WO1991006410A1

WO1991006410A1 - Composite material

Info

Publication number: WO1991006410A1
Application number: PCT/FI1990/000257
Authority: WO
Inventors: Pertti Törmälä; Timo Pohjonen; Pentti JÄRVELÄ; Tomi Tehomaa; Markku Tamminmäki; Juha Laiho
Original assignee: Biocon Oy
Priority date: 1989-10-31
Filing date: 1990-10-29
Publication date: 1991-05-16
Also published as: FI895172A0; AU6537990A

Abstract

The invention relates to a composite material manufactured from at least a non-thermotropic, thermoplastic, at least partly crystallizable polymer, copolymer or polymer blend. The composite material contains so-called self-reinforced structure especially for achieving the strength properties, the self-reinforced structure containing (a) binding material and (b) strengthening structure units. Said components (a) and (b) have the same chemical element composition. The composite material of this invention is in a particulate state, into which state it has been reduced, after manufacturing of the composite material, in at least one stage where a larger piece of the composite material is reduced to particulate pieces. The particulate composite material is aimed to be used as a manufacturing material for pieces to be manufactured especially by melt moulding techniques.

Description

COMPOSITE MATERIAL

The invention relates particularly to a composite material which is more closely described in the ingress part of claim 1.

Thermoplastic i.e. polymers that can be processed by melt moulding techniques can be classified into thermotropics and non-thermotropics.

Non-thermotropic thermoplastic polymers form at temperatures above their melting points amorphous, disordered melts (see e.g. P. Tδrmala, P. Jarvela and J.J. Lindbergh: "Polymeeritiede ja muoviteknologia, Osa II" (Polymer Science and Plastics Technology, Part II) , Otakustantamo, Espoo, 1983) . Polymers forming this kind of systems are e.g. so-called mass-production polymers, technical polymers and special polymers, their alloys or blends, like e.g. polyacetal (homo- polymers and copolymers) , polyacrylonitrile, cellulose acetate, polychlorotrifluoroethylene, fluorinated ethylene-propylene, polyvinyldenfluoride, polyamide 66, polyamide 610, polyamide 612, polybutylene, polybutylene terephtalate, polytehylene terephtalate, LDPE, HDPE, ethylene vinyl acetate, polyphenylene sulfide, polypropylene, PVDC-copolymers andabsorbable, partly crystalline thermoplastic polymers or polymer blends which have been presented e.g. in the patent publication FI 885983P by P. Tδrmala, M. Tamminmaki, S. Vainionpaa, P. Rokkanen and J. Laiho.

Thermotropic polymers (or polymer blends) form so- called liquid crystal structures at temperatures immediately above the melting point. In a thermotropic liquid crystal melt, polymer molecules or parts of them form ordered domains. Molecular ordering can be observed on the basis of optical anisotropy or Theolo¬ gical properties (see e.g. . Helfrich and G. Heppke, Liquid Crystals of One- and Two-Dimensional Order, Springer, Berlin, 1980 or A. Ciferri, . R. Krigbaum and R. B. Meyer, Polymer Liquid Crystals, Academic Press, New York, 1982) . A typical feature of the thermotropic liquid crystal polymers is the rigid structure of the polymer chains, which is usually achieved by cyclic like aromatic structure units (see above Ciferri et. al. or M. Gordon and N. A. Plate, Liquid Crystal Polymers II/III, Springer, Berlin, 1984) . Vast majority of the thermotropic polymers belong to polyesters but thermotropic polymers have been developed which belong to other chemical classes. From the natural polymers, melts of e.g. the bentzoyl, propionyl, acetohydroxopropyl derivatives of cellulose show a liquid crystal behaviour (see e.g. J. L. White and S. Onogi, U.S.-Japan Seminar on Polymer Liquid Crystals, John Wiley & Sons, New York, 1985) .

It is well known in polymer technology to use fibrous reinforcing units in thermoplastic polymers and polymer blends to improve the strength and rigidity of polymers and plastics. For instance glass, carbon etc. inorganic fibers are commonly used as reinforcing components in thermoplastic polymers (the matrix material) (see e.g. Modern Plastics Encyclopedia 89, McGraw-Hill, New York, 1988) .

Use of inorganic fibers as reinforcing components in thermoplastic polymers strongly impairs the fracture strain of polymers. Furthermore, mixing of fibers with the polymer requires a separate process stage where the reinforcing units (long or cut fibers) are united to the matrix polymer. A typical example is the addition of cut fibers to the polymer for instance so that the granulated polymer is melted in a mixing extruder and the reinforcing fibers are introduced into the polymer melt either in a cut form ( fiber length typically 1 mm - 5 mm) . The mixing extruder screw homogenizes th mixture of the polymer melt and the reinforcing fiber and then the mixture is granu¬ lated (reduced to particles) in the granulating nozzle of the mixing extruder. This fiber reinforced granulate can be used as a raw material in the manufacture of fabricated shapes by injection molding, melt ex¬ trusion, blow molding etc. melt moulding process. Fiber reinforced thermoplastic granules show some drawbacks. Granulation of the polymer matrix with inorganic fibers like that of glass or carbon induces shear forces within the polymer melt and thus causes breaking of the hard and brittle inorganic fibers so that, in a typical granulation in a mixing extruder, a great number of fibers with a length of only 100- 500 μm. is produced into the granulated material. Thus a great deal of the reinforcing capacity of the fibers is lost. Moreover, there is a low adhesion between fibers and polymer matrix due to their chemical differences. This presents problems especially in humid circumstances where water can easily diffuse onto the surface between the matrix polymer and the fiber thus impairing the strength properties of the composite. Adhesion can be improved by so-called adhesion promoters like silanes and titanates which, however, raise the price of the product and which in the case of many thermoplastic composites bring only a slight improvement in the moisture resistance (see e.g. above Modern Plastics Encyclopedia 89) .

Fiber reinforcement in polymers generally raises the price of the finished product in comparison with products without reinforcement since many reinforcing fibers like carbon have a much higher price than the polymer matrix.

