GB1589615A

GB1589615A - Production of oriented fibrillar products

Info

Publication number: GB1589615A
Application number: GB2951/77A
Authority: GB
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1977-01-25
Filing date: 1977-01-25
Publication date: 1981-05-13
Also published as: UST969008I4; JPS5394621A

Description

(54) PRODUCTION OF ORIENTED FIBRILLAR PRODUCTS (71) We, IMPERIAL CHEMICAL INDUSTRIES LIMITED, Imperial Chemical House, Millbank, London, SW1P 3JF, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a process for the production of oriented fibrillar products from certain polyarylene-oxadiazoles.

The term "polyarylene-oxadiazole" as used throughout the specification is meant to include polyarylene-1,3,4-oxadiazoles having the characteristic repeating unit

where R is an aryl radical, particularly a phenylene radical. These polymers are known and can be shaped into oriented articles which possess extremely good mechanical and thermal properties. Unforunately these polymers decompose before they melt and hitherto the only techniques proposed for fabricating shaped articles from them have involved starting from a solution or dope of the polymer. For example, it has been proposed to spin the polyarylene-oxadiazoles into fibres using a wet spinning method wherein a solution or dope of the polymer in concentrated sulphuric acid or oleum is spun through a die or spinneret into a non-solvent bath whereupon a filament of the polymer is precipitated.

We have now discovered that it is possible to produce oriented fibrillar products from certain polyarylene-oxadiazole polymers using a technique which does not involve fabricating a solution or dope of the polymer.

According to the present invention there is provided a process for the production of an oriented fibrillar product from a polyarylene-oxadiazole which is heat-softenable without substantial degradation when in an air-excluded inert atmosphere which process comprises extruding contiguously disposed particles of the polymer, which particles are heat-softened but non-molten and are blanketed in an air-excluded atmosphere of an inert fluid, through a die to produce a substantially non-degraded oriented fibrillar product, means being provided if necessary to substantially prevent relaxation of the orientation resulting from the extrusion.

It has been found that certain of the polyarylene-oxadiazoles may be heat-softened when in an air-excluded atmosphere of an inert fluid without any or without substantial degradation even though they cannot be properly melted, and may be used in the process according to the invention. In the process of the invention, the inert blanketing fluid serves the purpose of excluding air from the polymer particles since active agents such as oxygen in the air would cause substantial degradation of the heat-softened particles.

Polyarylene-oxadiazoles may be homopolymers, derived from a single dibasic aryl acid, or copolymers, derived from two or more different dibasic aryl acids. The polyarylene-oxadiazole homo- or copolymers may be further modified by causing some of the aryl positions to be substituted by bulky groups such as bromine and iodine, e.g. by reacting the polymer with bromine or iodine or by employing dibasic aryl acids one or both of which have been brominated or iodinated before polvmerisation. We have found that the homopolymers are generally crystalline materials although sufficient aryl substitution with bulky groups may significantly reduce or remove crystallinity.

It has been our experience thus far that crystalline homopolymers cannot be used in the process of the invention since they cannot be heat-softened even when in an airexcluded atmosphere of an inert fluid without substantial degradation occurring, or at any rate can only be acceptably heat-softened at a temperature which is too close for practical considerations to the temperature at which they significantly decompose.

Many of the copolymeric polyarylene-oxadiazones, on the other hand, can be successfully used in the process of the invention since they can be heat-softened when in an air-excluded atmosphere of an inert fluid over a wide temperature range below their decomposition temperatures. Such copolymers are preferably amorphous and those copolymers which are of particular use are the amorphous copolymers which have been substituted with a sufficient quantity of bulky groups to inhibit crystallisation.

Whether a particular polyarylene-oxadiazole can be heat-softened when in an airexcluded atmosphere of an inert fluid and is therefore suitable for use according to the invention should be determined experimentally. However a very good indication of whether or not the polymer is suitable can be found from the X-ray diffraction pattern. If the X-ray diffraction pattern of particles of the polymer shows a single reflection, then this indicates that the polymer is substantially amorphous and noncrystallisable and therefore very suitable for use in the process of the invention. A method for measuring the X-ray diffraction pattern of such polymers is given in our U.K. Patent Specification 1529360. Particularly preferred polyarylene-oxadiazoles for use according to the invention are the copolymers having the characteristic repeating units

(hereinafter described as Formula A) where R1 is a p-phenylene radical, R2 is a m-phenylene radical, the ratio of R1 radicals to R2 radicals is within the range 60/40 to 10/90, and the R1 and/or R2 radicals are sufficiently substituted with bulky groups to inhibit crystallisation of the polymer.

The amount of bulky substitution sufficient to prevent or inhibit crystallisation will of course depend inter alia on the ratio of R1 to R2. Preferably most or all of the bulky substituents are in positions ortho to the heterocyclic ring. It is particularly preferred that the bulky substituents are bromine atoms, the preferred minimum quantity of bromine in the polymer being 5% by weight of the polymer (R1/R21= 10/90) and the preferred range of bromine content being 5%--20% by weight of the polymer (R1/R2 = 10/90 to 60/40).

