Patent Application
20190002648
The present disclosure relates to high impact strength polymer composites, more specifically high impact strength polypropylene (HIPP) composites containing polypropylene coated multiwall carbon nanotubes and methods of making same.
For a detailed description of the preferred embodiments of the disclosed methods, reference will now be made to the accompanying drawings in which:
Disclosed herein are high impact strength polypropylene (HIPP) composites and methods of making same. In an embodiment, the HIPP composite can comprise a continuous polymeric phase having dispersed therein a plurality of polypropylene-coated functionalized multiwall carbon nanotubes (PP/f-MWNT), wherein the continuous polymeric phase can comprise a first polypropylene (PP), wherein the PP/f-MWNT can comprise functionalized multiwall carbon nanotubes (f-MWNT) coated with a second PP via non-covalent interactions, wherein the HIPP composite can comprise PP/f-MWNT in an amount of from about 0.0005 wt. % to about 5 wt. % f-MWNT, based on the total weight of the HIPP, and wherein the first PP and the second PP can be the same or different. In such embodiment, the HIPP can have an impact strength of from about 4.0 kJ/m2 to about 6.5 kJ/m2, as determined in accordance with ASTM D256. In an embodiment, the non-covalent interactions can comprise intermolecular CH-π interactions. In an embodiment, the non-covalent interactions exclude hydrogen bonding.
In an embodiment, a method of making a HIPP composite can comprise the steps of (a) blending PP/f-MWNT with a first PP to produce a PP and PP/f-MWNT mixture, wherein the PP/f-MWNT comprise f-MWNT coated with a second PP via non-covalent interactions, wherein the PP and PP/f-MWNT mixture comprises PP/f-MWNT in an amount of from about 0.0005 wt. % to about 5 wt. % f-MWNT, based on the total weight of the PP and PP/f-MWNT mixture, and wherein the first PP and the second PP can be the same or different; (b) melt blending at least a portion of the PP and PP/f-MWNT mixture to form a molten PP and PP/f-MWNT mixture; and (c) shaping at least a portion of the molten PP and PP/f-MWNT mixture to form the HIPP composite. In such embodiment, the step (c) of shaping at least a portion of the molten PP and PP/f-MWNT mixture can comprise injection molding.
In an embodiment, a HIPP composite can be made by using any suitable methodology. In an embodiment, a method of making a HIPP composite can comprise a step of blending PP/f-MWNT with a first PP to produce a PP and PP/f-MWNT mixture, wherein the PP/f-MWNT can comprise functionalized multiwall carbon nanotubes (f-MWNT) coated with a second PP via non-covalent interactions, and wherein the first PP and the second PP can be the same or different. In some embodiments, the first PP can comprise a PP homopolymer. In other embodiments, the first PP can comprise PP copolymers, such as ethylene/propylene copolymers, ethylene/propylene/diene terpolymers, and the like, or combinations thereof. In yet other embodiments, the first PP can comprise PP homopolymers, PP copolymers, blends thereof, or combinations thereof.
In some embodiments, the first PP and the second PP can be the same. In other embodiments, the first PP and the second PP can be the different.
In an embodiment, the first PP and/or the second PP can be isotactic, syndiotactic, atactic, or combinations thereof. Tacticity is a property of polymers comprising regular substituents (originating in the monomer(s) used for forming the polymer) on the polymer chain. When the substituents are arranged in an irregular, random fashion, the polymer is atactic. When the substituents are all on the same side of the chain, the polymer is isotactic. When the substituents alternate regularly from one side of the chain to the other, the polymer is syndiotactic. Isotactic and syndiotactic polymers are referred to as stereoregular, that is, polymers having an ordered arrangement of pendant groups along the chain. For example, in isotactic PP, all the methyl (—CH3) groups are arranged along the same side of the polymer chain. Generally, stereoregular polymers are usually high-strength materials owing to an uniform structure leading to close packing of the polymer chains, which can result in a high degree of crystallinity.
In an embodiment, the first PP and/or the second PP can be characterized by an isotacticity of from about 0% to 100%, alternatively from about 90% to 100%, alternatively from about 95% to 100%, alternatively from about 96% to about 99%, or alternatively from about 92% to about 96%, as measured by 13C nuclear magnetic resonance (13C NMR) spectroscopy. For example, for high stiffness applications (e.g., pipe extrusion, injection molding, thin wall injection molding) the PP (e.g., the first PP and/or the second PP) can be characterized by an isotacticity of from about 95% to 100%, or alternatively from about 96% to about 99%. As another example, for film applications, the PP (e.g., the first PP and/or the second PP) can be characterized by an isotacticity of from about 92% to about 96%.
In an embodiment, the first PP and/or the second PP can be characterized by a melt flow index (MFI) of from about 0.1 dg/min to about 250 dg/min, alternatively from about 0.1 dg/min to about 200 dg/min, alternatively from about 0.1 dg/min to about 1 dg/min, alternatively from about 1 dg/min to about 10 dg/min, or alternatively from about 10 dg/min to about 200 dg/min, as determined in accordance with ISO 1133 under a load of 2.16 kg. For example, for pipe extrusion applications the PP (e.g., the first PP and/or the second PP) can be characterized by an MFI of from about 0.1 dg/min to about 1 dg/min; while for injection molding, the PP (e.g., the first PP and/or the second PP) can be characterized by an MFI of from about 10 dg/min to about 200 dg/min.
In an embodiment, the first PP and/or the second PP can be characterized by a molecular weight distribution (MWD) of from about 1 to about 10, alternatively from about 2 to about 8, alternatively from about 2 to about 4, or alternatively from about 4 to about 8, as determined in accordance with size exclusion chromatography/differential viscometry (SEC/DV). Generally, MWD, also known as polydispersity index, is a measure of the distribution of molecular mass in a given polymer sample. MWD can be calculated by dividing the weight average molecular weight by the number average molecular weight. As an example, for fibers applications the PP (e.g., the first PP and/or the second PP) can be characterized by a MWD of from about 2 to about 4; while for injection molding, the PP (e.g., the first PP and/or the second PP) can be characterized by a MWD of from about 4 to about 8.
In an embodiment, the first PP can be dried prior to the step of blending PP/f-MWNT with the first PP. As will be appreciated by one of skill in the art, and with the help of this disclosure, the first PP can be dried to remove moisture (e.g., water) from the PP. Further, as will be appreciated by one of skill in the art, and with the help of this disclosure, exposure of the first PP to moisture at subsequent processing temperatures (e.g., temperatures during melt blending) can cause polymer chain hydrolysis, which can break long polymeric chains into shorter fragments, reducing polymer strength.
In an embodiment, the first PP can be dried at a temperature of from about 50° C. to about 100° C., alternatively from about 60° C. to about 95° C., or alternatively from about 70° C. to about 90° C. In an embodiment, the first PP can be dried for a time period of from about 30 minutes to about 24 hours, alternatively from about 1 hour to about 16 hours, or alternatively from about 2 hours to about 8 hours.
