Multi-constitutent fiber and method of making the same

Abstract

This invention provides a multi-constituent fiber and method of making the same. In one embodiment, said multi-constituent fiber is obtained by melt spinning of particles formed from a polymer blend, said polymer blend consisting essentially of: a) 40-80wt.% of polypropylene carbonate, said polypropylene carbonate has a weight-average molecular weight ≥100,000g / mol; b) 10-50wt.% of one or more semicrystalline polymer; and c) 0.1 to 10wt.% of an end-capping and cross-linking agent.

Description

MULTI-CONSTITUTENT FIBER AND METHOD OF MAKING THE SAME FIELD OF THE INVENTION

[0001] The present invention generally relates to multi-constituent fibers, particularly, multiconstituent shape-memory polypropylene carbonate fibers.BACKGROUND OF THE INVENTION

[0002] Polypropylene carbonate (PPC) is a biodegradable polymer using carbon dioxide as one of the building components. However, the mechanical and thermal properties of PPC are poor. Attempts have been made by many research groups in order to improve PPC’s mechanical and thermal properties. PPC has terminal hydroxyl groups which can be protected / end-capped to prevent back biting / unzipping-type degradation. The terminal hydroxyl groups of PPC can also be used for intermolecular crosslinking with another PPC molecule or other polymer molecules with reactive functional groups (e.g. hydroxyl, amine, carboxylic acid). PPC is an amorphous polymer. It has no crystalline structure, therefore the mechanical strength of pure PPC fiber cannot be enhanced by drawing. For semi-crystalline polymers such as polylactic acid (PLA), drawing can cause orientation-induced crystallization, and the alignment of polymer chains greatly increases the strength of fiber in the longitudinal direction. PPC has a glass transition temperature (Tg) located between 20 and 40°C. Composites made of PPC and other materials have been demonstrated to shown shape memory effect at around human body temperature. However, knitted fabrics and woven fabrics made from PPC fiber (PPC content at least 45 wt%) with enhanced thermal stability have not been developed.

[0003] Zhou, N. et al. has made polypropylene carbonate-polylactic acid core fiber by electrospinning, and it was published on Frontiers in Materials, 2023, 10: 1257394. In this case, PPC acts as a coating containing antimicrobial agent “benzalkonium bromide” forming a sheath on the core PLA fiber. Harmful organic solvent such as dimethylformamide (DMF) and acetone is used to prepare spinning solutions. Core-sheath fiber is a kind of bi-component fiber in which the two component polymers are not mixed but fused at the interface.

[0004] Shaharuddin, S.I.S. et al. has used a tailor-made melt-drawn spinning setup to produce PLA / PPC / curcumin monofilament fiber. Results were published on IIUM Engineering Journal, 2020, 21(2):197-211. Since no mechanical means such as extruder is used to force the molten polymer flow through the nozzle, the polymer moves simply by the force of gravity. There was irregular formation of bead-like structure on the lateral surface of the fiber due to the partial dispersion of curcumin particles in the PLA / PPC blend. The reason for the addition of curcumin (a natural active compound derived from turmeric (Curcuma longa) with antibacterial,antitumor and antioxidant properties) to the PLA / PPC blend is to manufacture therapeutic- eluting fibers which are used as suture, not textile.

[0005] Patent “CN 112724392 A” disclosed a method of preparing a bio-based modification of polypropylene carbonate by esterification with 2,5-furandicarboxylic acid or its derivatives in aprotic solvent such as tetrahydrofuran, methyl benzene, and dimethylformamide in the presence of catalyst such as titanium isobutyl acetate, p-toluene sulfonic acid, tin chloride, zinc acetate, and tetrabutyl titanate. After solution reaction or interfacial polycondensation, the product is a copolymer of polyfurandicarboxylate-polypropylene carbonate (PFPC). The PFPC pellets obtained are used for melt spinning of fibers. Molecular weight of PPC suggested on “CN 112724392 A” is in the range of 1,000 g / mol to 10,000 g / mol. As stated on the patent “CN 112724392 A”, biodegradation of PPC with high molecular weight is slow, while mechanical strength of PPC with low molecular weight is insufficient. Unfortunately, non- environmentally friendly solvent and catalyst are involved in this method of preparing PFPC.

