“Degradable bags” or carrier bags are made from starch-polyester blends, which combine
commercially manufactured hydrocarbons with starches derived from biomass fibressuch as corn,
potato, tapioca or wheat. Over time, these biodegradable polymers decompose and break down
into carbon dioxide, methane, water, inorganic compounds or biomass (Edwards & Fry, 2011, p.
13). The more commonly available form of biodegradable plastic carrier bags is oxo-degradable
bags. Oxo-degradable bags are those that are made from plastics with certain additives added in,
that promote the degradation process in the presence of natural daylight, and heat. Other forms
of degradable bags might include “biodegradable bags” which decompose into carbon dioxide,
methane, water, and inorganic compounds, or “compostable bags” which are degradable under
the action of microorganisms and achieve total conversion into carbon dioxide, methane, water
and inorganic compounds (Sustainability Victoria, 2007, p. 2).
In terms of environmental performance, oxo-degradable bags require 10% less raw materials to
produce as compared to HDPE bags (Edwards & Fry, 2011), and studies have also shown that “the
incineration of PP (Polyethylene Plastic) bags generates about double the amount of greenhouse
gases compared to the incineration of bio-bags” (Khoo & Tan, 2010, p. 341). Oxo-degradable bags
are also cited as having a lower impact in the littering stream. As compared to HDPE bags, they
require a much shorter period to degrade in the environment (Lewis et al, 2010).
However, depending on the type of degradable bag, the plastic may not break down into harmless
compounds, but rather, “microplastic” fragments, which can still be ingested by marine life
(Thomson, et al., 2004). Additionally, just like HDPE bags, oxo-degradable bags are neither thick
nor durable and are intended mainly for single use. Consumer complacency that a degradable bag
would disintegrate even if disposed might lead to higher rates of littering.
Oxo-degradable bags are also not designed for material recycling. A typical plastic recycling
process involves re-heating, during which biodegradable bags will decompose and make further
processing impossible. Furthermore, mixing of biodegradable bags in the feedstock of recycling
will damage the process and the quality of recycled products(Ren, 2003).
While bags made entirely of bio-based polymers might have a lower environmental impact than
the commonly available oxo-degradable alternative, the lack of these options in the market as of
2013 makes them an unlikely solution to the problem of plastic bag wastage for now.