual torque effect. Such a structure is also stretchable.

The process of the invention also has the advantage of eliminating intermediate steps which would be necessary to processes of the prior art to maintain the shape of a fibrous material.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of a process according to the present invention where the fibrous material is a fiber

Fig. 2 is a drawing showing a perspective view of the microwave reactor with a linear trajectory for the fiber path.

Fig. 2a is a drawing showing the constant and uniformly distributed electromagnetic field generated by a microwave reactor according to Fig.2 Fig. 3 is a drawing showing a perspective view of the microwave reactor with a sinusoidal trajectory for the fiber path.

Fig. 4 is a scanning electron microscopy picture of a cross section of a bundle of filaments of Example 1 of the present application. Fig. 4a is the related close-up of a single filament of Fig. 4.

Fig. 5 is a scanning electron microscopy picture of a cross section of a bundle of filaments of Example 2 of the present application.

Fig. 5a is the related close-up of a single filament of Fig. 5.

Fig. 6 is a scanning electron microscopy picture of a cross section of a bundle of filaments of Example 3 of the present application.

Fig. 6a is the related close-up of a single filament of Fig. 6.

Fig. 7 is a scanning electron microscopy picture of a cross section of a bundle of filaments of Example 4 of the present application.

Fig. 7a is the related close-up of a single filament of Fig. 7. Fig. 8 is a scanning electron microscopy picture of a cross section of a bundle of filaments of Example 5 of the present application.

Fig. 8a is the related close-up of a single filament of Fig. 8.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to FIG.1 , fiber 11 from supply tension regulated roll 12 is fed over rolling guide 13 to assure the desired alignment of the fiber. The fiber is fed to the pretreatment unit 14 where it can be watered so that the amount of water content in the fiber is at least 0.05 weight %. The water pretreatment can be optional in the case of a never-dried fiber having already more than 0.05 weight % water. The pretreatment unit 14 can alternatively be a dewatering unit to tailor the amount of water contained in the supply fiber 11. It can also be a temperature adjusting pretreatment and/or a coating or plasma or any suitable treatment. Optionally, the pretreatment unit can be a twisting unit or any texturizing unit imparting a filament deformation. From the pretreatment unit 14, the fiber is fed to tension-control roll 15 and then passes into the microwave resonant cavity reactor 16. The process can be tailored to include several resonant cavity reactors in any suitable arrangement in series or ir parallel. The microwave electromagnetic field is controlled through the microwave control 17. The fiber is maintained in the cavity at a relatively low tension, preferably suitable to maintain the shape of the fibrous material, preferably less than 0.2 g/denier. At the exit of the microwave, the fiber is fed to a tension-control roll 18 and then to a guide 19. The fiber is then fed to rolling guide 20 to assure the desired alignment of the fiber. The fiber is fed to the post-treatment unit 21 where it can be further heated, dried or surface treated by coating or plasma treatment for instance or by any other suitable post treatment. The use of the post-treatment unit is optional. The fiber then passes through a rolling-tension guide 22. Finally, the fiber is wound using a tension controlled precision winder 23. The process of Fig. 1 can be further modified to allow the treatment of several fibers run in parallel.

Referring now to FIG. 2, a cylindrical microwave resonant cavity reactor indicated generally as 30 suitable for use in the present invention is depicted. The reactor comprises a cavity defined by a cylinder 31 designed to support a TM010 (Transverse Magnetic 010) mode and the desired resonant condition at the center frequency which is generally set for industrial applications at 915 MHz or 2450 MHz. Suitable dimension for a 915 MHz resonant condition are provided on Fig. 2. Typical units are 915 MHz, 400 W amplifier coupled to a 28 VDC, 53 A switching power supply or 915 MHz, 800 W amplifier coupled to a 28 VDC, 107 A power supply.

The circular cross section reactor combines the radially symmetric electromagnetic field distributions and the well defined axial electromagnetic field profile. By "circular cross section" is meant herein a circular or an oval cross section.