It is also a known in plastics technology to produce fibrous polymer reinforcing units into a thermotropic polymer melt in liquid crystal state through orienta¬ tion of the melt by means of injection moulding or extrusion since the liquid crystals will form ordered structures in a flowing melt. As the melt is cooled the fibrous structures will remain permanently in the polymer matrix acting as reinforcement for the material. Liquid polymer crystals showing this be¬ haviour are also called self-reinforced (SR) liquid crystal polymers. Liquid crystal polymers do not require a separate stage for mixing the reinforcing fibers in the manufacture of finished or semi-finished products since the reinforcing units are readily produced within the matrix polymer itself during processing under suitable conditions as the polymer melt in a liquid crystal state is injected into the mold (e.g. injection moulding) or through the nozzle

(e.g. extrusion) . However, the method has a drawback in that the fibrous structure is formed in the surface layers of the piece, typically within a depth of only a few tenths of a millimeter. Pieces thicker than a few millimeters contain no fibers in the inside as the fiber orientation of the melt has enough time to vanish during the slow cooling of the core part of the piece. The interior part of such bodies is mecha- nically much weaker than the fiber reinforced surface part.

Not all polymer melts show liquid crystal state since its formation requires the presence of rigid molecular parts (like -aromatic rings) in the polymer chain. Furthermore, known thermotropic liquid crystal polymers are a much (typically 5-10 times) more expensive than normal thermoplastic polymers.

Although thermotropic liquid crystal polymers show very good mechanical properties, they cannot be fully exploited in polymer technology due to their high price. On the other hand, in many specialized applicat¬ ions ( like e.g. medical ) there is not enough infor¬ mation about the properties of liquid crystal polymers under special circumstances or the long-term proper- ties.

It is a known practice in polymer technology to generate a self-reinforced composite structure also into non-thermotropic polymers by working elongated profiles like bars, plates, tubes etc. through drawing and/or rolling in solid state, so that the spherulite crystal structure undergoes orientation and at least a partial transformation into a fibres (fibril struc¬ ture) so that the longitudinal axes of the fibrils align themselves along the direction of drawing. Profiles like bars, tubes etc. can be manufactured by the fibrillation technique, the profiles having extremely high strength properties in the direction of orientation (=the drawing direction) . (E.g. T. Konaka, K Nakagawa and S. Yamakawa, Polymer, 26, 1985, p. 462-468 obtained a tensile strength of 1.7 GPa and modulus of elasticity of 58 GPa for a tubular polyacetal (polyoxymethylene)) .

However, the fact that has formed an obstacle to the versatile technical utilization of known fibrillated materials is the simple shape the products must have since only elongated products (like bars, tubes, plates films etc.) can be manufactured by the fibril- lation method. However, these products can be manufac¬ tured into products of complicated forms by mechanical working. This kind of working requires, however, special facilities, it is slow and the direction of the reinforcing fibers cannot be altered once in a solid material. Quite unexpectedly, it was found in this invention that the above drawbacks present in reinforced thermo¬ tropic and non-thermotropic materials can be effecti¬ vely eliminated by making plastic products from so- called self-reinforcedparticulate compositegranulate. In order to attain this object the composite material according to the invention has mainly the characteris¬ tic features presented in the characterizing portion of claim 1. According to the invention, self reinforced profiles like bars, rods, thick filaments, plates, tubes etc. are made from non-thermotropic polymer, copolymer or polymer blend and said profiles are chopped into self-reinforced granulate i.e. self- reinforced composite granulate. From the self-rein- forced composite granulate it is, quite unexpectedly, possible to manufacture self-reinforced pieces having complicated geometric shapes by means of melt moulding techniques like injection molding, transfer molding, compression molding, blow molding, extrusion etc. where the material is only partly melted during processing and therefore the self-reinforced, oriented structure at least partly remains thus reinforcing the polymer matrix. In this invention a self-rein¬ forced, or at least partly so, composite granulate is described, which is made from a non-thermotropic thermoplastic polymer, copolymer or polymer blend and which unexpectedly can be used as a raw material in the manufacture of at least partly self-reinforced products, pieces or semi-finished products by means of melt moulding techniques.

Furthermore, in this invention a method is described wherein at least partly self-reinforced thermoplastic composite granulate is used in the manufacture of at least partly self-reinforced products, pieces or semi-finished products by means of melt moulding techniques. The characteristic features of the method are set forth in the characterizing portion of the independent claim relating to the method.

Furthermore, in this invention products like pieces, preforms, semi-finished products, parts or components or corresponding are presented which are at least partly self-reinforced and which are made from a composite material, non-thermotropic thermoplastic polymer, copolymer or polymer blend. Their main characteristics are set forth in the characterizing portion of the independent claim relating to them.

Non-thermotropic, at least partly self-reinforced polymer composite granulate denotes a particulate material containing oriented, structure reinforcing units inside the polymer material (composite) where the polymer binder (matrix) binds the oriented struc¬ ture units at least partly together. In this connec- tion, oriented structure units denote oriented mole¬ cular chains or molecular clusters or parts of them, oriented and/or deformed crystal lamellae or spheruli- tes or their parts, fibrils etc. morphological anisotropic structure units or their parts, fibres, filaments, film fibres, threads, cords, non-woven structures, nets, knitted or textured structures or corresponding. Oriented structure unit have a charac¬ teristic feature in that they show strength properties in the direction of orientation since the polymer molecules are strongly oriented along that direction. Specifically, the If-reinforced structure of the composite granulate of this invention denotes the fact that oriented structure units serving a rein¬ forcement and the polymer matrix serving as their binder have the same chemical element composition. The oriented structure units described above and their incorporation into a polymer matrix and/or their manufacture is described e.g. in publications US Pat.No. 4 743 257 and PCT publication WO 88/05312.

The invention is further illustrated with the following description and examples referring to the enclosed drawings. In the drawings

figure 1 shows different possible alternatives of the particulate forms, figure 2 shows schematically the manufacturing technique of the composite material, figure 3 shows schematically the manufacturing technique of the test pieces of example 1, figure 4 shows the dimensions of the test rod of example 1 and figure 5 shows the dimensions of the test rod of example 2.

According to figure 1, the shape of the particles in the self-reinforced composite granulate can be that of powder (figure la) , beads, closed or hollow balls (figure lb) , cylindrical bodies (figure lc) , flakes (figure Id) , short rods (figure le) , cubes (figure If) , cones (figure lg) , pyramids (figure lh) , bodies of irregular shapes etc. It is obvious that shapes other than those of figure 1 are also possible.

