Biologically degradable polymer fibre made of renewable raw materials

Abstract

The invention relates to a biologically degradable polymer fibre made of renewable raw materials with good physical properties, as well as a method for its production and its use. The Polymer blend fibre of the present invention is made from different biopolymers, each being an aliphatic polyester, and is biologically degradable under Home Composting conditions.

Description

[0001] Biologically degradable polymer fibre made of renewable raw materials

[0002] The invention relates to a biologically degradable polymer fibre made of renewable raw materials with good physical properties, as well as a method for its production and its use.

[0003] Polymer fibres, i.e. fibres based on synthetic polymers, are produced industrially in large volumes. For this, the underlying synthetic polymer can be processed in a melt spinning process. In this process, thermoplastic polymer material is melted and fed into a spinning beam in the liquid state by means of an extruder. The melted material is then fed from this spinning beam into so-called spinning nozzles or spinnerets. The spinning nozzle usually has a spinning plate having multiple drilled capillary holes from which the individual filaments of the fibres are extruded and stretched.

[0004] These filaments can be further processed to staple fibres. To that end, they are processed on a so-called stretch line or conversion line, where they are stretched, temperature treated and crimped, if needed. After that they are cut to a defined length to produce so-called staple fibres.

[0005] The polymer staple fibres produced this way are used for textile and / or technical applications. It is beneficial here if the polymer staple fibres have good dispersion properties in aqueous systems, e.g. in the production of wet-laid nonwoven. Moreover, it is beneficial for textile applications, if the polymer fibres have good mechanical firmness, for example, to be able to function well in the fibre postprocessing, e.g. for stretching on conveyor lines. For textile and technical applications, in particular for certain kinds of nonwovens, it is also beneficial if the polymer fibres have a low degree of thermal shrinkage.

[0006] For the respective end application or the necessary intermediate treatment steps, e.g. stretching and / or crimping, the polymer fibres usually modified or prepared by application of suitable finish or surfactant oil, which is applied on the surface of the finished or to be treated polymer fibres.

[0007] Another possibility of chemical modification can be implemented on the polymer base structure itself, for example, by integration of compounds with flame-retardant effect in the polymer main and / or side chain.

[0008] Besides this, additives such as antistatic agents or colour pigments can be introduced to the melted thermoplastic polymer or the polymer fibres during the multistage spinning process. The dispersion behaviour of a polymer fibre is affected, among other, by the nature of the synthetic polymers. In particular, for fibres of thermoplastic polymer, the dispersion properties in aqueous systems are therefore affected by the finish or layers applied on the surface.

[0009] Since the recent past, there has been an additional need for fibre systems, which not only meet the aforementioned requirements, besides being manufactured from renewable raw materials, but also require none or only the slightest of adjustments in the subsequent processing I application wherever possible, so that existing processes and machinery can continue to be used.

[0010] Therefore, the problem to be solved is providing a polymer fibre of renewable raw materials, which is to have good physical properties so that a good fibre postprocessing is possible, for example, in the stretching on conveyor lines, and which additionally are to have a low degree of thermal shrinkage while being biodegradable. It is furthermore beneficial if the polymer fibres of renewable raw materials have good dispersion properties, which will still be available even after a longer period of storage.

[0011] In addition to the above problem, the polymer fibre of renewable raw materials to be provided shall be biologically degradable under home composting conditions.

[0012] The problems described above are solved by the polymer blend fibre according to the invention, in which the polymer blend forming the polymer blend fibre comprises, preferably consists of,:

[0013] (i) a biopolymer A being an aliphatic polyester and

[0014] (ii) a biopolymer B being an aliphatic polyester, wherein the biopolymer B and the biopolymer A differ regarding their chemical structure,

[0015] (iii) the biopolymer A is present in an amount from 10 to 90 weight % based on the total weight of the fibre, preferably biopolymer A is a biopolymer comprising repeat units of the lactic acid,

[0016] (iv) the biopolymer B is present in an amount from 90 to 10 weight % based on the total weight of the fibre and being in a semicrystalline grade, preferably polyhydroxyalkanoates (PHA) and / or Polycaprolactone (PCL),

[0017] (v) the polymer blend fibre is biologically degradable under Home Composting conditions.

[0018] The above polymer blend material forming the fibre itself is already biologically degradable under Home Composting conditions and does not require any further additives and / or treatments to arrive at Home Composting conditions. However, to further increase biological degradability one may add further additives and / or treatments.

[0019] The polymer blend fibre according to the invention is usually stored as tow after the spinning process and then stretched and postprocessed on a conveyor line by means of a specific process. The tow can also be directly processed further and depositing the tow in so-called cannisters can be partly or entirely omitted.

[0020] The combination of certain biopolymers A and B in combination with a specific stretching program leads to polymer fibres having a low thermal shrinkage.

[0021] The polymer blend fibre according to the invention can be produced and processed on existing equipment so that capital expenditures are minimized.

[0022] Within the context of the present invention, grades with a degree of crystallization exceeding 20% are understood as semicrystalline grades. Preferably the degree of crystallization is at least 30%, more preferred at least 40%, to be semicrystalline and typically does not exceed about 80%.

[0023] Polymers

[0024] The polymers used for forming the polymer blend fibre according to the invention are thermoplastic polycondensates based on so-called biopolymers.

[0025] The “thermoplastic polymers” according to this invention mean a plastic, which can be (thermoplastically) moulded within a certain temperature range, preferably in the range from 25°C to 350°C. This process is reversible, i.e. it can be repeated optionally many times by cooling and reheating up to the fused state, for as long as no so-called thermal decomposition of the material from overheating occurs. This is where thermoplastic polymers are different from thermosetting resins and elastomers.

[0026] Among the thermoplastic polycondensates based on so-called biopolymers, synthetic biopolymers, especially synthetic biopolymers that are suitable for fibre melt spinning, are preferable.

[0027] The term “synthetic biopolymers” for the present invention refers to a material, which comprises biogenic raw materials (renewable raw materials). This is how they are distinguished from conventional, crude-oil based materials or plastics, e.g. polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC). Biopolymer A

[0028] Biopolymer A is a synthetic biopolymer and an aliphatic polyester, preferably biopolymer A is a synthetic biopolymer comprising repeat units of the lactic acid. Such polylactic acids are particularly preferred.

[0029] Biopolymer A is present in an amount from 10 to 90 weight % based on the total weight of the fibre.

[0030] Aliphatic polyesters are understood to be such polyesters, which have typically at least about 50 mol-%, in some preferable embodiments at least about 60 mol-% and in more preferable embodiments at least about 70 mol-% aliphatic monomers.

[0031] “Polylactic acid” is understood to mean polymers which comprise lactic acid units. Such polylactic acids are usually created by polycondensation of lactic acids, but also by the ring-opening polymerisation of lactides under suitable conditions.

