EXECUTIVE SUMMARY Stretch wrap2

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					                           EXECUTIVE SUMMARY



             Recycling Post-Consumer stretch Wrap Film



Literature Review


• Significant quantities of stretch wrap film is used to stabilise palletised products
   throughout the materials handling industry. The estimate of usage in Australia is 16,000
   tonnes are produced locally and 1,500 tonnes is imported as roll stock. Further film
   enters Australia as wrap around goods being imported



• Stretch wrap film is usually Linear Low Density Polyethylene (LLDPE) that has been
   compounded with a tackifier, usually 5% Polyisobutylene, (PIB) to ensure the film clings
   to itself when wrapped around goods. It is usually a thin film (20 microns) that is
   stretched to at least 300% in wrapping pallets or boxes making it even thinner ie less than
   10 micron.



• The unpigmented nature of the film makes it attractive to recycle however recycling is
   inhibited by the sticky surface that collects contamination and the tackifiers that make the
   unwrapped film difficult to handle and shred to size due to the rubbery nature of the
   material. Labels, other films and strapping often present difficult sorting challenges.



• Recycling of stretch wrap film has been developed by various companies in the USA
   such as Dow and Mobil where the film has been recycled into hand stretch wrap film,
   garbage bags and injection or blow moulded containers. Rubbermaid and Tucker
   Housewares produce waste bins from recycled PE blends. Mobil developed plastic
   lumber made from 50/50 stretch film and sawdust for outdoor applications.



• In Australia stretch wrap film is not recycled in large volumes however it is used as a
   component of plastic pallets by Vicfam and is used as a component in “builders film”
   which is used as a heavy gauge moisture barrier in building construction. The market
   price of waste stretch wrap film is usually low eg $100-150 per tonne and the finished
   recycled LDPE resins sell for approx $750 per tonne.



• Attempts to reuse stretch wrap film back into stretch film have not been successful when
   the film has come from post-consumer sources due to contamination. Recompounding of
   industrial film scrap is conducted by use of batch wise agglomerators that can densify the
   thin film into a popcorn-like particles that can be handled by conventional extruders and
   moulders. This process is slow and requires a skilled operator to control the process
   making the economics of recycling unattractive. Modern equipment has been devised by
   companies such as Sorema that operate on a continuous basis and remove the majority
   of contaminants, however processing rates a slower than for heavier gauge films.
Factory Scale Trials of Recycling of Stretch Wrap Film


Visy have installed a modern recycling plant for the washing and extrusion of Polyethylenes,
including LLDPE, LDPE and HDPE in the form of film and bottles.



The plant consists of the following:

1. Presorting area for inspection of infeed film.

2. Infeed conveyor that delivers the material to a Shredder.

3. A Shredder to reduce the film to small, free flowing pieces approx 100 mm square to
   facilitate removal of contamination

4. An inspection conveyor where contaminants can be removed.

5. A Wet Grinder that further reduces size to 10mm square and simultaneously washes off
   dirt and pulps paper labels.

6. A washing tank to further clean the film

7. A separation tank to remove heavy contaminants and plastics more dense than water
   such as PET, Polystyrene and PVC.

8. Centrifuges to separate the film from water.

9. Drying loops to dry the film .

10. An extruder that feeds the film via an agglomerator chamber to the feed throat of the
   extruder.

11. A pelletiser that cuts molten strands of LDPE and converts them into cylindrical pellets
   3mm in diameter and length.



By conducting four formal trials of processing stretch wrap film as well as many

on-line observations when stretch wrap film was present in high concentrations, the following
conclusions were reached:
1. Stretch wrap film is very difficult to shred due to its highly elastic nature. The film would
   often wrap itself around shafts causing throughput problems.



2. The film sourced from recyclers was frequently contaminated with PP strapping,
   multilayer LDPE/Nylon film, packaging tape and paper labels.



3. The grinding of film to smaller particles required a sharp set of blades to function on the
   stretchy film. The screen size had to be reduced from 22mm to 16mm and consequently
   the output of the grinders was reduced from 1500 kgs/hr (when running HDPE bottles)
   to a maximum of 300 kgs/hr due to the low bulk density of the film.



4. The fine gauge film ( 10 micron) was extremely difficult to wash, rinse and dry using the
   plant at Visy which was designed to run film at a rate of 800 kgs/hr. Drying was
   particularly problematic with up to 15% moisture being left with the film after the
   maximum drying conditions were applied. An additional drying loop was purchased to
   improve the drying effect however the moisture was reduced to 7% which still causes
   extrusion problems.



5. The extrusion of the film was made difficult by the light bulk density of the film (approx
   300 kgs/m3) and the residual moisture in the film. Both of these factors inhibit the feeding
   of the film into the extruder limiting the output of the extruder from 1300 kgs/ hr on
   HDPE bottle flake to 200 kgs/hr on the film. The low bulk density makes it difficult to fill
   the flights of the screw at the feed section of the extruder and the moisture in the film
   creates steam and causes a back pressure in the melt which inhibits the positive feeding
   of the incoming material.
6. The energy intensity of the agglomerator was increased by the use of elevated knives on
   the rotor of the agglomerator. This increased the output from 200 kgs/hr to 220 kgs/hr
   which was still a long way from the capacity of the extruder.

