AU2024353136A1 - Uhmwpe filaments, yarns and articles thereof - Google Patents

Abstract

Gel-spun ultra-high molecular weight ultra-high molecular weight polyethylene (UHMWPE) polyethylene filaments are disclosed which are optimized for their use in permanent load applications. Yarns comprising at least 25 permanent load optimized UHMWPE filaments, a titer of at least 50 dtex, a filament titer of at least 0.50 dtex, a tensile modulus of at least 1500 cN/dtex and a minimum creep rate of at most 5.0x10-7 s-1 when measured at 70°C under a load of 400 MPa are also disclosed. The UHMWPE may be a linear homopolymer of ethylene. The load optimized filaments and various products such as ropes, nets, medical devices, fabrics, laminates, composite articles and ballistic-resistant articles containing the filaments or yarns are also disclosed.

Description

UHMWPE FILAMENTS, YARNS AND ARTICLES THEREOF

This invention relates to gel-spun ultra-high molecular weight polyethylene filaments optimized for their use in permanent load applications, a yarn comprising at least 25 permanent load optimized filaments, the load optimized filaments and various products such as ropes, nets, medical devices, fabrics, laminates, composite articles and ballistic-resistant articles containing said filaments or yarns.

During the last decades, many research projects focused on improving the creep properties of synthetic yarns, since such yarns are extremely suitable for a wide range of applications where lightweight and strength are driving factors. One example of synthetic yarns is UHMWPE yarns, which meet successfully the weight and strength requirements of various applications. The almost unmatched strength of UHMWPE yarns combined with ultraviolet resistance, chemical resistance, cut and abrasion resistance and other favorable properties are the reasons that these yarns found an almost immediate utilization in rope mooring, composite reinforcement, medical devices, cargo nets and the like.

UHMWPE filaments and yarns have however one drawback that acts as an impediment for their optimal utilization in long-term applications, this drawback being related to their creep behavior. It was observed that an ultimate failure mode of a system using UHMWPE filaments and in particular of those systems placed under a long-term load, include rupture or failure due to creep. Such systems and particularly those intended for long-term or ultralong-term use must therefore be over-designed to last for a large number of years, e.g. more than 10 years and in some cases more than even 25 years. More than a decade of developments in the field of low creep UHMWPE yarns aimed at reducing creep rate (CR) and lately at increasing the creep lifetime (CLT) of the UHMWPE fibers and yarns.

For example, WO 2009/043597 relates to a process for producing gel-spun fibers from ultra-high molecular weight polyethylene (UHMWPE) and to fibers having high tensile strength and improved creep. UHMWPE yarns are disclosed having a combination of creep rate and strength, e.g. a creep rate of at most 5 x 10'⁷ s^_1 as measured at 70°C under a load of 600 MPa, and a tensile strength of at least 4 GPa. The process described in W02009/043597 uses a UHMWPE copolymer with a A5 of at most 42° and applies high drawing ratios in the air gap, the gel phase and the dry yarn. WO2012/139934 relates to a creep-optimized, ultra-high molecular weight polyethylene (UHMWPE) fiber, a process for producing the same and various products such as ropes, nets, medical devices, fabrics, laminates, composite articles and ballistic-resistant articles containing said UHMWPE fibers. Disclosed are fibers comprising UHMWPE comprising ethyl and butyl side chains and having a creep lifetime as high as 500 hours as measured at 70°C under a load of 600 MPa and tensile strengths as high as 4.1 GPa.

WO2018/060127 describes a gel-spun fiber comprising an ultra-high molecular weight polyethylene (UHMWPE), wherein the UHMWPE has an intrinsic viscosity (IV) of at least 4 dL/g and comprises at least 0.3 short chain branches per thousand total carbon atoms, characterized in that the fiber further comprises between 0.1 and 10 parts by weight of carbon black based on 100 parts by weight of the amount of the polyethylene forming the fiber.

Although the yarns described in the prior art have very good creep lifetime and/or creep rate, it appears that there remains a need to further optimize the properties of yarns. This is especially relevant for applications where not merely a permanent load is applied but where said permanent load is typically accompanied by a varying dynamic load. Such a challenging application is for example found in tension leg platforms (TLP), amongst others employed in floating offshore wind installations. Wind turbines unceasingly increase in height and blade diameter while suitable locations are more and more remote from the shores, at higher water depths. To meet the ever-increasing requirements, present commercial tendon solutions require large amounts of yarns per linear meter, also referred to as the linear density.

Patent publication WO2016001158 describes a structure comprising rigid elements connected together by interconnecting elements in such a way to form a statically determined structure or a statically over-determined structure, wherein said structure comprises at least one tension element comprising polymeric fibers having a stabilizing creep of at least 0.3 % and at most 10 % and a minimum creep rate lower than 1 x 10'⁵ % per second, said stabilizing creep and minimum creep being measured at a tension of 900 MPa and a temperature of 30°C.

The present invention aims therefore to provide advantages and/or alternatives over the known multifilament yarns. It aims in particular to provide a multifilament yarn and filaments that has an optimized performance when used in various applications for various technological fields. It may also be an object of the invention to provide multifilament yarns and filaments having a higher strength at break per filament than the known yarns and filaments. The invention particularly aims to provide yarns and filaments that have properties allowing the design of tendons for tension leg platforms meeting the load and lifetime expectations while reducing the required mass of UHMWPE yarns or filament in the tendons Or alternatively a yarn or filament that allows the construction of tendons with substantially higher load capabilities and lifetime expectation when compared to prior art materials.

This objective is surprisingly achieved by an ultra-high molecular weight polyethylene multifilament yarn having a titer of at least 50 dtex, at least 25 filaments, a filament titer of at least 0.50 dtex, a tensile modulus of at least 1500 cN/dtex and a minimum creep rate of at most 5.0x1 O'⁷ s^-1 when measured at 70°C under a load of 400 MPa, wherein the ultra-high molecular weight polyethylene is a linear homopolymer of ethylene.

As will be provide in more detail in the examples, the inventive yarns are utmost suitable for the use in tendons for tension leg platforms, providing tendon designs with substantially lower linear density and hence lower total mass of the tendon. Such effect comes as a surprise and stands in contrast to the general teaching in the prior art which emphasizes the need for ever lower minimum creep rates and creep lifetime. In contrast the present inventors identified that HMPE yarns and filaments according to the invention are substantially more suitable when used in more complex applications, where yarns or filaments are subjected to a variety of conditions, such as permanent load, bending, peak loads changing at low or high frequency, etc. Amongst other such complex applications can be found in tension legs, rigging, umbilical cords, deep see cables as well as composite structures like unidirectional sheets, laminates and fabrics.

Short Figure description

Figure 1 schematically represented a device to determine creep rate (CR) and creep lifetime (CLT) of multifilament yarns.

Figure 2 is a creep lifetime plot as recorded during the creep lifetime measurement. The depicted plot is for illustrative purpose only and does not show a plot of a yarn according to the invention.

Figure 3 schematically depicts the equipment used for the determination of filament properties such as linear density, tensile modulus and tenacity

Figure 4 schematically depicts a Tension Leg Platform according to the invention comprising a floater (100) and a mooring article according to the invention (401) arranged to connect the floater to the seabed (402). Detailed description

By multifilament yarn is herein understood an elongated body containing a plurality of filaments, i.e. at least 25 individual filaments, preferably at least 50, more preferably at least 100 individual filaments. Said filaments typically represent the main constituting component of the yarn, while other materials for example in the form of a coating or finish may be present for example to adjust mechanical or other properties of the yarn. The filaments in the yarn will typically be oriented parallel one to another, in side by side fashion. Typically the filaments in the yarn are not twisted, but may also be slightly twisted together. The twist of the yarn may hence be between 0 to 10 turns per meter or more.