[0032] According to the invention, especially suitable polylactic acids include poly(glycolide- co-L-lactide), poly(L-lactide), poly(L-lactide-co-e-caprolactone), poly(L-lactide-co- glycolide), poly(L-lactide -co-D,L-lactide), poly(D,L-lactide-co-glycolide), and poly(dioxanone). Such polymers are, for example, available in retail from the company Boehringer Ingelheim Pharma KG (Germany) under the trade names Resomer® GL 903, Resomer® L 206 S, Resomer® L 207 S, Resomer® L 209 S, Resomer® L 210, Resomer® L 210 S, Resomer® LC 703 S, Resomer® LG 824 S, Resomer® LG 855 S, Resomer® LG 857 S, Resomer® LR 704 S, Resomer® LR 706 S, Resomer® LR 708, Resomer® LR 927 S, Resomer® RG 509 S and Resomer® X 206 S.

[0033] For the purposes of the present invention, especially beneficial polylactide acids, in particular Poly-D, poly-L or poly-D,L-lactic acids.

[0034] The term "polylactic acid" generally refers to homopolymers of lactic acid, such as poly (L-lactic acid), poly (D-lactic acid), poly (DL-lactic acid), mixtures thereof, and copolymers containing lactic acid as the predominant component and a small proportion, preferably less than 10 mol%, of a co-polymerizable comonomer.

[0035] In a most preferable embodiment, biopolymer A is exclusively a thermoplastic polymer based on lactic acids. The polylactide acids used according to the invention have a number average molecular weight (Mn), preferably measured by gel permeation chromatography against narrowly dispersed polystyrene standards or end group iteration, of - typically - at least 500 g / mol, preferably at least 1 ,000 g / mol, more preferably at least 5,000 g / mol, most preferably at leastl 0,000 g / mol, in particular at least 25,000 g / mol. On the other hand, the number average is preferably at most 1 ,000,000 g / mol, more preferably at most 500,000 g / mol, most preferably at most 100,000 g / mol, in particular at most 50,000 g / mol. A number average of the molecular weight in the range of 10,000 g / mol up to 500,000 g / mol has also proven to be quite beneficial within the scope of the present invention.

[0036] The number average molecular weight (Mw) of preferred lactic-acid polymers, in particular around Poly-D, poly-L or poly-D,L-lactic acids, preferably measured by gel permeation chromatography against narrowly distributed polystyrene standards or end group iteration is preferably within the range between 750 g / mol and 5,000,000 g / mol, more preferably between 5,000 g / mol and 1 ,000,000 g / mol, most preferably between 10,000 g / mol and 500,000 g / mol, in particular within the range of 30,000 g / mol to 500,000 g / mol, and the polydispersity of these polymers is preferably in the range from 1.5 to 5.

[0037] The inherent viscosity of particularly suitable lactic-acid polymers, especially around Poly-D, poly-L or poly-D, L-lactic acids, preferably measured in chloroform at 25°C, 0.1% polymer concentration, is in the range between 0.5 dl / g and 8.0 dl / g, preferably in the range from 0.8 dl / g to 7.0 dl / g, in particular in the range from 1.5 dl / g to 3.2 dl / g.

[0038] Within the scope of the present invention, biopolymers, in particular thermoplastic synthetic biopolymers, are moreover extremely beneficial with a glass transition temperature higher than 20°C, preferably higher than 25°C, more preferably higher than 30°C, most preferably 35°C, in particular higher than 40°C. Within the scope of a most preferable embodiment of the present invention, the glass transition temperature of the polymer is in the range between 35°C and 75°C, in particular in the range between 40°C and 70°C.

[0039] In addition, polymers are particularly suitable, which have a melting temperature higher than 120°C, beneficially at least 130°C, preferably higher than 150°C, and at most 250°C, more preferably at most 210°C, and most preferably in the range between 120°C and 250°C, in particular in the range from 120°C to 180°C. For this, the glass temperature and the melting temperature of the polymer are determined preferably by means of Dynamic Scanning Calorimetry (“DSC” for short)

[0040] Biopolymer B is a synthetic biopolymer and an aliphatic polyester in particular an aliphatic polyester having repeat units, which differ from the repeat units of biopolymer A regarding their chemical structure.

[0041] Aliphatic polyesters are understood to be such polyesters, which have typically at least about 50 mol-%, in some preferable embodiments at least about 60 mol-% and in more preferable embodiments at least about 70 mol-% aliphatic monomers.

[0042] Biopolymer B is present in an amount from 10 to 90 weight % based on the total weight of the fibre, preferably polyhydroxyalkanoates (PHA) forms the biopolymer B. In a preferred version, Biopolymer B is present in an amount of 20 to 70wt% and in a more preferred version in an amount of 30 to 50wt% of the fibre.

[0043] Polyhydroxyalkanoates (PHA) are biodegradable aliphatic polyesters which contain a repeating unit represented by the following formula (1)

[0044] [-CHR-CH2-CO-O-] (1) wherein R is an alkyl group represented by CnH2n+i and n is an integer of 1 or more and 15 or less.

[0045] Preferably, the polyhydroxyalkanoates (PHA) is one or more species selected from poly(3-hydroxybutyric acid), poly(3-hydroxybutyric acid-co-3- hydroxyvaleric acid), poly(3-hydroxybutyric acid-co-3- hydroxyvaleric acid-co-3-hydroxyhexanoic acid), poly(3- hydroxybutyric acid-co-3-hydroxyhexanoic acid), poly(3-hydroxybutyric acid- co-4-hydroxybutyric acid or further homo- or co-polymer combinations of polyhydroxybutyrate, polyhydroxyvalerate and polyhydroxypropionate.

[0046] Preferably, the polyhydroxyalkanoates (PHA) having a monomer percentage of 3- hydroxybutyric acid in the poly(3-hydroxybutyric acid-co-3-hydroxyhexanoic acid) of 99.5 mol % or less and 88.5 mol % or more.

[0047] The polyhydroxyalkanoates (PHA) used in accordance with the instant invention may include one or more species selected from microorganism-produced PHAs, which are produced from microorganisms. Common PHAs include PHAs obtainable through chemical synthesis in addition to the microorganism-produced PHAs. In the microorganism-produced PHAs, their structural unit (monomer structural unit) is only a D-form (R-form) and therefore they are optically active, whereas in the PHA obtainable through chemical synthesis, structural units (monomer structural units) derived from a D-form (R-form) and an L- form (S-form) are bonded randomly and therefore they are optically inactive. In biochemistry, D / L is common for indicating the spatial arrangement of molecules, especially chiral compounds, whereas in synthetic polymer chemistry, R / S has become the standard nomenclature.

[0048] The microorganism-produced PHAs, are preferably an aliphatic polyester having a repeating unit represented by formula (1) above.