The maximum particle dimension of the composite granulate ( e.g. diameter, length, width etc.) is typically in the range 1 - 10 mm. However, finer or coarser materials can be used as the composite granu¬ late. Therefore, e.g. powders of composite granulate having a mean particle size (particle diameter) as low as 0.1 mm can be processed by melt moulding e.g. by compression molding and also by injection molding, extrusion etc. using equipment provided with forced feed. On the other hand, rod-like, flaky etc. par¬ ticles of the composite granulate may have a maximum dimension as high as 20 mm ( length or width) when entering the melting and homogenizing stage of the melt moulding apparatus.

Composite granulates can be produced (granulated) from oblong or continuous self-reinforced profiles by special granulating apparatuses in a separate proces- sing stage and then the material can be conveyed to the melt moulding equipment or, whenever necessary, stored in a suitable way before melt moulding.

Composite granulates can be produced (granulated) from oblong or continuous self-reinforced profiles feeding the material either straight into the feed funnel of the melt moulding equipment or into a chopper or similar granulator above or within the feed funnel wherefrom the material is transferred into the melt moulding equipment.

According to one beneficial embodiment of the inven¬ tion, the melt moulding equipment itself serve's as the granulator, so that oblong self-reinforced profiles or a continuous profile or a bundle of the profile are fed into the melt moulding equipment like injection press or extruder, wherein they are reduced to par¬ ticles of composite granulate by the effect of mecha¬ nical forces and/or especially by chopping blades, feed screw etc. The particles of the composite granulate thus formed are conveyed further into the melt moulding apparatus undergoing partial melting and homogenizing e.g. by the effect of a rotating screw in a cylindrical chamber, whereafter the material can be shaped into self-reinforced products through injection or molding.

Since the composite granulate is in particulate state it can be further processed by means of conventional apparatuses used in melt moulding of plastics like extrusion, transfer molding, blow molding, compression molding. Other techniques may also be applied, e.g. the composite granulate can be melted by hot gas flow, flame or heat radiation and then the partly melted powder of the granulated material can be injected onto a suitable surface where it forms a coating being at least partly self-reinforced.

When used in a typical melt moulding process, the composite granulate according of the invention is processed so that the composite granulate is only partly melted in a process equipment, so that a flowing melt is obtained where part of the oriented structure units of the composite granulate is in an unmelted state. This kind of partly melted, reinforced material can be pressure molded (e.g. by injection molding) or it can be forced through a forming die into a desired shape ( e.g. profile, tube, film, etc. by extrusion) and/or different kinds of surface textures like surface figures, scales, holes and so on can be formed on its surface by means of a die or mold or by mechanical means. By adjusting the process in a suitable way, the method of the invention facilitates a rapid and efficient production, from non-thermotropic polymers, of parts having complicated shapes and having at least a partial self-reinforcement and having clearly better mechanical and stiffness proper¬ ties compared to the corresponding products and semi- finished products manufactured from the same polymer by conventional melt moulding methods.

The non-thermotropic, at least partly self-reinforced composite granulates of the invention, the semi- finished products, products, parts, components etc. manufactured therefrom, can be used in many versatile ways in demanding technical applications where the composite must have good mechanical properties like high strength, good stiffness, fracture strength etc. Examples of application areas, where the materials of this invention can be used, are mechanical engineering, means of transport, electronics, sports equipment, medicine and hospital technique, household equipment etc.

The composite granulates according to the invention and the semi-finished products, products etc. manufac- tured therefrom have several benefits compared to (a) known materials manufactured by conventional melt moulding techniques from corresponding polymers and compared to (b) known fibre reinforced polymer mate¬ rials.

Products and materials manufactured from the composite granulate according to the invention show superior strength properties compared to the corresponding products and materials manufactured by conventional melt moulding techniques.

The reinforcing structure of the self-reinforced composite granulate is flexible, wherefore fibers do not break during melt molding as easily as they do with hard and brittle inorganic fibres.

In a self-reinforced structure, adhesion between reinforcing units and the matrix is also stronger due to their chemical similarity than in known materials with inorganic fibre reinforcement. Indication of the strong adhesion is e.g. the fact that, in a self- reinforced polyethylene, the matrix polymer crystal¬ lizes onto the surface of the reinforcing fibres (see e.g. T. He and R.S. Porter, J. Appl. Polym. Sci. , 3_5, 1988, 1945-1953).

Melt moulding also yields more homogenous parts when composite granulate according to the invention is used compared to those obtained with thermotropic self-reinforced polymers since, in the materials according to the invention, the fibre reinforcement remains throughout the whole piece not depending on the size of the piece, and the fibre reinforcement can be oriented in a desired way in different parts of the body by directing the flow of the material partly in a melted state through modifying the geometry of the mold or the die.

The composite granulate according to the invention can be utilized in an unexpectedly economic and efficient way in the manufacture of plastic products. For instance, one typical procedure for the processing of plastic products from the raw material into a finished product is the following. The raw polymer, for instance in particulate state or in a corresponding state as obtained from the polymerization reactor, is melted in a mixing extruder and necessary additives and intermediate agents are mixed in. The polymer melt is shaped in the outlet portion of the mixing extruder to a band, bar, thick fibre or corresponding profile, which is then chopped into granulate par¬ ticles. The granulate particles can then be used in the manufacture of plastic products or semi-finished products by melt moulding techniques. The granulation stage of the composite material according to the invention can be easily added to the manufacturing process in such a way that the material mixed and homogenized in the mixing extruder is forced through the die of the mixing extruder to form a band, bar, rod or corresponding profile, but the profile is not granulated at this stage but it is cooled and possibly re-warmed to a suitable temperature which is typically in the range between the melting and vitrification point of the material. The continuous blank will then be self-reinforced by drawing the blank in a suitable oven by applying known self-reinforcing techniques based on drawing. It Is after this self-reinforcement stage that the continuous self-reinforced profile is chopped into a composite granulate according to the invention. The necessary measures that have to be taken (cooling of the profile and drawing) do not in practice diminish the production capacity of the granulation line and, in addition, the necessary investments (oven, drawing apparatus) are moderate since one can use equipment which is available in the market. When the composite granulate produced in this way is used as raw material in melt moulding processes for the manufacture of plastic products, products with much better mechanical properties are obtained compared to products manufactured by conventional techniques. Therefore, the additional investments required by the measures according to the invention can be quickly amortized in the production technique through the fact that the ε srb properties of the products give possibilities for material savings and bring about competitive advantage. A characterizing feature of the use of omposite granulate in melt moulding processes is the fact that the material is not melted throughout but at least part of the rein¬ forcing structure units and possibly of the binding material of the particle remain in an unmelted state thus reinforcing the structure of the piece.

