When searching for an HDPE supply for your manufacturing applications, keep in mind that off grade HDPE can often be an excellent and cheap source of HDPE. What is off grade HDPE? Off grade HDPE is simply HDPE that does not meet the specifications for graded HDPE. There are many different grades of HDPE, used for various applications. Some examples of HDPE grades are Injection Molding Grade HDPE, Pipe Grade HDPE, and Blow Molding Grade HDPE. For every application, there is a grade standard which specifies certain properties that should be present in a batch HDPE to make it suitable for a particular type of application.
Off Grade HDPE is HDPE which does not meet the specifications for any HDPE Grade. Due to this fact it is not recommended for manufacturers who require a high level of performance from their HDPE. However, for many manufacturers who do not require an extremely high grade product, off grade HDPE can be a better option than purchasing the more expensive prime HDPE. For instance, some off grade HDPE may lack the tensile strength of prime grade HDPE. However, if your application is a lightweight bottle, this may not make any discernible difference to the quality of the end product.
How Is Off Grade HDPE Produced?
Off grade HDPE can result from faulty polymerization settings, or it may be a by product of a successful production of prime HDPE. Most often, off grade HDPE is produced when production is switched from one grade of HDPE to another. Take for example, an HDPE production plant where injection molding grade HDPE, which has a very low viscosity, is being produced. If production is then changed to, say, blow molding grade HDPE, which has a very high viscosity, then there is often a period and a few production runs in which the processes are tweaked and changed, and in which the resulting HDPE is not prime grade for either usage. This HDPE is off grade HDPE, and while not suitable for high stress blow molding or injection molding, it may still be useful in other applications.
What Isn’t Off Grade HDPE?
When searching for off grade HDPE, one has to keep one’s wits about one. Some unscrupulous purveyors sell contaminated reprocessed HDPE as “off grade”. However, this is not off grade HDPE, this is merely low quality HDPE, and is quite a different proposition altogether. Contaminated HDPE should be avoided, as it can cause defects in final products, and may not even be able to undergo processing and molding at all.
Off grade HDPE is simply HDPE that does not fall into defined HDPE grades, for instance Pipe Grade, or Injection Molding Grade, as was already mentioned. Off grade HDPE still retains its structural integrity, and is still a quality product, if not entirely suitable for highly demanding applications.
Off grade HDPE can come from virgin HDPE or reprocessed HDPE, off grade virgin HDPE is generally the “safest” form of off grade HDPE to purchase, but reprocessed off grade HDPE is also a decent source of HDPE if purchased from a reputable purveyor.
The reason why it is so important to purchase from an experienced and reputable HDPE seller, especially when it comes to reprocessed HDPE products, is the fact that scrap HDPE can easily be ruined if it is not handled well during reprocessing. Reprocessed HDPE has not only been exposed to contaminants during its life, so great care must be taken in the washing and filtration stages of reprocessing, but it has also been exposed to several heat cycles, and with every heat cycle it is more and more likely that the molecular structure of the HDPE will break down, and that the resulting HDPE will be of poor quality. If the HDPE is handled correctly however, these issues will not arise, and manufacturers can feel confident using reprocessed off grade HDPE in their products.
The other factor to take into account is the fact that reprocessed HDPE generally lacks the clean translucent white color of virgin HDPE, due to the fact that it has generally been exposed to dyes either in its previous product incarnation, or during reprocessing colors from other items of HDPE have leeched into the HDPE stream. There are some exceptions to this rule, but much reprocessed HDPE will be colored in some way. This is not important for some applications, but if you are looking to produce a product that is appealing to the eye, then off grade reprocessed HDPE may not be the best choice.
Conclusion
Purchasing off grade HDPE does not mean purchasing unsound or contaminated HDPE. Purchasing off grade HDPE means purchasing a low cost, quality source of HDPE that will keep material costs down whilst still producing a quality end product.
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