Fibrillated foamed textile products and method of making same

Abstract

A thermoplastic yarn is continuously produced from an extruded cellular foam material which has been oriented in the direction of extrusion by subjecting the oriented foamed material to forces which break down the cell walls to form a three-dimensional structure of interconnected fibre elements.

Parent Case Text

The present application is a continuation-in-part of application Ser. No. 468,269, filed June 30, 1965, by Samuel Baxter and John Harold Gilbert, now abandoned.

Description

This invention relates to textile yarns, and particularly to certain new yarns derived from polymeric materials.

It has been previously proposed to produce textile yarns from polymeric resins by a process in which a molten resin or a solution of the resin is extruded from a very small orifice and caused to solidify by one means or another; this produces a monofilament of the resin. A monofilament that is sufficiently thick and strong to be woven into cloth is, however, normally rather inflexible, and in order to improve the flexibility it is accordingly necessary to produce relatively fine monofilaments which are then used in conjunction to give the necessary strength. Sometimes for example the fine monofilaments are chopped up to form a staple fibre which is then spun.

A new kind of yarn has now been developed which possesses many of the attributes required of a yarn but which can nevertheless be produced directly by a process that avoids the necessity for the separate production of fine monofilaments.

The process of the invention for the production of the yarn comprises drawing a strand or ribbon of an extruded foamed thermoplastic material so that it becomes orientated essentially in the direction of extrusion and subjecting the drawn foamed material to forces such that the walls of the foam are broken down and converted into a three-dimensional structure of interconnected fibre elements.

The yarn obtained in this way can if desired be used as such, for example as a yarn in carpet production, because it is one of the features of the yarn produced by the process of the invention that the number of loose ends is small. The yarn can however optionally be subjected to a conventional type of spinning operation before use, in which instance it will have a certain amount of twist, although this may be only very slight. Higher degrees of twist can be applied if required, and for example a highly twisted yarn can be produced.

The invention also includes a new yarn that is a threedimensional structure of a multiplicity of interconnecting thermoplastic fibre elements, the fibre elements being aligned substantially in the direction of production of the yarn and some of them having cross-sections that are branched.

A yarn that has been twisted can for example be defined as a yarn comprising a three-dimensional structure of a multiplicity of interconnecting thermoplastic fibre elements arranged substantially as a series of helices having a common axis along the length of the yarn, some of the fibre elements having cross-sections that are branched.

Fibre elements are referred to and not fibres because in general the elements in question are essentially interconnecting in three-dimensions. Accordingly the number of loose "ends" in the yarn is normally low, and the yarn contains few "fibres" as such, that is to say fibres each of which has two ends.

FIG. 1 is a section view taken at right angles to the major axis of the fibre and showing the trilobate construction of a fibre element;

FIG. 2 is the section view of FIG. 1 showing the fibre element having a double trilobate construction;

FIG. 3 is an enlarged plan view of the yarn of this invention;

FIG. 4 is a section view of the yarn of FIG. 3 taken at right angles to the main axis of the yarn;

FIG. 5 is a front elevation view of the apparatus for breaking down the cell walls of the extruded cellular foam material to form the yarn of this invention; and

FIG. 6 is a side elevation view of the apparatus shown in FIG. 5.

Fibre elements that have a cross-section, at right angles to the major axis of the fibre element, that is branched are present in the yarn because the fibre elements are obtained from an orientated foamed thermoplastic material by the partial disintegration or break down of the walls of the cells or pores making up the foamed structure. The fibre elements accordingly consist of the remains of the cell walls, and because of this possess certain characteristic features as described below. Fibres that have cross-sections that are branched are derived from parts of the walls of several cells that were present in the original orientated foamed material, and the "branch" occurs where a fragment of the wall of one cell is joined to fragments of the wall of an adjoining cell or cells. In the simplest instance a branched cross-section of a fibre element can be termed "trilobate," because it consist of three lobes or arms, as is exemplified in the cross-sections shown in FIG. I, which are taken at right angles to the major axis of the fibre elements. Related but more complicated branched cross-sections can consist of two or more trilobate crosssections joined together, as for example shown in FIG. II. Crosssections such as are for example exemplified in FIGS. I and II are those which can exist at one point along the major axis of a fibre element, and a fibre element does not necessarily possess constant cross-section along its length. Not only does the cross-section usually change along the length of a fibre element, but the fibre element itself is not straight and parallel to the yarn as a whole. Accordingly a series of cross-sections across a yarn taken at right angles to the direction of production of the yarn will show the crosssection of a given fibre element in a number of different forms.

