Vulcanizing Agents、Accelerators and Activators

Vulcanizing Agents、Accelerators and Activators
During vulcanization, the long chain of the rubber molecules become crosslinked by reactions with the vulcanizing agent to form three-dimensional structures. In pratice, sulfur is used almost exclusively for vulcanization of rubber. Other vulcanizing agents, such as sulfur chloride, selenium, tellurium, and thiuram disulfide, are used only in special cases.
Accelerations can increase the speed of reaction between sulphur and rubber, or lower the vulcanization temperature. They can also decrease the physical and technical properities of the vulcanizate.
Inorganic accelerators were discovered accidentally early in the history of the rubber industry when inorganic compounds were added go rubber as coloring agents and fillers. Among the basic salts and metal oxide recommended as accelerators, line, magnesium oxide, and litharge were the most common ones, litharge is still used to some extent, but its blackening effect on the vulcanizate limits its application to black compounds.
Oenslager’s discovery, in 1906, of the acceleration effect of aniline marked the beginning of a long line of organic accelerators which belong to many different groups.
A very small quantity, about 1 per cent, of these organic compounds has a remarkable accelerating effect. Organic accelerators were classified according to their technical effects and were placed in the following categories:
ultra-accelerators
semi-ultra-accelerators
medium-fast-accelerators
slow accelerators
Activators activate accelerators. Most accelerators are much more active in presence of activators than they are alone. The activator reacts with the accelerators. As a result, an intermediate complex is formed. The complex is more effective in activating the sulphur present in the rubber mixture.
There are two large classes of activators: metal oxides and fatty acids. Representatives of both groups must be present simultaneously. The most common member of the first group is zinc oxide which is in the proportion of about 3 to 5 percent as activator in almost every rubber compound. The second group includes oleic palmatic and especially stearic acid. They are used in amounts of 0.5 to 3 percent.
New Words and Expressions
1. agent 剂，媒介物，代理人
2. activator 活化剂
3. vulcanization 硫化
4. chain 链，链条
5. molecule 分子
6. crosslink 交联
7. reaction 反应
8. dimensional 维的，度的，尺寸的
9. structure 结构
10. chloride 氯化物
11. selenium 硒
12. tellurium 碲
13. thiuram 秋兰姆
14. disulfide 二硫化物
15. special 特殊的，专门的
16. increase 增加，提高
17. temperature 温度
18. decrease 减少，降低
19. considerably 相当，大大地
20. inorganic 无机的
21. accidentally 意外地，无意地，偶然地
22. recommend 介绍，推荐
23. lime 氧化钙，生石灰
24. magnesium 镁
25. oxide 氧化物
magnesium oxide 氧化镁
26. zinc 锌
27. litharge 一氧化铅
28. limit 限制，限度
29. aniline 苯胺
30. organic 有机的
31. remarkable 显著的，明显的
32. according 依照
according to 按照，依据
33. technical 技术的，专门的
34. category 种类，部门，范畴
35. ultra 超，过渡的
ultra-accelerators 超促进剂
36. semi 半
37. medium 中等（的），适度，普通
38. activate 活化
39. intermediate 中间的
40. complex 络合物，合成物，复杂的
41. effective 有效的
42. representative 代表，代表的
43. simultaneously 同时发生地，同时进行
44. include 包括
45. oleic 油酸的
46. palmatic 棕榈酸
47. stearic acid 硬脂酸