A microwave source 32 initiates the microwave. The fiber 11 is fed through inlet port 33 and exits through outlet port 34. The fiber path is linear.

Referring to FIG. 3, a cylindrical microwave resonant cavity reactor 40 is depicted, similar to the one shown in FIG. 2 but comprising in addition ceramic guides 41 allowing the fiber path to be sinusoidal.

DETAILED DESCRIPTION "Fibrous material", as used herein, includes endless fibers such as filaments, short fibrous structures, short cut fibers, microfibers, multi- filaments, cords, yarns, fibers, felt, fabric, woven, knitted, braided, spiraled, felted structures or nonwoven forms. The fibers may be made into yarns of short fibrous structures which are spun into staple fibers, into yarns of endless fibers or into stretchbroken yarns which can be described as intermediate yarns between staple and continuous yarns. The yarn, fiber, fabric, woven, knitted, braided, spiraled, felted structure or nonwoven form may be made of continuous filaments, short fibers or pulp. "Shaped fibrous material" as used herein, includes any fiber, fabric, textile, garment, fibrous structure or finished product made of the fibrous material as defined above, having been submitted to any shaping process such as twisting, weaving, braiding, crimping, plying, knitting, spiraling, felting, unidirectionally laying down or any other deformation.

"Aqueous composition", as used herein, includes water, solvents, and/or mixture thereof under the form of a solution, an emulsion or a dispersion. It can contain salts, polymers, or other emulsified, dispersed or dissolved chemical compounds. Preferably, the aqueous composition is water. This aqueous composition may be present within the fibrous material under the free form and/or under the bound form. In a preferred embodiment of the invention, the aqueous composition is present under both forms, free and bound.

"Thermoplastic material", as used herein, means a material that softens when exposed to heat and returns to its original condition when cooled to room temperature. A non thermoplastic material does not soften when exposed to heat. The non thermoplastic fibrous material suitable in the present invention includes any natural or man made non thermoplastic fibrous material comprising at least one polymeric structure comprising amino groups. "Amino groups", as used herein, includes amine groups, amide groups and/or amino-acid groups. Man made and natural fibrous material include polyamides, polyamines, polyimides such as polybenzimidazole (PBI), polyphenylenebenzobisoxazole (PBO), natural silk, spider silk, hair and all natural fibers presenting amino-acid sequences. These groups can be part of a linear or branched, cyclic or heterocyclic, saturated or unsaturated, aliphatic or aromatic chemical structure. Preferred polymeric structures comprising amino groups include polyamides, polyamines, polyimides, aramids, blends and mixtures thereof. Preferably, the polymeric structure comprising amino groups is an aramid.

Aramids are polymers that are partially, preponderantly or exclusively composed of aromatic rings, which are connected through carbamide bridges or optionally, in addition also through other bridging structures. The structure of such aramids may be elucidated by the following general formula of repeating units:

(-NH-A1-NH-CO-A2-CO)n

wherein A1 and A2 are the same or different and signify aromatic and/or polyaromatic and/or heteroaromatic rings, that may also be substituted. Typically A1 and A2 may independently from each other be selected from 1 ,4-phenylene, 1 ,3-phenylene, 1 ,2-phenylene, 4,4'-biphenylene, 2,6- naphthylene, 1 ,5-naphthylene, 1 ,4-naphthylene, phenoxyphenyl-4,4'- diyelen, phenoxyphenyl-3,4'-diylen, 2,5-pyridylene and 2,6-quinolylene which may or may not be substituted by one or more substituents which may comprise halogen, C1-C4-alkyl, phenyl, carboalkoxyl, C1-C4-alkoxyl, acyloxy, nitro, dialkylamino, thioalkyl, carboxyl and sulfonyl. The -CONH- . group may also be replaced by a carbonyl-hydrazide (-CONHNH-) group, azo-or azoxygroup.

These aramids are generally prepared by polymerization of diacid chloride, or the corresponding diacid, and diamine.

