Page 80 - Materials Chemistry, Second Edition

Life cycle assessment and waste management

Table 6.6 Composition of all shopping bags modelled including assumptions 67
Bag material Composition Assumptions made
Degradable polymers
Starch polybutylene succinate/ 50% – starch from maize; 25% Adipic acid is manufactured
adipate (PBS/A) (e.g. Bionelle) – 1,4-butanediol; 12.5% – from cyclohexane (40%) and
succinic acid; 12.5% – adipic nitric acid (60%); succinic acid
acid is formed through
fermentation of corn-derived
glucose
Starch with polybutylene 50% – starch from maize; 25% 1,4-butanediol is derived
adipate terephthalate (PBAT) – 1,4-butanediol; 12.5% – either from natural gas or corn
(e.g. Ecoflex) adipic acid; 12.5% – glucose
terephthalate acid
Starch-polyester blend (e.g. 50% – starch from maize; 50% Maize-growing data is based
Mater-Bi) – polycaprolactone (PCL) on data from the Netherlands.
PCL is produced from
cyclohexanone (95%) and
acetic acid (5%).
Starch-polyethylene 30% – starch from cassava Cassava-growing data is based
blend (e.g. Earthstrength) (tapioca); 70% – high-density on cassava-growing data from
polyethylene the Netherlands
Polyethylene + prodegradant 97% – high density Additive was modelled as
(e.g. TDPA) polyethylene; 3% – additive stearic acid and a small
amount of cobalt metal to
represent the presence of
cobalt stearate
Polylactic acid (PLA) 100% polylactic acid Based on maize growing in
USA
Alternatives
Singlet HDPE HDPE Production of HDPE film
Kraft paper bag with handle Kraft virgin pulp Production of paper bags
PP fibre ‘green bag’ PP Production of PP film
Woven HDPE ‘swag bag’ HDPE Production of HDPE film
Calico Cotton Cotton processing
LDPE ‘bag for life’ LDPE Production of LDPE film
LDPE, low density polyethylene; HDPE, high density polyethylene; PBAT, starch with polybutylene adipate
terephthalate; PBS/A, starch polybutylene succinate/adipate; PCL, polycaprolactone; PLA, polylactic acid; PP,
polypropylene; TDPA, total degradable polymer additive.

and litter potential have contributed to increasing scrutiny of the environmental impacts
associated with their manufacture, use and disposal. Bags that are littered often become
entangled on fences, in trees or in waterways where they can threaten aquatic life and inter-
fere with the visual aesthetic of the natural environment. Alternative materials such as
calico, paper and woven polypropylene have been introduced as alternatives to ‘single-use’
HDPE. Degradable polymers have been marketed more recently as a possible solution that
would reduce the demand for a non-renewable resource (HDPE) by replacing it with a bio-
degradable renewable resource (e.g. maize-derived), thereby potentially reducing littering
problems and demand upon landfills.
In the study reported here (Scheirs et al. 2003), a streamlined LCA of a selection of degra-
dable plastics suitable for applications in film blowing and marketed as materials for shopping
bags were compared with HDPE, LDPE, PP, Kraft paper and calico (Table 6.6).

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