[0049] The microorganisms that produce microorganism-produced PHAs are not particularly limited as long as they have the ability to produce PHAs. For example, Bacillus megaterium is the first discovered poly(3-hydroxybutyrate) producing microorganism (hereinafter, poly(3-hydroxybutyrate) is abbreviated as "PHB"), which was discovered in 1925, and as natural microorganisms, Cupriavidus necator (formerly classified as Alcaligenes eutrophus, Ralstonia eutropha') and Alcaligenes latus are also known to be PHB-producing microorganisms. These microorganisms accumulate PHB in their cells.

[0050] Further, known microorganisms that produce copolymers of hydroxybutyrate and another hydroxyalkanoate are, for example, Aeromonas caviae, which produces poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (hereinafter, abbreviated as "PHBV") and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter, abbreviated as "P3HB3HH"), and Alcaligenes eutrophus, which produces poly(3-hydroxybutyrate-co- 4-hydroxybutyrate). Especially, regarding P3HB3HH, microorganism such as Alcaligenes eutrophus AC32, FERM BP-6038 (T. Fukui, Y Doi, J. Bateriol., 179, p. 4821-4830 (1997)), is more preferred as a PHA synthesis gene is introduced to improve the production of P3HB3HH. These microorganisms are cultured under proper conditions, and thus P3HB3HH can be accumulated in their cells. Besides the above microorganisms, genetically modified microorganisms in which various PHA synthesis-related genes are introduced in accordance with the intended type of PHA to be produced and optimized culture conditions including the type of the substrate, may also be used.

[0051] The polyhydroxyalkanoate (PHA) is not particularly limited with respect to its molecular weight as long as it substantially exhibits sufficient physical properties for the intended use in melt-spun fibre. However, if the molecular weight is excessively low, products tend to have low strength. On the other hand, if the molecular weight is excessively high, the polyhydroxyalkanoate will show difficult processability.

[0052] In view of such circumstances, the weight-average molecular weight of the polyhydroxyalkanoate is preferably in the range of 50,000 Da or more and 5,000,000 Da or less, and more preferably in the range of 100,000 Da or more and 3,000,000 Da or less.

[0053] It is noted that the weight-average molecular weight is determined from standard polystyrene molecular weight that is measured by using gel permeation chromatography (GPC) using a chloroform. Column used in the GPC may be any column suitable for measuring the molecular weight.

[0054] The melt flow rate of the polyhydroxyalkanoate (PHA) measured at 190° C under a load of 2.16 kg is preferably 0.1 g / 10min or more and 100 g / 10min or less, and more preferably 1 g / 10min or more and 50 g / 10min or less, and even more preferably 2 g / 10min or more and 40 g / 10min or less. The melt flow rate can be measured by a method in accordance with JIS K 7210 or ASTM D1238.

[0055] Examples of the polyhydroxyalkanoate include PHB [poly(3-hydroxybutyrate), poly(3- hydroxybutyric acid)], P3HB3HH [poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyric acid-co-3-hydroxyhexanoic acid)], PHBV [poly(3- hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyric acid-co-3- hydroxyvaleric acid)], P3HB4HB [poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid)], poly(3-hydroxybutyric acid-co- 3-hydroxyvaleric acid-co-3-hydroxyhexanoic acid), poly(3-hydroxybutyrateco-3- hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3- hydroxyoctadecanoate). Examples of those industrially produce easily include PHB, P3HB3HH, PHBV, poly (3-hydroxybutyric acid-co-3-hydroxyvaleric acid-co-3-hydroxyhexanoic acid), and P3HB4HB.

[0056] Regarding the average composition ratio of the repeating unit of the polyhydroxyalkanoate, from the viewpoint of the balance between flexibility and strength of the fibres, the composition ratio of poly(3-hydroxybutyrate) is preferably 80 mol % or more and 99.5 mol % or less, and more preferably 85 mol % or more and 99.5 mol % or less, and even more preferably 85 mol % or more and 97 mol % or less. If the composition ratio of poly(3-hydroxybutyrate) is less than 80 mol %, the rigidity tends to be insufficient, and if the composition ratio is more than 99.5 mol %, the flexibility tends to be insufficient.

[0057] The polyhydroxyalkanoate in the present invention, may be of one type or a mix of at least two types of PHAs; for example, a mix of two types of P3HB3HH having different poly(3-hydroxybutyrate) composition ratio can be used

[0058] When P3HB3HH is used as the polyhydroxyalkanoate, regarding the average composition ratio of the repeating unit of the polyhydroxyalkanoate, the percentage of 3-hydroxybutyric acid monomer in poly(3-hydroxybutyric acid-co-3- hydroxyhexanoic acid) is preferably 99.5 mol % or less and 85.0 mol % or more, and more preferably 95 mol % or less and 88.5 mol % or more. If the percentage of 3-hydroxybutyric acid monomer is 99.5 mol % or less and 85.0 mol % or more, the fibres are excellent in flexibility and mechanical strength.

[0059] Particularly suitable are biopolymers B, preferably polyhydroxyalkanoates (PHA), which are known as so-called semicrystalline grades. In contrast to purely amorphous grades, they comprise a crystalline phase, which is measurable e.g. by means of DSC, where the crystallization enthalpies and melting enthalpies are recorded as peaks. The enthalpy of these peaks can be used to determine the crysta 11 i n ity (https: / / analyzing-testing.netzsch.com / de / know-how / glossar / kristallinitaet- kristallinitaetsgrad): The melt enthalpy divided by the melt enthalpy of a 100% crystallized sample of the same polymer is the degree of crystallinity.

[0060] Amorphous grades are understood as grades where this degree of crystallization does not exceed 20%. Grades with a degree of crystallization exceeding 20% are understood as semicrystalline grades and typically do not exceed about 80%.

[0061] The melt enthalpy for a 100% crystallized PHB is reported to be 146 J / g (Barham, P.J., Keller, A., Otun, E.L. et al. Crystallization and morphology of a bacterial thermoplastic: poly-3-hydroxybutyrate. J Mater Sci 19, 2781-2794 (1984). https: / / doi.Org / 10.1007 / BF01026954).

[0062] In summary, the biopolymer B used to form the polymer blend fibre has a semicrystalline grade, having a degree of crystallization exceeding 20%, preferably the degree of crystallization is at least 30%, more preferred at least 40%, to be semicrystalline and typically does not exceed about 80%.

[0063] The crystallinity of a polymer grade can be manipulated by the addition of nucleation agents, that serve as seeds for crystallization processes. Nucleation agents are usually inorganic particles. They may be added in form of master-batches in the meltspinning process or may be present in the resin compound.

[0064] In Figure 1 the DSC of a semicrystalline PHB is shown.

