Assessing Property Deterioration Caused by Repeated Cycling by Injection Moulding

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Simple experiments can be performed to assess the effects of processing on properties.

Mouldings should be produced using the same conditions as used for full production to get useful and representative results.

The following three experimental procedures explore the recycling limitations of a plastic material. They identify the limits of reprocessing, as regards retention of mechanical and rheological properties, and allow the limits of recyclability to be assessed in terms of comparisons of closed loop recycling (Method 1A) and blending with virgin materials (Method 1B and Method 2). The results of these experiments can be used to determine if and when virgin material needs to be introduced into the recyclate mixtures and the likely properties of the resulting components.

Method 1A: Closed loop recycling with regrind only i. Mould 100% virgin material, keep some mouldings back for evaluation ii. Regrind a quantity of this 'first pass'

  1. Mould and keep some mouldings back for evaluation iv. Repeat for required number of passes, e.g., 'second pass', 'third pass', etc.
  2. Carry out evaluations on virgin and all passes (mechanical and/or rheological as required)
  3. Examine the results

A second set of useful experiments concern the effects of blending recyclates with virgin materials. This will depend on the results of the first set of experiments. For example, there may be no change after two passes, but the third pass may show a significant drop in properties. At the stage that the properties fall, for the sake of clarity we will say that in this case it is the third pass, blending with virgin material is used to boost the properties of the final mouldings.

Method 1B: Blending with virgin material i. Mould a blend of 50% virgin and 50% of the third pass material ii. Keep some mouldings back for evaluation iii. Blend 50% of this first blend with 50% virgin iv. Repeat for a number of passes, e.g., 5

  1. Carry out mechanical/rheological evaluation on the blend moulding samples 1-5
  2. Examine the results

Method 2: Cascading 100% regrind

As an alternative to closed loop recycling, a cascading method can be employed.

In this method regrind from each component goes into the next one. This is represented in Figure 3.4. The difference between this and

Closed Loop Cycling
Figure 3.4 Reprocessing by the cascade method

closed loop recycling such as described in methods 1A and 1B, is that here the regrind from each loop is used to make the subsequent component. This means that any heavily contaminated material can be discarded rather than being continually reprocessed.

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