In a typical cross-section of a yarn the number of crosssections of fibre elements which are branched may be a minority, such as 30 or 40% or less, but nonetheless their presence (even to the extent of from only 5 to 10% of the total) contributes a distinctive character to the yarn. In certain instances the proportion of branched cross-sections can be high (such as 60 or 70%), but in many cases it will for example be in the range of 5 to 50%, for instance from 10 to 40%, such as about 20%.

Because of the way in which they have been formed the fibre elements are in the main "elongated" in cross-section. Very often a cross-section of a fibre element contains at least one pair of substantially parallel sides, although at least in the instance of the fibre elements having a branched cross-section these parallel sides will usually be curved. Other cross-sections may be polygonal, for example quadrilateral, and can be rectangular or essentially rectangular; more than four sides can however be present. In considering a cross-section of a fibre element the longer (or longest) dimension is taken as the breadth and the smaller (or smallest) dimension is taken as the thickness. In general terms the elongated cross-sections can have a breadth to thickness ratio of from 3 to 1 to 20 to 1 or even more, such as for example 30 to 1. A proportion, for example up to 50% of the total, of the cross-sections can be compact, for example essentially square; often the number of compact cross-sections is small.

A further characteristic of the fibre elements of the yarns of the invention can be expressed as their surface area in square metres per gram. This can for example range from 0.04 to 1.5, particularly from 0.05 to 1.0. Useful yarns may for example contain fibre elements having a surface area of between 0.1 to 0.5, such as, for instance, about 0.2 or 0.3. In certain instances the surface area can be higher, such as up to about 2.0 square metres per gram. The surface areas can be controlled by operation of the process of production of the yarns, for instance a higher density foamed material normally results in a yarn having a lower surface area.

The thickness of the fibre elements is often in the range of from 0.0001 to 0.004 or 0.005, for example, between 0.0002 and 0.003 inch; it can, for instance, be between 0.0004 and 0.002 inch, such as about 0.0006 or about 0.001 inch.

The average distance between points of interconnection as referred to above can be for example from 5 or 10 to 750 times the average thickness of the fibre element or slightly more, for instance up to 1,000 times the average thickness. For example, useful yarns are obtained when the average distances between points of interconnection of fibre elements are from 20 to 500 times the average fibre element thickness, such as from 50 to 300 times. A distance of about 100 or 200 times the average thickness of the major fibre elements is often characteristic. In absolute terms the distance between points of interconnection is often in the range of 0.01 to 0.5 inch, such as from 0.02 to 0.3 inch, for instance, from 0.05 to 0.1 or 0.2 inch.

The yarns can be produced continuously and they can in any event be obtained in any length convenient for the intended purpose. Their cross-sections are those usual for yarns, and are normally compact. In special instances, for example where the yarn is to be subsequently twisted, the yarn cross-section can be more elongated, for instance it can be an elongated rectangle, and the yarn then can be in the form of a ribbon or strip, normally a narrow one. Such a ribbon or strip might for example be up to one-fourth inch wide. Where the yarn has the more normal compact cross-section this can be a circular or similar cross-section and can vary within wide limits; in general it will be at least 0.005 inch and can for instance be from 0.01 to 0.15 inch or more, such as from 0.02 to 0.05 or 0.1 inch. Thicker yarns can have a diameter up to perhaps 0.25 inch. Yarns having diameters in the upper part of this range are useful in the production of certain coarse fibre or yarn products. In terms of denier, that is to say the weight in grams of 900 meters of yarn, the yarns of the invention can for instance have values in the range of 15 to 25,000 , for example in the range of 100 to 1,000, such as 200 to 500.

