PSA Tapes Offer Environmental Advantages in Packaging

By Timothy B. Jensen, Technical Service Manager, 3M

Concern for the environment is an issue that is influencing decisions on packaging and packaging materials (1,2). This article addresses such concerns, both real and perceived, as they may relate to plastic film-backed pressure sensitive adhesive (PSA) tapes used in closing corrugated shipping containers and in bundling, reinforcing, and tamper-evident and consumer packaging.

Consumers encounter many products that claim to be environmentally beneficial. Such claims may include the packaging and often involve terms like degradable, biodegradable, recyclable, natural, safe, reusable, "contains ingredient x" or "does not contain ingredient x." In many instances, such terms are not well defined and, even if they are, their use may be misleading because they describe only part of the environmental ramifications.

So what are the environmental ramifications of plastic film-backed PSA tapes used in packaging? There are several ways of approaching this question, but for the present the following will be considered: performance, source reduction, life cycle, reusability/recyclability and compatibility.

Performance

Adequate packaging of goods for distribution and preservation is critical to modern society. A package that fails to protect the contents against damage - regardless of any claims that can be made for its environmental "goodness" - actually causes more harm to the environment; in most cases, the quantity of damaged goods will result in increased municipal solid waste (MSW) disposal. One example is the relatively poor water resistance of corrugated containers closed with reinforced gummed tape (RGT) compared to those closed with polypropylene pressure sensitive tapes, when both are exposed to the conditions described in Federal Specification MMM-A-250 as reported by Sheehan (3).

In a further measure of performance, drop tests were used to compare 3M #373 tape - PSA film tape using a bi-axially-oriented polypropylene backing (BOPP) - with reinforced gummed tape. Boxed closed with 2-in. wide #373 could withstand twice the drop height of boxes closed with 3-in. wide RGT for these tests. The text box was a 17 x 13.5 x 9.25-inc. regular slotted container (RSC) made of 275 psi C-flute corrugated. Wooden blocks were used as a test load for a gross weight of 40 lb. One of the drop test procedures in ASTM D-775 can be used to determine the critical height for causing damage to a package. The height at which a cycle of four drops (a corner and is three edges) would cause tape damage was determined. Results are shown in Table I.

The BOPP box sealing tapes described in this discussion use a block copolymer rubber resin adhesive. The results should not be generalized in all instances to include acrylic and natural rubber resin adhesive products. One further advantage, from an environmental point of view, is that block copolymers may be coated in the manufacturing process without organic solvents or the evaporation of water, thereby reducing both energy requirements and emissions to the atmosphere.

Source Reduction

This principle states that is packaging can be minimized, other things being equal, the total stress on the environment will be reduced. Thus, if a lesser amount of raw materials is required, shipping and disposable/recycling costs are reduced. Source reduction is primary in the EPA’s hierarchy of solutions to the MSW problem.

In 1989 the Coalition of Northeastern Governors (CONEG) published its "Preferred Packaging Guidelines" that listed the followiing in order of preference:

  • No packaging;
  • Minimal packaging;
  • Consumable, returnable or reusable packaging; and
  • Recyclable packaging or recycled material packaging

The second item includes "modifications to package design" aimed at source reduction. Note that the coalition places this objective well ahead of recyclability.

Table II shows the amount of different materials required to close an 18 x 12 x 12-in. corrugated container (RSC) that contains 30 lb. of goods and is subjected to moderate shipping and handling conditions.

In the representative example shown in Table II, the polypropylene PSA box sealing tape offers the best environmental option when the principle of source reduction is considered. Other examples of source reduction shown in Table III indicate that better than a 75% reduction can be achieved. The innovative use of modified PSA tape products may offer additional opportunities for source reduction. The recent development of tape handles by 3M has eliminated the need for paper or plastic bags in a number of applications for a major retailer. Tape handles consist of a length of PSA tape with a color-coded or printed piece of paper of equal width adhered to the center portion of the strips. This leaves two legs of equal length that adhere to the merchandise and create a handle for carrying the merchandise without a bag. Depending on the circumstances, tape handles typically offer 90% source reduction.

Life Cycle

This principle considers all aspects of interaction between packaging materials and the environment, from origin to ultimate end. Included in the life cycle accounting principle is total energy expended and all emissions to air and water in manufacturing, use and disposal - as well as expenditures of incidental material and energy relative to a given packaging material. Damage to packaged goods due to varying suitabilities of the packaging materials also would be considered by life-cycle comparison. This principle is more readily sated thatn employed. However, a good example of life cycle accounting was that of Hocking (4), which compared polystyrene with paper beverage containers for single use. Contrary to the perception that paper drink containers are environmentally friendly (at least on a comparative basis), it was found that the production, use and disposal/recycling of the paper container required more energy and produced two-and-a-half times more emissions than the plastic container’s life cycle.