The manufacturing methods of the composite granulate according to the invention can be divided into several main groups. The first group consists of those manufac¬ turing techniques where ".he matrix polymer and/or the oriented structure elements serving as reinforcement (both components of which can contain possible addi¬ tives) are brought into such physical state where they join together. This is most typically accomplished so that the melt of the absorbable polymer, copolymer or polymer blend is mixed with oriented reinforcing units like fibres or fibre structures which are made of a corresponding material. Then the mixture of the polymer melt and the oriented structure units is shaped either readily into granulated form or it is shaped into profiles like bars, plates, tubes etc. This profile is granulated in a separate granulating stage e.g. by mechanical chopping and/or heat and/or ultrasound and/or laser chopping or by some other suitable method.

The second main group of the manufacturing techniques comprise processes where the mixture of the polymer, copolymer, polymer blend and possible additives is melted into a flowing mass which is shaped into a continuous profile e.g. by extrusion. This profile is then cooled into solid state possibly followed by subsequent re-heating and then it is transformed into a self-reinforced structure by mechanical working e.g. by drawing and/or rolling the structure. In this way, at least part of the crystal structure of the material, originally in spherulitic form, is trans¬ formed into an oriented and/or fibrillic (fibrous) reinforcing structure. This kind of manufacturing techniques are described e.g. in a PCT publication WO 88/05132 and in a patent publication FI-891696. This kind of self-reinforced profile can then be chopped by a suitable method into particles of the composite granulate according to the invention.

Figure 2 shows schematically a side view of a typical apparatus and method for the manufacture of the composite granulate according to the invention. As shown in figure 2, fibre bundle, cord, band etc. is fed from the crosshead die 1 of the extruder E into the chamber 3, w e einto, on the other hand, the polymer 4 melted and homogenized in the extruder is fed through a suitable inlet channel 5. Suitably adjusting the delay time of the fibre structure in the chamber 3, sufficient wetting of the fibre struc¬ ture with the melt can be obtained in such a way that fibres are not, at the same time, too severely damaged or melted. The mass M comprising of fibres etc. and the melt matrix is then shaped into a desired form by means of the die 6 and the blank, which comes out from the die 6 partly in melted state, is cooled after it has come out and/or it is chopped into the composite granulate according to the invention. The blank can be drawn through the die by means of a drawing apparatus 7 after which chopping K takes place.

According to the third manufacturing principle, the composite granulate according to the invention can be manufactured from fibers of a non-thermotropic polymer, copolymer, polymer blend or corresponding. For in¬ stance, fibre mass like bundle, fibre cord, thread, fabric etc. fibre structure can be partly melted by bringing it into contact with a hot surface or by heating at least part of it with a hot gas, radiation, ultrasound etc. Then the heat being conducted into the fibre bulk or the heat generated therein will partly melt the fibre mass, whereupon the melt will at least partly wet the remaining fibre mass. Shaping the partly melted mass into a desired form and/or cooling and/or chopping it by means of a suitable method (e.g. mechanically, ultrasound, heat etc.) one obtains the composite granulate according to the invention.

According to the fourth manufacturing principle the composite granulate according to the invention can be manufactured by means of a melt moulding technique wherein the melt of a non-thermotropic polymer, copolymer or polymer blend is oriented in the mold or in the die with the aid of the melt flow and by cooling the flowing melt into an oriented state quickly and under high pressure so that orientation will not have time to release due to molecular relaxation but remains in the material, which crystallizes and/or solidifies with the aid of applied pressure, thus forming the self-reinforced structure. The self-reinforced body can then be chopped by either a continuous or a discontinuous method into the composite granulate according to the invention.

According to the fifth manufacturing principle, either the oriented structure units or the polymer matrix or both can be made swell by a suitable solvent, so that the physical properties of one or both of the com¬ ponents of the material change and the material components join together when pressure or possibly additional heat is applied. Thus, by means of compres¬ sion techniques, it is possible to manufacture self- reinforced material that can be chopped into a com¬ posite granulate either before, during or after evaporation of the solvent. Solvent technique can also be modified so that the polymer matrix is dis¬ solved by a suitable solvent and this solution is impregnated in the bulk of the reinforcing fibre and the material is compressed into a self-reinforced structure possibly applying some additional heat either before, during or after evaporation of the solvent. The solvent technique can still be modified so that the fibre mass is wetted by a suitable solvent thus dissolving the surface structure of the fibres.

Then the fibre mass is quickly compressed into a self-reinforced structure, the solvent is evaporated and the material is chopped into a composite granulate according to the invention either during or after evaporation of the solvent.

It is obvious that other methods, where at least part of the structure of a solid or melted non-thermotropic polymer is transformed into oriented structure units or where oriented structure units are joined and bound to the polymer matrix and the obtained material is then granulated, are suitable for the manufacture of the composite granulate according to the invention.

Naturally, the composite granulate according to the invention may contain different additives or aids like pigments, particle fillers, fibre reinforcements like glass- or carbon fibres, stabilizing agents, antioxidants, softeners etc., which are necessary or beneficial for the processing or for the use of the material.

According to one beneficial embodiment, the composite granulate according to the invention may contain some bioactive substance or substances like antibiotics, chemotherapeutics, hemostatic substances, growth hormones, anticonceptives, anticoagulants (like heparin) etc. This kind of bioactive substances and surgical instrument made therefrom can be especially advantageous in clinical use since, in addition to their mechanical influence, they also have biochemical, medical, etc. influence in tissues.