By filament is herein understood an elongated body, the length dimension of which is much greater than the transverse dimensions of width and thickness, or diameter. Typically, a filament is referred to as having a continuous length. In the context of the present invention, filament may as well be referred to as fiber. The in the art recognized form factor of a staple fibers having discontinuous length is not considered a filament in the context of the present invention. A filament may have regular or irregular cross-sections, typically the crosssection is circular, but may also be polygonal, oval or oblong. Especially once processed into an article, the shape of the cross-section may have been altered by the processing conditions. A yarn for the purpose of the invention is an elongated body containing a plurality of filaments.

The multifilament yarns and filaments of the present invention are ultra-high molecular weight polyethylene filaments, in the art also referred to as high performance polyethylene (HPPE) yarns or filaments or as high modulus polyethylene (HMPE) yarns or filaments. UHMWPE, HPPE or HMPE yarns and filaments are known in the art to have a high tenacity, whereby the relative term high is used in contrast to the tenacity of other synthetic or natural materials. Such naming is widely accepted in the field of UHMWPE yarns and filaments.

In a preferred embodiment, the ultra-high molecular weight polyethylene multifilament yarn has a minimum creep rate CR70/400 of at most 2.5x1 O'⁷ s’¹, more preferably of at most at most 1.5x1 O'⁷ s'¹ and most preferably of at most at most 1.0x1 O'⁷ s’¹. Such lower creep rates will show further advantages in the discussed applications.

Yarns according to the invention may have creep lifetime of up to and above 10⁶ seconds when measured under above mentioned CR70/400 conditions, corresponding to a several days to weeks of test durations. Therefore alternative creep measurement conditions can been chosen to quicker characterize the creep performance of the filaments, namely by increasing the applied load to 1200 MPa at identical temperature.

Accordingly, another embodiment of the present invention concerns a multifilament yarn having a titer of at least 50 dtex, at least 25 filaments, a filament titer of at least 0.50 dtex, a tensile modulus of at least 1500 cN/dtex and a minimum creep rate (measured at 70°C and at a load of 1200 MPa, CR70/1200) of at most at most 5.0x10'⁵ s’¹, whereby the modulus and the CR70/1200 are measured according to the corresponding methods described in the METHODS. Preferably the multifilament yarn has a CR70/1200 of at most at most 2.5x1 O'⁵ s^-1, more preferably of at most at most 1 .5x1 O'⁵ s^_1 and most preferably of at most at most 1 .0x1 O'⁵ s’¹.

In a preferred embodiment, the multifilament yarn of the invention has a modulus of at least 1600 cN/dtex, more preferably of at least 1700 cN/dtex, even more preferably of at least 1750 cN/dtex, yet more preferably of at least 1800 cN/dtex, and most preferably of at least 1850 cN/dtex. While there is no theoretical maximum to the stiffness, i.e. tensile modulus, of multifilament yarns, a realistic upper tensile modulus may be as high as 2500 cN/dtex. The inventors identified that with increasing tensile modulus of the yarn, the mechanical properties of the articles made thereof will be further improved. Amongst others it was observed that the mass of multifilament yarn in a tension leg or a unidirectional sheet may be further reduced while maintaining the specified performance of the article.

The yarn of the present invention preferably has a tenacity of at least 42.0 cN/dtex, preferably at least 44.0 cN/dtex, more preferably at least 46.0 cN/dtex, even more preferably at least 47.0 cN/dtex and most preferably at least 48.0 cN/dtex. The skilled person will be aware that there are theoretical and practical limits to the tenacity of the UHMWPE multifilament yarns, therefor the polyethylene filaments preferably have a tenacity of at most 70 cN/dtex, preferably at most 65 cN/dtex, more preferably at most 60 cN/dtex.

The yarn according to the invention is understood to be an elongated body comprising a plurality of filaments. The invention hence also relates to a yarn preferably having a titer of between 50 dtex and 10.000 dtex, more preferably between 100 dtex and 8.000 dtex, most preferably between 200 dtex and 5.000 dtex. It was identified that yarns with lower titer, also called linear density, have reduced robustness and make them less suitable for being processed into finished or semi-finished articles. Yarns with too low titer are prone to breakage due to their low force at break. Preferably, the inventive yarn has a number of filaments of at least 50, more preferably at least 100, even more preferably at least 160, and most preferably of at least 240 filaments. The skilled person will be aware that there is no theoretical limit to the number of filaments forming a yarn, while practical limits may be imposed by the manufacturing processes, therefor the yarn preferably has a maximum number of filaments of at most 100.000, more preferably at most 50.000 and most preferably at most 10.000 filaments per yarn.

While an embodiment of the present invention concerns a multifilament yarn having a titer of at least 50 dtex, at least 25 filaments, a filament titer of at least 0.50 dtex, a tensile modulus of at least 1500 cN/dtex and a minimum creep rate of at most 5.0x1 O'⁷ s^_1 when measured at 70°C under a load of 400 MPa (CR₇o,4oo), wherein the ultra-high molecular weight polyethylene is a linear homopolymer of ethylene, another embodiment of the present invention concerns the filaments, also called monofilaments, that may form the yarns of the invention. Said filaments may be isolated by means known to the skilled person from the yarns or other articles that have been obtained by processing said yarns. Depending on the nature and composition of said articles the isolation may take place through mechanical or physical treatment of the article, such as unraveling, untwisting, removal of foreign components by dissolution, filtration sieving or the like.

The filaments of the invention may have mechanical properties distinct in absolute value from the yarn or other article they form. Such is for example the case for strength measurements where the strength of a yarn is not the sum or average of the individual strengths of the filaments it contains. Likewise, the strength of a rope is not the sum or average of the individual yarn strengths or filament strengths it is composed from. The skilled person will be familiar with this efficiency loss when assembling filaments to yarns and yarns to yarn constructions. W02005066401 provides an indication of the dependency of tensile strength on the number of aggregated filaments. Accordingly, the present invention also concerns an inventive filament with its individual mechanical properties.

Therefor an embodiment of the present invention concerns a filament suitable for the multifilament yarn of the invention or other applications referred to herein, wherein the filament has a titer (also referred to as linear density) of at least 0.50 dtex, a modulus of at least 1700 cN/dtex, and a creep rate (measured at 70°C and at a load of 400 MPa, CR70/400) of at most at most 1 .0x1 O'⁷ s^_1 , whereby the modulus of the filament and the CR70/400 are measured according to the corresponding methods described in the METHODS. Preferably the filament has a CR70/400 of at most at most 8.0x1 O'⁸ s’¹, more preferably of at most at most 6.0x1 O'⁸ s^_1 and most preferably of at most at most 4.0x1 O'⁸ s^_1 . The theoretical lower limit of the creep rate of an UHMWPE filament may correspond to the absence of creep under the concerned test conditions, therefore the lower limit of the minimum filament creep rate of the filament may be as low as 1 .0x1 O'¹⁰ s^_1 or even as low as 1 .0x1 O'¹² s^_1.

Filaments according to the invention may have creep lifetime of up to and above 10⁶ seconds when measured under above mentioned CR70/400 conditions, corresponding to a week or more test durations. Therefore alternative creep measurement conditions can been chosen to quicker characterize the creep performance of the filaments, namely by increasing the applied load to 1200 MPa at identical temperature.

Accordingly, another embodiment of the present invention concerns a filament suitable for the multifilament yarn of the invention or other applications referred to herein, wherein the filament has a titer of at least 0.50 dtex, a modulus of at least 1700 cN/dtex, and a creep rate (measured at 70°C and at a load of 1200 MPa, CR70/1200) of at most at most 1.0x1 O'⁵ s^-1, whereby the modulus of the filament and the CR70/1200 are measured according to the corresponding methods described in the METHODS. Preferably the filament has a CR70/1200 of at most at most 8.0x1 O'⁶ s’¹, more preferably of at most at most 6.0x1 O'⁶ s^_1 and most preferably of at most at most 4.0x1 O'⁶ s’¹.