Where the yarn has been twisted, the common axis of the helices is normally coincident with the axis of the yarn, and the helices can for example have between 1/2 or 1 and 25 turns per inch, for example from 2 to 12 turns per inch (such as from 4 or 6 to 10 turns per inch). The twisted yarns have a cross-section that is substantially circular. A yarn having a low degree of twist is in general softer than one where the degree of twist is high.

If the yarn of the invention is to be twisted this can be carried out in any convenient way, and it can be performed as the extruded material is partially disintegrated or as a separate operation. In some instances the two procedures can be combined together in a single step. One yarn can be twisted to give a oneply twisted yarn, or two or three or more yarns can be produced and twisted together to give yarns consisting of several plies. The twisted yarns can if necessary be heat-set or wound under tension as in the conventional practice.

The process of the invention also includes a modification in which the yarns are produced by cutting or dividing up a band or web of the appropriate three-dimensional structure of interconnected fibre elements. In this modification the drawn foamed material will of course have a cross-section that is greater than that of the desired yarn, the drawn material is broken down and converted into a three-dimensional structure of interconnected fibre elements, and this structure is divided up longitudinally into a number of yarns having the required cross-sections. Yarns produced in this way can for example usefully be twisted together as described in the preceding paragraph.

Some indication of the nature of the yarns of the invention is given by the accompanying Drawings, where:

FIG. 3 -- shows a magnified (.times. 120) representation of the plan view of a yarn, and

FIG. 4 -- shows a magnified (.times. 200) view of a portion only of the same yarn along a cross-section taken at right angles to the direction of extrusion.

It can be seen from FIG. 3 that a large number of interconnections are present, and that in relation to the average thickness of the fibre elements, the interconnections are relatively close together. The portions of fibre elements which in FIG. 3 appear as ends were not necessarily in that state in the yarn. Some of the ends were formed when the small portion of material was broken away from the yarn for examination, whilst others are not in fact loose ends at all; they are portions of fibre elements which are curved and whose remaining portions are aligned either directly towards or directly away from the field of view. In FIG. 3 the distances between many of the major points of interconnections are about 0.01 inch. FIG. 4 shows the presence of cross-sections (about 20% of the total) that are "branched".

In general the new yarns of the invention have excellent flexibility, and are capable of being woven into cloth and textile materials, and of being converted into fibre and yarn products, for instance nets, ropes and twines. The strength in the direction of production is good, and as has been made clear virtually all the fibre elements are interconnecting throughout the three-dimensional structure of the yarn. The fibre elements are aligned substantially in a similar direction, but this does not of course mean that they are all aligned in precisely the same direction. The general appearance of a yarn as produced by the process of the invention is that it contains fibre elements which are substantially parallel, as they might be for example in a yarn having an essentially net-like form. In practice this means that the fibre elements are aligned substantially in the direction of production of the yarn. In general the yarns are attractive in appearance; for example they often possess a sheen on the surface.