[0065] As can be seen from Figure 1 , the measurement shows e.g. melting peaks at 83.5°C and 155,5°C and 166.7°C and recrystallization peaks at 91.9°C and 58.5°C. The measured total (all peaks) melt enthalpy is here 67.95 J / g in the heating phase and the total crystallisation enthalpy in the cooling phase is approximately 62.2 J / g. Thus, the degree of crystallization is 46.5%.

[0066] In Figure 2 the DSC of an amorphous PHB is shown.

[0067] As can be seen from Figure 2, in this measurement we see a pronounced glass transition at -19.4°C and an undefined melting peak in the region of 83°C, where the enthalpy does not exceed approximately 11.3 J / g even when selecting the baseline in a way that shows the maximum area. During cooling, a very weak crystallization peak of approximately 0.9 J / g is observed at 52.6°C. The crystallization degree calculated from the melt enthalpy is 7.7%.

[0068] Particularly suitable biopolymers B, preferably polyhydroxyalkanoates (PHA) have a melting temperature higher than 120°C, beneficially at least 150°C, preferably higher than 160°C, and at most 210°C, more preferably at most 200°C, and most preferably in the range between 150°C and 210°C, in particular in the range from 160°C to 180°C.

[0069] The glass transition temperature of biopolymer B, preferably polyhydroxyalkanoate (PHA), is preferably at least 5°C, more preferably at least 10°C, most preferably at least 15°C below the glass transition temperature of biopolymer A. The glass transition temperature is measured by means of DSC.

[0070] The Biopolymer B, which is used to form the blend for the later spinning the present fibre is semicrystalline and has a crystallinity (Degree of crystallization) of at least 20%, preferably at least 30%, more preferred at least 40% and typically does not exceed about 80%.

[0071] Biopolymer B which is present in an amount from 90 to 10 weight % based on the total weight of the fibre, preferably in an amount from 70 to 20 weight %, more preferred in an amount from 50 to 30 weight %, is preferably formed from polyhydroxyalkanoates (PHA), more preferred from polyhydroxybutyrate (PHB) as biopolymer B, such PHB having a crystallinity (Degree of crystallization) of at least 20%, preferably at least 30%, more preferred at least 40% and typically does not exceed about 80%. For PHB, this is equivalent to an enthalpy of melting of more than 29 J / g. The amorphous phase of the polymer does not contribute to the melting and crystallization enthalpy. The amorphous phase can be manifested by the parameters of glass transition. In a further embodiment of the present invention, the Biopolymer B - which is present in an amount from 10 to 90 weight % based on the total weight of the fibre - is polycaprolactone (PCL). In such embodiment, the PCL Biopolymer B is preferably present in an amount of 20 to 70wt% and in a more preferred version in an amount of 30 to 50wt% of the fibre.

[0072] Polycaprolactone (PCL) is a synthetic, semi-crystalline, aliphatic polyester which contain a repeating unit represented by the following formula and typically, is created by polymerizing the ring-shaped s-caprolactone in the presence of heat and a catalyst, usually an alcohol or a diol. The result is a regular polymer, which - typically - crystallizes in the form of spherulites to about 50%.

[0073] The number proportion of carbonyl and methylene components is typically 1 :5 as shown in the formula, but the number of methylene groups can also vary.

[0074] The melting temperature of Polycaprolactone typically ranges from about 55-65°C.

[0075] The glass transition temperature of Polycaprolactone is very low, typically about -60 C to about -70°C. At room temperature, short-chain, amorphous polycaprolactone is correspondingly soft and rubbery. However, due to its uniform structure, it is easy to crystallize, which solidifies the material. Therefore, crystalline Polycaprolactone is similar to polyethylene in terms of its crystal structure, e.g. having a melting temperature of around 63°C, a tensile strength of 26-42 MPa and an elongation at break of 600 to 1000%. The glass transition temperature of the amorphous polymer is around -70 °C, so it is rubbery at room temperature.

[0076] Polycaprolactone has a high tendency to crystallize, which also occurs when cooled quickly, increasing the glass transition temperature to around -60 °C.

[0077] As mentioned, Polycaprolactone (PCL) is a synthetic, semi-crystalline, aliphatic polyester and grades with a degree of crystallization exceeding 20% are understood as semicrystalline grade, preferably the degree of crystallization is at least 30%, more preferred at least 40%, to be semicrystalline and typically does not exceed about 80%. A further embodiment of the present invention is the use of a biopolymer B being an aliphatic polyester and having a semicrystalline grade for forming a polymer blend fibre, said polymer blend fibre comprising said biopolymer B being an aliphatic polyester and having said semicrystalline grade and a further biopolymer A being an aliphatic polyester and being different in its chemical structure from biopolymer B, said polymer blend fibre being biologically degradable under Home Composting conditions.

[0078] Additives in polymers A and B

[0079] The biopolymers A and B described above may contain common additives such as antioxidants. It has been proven in this regard that additives of the group of antioxidants are beneficial for the manufacturing and post-processing of the fibres, as the aforementioned biopolymers A and B are sensitive to oxidative decomposition.

[0080] Other common additives are pigments, stabilisers, surfactants, waxes, flow promoters, solid solvents, plasticisers and other materials, e.g. nucleating agents, which are added to improve the processability of the thermoplastic composition.

[0081] The biopolymers B described above, in particular the specific biopolymers B based on their described properties, can already do with a reduced quantity of additives, especially nucleating agents. Such nucleating agents, which are usually added, simplify the crystallisation during the cooling of the fibres, which simplifies their processing. One type of such a nucleating agent is a multiple carbon acid such as succinic acid, glutaric acid, adipic acid, pimelic acid, morphic acid, azelaic acid, sebacic acid and mixtures of such acids as described in US patent no. 6177193. The nucleating agents are typically present in biopolymer B in a concentration of less than about 0.5 wt. % in some embodiments less than about 0.25 wt.% and in some embodiments less than about 0.1 wt.%.

[0082] The polymer blend fibre according to the invention comprises at least 90 weight % of biopolymer A and biopolymer B and contains typically less than about 10 wt.%, preferably less than about 8 wt.%, more preferably less than about 5 wt.% additives.

[0083] The polymer blend fibre according to the invention are combined into tows after spinning and post-processed on a conveyor line using methods known from the prior art, in particular, they are stretched and, if necessary, further crimped or textured.

[0084] The above polymer blend material forming the fibre itself is already biologically degradable under Home Composting conditions and does not require any further additives and / or treatments to arrive at Home Composting conditions. However, to further increase biological degradability one may add further additives and / or treatments.

[0085] Polymer fibres

[0086] The polymer blend fibre according to the invention can be provided as finite length fibres, e.g. so-called staple fibres, or essentially infinite length fibres (filament).

[0087] For better dispersibility, the fibre is preferably present as a staple fibre. The length of the aforementioned staple fibres is not subject to any fundamental limitation, but it is generally between 2 and 200 mm, preferably 2.5 to 120 mm, more preferably 3 to 60 mm.

