Scrap HDPE – Label Contaminant Guide
Scrap HDPE is by its very nature, a product that needs to be handled with great care and expertise if it is to be reprocessed into a high grade raw material for new HDPE products. Unlike freshly manufactured HDPE, scrap HDPE has been exposed to all manner of uses and contaminants in its lifetime, and these must be rigorously sought out and removed if the end product is to be of a high quality.
Whilst the processes used for recycling scrap HDPE are very advanced, and generally produce a high quality product that is suitable for many applications, there are some contaminants that are more difficult to remove, and may make for lower grade scrap HDPE, or reprocessed HDPE with flaws that make it unsuitable for various applications.
A very common potential contaminant when it comes to scrap HDPE is bottle labels. A high amount of scrap HDPE comes in various bottle forms, which are very often covered in labels. Various manufacturers use different materials for their product labels, and each type of label can represent a unique challenge to the scrap HDPE purchaser and recycler.
In the interests of educating consumers of scrap HDPE, this is a listing of common label contaminants that are sometimes found in scrap HDPE, and of which once should be aware, so that they may be either avoided entirely, or in order to get a better price on what may very well be a lower grade HDPE product. This information is also very useful for purchasers of bailed HDPE, who should take time to note the types of labeling that are stuck on the bottles in the scrap HDPE bail. Doing so can ensure a higher quality end product, and being aware of various potential problems can save a great deal of time and money in the long run.
The sections are sorted into various types of problems that one may encounter in the final product, and the causes of these issues are then listed in each section. There is also a section on paper labels, which can produce some unique difficulties of their own.
Black HDPE Flakes
Some scrap HDPE products have black flakes in them. These are unsightly, and make the HDPE regrind unsuitable for many applications. There are two main sources of black flakes, and both should be avoided.
PVC Labels
PVC Labels are a much more problematic issue than many other labels, as their presence will often cause a black flecked appearance in the HDPE. It is not difficult to remove PVC, as like many other common contaminants, it is heavier than water, and will sink during the float/sink process. However, if the process is not undertaken for a sufficient length of time, or if it is not done completely thoroughly, some remnants of PVC may remain. These remnants of PVC cause particular trouble later on in the process when the HDPE is heated. During this heating process, whilst the HDPE melts, PVC quickly chars due to its much lower melting point, resulting in the tell tale black flecks in the final HDPE product.
Metallic Impregnated Labels
Another cause of black flecks or specks in HDPE resin are Metallic Impregnated Labels. Unlike PVC, which is relatively easy to remove as long as sufficient care is taken to ensure that the usual recycling processes are carried out thoroughly, Metallic Impregnated labels often become fragmented during the recycling process, spreading metallic particles throughout the HDPE. It is recommended that you strenuously avoid scrap HDPE with Metallic Impregnated labels, as they are not cost effective to handle, and small amounts can contaminate a whole batch, rendering it completely useless for producing new materials. Due to the difficult nature of these labels, many reprocessors refuse to deal with Metallic Impregnated labels altogether.
Colored HDPE Regrind
Low Density Polyethylene (LDPE) Labels
LDPE is HDPE’s low density cousin, and as such, is not nearly as problematic as other plastics can be in the HDPE recycling process. Small amounts of LDPE will not have a large effect on the quality of the finished HDPE, but larger quantities can cause problems, especially if there is color in the LDPE labels. Color can quite easily taint the entire batch of HDPE and produce colored regrind at the end of the process.
High Density Polyethylene (HDPE) Labels
At first it seems counterintuitive to suppose that HDPE labels might be a problem with recycling, or reprocessing HDPE, and to some extent, they are no problem at all. They possess the same properties as other forms of scrap HDPE, and are most suitable for reprocessing. However problems arise when the HDPE labels are colored. Most all product labels contain some form of ink, and it is this ink that can color the HDPE and make it unsuitable for certain end uses. The ink is almost impossible to remove entirely, even with the most advanced processes, and it is almost assured that if HDPE Labels are not removed, that the entire batch will be contaminated with color. Structurally however, the quality of the HDPE is unaffected, and HDPE regrind thus colored may still be suitable for applications where coloring is less important, such as in the instance of underground pipes, pallets, and the like.
Low Grade Regrind
Polypropylene Labels
Polypropylene Labels are problematic when it comes to scrap HDPE. Polypropylene is difficult to remove from HDPE bottles because, much like HDPE, it floats, and so is not so easily removed via the float/sink process. In small amounts, polypropylene contaminates the HDPE making it suitable only for low grade products, and in higher amounts, renders the HDPE completely useless. Great care should be taken to remove Polypropylene labels, and if possible, it is a good idea to avoid using scrap HDPE with Polypropylene labels altogether.
Polyethylene Terephthalate Labels (PET)
Unlike Polypropylene, PET labels are more easily removed due to the fact that PET will sink during the float/sink process, and can quite easily be removed during the usual HDPE recycling processes. The only problem with PET is the fact that if any is left in the HDPE, it will remain a solid, due to the fact that its melting point is nearly twice that of HDPE. This produces a contaminated flake. However, PET labels are not a huge problem as long as the float/sink process is carried out with due diligence.
The Problem Of Paper
Paper labels can be hugely problematic for HDPE reprocessing, depending on the type of paper label used. There are two main types of paper labels, plain paper labels, and wet strength paper labels.
Wet Strength Paper Labels
These labels are specially designed to resist water, which means that they hold up rather well during the HDPE washing process. Unfortunately, if they are not removed, they are often mixed in with HDPE flake material, and the result is a contaminated batch of HDPE which is essentially a mix of HDPE and paper label product. This is highly undesirable, and great care must be taken that these labels are removed prior to the HDPE washing process.
Paper Labels
Other forms of paper labels have no waterproof qualities whatsoever. When the HDPE is washed, these paper labels turn into a pulpy mess which blocks up the equipment and can cause a great deal of trouble for the HDPE reprocessor. The color in the labels is also leeched out during the washing process, and there is a significant chance that the resulting HDPE will be tainted with color. Paper labels are the bane of a HDPE reprocessor’s life, as they require the machines to be unclogged, and filters to be replaced with far more frequency than other types of labeling.