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Is there an industry standard about how much regrind is allowed?

Regrind: the ongoing nemesis in the plastic industry. Before we decide the amount of regrind that can be used we must understand the demands of the final product. First we must understand what regrind is. When a prime virgin material is first processed there is a molecular weight of the polymers that establishes both the flow and physical characteristics. There are also additives that come into play. A necessary one for many polymers is antioxidants. Each time the material is processed a certain amount of these additives are burnt off. This may affect the both the final properties and the rate at which the molecular structures break down.

The greatest problem with the continued addition of a certain percentage, is how many times has this particular lot or portion of this lot been processed. At some point the molecular structure may be gone or not have enough integrity.

One way to prove and maintain the properties and integrity of the final product is to run first 100% virgin, than 100% first pass regrind, than 100% second pass, 100% third pass and so on. This can help establish when the differentials that either the process or the final product take effect. If it is proven that process and final properties do not begin to show change until the 7th pass. Run five passes and sell the remaining regrind.

An easily moulded HIPS, may be processed many times before significant degradation occurs. A Polypropylene or other olefin material will usually show physical change earlier.

There is no exact % of how much you can recycle, it depends on the following and each company should consider each point value in their own priority order, the way I see it considering you already know which material you are going to use:
  • Strict material brand and grade requirements - You need to follow the material brand commitment and not so much that you could do about it.
  • type - due to change in characters after injection/casting each material has few % that could be recycle and it's not the same between all materials.
  • the material was special orders with color or general natural/black color - normally the impact of colored material is different (usually lower) therefore the allowance in recycling % is different.
  • you will add colorant and if yes., will it be "master batch" or powder? and if "master batch" will they use the same brand & grade as you are using?
  • product environmental requirements such as: indoor, outdoor, mobile, UV etc must be taken into consideration as well.
  • product Quality therefore its life time requirements, any life test?
  • type of mould you are using - in many cases it's not about the material - for instant with multi cavities mould + fully hot runner VG all over we never puts recycle material as it bad for the mould, reducing its life time, increasing maintenance and creating shutdown during mass production which increasing the production cost.
Each Factory has its own rule. Generally speaking I am "by my finger rule" using between 10-15%, more often recycling only the runner in cold runner moulds and 5% in hot runner system moulds.

Process you are using, the machine plasticizing capacity, the cycle time, the part thickness, weld line formation at critical areas. The reason being, if you are grinding the wastage and using again, the pellet structure may not be uniform and plasticizing time may be different. Any contamination in the product can come out near weld line and the strength may go down.

The issue can be avoided by selecting an injection moulder that has put procedures into place to prevent that from happening. We represent moulders that have addressed this issue and have put procedures into place to prevent that from happening. I have seen various moulders over my career and some just don't take the time to assure the product is being manufactured under the strictest of conditions, where others go the extra mile to make sure they will not be confronted with rejected product that will cost them a customer or possibly even financial loss through contractual penalties.

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