问题 问答题 简答题

热老化的主要原因是什么?热稳定剂如何起作用?作为热稳定剂的基本条件是什么?

答案

参考答案:

(1)聚氯乙烯(PVC)是应用非常广泛的热塑性树脂之一,但其热稳定性很差。一般来说,问道在100摄氏度以上即开始发生脱氯化氢、生成不饱和结构、出现大分子交联及热变色等降解现象,达到160-200℃时,这种降解更是剧烈,而且脱出的HCI具有自催化作用,因而脱去更多的HCI,如此恶性循环,塑料颜色变深,由黄色变为棕色甚至变黑,因而导致材料性能劣化。

(2)热稳定剂的作用机理是吸收中和HCI,抑制其自动催化反应。

(3)基本条件:能抑制脱HCI反应的进行或能结合高聚物降解时放出的HCI,终止它的自动催化作用,且与HCI生成的产物对制品无影响,与PVC相容性好,无毒或低毒,能破坏生成颜色的多烯体系,价廉等。一般均用复配热稳定剂,才能满足上述条件。

单项选择题
阅读理解

  If we bought only things we needed, there would be enough for everybody. What do we need? What you need depends on how old you are and your way of life. Rearrange the list of things you can buy and put the things you think we most need at the top of the list.

Coat             Designer jeans          Water       CD player

Dental check up   Restaurant meal     Telephone   Jewelry

Food          Shampoo             MP3 player  Beer

Toothpaste        Bar of chocolate        Cushion covers

If we don’t need to buy so much, we don’t need to work so much. We can take part-time jobs or reduce our working day from eight hours to six hours. Some people are leaving very well paid jobs to live a healthier life in the countryside or a more exciting life abroad. Parents can spend more time with their children and the unemployed are given more opportunities to work.

If we start to respect saving the earth more than spending money, we will become ‘conservers’ (保护者). When we are conservers, we try to choose environmentally friendly products that last a long time. We may find growing our own vegetables or making our own clothes more rewarding than buying them.

Next time you go shopping, think about what you really need to buy. Don’t deprive (剥夺) yourself of things you like, but decide what you should buy before you go out, so that you won’t be influenced by advertisements or promotions. If it is more expensive to buy goods that don’t have much packaging and things that are more durable (耐用的), buy less. If you can choose to work less, decide which things you would like to make, do or grow yourself. Even though you have less money, your life will become richer.

by Julie Bray

小题1: From the passage, we can see the author suggests us consumers ______.

A.find out more about a product instead of buying blindly

B.consider what we really need before going shopping

C.avoid regret at not buying enough

D.find a real bargain小题2:. The writer will agree with you if you buy products that are ______.

A.beautifully packaged

B.extremely cheap

C.usable for a long time

D.fashionable now小题3: According to the passage, if we don’t need to buy so much, the benefits  

will include ______.

a. we will have more time enjoying life

b. the employment rate will increase

c. we will get better paid jobs

d. we as consumers will have more choices of what to buy

A.abc

B.abd

C.ab

D.ad小题4:This passage is mainly written to _____.

A.persuade people to buy less and buy environmentally friendly products

B.put forward some questions so that you can become a smart buyer

C.introduce some good ways to make a wiser choice when shopping

D.criticize the consumer society in which people buy too much