The particularly preferred copolymers of Formula A are non-crystalline (amorphous) and substantially non-crystallisable. (It is believed that outside the range specified for R1/R2 no amount of substitution can prevent crystallisation). These copolymers may be readily prepared by reacting terephthalic acid, isophthalic acid and hydrazine (or a hydrazine derivative) in oleum or concentrated sulphuric acid as solvent. Polyphosphoric acid and chlorsulphonic acid are alternative polymerisation solvents. The resulting solution may then be treated to effect substitution in the phenylene ring, e.g. by bromination. Alternatively substitution (e.g. bromination) may be effected by treating one or both of the starting organic acids (e.g. with bromine) in the solvent before adding the hydrazine to effect polymerisation. Alternatively a polymer of low molecular weight may be made, treated with, e.g. bromine, and then further polymerised to higher molecular weight, e.g. by the addition of further hydrazine. The product is obtained in the form of solution or dope of the copolymer in the concentrated sulphuric acid or oleum solvent and may be brought out of solution by coagulation in a non-solvent such as water or an aqueous solution of a suitable salt.

The process of the invention is not a solution spinning process. Neither is it a melt spinning process since the individual particles of the polymer do not melt or coalesce before or during extrusion through the die and are thought to retain their individual identity after extrusion. Furthermore, the particles of the polymer are contiguously disposed, by which we mean that they are not in the form of a fluid (particularly a liquid) dispersion. The particles may, e.g. be in the form of externally dry powder, pellets, granules, or fibrids, or (more usually) in the form of a wet cake of such particles. The contiguous particles forcibly interact with each other when passing through the die and the resulting extrudcd product, which is often quite porous, comprises a tape, ribbon or sheet made up of bundles or bunches of very stiff fibrils; the product has the appearance and properties of a paper-like material and is appealing to the eye.

The blanketing fluid used in the process of the invention may be a vapour which is derived from a liquid associated with the particles which liquid undergoes vapourisation under the prevailing extrusion conditions (temperature, pressure, volume of the space not occupied by particles or liquid); at least part of the liquid will then exist as vapour during the extrusion. Conveniently, steam is a very suitable blanketing fluid for use in the process of the invention and is derived from water associated with the particles, this water being at least partly in the form of steam during the extrusion so as to provide the blanketing fluid. Alternatively, a liquid associated with the particles may itself provide the blanketing fluid for the particles, particularly in cases where the extrusion conditions are such that vapourisation will not occur. Water is conveniently a very suitable blanketing liquid in such cases and is able to encapsulate the particles (apart from where they touch) so as to provide an air-excluded inert atmosphere therefor.

It is also quite often the case that the conditions are such that the blanketing fluid will be partly in the form of vapour and partly in the form of liquid.

Fluids other than steam and water may sometimes be used as the blanketing fluid during the extrusion, e.g. vapourised and/or liquid organic compounds such as aliphatic hydrocarbons, chlorinated hydrocarbons, lower alcohols, lower ketones, and substituted amides such as dimethyl formamide.

In one embodiment of the invention (hereinafter termed Embodiment I) the protective blanketing fluid atmosphere is derived from a liquid associated with the particles which does not penetrate into the polymer particles to any significant extent and acts solely to provide a blanketing vapour and/or liquid for preventing or inhibiting decomposition during extrusion; the wet particles fed to the extruder are usually in the form of a wet cake. In this embodiment of the invention it is believed that each heat-softened polymer particles becomes elongated and hence oriented as it passes through the die, each elongated particle forming a bundle or bunch of fibrils and the elongated fibrinated particles adhering together slightly to form a ribbon or tape-like extrudate; if such an extrudate is crushed or twisted it readily fibrillates into individual or staple fibrils. The polymer particles for the extrusion may be readily prepared by thoroughly mixing dry particles of the polymer with a liquid for providing the inert fluid (e.g. watenconveniently used in an amount of a few percent by weight) and feeding this wet material to the extrusion apparatus. The polymer particles are heated to a temperature which is sufficient to heat-soften them so as to render them sufficiently pliable to be deformed when in the die of the extruder so as to provide the required oriented product; this may be done by heating the particles before they are fed to the extrusion apparatus and/or while they are in the extrusion apparatus. If a small quantity of water is used as the source of the inert fluid, then depending on the prevailing conditions of extrusion it may either be entirely or partly evaporated before the die during the extrusion so as to provide steam or a mixture of steam and water to displace the air and provide a protective blanket for the particles, or it may remain wholly as liquid during the extrusion so as to encapsulate the particles (apart from where they touch) thereby also providing an inert air-excluded protective blanket for the particles.

Accordingly there is provided in one embodiment of the invention (Embodiment I) a process for the production of an oriented fibrillar product from a polyarylene oxadiazole which is heat-softenable without substantial degradation when in an air excluded inert atmosphere which process comprises extruding contiguously disposed particles of the polymer, which particles are heat-softened but non-molten and are blanketed in an air-excluded atmosphere of an inert vapour and/or liquid which atmo sphere has been derived from a liquid associated with the polymer particles which has not internally penetrated the polymer particles, through a die to produce a substantially non-degraded oriented fibrillar product, means being provided if necessary to substan tially prevent relaxation of the orientation resulting from the extrusion.

In Embodiment I of the invention it is important that the individual particles of the polymer in front of the die should not be too large in diameter compared with the die diameter (in the case, e.g. of a die within a circular cross-section) or die gap (in the case, e.g. of a slot die, e.g. having a rectangular or annular cross-section), otherwise no extrusion will occur or the extrudate will be greatly distorted on the scale of the particles. Generally speaking, the largest polymer particle should be < 1/5 (preferably < 1/10) the diameter or gap of the die. However the ranee of permissible particle size will depend inter alia on the temperature of the extrusion, and the degree of softenability of the polymer being extruded at the temperature of the extrusion.