The self-reinforced composite granulates can be manufactured from non-thermotropic, thermoplastic, at least partly crystallizable polymers, copolymers, and polymer blends. Typical polymers of this kind are e.g. various mass production plastics, technical plastics, special plastics e.g. acetal polymers (both polymer homologues and copolymers) , crystallizable acrylonitrile polymer, cellulose acetate, cellulose acetate, cellulose acetobutyrate, cellulose acetopro- pionate, polychlorotrifluoroethylene, fluorinated ethylenepropylen polymer, polyvinylidenefluoride, PE- TFE-poly er, PE-CTFE-polymer, polyamides likepolyamide 6, polyamide 66, polyamide 610, polyamide 612, poly¬ amide 11, polyamide 11, polyamide 12 etc., polybutylen, thermoplastic polyesters like PBT and PET, polyether- ketone, polyethylenes, ethylene copolymers like ethylene-propylene copolymers, ethylenevinylacetate and ethylenevinylalcohol, polyphenylenesulfide, polypropylene, polypropylene copolymers, polyvinyli- denechloride and other at least partly crystalline mass production polymers, technical polymers or special polymers abounding in professional publications. The above polymers are typically moisture resistant and stabile maintaining their properties unchanged for years or decades. Furthermore, the composite granulates according to the invention can be manufactured from so-called absorbable polymers, copolymers or polymer blends. Absorbable polymers mean in this connection polymers which depolymerize and transform to their monomers in hydrolytic circumstances i.e. under influence of water or moisture and the small molecular compounds thus formed can possibly metabolize further in living organisms e.g. in micro-organisms or mammal tissues. Numerous absorbable polymers, copolymers and polymer blends of this kind are presented in profes¬ sional publications e.g. in S. Vainionpaa, P. Rokkanen and P. Tδrmala, "Surgical Applications of Biodegradable Polymers in Human Tissues", Progr. Polym. Sci., in press. Also in patent publication FI-891974 several absorbable polymers are presented.

It is obvious that composite granulates according to the invention can be manufactured, in addition to those mentioned above, also from other polymers, copolymers and/or polymer blends, which are thermo¬ plastic and at least partly crystalline and/or crystal¬ lizable.

The invention and its applicability is described with the aid of the following examples. EXAMPLE 1.

A cylindrical polymer preform with a spherical cross- section (6 mm in diameter) was prepared from HD- polyethene (HDPE 0906, manufactured by Neste Oy, Mw appr. 230 000) by means of a single screw extruder (model Axon BX 18) . The polymer preform was conducted from the extruder die straight into the cooling tank where it was cooled by tap v^ter. The length of the pool was 3 m. The temperatures of the extruder cylinder were 170, 180, 190, 200°C. Temperature in the cooling tank was appr. 50°C. The HD-polyethene preform was oriented and fibrillated in the following way. The preform was conducted from a coil to the tempering bath (water, temperature 75°C) whereafter it was conducted to the oven (T=80°C) . The warmed preform was forced through the die of the drawer where the tempe¬ rature was appr. 120°C. The preform was drawn by means of rollers. The thickness of the preform was adjusted by means of draw velocity. Figure 3 shows schematically the fibrillation line as a cross-sectio¬ nal side view. Figure 3 shows the preform coil 8, tempering bath 9, oven 10, draw die 11 and rollers 12. Table 1 gives the shear strengths ( the measuring equipment: JJ Loyd) of the oriented and/or fibrillated HD-polyethylene preforms as a function of the draw ratio (draw ratio = length of the preform after drawing/length of the preform before drawing) .

Table 1.

Draw ratio Shear strength (MPa) 1 (non-oriented) 22-29

2 25-30

5.3 75-85

6.3 75-85 modulus of elasticity was determined for the oriented preform at a draw ratio of 4.2. JJ Loyd universal materials tester was used for drawing with a drawing velocity of 5 mm/min, gauge length of 100 mm and grip length of 200 mm. The value of 0.3-0.5 Mpa was obtained for the modulus of elasticity of a non-oriented, extruded HD-polyethylene and the value of appr. 1.5 GPa for the modulus of elasticity of an oriented HD- polyethylene at a draw ratio of 4.2.

The preform oriented at a draw ratio of 5.2 was chopped by a mechanical chopper into cylindrical composite granulated particles. From the composite granulated particles, test rods were prepared by means of a table injection press ( model SP-2) provided with a piston, thickness of the test rods were 3.0 mm and other dimensions (in millimeters) as given in figure 4. The composite granulate particles were injection moulded so that the material was partly melted in the cylinder of the injection mould and the partly melted flowing mass was compressed by the piston into the mould. Melting time was appr. 5 min and temperature of the melt phase during compression was appr. 130°C. Shear strength, measured within the middle of the prepared test rods, of the composite granulate was 35 MPa. Moulded into similar moulds using the same raw material and the same equipment, HD-polyethene test rods were prepared for reference so that the material was totally melted in the cylinder of the injection moulding equipment. The injection temperature of the melt was appr. 160°C. Shear strength of 25 MPa was measured for test rods which were not reinforced containing normal spherulitic internal structure. EXAMPLE 2.

From the thermoplastic polymers of table 2, cylindrical preforms were prepared using the equipment described in example 1 by extrusion (Axon BX 18-extruder) or injection moulding according to normal melt moulding principles so that the diameter of the preforms was 6 mm (length of the injection moulded rods was 40 mm) .

Table 2. Extrusion of partiallycrystallineplastics into a cylindrical profile.

The preforms were rapidly cooled at room temperature and/or in water bath (extrusion) or in the mould (injection moulding) and their at least partly sphe¬ rulitic structure was changed to at least partly oriented and, in addition, possibly to a fibrillated, reinforced structure by drawing the preforms to draw ratios 4-12 at temperatures (T) Tm > T Tg, where Tm is the melting point of the polymer, copolymer or polymer blend and Tg is the vitrification point of the polymer, copolymer or polymer blend. Part of the draws were performed using the heatable drawing die according to example 1 and some of the draws were performed in a heated tube furnace. Drawn cylindrical preforms, having a thickness of 1.5 - 0.87 mm, were chopped by a mechanical cutter into a composite granulate which composed of 8mm long cylindrical particles. From these composite granulated particles, 4 mm thick test rods shown in figure 5 were prepared for bending tests by injection moulding ( injection machine model Engel ES 240/65) by partly melting the composite granulate in the injection mould and injec¬ ting the partly melted material containing self- reinforced structure units into the mould for the test rod. Using the same mould and corresponding raw materials and using normal melting and homogenizing melt moulding techniques, test rods were prepared whose crystal structure was mainly spherulitic. Bending strengths of the test rods prepared from the composite granulate according to the invention and those prepared by conventional methods were determined at room temperature by the three-point bending method. Table 3 shows the bending strengths of the rods prepared from composite granulate and conventional granulated material.

