Issue 03 – October 2012
PP Processing Degradation
4.6 4.4 4.2 4
3.8 3.6
0 1 Pass Number
In the case of “closed loop” type recycling operations it is worth considering the addition of stabilisers during the manufacturing process.
An example of 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.
2. Contamination As most plastics are incompatible, great care should be taken not to mix material types.
It is therefore essential that no purgings, or scrap product resulting from material changes are recycled and it is vital that machinery is thoroughly cleaned between material types.
Other sources of
contamination include: Oil
Dirt / Rubbish Masterbatch
All contaminated material should be eliminated from any recycling process and disposed of. Failure to do so will result in the contamination of more material and further scrap.
3. Dust
The mechanical abrasion that constitutes the regrind process tends to result in dust. Ideally this should be removed and disposed of. In the case of some polymers, dust will significantly affect the physical properties of the end product.
4. Fibre Fillers
The mechanical abrasion that takes place in the regrind process dramatically affects the physical properties of plastics that contain glass, carbon or other fibre reinforcement.
In addition to reducing the length of the fibres, any chemical coupling agent (size) will also be affected, and since the fibres depend upon their interface with the plastic that surrounds them, the grinding process can dramatically reduce physical properties.
5. Food and Medical Applications
In both these cases special consideration should be given to the use of regrind. In many cases, healthcare and medical clients will specify processing conditions in great detail, particularly where, for example, FDA approvals are involved. Normally in medical applications regrind is not used.
In the case of food packaging, careful evaluation must be undertaken to ensure that compliance with required standards are maintained as well as overall suitability for any given application.
17 2
MFR g/10min
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