In Embodiment I the polvarylene-oxadiazole, while being in the oriented state immediately after extrusion, will tend to rapidly undergo relaxation as evidenced by the extrudate swelling immediately after emerging from the die to form a compacted substantially powdery product. Presumably this is because the cooling of the polymer after leaving the die is insufficiently rapid, any cooling by evaporation of the liquid providing the blanketing fluid occurring only at the surface of the particles. To fix the orientation after extrusion in this embodiment it may therefore be desirable to haul off the extrudate in the extrusion direction. Preferably the haul off rate is such that the extrudate diameter (or thickness) is about the same as that of the die diameter (or gap), although the haul off rate can be such that the extrudate diameter (or thickness) is significantly less than the die diameter (or gap).

In another embodiment of the invention (hereinafter termed Embodiment II) the blanketing inert fluid atmosphere is a vapour and/or liquid (depending on the prevailing extrusion conditions) which is derived from a liquid associated with the polymer particles at least part of which liquid has significantly penetrated into the polymer particles prior to extrusion. There will often be surface liquid present as well on the particles fed to the extruder so that the particles used in this embodiment (as in Embodiment I) are often in the form of a wet cake. The internally liquid-penetrated particles for the extrusion may be prepared by precipitating the polyarylene-oxadiazole from a solution thereof using a liquid coagulant such that the polymer particles are internally swollen by the liquid coagulant. According to the extent of subsequent drying, preselected quantities of liquid may be allowed to remain within the particles. Hence in this embodiment the liquid coagulant provides the blanketing fluid for the extrusion.

As with Embodiment I the blanketing inert fluid is preferably steam and/or water.

The interpenetrated water may be readily incorporated into the particles for example by washing a granulated dope of the polymer in concentrated sulphuric acid or oleum with water so that the concentrated sulphuric acid or oleum is replaced by the water.

It is believed that in Embodiment II of the invention, the interpenetrated liquid (preferably water) separates each individual particle into very many regions or "domains" and each of these domains become elongated and oriented when the particle is extruded through the die each domain resulting in a coherent bunch or bundle of fibrils. Furthermore each particle is thought to retain its individual identity after passage through the die (although it is of course elongated). Thus on this theory, the fibrillated product made using Embodiment II would be expected to possess a more coherent and stable structure than the product made using Embodiment I since the bunches of fibrils exist within an already formed particle whose identity is unchanged by extrusion; the buches are not thus all basically discrete entities each corresponding to a polymer particle before extrusion through the die (as in Embodi ment I). This is in fact what is found in practice. It is most desirable that the liquid interpenetrated particles particles should initially be of irregular shape and entangled so that the final oriented extrudate is a fully integrated structure.

Accordingly there is provided in another embodiment of the invention (Embodiment II) a process for the production of an oriented fibrillar product from a polyarylene-oxadiazole which is heat-softenable without substantial degradation when in an air-excluded inert atmosphere which process comprises extruding contiguously dis posed particles of the polymer, which particles are heat-softened by non-molten and are blanketed in an air-excluded atmosphere of an inert vapour and/or liquid which atmosphere has been derived from a liquid associated with the polymer particles at least part of which liquid has significantly interpenetrated the polymer particles, through a die to produce a substantially non-degraded oriented fibrillar product, means being provided if necessary to substantially prevent relaxation of the orientation resulting from the extrusion.

In Embodiment II the ratio of the diameters of the polymer particles to the die diameter or gap is not so critical as in Embodiment I. Thus, e.g., th ediameters of the liquid-interpenetrated particles may often be up to two or three times greater than the diameter (or gap) of the die and yet the polymer will still exude satisfactorily to give an excellent product. When the particle diameters are more than five times the die diameter (or gap), an- unsatisfactory product may ensue. It is believed that the reason why so much larger particles can be employed in this embodiment is that the internally penetrated liquid behaves in some respects like an internal plasticiser (although there is no solution and no melting of the particles) and as mentioned above causes separated domains to exist in' a given particle. Each domain can be thought of as an individual particle so far as the die is concerned; hence in Embodiment II the small domains can be thought of as being equivalent to the individual particles as used in Embodiment I so that much larger particles can be used in Embodiment II.

As with Embodiment I, the optimum conditions in Embodiment II (among other things extrusion temperature, die diameter/particle diameter ratio) for a given system must be determined experimentally.

Also, as mentioned above, the blanketing inert fluid atmosphere in Embodiment II is a vapour and/or liquid and is derived from a liquid at least part of which has significantly penetrated into the polymer particles; thus when the interpenetrated liquid is water the inert blanket is provided by steam and/or water. Such an arrangement has the following additional advantages. Firstly, the vapour and/or compressed liquid provides a high pressure which provides a driving force for the extrusion. Secondly, the interpenetrated liquid (e.g. water) flashes off when the extrudate leaves the die rapidly cooling the extrudate through its entire thickness and fixing (i.e. "freezing in") the orientation even if the polymer molecules would otherwise tend to relax; this provides a highly oriented fibrillar extrudate and there is no need to haul off the product as in the case of Embodiment I to prevent relaxation (although hauling off can be carried out if desired and usually enhances the orientation of the product).

