A polypropylene comprising anionic NANO polyester fibers and a method for producing reinforced polypropylene

Abstract

The present invention relates to a polypropylene matrix, a polypropylene reinforced with anionic nano polyester fibers having a. diameter of 0.1 to 0.3 pm, a. hydrodynamic size of 30 to 120 nm and a zeta potential of (-20) to (-30) mEV dispersed in the said matrix and coated with at least one anionic surfactant and, a method for producing the said reinforced polypropylene.

Description

[0001] A POLYPROPYLENE COMPRISING ANIONIC NANO POLYESTER FIBERS AND A METHOD FOR PRODUCING REINFORCED POLYPROPYLENE

[0002] The present invention generally relates to reinforcement of thermoplastic materials and more specifically, to the reinforcement of polypropylene using anionic nano polyester fibers.

[0003] The invention particularly relates to the use of anionic nano polyester fibers for reinforcing polypropylene in the production of toughened polymer composites.

[0004] Polypropylene (PP) is a versatile thermoplastic material which is widely used in various industries due to its beneficial properties such as high heat distortion temperature, transparency, flame resistance and dimensional stability. Polypropylene is particularly suitable for producing composites and is often used as a matrix material combined with various fibers to form fiber-reinforced polypropylene composites (FRPCs). The mechanical properties of such composites substantially depend on the properties of the reinforcing fibers which are incorporated, including tensile strength, breaking strength, and stiffness. In the state of the art, carbon or glass fibers are known to be used for increasing the toughness of such composites significantly.

[0005] The use of nano-sized structures as reinforcing agents in polymers has been studied because of the superior physical and chemical properties compared to their macro forms. Such properties are attributed to quantum size and surface effects thereof. For example, nano-sized fibers have a relatively higher surface to volume ratio compared to macro-sized fibers, which dramatically improves their surface reactivity. This improved reactivity enables the fibers to function as strong binders in the selected matrix, which potentially leads to a radical improvement in the strength and stiffness of the polymers. However, the use of surface-modified nanofiber reinforced polymers has not yet matured. In compounding technology, there are problems with additives and main matrix compatibility, Compatibilizing agents such as maleic anhydride are often used to overcome such problems. However, the technology has not yet been developed sufficiently in terms of the use of naturally surface-modified fibers, such as anionic or cationic coatings on the fiber surface.

[0006] Chinese patent application no. CN103709590A, known in the state of the art, discloses a method for preparing nylon 6 nanofibers reinforced / toughened polyform aldehyde. However, the said method does not address the use of anionic or cationic coatings on the fiber surface for improved compatibility with the matrix material.

[0007] PCT application no. WO2018045476A1, known in the state of the art, discloses a reinforced polypropylene which is mixed with nano polyester (polyethylene terephthalate (PET) is provided as an example). In the said patent application, it is also disclosed that nano polyesters are subjected to surface treatments. However, such surface treatment differs from coating with an anionic surfactant.

[0008] European patent application no. EPl 810993 A2, another document known in the state of the art, discloses reinforced PET nanofibers and the method of preparation thereof.

[0009] European patent application no. EP21064666B1, another document known in the state of the art, discloses that the surfaces of nano- or meso-sized PET and polypropylene fibers can be functionalized either anionically or cationically.

[0010] The objective of the invention is to provide a reinforced polypropylene product which exhibits improved mechanical properties, particularly in terms of toughness. Also, the objective of the invention is to address compatibility issues between the additive and the main matrix in compounding technology. This is achieved in particular by using anionic nano polyester fibers, which are coated with an anionic surfactant. Such coating not only increases the surface reactivity of the fibers, but also improves their compatibility with the polypropylene matrix, thereby eliminating the use of additional compatibilizing agents.

[0011] In the reinforced polypropylene of the invention, anionic nano poly ester fibers are used as reinforcing agents in the polypropylene matrix. In a preferred main embodiment of the invention, an anionic surfactant coated nano PET fiber is used.

[0012] The reinforced polypropylene product of the invention comprises a polypropylene matrix and anionic nano polyester fibers which are dispersed within the matrix. The said fibers are coated with at least one anionic surfactant. In the main embodiment of the invention, the fibers are anionic nano polyester fibers having a diameter of 0, 1 - 0,3 gm, a hydrodynamic size of 30 - 120 nm and a zeta potential of (-20)-(- 30) mEV coated with at least one anionic surfactant.

[0013] The anionic surfactant can be selected from the group consisting of sodium decyl sulfate, sodium N-chloryl-N-methyltaurate, sodium tetradecyl sulfate, ammonium lauryl sulfate and ethoxylated phosphate ester.

