Recycling of Multilayer Packaging Film waste : A Review

Mithilesh P. Chandekar

Department of Plastic and Polymer Engineering, Govt. Polytechnic, Amravati

Abstract:

The average annual generation of multilayer packaging films is about 16 million tonnes, and with recent developments in packaging films the demands for reclaiming them has also became the outer most need, disclosed is a method of recovering a multilayered film which comprises a plastic layer including polyester (PET), polypropylene (PP), and polyethylene (PE) as main components, and an aluminum layer. The method comprises selective dissolution of aluminum, separation using a difference in specific gravity, selective extrusion using a difference in melting point, and selective dissolution using an organic solvent.

Generally recycling of multilayered packaging film is carried out by:

a) feeding the pulverized multilayered film waste having the aluminum layer into a reactor to treat the pulverized multilayered film waste with a solution for dissolving aluminum so that the aluminum layer is selectively dissolved to be separated from the film;for dissolving the aluminum layer, one or more alkali aqueous solutions selected from the group consisting of NaOH aqueous solution, KOH aqueous solution, Ca(OH)₂ aqueous solution, and LiOH aqueous solution.

b) separating the pulverized film waste, from which the aluminum layer is separated through dissolution, into a layer of pulverized pieces including polypropylene and polyethylene, having low specific gravity, as main components, and a layer of pulverized pieces including polyester, having high specific gravity, as a main component, using a difference in the specific gravityof 0.97 - 1.33.

c) drying the pulverized pieces which are separated using the difference in the specific gravity and include polyester as the main component and processed using an extruder, in which a maximum internal temperature is 220°C or lower, in such a way that a screen or a continuous-type screen changer is provided on a breaker plate between a screw and a die to filter polyester (PET) film which is not melted in the extruder while polyethylene and polypropylene are processed to form pellets or extrudates, adding the dried pulverized pieces into the reactor, and separating polypropylene and polyethylene therefrom through dissolution by heating the resulting pulverized pieces in combination with an organic solvent; the organic solvent used in is selected from the group consisting of hydrocarbons, including xylene and toluene, halogenated hydrocarbons, esters, ketones, and a mixture thereof. and

d) recovering an aluminum component, a mixture of polypropylene and polyethylene, and polyester from said separated materials.wherein the separating of polypropylene and polyethylene from the pulverized pieces, which include polyester as the main component and have the high specific gravity, comprises: heating the pulverized pieces in combination with the organic solvent to 70 - 95°C so that polyethylene is dissolved to be separated therefrom, and subsequently treating the remaining pulverized pieces using the organic solvent at 100°C to a

boiling point, so that polypropylene is dissolved to be separated from a undissolved polyester (PET) film layer; or heating the pulverized pieces in combination with the organic solvent to 100°C to the boiling point so that polyethylene and polypropylene are simultaneously dissolved, to be separated from the polyester film layer.

The present method relates to a technique of economically recovering multilayered packaging film waste, which comprises plastic film layers of polyester (polyethylene terephthalate, PET), polypropylene (PP), and polyethylene (PE), and an aluminum layer, so that PET, a mixture of PP and PE, and aluminum are separated to be reclaimed.

Origin:

Recently, multilayered packaging film, which comprises plastic film layers of PET, PP and PE and an aluminum layer, has been frequently used for various purposes, such as moisture proofing and providing an attractive appearance, during packaging of foodstuffs, and use of the multilayered packaging film is continuously growing. The plastic film layers may be subjected to printing, and an adhesive may be interposed between the film layers. When the multilayered film is used for packaging goods, a layering process, including a plurality of steps, and a printing process such as gravure printing, are conducted. In the layering process or the printing process, inferior products may be generated. In connection with this, the inferior products are almost all discarded. Multilayered packaging film wastes may be partially reclaimed without additional treatment. However, since PET, PP, and PE components are mixed in various ratios, and since an aluminum layer is used, it is difficult to conduct processing; as well, physical properties are poor. Thus, they are used only to produce low-grade plastic goods. Additionally, most multilayered packaging film waste that is discarded by homes is not reclaimed, but disposed of by incineration or burial.

Aluminum is reacted with an alkali or acid aqueous solution to be dissolved in an aqueous solution phase. Generally, a reaction rate of aluminum with an alkali is higher than that of aluminum with an acid. The reaction rate depends on the concentration and temperature of the alkali or acid aqueous solution, and on the rate of diffusion caused by agitation. A reaction equation of the alkali aqueous solution, which is demonstrated by sodium hydroxide (NaOH) aqueous solution, and aluminum is as follows.