Table 3. Bending strengths for injection pressed test rods (A) prepared from composite granulate and (B) prepared from the corresponding raw materials by normal melt moulding techniques.

It can be seen from the table that bending strengths of the self-reinforced test rods that has been prepared from the composite granulate according to the invention are clearly better than the bending strengths of the spherulitic test rods that has been prepared from conventional raw material by known methods. The values in table 3 are the mean values from 4-6 replicate determinations. For each material the deviation of a single determination was appr. 10% on both sides of the mean value.

EXAMPLE 3.

Fibres were prepared by melt spinning from polypropy¬ lene (Hostalen, manufacturer Hoechst, melt spinning extruder: model Fourne) and drawn to the final fibre thickness of 40 μm. A 3 mm thick cord was prepared from the fibres. The cord was drawn through the chamber of a cross-head die while the same polymer, which was melted in the extruder (temperature of the melt appr. 200 °C) , was fed into the chamber of the cross-head die. The preform (diameter appr. 3 mm) coming out from the cross-head die was rapidly cooled by water and chopped into a composite granulate (into cylinders of 6 mm in length) . The composite granulate was then processed into test rods according to example 2 by injection press through partially melting the composite granulate and injecting the compound into the mould of figure 5.

Bending strength was determined for the test rods made from a composite granulate according to the invention in the same way as in example 2. A value of 50±5 MPa was obtained for the bending strength. The bending strength of the test rods that were prepared by conventional technique was 40±7 MPa ( see Table 3).

EXAMPLE 4.

A polypropylene cord similar to example 3 was drawn at a velocity of 1 m/min through a 2 m long tube furnace (inner diameter appr. 5 cm) where the wall temperature at the beginning of the furnace was 60 °C and 280°C at the end. The surface of the cord was melted so that the melt phase of the cord at the exit constituted appr. 40 %. The preform was water cooled and chopped into particles of composite granulate wherefrom test rods were made according to example 3. The bending strength of the test rods was 48±5 MPa.

EXAMPLE 5.

A 0.2 mm thick monofilament was made from HD-polyethy¬ lene (HDPE Hostalen, manufacturer Hoechst) by single screw extrusion (model of the melt spinning extruder: Fourne) . From this monofilament and from fibres of DYNEEMA SK60 High Performance Polyethylene (manufac¬ turer Dyneema, the Netherlands) bundles of parallel fibres were made where the HDPE monofilaments and the Dyneema fibres were mixed as fully as possible. From these parallel bundles, cylindrical, self-reinforced polyethylene test rods, with a length of 70 mm and diameter 4.5 mm, were prepared by compression moulding so that a surplus of parallel fibre bundle was placed on the compression mould, so that the longitudinal axes of the fibres were mainly parallel with the longitudinal axis of the mould. The mould was then closed and a pressure of 2000 bar was applied and heated to 143°C. The HDPE-iilaments melted and wetted the Dyneema-fibres, which remained in an undamaged condition. Heating time was appr. 6 min and then the mould was quickly cooled to room temperature. The obtained self-reinforced polyethylene test rods were then chopped into 6 mm long composite granulated particles by means of a mechanical chopper. From the composite granulated particles test rods of figure 3 were made using a SP2 injection press so that the composite granulate was heated in the cylinder of the press up to appr. 144°C within 4 min and the partly melted mass was then pressed into the mould for the test rods. Bending strengths of the test rods were then measured by three-point bending. Bending strength values of 110±30 MPa were obtained. For reference, a cylindrical profile (diameter 4.5 mm) was prepared from the same HDPE raw material by melt moulding using extrusion and the profile was then granulated into 6 mm long granulated particles by means of a chopper. Test rods of figure 4 were then made from this granulated material by melt molding using a SP2 press and three-point bending measurement gave values of 35±5 MPa for the bending strength of the test rods. EXAMPLE 6 .

Glycolide/lactide copolymer (90/10) , with an internal viscosity of IΛJJ - 1.5 in 0.1 % hexafluoroisopropanol solution (T=25°C) was melted by a single screw extruder (model Axon BX 18, screw diameter 18 mm) and the melt (T appr. 180°C) was driven into the chamber of a cross-head die of figure 2, through which die con¬ tinuous fibre bundle, appr. 3 mm thick and braided from fibres of the glycolide/lactide copolymer, was drawn. Within the cross-head die, the fibre bundle was coated by the polymer melt which impregnated into the bundle partially melting its surface. The fibre bundle was drawn out of the die through a spherical nozzle with a 4 mm diameter, then the self-reinforced com¬ posite preform containing continuous fibres was cooled by cold water and it was chopped by a mechanical chopper into 3 mm long particles of composite granu¬ late.

The composite granulate was injection moulded by a screw type injection press (model Battenfeld BA23Q/45) by partly melting the composite granulate, injecting the partly melted compound into a mould chamber which was used for molding polymer screws. Length of the mould chamber was appr. 50 mm and the maximum diameter of the screw thread was 4.5 mm and the minimum diameter of the screw thread was 3.2 mm. In this way, screws were prepared from the composite granulate with a fibre content of appr. 30 % as estimated from a cross- sectional micrograph taken with a scanning electron microscope. Bending strength and shear strength of the screws were measured according to the publication: P. Tδrmala, J. Vasenius, S. Vainionpaa, J. Laiho, T. Pohjonen and P. Rokkanen: "Absorbable self-reinforced polyglycolide (SR-PGA) composite rods for internal fixation of bone fractures in vitro and in vivo study", J. Biomed. Mater. Res. (offered for publication) . Bending strength of 140 MPa and shear strength of 80 MPa was obtained for the screws according to the invention. As reference samples, screws were prepared from a non-reinforced powder of the same base material using the same equipment, the same mould and applying conventional injectionmoulding techniques. The polymer was melted and homogenized by an injection press and injected, at the melt temperature of 210°C, into the mould which was then quickly cooled. Bending strengths of the obtained screws were appr. 90 MPa and shear strengths appr. 50 MPa.

