Technical Field

The invention is related to polymer blends developed to be used in the packaging of fresh fruit and vegetables and the packaging film produced from these blends.

The invention is particularly related to polymer blends comprising poly(4-methyl-1-pentene), low density polyethylene or linear low density polyethylene, ethylene-vinyl acetate copolymer and polyglycerol ester, in order to provide differential and high gas permeability features and to create an atmospheric composition that is compatible with the respiration rate of fresh fruit and vegetables; a production method of polymer blends by means of a screw configuration that is formed to obtain the highest level of homogenous and balanced structure and to packaging films that are produced from these blends.

Prior Art

Millions of people on earth, do not even have access to staple food products depending on several negative factors such as global warming, climate changes, increasing population and economic crisis (1). At the moment approximately 21.000 people are dying due to reasons related with starvation and one out of nine people in the world faces starvation every night (2- 4). On the other hand, billions of tons of foodstuff produced annually are thrown away without being consumed by people, due to storage and packaging method deficiencies. For example approximately 40% of fresh fruit and vegetables and 35% of seafood is wasted due to only packaging and storage deficiencies (5-7). The on-site researchers have determined that reducing and preventing waste of foodstuff are the key factors that shall enable us to feed the world population which shall be reaching up to 12.3 billion people in the year 2100 (8,9). Due to this reason, the conservation of food products and increasing shelf life has become more crucial in comparison to past years.

In the prior art, in order to prevent losses, the recent studies are particularly focusing on conservation techniques that aim to improve storage conditions that are called packaging in modified atmosphere. Packaging in Modified atmosphere is defined as a packaging technology that enables to form a special atmospheric composition around the products in order to extend shelf life and to preserve food quality. For example, the most basic principle in modified packaging applications, which extends the shelf life of breathing food products such as fresh vegetables and fruits, is based on creating a natural atmospheric change as a result of an interaction between the respiration rate of the product stored in the package and the permeability of the packaging film (10-14). The modified atmosphere packaging (MAP) technology, allows the extension of the shelf lives of products that spoil following harvesting and it provides a packaging advantage that reduces distribution costs by having a minimum effect on the organoleptic quality of the product or the nutrition value of products (14). The modified atmosphere packaging technique can be seen as a revolutionary step that allows retailers to market fresh foods having extended shelf lives without requiring any major processing, or the addition of preservatives or chemical additives.

The MAP technology is divided into two basic groups as the passive and active (p.MAP and a. MAP) groups (15). Active modified atmosphere packaging technology (a. MAP) represents the technique of changing the atmosphere composition inside the package so as to prolong the desired shelf life by using various gases such as nitrogen, oxygen and carbon dioxide. Although this is a technique that can be used to prolong the shelf life of all kinds of food products, it is generally used for packaging of products such as meat stuff, fruit juices that go-off by due to oxidation. The atmospheric composition that is required to extend the shelf life of the product that is to be conserved inside a package, is created externally. The restriction that is encountered is that the packaging material to be used must have low gas permeability or in other words it must have barrier features. If this cannot be achieved, the gas composition inside the package will lose its permeability and the desired shelf life cannot be obtained.

The passive modified packaging in modified atmosphere technology (p.MAP) however, is a different and dynamic approach which takes as basis the interaction of the physiological processes (mostly respiration) of the fresh product and the film permeability in order to change the original atmosphere gas composition within the package (15,16). Passive modified atmosphere packaging technology (p.MAP) technique is used particularly for the preservation of breathing fresh food products such as fresh vegetables and fruits. The restriction that is encountered is that the packaging material to be used must have the high and selectively permeable. If this is not achieved, the desired atmospheric composition in the package that is intended to extend the shelf life will not be obtained and it will not be possible to extend the shelf life of the products.

Nowadays, there are many different commercial plastic raw materials used for the production of packaging that is compatible with modified atmosphere packaging technique, and packaging with different designs developed using these raw materials. Not only engineered packaging having low gas permeability features such as PET and PA, but also plastics called polyolefins having relatively higher gas permeability such as LDPE, LLDPE, HDPE and PP are used for the production of said packaging. Moreover, in many food packaging applications, these plastics are used together to form a layered structure. However, due to their low gas permeability values, these packages do not have the qualities that can be used for the storage of products that perform respiration such as fresh fruits and vegetables and in parallel, that require high gas permeability values.