In some embodiments, drying the first PP can occur under vacuum. In other embodiments, drying the first PP can occur at ambient pressure (e.g., without vacuum). In an embodiment, drying the first PP can occur at a pressure of from about 50 mbar to about 1,013 mbar, alternatively from about 100 mbar to about 900 mbar, or alternatively from about 200 mbar to about 800 mbar.
In an embodiment, the first PP can be a powder characterized by an average powder particle size of from about 10 μm to about 1 mm, alternatively from about 50 μm to about 750 μm, or alternatively from about 100 μm to about 500 μm. In embodiments where the first PP is not a powder, the first PP can be subjected to grinding, crushing, milling, chopping, and the like, or combinations thereof to form a first PP powder characterized by an average powder particle size of from about 10 μm to about 1 mm. As will be appreciated by one of skill in the art, and with the help of this disclosure, it is more efficient to dry the first PP in powder form, as more moisture can be removed from the PP when in powder form.
In an embodiment, the PP/f-MWNT as described herein can comprise f-MWNT in an amount of from about 0.5 wt. % to about 80 wt. %, alternatively from about 1 wt. % to about 60 wt. %, or alternatively from about 10 wt. % to about 50 wt. %, based on the total weight of the PP/f-MWNT; and the second PP in an amount of from about 20 wt. % to about 99.5 wt. %, alternatively from about 40 wt. % to about 99 wt. %, or alternatively from about 50 wt. % to about 90 wt. %, based on the total weight of the PP/f-MWNT.
In an embodiment, the second PP can coat the f-MWNT via non-covalent interactions. In an embodiment, the non-covalent interactions exclude hydrogen bonding. In some embodiments, the non-covalent interactions can comprise intermolecular CH-π interactions, wherein the intermolecular CH-π interactions can be characterized by an upshift in the CH2 torsion motion, when compared to the CH2 torsion motion of the same PP (e.g., second PP) used for coating the f-MWNT but in the absence of the f-MWNT; and wherein the upshift is an increase in the wavenumber of from about 4 cm to about 10 cm−1, alternatively from about 4 cm to about 9 cm−1, or alternatively from about 5 cm to about 8 cm−1, as determined by Fourier transform infrared spectroscopy (FTIR).
In an embodiment, the f-MWNT of the PP/f-MWNT can have a diameter of from about 5 nm to about 200 nm, alternatively from about 10 nm to about 150 nm, or alternatively from about 20 nm to about 100 nm. In an embodiment, the f-MWNT of the PP/f-MWNT can have a length of from about 0.5 microns to about 1 mm, alternatively from about 1 micron to about 750 microns, or alternatively from about 5 microns to about 500 microns. In an embodiment, the f-MWNT of the PP/f-MWNT can have from about 3 walls to about 100 walls, alternatively from about 5 walls to about 75 walls, or alternatively from about 8 walls to about 50 walls. The f-MWNT can be prepared by any suitable methodology, such as introducing carboxylic acid groups (—COOH) in the structure of multiwall carbon nanotubes (MWNT), for example by treatment with nitric acid.
In an embodiment, the PP/f-MWNT can have a PP coating thickness of from about 1 nm to about 10 nm, alternatively from about 1.5 nm to about 9.5 nm, or alternatively from about 2 nm to about 9 nm.
In an embodiment, the second PP of the PP/f-MWNT can be characterized by a thermal decomposition temperature, a crystallization temperature, and a melting temperature that can be increased when compared to a thermal decomposition temperature, a crystallization temperature, and a melting temperature, respectively, of the same second PP used for coating the f-MWNT but in the absence of the f-MWNT.
In an embodiment, the PP/f-MWNT can be dried prior to the step of blending PP/f-MWNT with a first PP. As will be appreciated by one of skill in the art, and with the help of this disclosure, the PP/f-MWNT can be dried to remove moisture (e.g., water) from the PP/f-MWNT. Further, as will be appreciated by one of skill in the art, and with the help of this disclosure, exposure of PP (e.g., first PP second PP) to moisture at subsequent processing temperatures (e.g., temperatures during melt blending) can cause polymer chain hydrolysis, which can break long polymeric chains into shorter fragments, reducing polymer strength.
In an embodiment, the PP/f-MWNT can be dried at a temperature of from about 50° C. to about 100° C., alternatively from about 60° C. to about 95° C., or alternatively from about 70° C. to about 90° C. In an embodiment, the PP/f-MWNT can be dried for a time period of from about 30 minutes to about 24 hours, alternatively from about 1 hour to about 16 hours, or alternatively from about 2 hours to about 8 hours.
In some embodiments, drying the PP/f-MWNT can occur under vacuum. In other embodiments, drying the PP/f-MWNT can occur at ambient pressure (e.g., without vacuum). In an embodiment, drying the PP/f-MWNT can occur at a pressure of from about 50 mbar to about 1,013 mbar, alternatively from about 100 mbar to about 900 mbar, or alternatively from about 200 mbar to about 800 mbar.
In an embodiment, the PP/f-MWNT can be a powder characterized by an average powder particle size of from about 10 μm to about 1 mm, alternatively from about 50 μm to about 750 μm, or alternatively from about 100 μm to about 500 μm. In embodiments where the PP/f-MWNT is not a powder, the PP/f-MWNT can be subjected to grinding, crushing, milling, chopping, and the like, or combinations thereof to form a PP/f-MWNT powder characterized by an average powder particle size of from about 10 μm to about 1 mm. As will be appreciated by one of skill in the art, and with the help of this disclosure, it is more efficient to dry the PP/f-MWNT in powder form, as more moisture can be removed from the PP/f-MWNT when in powder form.
In an embodiment, the PP/f-MWNT is of a type disclosed in U.S. Provisional Pat. App. No. 62/323,146, filed Apr. 15, 2016, and incorporated by reference herein in its entirety.
In an embodiment, the PP/f-MWNT can be blended with the first PP by using any suitable methodology to produce a PP and PP/f-MWNT mixture. In some embodiments, the PP/f-MWNT can be blended (e.g., dry blended) with the first PP in a blender, a powder blender, a ribbon blender, a paddle blender, a plow blender, a mixer, a powder mixer, a fluidized bed mixer, and the like, or combinations thereof.
In some embodiments, the step of blending PP/f-MWNT with a first PP can further comprise subjecting the PP and PP/f-MWNT mixture to grinding, crushing, milling, chopping, and the like, or combinations thereof to form a PP and PP/f-MWNT mixture powder, wherein the PP and PP/f-MWNT mixture powder can be characterized by an average powder particle size of from about 10 μm to about 1 mm, alternatively from about 50 μm to about 750 μm, alternatively from about 100 μm to about 500 μm. As will be appreciated by one of skill in the art, and with the help of this disclosure, when the PP/f-MWNT and the first PP are not in powder form when mixed, or when the powder particle size for either PP/f-MWNT or the first PP is larger than desired, the PP and PP/f-MWNT mixture can be further converted to a powder of a desired particle size.
In some embodiments, the PP and PP/f-MWNT mixture (e.g., PP and PP/f-MWNT mixture powder) can be dried prior to a step of melt blending at least a portion of the PP and PP/f-MWNT mixture. As will be appreciated by one of skill in the art, and with the help of this disclosure, the first PP and PP/f-MWNT mixture can be dried to remove moisture (e.g., water) from the PP and PP/f-MWNT mixture.