Thus the liquid associated with the polymer particles in Embodiment II performs four functions: - it provides an inert vapour and/or liquid atmosphere to inhibit or prevent degradation accordng to the invention, it is thought to act as an internal plasticiser to provide separated domains as discussed above, - it provides a driving force (as vapour and/or compressed liquid) for the extrusion, - it flashes off when the extrudate leaves the die leaving a highly oriented fibrillar stable product.

It is to be understood that the above discussed theories in connection with the process of our invention are not intended to be binding.

The contiguous polymer particles used in the process of the invention can vary in physical form; such forms include powder, granules, pellets, and unoriented amorphous fibrous material often of irregular shape and highly branched texture (fibrids).

As a general rule the smaller the partice size of the extrude feedstock the more uniform and coherent the product, the finer the constituent fibrils, and the better the mechanical and thermal properties of the product. The best products in terms of polymer properties are obtained by employing unoriented amorphous fibrous material for the extrusion.

The processability of the polyarylene-oxadiazoles in the present invention is not found to be dependent to any extent on molecular weight. This may seem surprising but is logical in the sense that the process is not one which entails the extrusion of a melt.

The extrusion apparatus employed in the process of the invention may be a conventional extruder employed for the extrusion of plastics materials. In its simplest form the extrusion apparatus may be a conventional ram extruder having a barrel (usually of circular cross-section) for holding a feedstock of the polymer particles and a suitable die. The die may optionally taper into the barrel (e.g. through a member of frusto conical cross-section) so that an entry angle is provided for the die.

The die orifice may be of any appropriate cross-section, e.g. circular, annular, or rectangular. The land length of the die is not critical, but as mentioned before the die diameter or gap should be appropriate to the sizes of the polymer particles being extruded, taking into account whether Embodiment I or Embodiment II is being employed. The force of the piston of the ram extruder during the extrusion may be such as to maintain a desired rate of volume displacement of extrudate.

The temperature range within which suitable extrusion can take place in the process of the invention will depend upon a number of things; it will, for example, depend upon the heat-softenability of the particular polymer being extruded, the ratio of the die size to the particle size, the required extrusion rate, whether or not Embodiment I or Embodiment II is being employed (Embodiment I generally requires a significantly higher polymer temperature for extrusion to occur than Embodiment I).

Generally speaking when using the particularly preferred copolymers of Formula A the temperature of the particles for acceptable extrusion may, other conditions being acceptable, be within the range 280-360 C and particularly within the range 300 340"C. However, as mentioned above, the optimum temperature range for the extrusion of any particular member of the preferred copolymers of Formula A will depend on very many parameters.

When the blanketing fluid atmosphere is derived from a liquid associated with the particles, the amount of liquid to employ in the process of the invention will depend inter alia upon the embodiment being employed, the particular liquid being used, the extrusion conditions, and the particular polymer being extruded. Taking the case where water is used to provide the blanketing inert fluid atmosphere: - in Embodiment I, an amount of water of at least 2% by weight on polymer is generally sufficient, preferably at least 5%. The upper limit for the water content is not critical since the water is merely acting as surface water; how ever the amount should not be so large that the particles would then be in the form of a dispersion. Normally the amount of water does not exceed 20% by volume and preferably does not exceed 10% by volume; - in Embodiment II where the water has significantly penetrated within the polymer particles, an amount of water of at least 10% by weight on polymer is generally required. The upper limit of the water content is not too critical, but it should not be too large, otherwise an explosive extrusion will occur giving a distorted extrudate. Generally speaking the upper limit should not be above 75% and preferably not above 45%. A typically acceptable range of internal water content in Embodiment II is from 1535% by weight on polymer, particularly 2030% by weight.

The product from the extruder as mentioned above is a paper-like tape, ribbon or sheet comprised of very stiff fibrils and usually of a somewhat porous nature. It has an attractive straw-like form which cannot be reproduced using a wet spinning technique. The extruded product may be used as such (if it is sufficiently coherent and smooth) for a variety of applications, e.g. slot-liners, non-woven sheet materials such as paper and the like. Alternatively if the product is not suitable for direct use (e.g. because it is too coarse and not coherent enough) it may be used as the basis of a feedstock for the production of paper in a conventional papermaking process.

The polyarvlene-oxadiazoles used in the present invention may be extruded in conjunction with other stiff fibre-forming polymers, e.g. polysuiphones, nylons, polycarbonates and polyesters. This enables a highly reinforced extrudate to be obtained.

The fibrous extrudate can also be used as a base within the interstices of which other monomers may be polymerised.

Accordingly there is further provided an extruded product which has been made using any one of the processes herein described according to the invention.

The present invention is now illustrated by a series of examples. The polymers used in the examples were brominated polyphenvlene-1,3,4-oxadiazole copolymers of Formula A having a ratio of R/R2 of 50/50 and bromine contents and inherent viscosities as indicated (inherent viscosity is defined as ln (17 rel)/C where C is the concentration, viz. 0.5 g of copolymer per 100 ml of solution, and n rel is the ratio of the flcw times of the copolymer solution and solvent as measured at 250C in a capillary viscometer; the solvent used is 9804 sulphuric acid).

The extruder employed in the examples was a simple ram extruder and unless otherwise specified comprised a cylindrical barrel of 10.6 mm diameter, a die having an orifice of circular section with a diameter of 2 mm and a land length of 6 mm, the die tapering to the barrel so as to form an entrv angle of 35". In most of the examples the piston was set to move at a fixed speed during extrusion and to deliver a rate of volume displacement Q = 78.5 X 10-9mJ/s.