[0014] The reinforced polypropylene product can be produced by means of an electrospinning method which comprises the processes of making a solution of polyethylene terephthalate in a mixture of tri fluoroacetic acid and dichloromethane, dissolving an anionic surfactant in the solution, spinning the solution to produce anionic nano / micro polyester fibers by means of electrospinning, and compounding the fibers with a poly propylene matrix using a twin-screw extruder.

[0015] The reinforced polypropylene product of the invention provides a mechanical improvement compared to raw polypropylene by using nano-sized polyester fibers. Nano-sized fibers have a relatively higher surface to volume ratio compared to macro-sized fibers, which improves their surface reactivity. The fibers exhibit a strong reactivity in the medium in which they are dispersed, therefore they are able to function as a strong binder in the selected matrix. Due to its homogeneous dispersion and strong interaction ability, nano-sized polyethylene terephthalate coated with an anionic surfactant provides an optimal solution for the reinforcement of the polypropylene matrix.

[0016] The reinforced polypropylene product of the invention provides a significant increase in the toughness of polypropylene by means of more lightweight reinforcing agents as nano-sized polyester fibers compared to glass fiber reinforcements. Anionic nanofibers generate repulsive forces between fibers, which ensures a homogeneous dispersion within the matrix and requires relatively low use or no use of compatibility agents during the compounding of polyester fiber with polypropylene matrix.

[0017] The reinforced polypropylene product of the invention is suitable for use in various fields of thermoplastics such as engineering plastics.

[0018] In one embodiment of the reinforced polypropylene of the invention, anionic nanofibers having a diameter of 0.3 pm and a zeta potential of -14.2 mEV provides a high degree of toughness to polypropylene. This makes polypropylene material suitable for a variety of applications which require resilient and flexible materials. The hydrodynamic size refers to the size of the fibers in a liquid medium and can also be controlled during the production process. A hydrodynamic size of 30-120 nm provides a strong interaction between the fibers and the polypropylene matrix. The hydraulic size between 30-120 nm is the result of hydrodynamic measurement in saline, NaCl solution. Hydrodynamic size and zeta potential measurements were performed in 5% NaCl solution. In one embodiment of the invention, the anionic surfactant which is used for coating fibers can be selected from the group consisting of sodium decyl sulfate, sodium N- chloryl-N-methyltaurate, sodium tetradecyl sulfate, ammonium lauryl sulfate and ethoxylated phosphate ester. Such surfactants provide the fibers with a negative charge, which may improve the dispersion of the fibers within the polypropylene matrix. This ensures a more homogeneous dispersion of fibers in the matrix and improves the mechanical properties of the reinforced polypropylene product. In particular, sodium decyl sulfate is a type of anionic surfactant which can provide fibers with a strong negative charge.

[0019] In one embodiment of the invention, the polypropylene comprises anionic nano polyester fibers which are produced by electrospinning method. Electrospinning is a versatile and applicable technique for producing ultra-fine fibers. This method comprises using an electric field to charge a polymer solution and spin it as a fine fiber. The charged solution is retained at the end of a capillary tube and subjected to an electric field. When the electric field reaches a threshold value, the repulsive electrostatic force in the solution exceeds the surface tension and causes the solution to be ejected from the capillary' tube as a jet. As the solvent evaporates, the polymer jet solidifies into fiber. The fiber is then collected on a grounded collector. The diameter of the fibers produced by means of electrospinning process can be controlled by adjusting the parameters of the electrospinning process, including the concentration of the polymer solution, the applied voltage and the distance between the capillary' tube and the collector.

[0020] The electrospinning process may comprise using high voltage to form an electrically charged jet of polymer solution. The charged jet is tensioned and elongated by the electric field, thereby leading to the formation of ultra-fine fibers. The fibers are then collected on a grounded collector. The use of electrospinning for producing anionic nano polyester fibers allows the production of fibers which have a substantially uniform and narrow' size distribution. This allows to obtain a reinforced polypropylene product having improved mechanical properties such as increased toughness and strength.

[0021] In one embodiment of the invention, polypropylene matrix and anionic nano polyester fibers are combined using a twin-screw compounding process. Twin- screw compounding is a basic process particularly for the plastics industry which uses twin-screw extruders having interlocking, co-rotating screws, and a specific hopper. The process starts with the introduction of raw materials, including base polymers and additives, into the hopper. As the materials move through the hopper, the twin screws provide controlled temperature and pressure conditions, triggering gradual melting and conveying. The subsequent stirring and dispersing stages benefit from the dynamic shearing and kneading effects which are generated by the interlocking screws. It ensures a complete blending of the molten polymer with the selected additives. This process ensures a homogeneous dispersion of anionic nano polyester fibers within the polypropylene matrix, which in turn improves the mechani cal properties of the reinforced polypropylene product.

