Preparação para vestibular 2011.1

UNIVERSIDADE ESTADUAL DO CEARÁ – COMISSÃO EXECUTIVA DO VESTIBULAR

VESTIBULAR 2009.2 – 1a FASE – 28 de junho de 2009

LÍNGUA INGLESA

TEXT

From: www.nytimes.com

April 27, 2009

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 University of Groningen in the

Netherlands have devised a thermoset plastic that,

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.

01. A tough kind of plastics to recycle is

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 Netherlands have found that a

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 University of Gronigen has the unique capability

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.