Atık tetra pak aseptik ambalajlarından karton, düşük yoğunluklu polietilen, alüminyum bileşenlerinin geri kazanımı
Recycling of paperboard, low density polyethylene, aluminium components from waste tetra pak asepti̇k packages
Yazar: ILGIM BALTACI
Danışman: PROF. DR. ONURALP YÜCEL
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Malzeme Bilimi ve Mühendisliği Ana Bilim Dalı / Malzeme Bilimi ve Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: Metalurji Mühendisliği = Metallurgical Engineering

Özet:
Bu tez çalışmasının amacı, dünyada oldukça yaygın olarak kullanılan çok katmanlı ve multi-materyal yapıya sahip gıda ambalajı Tetra Pak Aseptik kutuları oluşturan karton, düşük yoğunluklu polietilen ve alüminyum malzemelerinin birbirinden ayrıştırılması, ayrıştırmanın verimi ve geri kazanım yöntemlerinin araştırılmasıdır. 
Çalışma konusu kapsamında, hidropülp methodu ile Tetra Pak ambalajından selüloz kısmı ayrıştırılmıştır. Selüloz ayrıştırıldıktan sonra geride kalan PEAl fraksiyonundaki PE ve Al fazlarının birbirinden ayrılması için hidrometalürjik ve pirometalurjik deneyler gerçekleştirilmiştir. Elde edilen fraksiyonların karakterizasyonu için FTIR analizi, yüksek sıcaklık altındaki davranışlarını incelemek için TGA ve DTA yapılmıştır. Yapılan deneylerin sonuçları değerlendirilmiş ve alternatif yöntemler incelenmiştir.
Deneysel çalışmalarda kullanmak amacıyla, ev içi tüketim sonrası ortaya çıkan (evsel atık) Tetra Pak aseptik ambalaj atıkları toplanmıştır. Toplanan bu atıklara hidropülp deneyleri, hidrometalürjik ve pirometalürjik metotlar uygulanmıştır. Ek olarak, Kahramanmaraş Kağıt Sanayi tarafından gönderilen endüstriyel hidropülp uygulanarak içerdiği selüloz ayrılmış ve parçalanmış PEAl fraksiyonu bu çalışmanın hidrometalurji ve pirometalurji deneylerinde hammadde olarak kullanılmıştır.
Deneysel çalışmaların ilk aşamasında, Tetra Pak ambalaj atıkları temizlenip küçük parçalara ayrılarak belirli süre suda bekletilerek işlenmeye hazır hale getirilmiştir. Belirli sıcaklıkta su, deney süresi ve öğütme hızı altında yapılan blending işlemi ile ambalaj atığının öğütülmüş yığını elde edilmiştir. Daha sonra yaş eleme sistemiyle belirli aralıklarda elekler kullanılarak karton lapası, PEAl ile karton lapası karışımı ve PEAl fazlarının ayrı ayrı elde edilmesi sağlanmıştır. Fazların kurutulması ile hidropülp işlemi tamamlanmış, selüloz (karton), yanı sıra düşük yoğunluklu polietilen-alüminyum (PEAl) fazları ayrı ayrı elde edilmiştir. 
Deneysel çalışmaların ikinci aşamasında hidrometalurjik deneyler gerçekleştirilmiştir. Bu kapsamda TS 886'ya uygun bitkisel yağ içerisinde PE ve Al katmanlarının birbirinden ayrılması işlemi üzerine çalışılmıştır.  Deneyler manyetik karıştırıcılı ısıtıcı kullanılarak yapılmış olup farklı sıcaklıklarda, sürelerde ve karıştırma hızlarında LDPE ve Al katmanlarının birbirinden ayrılma performansı incelenmiştir. Deneyler sonucunda LDPE ve Al bileşenlerinin ayrılma durumuna göre en verimli deney parametreleri saptanmıştır. Artan sıcaklık ve sürenin katmanların birbirinden ayrılmasına olumlu etki ettiği gözlenmiştir. Çözücü olarak yağ kullanıldığı için sıcaklık belli bir değere kadar yükseltilmiştir.