Examples of aramids are poly-m-phenylene-isophthalamide and poly-p-phenylene-terephthalamide.

Additional suitable aromatic polyamides are of the following structure:

(-NH-Ar1-X-Ar2-NH-CO-Ar1-X-Ar2-CO-)n

in which X represents O, S, S02, NR, N2, CR2, CO.

R represents H, C1-C4-alkyl and Ar1 and Ar2 which may be same or different are selected from 1 ,2-phenylene, 1 ,3-phenylene and 1 ,4- phenylene and in which at least one hydrogen atom may be substituted with halogen and/or C1-C4-alkyl. Further useful polyamides are disclosed in U.S. Pat. No. 4,670,343 wherein the aramid is a copolyamide in which preferably at least 80% by mole of the total A1 and A2 are 1 ,4-phenylene and phenoxyphenyl-3,4'- diylene which may or may not be subsituted and the content of phenoxyphenyl-3,4'-diylene is 10% to 40% by mole.

Additives may be used with the aramid and, in fact, it has been found that up to as much as 10% by weight, of other polymeric materials may be blended with the aramid or that copolymers may be used having as much as 10% of other diamine substituted for the diamine of the aramid or as much as 10% of other diacid chloride substituted for the diacid chloride of the aramid.

In addition to the at least one polymeric structure comprising amino groups, the non thermoplastic fibrous material of the invention may also comprise at least one thermoplastic polymer. Such thermoplastic polymer includes polyvinylchloride, nylon, polyfluorocarbon, polyethylene, polypropylene and mixtures thereof.

"Constant and uniformly distributed electromagnetic field ", as used herein, means an electromagnetic field which is radially symmetric and axially invariant. Such an electromagnetic field may be produced by a microwave reactor. "Microwave", as used herein, means electromagnetic radiation in the range of frequency from 5 MHz to 500 GHz. Because of Government regulation and the present availability of magnetron power sources, the frequency normally is 915 or 2450 MHz for industrial applications. The microwave reactor suitable for the present invention is a single mode microwave reactor with a cylindrical geometry. In such a geometry, when the fibrous material is a fiber, the electromagnetic field is predictable, uniformly distributed around the fiber.

This circular cross section reactor, depicted in figures 2 and 3 combines the radially symmetric electromagnetic field distributions and the well defined axial electromagnetic field profile.

An example of a particularly suitable reactor for the invention is the single mode TM010 (Transverse Magnetic 010 mode) cylindrical resonant cavity, described in A.C. Metaxas and R.J. Meredith, Industrial Microwave Heating, Peter Peregrinus Ltd., London, England, 1983, pp. 183-193, equipped with an American Microwave Technology (AMT) solid-state amplifier as microwave power source, 32.7 cm wavelength, powered from a 28 VDC power supply and with a maximum power level of 400W, with dimensions of an inner length (L) of 30 cm and an inner radius ( R) of 12.5 cm and generating a resonant frequency of 915 MHz.

Associations in series or in parallel or any suitable arrangements of the previously described cavities are considered to be part of the scope of the invention.

"Under low tension", as used herein, means substantially very low tension. When the fibrous material is any fibrous structure but a fiber, it is preferably submitted to no tension at all. When the fibrous material is a fiber, the tension is preferably less than 0.2 gpd (grams per denier). "Permanence", as used herein, is measured according to the following test: the permanently shaped non thermoplastic fibrous material obtained through the process of the invention is "unshaped" : in other words, the basic fibrous material composing the permanently shaped fibrous material is taken back to the original linear position it had before it was ever imparted a shape. For instance, if the permanently shaped fibrous material is a twisted fiber, it is untwisted; if it is a crimped fiber, it is uncrimped; if it is a knitted fabric, it is unknitted so that the fibrous material is extented in its original linear position. This "unshaping process" must be done under a certain tension because of the natural elasticity acquired by the fibrous material through the process of the invention. Once the fibrous material is completely unshaped, ie once it is back to its linear original position, it is relieved of any tension and freed to come back to the shape it had before the "unshaping" process. By comparing the respective level of the shape of the fibrous material before and after the "unshaping" process, one can then measure the percentage of shape retention of the fibrous material. This percentage is the permanence of the shape. With the process of the invention, the permanence is at least 30%, preferably at least 50%, and more preferably at least 70%. That means that a shaped fibrous material submitted to the process of the invention retains at least 30% of its shape after "unshaping". When the shaped fibrous material is a twisted fiber, the fiber retains at least 70%, preferably at least 80%, more preferably at least 90%, and even more preferably at least 96%, of the twist imparted, this twist being measured as described in the examples below.