In an embodiment, the PP and PP/f-MWNT mixture can be dried at a temperature of from about 50° C. to about 100° C., alternatively from about 60° C. to about 95° C., or alternatively from about 70° C. to about 90° C.; for a time period of from about 30 minutes to about 24 hours, alternatively from about 1 hour to about 16 hours, or alternatively from about 2 hours to about 8 hours; and at a pressure of from about 50 mbar to about 1,013 mbar, alternatively from about 100 mbar to about 900 mbar, or alternatively from about 200 mbar to about 800 mbar.
In an embodiment, the PP and PP/f-MWNT mixture can comprises PP/f-MWNT in an amount of from about 0.0005 wt. % to about 5 wt. % f-MWNT, alternatively from about 0.001 wt. % to about 4 wt. % f-MWNT, alternatively from about 0.01 wt. % to about 3 wt. % f-MWNT, alternatively from about 0.1 wt. % to about 2 wt. % f-MWNT, or alternatively from about 0.5 wt. % to about 1 wt. % f-MWNT, based on the total weight of the PP and PP/f-MWNT mixture.
As will be appreciated by one of skill in the art, and with the help of this disclosure, the method of making a HIPP composite as disclosed herein is a master batch dilution method, wherein the PP/f-MWNT is the master batch. For purposes of the disclosure herein, the PP/f-MWNT can also be referred to as “PP/f-MWNT master batch.” Further, for purposes of the disclosure herein, the term “master batch” refers to a concentrated mixture of carbon nanotubes, which may be coated with a polymer (e.g., PP/f-MWNT); wherein the mixture is concentrated in carbon nanotubes. For example, the PP/f-MWNT master batch as described herein can comprise f-MWNT in an amount of from about 0.5 wt. % to about 80 wt. %, which represents a relatively high concentration of f-MWNT in the second PP. As will be appreciated by one of skill in the art, and with the help of this disclosure, the PP/f-MWNT master batch as produced will contain a certain amount of extraneous second PP that doesn't form a PP coating around the f-MWNT, and such extraneous second PP along with the polymer-coated carbon nanotubes forms the master batch. The PP/f-MWNT master batch can be diluted with the first PP as described herein, to produce the HIPP composite as described herein, wherein the HIPP composite can comprises PP/f-MWNT in an amount of from about 0.0005 wt. % to about 5 wt. % f-MWNT, which represents a relatively low concentration of f-MWNT in the first PP, when compared to the concentration of the f-MWNT in the master batch.
In an embodiment, a method of making a HIPP composite can comprise a step of melt blending at least a portion of the PP and PP/f-MWNT mixture to form a molten PP and PP/f-MWNT mixture. Melt blending generally involves the melting of a polymer or polymer mixture in the presence of any desired additives (e.g., PP/f-MWNT) to form a molten polymeric mixture, which is a viscous liquid. Some melt blending methods can involve the use of high shear rates to provide for an uniform dispersion of any additives (e.g., PP/f-MWNT) in the polymer melt.
In an embodiment, the melt blending can comprise one or more selected from the group consisting of compounding, melt mixing, and extruding. Compounding generally refers to a process of melt blending polymers with additives, such as reinforcing agents (e.g., PP/f-MWNT) for changing or improving physical (e.g., impact strength), thermal, electrical or aesthetic characteristics of the polymer subjected to compounding. A final product produced by a compounding process can be referred to as a “compound” or “composite,” for example a “nanocomposite” when the size of additive particles introduced to the polymer is in the nano size range. Melt mixing generally refers to a process of melt blending polymers with additives, such as reinforcing agents (e.g., PP/f-MWNT), wherein the process uses high shear for mixing the polymers and additives, to ensure that the additives do not form aggregates (e.g., the high shear disrupts aggregate formation). Extruding generally refers to a process of forming an extrudate (e.g., molten PP and PP/f-MWNT mixture), by forcing a polymeric mixture with the help of at least one rotating screw, preferably twin screw, through a die under controlled conditions of temperature and flow rate. Twin screw extruders generally provide extensive mixing and agitation that causes de-aggregation of suspended particles (e.g., PP/f-MWNT) in a molten polymeric mixture, thereby resulting in a uniform dispersion of particles in the molten mixture.
In an embodiment, the step of melt blending at least a portion of the PP and PP/f-MWNT mixture can comprise heating the PP and PP/f-MWNT mixture to a temperature effective to melt the first PP. In an embodiment, the step of melt blending at least a portion of the PP and PP/f-MWNT mixture can comprise heating the PP and PP/f-MWNT mixture to a temperature of from about 150° C. to about 240° C., alternatively from about 180° C. to about 240° C., or alternatively from about 185° C. to about 235° C., to form the molten PP and PP/f-MWNT mixture.
In an embodiment, a method of making a HIPP composite can comprise a step of shaping at least a portion of the molten PP and PP/f-MWNT mixture to form the HIPP composite. As will be appreciated by one of skill in the art and with the help of this disclosure, a molten polymeric mixture (e.g., molten PP and PP/f-MWNT mixture), which is a liquid (e.g., viscous liquid) has to be shaped or formed into a final composite, which is a solid. In an embodiment, the molten PP and PP/f-MWNT mixture can be shaped into the HIPP composite by using any suitable methodology.
In an embodiment, shaping at least a portion of the molten PP and PP/f-MWNT mixture can comprise one or more selected from the group consisting of molding, injection molding, extrusion molding, blow molding, compression molding, transfer molding, dip molding, rotational molding, matched molding, expandable bead molding, foam molding, vacuum plug assist molding, die casting, and extrusion.
In an embodiment, shaping at least a portion of the molten PP and PP/f-MWNT mixture can comprise injection molding. Generally, injection molding refers to a manufacturing process for producing plastic or polymeric parts by injecting or introducing a molten polymeric material into a mold, where it cools and solidifies into a final part.
In an embodiment, the step of shaping the molten PP and PP/f-MWNT mixture can comprise introducing (e.g., injecting) at least a portion of the molten PP and PP/f-MWNT mixture to a mold.
In some embodiments, the mold can be pre-heated, to prevent the molten mixture touching the mold from solidifying in a non-uniform manner. In an embodiment, the mold can be characterized by a temperature of from about 50° C. to about 120° C., alternatively from about 60° C. to about 100° C., or alternatively from about 70° C. to about 90° C.
In other embodiments, the mold can be characterized by a temperature that is about the same as the ambient temperature (e.g., the mold is not pre-heated). In such embodiment, the molten mixture that is inside the mold begins to cool as soon as it makes contact with an interior mold surface.
In an embodiment, the step of shaping the molten PP and PP/f-MWNT mixture can comprise cooling the molten PP and PP/f-MWNT mixture in the mold to ambient temperature, to form the HIPP composite. As the molten PP and PP/f-MWNT mixture cools inside the mold, it will solidify into the shape of the mold (e.g., the shape of the desired part), to form the HIPP composite.