EXAMPLE 7.

The glycolide/lactide copolymer of previous example was used for preparing appr. 100 μm thick fibres by extruding with a single screw extruder (Axon) a polymer preform with a thickness of 1 mm, which was then drawn at temperatures 70-150°C to the final thickness of 100 μm. Tensile strength of the t bers was 600 MPa. These fibres were then heated in a pressurized cylindrical mould (length 70 mm, diameter 4.5 mm) at the temperature of 180°C for 5 min in vacuum under pressure of 2000 bar, whereafter the mould was quickly cooled. Under said circumstances the fibres were partly sintered together forming a self-reinforced rod. These rods were made a sufficient number for further experiments. The rods were chopped by a mechanical chopper into cylindrical particles of the composite granulate with a length of 5 mm. Self- reinforced screws were made from these particles following the experimental arrangement of previous example. Bending strength of the screws according to the invention was 110 MPa and shear strength was 70 MPa. EXAMPLE 8 .

Polyglycolide sutures (Dexon R, size 2 USP) were heated in a pressurized cylindrical mould (length 70 mm, diameter 4.5 mm ) at temperature 218°C for 5 min under pressure of 2000 bar. Softened fibre material was partly sintered together and the mould was quickly cooled to room temperature. This kind of self-rein¬ forced fibres were then chopped by a mechanical chopper into composite granulate particles with a length of 7 mm. From this composite granulate, self-reinforced screws were prepared using the injection mould of the previous example by partly melting the composite granulate with the injection press so that temperature of the injected compound was appr. 230°C. Fibre content of the screws was 40 % as estimated from micrographs a scanning electron microscope. Bending strength of 220 MPa and shear strength of 160 MPa was measured for the screws. For reference, screws were prepared from a polyglycolide powder (manufacturer Boehringer- Ingelheim, Germany) using the same injection moulding equipment by fully melting the material in the injec¬ tion press and injecting the polymer melt (at a temperature of appr. 230°C) into the screw mould. Bending strength of 120 MPa and shear strength of 70 MPa was measured for the prepared screws.

EXAMPLE 9.

Isomers of absorbable polymers can also be used in the manufacture of the composite granulate according to the invention and products made thereof. For instance, isomers of polylactide like poly-L-lactide (PLLA) , poly-D-lactide (PDLA) , poly-DL-lactide (PDLLA) and copolymers of L-lactide and D-lactide, which contain different amounts of L- and D-units, can be used either alone or combined in different ways as oriented structure units of self-reinforced lactide composites and as the matrix material.

Fibres (diameter of fibres appr. 100 μm) of poly-L- lactide were prepared from polylactide with a molecular weight of appr. 300 000 (manufacturer Boehringer- Ingelheim, Germany) by extruding the raw material with a single screw extruder (Axon BX 18) to a preform with a diameter of l mm and drawing the preform into fibres in a furnace at appr. 100°C. Temperatures of the extruder cylinder were 175, 180, 185, 185°C. Fibres were prepared from the powder copolymer of L- lactide and D-lactide (PLDLA) (monomer ratio L/D=90/10, molecular weight appr. 300 000, manufacturer CCA Biochem, the Netherlands) using the corresponding technique. Tensile strength of the PLLA fibres was 600 MPa and that of PLDLA fibres was 200 MPa. A hawser of parallel fibres were prepared from PLLA and PLDLA fibres so that the PLLA and PLDLA fibres were evenly mixed with each other. The diameter of the cylindrical hawser was appr. 3 mm. The fibre hawser was conducted through a heated furnace (length 2 m) at a velocity of 2 m/min in nitrogen gas. Heating of the furnace was adjusted so that the surface of the fibre hawser warmed up to appr. 160°C whereupon the PLDLA fibres melted forming a matrix phase binding the PLLA fibres. After the furnace, the formed band of self-reinforced composite lactide was chopped by a mechanical chopper into 7 mm long particles of the composite granulate.

Self-reinforced lactide screws were prepared from the particles of the composite granulate by heating the lactide compound in the injection press to 175°C whereupon the PLDLA phase melted but PLLA fibres did not. This fibre reinforced melt was injected into a screw mould at room temperature. Bending strength of these self-reinforced lactide screws was 160 MPa and shear strength 70 MPa. Polylactide screws were prepared from both PLLA and PLDLA powders using conventional melt moulding techniques by melting and homogenizing the compound with the injection press so that, during injection moulding stage, temperature of the PLLA melt was 200°C and that of PLDLA melt was 180°C. Bending strength of 120 MPa and shear strength of 50 MPa was measured for the PLLA screws. Bending strength of 90 MPa and shear strength of 90 MPa was measured for the PLDLA screws.

EXAMPLE 10.

Polyglycolide powder (manufacturer Boehringer-Ingel- hei , Germany) was melted at an appr. temperature of 230°C. The polymer melt was injected, using a injection press (model SP-2) provided with a piston, into a cylindrical mould with a length of 70 mm and diameter of 3.2 mm and whose mould was loosely filled with Dexon R (manufacturer Davis and Geek, UK, size 2 USP) sutures of the length as the mould. Temperature of the mould was 20-25°C. The obtained rods had fibre content of appr. 30-40% (w/w) . A sufficient number of these rods was prepared and the rods were mechanically chopped into 8 mm cylindrical particles of the com¬ posite granulate. This composite granulate was used as raw material for preparing self-reinforced screws with conventional injection moulding techniques using the injection press and the mould of example. Shear strength of the self-reinforced screws was 110 MPa.

For reference, cylindrical polyglycolide rods were prepared using SP-2 press provided with a cylindrical mould (length 70 mm, diameter 3.2 mm) by melting the polymer powder (manufacturer Boehringer-Ingelheim, Germany) in the chamber of the injection press and pressing the melt (melt temperature appr. 240°C) into the mould. These rods were chopped by a mechanical chopper into 7 mm long unreinforced particles of composite granulate. This material was used for the preparation of screws by melting and homogenizing the granulate material in the chamber of the injection press with the aid of heat and the conveyor screw. Shear strength of 60 MPa was measured for the poly¬ glycolide screws.