[0006] Up to now, melt spinning with extrusion and drawing of multi-constituent polypropylene carbonate fiber for subsequent yarn spinning and knitting or weaving to produce knitted fabrics or woven fabrics has not been disclosed. US patent 5582667 defines multiconstituent fibers as prepared from two or more polymers, with at least one of these polymers being randomly dispersed through the fiber, in the form of domains. Multi-constituent fibers are different from multi-component fibers which consist of non-mixed components that are fused at the interface.

[0007] Methods of preparing blend of polypropylene carbonate, polylactic acid, and maleic anhydride have been described on CN patents 106479147A, 110283326A, and 113604020A. CN patent 106479147 A described a method of preparing a blend of PPC, PLA, maleic anhydride, calcium stearate, and superfine powder of calcium carbonate using a twin screw extruder. The prepared polymer pellets are used for producing biodegradable packaging material for clothing. CN patent 110283326A described a method of preparing a biodegradable PPC (molecular weight: 1,000 to 20,000 g / mol) modified with end-capping agent, such as isocyanate and maleic anhydride, and third component, such as PLA, polyglycolic acid (PGA), and poly(lactic-co-glycolic) acid (PLGA) by high-temperature reactor and in-situ polymerization. CN patent 11304020A described a method of preparing a modified PLA blended with a toughening agent (i.e. PPC solid state grafted with maleic anhydride) and a compatibilizer (i.e. triethyl citrate) in a Banbury mixer.

[0008] For instance, among the results obtained in the prior art processes, are bi-component fibers of PLA (core) and PPC (sheath), or PLA / PPC / curcumin fibers using a tailor-made melt-drawn spinning setup with no extrusion mechanism and no control on fiber dimensions, or pellets of polymer blends with PPC as one of the components without providing details of the subsequent fiber spinning process.SUMMARY OF THE INVENTION

[0009] This invention provides a multi-constituent fiber obtained by melt spinning of particles formed from a polymer blend. In one embodiment, said polymer blend consisting essentially of: a) 40-80wt.% of polypropylene carbonate, said polypropylene carbonate has a weightaverage molecular weight >100,000g / mol; b) 10-50wt.% of one or more semicrystalline polymer; and c) 0.1 to 10wt.% of an end-capping and cross-linking agent.

[0010] This invention also provides a method for forming said multi-constituent fiber of this invention. In one embodiment, said method comprises the steps of: i) Providing said particles to a melt spinning machine; and ii) Extruding at an extrusion temperature of 160°C to 190°C to form said multi-constituent fiber.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 illustrates an exemplary process for preparing multi-constituent polypropylene carbonate fibers.

[0012] FIG. 2 indicates the enhanced glass transition temperature of polypropylene carbonate after reaction with maleic anhydride.

[0013] FIG. 3 indicates the enhanced thermal decomposition temperature of polypropylene carbonate after reaction with maleic anhydride.

[0014] FIG. 4 indicates the shape memory progress of a PPC / PLA / MA (49.75 / 49.75 / 0.5) fiber.DETAILED DESCRIPTION OF THE INVENTION

[0015] This invention provides a multi-constituent fiber obtained by melt spinning of particles formed from a polymer blend. In one embodiment, said polymer blend consisting essentially of: a) 40-80wt.% of polypropylene carbonate, said polypropylene carbonate has a weightaverage molecular weight >100,000g / mol; b) 10-50wt.% of one or more semicrystalline polymer; and c) 0.1 to 10wt.% of an end-capping and cross-linking agent.

[0016] In one embodiment, said polymer blend comprises 40, 50, 60, 70 or 80 wt.% of polypropylene carbonate.

[0017] In one embodiment, said polypropylene carbonate has a weight-average molecular weight of 100,000g / mol to 300,000g / mol. In another embodiment, said polypropylene carbonate has a weight- average molecular weight of 100,000 g / mol, 150,000 g / mol, 200,000 g / mol, 250,000 g / mol, or 300,000g / mol.