In an embodiment, the HIPP composite as described herein can comprise a continuous polymeric phase having dispersed therein a plurality of PP/f-MWNT, wherein the continuous polymeric phase comprises the first PP, wherein the PP/f-MWNT comprise f-MWNT coated with the second PP via non-covalent interactions, and wherein the first PP and the second PP can be the same or different. In some embodiments, the first PP and the second PP can be the same. In other embodiments, the first PP and the second PP can be different. In an embodiment, the non-covalent interactions can comprise intermolecular CH-π interactions. In an embodiment, the non-covalent interactions exclude hydrogen bonding. Given the nanometer size of the PP/f-MWNT (e.g., a diameter of from about 6 nm to about 210 nm, alternatively from about 15 nm to about 175 nm, or alternatively from about 25 nm to about 150 nm), the HIPP composite can also be referred to as a “HIPP nanocomposite,” and the terms “composite” and “nanocomposite” can be used herein interchangeably with respect to the HIPP.
In an embodiment, the HIPP composite can comprises PP/f-MWNT in an amount of from about 0.0005 wt. % to about 5 wt. % f-MWNT, alternatively from about 0.001 wt. % to about 4 wt. % f-MWNT, alternatively from about 0.01 wt. % to about 3 wt. % f-MWNT, alternatively from about 0.1 wt. % to about 2 wt. % f-MWNT, or alternatively from about 0.5 wt. % to about 1 wt. % f-MWNT, based on the total weight of the HIPP.
In an embodiment, the HIPP composite can be characterized by a relatively uniform dispersion of PP/f-MWNT in the HIPP composite as a whole. In an embodiment, a volumetric concentration of the PP/f-MWNT in any 1 mm3 of HIPP composite differs by less than about 10%, alternatively by less than about 7.5%, alternatively by less than about 5% from an average volumetric concentration of the PP/f-MWNT in the HIPP composite as a whole.
In an embodiment, the HIPP composite as described herein can have an impact strength of from about 4.0 kJ/m2 to about 6.5 kJ/m2, alternatively from about 4.25 kJ/m2 to about 6.25 kJ/m2, or alternatively from about 4.5 kJ/m2 to about 6.0 kJ/m2, as determined in accordance with ASTM D256. Generally, the impact strength of a material refers to the capability of the material to withstand a suddenly applied load, and can be expressed in terms of energy lost per unit cross-sectional area (e.g., J/m2, kJ/m2, etc.).
In an embodiment, the HIPP composite as described herein can have an impact strength that is increased by equal to or greater than about 150%, alternatively equal to or greater than about 175%, or alternatively equal to or greater than about 200% when compared to an impact strength of the first PP without the PP/f-MWNT, wherein the impact strength is determined in accordance with ASTM D256.
In an embodiment, the HIPP composite as described herein can have a tensile modulus that is equal to or greater than a tensile modulus of the first PP without the PP/f-MWNT, wherein the tensile modulus is determined in accordance with ASTM D638. Generally, the tensile modulus of a material (also referred to as Young's modulus, or elastic modulus) defines the relationship between stress (force per unit area) and strain (proportional deformation) in the material.
In an embodiment, the HIPP composite as described herein can have a yield stress that is equal to or greater than a yield stress of the first PP without the PP/f-MWNT, wherein the yield stress is determined in accordance with ASTM D638.
In an embodiment, the HIPP composite as described herein can have a yield stress that is increased by equal to or greater than about 2.5%, or alternatively equal to or greater than about 5%, when compared to a yield stress of the first PP without the PP/f-MWNT, wherein the yield stress is determined in accordance with ASTM D638.
In an embodiment, the HIPP composite as described herein can have a strain to failure (STF) of from about 100% to about 400%, alternatively from about 150% to about 375%, or alternatively from about 200% to about 350%, as determined in accordance with ASTM D638.
In an embodiment, the HIPP composite as described herein can have a heat deflection temperature (HDT) that is increased by equal to or greater than about 5° C., alternatively equal to or greater than about 10° C., or alternatively equal to or greater than about 15° C. when compared to a heat deflection temperature of the first PP without the PP/f-MWNT, as determined in accordance with ASTM D648. Generally, HDT of a material (e.g., polymeric material) refers to the temperature at which the material deforms under a specified load. The higher the HDT, the greater the ability of the material to retain stiffness (e.g., form) at higher temperatures.
In an embodiment, the HIPP composite as described herein can have a thermal decomposition temperature that is increased by equal to or greater than about 20° C., alternatively equal to or greater than about 25° C., or alternatively equal to or greater than about 30° C. when compared to a thermal decomposition temperature of the first PP without the PP/f-MWNT. Generally, the thermal decomposition temperature of a material (e.g., polymeric material) refers to the temperature at which the material chemically decomposes.
In an embodiment, the HIPP composite as described herein can have a crystallization temperature that is increased by equal to or greater than about 1° C., alternatively equal to or greater than about 2.5° C., alternatively equal to or greater than about 5° C., or alternatively equal to or greater than about 8° C. when compared to a crystallization temperature of the first PP without the PP/f-MWNT, as determined by differential scanning calorimetry (DSC) thermal analysis in accordance with ASTM E794-06. Generally, the crystallization temperature of a polymer refers to the temperature at which polymer crystals form.
In an embodiment, the HIPP composite as described herein can have a crystallization half time at 135° C. of from about 1 minute to about 25 minutes, alternatively from about 2 minutes to about 20 minutes, or alternatively from about 3 minutes to about 15 minutes, as determined by DSC thermal analysis in accordance with ASTM E2070-13. The crystallization half time refers to the amount of time that it takes for the extent of crystallization to be at 50% of the total crystallization.
In an embodiment, the HIPP composite as described herein can be formed into any suitable article of manufacture by using any suitable methodology. In an embodiment, an article can be formed by injection molding of the HIPP composite. In some embodiments, the HIPP composite can be obtained by injection molding of the molten PP and PP/f-MWNT mixture, as previously described herein. In other embodiments, the HIPP composite (e.g., pellets of HIPP composite) can be melted to form a molten HIPP composite, wherein the molten HIPP composite can be injected into a mold to form an article.
Nonlimiting examples of articles that can be made from the HIPP composite of the present disclosure include containers, pipes, tanks, ducts, fittings, seals, membranes, automotive body parts, and the like, or combinations thereof.
In an embodiment, the HIPP composite can be produced by a process comprising the steps of (a) drying a first PP and PP/f-MWNT at a temperature of from about 50° C. to about 100° C., at a pressure of from about 50 mbar to about 1,013 mbar, and for a time period of from about 30 minutes to about 24 hours, to produce a dried first PP and dried PP/f-MWNT, respectively, wherein the first PP is a powder characterized by an average powder particle size of from about 10 μm to about 1 mm, wherein the PP/f-MWNT are a powder characterized by an average powder particle size of from about 10 μm to about 1 mm, wherein the PP/f-MWNT comprise f-MWNT coated with a second PP via non-covalent interactions, and wherein the first PP and the second PP can be the same or different; (b) blending at least a portion of the dried PP/f-MWNT with at least a portion of the dried first PP to produce a PP and PP/f-MWNT mixture, wherein the PP and PP/f-MWNT mixture comprises PP/f-MWNT in an amount of from about 0.0005 wt. % to about 5 wt. % f-MWNT, based on the total weight of the PP and PP/f-MWNT mixture; (c) melt blending at least a portion of the PP and PP/f-MWNT mixture at a temperature of from about 180° C. to about 240° C. to form a molten PP and PP/f-MWNT mixture; and (d) injection molding at least a portion of the molten PP and PP/f-MWNT mixture to form the HIPP composite.