The thermoplastic material from which the yarn is derived is one capable of being formed into an extruded foam; it is in practice usually a synthetic material, and one that is fibre-forming. Excellent results are obtained with a thermoplastic synthetic material, for example a polymer or copolymer obtained by polymerisation (which includes copolymerisation) of an ethylenically unsaturated monomer. Such a monomer can be an ethylenically unsaturated hydrocarbon, but it can be for instance a nitrile, such as acrylonitrile, or methacrylonitrile; vinyl or vinylidene chloride; a vinyl ester, such as vinyl acetate; or an acrylate ester, such as ethyl acrylate or methyl methacrylate. Where the monomer is a hydrocarbon this can be a mono-olefin, a diene, or a vinyl-substituted benzene, for instance ethylene, propylene, a butylene, a pentene or a hexene; butadiene; or a vinyl-substituted benzene, such as styrene or .alpha.-methylstyrene. For example the polymer can be polyethylene (low density or high density material), crystalline polypropylene, or polystyrene or a toughened polystyrene. A copolymer can be, for instance, one involving two or more, such as three, of any of the monomers referred to above. A comonomer can be, for instance, one of a type which will impart a degree of flame-retardance to the copolymer, and an example of such a substance is a vinyl halide, such as vinyl chloride, vinyl bromide or vinylidene chloride. Examples of other comonomers are vinylpyrollidone and a vinylpyridine such as methylvinylpyridine. A copolymer can be for example one derived from two hydrocarbon monomers, such as an ethylene-propylene or a styrenebutadiene copolymer; or a hydrocarbon and a different type of monomer, such as an ethylenevinyl acetate copolymer; or a copolymer derived from dissimilar monomers such as for example acrylonitrile and a minor proportion of vinyl acetate. The thermoplastic material can also consist of a mixture of two or more polymers or copolymers; it can for example comprise a mixture of a copolymer of acrylonitrile with a minor amount of vinyl acetate, for instance, about 10% by weight, and polyvinyl chloride; or a mixture of an acrylonitrile-vinyl acetate copolymer and a copolymer of acrylonitrile with methylvinylpyridine. Preferably the polymer is a thermoplastic resin material, but it can be an elastomeric material, for instance a copolymer derived from sufficient of a diene monomer, such as butadiene, to impart some degree of elastomeric properties to the copolymer; natural rubber; or a synthetic rubber such as for instance a polybutadiene, styrene-butadiene or acrylonitrilebutadiene rubber. A thermoplastic resin material can be non-crystalline, as in amorphous polystyrene, or crystalline, as in crystalline polyethylene or polypropylene. Other types of synthetic materials that can be employed include polyamides, such as for example nylon 11, nylon 610 and nylon 66; polyurethanes; polylactams, such as a polycaprolactam; and polyesters, such as of the polyethylene terephthalate type. Where the thermoplastic material is regenerated natural fibre it is preferably one based on cellulose, for example rayon, cellulose acetate, cellulose triacetate or cellulose acetate-butyrate.

In the process of the invention the starting material is an extruded foamed polymeric material, and if desired this can be produced by conventional extrusion techniques. However it is produced the extruded strand or ribbon of foamed material has a cross-section consistent with the ultimate aim of producing a yarn. The extruded strand, which includes a rod or ribbon, can be of virtually any relatively compact cross-section, but often the cross-section is circular or substantially circular, although it can also be square or rectangular. Where the yarn is for example to be twisted it can if desired have a less compact cross-section, and hence the extruded foamed material can (although this is not essential) have a cross-section that is a more elongated rectangle or similar shape, and the extruded material can then be a ribbon or strip, although a relatively narrow one. If desired, a suitable strand or ribbon can be obtained by slitting longitudinally a sheet or board of a drawn extruded foamed material. In general, and by way of example, where the extruded strand has a circular or roughly circular cross-section the average diameter can be between 0.1 and 1 inch for instance between 0.2 to 0.5 inch. The density of the foamed material can for instance be between 1 pound and 10 pounds or more per cubic foot, such as from about 2 to 4 or 5 pounds per cubic foot. The fact that the starting material is foamed can also be expressed in terms of the volume fraction of voids that it contains, and this can be as low as 0.5. However, in practice the volume fraction of voids is often not less than 0.9, so that the range can for instance be from 0.95 to 0.985, for instance from 0.96 or 0.97 to 0.98. A volume fraction of voids of 0.5 is equal to a ratio of the volume of foam over the volume of thermoplastic material it contains of two to one.