The plastic raw materials that are used in MAP designs and therefore the plastic Films, are the most crucial components for successful packaging applications that can prolong shelf life. To put it briefly, while polymeric films having low gas permeability, in other words barrier features are required for a. MAP applications, for p.MAP applications, polymer films having high gas permeability depending on the respiration rate of the fresh fruit and vegetables that are to be preserved, are required. To summarize, polymer material having high and selectively permeable features and in parallel packaging research are the most crucial points in extending shelf life of food products that can spoil easily, such as fruits and vegetables. However, even the permeability values of polyolefin group plastics such as LDPE, LLDPE, HDPE and PP, which are used extensively in packaging production and have relatively the highest gas permeability values among commercial plastics, are not sufficient for the long term shelf life desired in p.MAP applications For example the oxygen permeability value of the packaging films to be produced from LDPE derivative plastics which are commercial polymers that have the high gas permeability varies between 3.900-13.000 cc/m ² .day.atm, and their carbon dioxide gas permeability values vary between 7.700-77.000 cc/m ² .day.atm. The oxygen based respiration value of bananas which are the most important commercial products that are desired to be preserved in a packaging that is suitable to the passive modified atmosphere storage technique, varies between 30-120 cc.h Lkg ¹ . If said banana is desired to be preserved inside a 20 kg LDPE package, its daily oxygen consumption due to respiration shall be between 14.000-58.000 cc. As it can be seen this values is higher than the LDPE’s gas permeability value and as a natural result of this situation, at the end of the first or second day of storage, the oxygen inside the package will diminish and carbon dioxide shall increase. This condition leads to the commencement of anaerobic respiration and the ending of the aerobic respiration of the preserved product, therefore the preserved product shall be spoilt and the product will completely lose its commercial value.

In order to solve this problem, the practical and most recent method used in the prior art is to micro perforate the packages. By this method, it is aimed to provide the desired inner- package atmosphere composition for the product to be preserved, by opening micro-scale holes at different locations on the surface of the package. This represents a technique that is prevalently used nowadays. However depending on the product to be preserved and naturally the respiration rate, the designing of the number and positions of the perforations is important. It is not possible to say that a perforated product having the correct design and high performance has been developed until now. The design studies carried out in this field are continued intensively. There are also drawbacks that limit the efficiency of micro perforations, such as the need for an additional micro-perforation process after the production of the film, the closing of the opened holes due to the pressure difference during the preservation processes or by the preserved products themselves.

Some applications have been encountered related to embodiments used in packaging products such as fresh fruit and vegetables in the prior art. One of these is the patent application numbered CN107266820A. The application discloses a film that has high mechanical strength and can effectively inhibit the growth of bacteria, whose effect of keeping the foodstuff fresh can be improved, and preparation method thereof. The film subject of the invention is prepared from polyvinyl chloride, ethylene-vinyl acetate copolymer, polypropylene, stearic acid, lauramid ethyl sodium sulfate, sodium alginate, chitosan, ethyl acetate, vinyl trimethoxysilane, titanium dioxide, bamboo powder, phthalate esters and modified chitin fiber, as stated in the abstract section.

The patent application numbered TR 2016 05385 is related to packaging of fresh fruits and vegetables in the food sector. The application describes the method of synthesizing polyurethane films having different compositions, using monomers having different physical and chemical properties in varying proportions and turning them into films by a casting method and a hot pressing method and the packaging film produced by using this method. The film subject to the invention comprises PEG, castor oil and 1,4-butanediol.

In recent years, it has been observed that the studies carried out in order to provide the appropriate gas permeability properties required for said food packaging and to eliminate the limitations encountered in the prior art are directed to mixing commercial polymers and obtaining blends with new properties. Within this context, several studies have been published, that are related to the characterization and preparation of polymer blends having different structures with melt processing methods. However in most of these studies, it can be seen that the aim was to improve the gas barrier properties of polymeric materials in terms of packaging in active modified atmosphere. (17-20). However there are a limited number of studies related to increasing the gas permeability properties suitable to the packaging method in passive modified atmosphere (21, 22). As a result, due to the disadvantages and inadequacies mentioned above, it was deemed necessary to provide a novelty in the related technical field.