7. The product of the trials was used in builders film as a 10% blend along with 10% HDPE
   and with 80%of LDPE. This product was tested and found to meet the strength and
   impact requirements of building film.



8. The use of higher levels than 10% of stretch wrap film caused problems in “blocking” ie
   the adhesion of two layers of film together as well as weakening the film due to the effects
   of higher levels of the tackifier (PIB). The tackifiers’s effects can be countered by the use
   of antiblocking additives however these are considered too expensive for general use at
   the levels required in stretch wrap blends.



9. The overall conclusion reached in processing Stretch Wrap film in Sorema recycling
   equipment was that the output was reduced to 25% of the capacity of running film in the
   equipment used at Visy Plastics. The extrusion equipment was reduced to 17 % of its
   maximum capacity. Both of these effects illustrate that stretch wrap film requires
   equipment that can handle the problems of low bulk density and can process the film in
   the dry state. Such equipment is available from Sorema and Erema in the form of
   agglomerators that work by semi-melting the film and forming rough granules that can be
   processed at higher extrusion speeds.




Laboratory Scale Trials of recycling Stretch wrap film into stretch
wrap film.


Trials were conducted at RMIT’s Polymer Technology Centre on small scale extrusion
equipment as well as a plant size Reifenhauser film line. Investigations were conducted to
evaluate if recycled stretch wrap film resins produced by Visy Plastics could be blended
with virgin resins to produce useable stretch wrap films.

The following conclusions were reached from this study.

1. Residual film flake from the Visy washing system still had traces of caustic soda from the
   washing steps due to the high surface area associated with the film.



2. The Melt Flow Index of the recycled film was 0.76 grams per 10 mins which is less than
   the common stretch wrap film resins (0.9)indicating that some crosslinking was present
   due to the recycling process.



3. The level of gels in 100% recycled film was very high limiting the production of blown
   film to blends with virgin otherwise pinholes and other defects would be present. The
   level of gels was measured to be between 0.5% to 1.5%.



4. The use of antioxidant masterbatches did not reduce the incidence of gels in the film.



5. Reasonable film properties and appearance was achieved when at least 50 % of the
   blend was made from virgin resin.



6. Additional PIB was needed to restore the tack need Film made from virgin resin could
   be stretched at a wrap tension of 10 kg of force up to an extension of 600% with a
   maximum stress of 31 kgf.



7. Film made from 50/50 virgin/recycle plus 5% PIB could not be stretched at 10kgf of
   wrap tension due to failure at the numerous gels present. Stretching at 5kgf tension
   achieved an extension of 200% and at 3kgf extension of 300% was achieved.
8. Film made from 100% recycled film could not be stretched even at 1kgf tension due to
   the failure of the film at the numerous gels present.

9. The conclusion of the laboratory studies into making stretch wrap film from recycled
   stretch wrap is that it is possible to make a grade of film that is suited for Hand Wrap
   applications where low tensions and low stretch are used. To achieve this all of the
   problems of processing and purification need to be overcome. The hand wrap film will
   use typically double the amount of film to secure a load to a pallet due to the lower forces
   applied and the less stretch used on the film. This decreases the economics of using
   recycled film even further when compared to virgin film. The final cost of the recycled film
   was estimated to be $4/kg against $2.20/kg for virgin film. This emphasises the difficulty
   in developing the market in stretch film from recycled film.

CONLUSIONS AND RECOMENDATIONS
• Stretch wrap film demonstrates that it is problematic to recycle from a technical
   viewpoint due its tendency to collect contamination, its thin gauge, and the presence of
   the tackifier, PIB

• The opportunity to recycle Stretch Wrap film into Hand Stretch Wrap film is limited due
   to the low rate of reprocessing on recycling equipment and the subsequent high cost of
   the finished product.

• The presence of gels needs to be overcome to allow a useable film to be manufactured.
   Technological innovation to multilayer films that do not use PIB but use metallocene
   catalysed very low density LLDPE as a tacky surface may provide an improvement in
   the recycling of these films. Coordination with the major producers of the films may
   accelerate the investigation and application of this approach.

• The markets for Stretch Wrap films are currently as blends with other polyethylenes in
   applications such as builders film and pallets where it can be used as a 10- 15%
   component. The penetration of stretch films in these markets is not quantified and
   potentially the products could absorb larger quantities. Further applications such as these
   need to be developed in order to increase the end markets for this ubiquitous and rapidly
   growing packaging medium.
• An investigation of equipment dedicated to the processing of stretch wrap film into pellets
   may allow the processing economics to be reviewed and improved beyond those
   revealed by this study.

• A major deficiency of the current recycling strategy for these films is the lack of
   information supplied to users on how to deal with used films and the need to keep the
   films uncontaminated as much as possible.

• The development of plastic labels from LLDPE or HDPE would greatly assist in
   minimising contamination.

• The ideal scenario for recycling Stretch Film would be a closed loop service where used
   film would be collected as new film is delivered. This would capture much of the film
   since most users also have material that will have been used in previous packaging. The
   film could then be processed by the small number of companies that generate the 17,500
   tonnes of film roll stock. Alternately the producers could designate specific recyclers to
   carry out this task on their behalf.

				
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Description: EXECUTIVE SUMMARY Stretch wrap2