On the basis of the Newtonian concept of shear, the shear rate at the die wall 4Q 7=- rr1 where r is the radius of the die so that ? = lOOs- If the extrudate is hauled off such that it retains the same diameter as the die, the linear velocity of extrusion Q V = - 25 mm/s. nrP In the following examples, Examples 1, 7-9, 11, 15, 21-23, and 27 are intended to be comparative and not according to the invention, while Examples 2-6, 10, 12-14, 16-20, 24-26 and 28-30 are according to the invention. Examples 1-4, 7 and 9 illustrate the technique of Embodiment I while Examples 5, 6, 10-22, and 24-29 illustrate the technique of Embodiment II. Example 23 illustrates a technique which is a combination of the techniques of Embodiments I and II.

Example 1.

A brominated polyphenylene- 1 ,3,4-oxadiazole copolymer was prepared as follows.

83.05 parts of terephthalic acid, 1418 parts of 24% oleum and 202 parts of 100% sulphuric acid were charged to a straight sided reaction flask equipped with a mechanical stirrer, reflux condenser and silica gel guard tube to keep out moisture.

The temperature of the flask and contents were raised to 900C by means of a thermostatically controlled oil bath and 0.25 parts of iodine were added to the mixture. 34.3 parts of bromine were then slowly dripped into the flask over 3 hours. Agitation was continued for a further 3.5 hours until all traces of bromine fumes had disappeared.

The flask and contents were allowed to cool overnight. Next day, 83.05 parts of isophthalic acid and 135.5 parts of hydrazin extrusion direction. These fibrils were essentially continuous, more than 10 mm long and had a flat ribbon-like cross-section 10 Item wide and about 1 Km thick for the finest fibrils. The fibrils were examined by wide angle X-ray scattering which showed the azimuthal breadth at half maximum intensity of the equatorial diffraction area to be about 200, indicating that the product was very highly oriented for an amorphous material.

Example 3.

The same procedure as for Example 2 was followed (using the same copolymer powder) except that heating was continued to a temperature of 350"C. The pressure required to maintain the extrusion was about 70 atmospheres compared to 200 atmospheres at 3400 C. However the extrudate was darker than the original sample suggesting slight degradation had occured. Otherwise the extrudate had the same properties as Example 2.

Example 4.

The same procedure as Example 3 was adopted (using the same copolymer powder) except that the output rate was reduced to 7.85 X lO-Pms/s (i.e. 1/10 that in the previous examples). The extrusion pressure and extrudate quality were similar to that at the higher output rate.

Examples 1 to 4 are intended to exemplify the technique of Embodiment I and show the importance of providing means to freeze in the orientation in this embodiment.

Example 5.

A brominated polyphenylene- 1,3 ,4-oxadiazole copolymer was prepared as follows: 83.05 parts of terephthalic acid, 834.1 parts of 23.8% oleum and 305.3 parts of 65.6% oleum were charged to the reaction apparatus described in Example 1. The flask and contents were heated to 92dC by means of a thermostatted oil bath. 0.25 parts of iodine were added and 34.3 parts of bromine dripped into the mixture over 3 hours. Stirring was continued at 920C for a further 2.5 hours until all traces of bromine fumes had disappeared. The flask and contents were then allowed to cool overnight. 83.05 parts of isophthalic acid and 135.5 parts of hydrazine sulphate (4.15% excess) were charged to the cold solution which was heated to 1400C over 1.5 hours. One hour after reaching this temperature, 431 parts of 23.8% oleum and 49 parts of 100% sulphuric acid were added to the reaction over a period of 20 minutes. The flask and contents were held at 140"C for a total of 3.5 hours. A sample of polymer isolated from the solution or dope had an IV of 1.79 dl.gr1 and contained 16.2% bromine. The dope contained about 9% by weight of the polymer.

The dope was discharged into water in the form of spherical granules about 8-10 mm in diameter. These granules were washed free of acid with water and dried in an air oven at 1400C for 2 hours until all but 10% of the water had been removed; at this stage the granules were about 5 mm in diameter. A sample was charged to the barrel of the ram extruder at 3000 C. After 3 minutes the sample began to extrude accompanied by flash evaporation of water from the extrudate. The piston was set to discharge the reservoir at a volume flow rate of 78.5 X 109m9/s and the pressure was 60-70 atmospheres (note that the vapour pressure of water at 300"C is 85 atmospheres). The extrudate was straw coloured, tough and distorted.

Haul off was not required to fiix the orientation-presumably the evaporation of the water cooled the polymer freezing in the orientation. The extrudate could be fibrillated with difficulty, there being much greater tenacity between the component fibrils than in the previous examples.

Example 6.

The procedure of Example 5 was followed (using the same copolymer granules) except that the granules were charged to the extruder at 1000C pressurised and then heated to determine the lowest temperature at which they would extrude. This lowest temperature was found to be 280"C and the extrusion pressure was 90 atmospheres.

Example 7.

Foamed polymer obtained by Example 6 (substantially free of water) was recharged to the extruder at 3000C. It would not extrude. The temperature was then raised to 350"C at which it would extrude but gave an inhomogeneous extrudate with a very poor colour, parts of which fibrillated readily. From the severe discolouration of parts of the extrudate substantial degradation was assumed to have taken place.

Example 8.