In a preferred embodiment, the filament of the invention has a modulus of at least 1750 cN/dtex, more preferably of at least 1800 cN/dtex, even more preferably of at least 1850 cN/dtex, and most preferably of at least 1900 cN/dtex. While there is no theoretical maximum to the stiffness, i.e. tensile modulus of UHMWPE filaments, a realistic upper tensile modulus may be as high as 2500 cN/dtex. In the context of the present application, the modulus of a filament, also called the tensile modulus or stiffness of a filament is measured as the Chord Modulus between 10 and 15 cN/dtex as further described in the METHODS. The inventors identified that with increasing tensile modulus of the filaments, the mechanical properties of the articles made thereof will be further improved. Amongst others may the linear density or areal density of filaments needed in a tension leg or a unidirectional sheet be further reduced while maintaining the specified performance of the article.

In yet another preferred embodiment of the invention, the UHMWPE filament has a tenacity as measured according to the METHODS of at least 4.50 N/tex, preferably at least 4.75 N/tex, more preferably at least 5.00 N/tex, even more preferably at least 5.25 N/tex and most preferably at least 5.50 N/tex. The skilled person will be aware that there are theoretical and practical limits to the tenacity of the UHMWPE polyethylene filaments, therefor the polyethylene filament may preferably have a tenacity of at most 8.00 N/tex. Moreover, it was observed that the inventive yarns could be obtained with filaments having unexpected high linear density. This advantage was surprising and contrary to the approach in the prior art where yarn and product improvements are often achieved through increased the draw ratio and hence filaments and yarns with ever lower linear density. For example, the best yarns disclosed in WO 2009/043597 have a titer as low as 85 dtex for a 390 filament yarn. Having high linear density filaments and their corresponding yarns, various properties of the yarns, e.g. filaments breakages, yarn productivity and ballistic properties may be optimized. Hence, it is desirable from the point of view of both yarn productivity and applicability to have yarns having good creep performance, high modulus and containing high linear density filaments. For the first time to inventors’ knowledge, the present invention provides such yarns. Therefor a preferred embodiment of the present invention concerns filaments and yarns comprising such filaments, having a linear density of at least 0.60 dtex, preferably at least 0.70 dtex, more preferably of at least 0.80 dtex, even more preferably of at least 0.90 dtex and most preferably at least 1 .0 dtex. Yarns or articles comprising filaments with very low linear density have numerous disadvantages. The yarns and articles especially show a lower robustness since the filaments have reduced breaking forces and deteriorate faster during manufacturing and handling of the yarn or article. At a given filament count of a yarn, the low linear density of the filament will result in low titer yarns making them inadequate for certain applications. This deficiency may be compensated by raising the number of filaments in a yarn or by increasing the number of yarns with said lower linear density to achieve the required linear density or areal density of the final article. But this would shift the described problems to the manufacturing process where the lower breaking force and higher number of filaments during the spinning process render the process less robust and cumbersome. It short it can be said that the mentioned lower limits of filament linear density are caused by economics and technology of current manufacturing processes but also robustness in the applications.

The filaments of the invention and as present in the inventive yarns may have a linear density, typically also referred to as titer, of at most 6.0 dtex, preferably at most 5.0 dtex, more preferably at most 4.0 dtex, even more preferably of at most 3.0 dtex and most preferably of at most 2.5 dtex. It was observed that filaments with lower titers are especially more suitable in the construction of unidirectional sheets or fabrics resulting in more homogeneous constructions.

The UHMWPE present in the multifilament yarns and filaments of the present invention is an ultra-high molecular weight polyethylene having an intrinsic viscosity (IV) of at least 10 dL/g. The IV is determined on solutions of UHMWPE in decalin at 135°C and according to ASTM D1601 (2004) as further described in the methods. Preferably the IV is between 10 and 50 dL/g, more preferably between 12 and 40 dL/g and most preferably between 15 and 35 dL/g to provide fibers, yarns and objects with optimal mechanical properties.

Accordingly the multifilament yarn or the filaments of the invention are multifilament yarn or the filaments gel-spun yarns or gel-spun filaments comprising ultra-high molecular weight polyethylene (UHMWPE) with intrinsic viscosities as described above.

The UHMWPE present in the multifilament yarns and the filaments of the present invention is characterized as a linear homopolymer of ethylene. Nevertheless, it may further comprises very small amounts of side chains such as in form of short chain branches which originate from a co-monomer present in the UHMWPE. With very small amounts of co-monomer is herein understood that said comonomers and the therefrom resulting short chain branches are close to or below the current detection limits as further defined below. The short chain branches may originate for example from impurities present in the raw materials or manufacturing process or may have been added as very small amounts during manufacturing. Herein the co-monomer is preferably selected from the group consisting of alpha-olefins with at least 3 carbon atoms, cyclic olefins having 5 to 20 carbon atoms and linear, branched or cyclic dienes having 4 to 20 carbon atoms. An alpha-olefin refers to an olefin with terminal unsaturation having 3 or more carbon atoms, preferably from 3 to 20 carbon atoms. Preferred alpha-olefins include linear mono-olefins such as propylene, butene-1 , pentene-1 , hexene-1 , heptene-1 , octene-1 and decene-1 ; branched mono-olefins such as 3-methyl butene-1 , 3-methyl pentene-1 and 4-methyl pentene-1 ; vinyl cyclohexane, and the like. Alpha-olefins may be used alone, or in a combination of two or more.

In a preferred embodiment, the alpha-olefin has between 3 and 12 carbon atoms. Even more preferably the alpha-olefin is selected from the group consisting of propene, butene-1 , hexene-1 , octene-1. Most preferably propene, butene-1 , hexene-1 are present as co-monomer in the UHMWPE. The applicant found that these alpha-olefins may readily copolymerize and may show optimized strongest effect on creep lifetime properties according to the invention.

In the context of the present invention short chain branches may be distinguished from long chain branches that are herein defined as a branches containing more than 20 carbon atoms but are often of substantially higher lengths reaching the dimensions of polymer chains and resulting in a branched polymer architecture, for example with a Y, H or E arrangement of the branches of the polymeric chains. Polymers having substantially no long chain branches are commonly referred to as linear polymers. In the context of the present invention, the UHMWPE is a linear polyethylene with less than 1 long chain branch per 1 ,000 total carbon atom, preferably less than 0.2 per 1 ,000 total carbon atoms, even more preferable less than 0.1 long chain branch per 1 ,000 total carbon atoms and most preferably with no LCB, whereby such absence of LCB may be defined as being below common detection limits.

It is well known from literature that the presence of short and long chain branches, herein referred to as side chain branches (SCB), in the UHMWPE substantially improves the creep behavior, and especially reduces the minimum creep rate and increases the creep lifetime. The inventors identified that for the herein described invention, said improvements come at the detriment of the filament and yarn manufacturing process, especially the drawability of the filaments and yarns. A direct consequence of the presence of branches is that the achievable strength properties, especially the modulus of the fibers, is reduced. Accordingly, the effect of branches in the UHMWPE affects the mechanical properties of creep rate and modulus in opposite ways and it is a matter of judicious choices to trade the creep rate improvement for a reduction of the strength properties. The inventors identified that in a preferred embodiment of the invention, the UHMWPE present in the inventive filaments and multifilament yarns may comprises at most 0.10 side chains branches per thousand total carbon atoms (SCB/1000TC), more preferably at most 0.08 SCB/1000TC, even more preferably at most 0.05 SCB/1000TC and most preferably no detectable side chain branches. The lower limit of side chain branches in the UHMWPE is defined by its absence, i.e. 0.0 side chain branches per 1000 carbon atoms, but in the context of the present invention said absence will be defined as below a detection limit of 0.05 SCB/1000TC, preferably below a detection limit of 0.03 SCB/1000TC. Further details about the measurement of the SCB are given with the Methods.