Al + NaOH + H₂O → AlNaO₂ + 3/2 H₂

In other words, aluminum is dissolved in a sodium aluminate state in the aqueous solution, and hydrogen gas is generated as a result of the reaction.

With respect to the three plastics of polyester (PET), polypropylene (PP), and polyethylene (PE) as main components of a multilayered packaging material, polypropylene and polyethylene are compatible with each other due to their similar molecular structure. Thus, they are mixed with each other to some extent, and physical properties of the mixture are fair. PP and PE are called polyolefins in combination with an ethylene vinyl acetate (EVA) copolymer, polybutylene, and polyisobutylene, and are frequently used for the same purpose due to similar chemical and electrical properties. Currently, reclaimed PP and PE, which are distributed to homes, are mostly used in a form of mixture of PP and PE. However, since PE and PP both have no compatibility with PET, they are not mixed with PET, and physical properties of a mixture of them are poor. Accordingly, in order to reclaim each plastic, it is very important to separate PE and PP from PET.

Exposure of the latest method:

The present technique relates to a method of recovering a multilayered film. The method comprises selectively reacting the aluminum layer of the multilayered film with a solvent to separate it from the film through dissolution so that the multilayered film is divided into two or more layers, separating the layer of polypropylene and polyethylene from the polyester layer using the difference in their specific gravity, and extracting polypropylene and polyethylene from the separated polyester layer using an organic solvent in order to increase the purity of polyester separated with the difference in specific gravity.The method of recovering the multilayered film waste according to the present technique comprises

a) feeding the pulverized multilayered film waste having an aluminum layer into a reactor to treat the pulverized multilayered film waste with a solution for dissolving aluminum so that the aluminum layer is selectively dissolved, to be separated therefrom;

b) separating the pulverized film waste, from which the aluminum layer is separated through dissolution, into a layer of pulverized pieces including polypropylene and polyethylene, having a relatively lower specific gravity as main components, and a layer of pulverized pieces including polyester, having a relatively higher specific gravity as a main component, using a difference in the specific gravity;

c) drying the pulverized pieces, which are separated using the difference in the specific gravity and include polyester as the main component, adding the dried pulverized pieces into a reactor, and separating polypropylene and polyethylene therefrom through dissolution by heating the resulting pulverized pieces in combination with an organic solvent; and 
d) recovering an aluminum component, a mixture of polypropylene and polyethylene, and the polyester from the separated materials.

Multilayered packaging films, which were discarded after distribution in the market are collected, and then were analyzed in view of their components using a differential scanning calorimeter , an X-ray diffractometer, and a solvent-extracting method as described below.

EXAMPLE 1

Six multilayered films, which comprised aluminum layers and were printed for packaging, were cut in a square shape of 3 mm X 3 mm, and the aluminum layers were dissolved in a 10 % sodium hydroxide (NaOH) aqueous solution at 90°C. The time that was taken to completely dissolve each aluminum layer is described in Table 1. After the aluminum layers were completely dissolved, the films were generally divided into two or more layers. The reason the multilayered film was divided into three or more layers is believed to be that an adhesive component interposed between layers, as well as the aluminum, is dissolved by an alkali aqueous solution. After the aluminum layers were completely dissolved, pulverized products were filtered using a sieve, washed with water a few times, and immersed in water having specific gravity of about 1.0 so as to be divided into a layer floating on water and another layer sinking in water. Melting temperature was measured using a differential scanning calorimeter (DSC; Perkin Elmer DSC7) to confirm that the layer floating on water consisted mostly of PP and PE, and that the layer sinking in water consisted mostly of PET. The nondivided pulverized products were classified into the products floating on water and the

products sinking in water according to total specific gravity. The multilayered packaging films used in the present example were roughly classified into two categories: samples 1, 2, and 3 of Table 1, which comprised PET, PP, PE, and the aluminum layer, and samples 4, 5, and 6 of Table 1, which comprised PP, PE, and the aluminum layer. The dissolution time of aluminum in the multilayered film including the PET layer was shorter than that of the multilayered film lacking a PET layer. TABLE 1

Sample	Dissolution time of aluminum (min)	Number of Separated film layers	Layers floating on water	Layers sinking in water
1	5	3	2	1
2	5	3	2	1
3	10	3	2	1
4	30	3	3	0
5	30	2	2	0
6	30	3	3	0

Conclusion:

According to the currently reclaimed method for multilayered packaging film waste, which is conventionally buried or incinerated, can be divided into individual components for restoration, and separated polyester, polypropylene, polyethylene, and aluminum compounds can be used, depending on the purpose, like new products.