The granules used in Example 5 were crushed and then dried for 16 hours under vacuum at 600C until they were substantially free from water. This coarse powder would not extrude it at 3000C and it was only possible to extrude it at 360"C under a pressure of 100 atmospheres to give an extrudate similar to that described in Example 7.

Comparison of Examples 7 and 8 with Examples 5 and 6 show the important requirement of the presence of a blanketing inert fluid in the process of the invention.

Examples 5 and 1 are intended to exemplify Embodiments II and I of the present invention respectively.

Example 9.

The dried coarse powder used in Example 8 was stored for 5 days in water at 200C. This sample was then drained so that it contained about 10% of surface water and charged to the ram extruder at 3000 C; however it would not extrude. When the temperature was raised to 350"C an extrudate similar to that described in Example 7 was obtained. This example which uses the technique of Embodiment I, shows that the "plasticisation" effect of Embodiment II is due to water which is internally trapped within the polymer particles and not surface water. It also shows (compare Example 1) that if Embodiment I is employed then the particles must be quite small compared with the die size in order for acceptable extrusion to occur. Comparison of Example 9 with Examples 5 to 7 however show that by contrast the size of the particles for acceptable extrusion can be much larger when employing Embodiment II.

Example 10.

A brominated polyphenylene-1,3,4-oxadiazole copolvmer was prepared as follows.

124.6 parts of terephfhalic acid, 0.2 parts of iodine, 1491 parts of 23.8% oleum and 217 parts of 65.6% oleum were charged to a straight sided reaction flask as described previously. The flask and contents were heated to 900C using a thermostatically con trolled oil bath and 51.5 parts of bromine slowly dripped into the flask over 7 hours.

Stirring was continued for a further 5 hours until all traces of bromine fumes had disappeared. The flask and contents were then allowed to cool overnight. Next day, 124.6 parts of isophthalic acid and 204.9 parts hydrazine sulphate (5% excess) were added to the cold suspension which was then heated to 140"C in 1.5 hours. The contents were held at this temperature for 4 hours to produce a brown, viscous polymer solution. A sample of polymer isolated from this solution had an inherent viscosity of 1.07 dl.g=1 and contained 15.1% bromine.

Granules were prepared in the same way as described in Example 5. These granules were extruded in the same way as described in Example 5 to give a similar extrudate at a similar pressure. The IV of the extrudate was found to have dropped to 0.81, a reduction of about one quarter. This example suggests that the processability is not strongly dependent on molecular weight.

Examples 11 to 15.

Internally wetted granules of IV 1.07 prepared as described in Example 10 but containing about 75% by weight water were charged to the extruder at various tem peratures under a pressure of 500 atmospheres. After a certain time the polymer started to extrude and the ram was started to give a discharge rate of 78.5 X 10-9m.'/s. The extrusion conditions and results are shown in Table 1.

In Example 11 the extrusion temperature under these conditions was insufficient to provide an acceptable fibrillated product while the extrusion temperature in Example 15 was too high under these conditions since it gave an explosive extrudate which resulted in powder and degraded product being formed. Examples 12 to 14 suggest that the optimum temperature for extrusion under these conditions is in the range 320330 C.

Examples 16 to 23.

The same internally wetted granules as described in Examples 11 to 15 were dried to various extents and then extruded at about 330"C under the standard con ditions using the procedure outlined in Examples 11 to 15. The residual moisture in the samples was estimated by drying for 5 days under vacuum at 60"C. The results are shown in Table 2. In Examples 16 and 17 the high water content caused an explosive extrusion, but the extrudate was nevertheless not degraded and well fibril lated. Examples 18 and 19 suggest that the optimum level of water content under these extrusion conditions is 20-30%. In Examples 21 and 22, having water contents of 1% and ' < 1% respectively, the polymer was inadequately plasticised or blanketed from degradation. In Example 23 a 50/50 by weight mixture of the substantially dry polymer of Example 21 (1% water) and the internally wetted polymer of Example 16 (75% water) was employed. This extrudate showed less degradation than that of Example 16 illustrating that surface water can provide blanketing fluid to reduce degradation; however the extrudate was unsatisfactory since the polymer particles of Example 21 (about 5 mm diameter) were too large for the die and the surface water released from the internally wetted polymer of Example 16 was not able to internally wet the almost dry polymer of Example 21.

TABLE 1

Barrel set Time to start Extrusion Example temperature extrusion* pressure number ( C) (seconds) (atmospheres) Extrudate quality 11 284 400 300 Brittle: a mixture of powder and fibrils 12 300 240 70 Coarse fibrillar 13 323 200 70 Fine fibrils 14 328 180 70 Fine fibrils 15 360 150 80 Explosive extrusion Coarse fibrils and some powder; Evidence of degradation * During this time water is being driven off from the polymer and the temperature of the polymer is less than the set temperature. TABLE 2

Example Estimated number Drying procedure water content Extrudate quality 16 None 75% Explosive extrusion but fine fibrils, good colour 17 Dried at ambient 45% Excessive swelling, occasional humidity for 5 hours explosions, good colour, fine fibrils 18 Dried at ambient 30% No explosion, good colour, and humidity for 4 days fine fibrils 19 1 day under vac at 20% No explosion, good colour, and 600C fine fibrils 20 1 days under vac at 10% Irregular extrusion, a little 600C discolouration, fine fibrils 21 4 days under vac at 1% Poor extrusion, low degree of 600C fibrillation, significant discolouration 22 5 days under vac at < 1% Poor extrusion, low degree of 600C fibrillation, significant discolouration 23 50/50 (by wt of 75%-1% Low degree of fibrillation; polymer) mix of (or 38%) a little degradation completely dry and completely wet Examples 24 to 27.