In general in the production of the extruded foamed thermoplastic material the blowing agent will be a low boiling substance or a chemical blowing agent. The foamed material usually contains closed cells, although material (for instance polyethylene) can be employed which contains cells which to some extent are interconnecting or "open". In many instances the agent is a volatile substance, and is often one that is a gas or vapour under normal atmospheric conditions (such as 20.degree.C. and 1 atmosphere pressure), but which while under pressure before extrusion will be present in solution in the molten or semi-molten thermoplastic material. The blowing agent can however be one, such as pentane or a pentane fraction, which is a volatile liquid under normal conditions. Examples of volatile substances that can be used include lower aliphatic hydrocarbons, such as methane, ethane, ethylene, propane, a butane, or a pentane; low alkyl halides, such as methyl chloride, trichloromethane or 1,2-dichlorotetrafluorethane; acetone; and inorganic gases, such as carbon dioxide or nitrogen. The lower aliphatic hydrocarbons, especially butane, are useful in respect of polyolefinic materials, such as polystyrene and polyethylene. The blowing agent can also be a chemical blowing agent, which can for example be a bicarbonate such as for example sodium bicarbonate or ammonium bicarbonate, or an organic nitrogen compound that yields nitrogen on heating, such as for example dinitrosopentamethylenediamine or barium azodicarboxylate. From 3 to 30%, especially 7 to 20%, by weight based on the weight of the thermoplastic material is often a suitable proportion of blowing agent, and for example the use of from 7 to 15% by weight of butane in conjunction with a polyolefinic material has given excellent results. Sometimes the blowing agent will be employed in conjunction with a nucleating agent, which assists in the formation of a large number of small cells. A wide range of nucleating agents can be employed, including finely-divided inert solids such as for example silica or alumina, perhaps in conjunction with zinc stearate, or small quantities of a substance that decomposes at the extrusion temperature to give a gas can be used. An example of the latter class of nucleating agents is sodium bicarbonate, used if desired in conjunction with a weak acid such as for example tartaric acid or citric acid. A small proportion of the nucleating agent, for example up to 5% by weight of the thermoplastic material, is usually effective. A plasticiser can also be present where this is appropriate.

The drawing operation is preferably conducted on a continuous basis (although this is not essential), and the step of breaking down the foam may follow immediately or it may be carried out subsequently, for instance on discrete lengths of drawn foamed material. The extruded foamed thermoplastic material is drawn along the extrusion direction, and in doing so it is orientated unidirectionally (uniaxially) and the cells of the foam are elongated. The drawn material usually has a slightly higher density than the material before drawing. The precise conditions that are necessary in the drawing operation to achieve the required results depend on the particular thermoplastic material that is employed, but in general draw-down ratios of from 20:1 to 2:1 have been found useful, for example from 15:1 to 3:1. Good results have been obtained with a ratio between 12:1 and 5:1, for instance from 10:1 to 7:1. The temperature employed again depends on the particular thermoplastic material, but it is an elevated one in most instances, for example above 40.degree.C. or 50.degree.C. and up to 130.degree.C. or 140.degree.C. or rather more in some cases. A temperature in the range of 80.degree.C. to 100.degree.C. such as about 90.degree.C., is often useful. In principle it is desirable for the foamed material to be heated to a moderately elevated temperature, not high enough to damage the foam structure but high enough for the material to be sufficiently ductile. For instance, extruded foamed styrene can be drawn at from 120.degree.C. to 140.degree.C., while for foamed high density polyethylene a temperature between 40.degree.C. and 100.degree.C. is preferable. An amorphous thermoplastic material should normally be drawn above its glass transition temperature, whilst a crystalline thermoplastic material can be drawn at a temperature lower than its crystalline melting point. If the foamed material is still hot from the extrusion operation it may need to be cooled before it is possible to draw it in a subsequent operation, but in the more normal course of events a foamed material needs to be heated to a suitable temperature before it can be drawn, because for example even in a continuous operation the temperature of the foamed material can have dropped too low by the time it is possible to draw it. The heat treatment that is applied is as has been explained such that the extruded foam is sufficiently ductile to be drawn, and this can involve for instance either heating the foamed material at a steady temperature, or subjecting it to a relatively high temperature (perhaps as high as 200.degree.C.) for a short time followed by a period (normally longer) at a lower temperature. For example a foamed material that is produced in a form which has an outer "skin" of material (which has a higher density than the inner material) may give better results with a heat treatment which involves a short initial period at a higher temperature. This initial treatment can be useful in the instance of a thermoplastic material such as crystalline polypropylene, and can be as short as a few seconds. The precise conditions necessary in order to ensure that a foamed material is in a condition suitable for drawing can easily be found by simple experiments. In general any convenient method of applying heat can be employed. For example the extruded foamed material can passed through hot air or some inert gas, or through a heated bath of suitable inert liquid, such as water, glycerol or ethylene glycol. In certain instances the drawing can be performed at room temperatures, for example with nylon materials.