[0018] In one embodiment, said polymer blend comprises 10, 20, 30, 40 or 50wt.% of said one or more semicrystalline polymer.

[0019] In one embodiment, said polymer blend comprises 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10wt.% of said end-capping and cross-linking agent.

[0020] In one embodiment, said one or more semicrystalline polymer comprises one or more selected from the group consisting of polylactic acid, poly(hydroxybutyrate-co- hydroxyvalerate) and polycaprolactone.

[0021] In one embodiment, said polylactic acid is poly(L-lactic acid).

[0022] In one embodiment, said one or more semicrystalline polymer has a Mw at least 50,000 g / mol. In another embodiment, said one or more semicrystalline polymer has a Mw of 50,000 g / mol, 100,000 g / mol, 150,000 g / mol, 200,000 g / mol, 250,000 g / mol, 300,000 g / mol, 350,000 g / mol, 400,000 g / mol, 450,000 g / mol or 500,000 g / mol.

[0023] In one embodiment, said end-capping and cross-linking agent comprises one or more of acid anhydride, multi-functional carboxylic acid, diisocyanate, or epoxy resin.

[0024] In one embodiment, said end-capping and cross-linking agent comprises one or more of maleic anhydride, pyromellitic dianhydride, succinic acid, citric acid, 1, 2,3,4- butanetetracarboxylic acid, diisocyanate or epoxy resin.

[0025] In one embodiment, said particles comprise a decomposition temperature of 200°C to 230°C. In another embodiment, said decomposition temperature is 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, or 230°C.

[0026] In one embodiment, said particles comprise a glass transition temperature of 25°C to 40°C. In another embodiment, said glass transition temperature is 25°C, 30°C, 35°C or 40°C.

[0027] In one embodiment, said multi-constituent fiber comprises a tensile strength of > 0.8cN / dtex.

[0028] In one embodiment, said multi-constituent fiber comprises a tensile strength of 0.8cN / dtex to l.OcN / dtex.

[0029] This invention also provides a method for forming said multi-constituent fiber of this invention. In one embodiment, said method comprises the steps of: i) Providing said particles to a melt spinning machine; and ii) Extruding at an extrusion temperature of 160°C to 190°C to form said multi-constituent fiber.

[0030] In one embodiment, said extrusion temperature is 180°C to 190°C. In another embodiment, said extrusion temperature is 160°C, 165°C, 170°C, 175°C, 180°C, 185°C to 190°C.

[0031] In one embodiment, said extrusion of step (ii) further comprises one or more of the following steps: a) Said extrusion is conducted through a spinneret; b) Said multi-constituent fiber is drawn with a drawn ratio of at least 4; c) Quenching Said multi-constituent fiber with an air flow at or below 25°C; or d) Applying a lubricant onto said multi-constituent fiber.

[0032] In one embodiment, said particles are reactive blended by the steps of: a) Providing an appropriate amount of said polypropylene carbonate in dried form; b) Providing an appropriate amount of said one or more semicrystalline polymer in dried form; c) Mixing said polypropylene carbonate in dried form and said one or more semicrystalline polymer in dried form with an appropriate amount of said end-capping and cross-linking agent to form a mixture; d) Extruding said mixture to form filaments; and e) Processing said filaments into said particles.

[0033] In one embodiment, said polypropylene carbonate in dried form are produced by drying in vacuum at 10°C to 20°C for at least 48 hours.

[0034] In one embodiment, said one or more semicrystalline polymer in dried form are produced by drying in vacuum at 40°C to 50°C for at least 48 hours.