[0088] The single filament linear density or titer of the polymer blend fibre according to the invention, preferably staple fibre, is between 0.5 and 30 dtex, preferably 0.7 to 13 dtex. For some applications, e.g. tea bags and similar items, titers between 0.5 and 3 dtex and fibre lengths of < 10mm, preferably < 8mm, more preferably < 6mm, most preferably < 5mm are particularly well suited. Linear density or titer expressed in dtex represents the weight in grams of 10 km of filament.

[0089] The polymer blend fibre according to the invention indicates a low hot air thermal shrinkage within the range from 0% to 10%, preferably from > 0% to 8%, respectively measured at 110°C.

[0090] The polymer blend fibre according to the invention are generally manufactured by common procedures. At first, the polymers are dried, typically at 50°C, and mixed in solid form and are fed into an extruder. Then, the melted material is spun by means of common equipment with corresponding nozzles. The exit speed on the nozzle outlet surface is adjusted to the spinning speed so that a fibre is created with the desired linear density.

[0091] The fibres formed can have round, oval or further suitable cross sections and shapes.

[0092] The fibre filaments produced this way are integrated into yarns and these, in turn, are integrated into tows. The tows are initially placed in cannisters for the further processing. The tows intermittently stored in the cannisters are picked up and a large spun fibre tow is created.

[0093] The polymer blend fibre according to the invention are spun from a polymer blend comprising the aforementioned biopolymer A and biopolymer B, in which the biopolymer A is preferably a biopolymer comprising repeat units of the lactic acid and the biopolymer B is preferably polyhydroxyalkanoates (PHA) and / or Polycaprolactone (PCL). As already mentioned, such polymer blend fibre itself is already biologically degradable under Home Composting conditions. Thus, in an preferred embodiment, the polymer blend forming the polymer blend fibre does not include any other thermoplastic polymer.

[0094] In the aforementioned polymer blend from which the fibres are spun, it is particularly preferred to use polyhydroxyalkanoates (PHA) being semi-crystalline as described above. In contrast to purely amorphous grades, they comprise a crystalline phase, which is measurable e.g. by means of DSC, where the crystallization enthalpies and melting enthalpies are recorded.

[0095] The instant inventors found that the aforementioned polyhydroxyalkanoates (PHA) can be melt-spun on existing equipment at temperatures from 190 to 260°C using a low spinning speed of 300 to 800 m / min. For a person skilled in the art, the low spinning speed is surprising, as there has been common sense that spinning speeds of approx. 1000 to 1600 m / min are needed for an adequate pre-alignment of the polymer chains in the fibre. Spinning speed is understood to mean the speed at which the rigid filaments are pulled off.

[0096] The Biopolymer B which is present in an amount from 90 to 10 weight % based on the total weight of the fibre, preferably in an amount from 70 to 20 weight %, more preferred in an amount from 50 to 30 weight %, is preferably formed from semicrystalline polyhydroxyalkanoates (PHA) as biopolymer B. The PHA being present in the fresh melt-spun fibre having a crystallinity (Degree of crystallization) of at least 20%, preferably at least 30%, more preferred at least 40% and typically does not exceed about 80% (see https: / / analyzinq-testinq.netzsch.com / de / know- how / qlossar / kristallinitaet-kristallinitaetsqrad.

[0097] For a person skilled in the art, it was surprising that polyhydroxyalkanoates (PHA) being semi-crystalline and not being amorphous provide for polymer blend fibre according to the invention which are biologically degradable under home composting conditions. The use of polyhydroxyalkanoates (PHA) being semi-crystalline and not being amorphous reduces or totally eliminates problematic behaviour during the meltspinning process, e.g. unwanted shrinkage, filament breaks, spinning defects.

[0098] In Figure 3 the DSC of the semi-crystalline properties of the fresh-spun polymer blend fibre according to the invention are illustrated showing the DSC of the spun yarn, made of a PLA / PHB blend, prior to stretch line. As can be seen in Figure 3, the crystallization peak at 82.4°C clearly shows that the spun yarn comprises regions that have not yet crystallized but are capable of crystallizing. Crystallization enthalpy is 10.3 J / g.

[0099] The melting peaks of the PHA phase coincide widely with the peaks of the PLA phase at 163.6°C, indicating a melting enthalpy of 45.0 J / g.

[0100] In this example fibre, the portion of PLA is 70% and the portion of PHA is 30%. The PLA resin used for this fibre has a melting enthalpy of 43.2 J / g, which means that the crystallinity is 46.1%. As described above, the crystallinity of the PHA resin is 46.5%. The melt enthalpy of a 100% crystalline fibre at the given ratio of PHA and PLA would thus be 109.4 J / g. The melt enthalpy excluding the crystallization enthalpy in the DSC curve is (45.0-10.3) J / g = 34.7 J / g, so the crystallinity of the spun yarn is 31.7%.

[0101] The spun yarn has a lower crystallinity than each of the resins it comprises. This is because the different polymers hinder each other from crystallizing in the blend, e.g. due to stereochemical effect.

[0102] The fresh-spun polymer blend fibres of the present invention are typically drawn to arrive at the desired single yarn count (titer), said drawing influences the crystallinity as well.

[0103] In the following the semi-crystalline properties of the fresh-spun polymer blend fibre according to the invention are illustrated by Figure 1 showing the DSC of the spun yarn, made of a PLA / PHB blend, prior to stretch line.

[0104] Figure 4 shows the DSC of the final fibre made of PLA / PHB blend, after stretch line.

[0105] As can be seen in Figure 4, no crystallization peak is seen in the heating phase. This points at the completion of crystallization during stretching.

[0106] Melt enthalpy is 50.3 J / g. So, the crystallinity of the final fibre is 46.0%. Thus, crystallinity has increased by 14.3% through the stretching process to a crystallinity that coincides widely with the crystallinity of the polymer components PHA (46.5%) and PLA (46.1%).

[0107] It is assumed that using a PHA resin with a lower crystallinity would lead to a significantly lower crystallinity of the final fibre. However, evidence is not obtainable due to the lacking processability of the amorphous resin.

[0108] As described, the fibre filaments produced this way are integrated into spun filament bundles and these, in turn, are integrated into spun tows. The spun tows are initially placed in cannisters for the further processing. The spun tows intermittently stored in the cannisters are collected and a large spun fibre tow is created.

[0109] Typically, the post-treatment of the spun fibre tows, which commonly are 10-600 ktex, is performed using conventional conveyor lines with a common stretching condition. The feed speed of the spun fibre tow into the stretching or drawframe is preferably 10 to 110 m / min (feed speed). At this point, finish preparations can still be applied, which promote the stretching but have no negative effects on the resultant fibre properties.