The above-described branching characteristics of the UHMWPE in the filaments stand in contrast to the earlier cited documents concerning low creep products, such as WO 2009/043597 where yarns and filaments made from an UHMWPE with short and long chain branches are described. Therein the UHMWPE is characterized by a delta delta (A5) value of 42° or less. The UHMWPE present in the filaments of the present invention may hence be defined as linear polyethylene homopolymers with no long chain branches and no short chain branches, or at least that said side chain branches are below the above mentioned limits or even below current detection limits. Preferably the UHMWPE of the present invention has less than a total of 0.10 methyl end groups thousand carbon atoms, more preferably less than a total of 0.08 methyl end groups thousand carbon atoms and even more preferably less than 0,05 methyl end groups per thousand carbon atoms stemming from said long chain and short chain branches combined. Alternatively, the present linear polyethylene homopolymers, which may contain very small amounts of long chain branches and short chain branches as described above, may be defined as having a Ab value of at least 45°, preferably at least 46°, yet more preferably at least 47° and even more preferably of at least 48°, whereby the Ab value and/or the methyl end groups are characterized according to the corresponding methods in WO 2009/043597. While the Ab value of a perfectly linear UHMWPE may depend upon other polymer characteristics, an upper limit for the Ab value for the UHMWPE present in the filaments may be 55°, preferably 60°.

According to the invention, the inventive UHMWPE filaments and yarns are obtained by a gel spinning process. For the present invention, by gel-spinning process is meant a process comprising at least the steps of (a) dissolving the polyethylene in a solvent to form a polymer solution having a UHMWPE concentration of between 2 and 40 wt%, (b) spinning the polymer solution through a multi orifice die plate to form solution filaments, (c) cooling the solution filaments to below 80°C to form gel filaments, (d) drawing the filaments in at least one step to form a drawn filament and (e) removing at least a portion of the solvent before, during or after the drawing. The gel-spinning process may optionally contain more than one drawing step wherein the gel filaments and/or the solid filaments are drawn with a certain draw ratio. Gel spinning processes are known in the art and are disclosed for example in WO 2005/066400; EP 1 ,699,954 and in “Advanced Fibre Spinning Technology, Ed. T. Nakajima, Woodhead Publ. Ltd (1994), ISBN 185573 182 7, these publications and the references cited therein being included herein by reference.

According to the invention, a gel-spinning process may be used to manufacture the inventive UHMWPE filaments and yarns, wherein as already mentioned hereinabove, the ultra-high molecular weight polyethylene (UHMWPE) is used to produce an UHMWPE solution, which is subsequently spun through a spinneret and the obtained gel fiber is dried to form a solid fiber.

The UHMWPE solution is preferably prepared with a UHMWPE concentration of at least 2 wt%, more preferably of at least 3 wt%. Preferably the UHMWPE concentration in the solvent is between 3 and 25wt%, more preferably between 4 and 12 wt%. Preferably, the concentration is between 3 and 25 wt% for UHMWPE with an IV of the UHMWPE composition in the range 8-50 dl/g, preferably 12-40 dl/g. To prepare the UHMWPE solution, any of the known solvents suitable for gel spinning the UHMWPE may be used. Such solvents are also referred to herein as “spinning solvents”. Suitable examples of solvents include aliphatic and alicyclic hydrocarbons, e.g. octane, nonane, decane and paraffins, including isomers thereof; petroleum fractions; mineral oil; kerosene; aromatic hydrocarbons, e.g. toluene, xylene, and naphthalene, including hydrogenated derivatives thereof, e.g. decalin and tetralin; halogenated hydrocarbons, e.g. monochlorobenzene; and cycloalkanes or cycloalkenes, e.g. careen, fluorine, camphene, menthane, dipentene, naphthalene, acenaphtalene, methylcyclopentandien, tricyclodecane, 1 ,2,4,5-tetramethyl-1 ,4-cyclohexadiene, fluorenone, naphtindane, tetramethyl-p- benzodiquinone, ethylfuorene, fluoranthene and naphthenone. Also combinations of the aboveenumerated solvents may be used for gel spinning of UHMWPE, the combination of solvents being also referred to for simplicity as solvent. In a preferred embodiment, the solvent of choice is not volatile at room temperature, e.g. paraffin oil. It was also found that the process of the invention is especially advantageous for relatively volatile solvents at room temperature, as for example decalin, tetralin and kerosene grades. In the most preferred embodiment the solvent of choice is decalin.

The UHMWPE solution is then formed into gel filaments by spinning said solution through a multi orifice die plate, also called spinneret. By multi orifice die plate is herein understood a spinneret containing preferably at least 100, yet even more preferably at least 300, most preferably at least 500 spinholes. Preferably, the spinning temperature is between 150°C and 300°C, more preferably said temperature is chosen below the boiling point of the spinning solvent. In case the dissolution temperature in the extruder was higher than said boiling point, the UHMWPE solution may need to be cooled to the adequate spinning temperature. If for example decaline is used as spinning solvent the spinning temperature is preferably at most 190°C.

In a preferred embodiment, each spin-hole of the die plate has a geometry comprising at least one contraction zone. By contraction zone is herein understood a zone with a gradual decrease in diameter with a cone angle of preferably below 60°, from an initial diameter Do to a final diameter D_n such that a draw ratio in the spinplate (DR_sp) is achieved in the spin-hole. Preferably, the spin-hole further comprises upstream and/or downstream of the contraction zone, a zone of constant diameter.

Preferably, the multifilament yarn is issued from the spin-holes into an air gap and then into a quench zone, said air gap having a length of preferably between 1 mm and 20 mm. Although called air gap, said gap can be filled with any gas or gaseous mixture, e.g. air, nitrogen or other inert gases. By air gap is herein understood the distance between the spinning plate and the quench zone. The quench zone can be a liquid, e.g. water, containing bath at a temperature below the spinning temperature, e.g. about room temperature. Preferably, the multifilament yarn is drawn in the air gap with a draw ratio DR_ag, typically referred to in the art as draw down, of between 2 and 20, more preferably between 4 and 15, most preferably between 5 and 10. The inventors identified that to produce the inventive filaments and yarns with their optimized balance of physical and mechanical properties, they had to deviate from the common practice in decaline spinning process to apply high draw ratio in the air gap. In contrast the challenge was to optimize the DR_ag to sufficiently reduce the gel filament diameter for optimal cooling in the quench bath while keeping the gel filament diameter sufficiently high, making filaments with high linear density and optimized modulus and creep rate available. Such optimum showed beneficial effect on the creep performance of the yarns and filaments of the invention.

The gel filaments formed by spinning the UHMWPE solution through the spinneret may be extruded into an air gap, and then into a cooling zone, also called quench bath or quench zone, where they are cooled to below 80°C to form gel fibers or gel filaments from where they are picked-up on a first driven roller. In the cooling zone, the gel filaments are cooled preferably in a gas flow and/or in a liquid bath.

Subsequently to forming the gel filaments, said gel filaments are subjected to a solvent extraction step wherein the spinning solvent used to manufacture the UHMWPE solution is at least partly removed from the gel filaments to form solid filaments. The solvent removal process may be performed by known methods, for example by evaporation when a relatively volatile spinning solvent, e.g. decaline, is used or by using an extraction liquid, e.g. when paraffin is used as spinning solvent, or by a combination of both methods. Preferably the gel filaments are drawn with a draw ratio of preferably at least 1 .2, more preferably at least 1 .5, most preferable at least 2.0.

The manufacturing process further comprises drawing the filaments before, during and/or after said removal of the solvent. Preferably, the drawing of the filaments after removal of the solvent is performed in at least one drawing step, with a draw ratio of at least 3, more preferably at least 4, most preferably at least 5. More preferably, the drawing of filaments is performed in at least two steps, or even in at least three steps. Preferably, each drawing step is carried out at a different temperature that is preferably chosen to achieve the desired drawing ratio without the occurrence of filament breakage. Preferably, drawing is performed in more than two steps, and if UHMWPE is used preferably the drawing is carried out at different temperatures with an increasing profile between about 120 and 155°C. If the drawing of solid filaments is performed in more than one step, DR_SOiid is calculated by multiplying the draw ratios achieved for each solid individual drawing step.

Preferably, the overall draw ratio, i.e. the total draw ratio to which the filaments are subjected during their entire manufacturing process is at least 20, more preferably at least 25, even more preferably at least 30, most preferably at least 40. It was observed that by increasing the overall draw ratio, the mechanical properties of the inventive yarns were improved. In particular the tensile strength and modulus increased.