[0035] This invention provides a method for forming multi-constituent shape memory polypropylene carbonate fibers. In one embodiment, said multi-constituent shape memory polypropylene carbonate fibers comprises (i) polypropylene carbonate as the major component and (ii) one or more other polymers, with at least one of these polymers being randomly dispersed through the fiber and at least one of these polymers being semi-crystalline, the method comprising: a) drying polypropylene carbonate pellets in vacuum at or below 20°C for at least 48 hours prior to reactive blending; b) drying other constituent polymer pellets in vacuum at 50°C for at least 48 hours prior to reactive blending; c) preparing a dry blend of polypropylene carbonate and other constituent polymers in the presence of end-capping and cross-linking agent such as anhydrides (e.g. maleic anhydride, pyromellitic dianhydride) or multi-functional carboxylic acids (e.g. succinic acid, citric acid, 1,2,3,4-butanetetracarboxylic acid (BTCA)) or diisocyanate or epoxy resin for reacting with the terminal hydroxyl groups of polypropylene carbonate and / or any reactive functional groups (e.g. hydroxyl, amine, carboxylic acid) directly attached to main chain or end of other constituent polymers, colorants, fillers, compatibilizers, ultraviolet blocking agent, etc.; d) the dry polymer blend is extruded by either single screw extruder or twin screw extruder to filament form in diameter of maximum 4 mm; e) the polymer blend filament is chopped to pellets; f) feeding the polymer blend pellets to the hopper of melt spinning machine; g) extruding the polymer blend through a spinneret to form fibers; h) quenching the hot extruded fibers by an air flow at or below 25 °C; i) applying lubricant (e.g. stearates, low molecular wax) onto the fibers; j) drawing thefibers on hot godets with a draw ratio of at least 4; and k) collecting the drawn fibers (diameter: max. 100 microns) on a bobbin. The collected fibers can be used for subsequent yarn spinning, knitting or weaving into fabrics for textile applications.

[0036] In one embodiment, said polypropylene carbonate has a weight-average molecular weight from about 100,000 g / mol to about 300,000 g / mol and polymer dispersity index from about 1 to about 5.

[0037] In one embodiment, other constituent polymers include semi-crystalline polymers such as polylactic acid which contains at least 98% L-isomer, and it has a weight-average molecular weight from about 50,000 g / mol to about 200,000 g / mol and polymer dispersity index from about 1 to about 5.

[0038] This invention also provides a composition to be used in the method for forming multiconstituent shape memory polypropylene carbonate fibers of this invention. In one embodiment, said composition comprises: i) 45 to 90 wt% of polypropylene carbonate; ii) 10 to 50 wt% of semi-crystalline polymer; iii) 0.1 to 10 wt% of end-capping and crosslinking agent.

[0039] In one embodiment, reactive blending is done in extruders at temperature from about 160°C to about 190°C.

[0040] In one embodiment, the polymer blend is pelletized after reactive blending.

[0041] In one embodiment, fiber extrusion occurs at a temperature of from about 160°C to about 190°C.

[0042] In one embodiment, the polymer blend is extruded through a spinneret containing single or multiple patterned arrangements of holes.

[0043] In one embodiment, spin finishes including lubricant are applied onto the fibers extruded.

[0044] In one embodiment, the fibers extruded are drawn on the hot godets at about 70 °C to about 150°C with a draw ratio of at least 4.

[0045] This invention also provides a system of forming polypropylene carbonate and other constituent polymers blend. In one embodiment, the system comprises: i) a blender for mixing the polypropylene carbonate pellets, other constituent polymer pellets, end-capping and crosslinking agent, colorants, fillers, compatibilizers, etc. by mechanical means; ii) an extruder that is configured to reactively blend the polymers and other components of the mixture; iii) a pelletizer that is configurated to cut the polymer blend into pellets.

[0046] In one embodiment, the extruder is either a single screw extruder or a twin screw extruder.

[0047] In one embodiment, the pelletizer is either a strand pelletizer or a water-ring pelletizer or an underwater pelletizer.

[0048] This invention also provides a system for forming melt spun fibers. In one embodiment, the system comprises: i) a hopper for introducing the polymer blend pellets to the system; ii) a screw extruder for melting and pushing the polymer blend towards the static mixer; iii) extrusion barrels for housing and heating the screw; iv) a melt pump for pushing the molten polymer blend towards the spinneret; v) a spinneret for generating the extruded fibers with specific diameter; vi) a quenching chamber for solidification of the extruded fibers by cooling; vii) a spin finish applicator for applying spin finishing materials onto the extruded fibers; viii) a set of godets for drawing the fibers by a specific drawing ratio; ix) a winder for collecting the fibers on a bobbin.

