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The Good Regrind Guide


Regrind is typically a term that applies to plastic components/products, which have been mechanically, reduced in size to particles less than 10mm in diameter.


The source of these plastic components can be pre-consumer waste such as process scrap, or less commonly post-consumer waste (Typically this source of material is handled by specialist recycling companies).


This process takes place in a device called a grinder, in which the plastic components are fed in through the throat of the grinder and then pass into a chamber that typically contains rotating knifes which mechanically cut the plastic component dimensions to a size small enough to pass through a screen. This regrind may then be: -


1. Fed directly back into the manufacturing process on a continuous basis


2. Fed directly back into the manufacturing process on a batch basis


3. Used in another manufacturing process such as a component for a compounded material containing the regrind (and other ingredients).


Given that thermoplastics are by definition capable of being heated and re-shaped many times the use of regrind would appear to be an obvious solution to achieve greater rates of operational efficiency through the use of process scrap and/or reject components.


However care must be taken to ensure that the use of regrind does not significantly impact on either processing and/or the performance


of the product being manufactured and in order to determine the possibility to use regrind the following factors must be considered: -


Degradation Thermoplastic raw materials are inherently unstable at processing temperatures. The extent of degradation will be dependent upon: -


• Type of polymer • The use of stabilsers


• Thermal history (Time spent at processing temperature)


• Presence of other materials such as pigments and fillers


In the case of ‘closed loop’ type recycling operations it is worth considering the addition of additional staibisers during the manufacturing process.


The degree of degradation when processing a standard MFR 4 PPHP by injection moulding and subsequent granulation is depicted in the graph where the melt flow (an approximate measure of degradation) is increased by 13% after two cycles.


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