EXAMPLE 11.

Poly-L-lactide fibres (Mw appr. 700000) were prepared by means of a single screw extruder (model Axon) by melting the polymer powder and homogenizing it with the extruder chamber and extruding the homogenized melt monofilament with thickness of 1 mm, which was partly cooled in room temperature and drawn in solid state in a furnace at appr. 150°C into the final diameter of 100 μm. Temperatures of the extruder chamber were 205, 215, 225 and 230 °C. These polylac- tide fibres were sintered in a pressurized cylindrical mould at 175 °C for 6 min by a pressure of 2000 bar. The mould measured 3.2 mm in diameter and 70 mm in length. The softened fibre material was partly sintered together forming a cylindrical self-reinforced com¬ posite rod. The mould was quickly cooled to room temperature and opened. A sufficient number of these rods was prepared and they were mechanically chopped into 6 mm long particles of the composite granulate. Poly-L-lactide screws were prepared from these par¬ ticles using the injection press (model Battenfeld) of the previous example by partly melting the particles in the injection press so that the injection tempera¬ ture of the partly melted material was appr. 175- 180°C. The mould was at room temperature. The measured shear strength of these self-reinforced poly-L-lactide screws was 75 MPa. For reference, unreinforced polylactide rods were prepared from the same material by a compression mould and then the rods were chopped by a mechanical chopper into 6 mm long particles of unreinforced polylactide composite. These particles were used for preparation of polylactide screws by the Battenfeld injection press by melting and homogenizing the polylactide granulate so that the injection temperature of the melt was 190°C. Shear strength of 45 MPa was measured for these unreinforced poly-L-lactide screws.

Claims

1. Composite material manufactured from at least a non- thermotropic,thermoplastic, at least partly crystal¬ lizable polymer, copolymer or polymer blend, said compositematerial containing so-called self-reinforced structure, at least partly enabling especially the accomplishment of the strength properties, the self- reinforced structure containing a) binding material and b) reinforcing structure units, the components a) and b) having the same chemical element composition, characterized in that said composite material is in a particulate state, into which state it has been reduced in at least one stage subsequent to the manufacturing of the composite material, in which stage a larger piece of the composite material is reduced to parti¬ culate pieces, the particulate composite material being especially aimed to be used as a manufacturing material, or at least as one of them, for self-rein¬ forced or at least partly self-reinforced pieces.

2. Composite material according to claim 1, charac¬ terized in that the largest diameter of single par¬ ticles of the particulate state is 0.1-20 mm.

3. Composite material according to claim 1, charac¬ terized in that the structure units of the particulate state of the composite material are oriented and they are directional molecular chains or molecular bundles or parts of them, directional and/or deformed crystal lamellae or spherulites or parts of them, fibrils and like morphological anisotropic structure units or parts of them, fibres, filaments, film fibres, threads, cords, non-woven structures, nets, fabrics or knitted structures or corresponding.

4. Composite material according to claims 1,2 or 3, characterized in that the single particles of the particulate state are in a form of powder, beads, closed or hollow balls, cylinders, flakes, rods, cubes or pieces having irregular shape.

5. Composite material according to claims 1, 2, 3 or 4, characterized in that said composite material is manufactured from at least one mass production polymer, technical polymer or special polymer.

6. Composite material according to claims 1, 2, 3, 4 or 5, characterized in that said composite material is manufactured from an absorbable polymer, copolymer or polymer blend.

7. Method for manufacturing composite material, wherein, in the first stage, preferably an elongated piece of self-reinforced composite material like bar, rod, thick filament, sheet, tube is manufactured from at least a non-thermotropic, thermoplastic polymer, copolymer or polymer blend, which piece of self- reinforced composite material contains and/or into which is formed during manufacturing a) binding material and b) reinforcing structural units, the components a) and b) having the same chemical element composition, characterized in that said piece of self- reinforced composite material is reduced to particulate state in at least one stage of treatment of the • composite material, so that the self-reinforced structure remains in the particulate state.

8. Method according to claim 7, characterized in that said piece of self-reinforced composite material is reduced to particles having the largest diameter of 0.1-20 mm.

9. Method according to claim 7, characterized in that said piece of self-reinforced composite material is reduced to the particulate state in a melt moulding equipment.

10. Method for manufacturing pieces from composite material, wherein, in the first stage, preferably an elongated piece of self-reinforced composite material like bar, rod, thick filament, sheet, tube, is manu¬ factured from at least a non-thermotropic, thermoplas¬ tic polymer, copolymer or polymer blend, which piece of self-reinforced composite material contains and/or into which is formed during manufacturing a) binding material and b) reinforcing structural units, the components a) and b) having the same chemical element composition, characterized in that said piece of self-reinforced composite material is reduced to particulate state in at least one stage of treatment of the composite material, so that the self-reinforced structure remains in the particulate state, and that said particulate composite material is used as a manufacturing material, or at least as one of them, for self-reinforced or at least partly self-reinforced pieces to be manufactured especially by melt moulding techniques.

11. Method according to claim 10, characterized in that the particulate composite material is only partly melted during manufacturing of the piece by melt moulding, so that at least part of the reinforcing structure units essentially maintain their strength.

12. Method according to claim 10, characterized in that said piece of the composite material is reduced to particulate state in a melt moulding equipment, where said particulate composite material is used as a manufacturing material, or at least as one of them, for the pieces.

13. Pieces manufactured especially by melt moulding techniques from at least a non-thermotropic, thermo¬ plastic polymer, copolymer or polymer blend and at least partly from a composite material containing so- called self-reinforced structure, at least partly enabling especially the accomplishment of the strength properties, the self-reinforced structure containing a) binding material and b) reinforcing structure units, the components a) and b) having the same chemical element composition, characterized in that said pieces contain reinforcing structure units of the composite material, the structure units originating from the particles of the composite material, which is reduced to particulate state and is at least partly unmelted and which composite material is used as a manufacturing material or at least as one of them.