The same granules as described in Example 10 but dried to a water content of 30% were extruded at 3200C through different dies varying in land length, entry angle or diameter as shown in Table 3.

TABLE 3

Die Die Example diameter Land Length entry angle number (mm) of die (mm) (degrees) 24 2 6 35 25 2 1 180 26 2 15 180 27 1 -3 180 There was no significant difference in the products made using any of the 2 mm diameter dies (they were all good) except that the longer die of 15 mm (Example 26) required a higher driving pressure of 150 atmospheres compared to 70 atmospheres for the other dies. It was not possible to extrude the granules through the 1 mm die (Example 27). This shows that under these extrusion conditions using Embodiment II the die land length and entry angle are not critical, whereas the die diameter although not very critical does have to be considered. In fact all the runs with internally wetted granules gave extrudates which suggested a memory of the original granule boundaries, and it could be argued that the granules were too large to pass through a 1 mm die.

The following experiments were carried out on smaller particle size fibrillated feedstock (Examples 28 and 29).

Examples 28 and 29.

A brominated polyphenylene-1,3,4-oxadiazole copolymer was prepared as follows.

83.05 parts of terephthalic acid, 83.05 parts of isophthalic acid, 132 parts of hydrazine sulphate (1.5% excess), 1386 parts of 24% oleum and 238 parts of 65.6% oleum were charged to the glass vessel already described. The flask and contents were then heated to 140"C over 1.5 hours and held at this temperature for 4 hours. A sample of polymer isolated from this solution had an inherent viscosity of 2.94. 782 parts of this solution were removed from the flask and placed in a similar flask. 3246 parts of 23.8% oleum and 1836 parts of 100% sulphuric acid were added to the flask which was then heated to 90"C using a thermostatted oil bath. The contents of the flask were stirred for 6 hours until homogeneous. The reaction system was then heated to 950C and 0.2 parts of iodine added. 19 parts of bromine were slowly dripped onto the solution over 3 hours. The agitation was continued for a further 2.5 hours. A sample of polymer isolated from this solution had an inherent viscosity of 2.11 dl.g=1 and contained 18.5% bromine. The polymer was precipitated from solution in oleum into water to give substantially unoriented fibrids swollen with water. The process for making these fibrids was as follows.

100 ml of a 1% (wt/wt) solution of the copolymer in oleum was poured over a period of 2 minutes into a 5 litre beaker containing 2 litres of cold water agitated by a Silverson homogeniser (Model L2R) fitted with a sieve and 16 cutting rings of 6 mm diameter and operated at maximum speed (the word "Silverson" is a registered Trade Mark). The centre of the rotating paddle was positioned about 40 mm below the level of the water. Homogenisation was continued for 10 minutes after completion of the addition of the copolvmer solution to give a uniform, fine fluffy dispersion which did not settle on standing. The slurry was filtered and washed free of acid with cold water and stored in a wet state. In some runs using this technique the resulting fibrids were reasonably distinct from each other, the product being non-lumpy; in other runs the resulting fibrids were present in the form of lumps. Example 28 was carried out with non-lumpy product while Example 29 was carried out with lumpy product The fibrids (in both examples) were dried until they contained about 30% of water. This drying was achieved in 1 hour under vacuum at 60"C--a much shorter period than was required for the granules of the preceding examples presumably because of their finer texture. Samples were charged (in separate experiments) to the extruder which was temperature controlled at 3300C and after 70 seconds began to extrude; the ram was then started as described in Example 11. (The die in this case was 22 diameter and 10 mm long). The pressure to maintain the extrusion was about 130 atmospheres for both samples and there was little difference in their appearance.

The extrudates were much more uniform in appearance than those obtained from granular material but gave similar fibrillation. The extrudates also had a better colour than those obtained from granules. By comparison with Example 18 it is to be noted that the time taken to start extrusion was very much shorter with the fibrid feedstock than with the granules and it may therefore be anticipated that the minimum extrusion temperature of the polymer was well below 3000C.

In Examples 28 and 29 (and in all other examples of water-assisted extrusion using Embodiment II) it was observed that the extrudate instantly solidified as it came out of the die and was quite cool to the touch. It was presumed that the volatilising of the water cooled the sample freezing in the orientation so that it was not necessary to haul off the extrudate in a manner discussed in Examples 2 and 3 (Embodiment I) to retain a high orientation. However if the extrudates were hauled off and drawn down the fibrillar structure was even more pronounced.

The extrudates formed from this free extrusion in both Examples 28 and 29 were 3 mm in diameter, had an IV of 1.56 and a density of 320 kg/ms (the density of the polymer itself was 1,540 kg/m3). The extrudates were examined by wide angle X-ray scattering which showed the azimuthal breadth at half maximum intensity of the equatorial diffraction area to be about 250. While fibrils similar to those described in Examples 2 and 3 could be teased from the extrudate, the extrudate did not automatically break up into fibrils when crushed, bent or twisted as was the case with Examples 2 and 3-indeed it gave a tough appearance. The extrudates were tested in an Instron tensile testing machine (the word "Instron" is a registered Trade Mark) which provided a rough measure of the moduli, for the foamed samples, at low strain of 2 GN/m2 and a rough measure of the "breaking" stresses, for the foamed samples of 65 MN/m2. The breaking of the extrudates occurred as a shearing failure rather than a simple tensile failure, and there was obviously deformation between the fibrils as well as along them. The inference of these results for the fully densified material is: Modulus - at least 10 GN/m3 "Breaking" Stress - at least 310 MN/ms Example 30.

