Rubber dry rubber series – natural rubber
1 Current Situation of Chinese Natural Rubber
2 Ingredients in NR
3 The Structure of Natural Rubber
4. Nature of NR
1, the current situation of Chinese natural rubber
As everyone in the industry knows, NR mainly comes from Southeast Asia. Do you know why our country can’t produce NR rubber by itself?
As far as I know, there are mainly the following reasons: (1) Climate: the growing environment of NR can only be located at 18° south to 18° north latitude, and the southernmost part of China is at 19° north latitude. Therefore, Hainan is the main NR production base in China, but the planting area is very limited. The output in 2020 is only about 600,000 tons, and the self-sufficiency rate is only 13%. ② Backward production technology: The production line of China’s NR in Hainan is still the same as that of 10 years ago, with low production efficiency and a large amount of labor. As a result, China’s NR produced by itself cannot compete with Southeast Asian countries in terms of production capacity and quality. Meanwhile, the cost of China’s NR produced by itself is at least 1000-2000 yuan more expensive than that of Southeast Asian countries. The price fluctuation of NR is too big, especially the impact of this epidemic.
Now this situation, our country will face a lot of strategic problems, as we all know, fighter aircraft, large aircraft tires due to a large load, the strength of the requirements are particularly high, must use NR, but also must be NR in the highest strength of the cigarette glue, but our country is no way to supply to meet the requirements of the cigarette glue, completely rely on imports, This is a difficult place, so the country has been trying to change the living conditions of NR, hoping to change the cold tolerance of rubber trees by genetic means, so that rubber trees can be planted in more places in China. Of course, this technology is really difficult, our teachers in Beihua have done a lot of work, but no breakthrough has been made. At present, the main research in the academic world is dandelion, and this northernization has made a breakthrough. At present, the northernization has made tires by using dandelion. However, there is a particularly big problem that the NR latex that can be extracted from dandelion is too little, which cannot be realized in industrialization. What our teachers are doing now is to change the roots of dandelions through genetic technology, hoping to grow roots as big as turnip, so as to increase the yield of NR produced by dandelions.
2. Components of NR
It can be seen that NR has about 5-8% rubber components, and these non-rubber components will directly affect the final characteristics of NR.
3. Structure of natural rubber
The structure of NR is much more complex than that of polycis-isoprene, which is why isoprene rubber does not have the same properties as NR rubber. As can be seen from the figure, in addition to the main intermediate cis-isoprene, the molecular weight of natural rubber also contains two end-groups, -α and w’. The research results show that the α-end group is formed by the combination of phosphate ester group and phospholipid, and the w’ end group is formed by the combination of several trans-isoprene and some special proteins, which combines with the above structure. Here are two of the most important features of NR:
① The molecular weight is huge, can reach millions of levels, processing is difficult, gel content is high, need to plasticizer
The reason for the huge molecular weight is that natural rubber α-terminal group forms gel network through hydrogen bond or intermolecular force
4. Properties of NR
The main characteristics of NR have been clearly explained above, and I will summarize them briefly as follows:
The raw rubber green has high strength, good extrusion and calendering performance, smooth extrusion surface and low shrinkage rate
② Elasticity: natural rubber has medium elasticity, BR>NR>IIR, which is mainly considered from steric hindrance
③ Strength: NR has the best tensile property and excellent strength in general rubber
(4) Processing properties: large molecular weight, high viscosity of raw rubber Mooney, need to plasticize to further processing
⑤ Low temperature resistance: medium to high: glass transition temperature is about -70℃
⑥ Solvent resistance: if a material does not react with the solvent and is not miscible, the material is resistant to the solvent performance, and NR is non-polar rubber, non-polar gasoline, diesel, variable pressure oil, resistance to polar solvents: water, ethanol
⑦ Chemical reactivity: NR rubber has very high chemical reactivity, so the aging resistance of NR is poor, it must be anti-aging treatment; At the same time, the high chemical reactivity of NR can also be used to prepare epoxidized NR and hydrogenated NR. For the two special NR, there are still many ways to write an article on the chemical modification of rubber later.