The process of the invention allows to impart to para-aramid fibers permanent high twist level never reached before. For instance, for industrial fibers, the optimum twist level Tpm (turns per meter) is calculated for a generally accepted twist multiplier TM of 1.1 using the following relationship given in ASTM D 885-98 as formula (10).

Tpm = 960 (1.1 )/ (tex) 1/2

As an example for a 1670 dtex para-aramid fiber and a TM of 1.1 , the optimum calculated twist level is about 80 tpm. This value is given by:

Tpm = (1.1 ) 960 (tex)^" 1"/2" _ = (1.1 ) 960 (167)

In the case of a para-aramid fiber of a dtex of 1670 first twisted at 500 tpm and then submitted to the process of the invention, a permanent twist level of 400 tpm is observable.

In one embodiment of the invention, the fibrous material is a fiber. "Fiber", as used herein, means a fibrous material having a length at least 1000 times its diameter or width. The fibers are preferably polyamide fibers and more preferably aramid fibers. Fibers which are exclusively composed of aromatic polyamides are preferred. Para-aramid fibers which are formed of poly(p-phenylene terephthalamide) are more preferred. Preferably, the fiber has a modulus of about 10 to about 2500 g/den, preferably of about 1000 to about 2500 g/den, and a tenacity of about 3 to about 50 g/den, preferably of about 3 to about 38 g/den. The modulus and the tenacity are measured according to the ASTM D 885-98 method. The fibers are generally spun from an anisotropic spin dope using an air gap spinning process such as is well known and is described in United States Patent No. 3,767,756 or 4,340,559. Fibers are spun from an anisotropic spin dope at about 80°C, through an air gap, into an aqueous coagulating bath of about 5°C, and through an aqueous rinse and wash. The resulting fibers are so-called "never-dried" and include at least 0.05% by weight, preferably from 0.05 to 400%, by weight, water, this water content being measured according to ASTM D885-98 for the moisture regain level. This water is uniformly distributed along the length of the fiber. It is possible to use never-dried or partially or totally dried fibers as the fibrous material for the process of the invention : in the case of totally dried fibers, it is important that the fiber be immersed in an aqueous composition for several hours prior to the microwave processing, so that they include at least 0.05 weight % of an aqueous composition. It is also possible to use fibers comprising mixtures of the above materials including hybrid fibers, blends of different fibers such as natural and man made fibers. Furthermore, two-component fibers may also be used in accordance with the invention, for instance fibers in which the core consists of a different material from the skin or in which the various filaments are from different nature.

The fibers suitable for the present invention may be round, flat or may have another cross-sectional shape or they may be hollow fibers. In a preferred embodiment of the invention, the shaped fibrous material is a twisted fiber. The shaped fibrous material, preferably the twisted fiber, is processed through the constant and uniformly distributed electromagnetic field at a speed which may be adjusted between 0.01 and 2000 m/min. Typical speeds are 60 m/min for the fibrous material treatment other than during the spinning process, and 800 m/min for the speed during the manufacturing of the fibrous material.