Aims of the Invention

The present invention is related to polymer blends for fresh fruit and vegetable packaging applications and packaging films produced from these blends that meets the above mentioned requirements, eliminates all of the disadvantages and brings about some additional advantages.

The primary aim of the invention is to obtain polymer blends that have differential and high gas permeability properties that can create an atmospheric composition that is suitable to the respiration rate of fresh fruit and vegetables, to be used in plastic packaging applications.

The aim of the invention is to provide a packaging film that enables to prolong the shelf lives of food products that can easily spoil, such as fresh fruit and vegetables.

The aim of the invention is to obtain a packaging film that provides the gas permeability values that is required/shall be required to prolong the shelf life of the product that is desired to be preserved and to provide all of the desired technical values including the necessary mechanical properties that the package needs to have.

The aim of the invention is to obtain the blends that can provide the desired differential and high gas permeability properties by adding an isotactic polymethylpentene (PMP) copolymer at different ratios up to 75% by weight into the low density polyethylene (LDPE).

The aim of the invention is to produce packaging films with high gas permeability properties by means of the structural property of the PMP copolymer that forms the polymer blend and by means of the partial phase separations between the LDPE and PMP polymers.

The aim of the invention is to provide a packaging film that is more homogenously distributed in comparison to perforated packages and that has at least twice as higher gas permeability properties due to its LDPE/PMP blend structure.

An aim of the invention is to provide an embodiment that shall make it easier to increase the permeability values to higher levels by increasing the PMP ratio in the blend or by changing the thickness of the film that is produced from the blend. Another aim of the invention is to provide an extruder screw configuration that shall ensure successful blend production in a dual screw extruder that is used for the production of LDPE/PMP blends.

Another aim of the invention is to provide an extruder that can position the phase separations and incompatibilities between phases during the blend production at the desired ranges.

Another aim of the invention is to determine the thickness of the packaging film that is to be produced such that it meets the requirements, by taking into consideration the atmospheric composition inside the package that the product to be preserved needs, the respiration rate of the product and the gas permeability values of the package. The thickness of the packaging film can vary between 15-100 microns.

To reach the above mentioned aims, the invention is a polymer blend that has been developed to be used in the packaging of fresh fruit and vegetables, characterized in that it comprises PMP, LDPE, EVA and polyglycerol ester in order to provide differential and high gas permeability properties and to create an atmospheric composition that is compatible with the respiration rate of fresh fruit and vegetables.

To reach the above mentioned aims, the invention is the production method of a polymer blend that has been developed to be used in the packaging of fresh fruit and vegetables, characterized in that it comprises the below mentioned process steps in order to provide differential and high gas permeability properties and to create an atmospheric composition that is compatible with the respiration rate of fresh fruit and vegetables,

• mixing PMP, LDPE, EVA and polyglycerol ester in a mixer until a homogenous mixture is obtained,

• adjusting the screw configuration of the L/D 48/1 dual screw extruder to be used in order to position the phase separations and incompatibilities between phases at the desired ranges,

• adjusting the temperatures of the extruder casing to 220 °C at the entrance area where the raw materials shall be entering the extruder and increasing the temperature incrementally such as to reach 260 °C at the head form,

• feeding of the obtained blend without main dosing to the dual screw extruder. In order to reach these aims, the screw configuration if formed respectively of, 4 of 56x56 screws, 4 of 72x72 screws, 1 of 56x28 left screw, 2 of 30x7x72 crushers, 1 of 56x56 screw, 4 of 72x72 screws, 3 of 45x5x56 crushers, 3 of 30x7x72 crushers, 1 of 96x48 screw, 5 of 72x72 screws, 1 each of 56x28 left screws, 45x5x56 crushers, 60x4x56 crusher 3 of 45x5x56 crushers, 1 each of 56x56 screws, 96x48 screws, 2 of 72x72 screws, 3 of 96x96 screws and 1 of 56x56 screws.

To reach the aims of the invention the polymer blend is used in the production of packaging films in a passive modified atmosphere, where the packaging film creates an atmospheric composition that is compatible with the respiration rate of the fresh fruit and vegetables and it provides differential and high gas permeability properties.