[0110] The stretching can be implemented as a one-step procedure or, optionally, in application of a two-step stretching process (in this regard, for example, see US 3 816486). Before and during the stretching and in application of conventional methods, one or more finishes can be applied.

[0111] The stretching according to the invention takes place at a stretching ratio between 1.2 and 6.0, preferably between 2.0 and 4.0, wherein the temperature during the stretching of the spun tow is between 30°C and 80°C. The stretching therefore takes place within the range of the glass transition temperature of the spun tow to be stretched. The stretching according to the invention takes place under steam, i.e. in the so-called steam chest, so that the stretching point of the fibre is reached in the steam chest. The steam chest is usually operated at 3 bar pressure.

[0112] By stretching under steam in the aforementioned temperature range, the thermal shrinkage of the fibres can be reduced and adjusted in a deliberate and controlled manner.

[0113] The preferable conveyor line settings are as follows:

[0114] The stretching takes place in a one-step procedure in the steam chest between drawframe S2 and drawframe S1 , i.e. the stretching point of the fibres is reached in the steam chest. All godets (usually 7) of S1 have a temperature of 30 to 80°C. The steam chest is preferably operated at 3 bar steam pressure.

[0115] All godets (usually 7) of the following drawframe S2 are cold, wherein cold means room temperature (approx. 20 to 35°C).

[0116] This so-called “cold stretching” mode has the effect that the stretching is not fixed at high temperature on S2 under tension. The cold S2 has the benefit that there is no risk that the individual fibres get stuck on the hot godets of S2.

[0117] In spite of the “cold stretching,” the fibre is nonetheless insensitive to high temperatures with the tension-free fixation in the oven and can withstand temperatures up to 100°C without sticking

[0118] The Biopolymer B which is present in an amount from 90 to 10 weight % based on the total weight of the fibre, preferably in an amount from 70 to 20 weight %, more preferred in an amount from 50 to 30 weight %, being present in the drawn melt-spun fibre having a crystallinity (Degree of crystallization) of at least 20%, preferably at least 30%, more preferred at least 40% and typically does not exceed about 80%

[0119] (see https: / / analyzing-testing.netzsch.com / de / know-how / glossar / kristallinitaet- krista nitaetsgrad The titer of such drawn fibres is preferably between 0.5 and 30 dtex, preferably 0.7 to 13 dtex.

[0120] Likewise for the crimping / texturing of the stretched fibres, if necessary, conventional methods of mechanical crimping can be applied using generally known crimping machines. A mechanical device for fibre crimping is preferred, which works with the help of steam, e.g. a compression chamber. However, also fibres crimped using other methods can be used, e.g. three-dimensionally crimped fibres. To perform the crimping, the tow is initially brought usually to a temperature in the range from 50° to 100°C, preferably from 70° to 85°C, more preferably to about 78°C, and treated with pressure of the tow infeed rollers between 1.0 and 6.0 bar, more preferably at about 2.0 bar, a pressure in the crimping chamber between 0.5 and 6.0 bar, more preferably between 1.5 and 3.0 bar, with steam between 1.0 and 2.0 kg / min, more preferably 1.5 kg / min.

[0121] It is also possible to skip the crimping / texturizing process in order to make uncrimped fibres as needed for e.g. wetlaid processes like paper-making.

[0122] Insofar as the straight or, if applicable, crimped fibres are relaxed and / or fixated in the oven or hot air flow, this is also done at temperatures of at most 130°C.

[0123] To manufacture staple fibres, the straight or, if applicable, crimped fibres are taken up followed by cutting and packaging. The staple fibres of the present invention are preferably cut on the relaxation of a downstream mechanical cutting unit. To manufacture tow types, cutting can be omitted. These tow types are deposited uncut in the roll and pressed.

[0124] Thus, the process for melt-spinning a polymer blend fibre according to the present invention includes the steps of:

[0125] (i) mixing and optionally drying of a biopolymer A being an aliphatic polyester and a biopolymer B being an aliphatic polyester, wherein the biopolymer B and the biopolymer A differ regarding their chemical structure, the biopolymer A is present in an amount from 10 to 90 weight % based on the total weight of the fibre, preferably biopolymer A is a biopolymer comprising repeat units of the lactic acid, the biopolymer B is present in an amount from 90 to 10 weight % based on the total weight of the fibre and being in a semicrystalline grade, preferably polyhydroxyalkanoates (PHA) and / or Polycaprolactone (PCL) forms the biopolymer B,

[0126] (ii) feeding the mixture from step (i) into an extruder and melt-spinning fibre filaments at temperatures from 190 to 260°C at a spinning speed of 300 to 800 m / min., collecting the fibre filaments and forming a yarn, forming a tow from said yarns,

[0127] (iii) stretching the tow from step (ii) to an individual filament titer between 0.5 and 30 dtex, preferably 0.7 to 13 dtex.

[0128] Insofar as the fibres according to the invention are presented in a crimped embodiment, the crimping degree is preferably at least 2 crimps (fibre curls) per cm, preferably at least 3 crimps per cm, more preferably between 3 crimps per cm and 9.8 crimps per cm and most preferably between 3.9 crimps per cm and 8.9 crimps per cm. For applications to produce textile webs, values between 5 and 5.5 crimps per cm are most preferable for the crimping degree. For the production of textile webs by means of wet laying methods, the crimping degree may have to be adjusted in the individual case.

[0129] Textile webs can be made from the fibres according to the invention, which are also the object of the invention. Based on the good dispersibility of the fibres according to the invention, such textile webs are made preferably by means of wet laying methods.

[0130] The term “textile web” should therefore be understood within the broadest sense in the context of this description. A textile web can be all forms that include the fibres according to the invention and which have been manufactured according to a webforming technique. Examples of such textile webs are nonwoven, in particular wet- laid nonwoven, preferably on the basis of staple fibres, which are made by means of thermal bonding.

[0131] The fibres according to the invention also have good permanence of dispersibility, i.e. the fibres will continue to have very good dispersion quality even after longer periods of storage, e.g. several weeks or months, in the form of rolls or comparable forms. Moreover, the fibres according to the invention have good long-term dispersion qualities, i.e. if the fibres are dispersed in liquid media, e.g. in water, the fibres stay dispersed for longer and begin to settle only after a longer period of time

[0132] The fibres according to the invention, as well as the textile webs formed from such fibre are biologically degradable under home composting conditions.. Testing for home compostability is done as described in “Program OK 2 - Home compostability of products” by TUV Austria (Doc-Ref: OK02-e; https: / / be.tuvaustria.com / wp- using among other standards the well-known standard for industrial composting (EN

[0133] 13432) with adapted parameters as described in section 7.2 of said document.

[0134] The above textile webs formed from the polymer blend fibre according to the invention itself are already biologically degradable under Home Composting conditions and does not require any further additives and / or treatments to arrive at Home Composting conditions. However, to further increase biological degradability one may add further additives and / or treatments.

