Food grade recycled polypropylene (rPP) in packaging
WRAP is working in partnership with industry to develop a viable process to recycle post-consumer PP packaging waste into rPP suitable for use in the manufacture of new food packaging. The reports below provide an update on the progress made so far and the remaining challenges to overcome.
PP is used in a wide range of food and non-food packaging such as pots, tubs and trays. Retailers and brand owners want to be able to use rPP in new PP food packaging in order to realise the environmental benefits in the same way that they can with rHDPE (recycled high-density polyethylene) and rPET (recycled polyethylene terephthalate).
There have been technical barriers to achieving a food approved rPP material, as well as perceived risks and lack of evidence around the economic and technical viability of recycling PP to food grade quality in the UK.
WRAP is working in partnership with industry to address these barriers and has completed four phases of work so far.
Phase 1 – scoping study
WRAP tested whether a recycling process already used to produce food grade rHDPE in the UK could be adapted to recycle PP to meet food grade approval.
an automated process needs to be developed to sort food contact from non-food contact as hand sorting of food contact is not cost effective;
the food grade recycled PP can be both thermoformed and injection moulded and therefore is suitable for use in the common PP conversion processes; and
it has been possible to clean the PP in certain applications but an improved cleaning of heavier contaminants is required.
Phase 2 – development of a food grade recycling process for post-consumer PP
The aim of this phase of work was to develop a food grade recycling process that could decontaminate post-consumer PP packaging waste to the standards required by EU regulations for food contact and cope with the wider range of materials encountered in the post-consumer PP packaging stream.
A range of high performance processing and decontamination techniques were evaluated and a process consisting of two technologies combined was found to produce material that could be suitable for use in a wide range of food packaging applications.
Phase 3 – further development and testing of the recycling process
The work we carried out in this phase had three strands.
A) Polypropylene packaging market data
WRAP carried out an assessment of the UK market for PP packaging and estimated the amount of PP packaging waste that could be available for a food grade PP recycling process in the UK. The report provides a breakdown of the PP packaging market by type and discusses key aspects of PP packaging and their impact on food grade recyclability.
B) Decontamination of UK PP packaging waste
WRAP carried out decontamination trials on the process identified in Phase 2, using real PP packaging waste from UK households. Sample packaging was manufactured using rPP from this process and food grade testing was carried out. This work indicated that rPP could be used in a range of food packaging.
C) Sorting plastic that has previously been used with food
In order for food grade rPP to be produced in the UK, a technically and commercially viable automated solution is required to sort packaging that has been used with food from that which has not, because food grade recycled plastics must be made from >99% food contact raw material. This project determined that a marking and detection technique could be developed to identify food contact plastic packaging in recycling plants.
This work included an investigation into whether the use of lasers to identify diffraction gratings in packaging could potentially be used to sort packaging that has been used for food. This technique is also discussed in a 'diffraction grating – proof of concept’ report.
Phase 4 – further analysis of decontaminated rPP, and diffraction gratings
WRAP carried out further research and development work, which involved carrying out additional testing of decontaminated rPP to further assess its suitability to produce a food grade material, and researching sorting techniques identified in Phase 3.
Further analysis of the decontaminated rPP was undertaken to establish whether there were any substances of concern remaining in the material produced in Phase 3. This has answered remaining questions around its suitability for use in food contact applications. The research found that the two resins analysed (clear and white) are compliant for food use according to regulations used in the EU and USA.
It is hoped that these results will provide confidence to the packaging and recycling industry to continue to develop and commercialise a food grade recycling process for post-consumer PP packaging, using the testing methodology presented in the report.
Research has also shown that diffraction gratings could be an effective and economical way to identify food contact packaging. Recommendations for further work are provided in the report. WRAP will continue to work with the sector on identifying packaging that has been in contact with food as the technology investigated needs further research and development, and it has wider application to food grade plastics recycling in general (i.e. could also apply to PET and HDPE as well as PP). This therefore has the potential to be used by a range of food grade plastics reprocessors.
Phase 5 - Optimising the use of machine readable inks for food packaging sorting
Since the work with diffration grating was considered too expensive to be invested at this stage by the technology providers, further work looking at an alternative and economically viable solution was required.
The objectives of this work were to investigate and develop the use of machine readable inks that could be applied to the broadest range of materials and packaging types. This would assist identification of different types of polymers during sorting and recovery for recycling.
Fluorescent ink was identified as a suitable solution as it can be added and applied to existing products by conventional means. The material cost for the additional labelling was estimated as a fraction of a penny (0.003 to 0.108p per label). Required modifications on existing sorting equipment was also considered minimal. The sorted material achieved over 99% purity. Further tests will be required to identify what happens with the ink after reprocessing (e.g. if remains visible or is removed). For further information please read the project report.