Current World Environment

Introduction

The basic purpose of packaging is to provide protection from the environmental condition by maintaining the quality of food items from the manufacturing industry to normal consumers. The most important physical property in flexible packaging materials is water vapour and oxygen gas transfer rate.¹ The transfer rate depends on the type of the plastic, gas molecules quantity, the interacting time between gas and plastic.² Therefore special barrier packaging materials are on the high demand for the packaging of oxygen-sensitive food items. Whereas other properties like tensile strength, optical properties, thickness, gloss, printability, transparency, international and local food legislation.³ Currently to meet such requirements plastic manufacturing industries use additives, multilayers formation by using different polymers only few can be utilized due to crystal structure. The co-extrusion technique is mostly used for manufacturing of multilayer plastic films based on polypropylene(PP), High-density polyethylene (HDPE), Low-density polyethylene (LDPE), Polyethylene terephthalate(PET)etc. with suitable oxygen barrier material like Ethylene Vinyl alcohol ( EVOH). However traditionally low-cost aluminium coating with (Cast polypropylene) CPP, PET has been used as a good barrier just by increasing few micrometre thicknesses by a metallization process.⁴ But aluminium will restrict gas and water if the thickness of plastic sheet above 25.4 μm.⁵ Whereas, it may produce small hole or stress if manufactured in less thickness. Incorporation of aluminium into a film by lamination process better option but costly as compared to co-extrusion.

It is also very important to mention here that aluminium coated plastic materials are not recyclable and hence causes excess wastage.⁶ The key objective of the sustainable food packaging system is to maintain excellent quality of the packaged items, safe handling, minimizing post-harvested based loses and wastages. In developing countries like Pakistan about 25 to 50% food losses occurs due to improper food processing and packaging problems.⁷ However it is also proven that chemicals from packaging also migrate to the food items after some time of packing, the main hazards of these types of migrations on food safety has several questions if quantity of these migrated chemicals in food items greater than the specified standard, which can be minimized after adding some additives or metallic coating. The monitoring of migration is an important aspect of food quality.⁸

Plastic film with new intelligent technologies is one of the fastest growing forms of packaging with a number of benefits. At that minute, it is seen as an environmental burden, emission of Greenhouse gases (GHS) and wasting resources. The high hydrophobic level and the high molecular weight of Plastic makes it non-biodegradable and lethal of marine biota and vector of harmful algae and bacteria species transportation in floating water bodies.^16,17 By natural cycle degradation of PP is slow it is initiated by both biotic and abiotic factors of the environment. On the molecular symmetric continuous chain of methylene and absence of functional groups make it poor to microbial attachment thus resistant to biodegradation.¹⁸ The aim of the present research is to investigate and understand the physical properties of metalized and non- metalized PP film used in packaging industries with its potential effects on the environment.

Material and Method

Preparation of Polypropylene(PP) Samples

In this study, the PPmgranules purchased from Chemicals suppliers Ltd. with densities 0.9g/cc and melt flow index 8g/10min were used. Six samples of metalized and non-metalized types of PP films were manufactured by Cast extrusion process as shown in the process flow diagram Fig 5. According to which PP granules additives enter through hoppers into the extruder (Ext-01) of Filmax701 model, Mitsubishi, then melted (temperature 210 to 285^oC) PP granules introduces into the die Plug (D-0001). The finished plastic cools with chill roller machines (15 to 22^oC). Finally, Corona treatments were used to increase the surface tension. After that PP Film moves to wind section where the extruded film converted into film rolls. Similarly, metalized CPP films were produced by using Vacuum metalized (Model No: K5000)by adding a thin film of aluminium to PP films. The thickness of non metalized (20microns) and metalized PP films(60 microns) were measured by automatic gauge meter during the production. Physical test of Manufactured Polypropylene Plastic Film:

To analyze the biodegradation properties of metalized and non metalized PP films some physical test of the sample were performed as per American standard testing methods (ASTM)

First of all tensile and elongation test of both types of PP films were conducted by the universal tensile tester (AG-X Shimasdzu, Autograph, Japan) according to ASTM D- 882 methods, the PP films were conditioned for 48 hours at 25^oC about 50% relative humidity(RH). The samples were cut in specific shape and strips(100 x 10 mm) then tensile strength measured in both directions i.e. in the machine(md) and transverse direction(td) , since they can vary considerably from one direction to another, the Measurement was based on six replicate of each sample.

