There is a lack of consensus around whether consumers should replace caps on plastic bottles. This article describes the basis for the Australasian Recycling Label (ARL), which includes the following instructions " Crush Bottle and Replace Cap". The reason for this approach is to reduce litter and maximise material recovery whilst avoiding contamination.
Historically, the recycling industry has advised Councils and residents to leave caps off. This has been due to three main reasons:
1. Bottles may contain hazardous contents and therefore cause an OH&S risk
2. Bottles that contain other contents will not behave the same as an empty bottle at the Materials Recovery Facility (MRF) and so may not be captured. The contents also cause contamination
3. If the cap is left on an uncrushed bottle, the cap will pop off whilst the bottles are being baled under compression.
More recently, the China bans have meant that contamination has been raised as a reason why caps should not be left on bottles. The argument is that China has set contamination limits at 0.5% and the cap is more than 0.5% of the bottle's weight.
Plastic bottle caps are usually too small to be captured at the MRF ; they fall though with the glass fragments and then are rejected as waste.
Caps on plastic bottles are now usually made from coloured high density polyethylene (HDPE). The bottles are commonly made from PET or HDPE. A natural HDPE milk bottle therefore contains a coloured HDPE cap and these polymers are compatible, with the coloured and natural flakes being separated at the plastic recycling facility (PRF). A PET softdrink bottle is also compatible with a HDPE cap because these two polymers will separate at the caustic bath at the PRF as PET will sink and HDPE will float.
By asking consumers to crush bottles before replacing caps, there is less chance the bottle will contain any contents and the cap will not pop off during baling.
It is for these reasons that the ARL says "Crush Bottle and Replace Cap".
NSW Container Deposit Schemes
The ARL was launched in 2015 by Planet Ark with Officeworks and Blackmores being the first businesses the adopt the label scheme.
In late 2017, NSW launched its Container Deposit Scheme that includes reverse vending machines (RVMs), which allow consumers to recover the deposits paid at the time of purchasing the bottles. In 2018, we discovered that the RVMs require the bottles to be uncrushed so that the machine can read the barcode.
It is therefore important that the RVM managers clearly explain that the bottles shouldn't be crushed if the deposit is to be returned. The ARL will then apply only to when the consumer recycles the bottle at either domestic or away-from-home recycling bins.