The structural and characteristic properties of the invention and all of its advantages shall be more clearly understood by means of the detailed description provided below and therefore if an evaluation is to be carried out, it needs to be done so, and by taking into consideration this detailed description.

Figures describing the invention

Figure-1: Illustrative view of the screw configuration used in the production of the polymer blend in a dual screw extruder.

Figure-2: SEM image taken from the film sections produced from LDPE copolymer.

Figure-3: SEM image taken from the film sections produced from PMP copolymer.

Figure-4: SEM image taken from the sections of packages having a thickness of 20 microns, produced from LDPE/PMP blends comprising 20% PMP copolymer by weight.

Figure-5: SEM image taken from the sections of packages having a thickness of 20 microns, produced from LDPE/PMP blends comprising 30% PMP copolymer by weight.

The drawings don’t have to be scaled according to the original product and some details may have been omitted to clearly describe the invention. Parts that are identical to a great extent or that have equivalent functions have been represented with the same reference number.

Description of the part references

10. Screw configuration

11. 56x56 screw

12. 96x96 screw

13. 72x72 screw

14. 96x48 screw 15. 45x5x56 crusher

16. 60x4x56 crusher

17. 56x28 left screw

18. 30x7x72 crusher

Detailed Description of the Invention

In this detailed description, the polymer blends developed to be used in the packaging of fresh fruit and vegetables and the packaging film produced from these blends have been described only to provide further understanding of the invention, without intending to have a limiting effect on the invention.

The invention is related to polymer blends developed to be used in the packaging of fresh fruit and vegetables and packaging films produced from these blends. The most important feature of the invention is that it creates an atmospheric composition that is suitable to the respiration rate of fresh fruit and vegetables and provides differential and high gas permeability properties.

Formulation of the polymer blends subject to the invention;

PMP, represents copolymers that are named 4-methylpentene-1-based olefins. These copolymers are crystalline and they have high light permeability due to their special characteristic structures. Moreover it provides 10 times high gas permeability values in comparison to polyolefins that are intensively used in the packaging sector such as LDPE and LLDPE due to its unique structure. Its molecular weight (Mw) varies between 200.000- 700.000. The Melt Flow Index Rate (MFI/MFR) must be between 2 g/10 minutes to 180 g/10 minutes range under 5 kg loads and at 260 °C, in accordance with the ASTM D-1233 standard. The density rate must be between the range of 0.832 g/cm ³ and 0.834 g/cm ³ in compliance with the ASTM D1505 standard. All equivalent products that have a tensile strength of >10 MPA and elongation at break of >10% mechanical rate, that are in compliance with the ASTM D638 standards can be used. Primarily PMP DX845 and MX004, MX0020 and MX002 coded products can be used within the structure subject to the invention.

LDPE (low density polyethylene): Group plastics shall be used for the production of general packaging films called low density polyethylene. It contains antiblock additives called amorphous silica with slip additives that are erucamide and oleamide based. The Melt Flow Index Rate (MFI/MFR) of the related composition must be between 0.1 g/10 minutes to 2 g/10 minutes range under 2.16 kg loads and at 190 °C, in accordance with ISO 1133 standard. The density rate can be about of 0.918 g/cm ³ in compliance with the ASTM D1505 standard. All equivalent products that have a tensile strength of >10 MPA and elongation at break of >300% mechanical rate, that are in compliance with the ASTM D882 standards can be used.

Group plastics that have been developed for the production of general packaging films called LLDPE, butene linear low density polyethylene shall be used. It contains antiblock additives called amorphous silica with slip additives that are erucamide and oleamide based. The Melt Flow Index Rate (MFI/MFR) of the related composition must be between 0.1 g/10 minutes to 2 g/10 minutes range under 2.16kg load and at 190 °C, in accordance with ISO 1133 standard. The density rate must be lower than the rate of 0.92 g/cm ³ in accordance with the ASTM D1505 standard. All equivalent products that have a tensile strength of >20 MPA and elongation at break of >300% mechanical rate, that are in compliance with the ASTM D882 standards can be used.