Deneysel çalışmaların üçüncü aşamasında piroliz yöntemi uygulanmıştır. Hidrometalurjik yönteme alternatif olarak, yüksek sıcaklıkta polietilenin buharlaştırılması ile Al metal fazı elde edilmesi amaçlanmıştır. 2 ayrı piroliz çalışması yapılmıştır, ilkinde açık atmosfer altında sıcaklık (400, 500, 600°C) ve sürenin (2, 3, 4 h) çeşitli kombinasyonları ile ilerletilmiştir. İkinci piroliz çalışmasında PEAl nikel tepsiye yerleştirilerek kül fırınına çeşitli sıcak ve süre kombinasyonları altında içerdiği LDPE'nin buharlaşması sağlanmıştır. Her iki metodolojinin (hidrometalurjik ve pirometalurjik) son ürünü olan ayrılmış fraksiyonlar (LDPE ve Al) XRF, XRD ve FT-IR yöntemleri ile karakterize edilmiş, termogravimetrik davranışları TGA, DTA ile incelenmiş ve geri kazanım verimlerine etki eden unsurlar incelenmiştir. 
Tetra Pak aseptik ambalaj atıklarının içerdiği selülozik kısım hidropülp işlemi ile verimli bir şekilde PEAl katmanlarından ayrılmıştır. Hidropülp işleminin ardından elde edilen PEAl fraksiyonunu oluşturan LDPE ve Al malzemelerini birbirinden ayırmak için hidrometalurjik çalışmalar yapılmıştır. Bu metotta PEAl parçaları 140ºC, 100 rpm karıştırma hızında ayçiçek yağında deneye alınmıştır. İşlem sonucunda Al fazında yüksek miktarda LDPE içeriğine rastlanmıştır. Hidrometalurjik yola alternatif olarak yapılan piroliz deneylerinde 400, 500 ve 600°C sıcaklıkların her birinde numuneler 2,3 ve 4 saat açık atmosferde yüksek sıcaklıkta bekletilmiştir. Bu işlem sonucunda LDPE'nin Al'den uzaklaştırılması başarıyla sonuçlanmış ve bunun için optimum koşullar 500°C'de 3 saat olarak belirlenmiştir.

Abstract:
The aim of this study, to separate the fractions of Tetra Pak aseptic package which are paperboard, low density polyethylene, aluminium, to observe the separation efficiency and to investigate recycling and regaining methods. At the end of the analysis these topics and alternative methods were evaluated.
Situations such as increase in population, changes in consumption habits, increase in living standards cause an rise in the sales of packaged consumer goods, as well as changes in the composition of solid waste. When the results of this state of affairs are examined in general; packaging wastes including paper-cardboard, plastic, glass, metal, wood, composite packaging, constitute 20 % by weight and 50 % by volume of this solid waste. According to the researches, in developing countries the content of solid waste consists of mainly from households, markets and commercial areas. As it is stated in the publication of the United States Environmental Protection Agency, 28.1% of the total solid waste generated in 2018 consists of container and packaging wastes. Paper and cardboard-based container waste, containing cardboard-based aseptic beverage packaging, constitutes 14.3% by mass of the total solid waste generated.
Food package is defined as materials that ensures protection of food product from outer factors such as environmental contamination, shock effects, temperature, physical damage, light, microorganisms, moisture, oxygen and facilitate the transportation and storage of food throughout the entire process. Most of the food products are sent to different regions in a short time after their production, and all of them have different shelf lives; so, it is important taking into consideration criteria such as food quality, shelf life and freshness while preserving the food product properly.
The aforementioned today's life conditions determined by developing technology and the changing consumption habits have some positive effects on food industry in terms of packaging as the quality and physical safety of food, logistics and market display, and ease of consumption. Multi-layer packaging is a comprehensive example that has emerged by combining the functions of various materials to offer the industry a package with enhanced performance, protection and durability. By the help of with these features, multi-layer packages ensures that high quality and fresh food products reach to the consumer reliably. Because of its production technology, it protects the products and extends the shelf life of foods while keeping them sterile. Multi-layer packaging combines the beneficial properties of each layer to offer increased barrier and functional features and mechanical integrity as a single formation. The primary function of the inner layer is sealing, while that of the outer layer is abrasion resistance, hardness, printing (design) and in some cases moisture barrier properties. The middle layer provides various functional benefits such as oxygen and light barrier. Multi-layered food packaging consists of at least three and at most seven layers.
