问题 问答题 论述题

三元乙丙橡胶(EPDM)的特性。

答案

参考答案:

三元乙丙橡胶是乙烯、丙烯以及非共轭二烯烃的三元共聚物。EPDM最主要的特性就是其优越的耐氧化、抗臭氧和抗侵蚀的能力,作屋面防水卷材。由于三元乙丙橡胶属于聚烯烃家族,它具有极好的硫化特性。一般丙烯的含量在30~40%(mol)时是较好的弹性体,为使第三单体在乙丙胶中分布均匀,聚合时一般采取分批加入的方法。第三单体用量多时,不饱和度高,硫化速度快,与不饱和橡胶相容性好,可与不饱和橡胶并用,但是耐热性和老化性下降。

阅读理解

The world’s population has reached 7 billion(十亿)according to the United Nations(联合国)by 2011. It comes just 12 years since the total reached 6 billion - with official estimates saying the population will top 8 billion in 2025 and 10 billion before the end of the century.

And it is most likely that the 10-billionth baby will be born in the Asia-Pacific region - where the population growth rate is higher than anywhere else in the world.

Of the 2.3 billion people, the United Nations believes will be added by 2050, more than 1 billion will live in sub-Saharan Africa. The Indian subcontinent(次大陆)will add some 630 million people.

With more people to feed, more houses & medical care to provide, experts say the world’s resources(资源)will face more strain than before.

小题1:According to the picture, the population of the world reached 6 billion in ________.

A. 1987                     B. 1999                     C. 2011

小题2:We know that more than 1 billion will live in  _______ by 2050.

A. sub-Saharan Africa

B. Indian subcontinent

C. the United States

小题3:According to the picture, _______ will have the largest population in 2050.

A. China                        B. India                        C. Nigeria

小题4:The underlined word “strain” in the last paragraph(段落)means “_________”.

A. 破坏                     B. 关闭                     C. 压力

小题5:The population of the world grows ________ according to the picture.

A. slower and slower

B. faster and faster

C. smaller and smaller

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