In an embodiment, the HIPP composite can comprise a continuous polymeric phase having dispersed therein a plurality of PP/f-MWNT wherein the continuous polymeric phase can comprise a first PP, wherein the PP/f-MWNT can comprise f-MWNT coated with a second PP via non-covalent interactions, wherein the HIPP composite can comprise PP/f-MWNT in an amount of from about 0.0005 wt. % to about 5 wt. % f-MWNT, based on the total weight of the HIPP; wherein the first PP and the second PP can be the same or different; and wherein the HIPP composite can have an impact strength that is increased by equal to or greater than about 150% when compared to an impact strength of the first PP without the PP/f-MWNT, wherein the impact strength is determined in accordance with ASTM D256. In such embodiment, the non-covalent interactions can comprise intermolecular CH-π interactions; and the non-covalent interactions exclude hydrogen bonding.
In an embodiment, the HIPP composite comprising PP/f-MWNT, and methods of making same, as disclosed herein can advantageously display improvements in one or more composition characteristics when compared to an otherwise similar composition comprising the first PP without the PP/f-MWNT. In an embodiment, the HIPP composite comprising PP/f-MWNT can advantageously display an increased impact strength, increased heat deflection temperature, and increased thermal decomposition temperature, while maintaining similar tensile modulus and yield stress, when compared to an otherwise similar composition comprising the first PP without the PP/f-MWNT.
In an embodiment, the HIPP composite comprising PP/f-MWNT can advantageously display an increased crystallization temperature when compared to a crystallization temperature of an otherwise similar composition comprising the first PP without the PP/f-MWNT.
In an embodiment, the HIPP composite comprising PP/f-MWNT can advantageously display a decreased crystallization half time when compared to a crystallization half time of an otherwise similar composition comprising the first PP without the PP/f-MWNT. Such decreased crystallization half time of the HIPP composite comprising PP/f-MWNT can result in faster de-molding times during part processing, which in turn can result in shorter cycle times, and hence cost effectiveness. Further, such decreased crystallization half time of the HIPP composite comprising PP/f-MWNT can impact a variety of processes, for example prepreg fabrication, laminate and insert manufacturing, semi-finished goods manufacturing and fabrication processes such as injection molding, injection over molding, pultrusion, filament winding, and the like, or combinations thereof. Additional advantages of the HIPP composite comprising PP/f-MWNT, and methods of making same, as disclosed herein can be apparent to one of skill in the art viewing this disclosure.
The subject matter having been generally described, the following examples are given as particular embodiments of the disclosure and to demonstrate the practice and advantages thereof. It is understood that the examples are given by way of illustration and are not intended to limit the specification of the claims to follow in any manner.
Materials.
Homopolymer polypropylene (PP) (melt flow rate 10 g/10 min) was supplied by SABIC, Netherlands. Multiwall carbon nanotube (MWNT)-grade SMW200 were purchased from Southwest Nanotechnology, Norman Okla. Average number of walls (9 to 10) and average diameter (12±3 nm) were determined from full width at half maximum (FWHM) of 20-25.8° integrated peak from wide angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM), respectively. MWNT impurity content was 2.3 wt. % based on thermogravimetric analysis (TGA) in air. Maleic anhydride grafted polypropylene (MA-g-PP: Epolene E-43) was obtained from Westlake Chemical Corporation, Longview Tex. Molecular weight of MA-g-PP was 9100 g/mol. Butanol, xylene, and nitric acid were purchased from Sigma Aldrich and were used as received.
Characterization.
Izod impact testing was carried out on notched samples according to ASTM D256 standard. Tensile testing was carried out according to ASTM D638 standard with 10 mm gauge length. Rate of crosshead displacement was 25.4 mm/min. Tensile tests were conducted using an Instron 5567. Extension was measured using an extensometer 2630-101, in the strain range of 0.1 to 0.4%. Heat deflection temperature (HDT) of the nanocomposites was measured on rectangular specimens. These specimens were similar to the ones used for impact testing. TA DMA Q800 was used to study the heat deflection temperature. ASTM D648 standard was followed for these tests using three point bending test geometry. To obtain HDT, static force of 0.85 N (0.45 MPa as recommended in ASTM D648) was applied to the sample and temperature was increased from 30° C. to 150° C. at the rate of 2° C./min. The HDT reported here corresponds to the deflection of 244 μm (0.2% strain as recommended in ASTM D648). In each case, a minimum of 5 samples were tested for impact, as well as for tensile tests, while a minimum of 2 samples were tested for heat deflection temperature.
A polarized light optical microscope (Leica, DM 2500P) equipped with Linkam LTS420 heating stage was used to study the crystallization behavior. For this purpose, thin and small pieces of the injection molded samples were heated on glass plates covered with microscope cover slips. Samples were heated to 200° C. for 5 minutes and then cooled to 135° C. at a rate of 20° C./min, and held at this temperature for monitoring crystallization behavior over a period of time. WAXD was performed using Rigaku MicroMax-002 beam generator (Cu Kα λ=0.1542 nm, operating voltage and current 45 kV and 0.65 mA, respectively) equipped with R-axis IV++ detector.
For the isothermal crystallization study (using a TA Instrument Q100 DSC), samples were heated to 220° C. at a heating rate of 10° C./min and held at 220° C. for 5 min. These samples were then cooled at a rate of 100° C./min to 135° C. and then held at that temperature for crystallization. The crystallization half-time, t1/2 is defined as the time at which the extent of crystallization is 50% of total crystallization. The crystallization half-time can be calculated from the total crystallinity according to equation (1):
(Xt)=∫0t(dHc/dt)dt/∫0∞(dHc/dt)dt (1)
wherein t is the crystallization time and dHc/dt is the heat evolution rate during the crystallization process. For non-isothermal crystallization studies, samples were heated by differential scanning calorimetry (DSC) at 2.5° C./min from room temperature to 220° C. and then cooled at the same rate to room temperature and then heated again at 2.5° C./min to 220° C. Crystallization temperature (Tc) was derived from the cooling cycle.
Impact-fractured surfaces of polypropylene-coated multiwall carbon nanotubes (PP/MWNT) nanocomposite containing 1 wt. % MWNT were investigated by scanning electron microscopy (SEM) using Zeiss Ultra 60 FE-SEM at an accelerating voltage of 2 kV. A thin layer of gold was sputter coated onto these samples before imaging. SEM studies were also conducted on etched surfaces. For etching, impact fractured specimens were placed in a vial containing a 60:40 mixture of orthophosphoric acid (H3PO4) and sulfuric acid (H2SO4) with approximately 0.5 wt. % potassium permanganate (KMnO4). Etching was carried out in the vials in an ultrasonic bath for 2 hours at room temperature. After the etching treatment, samples were repeatedly washed in deionized water followed by washing in acetone. These samples were then dried in an oven for 1 hour at 40° C.