[0049] In one embodiment, the screw extruder is either a single screw extruder or a twin screw extruder;

[0050] In one embodiment, the extrusion barrels is able to heat the screw to temperature at about 160°C to about 190°C;

[0051] With reference to ASTM D123 and US patent 5582667, the term “multi-constituent fiber” is defined as a material which has a length at least 100 times its diameter, and consists of two or more polymers, with at least one of these polymers being randomly dispersed through the fiber. Multi-constituent polypropylene carbonate (PPC) fibers are prepared from PPC and one or more other polymers, with at least one of these polymers being semi-crystalline, in the presence of a crosslinking agent using reactive extrusion.

[0052] Polymers suitable for making multi-constituent PPC fibers of the invention include the polypropylene carbonate (PPC), preferably those having a weight average molecular weight, Mw, at least 100,000 g / mol; polylactic acid (PLA), such as poly(L-lactic acid) (PLLA), preferably those having a Mw at least 50,000 g / mol; poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), preferably those having a Mw at least 50,000 g / mol; polycaprolactone (PCL), preferably those having a Mw at least 50,000 g / mol. In general, mechanical properties of polymers are enhanced as the molecular weight of the polymers increase.

[0053] Polypropylene carbonate (PPC) is a copolymer of carbon dioxide and propylene oxide, and it is a biodegradable amorphous thermoplastic polymer. There are numerous carbonate ester groups in the hydrocarbon chain of PPC. At the end of the PPC polymer chain are terminal hydroxyl groups, or carboxyl groups. At temperature above 180°C, degradation occurs by backbiting or unzipping due to attack of the terminal hydroxyl group onto a carbonate linkage. Backbiting can be inhibited by blocking the terminal hydroxyl groups with an end-cappingagent such as acid anhydride, acyl halide, alkyl silicate, etc. In addition to end-capping, the terminal hydroxyl groups can also be used for crosslinking two PPC polymers or one PPC polymer and another polymer consisting of reactive functional groups such as hydroxyl, amine, carboxylic acid, etc. or two polymers (other than PPC) consisting of reactive functional groups. Since polypropylene carbonate has no crystalline structure, at least one semi-crystalline polymer shall be blended with PPC to form the multi-constituent fiber in order to make use of drawing-induced crystallization to enhance the tensile strength of fiber.

[0054] Polylactic acid (PLA) is an aliphatic biodegradable polyester derived from lactic acid (2-hydroxypropionic acid). It can have terminal hydroxyl groups, acetoxy groups, or carboxyl groups. Lactic acid is a chiral molecule, and it has two optical isomers, L-lactic acid and D- lactic acid. PLA exists in three optical isomeric forms poly(L-lactic acid) (PLLA), poly(D- lactic acid) (PDLA), and poly (D, L-lactic acid) (PDLLA). The PLLA and PDLA both are semicrystalline polymers. However, a racemic blend (50% L and 50% D) gives an amorphous polymer. Commercial PLA grades are usually based on an L-rich mixture as the majority of bacteria used in fermentation processes produce L-lactic acid predominantly. Also, PLLA displays the best thermomechanical properties among polylactic acids. Semi-crystalline polymeric fibers can have various levels of molecular orientation, ranging from random distribution to highly align in the fiber axis direction. As reported by Ghosh, S., and Vasanthan, N., Journal of Applied Polymer Science, 2006, 101, 1210-1216, molecular orientation was low for undrawn samples as expected. A higher level of molecular orientation was achieved after drawing the filaments.

[0055] Preparation of polymer blend is done by reactive extrusion at high temperature (around 160-190°C in this invention). The presence of moisture in the polymer pellets fed into the extruder may cause hydrolysis of polymers such as polycarbonate and polyester. Therefore, it is necessary to dry the polymer pellets before extrusion. Because of the glass transition temperature of polypropylene carbonate is in the range of 20°C to 40°C, PPC pellets are dried in vacuum at temperature below 20°C for at least 48 hours. Otherwise, the PPC pellets will stick together. For other polymers, higher temperature can be used, depends on their glass transition temperature. For example, a drying temperature of 50°C is used for polylactic acid which has a glass transition temperature at around 60°C to 65°C.

