TEREPHTHALATE (PET)

The present invention relates broadly to the field of packaging material. More particularly, the present invention relates to polymer based packaging material which, are infused with nanomaterials to obtain a nanocomposite packaging material with desirable packaging characteristics.

BACKGROUND OF THE INVENTION

Over the past few decades, industrial scale composite materials have been produced by adding numerous minerals and metals to thermosetting, thermoplastic and elastomeric polymers. As compared to bulk polymers, these composites have shown moderate mechanical performance improvements in properties such as Young's modulus, tensile strength, abrasion resistance and storage modulus. However, recent advances in nanoscale particle synthesis have dramatically accelerated the growth of the composite industry. The capacity to synthesize and characterize atomic-level particles has produced a new generation of high-performance fillers. The incorporation of these sub-micron fillers in polymers results in the formation of nanocomposites which result in composite material of unparalleled performance improvements as compared to conventional composite material. Commercial demand for nanocomposite materials has exploded. The possible applications for such materials cover a wide range of industries including food packaging, gasketing, automotive applications, portable electronic devices, etc.

In recent years, research having regard to composite materials have focussed in the area of nanoparticle filled polymer composites (NCs) in which the nanoparticle has dimensions comparable to those of the polymer chains, has a high aspect ratio of more than 100 and is uniformly dispersed in the polymer matrix. There are several filler materials that have been extensively studied for improvement of mechanical properties, electrical and thermal conductivity of polymer material. Examples of these extensively studied nanoparticles include fractal agglomerated nanoparticles such as silica and carbon black, carbon nanotubes (CNTs), inorganic clays and alumina Silicate nano-plates. Nano-particle use as a filler to form nanocomposite polymers suffer from a few disadvantages that include a high cost of production and the requirement for chemical or mechanical manipulation to achieve good dispersion which is commercially not attractive and impractical for large scale manufacturing.

Graphene is a relatively new nanomaterial which comprises a single layer of carbon atoms similar to an unzipped single walled carbon nanotube. Single layer graphene generally is twice as effective as CNTs in reinforcing polymers since graphene has two surfaces for polymer interaction whereas a CNT comprises only one exterior surface for polymer interaction. Moreover due its excellent electrical and mechanical properties, graphene is increasingly sought after as a nanoparticle filler to replace other types of nanoparticle fillers for the production of nanocomposites. It will be appreciated that the recent development of graphene synthesis methods in conjunction with introduction of new graphene-based nanomaterials such as graphene oxide, expanded graphite, and graphene nano platelets, has made graphene commercially viable.

Polyethylene terephthalate (PET) is an aromatic semi-crystalline, thermoplastic polyester synthesized in the early 1940s. PET is well known for its strength and toughness, high glass transition and melting points, chemical resistance, and optical properties. Today PET use is ubiquitous in a myriad of applications that include the packaging of commercial food and drink products due to its relatively low cost. PET is characterized by a microstructure wherein longitudinal stretching forms strong fibres with high molecular chain orientation, as well as bi-axial stretching forming strong films. Linear PET is naturally semi-crystalline. Thermal and mechanical history, such as rate of cooling and stretching, respectively, can drive PET to be amorphous or more crystalline, and thus influence its mechanical properties. Although PET is utilized extensively in packaging, its use is constrained due to inherent limitations in certain physical characteristics that include among others, gas barrier performance.

Research in improving properties of PET as packaging material, is at present an on-going process undertaken by many research organizations due to its potential for application in the commercial market place which is underscored by its inherent low cost of production resulting from economics of scale and thus its present widespread use as the packaging material of choice despite its inherent limitations. On-going research in developing nanocomposite PET material is needed to improve the inherent material properties of intrinsic PET, particularly having regard to its gas barrier properties, to hence improve its feasibility and attractiveness for application as a packaging material in the food and beverage industry, as an improved gas barrier property of a packaging material will go a long way toward extending a shelf life of a given packaged F&B product.

Thus far research has yielded a number of nanomaterials that can be used as fillers to form PET nanocomposites, and Graphene nano-platelets represent a good choice of such a nanomaterial. Accordingly it would be advantageous if a cost-effective method for producing a graphene nano-platelet infused PET nanocomposite exhibiting an improved gas barrier property is conceived.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

It is an advantage of the present invention to provide a polymer nanocomposite that exhibits among others, good mechanical strength.

It is another advantage of the present invention to provide a polymer nanocomposite that exhibits an improved gas barrier performance that hence renders the polymer nanocomposite ideal for use as a packaging material for a food and beverage product.