To determine the statistical significance of the MWNT effect on properties, a Student's t test was performed on the data using JMP11 software at 95% confidence limit.
Rheological behavior was measured on an ARES rheometer (Rheometric Scientific Inc., USA) in the linear viscoelastic regime at a strain of 5%. Dynamic frequency sweep test was performed at 200° C. in the range of 0.1 to 500 rad/s using parallel-plate geometry (plate diameter 25 mm and the gap between the plates was 1 mm). Raman spectra (Horiba Explora One, λ=785 nm) were collected to determine MWNT orientation using parallel (VV) and crossed (VH) polarizers, with the sample axis rotated in 10 degree increments from 0 to 90°. Equation (2) was used to determine CNT orientation, fCNT:
PP nanocomposites were prepared as follows. PP/MWNT nanocomposites were produced using master batch approach. As-received SMW200 MWNT were homogenized in deionized water at a concentration of 150 mg/dl for 20 minutes at 7000 rpm. 70% nitric acid was added to the mixture to make a final acid concentration of 10 M (40 mg/dl). MWNT-acid slurry (40 mg/dl) was sonicated for 30 minutes using Branson bath sonicator 3510R-MT (100 W, 42 kHz) maintained at 25° C. to 30° C. The sonicated dispersion was refluxed at 120° C. for 24 hours. The resulting suspension was repeatedly centrifuged using deionized water until the pH of the suspension reached a neutral value in the range of 6 to 7. Then the final centrifugation cycle was carried out using butanol and the suspension was filtered using repeated butanol wash. The filtered functionalized nanotubes (f-MWNT) were dispersed at a concentration of 5 mg/dl in butanol using bath sonication for 48 hours. Generally, carboxyl groups (—COOH) can be introduced on a carbon nanotube surface through nitric acid treatment to promote its solubility in polar solvents such as butanol.
MA-g-PP or PP was dissolved in xylene (190 mg/dl) at 130° C. The MA-g-PP or PP solution was then added drop by drop to the f-MWNT/butanol (5 mg/dl) dispersion kept at 55° C. to 60° C. The ratio of butanol to xylene in the final mixture was 2:1. This dispersion, maintained at 55° C. to 60° C. and kept under continuous stirring, was dried under vacuum at ˜100 mbar for approximately 48 hours to obtain a master batch containing 5 wt. % f-MWNT in PP or in MA-g-PP.
Master batches of MA-g-PP-coated functionalized multiwall carbon nanotubes (MA-g-PP/f-MWNT) and PP-coated functionalized multiwall carbon nanotubes (PP/f-MWNT) were diluted using homopolymer PP to prepare the corresponding nanocomposites. As received PP powder was dried in vacuum oven at 80° C. for about 4 hours prior to its use in melt processing. The MWNT concentrations in the nanocomposites were 0.001, 0.005, 0.01, 0.1, 0.3, 0.5 and 1 wt. %. Mixing the master batch powder with PP powder was carried out manually using a mortar and pestle. Samples with the above MWNT concentrations were also prepared from pristine MWNT (referred to as p-MWNT) by manually mixing using a mortar and pestle with the as received PP. p-MWNT refer to MWNT that have not been subjected to a step of chemical functionalization. Various physical mixtures were melt blended using a micro compounder followed by injection molding. In addition, to compare to the PP/f-MWNT master batch processing conditions, PP powder was solution processed by dissolving in butanol-xylene mixture followed by solvent evaporation as was done for PP/f-MWNT master batch processing, except in this case nanotubes were not used. For comparison, as received PP powder, and as received PP powder along with 1.9 and 19 wt. % solution processed PP were melt compounded and injection molded using the same protocol, as used for the various nanocomposites. 1.9 and 19 wt. % solution processed PP corresponds to the amount of solution processed PP in the 0.1 and 1 wt. % MWNT containing corresponding nanocomposites, respectively.
Dry blended PP/MWNT mixtures were fed to a 15 cc micro-compounder (Xplore Instruments, Netherlands). Compounding conditions for all the samples were kept the same. Temperatures of three heating zones of the barrel were set at 185° C., 215° C. and 215° C. (
PP control samples and PP nanocomposite samples were prepared as described in Example 1 and were subjected to impact strength testing.
At 0.01 wt. % p-MWNT loading, the impact strength increased by 13.8%, and the p-value test showed that this increase was statistically significant. However, further increase in p-MWNT loading to 0.5 wt. %, decreased the impact strength of the nanocomposites to the level of the control PP, and at 1 wt. % p-MWNT, impact strength value was lower than that of the control PP. Previous studies have shown an increase of 56% and 47% in impact strength of polypropylene-coated carbon nanotubes (PP/CNT) nanocomposites produced by melt processing for 1 wt. % and at 0.6 wt. % CNT loadings, respectively, as well as an impact strength decrease at higher CNT concentrations of 1.5 wt. % and 1 wt. %.
Impact strength for MA-g-PP/f-MWNT master batch based nanocomposites showed statistically significant difference at f-MWNT concentration of 0.3 wt. % or higher. At 0.5 and 1 wt. % f-MWNT, impact strength values were 3.95 and 4.03 kJ/m2, and these represent an increase of 65% and 69%, respectively, over that of the control PP. PP/f-MWNT master batch containing samples showed statistically significant difference at or above 0.1 wt. % f-MWNT, and at 1 wt. % f-MWNT, impact strength was 6.04 kJ/m2. This is an increase of 152% over the control PP sample.
PP control samples and PP nanocomposite samples were prepared as described in Example 1 and were subjected to tensile testing. The tensile modulus values are presented in
Tensile modulus of the PP/p-MWNT composites increased gradually until about 0.5 wt. % MWNT content in the composite. At 0.5 wt. % p-MWNT, the tensile modulus of the composite increased by 24% as compared to the control PP sample. An increase in p-MWNT loading to 1 wt. % had no further effect on the tensile modulus. In MA-g-PP/f-MWNT MB based samples, at low f-MWNT loadings (0.001 to 0.1 wt. %), tensile moduli of the nanocomposites were comparable to the control samples. About 10% increase in tensile modulus of the nanocomposites containing 0.3 wt. % f-MWNT was observed as compared to the control sample. However, no further enhancement in the tensile modulus of the nanocomposites containing up to 1 wt. % f-MWNT was seen. In PP/f-MWNT MB based nanocomposites, an increase of 8 and 13% in the tensile modulus was observed at 0.001 and 0.01 wt. % f-MWNT loading, respectively, as compared to the control PP. With further increase in f-MWNT loading up to 1 wt. %, the modulus values decreased. Among the three types of nanocomposites, PP/f-MWNT MB based nanocomposites showed the highest tensile modulus at low MWNT loadings of 0.001 and 0.01 wt. %. PP/p-MWNT composites exhibited the highest tensile modulus in the MWNT loading range of 0.3 to 1 wt. %, when compared to the MA-g-PP/f-MWNT and PP/f-MWNT composites.