The EVA copolymer is used in the invention, to improve the heat adhesion and the water vapor permeability properties of the packaging. The EVA copolymer used, has a VA (Vinyl Acetate) content that varies between 12% to 21%. The Melt Flow Index Rate of the related composition must be between 0.40 g/10 minutes to 4 g/10 minutes range under 2.16kg load and at 190 °C, in accordance with ASTM D12388 standard. The density rate must be between the range of 0.935 g/cm ³ and 0.953 g/cm ³ in compliance with the ASTM D1505 standard. Within the scope of the invention, first of all Escorene™ Ultra LD and then Escorene™ Ultra LD 705. MJ coded EVA copolymer or their equivalents are used.

Maleic grafted copolymers (PE.g.MA or POE.g.MA) are used to restrict the incompatibilities between the LDPE/PMP blends and in parallel to limit the phase separation, and the grafted copolymers that preferably vary in ratio by weight of 5-10% can be added into the blend of the invention. Polyolefin elastomeric graft maleic anhydride or Linear Low Density Polyethylene grafted maleic anhydride can be used as the grafted copolymer. The rate of the maleic anhydride graft must be above 0.5%. The Melt Flow Index Rate (MFI/MFR) of the related composition must be between 0.40 g/10 minutes to 100 g/10 minutes range under 2.16kg load and at 190 °C, in accordance with ASTM D12388 standard. The density rate must be between the range of 0.935 g/cm ³ and 1.02 g/cm ³ in compliance with the ASTM D1505 standard.

Polyglycerol ester is used as an antifog agent. One of the most important technical properties of the packages that are suitable to the passive modified atmosphere technique is that fog should not form on the surface of the packaging during storage. In order to prevent fogging, various vegetable or animal fats are added into the structure of the package as being migrated on the surface of said packages that change the surface energy of the packaging by dissolving inside the water droplets that accumulate on the surface. Within the scope of the invention, a sorbitol ester component that is plant based is added into the content, during the blend production processes. The ratio within the structure of the related component can vary between 1-5% by weight. Within the scope of the invention a patented product of the company Croda® is used. As antifogging properties of the packaging is crucial, an antifogging agent that is preferably 2% by weight is used within the content of the polymer blend formulation. During mass production, this rate changes between 1-5% depending on the properties that shall be required.

By means of the invention, polymer blends that have differential and high gas permeability properties, that can create an atmospheric composition that is suitable to the respiration rate of fresh fruit and vegetables, to be used in plastic packaging application are obtained. The alloys that have the desired differential and high gas permeability properties are obtained by adding an isotactic polymethylpentene (PMP) copolymer at different ratios up to 75% by weight into the low density polyethylene (LDPE). The LDPE/PMP blends and the polymers within the blend are produced using a dual screw extruder that is suitable to the melt blending method.

Within this context the screw configuration of the dual screw extruder has been re-designed in order to obtain the highest level of homogenous and stable structure. In Figure 1, the illustrative view of the screw configuration (10) used in the production of the polymer blend in a dual screw extruder is shown. Therefore the screw configuration (10) that is used in the production of LDPE/PMP blends in a dual screw extruder if formed respectively of, 4 of 56x56 screws (11), 4 of 72x72 screws (13), 1 of 56x28 left screw (17), 2 of 30x7x72 crushers (18), 1 of 56x56 screw (11), 4 of 72x72 screws (13), 3 of 45x5x56 crushers (15), 3 of 30x7x72 crushers (18), 1 of 96x48 screw (14), 5 of 72x72 screws (13), 1 each of 56x28 left screws (17), 45x5x56 crushers (15), 60x4x56 crusher (16), 3 of 45x5x56 crushers (15), 1 each of 56x56 screws (11), 96x48 screws (14), 2 of 72x72 screws (13), 3 of 96x96 screws (12) and 1 of 56x56 screws (11).

The production method of the polymer blend subject to the invention is as follows;

• PMP, LDPE or LLDPE, ethylene-vinyl acetate copolymer, maleic anhydrite grafted LLDPE and polyglycerol ester is mixed in a mixer until a homogenous mixture is obtained,

• The screw configuration of the L/D 48/1 dual screw extruder is adjusted to be used in order to position the phase separations and incompatibilities between phases at the desired ranges,

• The temperatures of the extruder casing is adjusted to 220 °C at the entrance area where the raw materials shall be entering the extruder such that the temperature is increased incrementally to reach 260 °C at the head form,

• The obtained blend without main dosing is fed to the dual screw extruder and a polymer blend is obtained at the outlet of the extruder.

