Lesson- 31 Recycling of packaging

30. Introduction

Materials plays an increasing role in packaging and numerous applications can already be found in the market. Ten or twenty years ago most post-consumer packaging waste was going into landfill sites or to incineration. Traditionally, only glass and paper/board were recycled into new applications. In the case of packaging plastics the situation is quite different. Only uncontaminated in-house production waste was collected, ground and recycled into the feed stream of the packaging production line without further decontamination. With increasing environmental demands, however, post-consumer plastics packaging materials have also been considered more and more for recycling into new packaging.

But recycling of packing plastics is also a question of recycling technology and collection of packaging waste. Today many countries have established collection systems for post-consumer packaging waste, like the green dot systems. Such country-wide collecting systems guarantee increasing recovery rates. Together with new developments of recycling systems and with increasing recycling capacity the way is open for some plastics for a high value recycling of packaging waste. Due to health concerns most of the recycled post-consumer plastics are going into less critical non-food applications, but in recent years there have also been efforts to recycle post-consumer plastics like PET into new food packaging applications.

30.1. Recycling technology

Today a considerable diversity in recycling technologies can be found, although all of them have the same objective which is to clean up post-consumer plastics. Most of them first use a water-based washing step to reduce surface contamination and to wash off dirt, labels and clues from the labels. The material is also ground to flakes during one of the first steps in the recycling process. In most cases these washing steps are combined with separating steps where different materials like polyolefin’s of PET are separated due to their density. It is obvious, that the cleaning efficiency of these washing processes is normally very different, depending on time, on hot or cold water-based washing or depending on the detergents added to the washing solution. However, typical washing processes are able to remove only contaminants from the surface of the polymers. They are not able to remove organic substances which have migrated in the polymer. Therefore the purity of washed flakes is usually not suitable for closed-loop recycling. A simple remelting or re-extrusion of the washed fakes has an additional cleaning effect; however the purity is usually not sufficient for reuse in the sensitive area of food packaging. Three types of recycling are possible for packaging: mechanical, chemical, and biological.

30.1.1. Mechanical Recycling

The most common type is mechanical recycling, involving reprocessing of recycled materials through physical steps that can include cleaning, shredding/grinding, separating, and reforming. These steps result in metal and glass containers that are acceptable for use with foods. However, they generally do not ensure removal of all possible contaminants from paper and plastic materials to allow use of the recycled-content package with foods involving long-term contact. The FDA reviews food contact applications of these recycled materials on a case-by-case basis that includes consideration of source control to ensure cleanliness, recycling process ability to remove possible contaminants, and the proposed food-contact application(s). FDA has approved several food-contact applications of mechanically-recycled plastics, including HDPE grocery bags, PS egg cartons, HDPE and PP crates for transporting fresh fruits and vegetables, and PET pint and quart baskets for fresh fruits and vegetables. All these applications involve a limited time and area of food contact at ambient and refrigerated temperatures, along with expectation that the food is normally cleaned before use or that the food is protected by a barrier (e.g., egg shell). FDA has also approved use of recycled plastic when it is co-extruded with a virgin layer of the plastic that is the food-contact surface.

30.1.2. Chemical Recycling

Chemical recycling involves depolymerization of plastic polymers to monomers or oligomers and then repolymerization to the polymer. This process allows removal of all possible contaminants, with the repolymerized polymer identical to virgin polymer. Several processes have been developed for chemical recycling of PET. An ideal plastics recycling process would take mixtures of plastic and convert them at high temperature and pressure to an economical petrochemical process stream.

30.1.3.   Biological Recycling

Polymers based on renewable resources can be grouped into three categories.

  • Polysaccharides and proteins extracted from plant, marine or animal sources (e.g., starch, chitosan and whey protein)
  • Polymers synthesized from renewable, bio-derived monomers (e.g., polylactate)
  • Polymers produced by microorganisms (e.g., polyhydroxyalkanoates)

Many of the same polysaccharides and proteins being explored for edible films and coatings are also candidates for biodegradable packaging. Biodegradable polymers are generally more expensive than synthetic polymers. Biodegradable packaging must be stable and function properly at the conditions of use, so as not to compromise the quality and safety of the food, and then biodegrade efficiently upon exposure to the appropriate microorganism(s) and environment. Biological recycling must also compete with mechanical and chemical recycling concepts that allow reusing materials rather than degrading them. Finally, biodegradable polymers must be made easily distinguishable from nonbiodegradable polymers so as not to interfere with the mechanical and chemical recycling processes. Reasons for considering use of a biodegradable polymer for packaging include.

Life of the packaged product is short

Mechanical or chemical recycling is not feasible

Biological recycling is favored by consumers

Biodegradability is legally mandated

The numbers of biodegradable packages have been developed for a number of foods are as follows:

  • Pulp containers for fruits
  • Wood pulp-starch trays for fresh beef and chicken
  •  Nitrocellulose-coated cellophane films for cheese, fruits, and confections
  •  Starch-based foamed shells for hamburgers and sandwiches
  •  Starch-based grocery bags

 Polylactic acid (PLA) bottles for water and tubs for fresh-cut produce and salads

Other possible food applications being explored for biodegradable polymers include fast-food containers, cups, plates, and cutlery.

Last modified: Wednesday, 3 July 2013, 9:48 AM