Recycling scrap plastic bottles can be a complex procedure with mixed results. It may take as many as 14 different steps, lots of water and intermediate steps often carried out at different facilities requiring baling and in-between transportation.
Most engineering efforts to improve recycling material quality and quantity are done at the end of the process. We must also look at the starting point, before recycling begins. That includes looking into labels and neck rings.
An often overlooked aspect in easing plastic recycling is the relative difficulty of removing labels, caps and neck rings from scrap bottles. To have good quality end product these materials must be removed somewhere along the process of converting scrap bottles into pellets. Work with labels that are easier to remove has been done mostly for thermoforms. Now we can go a step further.
When testing the relative ease or difficulty of removing labels from a wide range of PET beverage containers, mainly water and soda bottles, to my amazement I found some labels are attached to survive a trip to the moon. Practically all labels, either paper or plastic, were directly attached to the bottle using different types and amounts of glue or adhesive. Some glue strips are more than one-half inch wide along most of the bottle length, attaching both sides of the label. Some adhesives are yellowish in color and many labels are practically impossible to remove fully by hand. Glue amounts often seem excessive for the intended purpose, representing additional material cost besides hampering recycling.
Simple labeling and capping procedure modifications at the bottling plant site can help. Instead of applying glue directly to the bottle, the bottling industry may modify the process and use a pre-glued wraparound label. The pre-glued label adhesives may be a contact type or perhaps one activated by heat. Adding a small tab at one end of the label makes removal even easier.
A pre-glued label roll eliminates the step of applying the adhesive directly to the bottle, as well as the equipment for this purpose. Bottling companies also can implement simple labeling modifications designed to:
- reduce the amount of adhesive used;
- reduce the size of the glue strip; and
- use clear contact glues that are easier to remove and that will not darken upon reaching PET melting temperatures.
When removing the cap, the neck ring remains on the bottle. Because the neck ring is made of a different plastic, this reduces recycled PET (rPET) quality. Ring removal by hand using a cutter or sharp hook nvolves additional labor. When twisting open a bottle made in France, I noticed that the neck ring broke in several locations without too much effort, and the neck pieces remained attached to the cap. A truly simple design makes this possible.
The neck section is fabricated with several notches that, upon twisting, break along weaker sections and remain attached to the upper cap. Thus, both cap and neck are removed together simultaneously. This method makes possible salvaging both caps and necks in a separate container, providing a source of additional revenue to the processor. Some neck rings already have notches, so it’s a matter of increasing their depth to make removal easier.
The proposed modifications in labeling and capping methods involve the combined efforts of beverage companies, bottling companies and label and cap makers. Not only this is a step further for zero waste, but also a step forward towards better rPET quality.