UNIVERSIDADE ESTADUAL DO CEARÁ – COMISSÃO EXECUTIVA DO VESTIBULAR
VESTIBULAR 2009.2 – 1a FASE –
LÍNGUA INGLESA
TEXT
From: www.nytimes.com
Most of the plastics that are recyclable today —
water bottles and grocery bags, for instance — are
what are called thermoplastics. They are polymers
that can be melted down and molded into
something else.
But there is another category of plastics, thermoset
resins, that can’t be easily recycled. These
polymers — the stuff of circuit boards, electrical
insulation and epoxy glue, among other things —
have strong cross-links and when heated tend to
decompose. Most products made from these
plastics end up as waste.
But chemists at the
rather than decomposing, heals itself when heated.
Writing in the journal Macromolecules, the
researchers, Youchun Zhang, Antonius A. Broekhuis
and Francesco Picchioni, say the material has the
potential to be recycled and reused many times.
The building blocks of the polymer are polyketones,
and they are cross-linked using another organic
compound, bismaleimide. One secret to the
material’s success is that the cross-linking reaction
is reversible: when heated to about 300 degrees
Fahrenheit, the material becomes unlinked, but as
it cools the links re-form, creating a rigid polymer
once again.
The researchers demonstrated that the material can
be shredded, melted and remolded at least seven
times with no loss of mechanical properties. Their
discovery, they say, adds to scientific
understanding of the nature of self-healing
materials, and with more research may eventually
lead to the full development of recyclable thermoset
plastics.
A) the one containing an acid in its molecules.
B) the type called thermoset resins.
C) a kind that only decomposes at 100
degrees Fahrenheit.
D) water bottles thrown in the ocean.
02.Researchers in the
specific type of plastic can
A) replace its micromolecules.
B) improve weak cross-links.
C) heal itself instead of decomposing.
D) be reused up to fifty times.
03. The thermoset plastic that has been discovered at
the
of
A) being recycled lots of times.
B) being stored in cold temperatures.
C) recreating polyketones.
D) remodeling temperature patterns.
04. Another positive aspect of this recently devised
plastic is that it
A) recycles grocery bags faster.
B) does not use an organic compound.
C) has an unchangeable cross-linking reaction.
D) retains its mechanical characteristics.
05.The Dutch chemists’ discovery is relevant because it
A) makes plastic recycling more affordable.
B) contributes to scientific understanding of
self-healing plastics.
C) enables plastic factories to work faster.
D) increases the greenhouse effect.
06. One aspect that characterizes thermoset resins is
that they
A) do not reverse the cross-linking reaction.
B) are used to make water bottles
C) create a soft polymer.
D) often decompose with heat.