After the foamed thermoplastic material has been drawn it is partially disintegrated to the yarn, i.e. it is broken down into the three-dimensional network of interconnected fibre elements. In this operation the walls of the elongated cells of thermoplastic material are broken down or "fibrillated" to give fibre elements. The solid three-point connections at the ends of the cells are in some instances the junction points of a number of interconnecting fibre elements. The disintegration can for example be effected by mechanically working the drawn material so that some shear is applied to it, preferably in a transverse direction, and several ways of doing this can be employed, including rubbing, rolling, twisting, shaking, beating or otherwise subjecting the material to forces tending to draw it laterally at right angles to the direction of orientation. For example there can be employed a reciprocating "nip" in conjunction with an adjacent stationary nip, as is described later. Other methods can entail use of two cylindrical brushes, one stationary and one revolving; a hammer mill; and moving rubber surfaces, in the form of plates, belts or rolls. Ultrasonic vibrations can also be used, or suitable directed jets of air. In general in the instance of thermoplastic resins the temperature at which the partial disintegration is carried out is room temperature, 20.degree.C., or somewhat higher perhaps up to 30.degree.C. In the instance of certain specific thermoplastic resins, particularly those which possess a degree of elasticity and are therefore relatively tough, and of elastomeric materials in general, the temperature used is normally lower then room temperature, for instance 5.degree.C. or 0.degree.C. or even lower.

The reciprocating and stationary nips referred to above can in practice for example consist of two pairs (1 and 2) of metal bars as shown in end elevation in FIG. 5 an in side elevation in FIG. 6. The bars 1 and 2 are of square cross-section, with radiused edges, and each pair consists of two similar bars mounted vertically above each other. The bars in each pair are maintained lightly in contact by means of the spring-loaded guides 3. The left hand pair of bars 1 are stationary, and are maintained in contact with the bars 2 by the action of a leaf spring 4. Supporting means (not shown) are provided for supporting the assembly of bars. The bars 2 are moved reciprocally up and down by the freely-moving vertical plunger 5, which is driven by a circular eccentric 6 on the shaft of an electric motor (not shown). The drawn foamed material moves through the bars from right to left, by means of the pair of driven rollers 7.

The three-dimensional network of fibre elements as obtained by breaking down the drawn foam can be disintegrated to a greater or lesser extent, to give yarns which are potentially more or less voluminous respectively. The yarns as produced can if desired to "teazed out" to give bulkier and lighter-weight products, and this operation can be carried out by conventional textile means, for instance mechanically, such as by corrugated rollers, or by use for example of air jets.

In certain of the yarns some of the fibre elements may be present as "bundles," with some of the component fibres being interconnected to the fibres of adjacent bundles. The bundles occur particularly where the yarn has been produced using only a low degree of disintegration of the drawn extruded foam.

Additional operations, for example dyeing or sizing, can be carried out on a yarn of the invention if desired.

The invention is illustrated by the following Examples.

EXAMPLE 1

This Example described a new high density polyethylene yarn of the invention and a process for its production.

The starting material was a strand, or rod, of foamed high density polyethylene having a circular cross-section of diameter 0.4 inch, which had been produced by extrusion, through an orifice die 0.1 inch in diameter and of "land" 0.3 inch, of a foamable polyethylene composition containing 100 parts by weight of a high density polyethylene of density 0.96 grams per cc., 12 parts by weight of butane as blowing agent, and 1 part of finely-divided silica as a nucleating agent. The foamed strand was passed through an ethylene glycol bath at about 110.degree.C. and whilst at this temperature was drawn in the longitudinal direction to approximately 10 times its original length; this caused orientation in a longitudinal direction of the cells of the foamed polyethylene. The drawn material was allowed to cool to room temperature, and was subjected to a shearing action from the reciprocating motion of a nip (of the type described above and shown in FIGS. 5 and 6) through which the orientated foamed polyethylene was passed. This procedure resulted in the yarn of the invention.

The bars 1 and 2 of the nip assembly were of polished aluminium, and each was 4 inches long with a cross-section of one-fourth inch by one-fourth inch. The speed of the electric motor was 1,400 revolutions per minute, and the vertical movement of the bars 2 was one-half inch. The foamed drawn thermoplastic material was passed through the nip assembly at a linear rate of 2 feet per minute.

