Field of the Invention

The present invention relates to a composite packaging product in which hydroxyapatite reinforced polyethylene terephthalate is used in the packaging of all food products that may be affected by sunlight, such as milk and dairy products and fruit juices.

Background of the Invention

Liters of liquid food products such as milk, dairy products and fruit juices are consumed every year around the world, and a significant portion of them are packaged with various cardboard boxes, comprising an aluminum layer therein, in order to prevent them from being adversely affected by sunlight and to reduce the cost of packaging materials. Towards the end of the 1960s, beverage cans started to be made of aluminum, and the use of aluminum increased especially due to recycling of aluminum. However, aluminum in beverage cans is an element that is considered a toxic metal for humans. In this context, various studies have been carried out in the state of the art and studies have been carried out on determining aluminum concentrations in milk and dairy products, estimating aluminum intake through consumption of milk and dairy products, and the migration of aluminum from containers into dairy products during processing and storage [1],

In the state of the art, cardboard and PS (Polystyrene) materials with aluminum inner coating are used in the packaging of milk and dairy products that are adversely affected by sunlight. These aluminum-coated cardboard packagings that are currently used protect the product they store from sunlight, however, in these packagings, the migration of the aluminum element, which may be harmful to human health, and the transition of the aluminum element to the product therein may occur. Furthermore, in terms of production method, it is more costly and its recycling cost is higher compared to PET bottle production.

On the other hand, PET material is widely preferred in food packaging applications due to PET’s high mechanical strength and low moisture, oxygen and carbon dioxide permeability. PET material, which is used in the packaging of various beverages, is transformed into bottles in two stages namely first preform by means of injection method and then blow molding method. In the injection stage, PET is melted at a temperature range of 260-280°C and compressed into the preform mold with the help of a screw. Then, in the blow molding process, the bottle is blown into the mold with the help of both stretch rod and air [2]. In both processes, the PET material undergoes chemical degradation due to both mechanical and thermal factors and releases chemicals that are harmful to human health.

Hydroxy apatite is resistant to organic and inorganic solvents except acids. The use of hydroxy apatite, which can be obtained naturally and synthetically, as an additive in packaging material will not be harmful to human health due to its biomaterial properties [3],

Summary of the Invention

The objective of the present invention is to provide a packaging material that is not harmful to human health and can also be used conveniently in terms of food safety in the packaging of milk and dairy products.

Another objective of the present invention is to eliminate the possibility of aluminum migration to the food product therein, which can arise from the traditional aluminum inner-coated cardboard packaging structure. A further objective of the present invention is to reduce the light transmittance of PET material having 100% light transmittance by absorbing a significant part of the light arriving thereon by means of the addition of hydroxyapatite. Therefore, migration which threatens human health as a result of chemical degradation of PET material will be reduced.

Detailed Description of the Invention

“A Composite Packaging Material Comprising Hydroxyapatite Reinforced Polyethylene Terephthalate for Protection of All Food Products that can be Affected by Sunlight against Light” developed in order to fulfil the objectives of the present invention is illustrated in the accompanying figures; in which:

Figure 1- is a side and perspective view of the preform structure of a bottle (175 cc) obtained with a packaging product in which hydroxyapatite reinforced polyethylene terephthalate developed within the scope of the invention is used.

Figure 2- is a side view of a bottle (175 cc) obtained through the preform shown in Figure 1.

Figure 3- is a graphical representation of the stretch-blow-molding method (SBM) process parameters.

Figure 4- is a photographic representation of the preform temperature profile.

Figure 5- is a graphical representation of UV transmittance spectra of pure PET and PET/HAP composites developed experimentally within the scope of the invention.

The invention is a composite packaging material comprising hydroxyapatite (tricalcium phosphate (Cas(PO4)3OH); bone powder; HAp) and polyethylene terephthalate (PET) used for the packaging of all food products which may be affected by sunlight, such as milk and dairy products, and fruit juices. Within the scope of the invention, in PET/Hydroxyapatite bottle production, PET with a viscosity value of 0.84±0.02 dl/g and an AA content of 1 ppm maximum is used with an addition of HAp in an amount more than 1% as powder into PET. First, PET/Hydroxy apatite composite is prepared by means of any twin screw extruder, and then packaging material can be produced by injection molding or extrusion film drawing method, in the form of bottles or films depending on the technical field in which it will be used.

The packaging material developed within the scope of the invention does not comprise any chemical which may cause migration to the food product therein and pose a threat to human health, unlike traditional applications. With the packaging material of the present invention, which is completely biocompatible, the final product can be obtained by a simpler production method compared to the existing ones, and without needing any additional equipment.

