470
TEST 187 READING PASSAGE 1
You should spend about 20 minutes on
Questions 4-8
which are based on
Reading Passage 1 below.
[Note: This is an extract from READING PASSAGE 1 about BAKELITE - The
birth of modem plastics]
The term ‘plastic’ comes from the Greek plassein, meaning ‘to mould’ Some plastics
are derived from natural sources, some are semi-synthetic (the result of chemical
action on a natural substance), and some are entirely synthetic, that is, chemically
engineered from the constituents of coal or oil. Some are ‘thermoplastic’, which
means that, like candlewax, they melt when heated and can then be reshaped.
Others are ‘thermosetting’: like eggs, they cannot revert to their original viscous
state, and their shape is thus fixed for ever Bakelite had the distinction of being
the first totally synthetic thermosetting plastic.
The history of today’s plastics begins with the discovery
of a series of semi-
synthetic thermoplastic materials in the mid-nineteenth century. The impetus
behind the development of these early plastics was generated by a number of
factors - immense technological progress in the domain of chemistry, coupled with
wider cultural changes, and the pragmatic need to find acceptable substitutes for
dwindling supplies of ‘luxury’ materials such as tortoiseshell and ivory.
Baekeland’s interest in plastics began in 1885 when, as a young chemistry student
in Belgium, he embarked on
research into phenolic resins, the group of sticky
substances produced when phenol (carbolic acid) combines with an aldehyde (a
volatile fluid similar to alcohol). He soon abandoned the subject, however, only
returning to it some years later. 8y 1905 he was a wealthy New Yorker, having
recently made his fortune with the invention of a new photographic paper. While
Baekeland had been busily amassing dollars, some
advances had been made in
the development of plastics. The years 1899 and 1900 had seen the patenting of
the first semi-synthetic thermosetting material that could be manufactured on an
industrial scale. In purely scientific terms, Baekeland’s major contribution to the
field is not so much the actual discovery of the material to which he gave his name,
but rather the method by which a reaction between phenol and formaldehyde could
be controlled, thus making possible its preparation on a commercial basis. On 13
July 1907, Baekeland took out his famous patent
describing this preparation, the
essential features of which are still in use today.
The original patent outlined a three-stage process, in which phenol and formaldehyde
(from wood or coal) were initially combined under vacuum inside a large egg-shaped
kettle. The result was a resin known as Novalak, which became soluble and malleable
when heated. The resin was allowed to cool in shallow trays until it hardened, and then
broken up and ground into powder. Other substances were then introduced: including
fillers, such as woodflour, asbestos or cotton, which increase strength and moisture
resistance, catalysts (substances to speed up the reaction
between two chemicals
without joining to either) and hexa, a compound of ammonia and formaldehyde which
supplied the additional formaldehyde necessary to form a thermosetting resin. This resin
was then left to cool and harden, and ground up a second time. The resulting granular
powder
was raw Bakelite, ready to be made into a vast range of manufactured objects.
In the last stage, the heated Bakelite was poured into a hollow mould of the required
shape and subjected to extreme heat and pressure, thereby ‘setting’ its form for life.