[0056] Acid anhydrides such as maleic anhydride (MA) can be used as both end-capping agent and crosslinking agent. According to Yao, M., et al., Journal of Applied Polymer Science, 2011, 120, 3565-3573, a maleic anhydride molecule first reacts with the terminal hydroxyl group or carboxyl group of a PPC polymer, then the terminal carboxyl group of MA-PPC will react withthe terminal functional group of another PPC polymer to complete the macromolecular coupling or crosslinking reaction. The high temperature in reactive extrusion (around 160- 190°C in this invention) is used to provide the activation energy of the crosslinking reaction. The amount of maleic anhydride shall be kept at maximum 2 wt.% of the polymer blend, otherwise the resulting blend turns yellowish-brown. At high content of maleic anhydride, homo-polymerization of MA occurs during reactive extrusion, and polymaleic anhydride is a brittle coloured solid. No radical initiator is used, because it is not desirable to have branched polymer. As stated in Hwang, S.W., et al., Polymer Testing, 2012, 31, 333-344, irregular chain branching of maleic anhydride onto the polymer backbone might decrease regularity and hinder the crystalline growth of PLLA, resulting in lower crystallinity. Also, intramolecular chain scission is promoted in the presence of radical initiator, leading to degradation of the polymer.

[0057] An exemplary process for preparing multi-constituent polypropylene carbonate fibers is shown on FIG. 1. It includes the introduction of raw materials (i.e. polymers and crosslinker) to a mixing apparatus for a brief mixing with no heating. Then, the mixture is fed into the hopper of an extruder for reaction extrusion to form a filament of about 2mm in diameter. Next the filament is pelletized into pellets. The pellets go through melt spinning at 160°C to 190°C with a draw ratio of around 4 resulting in filaments of enough mechanical strength for subsequent yarn spinning.

[0058] A plot of differential scanning calorimetry (DSC) results of neat PPC and a PPC / MA reaction product is shown on FIG. 2. It indicates that the glass transition temperature of neat PPC has been increased from 25.5°C to that of PPC / MA reaction product at 37.4°C which is close to the human body temperature. Textile products made from such maleic anhydride endcapped and crosslinked polypropylene carbonate may possess shape memory performance.

[0059] A plot of thermogravimetric analysis (TGA) results of neat PPC and a PPC / MA reaction product is shown on FIG. 3. It indicates that the decomposition temperature at 5% weight loss of neat PPC has been increased from 198.0°C to that of PPC / MA reaction product at 232.2°C. There is an over 30°C increase in the thermal decomposition temperature. The enhanced thermal stability of PPC makes thermal processing of PPC textile products feasible.

[0060] The effect of draw ratio on the tensile properties of multi-constituent PPC / PLA (1 / 1) fiber has been studied, and data are shown on Table I. It is found that the tensile strength of the PPC / PLA fiber is proportional to the draw ratio in the range of 1 to 4, and reaches around 0.83 cN / dtex at draw ratio of 4. A neat PLA fiber prepared by the same melt spinning method described herein has a tensile strength of 0.85 cN / dtex at draw ration of 4. The tensile strength of the PPC / PLA (1 / 1) fiber is comparable with that of the neat PLA fiber.Table I: Tensile properties of multi-constituent PPC / PLA (1 / 1) fiber

[0061] The effect of amount of maleic anhydride on the tensile properties of multi-constituent PPC / PLA (1 / 1) fiber (draw ratio: 4) has been studied, and data are shown on Table II. It is found that the tensile strength of the PPC / PLA fiber is around 1.0 cN / dtex in the range of maleic anhydride content 0.5 wt.% to 1.5 wt.%. An increase of around 0.2 cN / dtex in textile strength is observed.Table ILTensile properties of multi-constituent PPC / PLA (1 / 1) fiber at draw ratio of 4

[0062] The shape memory performance of the PPC / PLA / MA fiber has been evaluated by coiling the fiber around a cylindrical object at 37°C and fixed via quenching. Then, the fiber recovers the original shape after reheating at 37°C. Images of the fiber at different stages are shown on FIG. 4.