It is yet another advantage of the present invention to provide a cost effective method for the production or manufacture of a polymer nanocomposite with improved gas barrier performance. More particularly in one aspect the present invention provides a Graphene Nano platelet infused Polyethylene Terephthalate (PET) nanocomposite that exhibits superior gas barrier performance over neat Polyethylene Terephthalate (PET) polymer which hence renders said nanocomposite suitable for use as a packaging material for a food and beverage product.

In another aspect, the present invention provides method for producing a Graphene Nano-platelet/Polyethylene Terephthalate (PET) nanocomposite. The method is apparently a solvent casting method comprising: a step of mixing 2.0% wt. of Graphene Nano-platelets (GNP) with a predetermined amount of PET material; a step of drying the mixture obtained in the preceding step in an oven at a temperature of 70°C ; a step of adding phenol/1 ,1 ,2,2-tetrachloroethane to the composite in a 1 :1 ratio with respect to the composite; a step of stirring the mixture comprising the solvent, polymer and 2.0% wt.

Graphene Nano-platelets at a speed of 250 rpm.; a step of dispensing the homogenous mixture resulting from the preceding step on to a casting mould; and a final step of allowing the solvent within the mixture disposed in the mould in the preceding step to evaporate to hence produce GNP/PET nanocomposite film.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the detailed description taken in conjunction with the accompanying drawings, in which: Figure 1 is a graph of gas transmission rate versus percentage weight of polymer base material of infused Graphene Nano-platelets (GNP) disposed within a Polyethylene Terephthalate (PET) polymer matrix;

Figure 2 comprises Figures 2(a) to 2(e) which each comprise a SEM micrograph image of a tensile fracture at 1000 times magnification (i.e. images disposed on the left) and a SEM micrograph image illustrating a surface morphology at 750 times magnification, of a neat PET polymer, in the case of Figure 2(a), and resulting GNP/PET polymer nanocomposites in the case of Figures 2(b) to 2(e) produced in accordance to embodiments of a method as provided in an aspect of the present invention;

Figure 3 is a bar-chart of tensile strength versus infused Graphene Nano-platelet (GNP) content of neat PET polymer and PET/GNP nanocomposites formed by infusion of 0.5% wt., 1.0% wt., 1.5% wt. and 2.0% wt. of Graphene Nano-platelets in a PET polymer base material; and

Figure 4 is a bar-chart of tensile modulus versus infused Graphene Nano-platelet (GNP) content of neat PET polymer and PET/GNP nanocomposites formed by infusion of 0.5% wt., 1.0% wt., 1.5% wt. and 2.0% wt. of Graphene Nano-platelets in a PET polymer base material.

DETAILED DESCRIPTION OF THE INVENTION

The detailed description set forth below in connection with the appended drawings is intended as a description of an exemplary embodiment and is not intended to represent the only form in which the embodiment may be constructed and/or utilized. The description sets forth the functions and the sequence for constructing the exemplary embodiment. However, it is to be understood that the same or equivalent functions and sequences may be accomplished by different embodiments that are also intended to be encompassed within the scope of this disclosure.

As mentioned in a preceding section, the present invention relates to nanocomposite material and in particular provides a nanocomposite material having an improved gas barrier property. More particularly in one aspect the present invention provides a Graphene Nano-platelet (GNP) infused Poly- Ethylene Terephthalate (PET) polymer nanocomposite material. In another aspect, the present invention provides a cost effective method 100 for manufacturing aforementioned Graphene Nano-platelet (GNP) infused Poly- Ethylene Terephthalate (PET) polymer nanocomposite.

Before proceeding further, by way of introduction, polymer nanocomposites are sought after in industry due to the promise it holds having regard to improving properties of neat polymer materials that are already in ubiquitous use. Due to inherent disadvantages of conventional nanomaterial such as carbon nanotubes when used as fillers in polymers to produce nanocomposites that include among others, a high cost of production of aforementioned nanomaterial, Graphene sheets have emerged as the nanomaterial of choice because of its excellent properties and natural abundance of its precursor, Graphite.

Graphene is a two-dimensional, one-atom-thick carbon sheet with a planar honeycomb lattice. Defect-free graphene presents outstanding physical properties, such as high intrinsic mobility and ballistic transport, high thermal conductivity and Young’s modulus, an optical transmittance of almost 98% and large specific surface area. To date the most cost effective method for the production of Graphene sheets is by way of exfoliation of Graphite and or its derivatives, namely graphite oxide as it enables high yield production and is hence a cost effective and scalable process.