Tetra Pak packages which are multi-layered composite materials (approximately 75% cardboard-cellulose, 20% LDPE and 5% Al by weight) facilitate the distribution of particular food products and aid to preserve some food properties for a long time via aseptic production technology. Materials forming Tetra Pak Aseptic have their own characteristic features that enhance the last package specification such as cellulose gives a rigid form and improve the resistance of the package; low density polyethylene prevents the contact and interaction between paperboard layer and environment and also aluminium layer and food product in Tetra Pak. Moreover, by the help of heat during production of the package, LDPE laminates the layers. The barrier properties against oxygen, water vapour, light, aroma makes the aluminium layer unique. As well, due to its composite structure, these materials are more complicated to recycle than mono-material packages. In this aspect, the environmental awareness, the increasing importance of sustainability in the industry and the concepts of circular economy have also influenced the food packaging industry heavily.
The most common definition of "sustainability" uses three interrelated concepts which are economic, social and environmental (or ecological) factors or with the other word, targets. This triad is presented as an intersecting circle of society, environment and economy, and sustainability stands out at the intersection of these perspectives. In 1987, the United Nations Brundtland Commission defined sustainability as "meeting the needs of the present world without compromising the ability of future generations to meet their own needs". Recycling is the process of transforming the materials to be disposed of as garbage into new raw materials by subjecting them to physical (mechanical) or chemical processes after they are collected and separated. Physical recycling basically consists of the stages of collection, classification, cleaning and grinding of the material. Depending on the source and composition of the waste, the steps may take place several times, in different order. Chemical recycling has high potential for heterogeneous and contaminated waste material where separation is not technically feasible.
When recycling types are examined in detail, primary recycling which includes reprocessing the waste material and using them for their original purpose, clearly is not appropriate for regain of Tetra Pak aseptic packages. Reuse of a material after the recycling process in different domains that have no requirements of the original raw material properties, is secondary recycling. This method is commonly used for separated cardboard material in paper products. Converting the waste material into new various products by breakdown into its chemical components is tertiary recycling. The last sort is quaternary recycling meaning that energy recovery by burning waste product; while this method is the most unwelcomed recycling, regrettably it is a prevalent method in Turkey.
In most cases, Tetra Pak waste recycling is only possible with energy recovery or to process wastes into low quality products, if hydropulping is not an option. Here, what is meant by energy recovery could be incineration, gasification or pyrolysis and sometimes it includes municipal solid waste mixture.
In this study, experiments were proceeded to separation of the layers of Tetra Pak aseptic packages efficiently from each other and their recycling. 
Hydropulping process were carried out for the separation of the celluloses part which is paper for this material; then, hydrometallurgical and pyrometallurgical treatments were followed through for partition of polyethylene and aluminium, which are PEAl fractions, from each other.  The hydropulping process was applied in two stages; at first, the separation process was applied on the Tetra Pak aseptic packages. The packages without lids were cleaned from food wastes, cut into small pieces and kept in water, afterwards, pieces were chopped via blender with water, the mass was sieved under water with three-layer sieve system. At the end, separated fractions on sieves were collected and dried in oven. 
The second part of the hydropulping process was for PEAL fraction which was collected from the sieves. The fraction was chopped and sieved under water again in order to decrease the size of PEAl pieces and extinguish all of cellulose; then, the fractions were dried again. Experimental studies were pursued in hydrometallurgical and pyrometallurgical routes to separate LDPE and Al from each other. In hydrometallurgical pathway, PEAl samples were put in vegetable oil, appropriate to TS 886, observed according to increasing temperature, time and solid/liquid ratio parameters, at the end the LDPE and Al phases were purified. The pyrometallurgical studies, which is pyrolysis, was carried out with various time and temperature combinations, and efficiency of Al recovery from PEAL fraction were investigated.
At the end of the experiments, the separated fractions which are end products of both methodologies were characterized by means of XRF, XRD and FT-IR methods, their thermogravimetric behaviours were investigated by TGA, DTA and, the recovery efficiencies were calculated. Tetra Pak aseptic wastes were separated from the cellulose part first with the hydropulping process efficiently. As a second step, in hydrometallurgical route PEAl part of the waste was put in a vegetable oil which is sunflower, to separate PE and Al fractions at 140ºC, 100 rpm stirring. At the end of this route, it was seen that in the Al phase there is high amount of LDPE remaining. PEAl samples were pyrolyzed for 2, 3 and 4 h at 400, 500 and 600°C. PE-free Al was produced successfully by pyrometallurgical method. The optimum conditions were chosen as 3 h at 500 °C.