[0135] Test methods:

[0136] Unless already indicated in the foregoing description, the following measuring or test methods are used:

[0137] Linear density or titer:

[0138] The yarn count was determined according to DIN EN ISO 1973.

[0139] Dispersibility:

[0140] For the assessment of the dispersibility, the following test method was developed and applied according to the invention:

[0141] The fibres according to the invention are cut to a length of 2 to 12 mm. The cut fibres are placed at room temperature (25°C) into a glass vessel (dimensions: 150 mm length, 200 mm width, 200 mm height), which is filled with DI water (DI = deionised). The quantity of fibres is 0.25g per litre DI water. For better assessment, usually 1g fibres and 4 litres of DI water are used.

[0142] Then, the fibre / DI water mixture is stirred using a normal laboratory magnetic mixer (e.g. IKAMAG RCT) for at least three minutes (rotation speed around 750-1500 rpm), after which the mixer is switched off. It is then determined if all fibres have dispersed.

[0143] This dispersion behaviour of the fibres is now evaluated as follows: not dispersed (-) partly dispersed (o) fully dispersed (+) The evaluation above is made based on defined intervals of time.

[0144] Home Compostability:

[0145] The determination is made according to DIN EN 13432 (Requirements for packaging recoverable through composting and biodegradation - Test scheme and evaluation criteria for the final acceptance of packaging) for industrial compostability and according to e.g. “Program OK 2 - Home compostability of products” by TUV Austria (Doc-Ref: OK02-e; https: / / be.tuvaustria.com / wp- content / uploads / sites / 73 / 2024 / 03 / CS-OK02-EN OK compost HOME.pdf) for homecompostability of the final product.

[0146] Number average molecular weight (Mn):

[0147] Determination by means of gel permeation chromatography against narrowly distributed polystyrene standards of by end group titration.

[0148] Weight average of molecular weight (Mw):

[0149] Determination by means of gel permeation chromatography against narrowly distributed polystyrene standards of by end group titration. Preferred eluent is chloroform with a sample concentration of 0.2% w / v.

[0150] Inherent viscosity:

[0151] Determination measured in chloroform at 25°C, 0.1% polymer concentration via GPC.

[0152] Glass transition temperature and melting temperature:

[0153] Determination by means of Dynamic Differential Scanning Calorimetry (“DSC” for short) according to the following procedure:

[0154] Performance of the DSC measurement under nitrogen, calibration against indium. Nitrogen flow is at 50 ml / min; initial weight of fibres in the range of 2 to 3 mg.

[0155] Temperature range between -50°C to 210°C @ 10 K / min, then isothermal hold for 5 min and finally cooling to -50°C @ 10 K / min

[0156] The highest temperature is generally about 50°C above the highest expected melting point.

[0157] The DSC measurement is performed by means of a TA / Waters Modell Q100.

[0158] Melt viscosity:

[0159] The Melt viscosity is determined by means of a Gbttfert Rheo Tester 1000 at a temperature of 190°C, at 200s-1(shear) and 1200s-1(shear). Apparent viscosity:

[0160] The determination is made as explained in WO 200 / / 070064

[0161] Melt flow index:

[0162] The determination is made according to the ASTM test method D1238-13 (ASTM D1238-13, Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer, ASTM International, West Conshohocken, PA, 2013, www.astm.org). The melt flow index is the weight of a polymer (in grams), which can be pressed through an extrusion rheometer opening (0.0825-inchdiameter) if it is exposed to a force of 2160 grams in 10 minutes at 190°C.

[0163] Latent melting heat:

[0164] The latent melting heat (AHf), the latent crystallinity heat (AHC) and the crystallization temperature is measured by means of digital scanning calorimetry ("DSC") according to ASTM D-3418 (ASTM D3418-15, Standard Test Method for Transition Temperatures and Enthalpies of Fusion and Crystallization of Polymers by Differential Scanning Calorimetry, ASTM International, West Conshohocken, PA, 2015, www.astm.org).

[0165] Thermal shrinkage:

[0166] From the tow sample, 12 individual fibres (measuring samples) are extracted. By means of tweezers, they are clamped on one end into a multi-clamp and a decrimping weight is fastened on the other end.

[0167] The multi-clamp loaded with the measuring samples is fastened with stand so that the measuring samples hang freely under prestressing force in the stand. The chosen starting length (normally 150 mm) is marked there on each fibre. This is done by means of marking lines on the stand and marking points that are put on the samples. After the marking, the loaded multi-clamp is taken down and placed onto a velvet sheet. The decrimping weights are taken off there and the free fibre ends are clamped into a second multi-clamp. The measuring samples that are clamped between two multi-clamps are hooked into a wire rack free from tension. This wire rack is inserted centred into the pre-heated shrink oven heated to the correct treatment temperature (regular temperatures are 200°C, 110°C, 80°C). After a treatment time of 5 minutes, the wire rack is taken out of the oven. After the two multi-clamps have cooled down, they are taken out with the measuring samples and placed onto the velvet sheet. After an acclimatisation time of 30 minutes, the posttreatment measurement can be taken. For this, the measuring samples are loaded with the decrimping weights again and hooked into the stand. The adjustable marking line of the stand is positioned for the back measurement so that the upper edge of each marking point can be covered by the marking line. Now, the length between the markings on the counter of the stand is read for each fibre separately precise to 1 / 10 mm.

[0168] Calculation of the length change.Change in length [%] =

[0169] The average value of all 12 measuring samples is then reported.

[0170] The invention is explained by the following example without limiting its scope to this.

[0171] Example

[0172] The raw materials PLA 6202D of NatureWorks and a commercially available PHA grade with a crystallinity of 46.5% were mixed in a dryer and dried at 50°C. The mixture contains 70 wt.% of PLA and 30 wt.% of PHA. The dried mixture was transferred into a melt-spin extruder, heated to 217°C and fibres are spun at a throughput of 0.6 g / min / hole and a haul-off speed of 600 m / min resulted in a spun yarn count of 10 dtex.

[0173] Additives, e.g. an antioxidant, with <0.05 wt.% active substance concentration, were added to reach a corresponding good spinning behaviour at the spinning temperature of 217°C.

[0174] As usual, finish was applied on the spinning material to permit further processing.

[0175] Then, the spun product was processed at an unstretched tow length of approx. 42 ktex on a conventional staple fibre line.

[0176] Stretched in steam medium of 2.2 dtex and fixated at 90°C in the circulating air oven, the following textile technology key values of the uncrimped variant resulted for the further processing in the wetlaid procedure:

[0177] Linear density: 2,4 dtex

[0178] Tensile modulus: 25 cN / tex

[0179] Stretching: 30%

[0180] Shrinkage (110°C): 4%

[0181] Crimping: not crimped

[0182] The polymer blend thus produced satisfies Home Composting conditions as determined according to DIN EN 13432 (Requirements for packaging recoverable through composting and biodegradation - Test scheme and evaluation criteria for the final acceptance of packaging) for industrial compostability and according to “Program OK 2 - Home compostability of products” by TUV Austria (Doc-Ref: OK02- e; htps: / / be.tuvaustria.com / wp-content / uploads / sites / 73 / 2024 / 03 / CS-OKQ2- EN OK compost HOME. pdf.