The inventive gel spun filaments or yarns comprising the gel spun filaments are suitable filaments and yarns for typical filament and yarn applications. Hence one embodiment of the present invention concerns an article comprising the multifilament yarn or the filaments according to the invention, preferably the article is selected from the group consisting of yarns, ropes, cables, nets, fabrics, and protective appliances such as ballistic resistant articles.

The inventive UHMWPE filaments or yarns have properties which make them an interesting material for use in ropes, cordages and the like, preferably ropes designed for heavy-duty operations as for example marine, industrial and offshore operations. Rigging ropes and ropes used in sports applications such as yachting, climbing, kite flying, parachuting and the like are also applications where the filaments and yarns of the invention may perform well. In particular it was observed that the inventive UHMWPE filaments are particularly useful for longterm and ultralong-term heavy-duty operations.

Heavy duty operations may further include, but not restricted to, crane ropes, ropes for deep-sea deployment or recovery of hardware, anchor handling, mooring of support platforms for offshore renewable energy generation, mooring of offshore oil drilling rigs and production platforms such as offshore production platforms and the like. It was surprisingly observed that for such operations, and in particular for offshore mooring, the installation of ropes and tendons designed therefor may be optimized, e.g. the ropes, tendons umbilicals or cables can be installed using less complex hardware or smaller and lighter installation equipment. Accordingly an embodiment of the present invention concerns articles wherein the article is a one-dimensional article selected from the group consisting of rope, sling, chain, tendon, tether, umbilical and cable. Preferably the article is a rope or a parallel wound tendon. The inventive UHMWPE filaments and yarns are also very suitable for use as a reinforcing element, for example in a liner, for reinforced products such as hoses, pipes, pressurized vessels, electrical and optical cables, especially when said reinforced products are used in deepwater environments where reinforcement is required to support the load of the reinforced products when free hanging. The invention therefore also relates to a liner and a reinforced product containing reinforcing elements or containing said liner, wherein the reinforcing elements or the liner contain the inventive UHMWPE filaments or yarns.

Most preferably, the inventive UHMWPE filaments or yarns are used in applications where said filaments and yarns experience static or dynamic tension or static and dynamic loads and in particular long-term and ultralong-term tension or loads. By static and dynamic tension is herein meant that the filament or yarn in the application is always or most of the time under tension irrespective if the tension is at constant level (for example a weight hanging freely on a rope comprising the filaments or yarns) or varying level (for example if exposed to thermal expansion or water wave motion). Examples of applications wherein static and dynamic tensions are encountered are for example many medical applications (for example cables and sutures) but also mooring ropes, and tension reinforcement elements, as the improved mechanical properties of the present filaments and yarns lead to improved performances of these in similar applications. A particular application of the inventive UHMWPE filaments and yanrs is in crane ropes or tendons where the article can reach an elevated temperature as result of ambient temperatures and/or internal heat generation due to vibrations, bending or friction.

The invention further relates to composite articles containing the inventive UHMWPE filaments or yarns. In a preferred embodiment, the composite article contains at least one monolayer comprising the UHMWPE filaments of the invention. The term monolayer refers to a layer of filaments, i.e. filaments in one plane. In a further preferred embodiment, the monolayer is an unidirectional monolayer. The term unidirectional monolayer refers to a layer of unidirectionally oriented filaments, i.e. filaments in one plane that are essentially oriented in parallel. In a yet further preferred embodiment, the composite article is multi-layered composite article, containing a plurality of unidirectional monolayers the direction of the filaments in each monolayer preferably being rotated with a certain angle with respect to the direction of the filaments in an adjacent monolayer. Preferably, the angle is at least 30°, more preferably at least 45°, even more preferably at least 75°, most preferably the angle is about 90°. Multilayered composite articles proved very useful in ballistic applications, e.g. body armor, helmets, hard and flexible shield panels, panels for vehicle armoring and the like. Therefore, the invention also relates to ballistic-resistant articles as the ones enumerated hereinabove containing the UHMWPE filaments of the invention. Accordingly an embodiment of the invention concerns two dimensional articles, preferably articles selected from the group consisting of interlaced fabrics such as woven, braided or knitted fabrics, and non-interlaced fabrics such as felts, unidirectional sheets, or membranes.

The inventive UHMWPE filaments and yarns of the invention are also suitable for use in medical devices, e.g. sutures, medical cables, implants, surgical repair products and the like. The invention therefore further relates to a medical device, in particular to a surgical repair product and more in particular to a suture and to a medical cable comprising the UHMWPE filaments and yarns of the invention.

It was also observed that the inventive UHMWPE filaments and yarns are also suitable for use in other applications like for example, synthetic chains, conveyor belts, tensiarity structures, concrete reinforcements, fishing lines and fishing nets, ground nets, cargo nets and curtains, kite lines, dental floss, tennis racquet strings, canvas (e.g. tent canvas), nonwoven cloths and other types of fabrics, webbings, battery separators, capacitors, pressure vessels (e.g. pressure cylinders, inflatables), hoses, (offshore) umbilical cables, electrical, optical fiber, and signal cables, automotive equipment, power transmission belts, building construction materials, cut and stab resistant and incision resistant articles, protective gloves, composite sports equipment such as skis, helmets, kayaks, canoes, bicycles and boat hulls and spars, speaker cones, high performance electrical insulation, radomes, sails, geo-textiles such as mats, bags and nets, and the like. Therefore, the invention also relates to the applications enumerated above containing the UHMWPE filaments or yarns of the invention.

The invention also relates to an elongated object comprising a plurality of the UHMWPE filaments of the invention, wherein said filaments are at least partly fused to each other. In one embodiment said elongated object is a monofilament. In a different embodiment, said elongated object is a tape. By at least partly fused filaments is herein understood that individual filaments are fused at multiple locations along their length and disconnected between said locations. Preferably, said filaments are fully fused to each other, i.e. the individual filaments are fused to each other over essentially their whole length. Preferably, the fusing is carried out by at least compressing said plurality of UHMWPE filaments under a temperature lower than the melting temperature of the filaments. The melting temperature of the fibers can be determined by DSC using a methodology as described at pg. 13 of WO 2009/056286. Processes of fusing UHMWPE filaments into monofilaments and tapes are known in the art and disclosed for example in W02006/040190, W02009/056286 and WO2013/131996. It was observed that by using the filaments of the invention, monofilaments and tapes having optimized creep properties were achieved. Such products were suitable for utilization in applications such as fishing lines; liners; reinforcing elements; antiballistic articles such as armors; car parts; and architectural applications such as doors.

The invention is further explained by means of the following examples, without being limited thereto.

METODS as referred to in the present application, are as follows:

• Elonqational stress (ES) of an UHMWPE is measured according to ISO 11542-2A.

• Intrinsic Viscosity (IV) is determined according to method ASTM D1601 (2004) at 135°C in decalin, the dissolution time being 16 hours under mild agitation via shaking, with BHT (Butylated Hydroxy Toluene) as anti-oxidant in an amount of 2 g/l solution, by extrapolating the viscosity as measured at different concentrations to zero concentration.

• Yarn titer was measured by weighing 100 meters of yarn. The titer of the yarn is calculated by dividing the measured weight by the length and converting to the corresponding dtex unit of g/10,000 m.

• Filament linear density (titer) and mechanical properties (Filament tenacity and filament tensile modulus) measurement is carried out on a semiautomatic, microprocessor controlled tensile tester (Favimat, tester no. 37074, from Textechno Herbert Stein GmbH & Co. KG, Mbnchengladbach, Germany) which works according to the principle of constant rate of extension (DIN 51 221 , DIN 53 816, ISO 5079) with integrated measuring head for linear density measurement according to the vibroscopic testing principle using constant tensile force and gauge length and variable exciting frequency (ASTM D 1577). The Favimat tester is equipped with a 1200 cN balance, no. 14408989. The version number of the Favimat software: 3.0.3625.

