Emerging Technologies in Plastics Recycling - American Chemical

Chapter 21

Multilayer Packaging in the Environment One Company's Positions and Programs S. J. Fritschel

Downloaded by CORNELL UNIV on September 1, 2016 | http://pubs.acs.org Publication Date: November 13, 1992 | doi: 10.1021/bk-1992-0513.ch021

Packaging & Industrial Polymers Division, Du Pont Polymers, P.O. Box 80011, Wilmington, DE 19880-0011

The solid waste issue has been one of the key topics of discussion in the packaging industry over the last two years. All packaging has been subjected to increasing scrutiny for its "friendliness" to the environment. Plastic packaging has been singled out by some as being a major contributor to the solid waste problem. Multilayer packaging, in particular, has been cited as being "unfriendly". This paper will try to separate myth from fact, and will discuss Du Pont's programs to address the issue of multilayer packaging from an environmental point of view.

The Scope of the Problem Surveys have shown that the average person believes that well over half of what they throw away is plastic. In fact, the most recent studies by Franklin Associates show that plastics occupy about 20% of the municipal solid waste stream by volume. The same study shows that 40% of this stream is plastic packaging. In other words, 8% of the municipal solid waste stream by volume is plastic packaging. The plastic packaging volume is broken down into 5.6% rigid packaging and 2.4% flexible packaging. This reflects the weight to volume advantage of flexible packaging over rigid packaging. This paper is concerned with multilayer packaging, so these figures must be broken down further. The Flexible Packaging Association reports that 50% of all flexible packaging solid is coated or uncoated polyethylene. Another 33% is oriented polypropylene or other polypropylene monofilms, 13% are coextruded and 4% are laminated films. If one counts all coextruded and laminated films as multilayer, then the volume contribution to the solid waste stream of flexible multilayer films is 17% of 2.4%, or 0.4%. For rigid

0097-6156/92/0513-0266$06.00/0 © 1992 American Chemical Society

Andrews and Subramanian; Emerging Technologies in Plastics Recycling ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

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packaging, the Plastic Bottle Institute reports that 90% of all bottles are monomaterial bottles. Figures are very similar for tubs, trays, and other rigid, nonbottle packages. So the volume contribution for rigid multilayer packaging is, at most, 10% of 5.6% or 0.6%. This means that, in total, multilayer plastic packaging comprises, at most, 1% by volume of the municipal solid waste stream. Despite this relatively small contribution to the problem, multilayer packaging has been a target of controversy in the solid waste debate. Several proposals to ban multi-layer plastic packaging were made during 1989 and 1990 legislative sessions in several areas of the country. These proposals were justified based upon the perceived lack of recyclability of the multilayer packages. D u Pont and others have developed the data which refute these claims. The integrated waste management system recommended by the E P A for the management of the municipal solid waste stream also applies to multilayer plastic packaging. That system includes source reduction, recycling, incineration, and land-filling.

Source Reduction In many instances, multilayer packaging is the most efficient way to deliver the required shelf life for a product. Use of a thin layer of a high barrier polymer like ethylene vinyl alcohol ( E V O H ) provides product protection that would require the use of far more of a mono-layer polymer. In many cases, multilayer plastic packages replace more traditional glass and metal packaging. The replacement of #10 metal cans by flexible multilayer pouches reduces both the weight and volume of waste generated by at least 60%. Weight savings of multilayer plastic packaging over metal and glass also reduces the amount of energy used in product distribution as well as reducing waste due to breakage or dented product. More efficient barrier, adhesive, and sealant resins for multilayer packaging are being developed. For example, a new E V O H type resin offers three times the barrier per mil of traditional E V O H resins. This can allow the packager to either increase shelf life at a constant thickness of barrier resin or to downgauge the barrier resins while maintaining shelf life. Another material in the development stage will offer increased flexibility to re-use process regrind, thereby reducing the amount of scrap generated by the converter.

Recycling Unlike packaging made of homogeneous plastics like H D P E milk, juice, and water jugs or readily separable plastics like P E T soda bottles, multilayer packages contain several different polymers and adhesives that cannot easily be



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RECYCLING

separated into their component parts for recycling. This has led to the erroneous view that multilayer plastics cannot be recycled. A number of companies have shown that it is not necessary to separate multilayer packages into single components to recycle them. Because it is probably the best known use of multilayer packaging, the ketchup bottle has been singled out as the example of non-recyclable packaging. A joint program with the Technical Committee of the Plastic Bottle Institute of the SPI helped demonstrate the recyclability of the multilayer P P / E V O H ketchup bottle. In order to replicate real recycling conditions as closely as possible, the bottles used for this project were bottles manufactured for commercial use by American National Can, Continental Can, and Owens-Brockway. The bottles were filled with ketchup by D e l Monte, Heinz, and Beatrice/Hunt-Wesson. The containers were emptied and then shipped to the Center for Plastics Recycling Research at Rutgers University. The containers that arrived at Rutgers for processing were rinsed to remove any residual ketchup. The bottles went through the same process as that used for P E T bottles: granulated to reduce to flakes put through a cyclone with a baghouse to remove paper remnants washed with soap to remove dirt and traces of ketchup rinsed to remove traces of soap put through a hydrocyclone separator (used for post-consumer soft drink bottles to separate P E T from high-density polyethylene used for base cups) passed through a dryer, which also removes fine particle contamination packaged in gaylord boxes for shipping. In this test project, bottles were processed with caps on. Ketchup bottle caps are made of polypropylene, the same resin as the bottle, but the caps are pigmented; in addition, they have an aluminum foil liner. Asking consumers to remove bottle caps (as they do with glass bottles) before recycling the containers will result in a clearer recycled flake; however, if caps are included during processing, the material will still perform like polypropylene but will have the pigment color. The flake received from Rutgers was used to formulate a thermoplastic olefin (TPO). The final product contained 75% ketchup bottle flake with the other 25% composed of E P D M rubber tougheners and anhydride modified E P D M compatibilizers. T P O compositions based on virgin polypropylene would contain similar amounts of compatibilizers and tougheners. The small amount of aluminum present from the package inner seals was removed by melt filtration during the compounding step.