In a preferred embodiment of the invention, production can be carried out without mixing using a dual screw extruder having gravimetric main and sub dosing mechanisms.

In the production method mentioned above, a melt blending method is used and the extruder screw diameter can vary between 26-70 mm. The screw revolution can vary between 200- 500 rpm depending on the desired production capacity.

The blends obtained using the production method according to the invention is used in producing packaging films with passive modified atmosphere. The production of the packaging film is carried out by means of a blow film extrusion method. The screw diameter of the blow film machine can vary between 20-70 mm, and the headform diameter can vary between 50-500 mm depending on the dimensions of the desired packaging. A special screw configuration is not required for film production. For the production of the packaging film the extruder casing temperatures must be adjusted to vary between 220-260 °C. The thickness of the packaging film that is to be produced can vary between 15-100 microns such that it meets the requirements, by taking into consideration the atmospheric composition inside the package that the product to be preserved needs, the respiration rate of the product and the gas permeability values of the package. By means of the blend structure and the production process subject to the invention, all of the desired technical values can be easily created, such as primarily the gas permeability values that are required/shall be required to prolong the shelf life of the product that is desired to be preserved and the desired technical values including the necessary mechanical properties that the package needs to have. The oxygen permeability values (OTV) of the films obtained by means of the polymer blends of the invention are determined according to ASTM F2622 standards and the Carbon dioxide gas permeability values (COTV) have been determined according to the ASTM F2476 standard. The oxygen transition of the packaging films obtained by the LDPE/PMP blends at different temperatures in comparison to the packaging films used in the prior art are given in Table-1 and in Table-2 the carbon dioxide transition results are given.

Table 1: The oxygen permeability of the packaging films obtained by the LDPE/PMP blends at different temperatures in comparison to the packaging films used in the prior art

Table 2: The carbon dioxide premeability of the packaging films obtained by the LDPE/PMP blends at different temperatures in comparison to the packaging films used in the prior art

As it can be understood from Table-1 and 2, higher gas permeability values can be obtained by means of the polymer blend subject to the invention in comparison to the micro perforation technique that is intensively used in the prior art. The high gas permeability properties are obtained by means of the structural features of the PMP copolymer and the phase separation between the LDPE and PMP polymers. Although the LDPE/PMP blends in Table-1 and 2 must have a composition of 70%/30%, twice more gas permeability values are obtained in comparison to micro-perforated packages. The permeability values can be easily increased by increasing the PMP ratio in the blend or by changing the thicknesses of the films that are produced from the blend. A disadvantage such as the pores being closed as in micro perforated packaging is not encountered in the present invention. By means of the LDPE/PMP blend structure, a more homogenously distributed gas permeability is obtained in comparison to perforated packages. In other words, each area of the package exhibits similar gas permeability values, in comparison to the micro perforated structure.

Gas permeability analyzes were also performed on packaging film samples that have a thickness of 100 microns, from the blends subject to the invention in order to ensure that the values obtained are consistent with the literature. In Table-3, the gas permeability values of oxygen and carbon dioxide determined under 90% Relative Humidity and at 25 °C of the packaging films having a thickness of 100 microns obtained from LDPE/PMP blends have been given, and in Table-4, the gas permeability values of oxygen and carbon dioxide determined under 90% Relative Humidity and at 25 °C of the packaging films having a thickness of 20 microns obtained from LDPE/PMP blends have been given. Table-3: The gas permeability values of oxygen and carbon dioxide determined under 90% Relative Humidity and at 25 °C of the packaging films having a thickness of 100 microns obtained from LDPE/PMP blends Table-4: The gas permeability values of oxygen and carbon dioxide determined under 90% Relative Humidity and at 25 °C of the packaging films having a thickness of 20 microns obtained from LDPE/PMP blends. According to the values in Table-3, the gas permeability values can be increased up to 2, 5 times, and the carbon dioxide values can be increased up to 4, 5 times compared to LDPE derivative packages. As it can be understood from the table-4, where the results of the analysis performed by reducing the package thickness to 20 microns are shared, much higher permeability values can be obtained by reducing the package thickness. When the thickness increase and PMP ratios are taken into consideration together and the permeability increase is examined, it is observed that the increase in gas permeability are much higher than the reduction of the package thickness. This situation is thought to be due to the increase in the phase separations of LDPE and PMP blends, as the packaging gets thinner. The invention provides an advantage for cost effectively adjusting the permeability of the packaging.