This yarn was very flexible and possessed a useful tensile strength; it could be employed as a twine or made use of as a yarn in weaving a cloth. The yarn consisted of a mass of high density polyethylene fibres that were interconnected in three dimensions at a large number of points. The fibres were substantially parallel to the length of the yarn (although there were many "bridging" or interconnecting fibres that were not parallel to the main body of fibres), and there were very few unconnected or "loose" ends of fibre. The fibre elements had on average a mean thickness of about 0.001 inch, and their appearance was substantially as shown in FIGS. 3 and 4. The average surface area of the fibre elements was 0.35 square metres per gram.

A sample of the yarn was twisted to the extent of 10 turns per inch to give a twisted yarn with an average diameter of 0.06 inch; again it was flexible with an excellent tensile strength.

A further sample of the yarn as produced was twisted to the extent of 4 turns per inch, and then three lengths of this were twisted together to the extent of 6 turns per inch. The resulting product was doubled and twisted again to the extent of 6 turns per inch. The denier of this 2 .times. 3 ply yarn was 4,600, and its tensile strength was 1.2 gram per denier.

Using as starting material a foamed strand of diameter 0.07 inch, the other conditions being similar, there was produced a finer yarn. In twisted form this had an average diameter of 0.01 inch.

EXAMPLE 2

This Example describes a new yarn obtained from crystalline polypropylene, having a melt index of 0.3.

Extruded foamed polypropylene was obtained by extrusion of a mixture of the polypropylene and 12% by weight of butane. A 1 inch extruder was employed, with a circular aperture of diameter five sixty-fourths inch, the land being one-half inch long. The extrusion temperature was 140.degree.C. and the die pressure 1,000 pounds per square inch. The resulting foamed polypropylene consisted of a rod of material about one-half inch in diameter having a density of 1.28 pound per cubic foot; the material was fairly flexible, with a silvery skin.

The foamed material was heated by passing it through a zone fitted with electric heaters; the heat treatment was for 15 seconds at 250.degree.C. The temperature was then allowed to fall to 90.degree.C., and at this temperature the material was drawn at a rate of 7,000% per minute to give an elongation of 1,300%.

The extruded drawn material was cooled to room temperature and then passed through the reciprocating nip referred to in Example 1. There resulted in a length of very flexible yarn having a thickness of about 0.08 inch, and consisting of a mass of interconnected fibre elements having a few loose ends. The surface area of the yarn was 0.26 square metres per gram. As produced the yarn possessed a useful tensile strength, of 4 - 5 pounds at 90.degree.C. and 10,000% per minute rate of elongation. The thickness of the fibre elements varied between 0.0008 and 0.006 inch and the breadth between 0.0076 and 0.112 inch. The tensile strength could be increased by twisting the yarn, for instance in the range of 1/4 to 10 turns per inch.

Three lengths of the yarn as produced were each twisted to the extent of 4 turns per inch and then twisted together to the extent of 6 turns per inch. The resulting 3 ply yarn had a denier of 8,150 and a tensile strength of 1.9 per denier.

EXAMPLE 3

This Example describes a yarn of the invention produced from polystyrene.

The starting material was a long rod of foamed polystyrene which had been produced by extrusion through a circular die of a foamable polystyrene composition containing a butane blowing agent and finely-divided silica as a nucleating agent. The rod of foamed polystyrene, which was one-half inch thick and had a density of 2 pounds per cubic foot, was passed through a bath of glycerol at 130.degree.C. and whilst at this temperature was drawn to 6 times its original length. This caused orientation in a longitudinal direction of the cells of the foamed polystyrene, which was now about 0.1 inch in diameter.

The drawn foamed material was cooled to room temperature and passed through the reciprocating nip referred to in Example 1. The resulting yarn possessed an attractive white "satiny" sheen and it was very flexible. It consisted of a mass of polystyrene fibre elements that were interconnected in three dimensions at a large number of points. The fibre elements were substantially parallel to the direction of extrusion, although there were many "bridging" or interconnecting fibre elements that were not parallel to the main body, and there were very few loose ends.

An increase in tensile strength was achieved by twisting the yarn to the extent of 10 turns per inch.