During the process of the invention, the fibrous material is maintained at a very low tension. It preferably undergoes no tension at all. When the fibrous material is a fiber, the tension is preferably less than 0.2 g/d. It is very important that the fibrous material be not degraded during the process of the invention. In this view, the rate of the increase of temperature of the fibrous material is less than 300°C/s during the time it is submitted to the electromagnetic field. In a preferred embodiment of the invention, the dwell time of the fibrous material in the microwave reactor is more than 0.1 s, and more preferably it is the necessary time so that the difference between the temperature of the outcoming fibrous material and the temperature of the incoming fibrous material is less than 300°C.

The temperature of the incoming fibrous material may be selected and is only limited by the temperature resistance of the components, this being valid for very low as well as very high temperatures. Nonetheless a range of 10 °C to 100 °C is preferred, with a range of from 15 °C to 45 °C being more preferred.

When the fibrous material is a fiber, the fiber path may be a linear trajectory perfectly coinciding with the reactor main central axis, as shown on fig 2. The fiber path may alternatively be sinusoidal as shown in figure 3: in such a case, one obtains a periodically varying electromagnetic profile along the fiber which can result in special fiber mechanical and chemical properties uniformly distributed along the fiber length. Furthermore the sinusoidal fiber path can be offset from the geometric center of the reactor producing similar effects. Alternatively inserts placed appropriately in the reactor can be engineered to produce a similar periodic fiber treatment. Additionally, such inserts, with for example variable thickness, can be used to produce a gradient distribution of the axial electromagnetic field matching the variation of absorbency of the fiber from its entry in the reactor to its outlet. This later case can be used for the linear fiber path still producing a gradient from the inlet to the outlet of the reactor. Other variations, such as a sinusoidal fiber path with variable amplitude, or a non-circular but oval cavity cross section, are possible within the scope of the invention which should not be restricted to the above alternate constructions and fiber path configurations.

In a preferred embodiment, nitrogen or air can be circulated through the reactor to evacuate water vapor.

At the exit of the microwave reactor, the temperature of the outcoming fibrous material is preferably less than 100°C, and more preferably less than 45°C.

At the exit of the microwave reactor, the fibrous material may undergo an additional treatment. For instance, it may be further heated or surface treated or coated with various polymeric solutions, like epoxy-latex formulations for a pneumatic production line. It can also be subject to a plasma, an electrostatic discharge, or a corona treatment. With the specific design of the reactor of the process of the invention, the fiber, which initially has a fixed microwave loss factor along its length, is exposed to the same electromagnetic field strength over its entire length, except for the inlet and outlet which are special boundaries. The fiber therefore undergoes an isotropic treatment all along its length and therefore shows constant properties as regards tenacity, modulus, residual water content, twist uniformity and permanent shaping.

The permanently shaped fibers obtained through the process of the present invention show no internal cracks. Their morphology and density remain almost unchanged. They exhibit no shrinkage during the process They usually have a specific breaking strength of about 2.65 to about 33.5 cN/dtex (about 3 to about 38 g/den, preferably about 15 to about 38 g/den) and a specific modulus of about 8.83 to about 2297 cN/dtex (about 10 to about 2500 g/den, preferably about 1000 to about 2500 g/den). The invention will be explained in more detail with reference to the following examples.

EXAMPLES

Example 1

A regular bobbin of Kevlar® 29 para-aramid yarn made of 1000 filaments of 1.5 denier per filament, equivalent to a total of 1670 dtex linear density, has been used as a feed material for all the examples cited below. This material is thereafter referred to as K29. The moisture content measured on K29 using ASTM D885-98 is 5.9 weight percent. A sufficient amount of K29 yarn has been twisted, using a SAURER ALLMA® elasto-twister AZB 200/240 Kevlar® set at 500 tpm, and directly wound on plastic cylindrical tubes, which tubes are known to resist to water exposure without appreciable swelling or shrinkage. The twisted 500 tpm K29 yarn is thereafter referred to as M3D. Using a twist counter, Zeigle D311 , the real tpm was confirmed to be 609 tpm which is quite a usual divergence vs. the set point of 500 tpm since it is a high twist level using a manual control of the twisting machine.