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The compounded material, in pelletized form, was shipped to D u Pont's Troy, Michigan Automotive Development Center for molding trials. A 4000 ton Cincinnati Milacron injection press was utilized, together with a production mold for a 1984 Chevrolet Cavalier rear bumper fascia. A 4.75 pound shot was molded on a 99 second cycle. Trimmed part weight was 4.45 pounds. Injection molding pressures were 1200 psi injection, 900 psi pack and 750 psi hold. Back pressure was maintained at 50 psi, and clamp pressure was 3300 tons.


The compounded material processed satisfactorily and no problems were encountered during molding. The parts produced were yellow due to the incorporation of yellow caps during the recycling process. The composition was tested by standard A S T M methods and compared with a commercial T P O based on virgin polypropylene. The results are shown in Table I.

Table I. Comparative Property Data

Property

Temp.

Commercial TPO Genesis AP 8210*

Ketchup Bottle Composition

Tensile Strength

R.T.

2,200 psi

3,600 psi

Flexural Modulus

R.T.

90,000 psi

75,400 psi

Gardner Impact

R.T.

>320 in-lbs

>320 in-lbs

-30°C

>320 in-lbs

>320 in-lbs

*data from product literature

The experimental composition provided a reasonable match for the commercial composition. If additional flexural modulus were needed, the ratio of rubber to bottle flake could probably be modified to produce a more exact match without losing the critical impact properties. Injection molded plaques of the experimental T P O were painted at D u Pont Automotive Products' Troy Laboratory. A variety of paint systems were evaluated versus steel controls. O f the systems tested, the most satisfactory was a coat of D u Pont 800R adhesion promoter followed by a coat of D u Pont Centari 871/2 base coat and then a layer of Centari RK3939 flexible clear coat. This system provided results for adhesion, cold crack, gloss, and distortion of image which compared favorably with systems used commercially for automotive components. (Table II) This system was used to paint the molded fascia.


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Table II. Painting Study Results Substrate

Experimental TPO

Steel Control

Adhesion Promoter Primer Base Coat Clear Coat

800R None 872-Black RK-3939

None 764-189GX 872-Black RK-3939

Initial Gloss Initial Distortion of Image Initial Adhesion (samples/passes)

89 81 10/8

90 78 10/10

96 Hr. Adhesion (samples/passes) Blistering Dulling

10/10 None None

10/10 None None


10/10 None None

10/10 None None


10/9 None None

10/10 None None

Humidity Test X Tape/Cross Hatch

This test showed that multilayer P P / E V O H bottles could be handled using existing recycling processes and that the recycled material could be substituted for virgin polymer in a demanding end use.

Incineration Recycling of multilayer plastic packaging may not always be viable due to collection, separation, or other economic issues. In these cases, waste-toenergy incineration is the preferred method of disposal. Like all plastic materials, multilayer plastics are an efficient contributer to the clean burning of municipal solid waste. Their high B T U content makes them especially desirable in waste-to-energy systems. Data from the E P A and other sources suggest that properly designed and operated waste-to-energy facilities can recover 40% of the energy stored in the plastic, while still meeting all environmental regulations.



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D u Pont is working actively to help ensure that state of the art waste-toenergy incineration is built in various parts of the country. For example, in Brevard, North Carolina and Chattanooga, Tennessee, steam and electricity generated from municipal waste-to-energy incinerators are purchased for use in manufacturing operations. These long term purchase contracts allow the incinerator operators to obtain financing at attractive rates. At Parkersburg, West Virginia, the company also operates its own plastic waste-to-energy incinerator. This incinerator handles non-recyclable, non-hazardous waste generated in our own processes, and is expected to also accept similar materials from our customers. The facility is capable of handling six thousand pounds of waste per hour which would generate 27,000 pounds per hour of steam. The steam is used in polymer production operations at the site. Construction of this facility allowed the plant to defer construction of new coalfired boilers.

Landfill Properly designed landfills are an essential part of any integrated solid waste management system. If the more desirable recycling or waste-to-energy incineration facilities are not locally available, multilayer plastic packaging can be landfilled.

Acknowledgments The cooperation of the Technical Committee of the Plastic Bottle Institute and the technical contributions of Dr. P. M . Subramanian are gratefully acknowledged. RECEIVED

June 1, 1992


Emerging Technologies in Plastics Recycling - American Chemical

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