The packaging material of the present invention is a composite material with hydroxy apatite (HAp) reinforced PET matrix. As it is known, PET is a good material in terms of both mechanical and barrier properties. However, since its light transmittance is 100%, it is not preferred for packaging food products which are adversely affected by sunlight, such as milk and dairy products. In order to eliminate this disadvantage, biocompatible hydroxy apatite (HAp) having very low light transmittance is used within the scope of the invention as an inorganic additive. HAp absorbs most of the light arriving thereon and converts it into heat energy for the molecule; thereby the light transmittance is significantly reduced. In the studies carried out during the development process of the invention, it was determined that both light absorbance and light emitting properties of hydroxyapatite (HAp) were almost zero in the visible region (Figure 5). Accordingly, with the use of the technical benefit of light transmittance, the light transmittance of the final product can be reduced to zero depending on the addition amount of HAp. The HAp reinforced PET packaging material of the present invention is a material that can be preferred over and substitute especially cardboard packaging in the food industry. Within the scope of the invention, the method of producing packaging material in the form of a bottle or a film from a composite packaging material having the features described above comprises the steps of

- Drying the PET granules in an oven at 110°C for 12 hours in order to remove the moisture therein before feeding the PET granules to a twin screw extruder,

- Feeding the dried PET granules and HAp to the extruder with screw speed of 150 rpm,

- Collecting the PET/HAp composites, which are blended by addition of HAp, provided that it is more than 1%, from the extruder in the form of granules,

- Drying the PET/HAp granules again at 80°C for 12 hours before injection molding,

- Mixing the granules thoroughly in order to obtain a homogeneous mixture,

- Injecting the composite mixtures into the preform mold using a vertical or horizontal injection device for preform production,

- Applying heat to the preform in a heating furnace via 8 IR lamps mounted in different positions therein, by means of a Stretch-Blow-Molding Method (SBM) machine,

- Keeping the pressure at 0.9 bar for 0.5 seconds and then gradually increasing it up to 25 bars at 2 second intervals and finally keeping at the same pressure for 2 seconds,

- Subjecting the preforms to a stretch and blow process immediately after being removed from the heating furnace again,

- Obtaining a composite packaging material in the form of a bottle or film as the final product.

EXPERIMENTAL STUDIES

Production of PET/HAp composites by extruder process is provided in three stages, namely 1. Production of PET/HAp composites by extruder process

2. Production of preform by injection process

3. Production of bottles by Stretch-blow-molding method (SBM)

1. Production of PET/HAp composites by extruder process

PET/Hydroxyapatite (HAp) composite materials were produced by melt blending method using a twin screw extruder (screw diameter D=16 mm, screw length/diameter ratio (L/D)=40) (Gulnar/Turkey) with screws rotating in the same direction. Extruder and other process parameters are given in Table 1. Before the PET granules were fed into the extruder, the PET granules were dried in an oven at 110 °C for 12 hours in order to remove the moisture therein. The dried PET granules and HAp were fed to the extruder with screw speed of 150 rpm. The temperatures of the six zones (from the feeding, towards the mold exit) in the extruder device were adjusted as 75 °C, 230 °C, 235 °C, 240 °C, 235 °C and 230 °C, respectively. PET/HAp composites, which were blended by addition of HAp, provided that it is more than 1%, were collected from the extruder in the form of granules.

Table 1. Process parameters of Injection molding machine

SCREW

Diameter (mm) 20

Screw Speed (rpm) 50-100

Nozzle Diameter (mm) 2

BARREL TEMPERATURE (°C)

Middle 280

Rear 275

Nozzle 260

INJECTION PRESSURE

Primary (MPa) 6 Injection Speed (g/s) 6

Extrusion Volume (m ³ ) 1.5 10' ⁶

BLOWING EXPANSION

MOLDING

Cold Preform Temperature (°C) 15

Front Pulse (MPa) 0.09

Last Pul se (MPa) 1.5

Stretch Rod Speed (m/s) 0.75

Outer Diameter of the Stretch Rod

(mm) 12

2. Production of Preform by Injection Process:

The PET/HAp granules were dried again at 80 °C for 12 hours before injection molding and the granules were thoroughly mixed to obtain a homogeneous mixture. Composite mixtures were injected into the preform mold using a vertical injection device (YH-15V, Yuhdak Machine, Taiwan) for preform production. The dimensions of the produced preform and bottle are given in Figures 1 and 2, respectively. In the vertical or horizontal injection device, the mold temperature was selected as 15°C and the nozzle temperatures were selected as 265°C, 270°C and 280°C, respectively. The other process parameters are given in Table 1. The weight of the preform produced using pure PET was determined as 9 g.

3. Production of Bottles by Stretch-Blow-Molding Method (SBM)

SBM machine is semi-automatic and custom production. SBM process parameters and the preform surface temperature profile at the time when the preform comes out of the heating furnace are given in figures 3 and 4, respectively. The heating process is provided by 8 IR lamps mounted at different positions in the furnace. The temperature throughout the preform is in the range of 30-35 °C. All other process parameters were kept constant. The pressure was kept at 0.9 bars for 0.5 seconds and then it was gradually increased up to 25 bars at 2 second intervals and finally it was kept at the same pressure for 2 seconds. The stretch rod speed was measured as 0.75 m/s and reached the bottom of the bottle in 0.375 seconds.

The preforms were subjected to a stretch and blow process immediately after being removed from the heating furnace again. During the blow process, the mold temperature was determined as 20 °C and the residence time in the mold was determined as 2 seconds.

REFERENCES

[1]. Meshref, A., et.al.: “Aluminium Content in Milk and Milk Products and its Leachability from Dairy Utensils”; September 2015; International Journal of Dairy Science 10(5):236-242; DOI:

10.3923/ijds.2015.236.242.

[2]. Demirel, Bilal. "Optimisation of mould surface temperature and bottle residence time in mould for the carbonated soft drink PET containers." Polymer Testing 60 (2017): 220-228.

[3]. Wang, M., Bonfield, W., 2001. Chemically coupled hydroxyapatite- polyethylene composites: structure and properties. Biomaterials 22, 1311-1320.