A 50 cm sample of M3D is freed to relax and let untwist to its natural equilibrium level. Using a twist counter, the relaxed sample of M3D is untwisted completely to measure the residual twist. The zero twist level is confirmed by driving a pin through the middle and along the axis of the filament bundle. One should be able to freely move the pin in the axial direction from one boundary of the sample to the other without being stopped by a blockage of the pin . The residual twist level was measured to be 309 tpm , i.e. 51% of the initial twist. The permanence is therefore 51 %. The water content of the relaxed sample remains unchanged at about 5.9 weight percent.

The SEM (Scanning Electron Micrograph) analysis of the morphology of a sample of M3D shows that the filaments are unchanged and in particular no crack parallel with the longitudinal axis of the filaments have been observed. Fig. 4 shows the cross section of a bundle of filaments of M3D and Fig. 4a of the unaltered cross section of a single filament of M3D. By unaltered cross section is meant that the cross section is undamaged, in other words that there are no cracks across the section.

Example 2

A sufficient amount of K29 yarn has been twisted, using a SAURER ALLMA® elasto-twister AZB 200/240 Kevlar® set at 500 tpm, and directly wound on plastic cylindrical tubes, which tubes are known to resist to water exposure without appreciable swelling or shrinkage. The twisted 500 tpm K29 yarn is thereafter referred to as M3D. Using a twist counter, Zeigle D311 , the real tpm was confirmed to be 617 tpm which is quite a usual divergence vs. the set point of 500 tpm since it is a high twist level using a manual control of the twisting machine.

A sufficient number of bobbins of M3D were immersed for 48 hours in a recipient containing de-ionised water; the resulting fiber is hereinafter referred to as M1500. The moisture content measured on M1- 500 using ASTM D885-98 is 22.1 weight percent.

A 50 cm sample of M1-500 is freed to relax and let untwist to its natural equilibrium level. Using a twist counter the relaxed sample of M1- 500 is untwisted completely to measure the residual twist. The zero twist level is confirmed by driving a pin through the middle and along the axis of the filament bundle. One should be able to freely move the pin in the axial direction from one boundary of the sample to the other without being stopped by a blockage of the pin . The residual twist level was measured to be 409 tpm , i.e. 66 % of the initial twist. The permanence is therefore 66%. The SEM (Scanning Electron Micrograph) analysis of the morphology of a sample of M 1-500 shows that the filaments are unchanged and in particular no crack parallel with the longitudinal axis of the filaments have been observed. Fig. 5 shows the cross section of a bundle of filaments of M 1-500 and Fig. 5a of the unaltered cross section of a single filament of M1 -500.

Example 3

A sufficient amount of K29 yarn has been twisted, using a SAURER ALLMA® elasto-twister AZB 200/240 Kevlar® set at 500 tpm, and directly wound on plastic cylindrical tubes, which tubes are known to resist to water exposure without appreciable swelling or shrinkage. The twisted 500 tpm K29 yarn is thereafter referred to as M3D. Using a twist counter, Zeigle D311 , the real tpm was confirmed to be 611 tpm which is quite a usual divergence vs. the set point of 500 tpm since it is a high twist level using a manual control of the twisting machine.

A sufficient number of bobbins of M3D were immersed for 48 hours in a recipient containing de-ionised water. A bobbin was taken off the recipient and was fed at 6 meters per minute to the off-line treatment unit of figure 1. The corresponding resident time in the cylindrical TM010 resonant cavity was 3 seconds. The resonant cylindrical cavity is depicted on Fig. 2 which also provides its dimensions. The fiber temperature entering the cavity was about 20 degree centigrade compared to less than 40 degree centigrade for the "treated" fiber exiting the cavity. The water content, using ASTM D885-98 method, of the fiber entering the cavity was 22.1 weight percent compared to 18.8 weight percent for the "treated" fiber exiting the cavity. The exiting fiber, referred thereinafter as to M3A, was wound onto cylindrical plastic tubes.

