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Optimisation of Recycling of Plastics Process Waste

Summary and conclusions

• Background and purpose
• The project
• Project results

The possibilities for a better utilisation of discarded process materials (process waste) from the plastic industry has been studied in a co-operation between the Danish Plastics Federation and Danish Technological Institute.

The project has shown that a considerable sum of money can be saved by recycling discarded process materials either as secondary materials for the production in the company, by selling the material for recycling elsewhere or by thinking in untraditional ways of recycling.

Background and purpose

In the manufacturing of different products of plastics there will always be a certain amount of waste of process materials originating from the running-in period of machinery, cut off pieces and punch out pieces, errors in production, discarded products from quality control etc.

The possibilities of recycling the process material depend on a number of factors including how precise the composition of the waste and the purity of the material can be described. It is more likely that the composition of the waste can be well described if the waste is collected close to the actual process where it originates.

The raw material for plastic production may contain a number of additives which in certain circumstances may have a significant influence on the possibilities for recycling.

For thermoset plastics like polyurethane it is not possible to re-melt the plastics as it is a big three-dimensional molecule. However, recycling can be performed by appropriate downsizing of the process material. The possibilities of recycling in different products depend on the quality obtained after the downsizing.

For production of expanded polystyrene (EPS) the recycling of externally collected packaging material is relevant in connection with obtaining an increased recycling. This is also of importance regarding the new demands for recycling in the Eu directive for packaging waste where the recycling will have to be increased to 22,5% on 31.december 2008

Most producers of plastic products recycle a part or even all their process material internally. However, in a number of circumstances the recycling is not optimised for different reasons. An example could be that the upper limit of addition of secondary process material is not known. Another example could be that the process material is complex and therefore difficult to recycle internally.

For a number of products like packaging material for foods or products for medical purposes, specific demands exist in connection with recycling of process material.

An overview of norms and regulations which companies have to obey in connection with recycling of process material is lacking.

The overall purpose of the project has been to map amounts of discarded process material divided after type and production process and at the same time study the possibilities for reducing consumption of resources in the production of products of plastics by optimising the recycling of discarded process material either by internal or external recycling.

The project

The project has been performed in co-operation between the Danish Plastics Federation (later called PD) and Danish Technological Institute. From PD eight companies have participated in the project. The companies represent the different processes and types of material which are used for producing typical products in the plastics industry.

The project results have been presented at a workshop and at a conference in 2003.

During the project a guidance on recycling of process materials for the plastics industry has been prepared and a draft for ideas to a contact forum for recycling of process materials has been proposed.

The guidance includes discarded process materials of thermo-plastics as well as thermoset plastics. Apart from this, the recycling potential of externally collected EPS packaging waste is included in the guidance. The guidance is based on the practical experience obtained in connection with the experimental and developmental work performed in the project and on the answers to questionnaires sent to 50 plastic producers.

The guidance includes decision trees which make it easy for the users to obtain an overview of technique, economy and possibilities for recycling of a given plastic fraction.

Main conclusions

In connection with developmental work focusing on an increased recycling of EPS-waste in new products, it has surprisingly been found possible to recycle up to 30% external EPS waste in new products without consequences for the mechanical properties when compared to products based on virgin EPS. This is an important recognition in relation to the demands for recycling in the EU directive for packaging waste.

During the research and developmental work performed in the project, the suitability of new recycling methods has been demonstrated, and the possibilities for using untraditional solutions for the use of complex discarded process material have been pointed out.

The project has demonstrated that producers of plastic can save expenses for deposit or incineration and at the same time save expenses for virgin material by recycling the discarded process material.

The project has shown a considerable interest in a contact forum for buying and selling process materials if possible placed on PD's homepage. Ideas for such a solution have been produced.

The project has contributed with new knowledge on:

• Amounts of process material divided after type of material and process of production
• Status for the European work in norms for recycled materials of plastics
• Simple test methods
• The possibility for use of recycled process material by mixing with new raw material
• The possibility for using new recycling technologies
• The possibility for recycling discarded process waste which originates from complex products

Project results

The survey
A survey of amounts and composition of discarded process material in the plastic industry has been performed by Danish Technological Institute and the Danish Plastics Federation. Results for amounts of discarded process materials and the used treatment are shown in Table 0.1.

Table 0.1 Discarded process material and treatment

The amounts in the table are based on a questionnaire where companies were requested to specify amounts in pre-defined logarithmic ranges. Therefore there is some uncertainty on the given amounts. Questionnaires were sent to 50 companies and 25 answers were received. The companies were selected from a larger survey where they had stated that recycling of discarded process material had a high priority and that the amount of discarded process material was larger than 5%.

Table 0.2 shows amounts distributed on production processes. Nearly half of the process materials originate from extrusion processes. The survey also showed that more than 50% of the process materials were based on polyethylene (PE) og polypropylene (PP).

Table 0.2 Weight based distribution of discarded process material on production processes

Handling of discarded process materials
When a company wishes to recycle discarded process material, it is very important that the handling of the process materials from which they originate till they are recycled is well planned.

There are some clear messages to the industry regarding handling of discarded process materials if they are supposed to be recycled:

• Handle and store the discarded process materials as if it was virgin material
• Make it simple for the personnel to keep different materials apart
• Apply a good and simple logistic for the discarded process materials
• Motivate and instruct the personnel regarding good hygiene when in contact with discarded process material.

The project has shown that it is important to keep the discarded process material clean as dust, moisture and impurities like sand and earth make recycling to quality products impossible. It is also important to avoid mixing of different types of plastics or colours as this may make recycling impossible or more difficult.

It has also been shown that it is difficult to recycle complex discarded process material based on two or more different types of plastics or other materials. However, by looking into untraditional areas of utilisation there may still exist interesting possibilities for recycling.

In the project a guidance for the plastic industry has been prepared with good advise on recycling of process materials. The guidance is based on decision trees which lead the user through a number of decisions necessary for choosing the optimal solution in consideration of environmental and economic issues.

The guidance also describes some simple test methods which can be used in connection with the assessment of process material.

The status of the European work on norms in CEN regarding methods for characterisation of recycled plastics is also described.

Activities at the participating producers In the project has been focused on a number of actual recycling issues in relation to the participating companies.

It has very positively been shown that quite high amounts of external EPS-packaging waste can be added to virgin material after downsizing without problems with the mechanical strength of the products. The influence of different additions on E-module and compressive strength is shown in Table 0.3.

Table 0.3: Experimental results from Danish Technological Institute.

1 Numbers en paranthesis represent the standard deviation for the measurement

Within the group of thermoset plastics, a number of experiments regarding recycling of discarded process material from polyurethane based products to new products has been performed. Experiments have been performed with re-feeding of the material in the reaction casting process, embedding in rubber, and embedding in polyurethane. Most promising have been the experiments with embedding in pre-polymerised icocyanate/polyole.

Experiments have been performed with mixed polypropylene granulate in different colours for production of buckets. Here it has been shown that it is possible to obtain nice buckets by recycling of white granulate with print on one side by optimising the casting parameters. This has not been possible with the very coloured mixed granulates. However, a demonstration of separation technologies based on colour sensors and nozzles with pressurised air showed that it was possible to separate a selected colour to a purity of 99.9% using two sorting steps and particle sizes from 2-6 mm.

A number of downsizing experiments have been performed on different granulators. The downsized material includes material based on complex products with several layers. For these types of material possibilities of untraditional use have been suggested for the downsized fractions.

Finally, experiments with a better sorting of discarded process material have been performed. The experience helped increase the degree of internally recycled material.

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Version 1.0 Juni 2004, © Miljøstyrelsen.