The idea of degradability figures prominently in most discussions of packaging and the environment with the tacit assumption that degradable packing is better. The assumption that "degradable" products degrade, at least in sanitary landfills, may not be true. The work of Rathje at the University of New Mexico (5) has shown that these landfills function as tombs and not as compost piles. For example, food and paper products, generally considered to be degradable, survive in landfills for decades with little degradation because oxygen is severely limited. In fact, the CONEG guidelines mentioned previously dismiss the idea of degradable packaging as a viable solution by excluding it in their guidelines.

The National Audubon Society publishes the magazine Audubon and mails it in a plastic wrapper. A competitive magazine that has used a similar plastic wrapper changed to a brown kraft paper wrapper and claimed environmental advantages. The society did not change from plastic wrappers and, after considerable study, made the following statement: "Contrary to popular belief, which considers anything ‘plastic’ as inherently bad, studies show that the least environmentally damaging packaging materials, as far as pollution is concerned, usually is the one that weighs less. Research by the (former) West German Federal Office of the Environment, for instance, found that brown paper shopping bags produce more pollution, pound for pound, than polyethylene bags in their manufacture. Moreover, since the kraft wrappers to which (the competitive magazine) has returned weigh several times more than polybags, they consume significantly more space in landfills." (6)

Owing to the complexity of life cycle accounting and the brevity of this discussion, we cannot consider this principle in detail here except to note that life cycle considerations must be taken into account when environmental concerns are addressed.


Recyclability/Reusability

Perhaps no terms has been more abused in the oversimplification of environmental concerns than "recycling." As a means of reducing environmental stress, recycling is valid only when considered within the scope of life cycle accounting. The corrugated container discussed in Table II weights approximately 35 ox. The various closure materials range in weight from 0.1-0.4 oz., or about 0.3-1.2% of the total container’s weight. Obviously, recycling strategies should focus on the corrugated container rather than the closure material since 44-50% of all containers are recycled.

PSA box sealing tape products using plastic film backing do not appreciably interfere with the corrugated recycling process and need not be removed prior to recycling. These processes are equipped with separation devices to remove extraneous material. Tests have been completed at Western Michigan University to confirm earlier observations made in various recycling facilities. Additional tests conducted at Forest products Laboratory, Madison, WI, also confirmed these observations and indicated that the adhesive stayed with the polypropylene film during the recycling and separation steps and thus would not contribute to the "stickies" problem. This problem occurs in paper recycling operations and results from adhesive, glue and other low molecular weight resins found in miscellaneous paper scrap. Stickies may cause unacceptable blemishes in the recycled paper product, thereby reducing visual quality. Comments from recyclers indicate that wax and hot melt glues are the major contributors to stickies.

In addressing the issue polypropylene tapes on corrugated carton, Johnson (7) stated that "OPP can normally by recycled with the carton. The presses developed by the carton industry allow for the presence of small quantities of tape."

The considerations are reflected in the German "Verpackungsverordnung" (packing ordinance) of June 12, 1991, which obligates manufacturers and suppliers to reclaim used shipping containers and to either reuse them or to transmit them for recycling rather than discard them through public waste collection. This, of course, is a very simplified summary of the law, but the principal means of compliance expected in Germany will be the RESY-Recycling System, an association of the corrugated, packaging and recycling industries in Germany.

In a January 1992 RESY publication entitled "In Explanation of the Recyclability of Packaging Made of Paper or Cardboard," the following statement is made about PSA box sealing tapes: "Adhesive tape and stick-on labels are packaging aids which are not supposed to hinder the recycling process. This requirement is met when they disintegrate as little as possible in the slushing phase and can already be completely - which means both the adhesive material as well as the bearing material (plastic or paper) - separated in the pulper or in the following sorting phase." The intention behind this statement is to minimize the occurrence of stickies, contaminants that might interfere with repulping equipment or cause spots on recycled paper. In other words, if the adhesive remains with the backing during repulping, it will not contribute to the stickies.

Tape removed in the recycling process may be safely landfilled, incinerated in appropriate facilities with the heat energy reclaimed, or presumably recycled into useful products when plastic recycling processes like the klobbie Process come into common usage (8). In any case, it should be noted that the plastic film-backed pressure sensitive tapes are estimated to constitute less than 100 parts per mission (0.01% by weight) of the total MSW stream in the United States.

Concerning the reclaiming of heat energy, Johnson (7) makes a further statement that may also be tied in with life cycle analysis: "Recycling in the material sense is only environmentally sound if there is a net gain in resources. In the case of plastic-based materials there is usually a larger net gain in resources if waste materials are burned with energy recovery and then fresh oil used to make fresh plastic, rather than using fresh oil for energy and re-using the plastic. Overall, 2% of mineral oil is used to make plastic packaging of all types, and this plastic packaging still contains typically 95% of the original oil energy."

The desirable option of recovering heat energy from packaging waste is set forth in the European Community’s Directive on Packaging and Packaging Waste (draft, Dec. 18, 1991), as reported by Bates and Hacker, Brussels: "a unit of packaging must . . . be capable of being easily ‘recovered,’ i.e. recycled or burned to provide energy." Other considerations in the draft require source reduction and minimization of the content of certain heavy metals.