[0183] PLA 6202D is a polylactide acid with a relative density of 1.24 g / cm3(according to ASTM D792) and a melt flow index (g / 10min@210°C) in the range of 15-30. The glass transition temperature is 55-60°C (according to ASTM D3417) and the crystalline melt temperature is 160-170°C (according to ASTM D3418).

[0184] PHA is a polyester produced by microorganisms primarily as energy storage. Thus, PHA is intrinsically biodegradable. A multitude of different PHA monomers is known, which can be combined to achieve different properties. For example, the PHA copolymer PHBV (poly(3-hydroxybutyrate-co-3-hydroxyvalerate) has the right material properties to serve as packaging material.

[0185] Commercial PHAs are offered by e.g. the company Danimer Scientific.

Claims

Patent Claims1. Polymer blend fibre, said polymer blend fibre comprises:(i) a biopolymer A being an aliphatic polyester and(ii) a biopolymer B being an aliphatic polyester, wherein the biopolymer B and the biopolymer A differ regarding their chemical structure,(iii) the biopolymer A is present in an amount from 10 to 90 weight % based on the total weight of the fibre,(iv) the biopolymer B is present in an amount from 90 to 10 weight % based on the total weight of the fibre and being a semicrystalline grade.(v) the polymer blend fibre is biologically degradable under Home Composting conditions.

2. The polymer blend fibre of claim 1 , characterized in that Home Composting condition is determined according to DIN EN 13432 (Requirements for packaging recoverable through composting and biodegradation - Test scheme and evaluation criteria for the final acceptance of packaging) for industrial compostability and according to “Program OK 2 - Home compostability of products” by TUV Austria (Doc-Ref: OK02-e; https: / / be.tuvaustria.com / wp- content / uploads / sites / 73 / 2024 / 03 / CS-QK02-EN OK compost HOME.pdf).

3. The polymer blend fibre of claim 1 or 2, characterized in that the biopolymer A and the biopolymer B are thermoplastic polymers.

4. The polymer blend fibre as claimed in one or more of claims 1 to 3, characterized in that the biopolymer A is (i) a biopolymer comprising repeat units of the lactic acid and the biopolymer B is polyhydroxyalkanoates (PHA) biopolymer or (ii) a biopolymer comprising repeat units of the lactic acid and the biopolymer B is Polycaprolactone (PCL) biopolymer or (iii) a biopolymer comprising repeat units of the lactic acid and the biopolymer B is a mixture of polyhydroxyalkanoates (PHA) and Polycaprolactone (PCL).

5. The polymer blend fibre as claimed in one or more of claims 1 to 4, characterized in that the biopolymer B has a semicrystalline grade crystallinity (Degree of crystallization) of at least 20%, preferably at least 30%, more preferred at least 40%, preferably said biopolymer B is polyhydroxyalkanoates (PHA) and / or Polycaprolactone (PCL).

6. The polymer blend fibre as claimed in one or more of claims 1 to 5, characterized in that the polymer blend fibre is a drawn melt-spun fibre having asingle filament titer between 0.5 and 30 dtex, preferably 0.7 to 13 dtex7. The polymer blend fibre as claimed in one or more of claims 1 to 6, characterized in that the biopolymer B is polyhydroxyalkanoates (PHA) having repeating unit represented by the following formula (1 )[-CHR-CH2-CO-O-] (1 ) wherein R is an alkyl group represented by CnH2n+i and n is an integer of 1 or more and 15 or less.

8. The polymer blend fibre as claimed in one or more of claims 1 to 7, characterized in that the biopolymer B is one or more species selected from poly(3-hydroxybutyric acid), poly(3-hydroxybutyric acid-co-3- hydroxyvaleric acid), poly(3-hydroxybutyric acid-co-3- hydroxy valeric acid-co-3- hydroxyhexanoic acid), poly(3- hydroxybutyric acid-co-3-hydroxyhexanoic acid), poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid or further homo- or copolymer combinations of polyhydroxybutyrate (PHB), polyhydroxyvalerate and polyhydroxypropionate, polyhydroxyalkanoate including PHB [poly(3- hydroxybutyrate), poly(3-hydroxybutyric acid)], P3HB3HH [poly(3- hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyric acid-co-3- hydroxyhexanoic acid)], PHBV [poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid)], P3HB4HB [poly(3- hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyric acid-co-4- hydroxybutyric acid)], poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid-co-3- hydroxyhexanoic acid), poly(3-hydroxybutyrateco-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3- hydroxyoctadecanoate).

9. Process for melt-spinning a polymer blend fibre as defined in one or more of claims 1 to 7, said process include the steps of:(i) mixing and optionally drying a biopolymer A being an aliphatic polyester and a biopolymer B being an aliphatic polyester, wherein the biopolymer B and the biopolymer A differ regarding their chemical structure, the biopolymer A is present in an amount from 10 to 90 weight % based on the total weight of the fibre, preferably biopolymer A is a biopolymer comprising repeat units of the lactic acid, the biopolymer B is present in an amount from 90 to 10 weight % based on the total weight of the fibre and being in a semicrystalline grade, preferably polyhydroxyalkanoates (PHA) and / or Polycaprolactone (PCL) forms the biopolymer B,(ii) feeding the mixture from step (i) into an extruder and melt-spinning fibre filaments at temperatures from 190 to 260°C at a spinning speed of 300 to800 m / min., collecting the fibre filaments and forming a yarn, forming a tow from said yarns,(iii) stretching the tow from step (ii) to an individual filament titer between 0.5 and 30 dtex, preferably 0.7 to 13 dtex.

10. The process as claimed in claim 9, characterized in that the spun fibre tow has 10-600 ktex.

11. The process as claimed in claim 9 or 10, characterized in that the feed speed of the spun fibre tow into the stretching or drawframe is 10 to 110 m / min (feed speed).

12. The process as claimed in one or more of claims 9 to 11 , characterized in that the stretching ratio is between 1.2 and 6.0, preferably between 2.0 and 4.0, wherein the temperature during the stretching of the spun tow is between 30°C and 80°C.

13. Use of a biopolymer being an aliphatic polyester and having a semicrystalline grade for forming a polymer blend fibre, said polymer blend fibre comprising said aliphatic polyester and having said semicrystalline grade and a further biopolymer being an aliphatic polyester and being different in its chemical structure, said polymer blend fibre being biologically degradable under Home Composting conditions.

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