In Table-5, the mechanical values obtained as a result of the tension test that is carried out according to the ASTM D882 standards. Mechanical tests are carried out on films having 100 micron thickness that have been rolled from LDPE/PMP blends that can represent packaging that are suitable to the preservation technique in a passive modified atmosphere. Analysis results show that the tensile strength rates increase in proportion to the PMP copolymer rate added to the structure, and in parallel that the % elongation rates decrease. These rates that are determined clearly show that the blends can be used in the production of packaging without any problems.

Table-5: The mechanical analysis results of the packaging films having 100 micron thickness obtained from LDPE/PMP blends according to LDPE/PMP blends

The SEM images were obtained from a section by means of the scanned electron microscope from the films produced from LDPE and PMP copolymers used in the composition of LDPE/PMP blends. In Figure-2, the SEM images taken from the sections of the films produced from LDPE copolymer, and in Figure-3, the SEM images taken from the sections of the films made of PMP copolymer are given. The SEM images clearly show that the films have a quite homogeneous structure and that they do not contain any impurities.

In Figure-4, SEM images taken from a section of the packages having 20 micron thickness produced from LDPE/PMP blends containing 20% PMP copolymer by weight, and in Figure- 5, SEM images taken from a section of the packages having 20-micron thickness produced from LDPE/PMP blends containing 30% PMP copolymer are given. The layered structure that can be seen in the SEM images, represent the phase separation of the components within the LDPE and PMP blends. The high gas permeability values arise from these phase separations, besides the PMP copolymer having high gas permeability values.

Experimental study 1; Green bananas have been preserved inside a packaging film made of 100% LDPE and their shelf lives have been analyzed. The packaging film has a 4L inner volume and has the dimensions of 200x300mm. 500 gr green bananas have been placed inside the packaging film. In Table-6, the analysis results of the changes in atmospheric composition within the package in time, are given as indicators of green banana storage and shelf life in a packaging film made of 100% LDPE. The average ethylene concentration calculated after 14 days was 0.00554 ppm/g.l.day.

Table-6: The analysis results of the changes in atmospheric composition within the package in time, as indicators of green banana storage and shelf life in a packaging film made of 100% LDPE.

Experimental study 2;

Green bananas have been preserved inside a packaging film made of an LDPE/PMP blend comprising 10% PMP copolymer and their shelf lives have been analyzed. The packaging film has a 4L inner volume and has the dimensions of 200x300mm. 510 gr green bananas have been placed inside the packaging film. In Table-7, the analysis results of the changes in atmospheric composition within the package in time, are given as indicators of green banana storage and shelf life in a packaging film made of an LDPE/PMP blend comprising 10% PMP copolymer. The average ethylene concentration calculated after 14 days was 0.00472 ppm/g.l.day.

Table-7: The analysis results of the changes in atmospheric composition within the package in time, as indicators of green banana storage and shelf life in a packaging film made of an LDPE/PMP blend comprising 10% PMP copolymer.

Experimental study 3;

Green bananas have been preserved inside a packaging film made of an LDPE/PMP blend comprising 25% PMP copolymer and their shelf lives have been analyzed. The packaging film has a 4L inner volume and has the dimensions of 200x300mm. 508 gr green bananas have been placed inside the packaging film. In Table-8, the analysis results of the changes in atmospheric composition within the package in time, are given as indicators of green banana storage and shelf life in a packaging film made of an LDPE/PMP blend comprising 25% PMP copolymer. The average ethylene concentration calculated after 14 days was 0.00218 ppm/g.l. day.

Table-8: The analysis results of the changes in atmospheric composition within the package in time, as indicators of green banana storage and shelf life in a packaging film made of an LDPE/PMP blend comprising 25% PMP copolymer.

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