Clamp slippage during filament tensile testing, preventing filament fracture, is eliminated by adaption of the Favimat clamps according to figure 3.

The upper clamp 121 is attached to the load cell (not shown). The lower clamp 122 moves in downward direction (D) with selected tensile testing speed during the tensile test. The filament (125) to be tested, at each of the two clamps, is clamped between two jaw faces 123 (4x4x2 mm) made from Plexiglass® and wrapped three times over ceramic pins 124 and 125. Prior to tensile testing, the linear density of the filament length between the ceramic pins is determined vibroscopically. Determination of filament linear density is carried out at a filament gauge length (F) of 50 mm (see figure 3), at a pretension of 6.0 cN/tex (using the expected filament linear density calculated from yarn linear density and number of filaments). Subsequently, the tensile test is performed at a test speed of the lower clamp of 25 mm/min with a pretension of 0.50 cN/tex, and the filament tenacity is calculated from the measured force at break and the vibroscopically determined filament linear density. The elongational strain is determined by using the whole filament length between the upper and lower plexiglass jaw faces at the defined pretension of 0.50 cN/tex. The beginning of the stress-strain curve shows generally some slackness and therefore the tensile modulus is calculated as a chord modulus between two stress levels. The Chord Modulus between 10 and 15 cN/dtex is given by equation (1):

ChordModulusbetweenl 0 and 15 cN/dtex = CM(10: 15)= — — — (N/tex) (1)

^£15 “ ^£10 where:

E10 = elongational strain at a stress of 10 cN/dtex (%); and Ei5 = elongational strain at a stress of 15 cN/dtex (%).

The measured elongation at break is corrected for slackness as by equation (2):

EAB= EAB(measured) ( where:

EAB = the corrected elongation at break [%]

EAB (measured) = the measured elongation at break [%] E₅ = elongational strain at a stress of 5 cN/dtex [%]

CM(5:10) = Chord Modulus between 5 and 10 cN/dtex [N/tex],

• Areal density (AD) of a panel, sheets or monolayer was determined by measuring the weight of a sample of preferably 0.4 m x 0.4 m with an error of 0.1 g.

• Linear Density (LD). Unless provided differently herein, the linear density of an article is defined by its weight per unit of length. Said linear density may be measured by for example isolating a defined length (e.g. 1 m) of said article and weighing said article. Dividing the weight of the article by its length will provide the linear density thereof.

• Ballistic performance of molded articles was determined by calculating the V50 value of 8 individual shots on 8 individual panels. The square sample panels had the dimension of 200 mm x 200 mm with the filament orientations being respectively parallel to its sides. The sample panels were fixed behind a target holder frame with one side parallel to the ground and maintained in place by a small piece of adhesive tape. The shooting distance was 10 meters and the shots were aimed perpendicular, at the center of the panel. Projectile used is 7.62 x 39 mm MSC (AK47) as for example supplied by Sellier and Bellot, Czech Republic. The first shot is fired at a projectile speed (V50) at which it is anticipated that 50% of the shots would be stopped. If a stop is obtained, the next shot is fired at an anticipated speed being 40 m/s higher than the previous speed. If a perforation occurs, the next shot is fired at an anticipated speed 40 m/s lower than the previous speed. The speed of the projectile was measured 1 meter before the impact. The result for the experimentally obtained V50 value is the mean average of the four highest stops and the four lowest perforations. When there is a surplus on stops or penetrations, then these surpluses needed to be eliminated until the number of shots that resulted in a stop and the number of shots that resulted in a penetration are the same. This is accomplished by the elimination of the stops with lowest shooting velocity, or the elimination of the penetrations with the highest shooting velocity.

• Spaced Back Face Deformation (Spaced BFD) was measured according to a captive method using a 9 mm 124 grain FMJ Remmington threat shot at 430 +/- 9 m/s.

The 200 mm by 200 mm panel is positioned in front of Roma clay of 12 cm thickness. Between the panel and the clay an aluminum spacer frame of 1/2“ (12.7 mm) thickness is positioned such that the back side of the panel is half an inch away from the clay surface, simulating actual positioning of anti-ballistic panels with respect to the human body. The assembly of panel/spacer/clay is kept in place by the use of rubber bands on the edges of the construction. A single shot in the center of the panel is performed and the indentation of the clay is measured in mm. The average indentation depth of 8 samples is reported. For cold spaced back face deformation, the panel is tested at room temperature while hot spaced back face deformation is performed on a panel that was been conditioned for at least 4 hours in an oven at 71 °C (160 F).

• Tensile properties of multifilament yarns: elongation at break, tenacity, tensile strength, tensile modulus are defined and determined on multifilament yarns as specified in ASTM D885M, using a nominal gauge length of the fiber of 500 mm, a crosshead speed of 50 %/min and Instron 2714 clamps, of type “Fiber Grip D5618C”. On the basis of the measured stress-strain curve the modulus is determined as the gradient between 0.3 and 1 % strain. For calculation of the modulus and strength, the tensile forces measured are divided by the titre. The tensile properties of UHMWPE yarns may be converted by employing the specific weight of highly oriented polyethylene, 970 kg/m³.

• Creep properties of yarns are determined in accordance with the methodology described in the paper “Predicting the Creep Lifetime of HMPE Mooring Rope Applications" by M. P. Vlasblom and R.L.M. Bosman - Proceedings of the MTS/IEEE OCEANS 2006 Boston Conference and Exhibition, held in Boston, Massachusetts on September 15-21 , 2006, Session Ropes and tension Members (Wed 1 :15 PM - 3:00 PM). More in particular the creep rate (CR) and creep lifetime (CLT) may be determined with a device as schematically represented in Figure 1 , on untwined yarn samples, i.e. yarn with substantially parallel filaments, of about 1500 mm length. The yarn samples are slip-free clamped between two clamps (101) and (102) by winding each of the yarn ends several times around the axes of the clamps and then knotting the free ends of the yarn to the yarn body. The final length of the yarn between the clamps (200) is about 180 mm. The clamped yarn sample was placed in a temperature-controlled chamber (500) at a temperature of 70°C by attaching one of the clamps to the ceiling of the chamber (501) and the other clamp to a specific counterweight (300) to result in a predetermined load on the yarn (400 or 775 MPa as reported in the examples). The load is achieved by adjusting the weight of the attached counterweight (300) while considering the titer of the yarns. The position of the clamp (101) and that of clamp (102) can be read on the scale (600) with the help of the indicators (1011) and (1021). The initial position of the counterweight is the position wherein the length of the yarn (200) equals the distance between (101) and (102) as measured on (600). The elongation of the yarn in time was followed on the scale (600) by reading the position of the indicator (1021). The time needed for said indicator to advance 1 mm is recorded for each elongation of 1 mm until the yarn breaks.

The elongation of the yarn £, [in mm] at a certain time t is herein understood the difference between the length of the yarn between the clamps at that time t, i.e. L(I) , and the initial length (200) of the yarn between the clamps. Therefore: s; (t in mn =L(t)-L₀

The elongation of the yarn [in percentages] is:

The creep rate [in s^_1] is defined as the change in yarn’s length per time step and was determined according to Formula (1) as: wherein and f^ are the elongations [in %] at moment z and at the previous moment and t_j are the time (in seconds) needed for the yarn to reach the elongations , respectively. The creep rate [1/s] was then plotted on a logarithmic scale vs. the elongation in percentage [%] to yield a plot (100) as for example shown for an unrelated yarn in Figure 2. The minimum (1) of the plot in Figure 2 is then determined and the linear portion (2) thereof after said minimum (1) is fitted with a straight line (3) which contains also the minimum (1) of the plot. The elongation (4) where the plot (100) begins to deviate from the straight line is used to determine the time at which initial breakage of individual filaments occurs, also called beginning of regime-3. This time is considered as the lifetime to failure of the yarn under investigation. Said elongation (4) is considered as the elongation during the creep lifetime, elongation until time-to-failure.

The minimum in the plot is also referred to as the minimum creep rate, and in the context of the present invention are used interchangeably with creep rate, CR, whereby the temperature and the load are reported as indices, CR₇o,4oo.