A 50 cm sample of M3A is freed to relax and let untwist to its natural equilibrium level. Using a twist counter the relaxed sample of M3A is untwisted completely to measure the residual twist. The zero twist level is confirmed by driving a pin through the middle and along the axis of the filament bundle. One should be able to freely move the pin in the axial direction from one boundary of the sample to the other without being stopped by a blockage of the pin . The residual twist level was measured to be 589 tpm , i.e. 96 % of the initial twist. The permanence is therefore 96%.

The SEM (Scanning Electron Micrograph) analysis of the morphology of a sample of M3A shows that the filaments are unchanged and in particular no crack parallel with the longitudinal axis of the filaments have been observed. Fig. 6 shows the cross section of a bundle of filaments of M3A and Fig. 6a of the unaltered cross section of a single filament of M3A.

Example 4 A sufficient amount of K29 yarn has been twisted, using a

SAURER ALLMA® elasto-twister AZB 200/240 Kevlar® set at 500 tpm, and directly wound on plastic cylindrical tubes, which tubes are known to resist to water exposure without appreciable swelling or shrinkage. The twisted 500 tpm K29 yarn is thereafter referred to as M3D. Using a twist counter, Zeigle D311 , the real tpm was confirmed to be 604 tpm which is quite a usual divergence vs. the set point of 500 tpm since it is a high twist level using a manual control of the twisting machine.

A bobbin of M3D was fed at 6 meters per minute to the off-line treatment unit of figure 1. The corresponding resident time in the cylindrical TM010 resonant cavity was 3 seconds. The resonant cylindrical cavity is depicted on Fig. 2 which also provides its dimensions. The fiber temperature entering the cavity was about 20 degree centigrade compared to less than 40 degree centigrade for the "treated" fiber exiting the cavity. The water content, using ASTM D885-98 method, of the fiber entering the cavity was 5.9 weight percent compared to 1.5 weight percent for the "treated" fiber exiting the cavity. The exiting fiber, referred thereinafter as to M3C, was wound onto cylindrical plastic tubes.

A 50 cm sample of M3C is freed to relax and let untwist to its natural equilibrium level. Using a twist counter the relaxed sample of M3C is untwisted completely to measure the residual twist. The zero twist level is confirmed by driving a pin through the middle and along the axis of the filament bundle. One should be able to freely move the pin in the axial direction from one boundary of the sample to the other without being stopped by a blockage of the pin . The residual twist level was measured to be 483 tpm, i.e. 80 % of the initial twist. The permanence is therefore 80%.

The SEM (Scanning Electron Micrograph) analysis of the morphology of a sample of M3C shows that the filaments are unchanged and in particular no crack parallel with the longitudinal axis of the filaments have been observed. Fig. 7 shows the cross section of a bundle of filaments of M3C and picture Fig. 7a of the unaltered cross section of a single filament of M3C.

Example 5 A sufficient amount of K29 yarn has been twisted, using a

SAURER ALLMA® elasto-twister AZB 200/240 Kevlar® set at 500 tpm, and directly wound on plastic cylindrical tubes, which tubes are known to resist to water exposure without appreciable swelling or shrinkage. The twisted 500 tpm K29 yarn is thereafter referred to as M3D. Using a twist counter, Zeigle D311 , the real tpm was confirmed to be 583 tpm which is quite a usual divergence vs. the set point of 500 tpm since it is a high twist level using a manual control of the twisting machine.