Similarly, barrier properties in terms of water vapour transmission rate (WVTR) and oxygen transmission rate(OTR) of the sample were tested in accordance with American standard testing method. The PP samples tested for WVTR at 80 to 90% relative humidity (RH) and 20-25^oC by means of a special type of permeability cups as per ISO 2528 and as mentioned by Lopez-de-Dicastillo.²³ These cups were filled specifically with silica gel then sealed with the sample pp films. However, the cups were stored in desiccators to maintain the required humidity. The cups were weighed and the increase in weight versus time was used to calculate WVTR. These values were then divided by water vapour gradient and multiplied by sample thickness to obtain the exact value.

Similarly, the oxygen transmission rate (OTR) of the non-metallized and metalized PP films was measured at 23°C with 50 to 55% RH. First of all PPfilm samples were clamped in a diffusion chamber of the OTR analyzer. Pure oxygen (99.9%)was introduced into the upper half of the chamber whereas nitrogen(99.999 % zero grade N₂) carrier gas flows through the lower half. The oxygen transmission rate of both types of PP films was displayed as (cc/m²/atm/day).
 

Figure 1: FTIR result of Non-metalized PP with control (Red) and treated with fungi ( Blue) spectrum. Click here to view Figure

Figure 2: FTIR analysis result of metalized (red spectrum control) and metallized film (purple spectrum) after treated with fungi. Click here to view Figure

Degradation Test

The samples of metalized and non metalized PP films were further analyzed for their biodegradation properties. The samples were washed aseptically with alcohol and poured into sterile Sabouraud Dextrose Agar and consortium of Aspergillus spp and Penculliumspp respectively. The plates were incubated at 28°C for one week. After incubation, the plastic with fungus growth transfer into the minimal media (MgSo_4. 7H₂O (1gm/L), FeSO₄ (0.002g/L), NaCl (0.2g/l), K₂HPO₄1O.5 g/l), KH₂PO₄ (0.08 gm/l), NH₄NO₃ (2.0 g/l) and Agar (0.7%) containing no source of carbon accept plastic.¹⁹

Figure 3: SEM photomicrographs of metalized cpp film exposed by Aspergillus spp and Pencilliumsppat(a)500x (b)1000X (c)7000x (d)10,000x (e)15000x respectively after 30 days of incubation Click here to view Figure

Figure 4: SEM photomicrographs of Non-metalized cpp film exposed by Aspergillus spp and Pencilliumsppat(a)500x (b)1000X (c)7000x (d)10,000x (e)15000x respectively after 30 days of incubation Click here to view Figure

After the interval of 02 months the weight of plastic measured by the gravimetric method by using ASTM D6003-96.¹⁴ Change in the chemical structure of the plastic film was recorded by using Fourier Transform infrared (FT-IR) (Thermo Scientific Nicolet TM iS10), from a wave number of 400–4000 cm^-

Scanning Electron Microscopy (SEM)

The PP film after incubation period with fungal stains was removed and dried in Petri plate for 24 hours. The sample was coated with 300°A gold and analysis under a high-resolution electron microscope (Jsm-6380 A, Japan).
 

Figure 5: Mean strum test result of metalized and non metalized film Click here to view Figure

Strum Test

Strum test (OECD 301B: ASTM D5209) was used for the evaluation of biodegradability of polymer material. The sterile piece of film was added to 300 mL basal salt medium as the only carbon source. Spore suspension of Aspergillus niger and Penicillium spp were used for the degradation of polyethene. Control bottles were prepared without any plastic. degradation test was performed at room temperature for the duration of four weeks. Before set the system Ba (OH)₂ filtered and stored in the airtight bottles to prevent atmospheric contamination of CO₂ absorption in the system. Evolution of carbon dioxide, which was trapped in absorption bottle containing 0.01M, Ba(OH)₂ was monitored every week, The amount of CO₂ evolved during the test duration was measured by the gravimetric method. As BaCO₃ is insoluble in water and formed precipitates as it is shown in Eq. 1.

Ba(OH)_{2 +} CO₂ → BaCO₃+ H₂O

Results and Discussion

Material Characteristics

The barrier properties of packaging material are responsible for product quality deterioration, the detailed understanding of the characteristics of coated films is great practical and commercial importance. Generally, polypropylene film has a good barrier to moisture vapours and low barrier to oxygen transmission. But by manufacturing the CPP films with standard PP granules after metalized coating shows better results in terms of OTR barrier as well as other properties. Results are based on the six samples of each metalized and non-metalized cast polypropylene film. From data are given in Table 1 substantial differences between the barrier properties of the investigated coated and uncoated cast, PP films were estimated. To make the polymer more stable in terms of barrier properties a thin layer of metal i.e. Aluminum (Al), aluminium oxide (AlOx), silicon oxide (SiOx), or magnesium oxide (MgOx)is used [20]. Table 1 includes the properties of non-metalized and metalized cast polypropylene film with aluminium coating. Results show that cast polypropylene film without metallization has high WVTR which is not acceptable for some food packaging industry. But after metalization with aluminium PP films results proved to be better.

