Technical solutions for recycling post-consumer agricultural films

• Agricultural films – a challenge for recyclers
• Films account for biggest share of plastics used in agricultural applications
• Market drivers for recycling
• Case studies

The first use of plastic film for agricultural purposes happened in 1948 in an effort to make a cheaper version of a glasshouse. After this introduction to agriculture plastic film began being used at a larger scale around the world by the early 1950’s and replaced paper for mulching vegetables. Since then, plastic films have been designed to increase produce yield and produce size and shorten growth time. Developments in plastic film include durability, optical properties (ultraviolet, visible, near infrared, and middle infrared), and anti-drip or anti-fog effects. UV-blocking, NIR-blocking, fluorescent, and ultra-thermic films have recently been developed to further improve the usage of agricultural films.

Protection of the crops

Weather, animals, microbes, etc. – all can harm the carefully planted and grown crops during the growth season. Agricultural films are primarily used to protect the plants against all kinds of hazards, but also against sun and drying of the soil. This way, water usage can be reduced significantly. Further use of plastic films includes storage and transport of the harvested crops.

In 2013, 510,000 tons of films for agricultural use were sold in Europe, the majority of them in Spain (95,000 t), Italy (80,000 t) and France (55,000 t). Other major users are Germany, the UK and Poland .

Films account for the biggest share of plastics used in agricultural applications, around 70 %, and are mostly made of LDPE. They are used for

• Stretch
• Greenhouse and tunnels (fastest growing)
• Silage, wrapping for bale
• Mulching
• Low tunnels

The market for agricultural film has been experiencing steady growth over the past decade. Generally, growing food demand paired with a decrease in arable land, soil protection to prevent water shortage, and increasing cost efficiency are the major drivers in the use of agricultural films. The rising standards of global farming as well as the global export of products, which requires protective packaging during transport, further add to the growth.

Studies valued the global market for agricultural films at 4 million tons in 2015 and expect a growth at a CAGR of 5.6 % from 2015 to 2030. China emerged as the leading consumer of agricultural film worldwide and accounted for more than 61 % of the total demand in 2012. Asia and Australasia are the regions with the fastest growing demand on agricultural films, followed by Europe, CIS and Russia, and the Americas.

Market drivers for recycling

The growing quantities of film used for agricultural purposes accounts for increasing amounts film waste. As many countries have implemented restrictions for landfilling, the need to recycle the film waste arises. The fact that collection schemes for agricultural films already exist or are being installed in many countries – e.g. in Germany since 2014 and in Spain and the UK by 2015 – makes collection easy and helps to increase the amount of post-consumer agricultural film that enters the closed-loop economy.

Challenges in recycling of post-consumer agricultural films

The recycling of post-consumer agricultural film poses some challenges for recyclers. When the collected materials arrive for recycling, they are mostly a variety of polymers mixed together. Also, contamination is a big issue. As the waste film very often is pressed into bales for transportation, it is hard to determine the type and degree of contamination. Often, there is a lot of organic matter on the film which might already have started to decompose, and possible solid and/or abrasive contaminants must be removed by means of special melt filtration before pelletizing.

Humidity from outside storage and/or washing requires special pre-drying to allow trouble-free further processing. Depending on the moisture content, different drying methods such as venting or air flushing must be employed. Thermic drying is very energy intensive in this case due to the very thin material and the large surface. Also, a significant share of material is lost as fluff in the drying process in the cyclone. If the moisture content in the input material is less than 2 %, it can be processed without venting. A moisture content of up to 4 % requires venting, and if it reaches up to 6 %, air flushing is required. Materials with a very high moisture content – up to 8 % – can be processed on recycling lines equipped with air flushing combined with a reinforced agglomerator drive. A cascade agglomerator allows the processing of materials with an even higher moisture content – up to 15 % is possible.
Flexibility is another important matter. Due to seasonally fluctuating availability of input material the recycling equipment must also allow the processing of other materials such as geotextiles, irrigation pipes, containers, and others in the meantime. In addition, the equipment should be wear resistant and have a high uptime.