Reusability of corrugated containers is an area where polypropylene PSA box sealing tape offers significant advantages over some competitive closure materials. Unlike hot melt adhesives, the tape does not cause delamination of the box flaps, because it may be slit open while boxes closed with hot melt adhesives may not. Unlike staples, it does not weaken the box flaps with holes.

The arguments made on behalf of gummed paper tapes because of their presumed recyclability deserve examination. Consider 100 RSCs (Table II) closed with either polypropylene PSA box sealing tape or RGT. Those closed with the former would require approximately 300 g of tape while those closed with the latter would need 1200 g of tape. If it is assumed that none of the polypropylene PSA box sealing tape is recycled, regardless of the fate of the 100 RSCs, then 300 g of tape will be landfilled or incinerated. If it is assumed that 50% of the 100 RSCs closed with RGT are recycled (the 50% figure represents the high end of current estimates for corrugated) and that the RGT is totally recyclable, which may not be completely accurate, then 600 g of RGT are recycled. However, it also means that the 600 g of RGT on the other 50 RSCs will be landfilled or incinerated. The irony of this situation is that the "recyclable" paper tape produces twice as much MSW as the plastic tape. This example illustrates the fallacy of selecting products solely on the basis of recyclability and why source reduction must always be considered in any reasoned analysis.

The availability of high performance PSA box sealing tape (e.g. 3M #375) permits the proper closure of corrugated cartons made from fiberboard containing a high fraction of recycled pulp. This fiberboard typically has a surface roughness of 6.5 microns, compared to the 4-micron roughness of lower recycle fraction material. Containers made from such corrugated materials tend to have less strength, and the rougher surface offers a poorer substrate for adhesion. High performance tapes with relatively heavy adhesive coating weights will completely wet the surface, providing a good adhesive bond. This allows the shipper to use containers with a higher percentage of recycled materials, thereby promoting recycling of corrugated, the dominant portion of the total container.

The question of using post consumer polypropylene for box sealing tape has been considered. However, for reasons of consumer safety, FDA and other regulations may preclude the use of recycled polypropylene and other resins in the production of PSA tapes that might come in contact with food and other critical products.

Compatibility

A dictionary definition of compatible is "capable of living together harmoniously or getting along together; in agreement; congruous." In this respect, 3M’s box sealing tapes may be considered environmentally compatible for the following reasons:

  • Most of the components used in making these products are cleared as indirect food additives, so the products do not contain toxic materials.
  • The products are safe and stable in low oxygen landfill situations and would make no adverse contributions to leachate.
  • They may be safely incinerated in appropriate facilities.
  • If inadvertently littered, they are environmentally degradable in sunlight.
  • They can be a positive factor in source reduction.
  • They offer important advantages from a life cycle viewpoint.
  • Their use facilitates corrugated container reusability and does not appreciably interfere in corrugated recycling.

Conclusion

In summary, environmental considerations in the selection of closure materials for corrugated containers appear more complex in reality than in initial perceptions.

References

(1)     Rzepecki, E.L. 1991. Packaging and Environmental Issues, St. Thomas Technology Press.

(2)     Selke, S.M. 1990. Packaging and the Environment. Technomic Publishing Co. Inc.

(3)     Sheehan. 1991. The Chemical Packaging Review.

(4)     Hocking. 1991. Science Magazine.

(5)     Rathje. 1989. Atlantic Monthly.

(6)     Audubon Society letter to members. 1990

(7)     Johnson. 1991. AFERA Congress, Amsterdam.

(8)     New Scientist. 1990.

Table I - Average Drop Height to Tape Damage

Tape

Height, in.

   

2-in. 3M #373

23.1

   

3-in. RGT brand A

11.4

   

3-in. RGT brand B

10.2

   

3-in. RGT brand C

9.0

   

3-in. RGT brand D

9.0

Table II - Weight and Mass of Box Closure Materials

Material

Weight, oz.

Mass, g

     

Polypropylene: PSA box sealing tape (2-in., 3M #373)

0.1

3

     

Staples

0.3

9

     

Hot Melt Adhesive (applied to box flaps)

0.2

6

     

None-metallic strapping

0.3

9

     

Reinforced gummed tape (3-in. fiberglass-reinforced paper)

0.4

12


Table III - Source Reduction Through Use of PSA Tapes

Product shipped (container/unit)

Operation

Previous closure, combining or unitizing material (weight, oz)

Tape closure, combining or unitizing material (weight, oz)

Source reduction using 3M packaging tape products, %

Game box (chipboard)

Closure

Shrink wrap (0.110)

Two "L" clips and 1/2x2-in. 3M #600 tape (0.004)

94

Soft drinks (12-pack)

Combining

Corrugated tray (3.7)

Two strips of 2x41/2-in. 3M #8469 tape (0.05)

98

Miscellaneous (pallet loads)

Light duty unitizing

Stretch wrap (5.0)

Two or more wraps of ½-in. x 16-ft. 3M #898 tape (1.0)

80

Laundry items (18x12x12-in. corrugated)

Closure

Reinforced gum tape (0.4)

3M #373 tape (0.1)

75