Similar polystyrene yarns were obtained from a web 0.1 inch thick of the interconnected fibre elements, which had been produced by drawing a sheet of extruded foamed polystyrene and then breaking down the walls of the foam. The web was cut longitudinally into narrow ribbons each one-fourth inch wide, three of which could be twisted together to give a yarn.

EXAMPLE 4

This Example describes a new fibre assembly obtained from a nylon, which was a copolymer type having a low melting point (160.degree.C.) and known as a 6, 6:6 and 6:10 copolymer; it was sold under the trade-mark Maranyl DA. This nylon copolymer comprised an interpolyamide of caprolactam, hexamethylene adipamide and hexamethylene sebacamide.

Foamed material was obtained by extruding a mixture of the nylon, 5% by weight of acetone and 2% by weight of finely-divided silica through a circular die of diameter 3/32 inch, using a 11/2 inch extruder; the die temperature was 131.degree.C. and the pressure 1,200 pounds per square inch. The cooled extruded foamed strand had a diameter of about one-fourth inch.

The foamed strand was heated to a temperature of 60.degree.C. in a hot air oven, and then was drawn to over 1000% at 1000 - 10,000% per minute rate of elongation.

The surfaces of the drawn extruded strand were moistened with ethyl alcohol, and then passed through the mechanical nip described in Example 1 to give a length of yarn having a three-dimensional structure of interconnected nylon fibre elements.

Claims

What is claimed is:

1. An extruded thermoplastic yarn comprising a network of randomly interconnected fibre elements generally residing longitudinally with respect to the direction of extrusion, said fibre elements being branched and being interconnected by having common branches and at least portions of said fibre elements having a trilobate construction in cross-section with respect to the direction of extrusion said branched fibre elements and said trilobate construction being formed by the breaking down of an extruded and drawn cellular foam rod-shaped material, said rod shaped material being drawn in the direction of extrusion.

2. The yarn of claim 1 wherein said yarn is provided with from 1 to 25 twists per inch.

3. The yarn of claim 2 wherein said yarn has a diameter of from 0.005 to 0.15 inches.

4. The yarn of claim 1 wherein a cross-section taken at right angles to the axis of said yarn shows from 10 to 40% of said fibre elements being branched.

5. The yarn of claim 4 wherein said fibre elements have a surface area of between 0.05 and 1.5 square meters per gram.

6. The yarn of claim 5 wherein the average distance between points of interconnection between the fiber elements is from 10 to 740 times greater than the average thickness of the fibre elements.

7. The yarn of claim 6 wherein the fibre elements are composed of a thermoplastic material which is a synthetic polymer selected from the group consisting of a polyamide, a polyester and a polylactam.

8. The yarn of claim 6 wherein the fibre elements are composed of polyethylene.

9. The yarn of claim 6 wherein the fibre elements are composed of polypropylene.

10. The yarn of claim 6 wherein the fibre elements are composed of polystyrene.

11. The yarn of claim 6 wherein the fibre elements are composed of a copolymer of acrylonitrile and vinyl acetate.

12. A fabric woven from the yarn of claim 1.

13. A cord comprising a plurality of twisted yarn of claim 1.

14. A foamed, thermoplastic yarn structure comprising a plurality of spaced apart, longitudinally extending fiber elements integrally joined to one another by a plurality of spaced apart, cross fibers to produce an integral net-like structure, the fibers of said structure being characterized by internal voids throughout the fibers, surface unevenness, and surface pits.

15. A foamed, thermoplastic structure comprising a plurality of spaced apart, longitudinally extending fiber elements integrally joined to one another by a plurality of spaced apart, crossed fibers to produce an integral net-like structure, the fibers of said structure being characterized by internal voids throughout the fibers, surface unevenness, and surface pits.

16. A process for manufacturing a fibrous product comprising the steps of:

a. forming a cellular thermoplastic structure with the cells having been formed by the expansion of a blowing agent;

b. drawing said cellular thermoplastic structure at a ratio of at least about 3:1 to orient said structure and increase its longitudinal strength relative its transverse strength; and

c. forming a network of spaced apart and interconnected fiber elements generally being aligned in the direction of drawing, said fiber elements being branched and being interconnected by having common branches, by subjecting said structure to fibrillating forces such that the walls defining said cells are broken down and are converted into said network of interconnected fiber elements.