[0063] EXAMPLE 1

[0064] Polypropylene carbonate pellets were dried in vacuum at 4°C for at least 48 hours. Polylactic acid pellets were dried in vacuum at 50°C for at least 48 hours. The dried PPC pellets and the dried PLA pellets were mixed in a weight ratio of 1 : 1. Maleic anhydride was added to the polymer mixture in 0.5 weight % of the polymer blend. Therefore, the final weight % of PPC, PLA, and maleic anhydride are 49.75%, 49.75%, and 0.5%, respectively. The solid mixture was physically mixed using a blender. The mixed solid mixture was then extruded to form filaments of around 2 mm in diameter. The filaments were pelletized for subsequent fiber spinning. In the melt spinning process, barrel temperature is the range of 160°C to 190°C, anda draw ratio of 4 was used. The mechanical properties such as tensile strength, elongation at break, and Young’s modulus of the resulting multi-constituent PPC fibers were determined and recorded as 1.097(+ / -0.300) cN / dtex, 35.0(+ / -14.7) %, and 2.28(+ / -0.54) GPa, respectively.

Claims

What is claimed is:

1. A multi-constituent fiber obtained by melt spinning of particles formed from a polymer blend, said polymer blend consisting essentially of: a. 40-80wt.% of polypropylene carbonate, said polypropylene carbonate has a weight-average molecular weight >100,000g / mol; b. 10-50wt.% of one or more semicrystalline polymer; and c. 0.1 to 10wt.% of an end-capping and cross-linking agent.

2. The multi-constituent fiber of claim 1, said one or more semicrystalline polymer comprises one or more selected from the group consisting of polylactic acid, poly(hydroxybutyrate-co-hydroxyvalerate) and polycaprolactone.

3. The multi-constituent fiber of claim 2, wherein said polylactic acid is poly(L-lactic acid).

4. The multi-constituent fiber of claim 2, wherein said one or more semicrystalline polymer has a Mw at least 50,000 g / mol.

5. The multi-constituent fiber of claim 1, said end-capping and cross-linking agent comprises one or more of acid anhydride, multi-functional carboxylic acid, diisocyanate, or epoxy resin.

6. The multi-constituent fiber of claim 5, said end-capping and cross-linking agent comprises one or more of maleic anhydride, pyromellitic dianhydride, succinic acid, citric acid, 1,2,3,4-butanetetracarboxylic acid, diisocyanate or epoxy resin.

7. The multi-constituent fiber of claim 1, said particles comprise a decomposition temperature of 200 °C to 230°C .

8. The multi-constituent fiber of claim 1, said particles comprise a glass transition temperature of 25°C to 40°C .

9. The multi-constituent fiber of claim 1, said multi-constituent fiber comprises a tensile strength of > 0.8cN / dtex.

10. A method for forming said multi-constituent fiber of claim 1, comprising the steps of: i. Providing said particles to a melt spinning machine; ii. Extruding at an extrusion temperature of 160°C to 190°C to form said multiconstituent fiber.

11. The method of claim 10, wherein said extrusion temperature is 180°C to 190°C.

12. The method of claim 10, wherein said extrusion of step (ii) further comprises one or more of the following steps: a. Said extrusion is conducted through a spinneret; b. Said multi-constituent fiber is drawn with a drawn ratio of at least 4;c. Quenching Said multi-constituent fiber with an air flow at or below 25°C; or d. Applying a lubricant onto said multi-constituent fiber.

13. The method of claim 10, wherein said particles are reactive blended by the steps of: a. Providing an appropriate amount of said polypropylene carbonate in dried form; b. Providing an appropriate amount of said one or more semicrystalline polymer in dried form; c. Mixing said polypropylene carbonate in dried form and said one or more semicrystalline polymer in dried form with an appropriate amount of said endcapping and cross-linking agent to form a mixture; d. Extruding said mixture to form filaments; and e. Processing said filaments into said particles.

14. The method of claim 13, wherein said polypropylene carbonate in dried form are produced by drying in vacuum at 10°C to 20°C for at least 48 hours.

15. The method of claim 13, wherein said one or more semicrystalline polymer in dried form are produced by drying in vacuum at 40°C to 50°C for at least 48 hours.

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