PP control samples and PP nanocomposite samples were prepared as described in Example 1 and were subjected to yield stress testing. The yield stress data are presented in
For the p-MWNT based nanocomposites, yield stress increased gradually with the increase in MWNT concentration and reached the highest value (among the three types of composites in the current study) of 44.4 MPa at 1 wt. % MWNT loading. This was an 18% increase over the control PP. A statistically significant difference in yield stress was observed at as low as 0.1 wt. % for p-MWNT, at 0.3 wt. % for MA-g-PP/f-MWNT based samples, and at 1 wt. % for PP/f-MWNT based samples. At 0.5% CNT, yield stress of MA-g-PP/f-MWNT based nanocomposite increased by 8% compared to that of the control PP. For the PP/f-MWNT based nanocomposite, the increase in yield stress compared to that of the control PP was 5% at 1 wt. % CNT loading.
PP control samples and PP nanocomposite samples were prepared as described in Example 1 and were subjected to strain to failure (STF) testing. The strain to failure data are presented in
Control PP sample showed ductile behavior with a strain to failure value of 329%. In p-MWNT based nanocomposites, strain to failure dropped to 12.5% at 1 wt. % p-MWNT loading. Strain to failure decreased with statistically significant difference to below 218% even with p-MWNT loading in the range of 0.001 to 0.01 wt. %. At 0.1 wt. % p-MWNT, strain to failure decreased to 17.7%. Further, for MA-g-PP/f-MWNT based nanocomposites, good to excellent strain to failure was retained even at 0.3 wt. % f-MWNT. However, in going from 0.3 wt. % to 0.5 wt. % f-MWNT, strain to failure decreased from 226% to 16.8%. PP/f-MWNT based nanocomposite samples exhibited the best ductile behavior amongst the three categories of nanocomposite samples investigated. The strain to failure of 1 wt. % MWNT containing PP/f-MWNT based nanocomposite was 113% compared to 12.5% and 19.9% for p-MWNT based and MA-g-PP/f-MWNT based nanocomposites, respectively.
PP control samples and PP nanocomposite samples were prepared as described in Example 1 and were investigated for changes in mechanical properties, structure, morphology, and crystallization behavior.
At 1 wt. % MWNT concentration, optical and scanning electron microscopies show that MWNT dispersion was relatively poor in p-MWNT sample (
Optical micrographs (
While many individual p-MWNT were observed (
From the SEM images, at 1 wt. % MWNT loading, the average distance between MWNT was found to be about 400 nm in the two master batch based samples, while this same type of distance was greater (˜700 nm) in p-MWNT containing samples, due to the presence of more frequent and larger MWNT aggregated regions in the latter case (
Impact strength of polymers is known to increase with decrease in spherulite size. While spherulite size was not quantitatively determined in this study, from polarizing optical microscopy (
As will be appreciated by one of skill in the art, and with the help of this disclosure, the presence of β crystals is also positively known to affect the impact strength of polypropylene. Further, as appreciated by one of skill in the art, and with the help of this disclosure, while a crystals have higher modulus due to their interconnected lamellar network, β crystals are tougher because they slide over one another in the interlamellar amorphous zones during shear deformation. Previous studies have shown that maleic anhydride grafted propylene-butadiene copolymer (MPPB) results in the formation of β crystals. In the present investigation, β crystals were observed in MA-g-PP containing sample, but they were not observed in control PP, p-MWNT, and PP/f-MWNT based samples. This has been ascertained from WAXD (
WAXD study showed that MA-g-PP/f-MWNT master batch based nanocomposites contain a β crystal peak at 20=16.1° (
Impact strength improvements in MA-g-PP/f-MWNT containing samples at least in part, can be attributed to the presence of β crystals. The largest improvement in impact strength was observed in PP/f-MWNT based samples that contained no β crystals and these samples exhibited spherulite size somewhat larger than that for p-MWNT containing samples. 1 wt. % MWNT samples based on PP/f-MWNT master batch had yield stress and modulus values statistically comparable, while the impact strength was 152% higher than that for the control PP. Tensile testing was done at a relatively low strain rate of 2.54/min, while significantly higher strain rates were realized in Izod notched impact testing (1.8×104/min). MWNT in PP/f-MWNT master batch were coated with PP, which was then embedded in a PP matrix. Further, MWNT in MA-g-PP/f-MWNT master batch were coated with MA-g-PP, while p-MWNT had no coating. PP interacts with p-MWNT as seen from high crystallization nucleation rate and low crystallization times for the PP/p-MWNT system (
It appears that the most coherent PP/MWNT interface is present in the PP/f-MWNT containing samples. During solution master batch processing, entanglements can be minimized both in PP and MWNT. Without wishing to be limited by theory, during melt blending of PP with p-MWNT, due to higher degree of entanglements, both in PP and in MWNT, the length of the interface could be relatively small, as compared to the interface length in PP/f-MWNT master batch based sample. The high impact strength of PP/f-MWNT master batch containing sample can be attributed to this long and coherent interface coupled with small spherulite size, while relatively low impact strength of p-MWNT can be attributed to MWNT aggregate. Higher molecular weight of PP when compared to the molecular weight of the MA-g-PP, could also be responsible for differences in impact strength between PP/f-MWNT and MA-g-PP/f-MWNT master batch based samples.
The role of the presence of solution processed PP on the impact strength was also investigated, as 1 wt. % MWNT containing samples prepared from the PP/f-MWNT master batch contain high concentration (19 wt. %) of solution processed PP. Without wishing to be limited by theory, the dilute solution processed PP is expected to have fewer entanglements than melt processed PP, and this can affect crystallization, which in turn can affect mechanical properties. As such, PP was processed from dilute solution in the same way as PP/f-MWNT master batch (as described in Example 1), except that in the solution processed PP, no f-MWNT were used. PP/solution processed PP (19 wt. %) was melt compounded and injection molded using the same process parameters as used for various nanocomposites, as described in Example 1. PP/solution processed PP (19 wt. %) exhibited higher nucleation rate (
1from 1st cooling cycle;
2from 2nd heating cycle;
3from 1st heating cycle
Without wishing to be limited by theory, the influence of solution processed PP is similar to the effect of plasticizers on the nucleation rate and crystallization temperature of polymers. WAXD results of PP/solution processed PP are presented in
Higher PP orientation (lower FWHM of 040 crystal peak) in the PP/solution processed PP (19 wt. %) sample than in the control PP can be attributed to the less entangled solution processed PP chains (Table 7). The impact strength of PP/solution processed PP was 55% higher than that for the control PP (Table 8), while the impact strength of 1 wt. % MWNT containing sample based on PP/f-MWNT master batch was 152% higher. Table 8 displays Notched Izod impact strength of PP/MWNT nanocomposites prepared from PP/f-MWNT master batch and PP/solution processed PP (SpPP). The corresponding SpPP concentration in 0.1 wt. % and 1 wt. % PP/f-MWNT nanocomposites were 1.9 and 19 wt. %, respectively.