Exfoliation of Graphite Oxide to obtain Graphene Oxide followed by a reduction process executed by way of heat treating the obtained Graphene Oxide to obtain Graphene is a preferable choice for obtaining Graphene Nano-platelets as utilized in the method 100 for producing a Graphene Nano-platelet/Polyethylene Terephthalate (PET) nanocomposite as provided in accordance to an aspect and embodiment of the present invention as disclosed herein. The resulting Graphene nanomaterial obtained from aforementioned exfoliation followed by heat treatment is readily dispersed in polar solvents. Hence, the method 100 disclosed herein for producing a Graphene Nano-platelet/Polyethylene Terephthalate (PET) nanocomposite in accordance to an embodiment of the present invention, is a solution casting or solvent blending method which takes advantage of the fact that the resulting Graphene nanomaterial (i.e. Nano-platelets) obtained by aforementioned exfoliation followed by heat treatment is readily dispersed in a solvent, specifically polar solvents.

More particularly, in accordance to an aspect of the present invention, there is provided a method 100 for producing a Graphene Nano-platelet/Polyethylene Terephthalate (PET) nanocomposite utilizing a solvent casting method that comprises: a step 101 of mixing Graphene Nano-platelets (GNP) with an amount of PET polymer material to obtain a mixture, the percentage weight of the Graphene nano-platelets measured in relation to the weight of the amount of PET polymer material selected to be utilized as a polymer base material for the nanocomposite; a step 102 of drying the mixture obtained in the preceding step 101 in an oven at a predetermined temperature; a step 103 of adding a solvent to the composite in a 1 :1 ratio with respect to a mass of the mixture to obtain a solution; a step 104 of stirring the solution of the preceding step 103 to obtain a homogeneous mixture; a step 105 of dispensing the homogenous mixture resulting from the preceding step 104 on to a casting mould; and a final step 106 of allowing the solvent within the mixture disposed in the mould in the preceding step 105 to evaporate to hence produce a GNP/PET nanocomposite film.

In accordance to an embodiment of the method 100 as provided in the aforementioned aspect of the present invention, the step 101 of mixing Graphene Nano-platelets (GNP) with an amount of PET polymer material to obtain a mixture, comprises of mixing 0.5% wt. of Graphene Nano-platelets (GNP) relative to a weight of the amount of PET polymer material. In accordance to another embodiment, aforementioned step 101 comprises mixing 1.0% wt. of Graphene Nano-platelets (GNP) relative to a weight of the amount of PET polymer material. In accordance to yet another embodiment, aforementioned step 101 comprises mixing 1.5% wt. of Graphene Nano-platelets (GNP) relative to a weight of the amount of PET polymer material. In yet another further embodiment, aforementioned step 101 comprises mixing 2.0% wt. of Graphene Nano-platelets (GNP) relative to a weight of the amount of PET polymer material. Having regard to aforementioned step 102, the mixture obtained in step 101 in accordance to an embodiment of the method 100 as provided in an aspect of the present invention disclosed herein, the mixture of Graphene Nano-platelets and Polyethylene Terephthalate (PET), is dried in an oven at a temperature of 70°C, for a duration of approximately 4 hours to ensure that all absorbed moisture (i.e. moisture content) is eliminated to thus prevent void formation during casting.

Alluding to step 103 of the method 100 as provided in an aspect of the present invention, aforementioned step 103 in accordance to an embodiment comprises of adding a polar solvent to the mixture of Graphene Nano-platelets and Polyethylene Terephthalate (PET) polymer material that has been subjected to drying in step 102. More particularly, in aforementioned embodiment, step 103 comprises of adding phenol/1 ,1 ,2,2-tetrachloroethane which serves as a solvent to disperse the Graphene Nano-platelets into the Polyethylene Terephthalate polymer material (i.e. polymer matrix) in a 1 :1 ratio with respect to the weight of the combined mixture that has been subjected to drying in step 102, to hence provide a solution comprising aforementioned phenol/1 ,1 ,2,2-tetrachloroethane, Graphene Nano-platelets and Polyethylene Terephthalate polymer material.

Subsequently in step 104, in accordance to an embodiment, the solution obtained in step 103, is stirred or mixed by way of a mechanical stirrer at a speed of 250 revs/min, (rpm). In an alternative embodiment, step 104 may encompass ultrasonic mixing. The resulting mixture obtained from step 104 is a mixture that is free from any apparent agglomeration of aforementioned Graphene Nano platelets, i.e. a homogeneous mixture, is obtained.