• Creep properties of a filament are performed in a similar method to the method for yarns as described here above, by subjecting single filaments to a permanent load (400 MPa, 775 MPa, 1200 MPa) at a constant temperature while recording the elongation over time. The filament creep testing is carried out on a RSA-G2 Solids Analyzer (tester no. 4020- 0014, from Waters I TA Instruments, New Castle, England). The RS-G2 Solids Analyzer is equipped with a 35 N balance and is controlled via TA instruments software TRIOS. The clamping setup on the RSA-G2 Solids Analyzer is build up analogue to the Favimat setup shown figure 3 and described above. The upper clamp 121 is attached to the load cell (not shown) and moves in upward direction till selected creep load is reached. The filament (125) to be tested, at each of the two clamps, is clamped between two jaw faces and wrapped three times over ceramic pins 124 and 125.

To determine the permanent load to be applied during the creep measurement, the linear density of the respective filament is determined according to the Favimat method described here above, on a semiautomatic, microprocessor controlled tensile tester (Favimat, tester no. 37074, from Textechno Herbert Stein GmbH & Co. KG, Monchengladbach, Germany) with the difference that the determination of filament linear density is carried out at a filament gauge length (F) of 100 mm, at a pretension of 10 cN/tex (using the expected filament linear density calculated from yarn linear density and number of filaments). Since the vibroscopic measurement is non-destructive, the 100 mm sample of filament is used to determine creep properties of said filament.

As in the yarn measurements, regime-1 and regime-2 creep are observed, corresponding to the reversible elongation and the actual creeping of the filament. The minimum in regime-2 is reported as the minimum creep rate, or simply creep rate. A regime-3 is not observed for single filaments since rupture of the sole filament represents the end of the measurement.

Side chains per 1000 total carbon is determined by NMR techniques. The amount of methyl groups present in the UHMWPE for example as methyl side groups and as methyl end groups (in ethyl or butyl short side chains as well as the methyl end groups of long chain branches and the methyl end groups of the polyethylene chains) are identical to the amounts of methyl groups per thousand carbon atoms contained by the UHMWPE as determined by proton ¹H liquid-NMR, hereafter for simplicity NMR, as follows:

3 - 5 mg of UHMWPE were added to a 800 mg 1 ,1 ’,2,2’-tetracholoroethane-d₂ (TCE) solution containing 0.04 mg 2,6-di-tert-butyl-paracresol (DBPC) per gram TCE. The purity of TCE was > 99.5 % and of DBPC > 99 %.

The UHMWPE solution was placed in a standard 5 mm NMR tube which was then heated in an oven at a temperature between 140° - 150°C while agitating until the UHMWPE was dissolved.

The NMR spectrum was recorded at 130°C with a high field (> 400 MHz) NMR spectrometer using an 5 mm inverse probehead and set up as follows: a sample spinrate of between 10 - 15 Hz, the observed nucleus - ¹H, the lock nucleus - ²H, a pulse angle of 90°, a relaxation delay of 30 sec, the number of scans was set to 1000, a sweep width of 20 ppm, a digital resolution for the NMR spectrum of lower than 0.5, a total number of points in the acquired spectrum of 64k and a line broadening of 0.3 Hz. The recorded signal intensity (arbitrary units) vs. the chemical shift (ppm), hereafter spectrum 1 , was calibrated by setting the peak corresponding to TCE at 5.91 ppm.

- After calibration, the two peaks (doublet) of about equal intensity to determine the amount of methyl side groups can be identified in the ppm range between 0.8 and 0.9 ppm. The first peak should be positioned at about 0.85 ppm and the second at about 0.86 ppm. The three peaks (triplet) to determine the amount of methyl end groups which are also present in the ppm range between 0.8 and 0.9 and can be located after the second peak of the methyl side groups towards increasing the ppm range.

The deconvolution of the peaks was performed using a standard ACD software produced by ACD/Labs;

The accurate determination of the areas A1 methyl side groups, hereafter A1 of the deconvoluted peaks used to determine the amount of methyl side groups, i.e. A1 = A1 first peak + Al second peak was computed with the same software.

The accurate determination of the areas A2_methyi end groups, hereafter A2 of the deconvoluted peaks used to determine the amount of methyl end groups, i.e. A2 = A2fj_rst peak + A2second peak + A2_third peak was computed with the same software.

Further an area A3 is identified, corresponding to the area of the peak given by the CH₂ groups of the main UHMWPE chain, being the highest peak in the entire spectrum and located in the ppm range of between 1.2 and 1.4.

The amounts of methyl groups per thousand carbon atoms was computed as follows:

1000x(— +— ) methyl groups per 1000C = 2 x -

Since this is the total amount of methyl groups present in the UHMWPE, the amount of side chains is determined by deducting from the total amount of methyl groups the terminal methyl groups of the polymeric chains. Dividing the number average molecular weight of the UHMWPE (Mn) by 14 g/mol provides the total average amount of carbon atoms per polymeric chain, each chain having 2 terminal methyl groups, therefor the to be deducted number of terminal methyl groups per 1000C can be calculated via the formula terminal methyl groups per 1000C = 2 x ¹^¹⁰

Side chains per 1000 total carbon atoms is hence obtained by subtracting the terminal methyl groups from the total methyl groups of the UHMWPE.

EXPERIMENTAL

Commercial scale yarn grades have been employed to design tension members for a floating offshore wind platform. Mechanical and physical characteristics are reported in Table 1 , Table 2 and Table 3 below. Herein Yarn A is an ultra-low creep yarn with 780 filaments and a yarn titer of 1760 dtex and comprising a UHMWPE with an IV of about 16 dL/g and with about 0.5 short chain branches per 1000TC, manufactured according to a technology similar as described in WO2012/139934, Yarn B is a low creep yarn with 780 filaments and a yarn titer of 1760 dtex comprising a UHMWPE with an IV of about 17 dL/g and about 0.3 short chain branches per 1000TC and manufactured according to a technology similar as described in WO 2009/043597 and Yarn C is a high tenacity yarn with 780 filaments, a yarn titer of 880 dtex and comprising a linear UHMWPE with an IV of about 22 dL/g, manufactured in accordance with the technology as described in W02005066401 .

For Yarn 1 , a 4 wt% slurry in decalin of a UHMWPE homopolymer powder having an ES of 0.92 N/mm² was prepared. The UHMWPE had no detectable amount of short chain or long chain branches. The slurry was fed to and heated in a 133 mm co-rotating twin screw extruder where the slurry was transformed into a homogeneous solution of 187°C. Passed the extruder, the solution temperature was brought down to 180°C and transported by a gear pump through a spin plate having 780 spin holes with a rate of 2.4 g/min per hole.

The spin holes had an initial cylindrical channel of 3 mm diameter followed by a conical contraction with a cone angle of 30° into a cylindrical channel of 1.0 mm diameter and length of 10 mm. The fluid filaments issued from the cylindrical channel entered an air gap of length 15 mm. The fluid filaments were taken-up at such rate that a drawdown of 7 was applied to the fluid filaments in the air-gap and then cooled to room temperature in a water bath.

The filaments subsequently entered an oven. In the oven the filaments were further stretched 8 times at about 147°C and the decalin evaporated. The yarn was drawn in a second step at a temperature of 152°C with a draw ratio of 4. A yarn with an IV of 33 dL/g and the mechanical and physical characteristics as reported in Table 1 , Table 2 and Table 3 was obtained.

Table 1

Table 2

Table 3

Comparative Experiments 1.1 , 1.2 and 1.3 and Example 1 The design of tendons for floating offshore wind installations is heavily depending upon multiple factors. When designing a tension leg platform, the dynamic stiffness (EA) of the tendons is a critical design parameter since it defines the dynamic stability of the platform with the goal to avoid resonance upon common excitation. Next to the requirement of dynamic stiffness the tendons should also be able to withstand permanent and peak stresses on the tendons during its required lifetime. Last but not least, by the buoyancy of the floater of the platform the tendons will be preloaded with a mean load, while the weather and tide induced dynamic loading will add a time-varying load around this mean.