A sufficient number of bobbins of M3D were immersed for 48 hours in a recipient containing de-ionised water. A bobbin was taken off the recipient and was fed at 50 meters per minute to the off-line treatment unit of figure 1. The corresponding resident time in the cylindrical TM010 resonant cavity was 0.4 seconds. The resonant cylindrical cavity is depicted on Fig. 2 which also provides its dimensions. The fiber temperature entering the cavity was about 20 degree centigrade compared to less than 40 degree centigrade for the "treated" fiber exiting the cavity. The water content, using ASTM D885-98 method, of the fiber entering the cavity was 22.1 weight percent. An almost unchanged weight percent for the "treated" fiber exiting the cavity was found. The exiting fiber, referred thereinafter as to M4A, was wound onto cylindrical plastic tubes. A 50 cm sample of M4A is freed to relax and let untwist to its natural equilibrium level. Using a twist counter the relaxed sample of M4A is untwisted completely to measure the residual twist. The zero twist level is confirmed by driving a pin through the middle and along the axis of the filament bundle. One should be able to freely move the pin in the axial direction from one boundary of the sample to the other without being stopped by a blockage of the pin . The residual twist level was measured to be 357 tpm , i.e. 61 % of the initial twist. The permanence is therefore 61 %. The SEM (Scanning Electron Micrograph) analysis of the morphology of a sample of M4A shows that the filaments are unchanged and in particular no crack parallel with the longitudinal axis of the filaments have been observed. Fig. 8 shows the cross section of a bundle of filaments of M4A and Fig. 8a of the unaltered cross section of a single filament of M4A.

These results show that a fibrous material submitted to the process of the invention can retain up to 96% of its shape.

Claims

1. Process to impart permanence to a shaped non thermoplastic fibrous material comprising submitting, under low tension, the shaped non thermoplastic fibrous material to a constant and uniformly distributed electromagnetic field generated by a single mode Transverse Magnetic 010 mode cylindrical resonant cavity microwave reactor,

- the constant and uniformly distributed electromagnetic field being operated at frequencies of from 5 MHz to 500 GHz, - the shaped non thermoplastic fibrous material being processed through the constant and uniformly distributed electromagnetic field at a rate of from 0.01 to 1200 m/min, the rate of the increase in temperature of the shaped non thermoplastic fibrous material being less than 300°C/s, - the shaped non thermoplastic fibrous material comprising i) at least one polymeric structure comprising amino groups and ii) at least 0.05 weight % of an aqueous composition.

2. Process of claim 1 , wherein the polymeric structure comprising amino groups includes polyamides, polyamines, polyimides, aramids, blends and mixtures thereof.

3. Process of claim 2, wherein the polymeric structure comprising amino groups is an aramid.

4. Process of claim 3, wherein the aramid includes poly-m-phenylene- isophthalamide and poly-p-phenylene-terephthalamide.

5. Process of claim 1 , wherein the non thermoplastic fibrous material also comprises at least one thermoplastic polymer.

6. Process of claim 1 , wherein the aqueous composition is water present in the fibrous material under the free and the bound forms.

7. Process of claim 1 , wherein the temperature of the outcoming fibrous material is less than 45°C.

8. Process of claim 1 , wherein the fibrous material is a fiber.

9. Process of claim 8, wherein the fiber is twisted.

10. Process of claim 8, wherein the fiber is submitted to a tension of less than 0.2 g/d.

11. Permanently shaped non thermoplastic fibrous material obtained by the process of claim 1.

12. Structure comprising the permanently shaped non thermoplastic fibrous material of claim 11.

13. Method of imparting permanence to a shaped non thermoplastic fibrous material comprising submitting said shaped non thermoplastic

, fibrous material to a constant and uniformly distributed electromagnetic field generated by a single mode Transverse Magnetic 010 mode cylindrical resonant cavity microwave reactor.

14. Process to impart permanence to a twisted para-aramid fiber comprising submitting said fiber, under a tension of less than 0.2 gpd, to a constant and uniformly distributed electromagnetic field produced by a single mode Transverse Magnetic 010 mode cylindrical resonant cavity microwave reactor,

- the fiber comprising at least 0.05 weight % of an aqueous composition.

15. Process according to claim 14, wherein the aqueous composition is water present in the fiber under the free and the bound forms.

16. Permanently twisted para-aramid fiber obtained by the process of claim 14.

17. Fiber according to claim 16, having a permanence of at least 70%.