Table 1: Comparative study of the Tensile and Barrier Properties of the Non metalized and Metalized PP Films

Biodegradebilty Results

Synthetic polymeric materials have been widely used because of low density, cheap in cost and good possibility. To make the polymer more stable in the environmental condition a thin layer of metal i.e Al is used.²⁰ However, the biodegradability is considerably less, and the materials easily accumulate in the environment. Polypropylene (PP) is one of such synthetic polymeric constituents and is known as a non-biodegradable one. Generally, large molecule such as PP cannot easily enter into cells of microorganisms. Therefore, PP is hard to be metabolized in microorganisms.^9-10 The microorganism once attached to the surface on the plastic used it as the sole source of carbon, leading to the formation of a low molecular fragment of polymer i.e. oligomer or monomers.¹² The biodegradation of plastics by bacteria and fungi proceeds differently under different conditions according to their properties. The different factors that rule biodegradation are a type of organism, polymer characteristics.¹¹ Our result is somehow is the same in case of metalized and non-metalized pp film, FTIR results show very few changes in the peak after exposed to the fungi in mineral media. The spectrum peak in the control of non-metalized film observe at 37736 cm^-1, 38913 cm^-1 and 6742 cm^-1, which are absent after degradation with fungi consortium namely Aspergillussppand Pencilliumspp. Similarly in metalized plastic peaks at 3779.8 cm^-1 , 3771.1 cm^-1, 2357.2 cm^-1 and 2007.2 cm^-1 were disappear after degradation with fungal species. Peak shifted is also recorded in the region of 1500-1000 cm^-1 (Fig-1 and Fig 2). The results indicated the far acceptable degradation of the metalized film as compare to un-metalized, but somehow it can be due to the removal of metallization layer on pp film. The shift of peaks and new peak formation in the spectrum is the sign of degradation which is due to the enzymes produced by microorganism once it's attached to the surface and used the subtract as a source of their food. Aspergillussppwere reported as the degrading agent of Polyethylene film, the rate of degradation reported as 26% in 6 months.¹² Khan et al.,¹³ proved that the degradation of Polyurethane film (PU)up to 90% by Aspergillustubingensis. He observed the changes in the spectrum at 3321 cm^-1 as hydrogen bond (NH), which is absent in control. He reported these changes as a sign of degradation and formation of new products in degradation. Similarly, weak band generate at the shoulder of band 2954.8 cm^-1 in the sample spectrum which is also absent in control.

Scanning electron microscopy (SEM) images of film samples after degradation test revealed the significate surface degradation and structural changes of Metalized and non metalized PP film at a resolution of 500x to 15000x. In the present work Incubated Film colonized by fungi shows important morphological changes i.e formation of cavities and erosions (fig 4 & 5). The observed rough and erosion Surface by fungal is the primary reason of mass loss. SEM photographs of control polyethene did not show any disruption on the surface. These results show that AspergillussppandPencilliumspp could utilized metalized and non metalized film and promote their growth mechanism. The Cracks and holes appeared in film after degradation is due to the dispersion of fungal mycelium and penetration of hyphae (Khan et al., 2017). Nature of microorganism and nature of pretreatment is the important factor of degradation. According to the Griffin 1980, growth of fungi cause cracking, bursting and swelling of plastic as fungi penetrate on the polymer.

Conclusion

PP plastic is mostly used for packaging of material possibly separating the product from the external environment. From the above-mentioned results and discussion we can assess that:

The film with aluminium metallization has excellent barrier properties than non-metalized.

It is concluded that use cast polypropylene film with aluminium coating for the better shelf life of food products.

It is also concluded that specified grades of polypropylene and additives have also some impact on the properties of the film. Therefore it is better to use mentioned polypropylene grades and additives.

From an environmental point of view, they are persistent in nature and not easily biodegradable. Therefore, in this era of innovation technology design material should be manufacture as must be resistant during their use and must biodegrade at the end of their useful life.

Acknowledgements

The author would like to express their gratitude to the Pakistan Council of Scientific and Industrial Research, Karachi, Pakistan

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