The exact details on the magnitude of the preload, dynamic stiffness, and lifetime requirement will differ from design to design of the installation and are further affected by tendon design, such a braiding structure and angle. Nevertheless, for typical water depths (between 100 and 500 meter), pretensions as a result of buoyancy are typically in the order of 10,000 kN per leg. In order to avoid resonance excitations, the stiffnesses was set at 5,000 MN for each leg and to ensure identical dynamic response, the dynamic stiffness should be increased proportionally with increasing water depth. As a working example, tendon for 100 m water depth may require a dynamic stiffness of 5,000 MN and a tension preload of 10,000 kN and must last for 25 years, whereby a required safety factor of 3 results in a 75 year design lifetime at an average ambient temperature of 20°C. In case the platform is install at a water depth of 50, 200 m or 300 m, the preload remains constant but the required dynamic stiffness changes proportionally to 2,500 MN, 10,000 MN and 15,000 MN.

The required linear weights of the tendons to meet the above mentioned criteria of dynamic stiffness, peak loads and lifetime are reported here below.

Table 4

When comparing in Table 4 the required linear weights of Comparative Experiments 1.1 , 1.2 and 1.3, respectively representing tendon designs with Yarn A, Yarn B and Yarn C, for their efficiency at different water depth, it is visible that the low creep grades Yarn A outperforms the other yarns at limited water depths, but fail to meet requirements when a given dynamic stiffness is required over a higher length, e.g. depth. A yarn and filaments according to the invention, namely a yarn with a modulus of 1 ,845 cN/dtex and a minimum creep rate of 1x1 O'⁷ s^{_ 1} proves to be the material of choice to provide tendons with low linear density, i.e. mass of filaments per meter, and outperforms the other known synthetic fibers.

This demonstrates that Yarn 1 according to the invention offers significant improvement on the dynamic response of UHMWPE yarn tension members without significant compromise on fatigue performance.

It was furthermore identified that the inventive yarns and filaments could be used for the manufacture of other fibrous articles such as for example ballistic resistant sheets. Surprisingly also in these applications the new and unique mechanical properties provide an advantage, for example back face deformation. Back face deformation is effectively the size of the impact dent measurable on the non-impact side of a ballistic assembly. It is typically measured in mm of greatest deformation perpendicular to the plane of the impacted surface of the ballistic resistant article. It was surprisingly observed that the size of the impact dent is small, if molded articles are produced with filaments according to the invention. In other words, the back face deformation is small. Such armor will be especially suitable for combat helmet shells, because they show reduced back face signature on stopping projectiles, thus reducing trauma on the human skull and brain after being hit by a stopped projectile.

Comparative Experiments 2.1

A composite monolayers of polyethylene filaments was prepared according to the process as described in W02005066401 . The above mentioned multifilament Yarn C having 780 filaments with a yarn titer of 880 dtex and a modulus of 1590 cN/dtex, was used to make a uni-directional (UD) mono-layer by feeding the yarn from several bobbins from a creel, spreading the filaments, and impregnating the filaments with an aqueous dispersion of Kraton® D1107 styrene-isoprene-styrene blockcopolymer as binder material. After drying the UD monolayer had an areal densities of 34 g/m² with a binder content of about 17 wt%.

Four such unidirectional layers were cross plied in a 0° 90° 0° 90° sequence and consolidated for 30 seconds at a pressure of 30 bar and a temperature of 115°C. The resulting sheet, had an areal density of 136 g/m².

Example 2

CE 2.1 was repeated with the difference that the Yarn C was replaced by Yarn 1 as described above, i.e. a multifilament yarn having 780 filaments with a yarn titer of 810 dtex and a modulus of 1845 cN/dtex. The slight lower yarn dtex resulted in UD monolayer with an areal densities of 30 g/m² and a binder content of about 15 wt% while the resulting sheets had an areal density of 120 g/m².

Multiple sheets of CE 2.1 and Ex 2 were stacked to form assemblies having targeted panel areal densities of 6.8 kg/m² and 9.8 kg/m². In total, 50 and 72 sheets of CE 2.1 and 57 and 82 sheets of Ex 2 were respectively stacked, with the alternating 0790° direction of filaments in adjacent monolayers maintained throughout the stack. The assemblies of sheets were pressed at 16.5 MPa at 138°C for 40 minutes followed by a cooling period of 20 min at 2 MPa and finally cut to 200 mm x 200 mm panels for ballistic testing. The molded panels are reported as CE 2.1 and Ex 2 in table 3. The molded panels with an areal density of 9.8 kg/m² were shot with a 7.62 x 39 mm MSC (AK47) bullet in order to determine its V50. The molded panels with an AD of 6.8 kg/m² were shot with a 9 mm FMJ Remington bullet to determine cold and hot spaced back face deformation as described in the methods.

Table 5 As can be seen, when compared at identical areal density, the hard ballistic assemblies comprising the inventive yarn show an unexpected improvement with respect to their cold and hot back face deformation performance.

Claims

1 . A multifilament ultra-high molecular weight polyethylene (UHMWPE) yarn having at least 25 filaments, a titer of at least 50 dtex, a filament titer of at least 0.50 dtex, a tensile modulus of at least 1500 cN/dtex and a minimum creep rate of at most 5.0x1 O'⁷ s’¹ when measured at 70°C under a load of 400 MPa, wherein the ultra-high molecular weight polyethylene is a linear homopolymer of ethylene.

2. The multifilament yarn of claim 1 wherein the yarn has a tenacity of at least 42.0 cN/dtex.

3. The multifilament yarn of claim 1 or 2 wherein the yarn has a minimum creep rate CR70/400 of at most 2.5x1 O'⁷ s’¹.

4. The multifilament yarn of anyone of the claims 1 to 3 wherein the multifilament yarn comprises at least 50 filaments.

5. A filament suitable for any of the multifilament yarns of claims 1 to 4, wherein the filament has a titer of at least 0.50 dtex, a modulus of at least 1700 cN/dtex, and a creep rate (measured at 70°C and at a load of 400 MPa, CR70/400) of at most at most 1 .0x1 O'⁷ S’¹, whereby the modulus of the filament and the CR70/400 are measured according to the corresponding methods described in the METHODS.

6. A filament suitable for any of the multifilament yarns of claims 1 to 4, wherein the filament has a titer of at least 0.50 dtex, a modulus of at least 1700 cN/dtex, and a creep rate (measured at 70°C and at a load of 1200 MPa, CR70/1200) of at most at most 1.0x1 O’⁵ s’¹, whereby the modulus of the filament and the CR70/1200 are measured according to the corresponding methods described in the METHODS.

7. The filament of claim 5 or 6 wherein the filament has a modulus of at least 1800 cN/dtex.

8. The multifilament yarn or the filament according to anyone of the claims 1 to 7 wherein the multifilament yarn or the filament comprises a UHMWPE with an intrinsic viscosity of at least 10 dL/g.

9. The multifilament yarn or the filament according to claims 8 wherein the UHMWPE of the yarn or the filament has an IV of between 12 and 40 dL/g.

10. The multifilament yarn or the filament according to anyone of the claims 1 to 9 wherein the UHMWPE of the yarn or the filament comprises at most 0.10 side chain branches per thousand total carbon atoms.

11 . The multifilament yam or the filament according to anyone of the claims 1 to 10 wherein the filaments of the yarn or the filament have a titer of at least 0.80 dtex.

12. An article comprising the multifilament yarn according to any one of the claims 1 to 4 or 8 to 11 or the filament according to any of the claims 5 to 11 .

13. The article of claim 12 wherein the article is a one-dimensional article selected from the group consisting of rope, sling, chain, tendon, tether, umbilical and cable.

14. The article of the claim 13 wherein the article is a two dimensional article from the group consisting of interlaced fabrics such as woven, braided or knitted fabrics, and noninterlaced fabrics such as felts, unidirectional sheets, or membranes.