Technical solutions for recycling washed post-consumer films

Depending on the quality of the regranulate, recycled agricultural film can be reused in film production or other applications such as extrusion and injection moulding (tubes and pipes, containers, etc.).
Starlinger recycling technology, a business unit of the Austrian mechanical engineering company Starlinger & Co. GmbH, supplies recycling equipment and has already installed a number of recycling lines for applications such as agricultural films. Starlinger’s recoSTAR dynamic recycling lines – the successor of the recoSTAR basic series and on the market since spring 2015 – are especially designed for the processing of highly contaminated and washed post-consumer film. Depending on the requirements of the application the lines can be equipped with various types of degassing units, for example the integrated but independent C-VAC module, discontinuous and continuous melt filters, and four different types of pelletizers.

Maximum degassing capacity and best possible melt filtration

In order to obtain the high quality granulate required for applications such as injection moulding and film extrusion, the melt needs a high degree of purification. Depending on the type and amount of contaminants the melt contains, gas is formed that could cause foaming in the melt and consequently entrapped air in the granulate. Air bubbles in the regranulate generate problems in the subsequent production process, e.g. specks and holes in the produced film, etc. The high-capacity degassing module C-VAC can be combined with any Starlinger recycling extruder. It increases the degassing surface of the melt and thus enhances degassing efficiency, removing effectively all the gases which have formed during the extrusion process due to the composition of the input material. With the C-VAC module, difficult-to-recycle scrap can be turned into high-quality regranulate that is apt for use in a wide range of applications and sells at higher prices. The line concept also allows up-cycling by adding additives – another option that widens the possible usage of the produced regranulate.

Case studies

Case Study 1: Mixed post-consumer waste

Input material:
• washed LDPE film (sometimes up to 40 % of the surface printed); washed PP big bags (sometimes up to 40 % of the surface printed); washed agricultural film
• contamination/humidity: moisture (films: up to 6 %, big bags up to 10 % humidity)

Target:
• Compounding of additives: up-cycling through adding calcium carbonate (CaCO3) powder

Equipment:
• recoSTAR basic 165 VAC

Special features:
• Agglomerator airflush and active air heating
• Two masterbatch dosing units
• continuous rotation filter
• Wear-resistant design of barrel & screw

Regranulate used for:
Five different types of regranulate are produced which are then used for manufacturing various products such as pipes, industrial containers, waste bins, crates, polyethylene films, waste disposal bags, etc.

Case Study 2: LDPE/LLDPE agricultural film flakes

Input material:
• washed LDPE and LLDPE film flakes from 100 % agricultural film
• contamination/humidity: up to 8 % surface moisture, organic contaminants

Target:
• handling high humidity without reducing quality and output rate

Equipment:
• recoSTAR basic 125 VAC

Special features:
• flushing of agglomerator with hot air from the extruder
• single-piston backflush filter with power backflushing

Regranulate used for:
The regranulate is used again to produce agricultural films and waste disposal bags.

Case Study 3: PE film from greenhouse

Input material:
• washed flakes of PE post-consumer greenhouse film waste; LDPE and PP film production waste, highly printed (80 – 90 % of the surface)
• contamination/humidity: minimal

Target:
• handling of high moisture, filtration (because of reuse)

Equipment:
• recoSTAR basic 125 C-VAC

Specials:
• masterbatch dosing units (colour)
• C-VAC degassing
• online throughput and online power measurement for visualisation of kWh/kg

Regranulate used for:
The regranulate is used for producing watering pipes for agriculture.

Case Study 4: LDPE agricultural film

Input material:
• washed post-consumer LDPE agriculture film; PE with PET, PE with aluminium (from laminated cardboard drink containers)
• contamination/humidity: low level (organic contaminations like wood), high humidity – up to 10 %

Target:
• removal of humidity and contamination, processing of different materials

Equipment:
• recoSTAR basic 165 C-VAC

Specials:
• 2 masterbatch dosing units
• wear-resistant barrel and screw
• continuous rotation filter
• C-VAC degassing
• inline throughput measurement

Regranulate used for:
The regranulate is used for injection moulding parts for outdoor furniture.