The data in Tables 6, 7, and 8, and in
Without wishing to be limited by theory, during master batch preparation, dilute solution processing allows polymer chains to interact with f-MWNT more effectively by reducing the entanglements of both the components, and this promotes higher order for the interphase polymer than the bulk polymer; and as such, in the master batch based nanocomposites, the coherent PP/CNT interface can result in more ordered interphase region. As shown from the DSC endotherm in
The impact fractured surfaces of various samples prepared as described in Example 1, and of control samples prepared as described in Example 7, and tested as described in Example 3 were also investigated.
The photographs of the fractured surfaces of the impact tested control PP and 1 wt. % CNT containing samples are given in
Under SEM, observation at relatively low magnification, the entire impact-fracture surface of the p-MWNT based nanocomposite was relatively smooth as compared to the two master batch based samples (
The topography of the etched samples in
The data in
Spherulites were investigated for impact fractured surfaces of various samples prepared as described in Example 1, and tested as described in Example 3 were also investigated.
Generally, a spherulitic boundary is typically considered to be the weak point and is often the initiating point for mechanical failure. Two strategies are conventionally used to improve the fracture toughness of polypropylene, for example reducing the spherulite size and strengthening the spherulite boundaries. The former can be easily achieved through the introduction of nucleating agents such as sodium benzoate, while the latter has been approached through creating of inter-spherulitic links and tie molecules at spherulite boundaries, as well as in the interlamellar regions with the help of a multiblock copolymers of isotactic and atactic polypropylene (iPP,aPP) or a random ethylene-propylene copolymer. Copolymer regions are unable to crystallize (while isotactic PP segments crystallize) and hence these non-crystallizing regions can migrate to the boundary sites and can become connecting chains between adjacent spherulites.
Without wishing to be limited by theory, in the PP/MWNT nanocomposites, some of the MWNT that do not nucleate PP crystallization will be excluded from PP crystals, and these MWNT can become the connecting links between spherulites and in between interlamellar amorphous regions. In
The crystallinity of various samples prepared as described in Example 1 was also investigated. WAXD data on various samples are given in
1Xc: crystallinity from integrated radial scans;
2LPP: crystal size of (110) at 2θ~14.1° according to Scherrer's equation with K = 0.9; and
3fPP: FWHM of (040) at 2θ~16.9.
The formation of β crystals in the injection molded tensile specimens was not as pronounced as in the injection molded impact bars in MA-g-PP/f-MWNT master batch based nanocomposites. Without wishing to be limited by theory, this could likely be due to the differences in the processing history encountered in the two cases during injection molding. Transformation from β crystal to a crystal under shear force has been previously reported. γ crystals have also been previously observed in the three types of nanocomposites at relatively high CNT loadings, but no γ crystals were observed in the neat PP.
The polymer orientation data along the flow direction during injection molding is also given in Table 9. As MWNT concentration increased, polymer chains became more aligned in all three nanocomposites. The degree of alignment was related to the melt viscosity at 300 s−1 (corresponding to the calculated shear rate at the exit of the melt transfer device to the mold). That is, the MA-g-PP/f-MWNT based sample had the lowest viscosity and the highest polymer orientation followed by the p-MWNT and then by the PP/f-MWNT based sample, which has the highest viscosity and lowest polymer orientation (
The MA-g-PP containing sample was expected to have lower viscosity due to its lower molecular weight than PP. Better dispersion as well as interaction of f-MWNT in PP/f-MWNT based sample resulted in higher viscosity and lower polymer orientation compared to the p-MWNT and MA-g-PP/f-MWNT based nanocomposites.
The data in Table 9 shows that there is a modest increase in crystallinity from 69% in the control PP to 72-73% in the three nanocomposites at 1 wt. % CNT, and at the same time there is a modest decrease in crystal size [for (110) plane] from 11.3 nm to 10.2-10.9 nm in the three nanocomposites at the same MWNT concentration. Without wishing to be limited by theory, MWNT align along the drawing direction during the tensile test. The orientation of MWNT (fCNT) after tensile testing (
Raman spectra were collected to determine CNT orientation using a Holoprobe Research 785. A Raman microscope made by Kaiser Optical System (λ=785 nm) using parallel (VV) and crossed (VH) polarizers, with the sample (
The MWNT orientation was determined using Raman spectroscopy. At 1 wt. % MWNT concentration, there was practically no MWNT orientation developed during tensile testing. The strain to failure in p-MWNT and MA-g-PP/f-MWNT based samples was low (11 and 22%) for these two tested samples. However, the PP/f-MWNT based sample (at 1 wt. % MWNT) with a strain of 283% also did not exhibit any MWNT orientation. At low MWNT concentration of 0.01 wt. %, reasonably good MWNT orientation (in range of 0.3 to 0.42) was observed in all three nanocomposites at strain values in the range of 285 to 335%. At MWNT concentrations between 0.01 and 1 wt. %, an intermediate level of MWNT orientation values were observed, and reasonably good MWNT orientation was observed at up to 0.5 wt. % MWNT in PP/f-MWNT master batch based samples, while MWNT orientation was observed at up to 0.3 wt. % MWNT in MA-g-PP/f-MWNT based samples, and good MWNT orientation was observed only at 0.01 wt. % in the case of p-MWNT. These data provide further support of good interaction between MWNT and PP in the case of PP/f-MWNT based samples, as compared to the other two types of nanocomposites.
The heat deflection temperature of various samples prepared as described in Example 1 was also investigated.
Incorporation of MWNT in the PP resulted in higher heat deflection temperature (HDT) as compared to the control PP (
Higher HDT values are generally attributed to the ability of a material to retain stiffness at higher temperatures. In
The thermal decomposition temperature of various samples prepared as described in Example 1 was also investigated.
To study the thermal decomposition behavior of PP in the composites, the samples were heated from room temperature to 600° C. using a TGA (TA Instruments Q500), and the mass loss of each sample was measured as a function of temperature in air environment at a heating rate of 20° C./min. The temperature was calibrated using high purity standard (Ni) over a specific range of heating rates with a calibration parameter.
Incorporation of MWNT in the PP resulted in higher thermal decomposition temperature as compared to the control PP (
Thermal decomposition temperatures of PP/MWNT nanocomposites prepared from p-MWNT, MA-g-PP/f-MWNT master batch, and PP/f-MWNT master batch were higher than that of the neat PP. Thermal decomposition temperature of 1 wt. % MWNT containing PP/MWNT nanocomposites prepared from PP/f-MWNT master batch was 24° C. higher than that of the neat PP.
Impact strength, while maintaining good tensile properties and HDT, can be important for some PP applications. Table 13 summarizes the data for various nanocomposites formed from p-MWNT; MA-g-PP/f-MWNT master batch; and PP/f-MWNT master batch.
1a broad shoulder was observed peak before the major endotherm.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2016/064577 | 12/2/2016 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62272468 | Dec 2015 | US | |
| 62323146 | Apr 2016 | US | |
| 62323151 | Apr 2016 | US |