The extrudate obtained in Example 28 was compressed flat at 250C to give a ribbon 5 mm wide, 0.5 mm thick with a density of 900 kg/cm3. This ribbon was tough and coherent both in a simple tensile mode and across the principle orientation direction. This example shows that the extruded foam-like product can easily be rolled into a tape or film product.

Claims

WHAT WE CLAIM IS:-

1. A process for the production of an oriented fibrillar product from a polyaryleneoxadiazole which is heat-softenable without substantial degradation when in an airexcluded inert atmosphere which process comprising extruding contiguously disposed particles of the polymer, which particles are heat-softened but non-molten and are blanketed in air-excluded atmosphere of an inert fluid, through a die to produce a substantially non-degraded oriented fibrillar product, means being provided if necessary to substantially prevent relaxation of the orientation resulting from the extrusion.

2. A process according to claim 1 wherein the polyarylene-oxadiazole used in the process is a copolymer having the characteristic repeating units

where Rl is a p-phenylene radical, R?. is a m-phenylene radical, the ratio of Rl radicals to R2 radicals is within the range 60/40 to 10/90, and the Rl and/or R2 radicals are sufficiently substituted with bulky groups to inhibit crystallisation of the polymer.

3. A process according to claim 2 wherein the bulky groups of the polyaryleneoxadiazole used in the process are bromine atoms, the minimum quantity of bromine in the polymer being 5% by weight of the polymer (Rl/R2 = 10/905 and the range of bromine content being 5%20% by weight of the polymer (R,/R, = 10/90 to 60/40).

4. A process according to any one of the preceding claims wherein the blanketing fluid is selected from steam, water, and a mixture of steam and water.

5. A process according to any one of the preceding claims wherein said particles are blanketed in an air-excluded atmosphere of an inert vapour and/or liquid during extrusion, which atmosphere has been derived from a liquid associated with the polymer particles which has not internally penetrated the polymer particles.

6. A process according to claim 5 wherein water is used to provide the blanketing inert atmosphere, the amount of water employed being at least 2% by weight on polymer.

7. A process according to any one of claims 1 to 4 wherein said particles are blanketed in an air-excluded atmosphere of an inert vapour and/or liquid which atmosphere has been derived from a liquid associated with the polymer particles at least part of which liquid has significantly interpenetrated the polymer particles.

8. A process according to claim 7 wherein water is used to provide the blanketing inert atmosphere, the amount of water employed being at least 10% by weight on polymer.

9. A process according to any one of the preceding claims wherein said polymer particles used in the process are in a form selected from powder. granules, pellets and unoriented amorphous fibrids, in an externally dry or wet cake state.

10. A process according to any one of the preceding claims wherein the extrusion temperature of said particles is within the range 280-3600C.

11. A process substantially as described herein with reference to any one of the Examples 2-6, 10, 12-14, 16-20, 24-26 and 28-30.

12. A substantially non-degraded oriented fibrillar product which has been made by a process which comprises extruding contiguously disposed particles of a polyarylene-oxadiazole which is heat-softenable without substantial degradation when in an air-excluded inert atmosphere, which particles are heat-softened but non-molten and are blanketed in an air-excluded atmosnhere of an inert fluid, through a die to produce said product, means being provided if necessary to substantially prevent relaxation of the orientation resulting from the extrusion.

13. A product according to claim 12 wherein the polyarylene-oxadiazole is a copolymer having the characteristic repeating units

where R1 is a p-phenvlene radical, R is a m-phenvlene radical, the ratio of Rl radicals to R? radicals is within the range 60/40 to 10/90. and the R, and/or R2 radicals are sufficiently substituted with bulky groups to inhibit crystallisation of the polymer

14. A product according to claim 13 wherein the bulky groups of the polyaryleneoxadiazole are bromine atoms, the minimum quantity of bromine in the polymer being 5% by weight of the polymer (R1/R2 = 10/90) and the range of bromine content being 5%-20% by weight of the polymer (R1/R = 10/90 to 60/40).

15. A product according to any one of claims 12 to 14 which has been made by a process in which said particles are blanketed in an air-excluded atmosphere of an inert vapour and/or liquid during extrusion, which atmosphere has been derived from a liquid associated with the polymer particles which has not internally penetrated the polymer particles.

16. A product according to any one of claims 12 to 14 which has been made by a process in which said particles are blanketed in an air-excluded atmosphere of an inert vapour and/or liquid which atmosphere has been derived from a liquid associated with the polymer particles at least part of which liquid has significantly interpenetrated the polymer particles.

17. A product according to any one of claims 12 to 16 which has been made by a process in which said polymer particles used in the process are in a form selected from powder, granules, pellets and unoriented amorphous fibrids.

18. A product according to any one of claims 12 to 17 which is in the form of a porous paper-like tape, ribbon or sheet comprised of bundles or bunches of stiff fibrids.

19. A product substantially as described herein with reference to any one of the Examples 2-6, 10, 12-14, 16-20, 24--26 and 28-30.