In the final steps of the method 100 as provided in an aspect of the present invention, the resulting homogeneous mixture obtained in step 104 is subsequently dispensed onto a casting mould in step 105 and left to dry in step 106 to allow for evaporation of the phenol/1 ,1 ,2,2-tetrachloroethane solvent and the formation of a film of Graphene Nano-platelet infused Polyethylene Terephthalate (PET) nanocomposite material.

In accordance to an embodiment of the method 100 as provided in an aspect of the present invention, the drying in aforementioned step 106 takes place in a fume cupboard at room temperature for a period of 24 hours, after which, said film of Graphene Nano-platelet infused Polyethylene Terephthalate (PET) nanocomposite material is obtained.

EXPERIMENTAL EXAMPLE

With reference to Figure 1 appended together with this description, there is shown a graph of gas transmission rate of Oxygen (0 ₂ ) and Nitrogen (N ₂ ) respectively versus percentage weight of infused graphene nanoparticles with respect to polymer base material, disposed within a Polyethylene Terephthalate (PET) polymer matrix as is obtained by execution of the method 100 as provided in an aspect and embodiments of the present invention.

It is observed from aforementioned figure 1 , that as the percentage weight of the graphene nanoparticles, i.e. in our case Graphene Nano-platelets (GNP) that are infused within the polymer matrix formed by the Polyethylene Terephthalate (PET) polymer material is increased from 0.5% wt. to 2.0% wt. in increments of 0.5% wt., the intrinsic gas barrier capability of the formed nanocomposite (i.e. the GNP/PET nanocomposite) is improved. Specifically, having regard to the formed GNP/PET nanocomposite produced in accordance to embodiments of the method 100 as provided in an aspect of the present invention, it is observed that as the % wt. of infused Graphene Nano-platelets increases, the gas transmission capability of the formed nanocomposite decreases. Accordingly with reference to aforementioned figure 1 , the GNP/PET nanocomposite formed by the infusion of 2.0% wt. Graphene Nano-platelets is most desirable, as it is least permeable and exhibits the lowest oxygen and nitrogen transmission rate.

Figure 2 comprises Figures 2(a) to 2(e) which each comprise a SEM micrograph image of a tensile fracture at 1000 times magnification (i.e. images disposed on the left) and a SEM micrograph image illustrating a surface morphology (i.e. images disposed on the right) of a neat PET polymer, in the case of Figure 2(a), and GNP/PET polymer nanocomposites in the case of Figures 2(b) to 2(e) at 750 times magnification. Specifically Figure 2(a) alludes to a neat PET polymer material, whereas Figure 2(b) to 2(e) respectively allude to GNP/PET nanocomposites formed respectively by 0.5% wt., 1 .0%wt., 1 .5%wt. and 2.0% wt. of Graphene Nano-platelet infusion.

Aforementioned figures 2(a) to 2(e) are directed toward providing a mechanical characterization of the polymer and various composites referenced therein. It is evident from the diagrams on the left hand side which allude to results of mechanical strength testing (i.e. a tensile strength test) in accordance with ISO 572-3 in which 150mm x 10mm samples of aforementioned neat PET polymer material and aforementioned 0.5% wt., 1.0% wt., 1 .5% wt. and 2.0% wt. GNP/PET polymer nanocomposites are subjected to an applied tensile load of 5kN, that as percentage weight of Graphene Nano-platelets increases from 0 to 2.0%, so too does the mechanical strength of the sample. This is deduced from the patterns exhibited by the fracture in the SEM images. In other words, aforementioned SEM images disposed on the left hand side of Figures 2 (a)-(e) show tensile fracture specimens of a neat PET and PET/GNP nanocomposites with varied content of infused GNP ranging from 0.5% wt. to 2% wt. while the SEM images disposed on the right hand side of figures 2(a)-(e) show the surface morphology of the samples. The addition of GNP to a PET polymer matrix shows a proportional increase of tensile strength of a resulting GNP/PET nanocomposite. This is attributed to the strong interfacial bonding between the PET matrix formed by the base PET polymer material and the GNP nanomaterial. From the images disposed on left hand side of figures 2(a) to 2(e), it can be ratified that neat PET (figure 2(a) undergoes ductile fracture), whereas as the contents of GNP increase, the ductility of the resulting GNP/PET nanocomposite decreases (i.e. figures 2(b) to 2(e)). Moreover with reference to figures 2, 3 and 4 it can be concluded that the addition (i.e. infusion) of GNP to PET base material can result in the improvement of strength of the resulting GNP/PET nanocomposite over neat PET material in terms of tensile strength and tensile modulus.

Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description.