[0022] The reinforced polypropylene of the invention comprises at least one anionic nano polyester fiber having a DTEX value of 0.3 and a cut length of 3 mm. DTEX or decitex is a measurement of the linear bulk density of fibers and is defined as the mass in grams per 10.000 meters of a fiber. A low DTEX indicates a finer fiber. In this case, a DTEX of 0.3 indicates that the fibers are considerably fine, and this property contributes to an even dispersion of the fibers within the polypropylene matrix and improves the mechanical properties of the reinforced polypropylene product.

[0023] In the method for obtaining reinforced polypropylene of the invention, a mixture of trifluoroacetic acid and di chloromethane is used to prepare the polyethylene terephthalate solution. Polyethylene terephthalate is dissolved in the mixture to form a solution which is suitable for the electrospinning process. In one embodiment of the invention, the ratio of trifluoroacetic acid to dichloromethane can be approximately 80 / 20 by weight, but other ratios can also be used depending on the specific requirements of the electrospinning process. The use of this mixture facilitates the dissolution of polyethylene terephthalate and improves the electrospinning process, which leads to the production of anionic nano polyester fibers with desired properties.

[0024] In one embodiment of the invention, in the method for producing reinforced polypropylene, in particular, PET solution in a ratio of 10-15% by weight is used for electrospinning. This weight percentage is chosen to provide a suitable concentration of PET for the electrospinning process. A higher concentration may result in fibers having a larger diameter, while a lower concentration may result in fibers having a finer diameter. Therefore, PET solution in a ratio of 10-15% by weight provides a balance between these two points and results in fibers having the desired diameter for reinforcing the polypropylene product. Further, the use of PET solution in a ratio of 10-15% by weight allows precise control over properties such as diameter, hydrodynamic size, and zeta potential of the fibers. This results in a customized reinforced polypropylene product with properties suitable for specific applications.

[0025] The reinforced polypropylene product of the invention may be considered as a thermoplastic composite. Such composite comprises a polypropylene matrix and anionic nano polyester fibers dispersed in the said matrix. The fibers are coated with an anionic surfactant and in a preferred embodiment of the invention, the said nano polyester fibers have a diameter of 0,3 pm and a zeta potential of -14,2 mEV. This configuration provides the composite with a high degree of toughness, which can make it suitable for a variety of applications that require resilient and flexible materials, such as engineering plastics.

Claims

CLAIMS1. A polypropylene comprising a polypropylene matrix and reinforced with ananionic nano polyester fibers coated with at least one anionic surfactant having a diameter of 0,1 to 0,3 pm, a hydrodynamic size of 30 to 120 nm and a zeta potential of (-20) to (-30) mEV dispersed in the said matrix.

2. A polypropylene according to Claim 1, characterized by a nano polyethylene terephthalate (PET) fiber coated with an anionic surfactant.

3. A polypropylene according to Claim 1 or 2, characterized by a nano polyester fiber coated with at least one anionic surfactant selected from the group consisting of sodium decyl sulfate, sodium N-lauroyl-N-methyltaurate, sodium tetradecyl sulfate, ammonium lauryl sulfate and ethoxylated phosphate ester.

4. A polypropylene according to any one of Claims 1 to 3, characterized by at least one anionic nano polyester fiber produced by the method of electrospinning.

5. A polypropylene according to any one of Claims I to 4, characterized by at least one anionic nano polyester fiber having a DTEX value of 0.1 to 0.3 and a cut length of 1 to 3 mm.

6. A polypropylene according to any one of Claims 1 to 5, characterized by anionic nano polyester fiber between 5% and 50% by weight.

7. A method for producing a polypropylene reinforced with an anionic nano polyester fiber, characterized in that it comprises the steps of preparing polyethylene terephthalate solution in a mixture of tri fluoroacetic acid and dichloromethane,- dissolving an anionic surfactant in the said solution,- producing anionic nano polyester fibers by electrospinning the said solution and,- compounding the said fibers with a polypropylene matrix using a twin- screw extruder.

8. A method according to Claim 7, characterized by the step of coating polyester with at ieast one anionic surfactant selected from the group consisting of sodium decyl sulfate, sodium N-lauroyl-N-methyltaurate, sodium tetradecyl sulfate, ammonium lauryl sulfate and ethoxylated phosphate ester.

9. A method according to Claim 7 or 8, characterized by using polyethylene terephthalate having an average molecular weight of 100.000 g / mol.

10. A method according to any one of Claims 7 to 9, characterized by using a solution of polyethylene terephthalate prepared in a mixture of trifluoroacetic acid and di chloromethane in a ratio of 80 / 20 by weight.