Impact of - IDL-BNC @ IDRC - International Development Research ...

design flexibility and were suitable for aqueous products, they could not be
used for aromatic solvents, which are the base for most liquid agrochemical
formulations.
A major breakthrough was achieved with the discovery of polyethylene
terephthalate (PET). This plastic is widely used for carbonated soft drinks and,
more recently, for alcoholic spirits sold by airlines. When this polymer is
biaxially stretched during blow-moulding, it produces a bottle that is compatible
with aromatic solvents. The potential benefits of this plastic for the
agrochemical industry were seen immediately by three companies, who collaborated
to carry out the basic testing. PET bottles are now widely used for
agrochemicals. They are transparent and very tough. New bottles have design
features such as wide necks to avoid spattering.
However, farmers continued to use the cap of the PET bottles as a measuring
container, thereby contaminating the outside of the bottle. Shell overcame this
problem by designing a standard volume dispenser that is welded into the
neck of the bottle during manufacture. Not only does this prevent the cap
being used, it also allows for precise measurement and keeps the contents from
spilling if the bottle is accidentally knocked over when the cap is off. A further
safety benefit is that the bottles cannot be reused without cutting the neck off.
PET bottles with dispensers have proven to be popular with small-scale
farmers in Africa. The principal limitations of PET bottles are their unsuitability
for ketones or products that are susceptible to water degradation because
water vapour can permeate the bottle wall.
Two other recent developments in container technology have been the use of
fluorinated high-density polyethylene (HDPE) and the design of multilayered
containers. In the former, gaseous fluorine is included either during or after
the blow-moulding process. This forms an extremely thin layer of fluorinated
HDPE, which is highly resistant to the solvents commonly used in agrochemicals.
A layer of only 150 A is usually considered sufficient.
Containers with walls comprising two or more polymer layers are produced
by coextrusion. Bottle strength is attained from a support layer, usually HDPE,
and resistance to the chemical product is provided by a layer of barrier
material such as polyamide (nylon). The various layers are bonded together
using adhesives.
Plastics permit considerable flexibility in packaging agrochemicals. For example,
5-L tins are not easy to handle when wearing protective gloves, whereas
easy-to-grip handles can be incorporated into plastic containers of this size. A
common problem with early plastic containers was the retention of product
in the hollow handles. This problem has been overcome by pinching off the
base of the handles during blow-moulding to prevent liquid ingress. Similarly,
wider necks on plastic bottles prevent splashing of contents during pouring.
Drainability of containers has also been improved to reduce risk if the container
is reused for drinking water or foodstuffs. This is a particular advantage
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