There are many kinds of rubber, but rubber itself is non-toxic. The toxicity of some industrial rubber products comes from chemical additives and has nothing to do with rubber. However, due to the use of many chemical additives in rubber processing, various toxic substances/gases/pollutants may be produced during the processing. Rubber products used for contacting/packaging/processing food are strictly in accordance with national regulations during processing, and the final product can be considered as non-toxic.
Early rubber was made of latex of rubber tree, rubber grass and other plants. After processing, it was elastic, insulating, impermeable to water and air. High elastic polymer compound. It is divided into natural rubber and synthetic rubber. Natural rubber is made from rubber tree, rubber grass and other plants after extracting gum; Synthetic rubber is polymerized from various monomers. Rubber products are widely used in all aspects of industry or life.
Chemical composition of rubber
There is an unsaturated double bond in the skeleton of linear polymer chain, which can be opened in the presence of oxygen and sulfur, and cross-linking is formed between adjacent bonds. It will cure into thermosetting polymer TS. The monomer of the homeopathic polybutadiene can be opened.
Introduction of rubber types
Rubber is divided into natural rubber and synthetic rubber according to raw materials. According to the form, it is divided into block raw rubber, latex, liquid rubber and powder rubber. Latex is a colloidal water dispersion of rubber; Liquid rubber is an oligomer of rubber, which is usually a viscous liquid before vulcanization; Powder rubber is made by processing latex into powder, which is convenient for batching and processing. The thermoplastic rubber developed in the 1960s was formed by the processing method of thermoplastic without chemical vulcanization. Rubber is divided into general type and special type according to its use. It is an insulator, which is not easy to conduct electricity, but it may become a conductor when it meets water or different temperatures. Electrical conductivity means that electrons of molecules or ions in a substance are easily conducted.
Rubber classification
Classification by source and use: natural rubber and synthetic rubber; Synthetic rubber is divided into general synthetic rubber and special synthetic rubber.
natural rubber
Natural rubber mainly comes from rubber tree with three leaves. After the epidermis of this rubber tree is cut, milky white juice will flow out. This juice is called latex. Natural rubber is obtained by coagulation, washing, molding and drying. Rubber products Synthetic rubber is artificially synthesized, and different kinds of rubber can be synthesized by using different raw materials (monomers). From 1900 to 19 10, chemist C. D. Harris determined that the structure of natural rubber was a high polymer of isoprene, which opened a way for synthetic rubber. 19 10 years, Russian chemist Lebedev (1874- 1934) polymerized 1 3- butadiene into sodium butadiene rubber, cis-1,4-polybutadiene rubber, chloroprene rubber and many others. The output of synthetic rubber has greatly exceeded that of natural rubber, and the largest output is styrene-butadiene rubber.
Universal synthetic rubber
Refers to rubber varieties that partially or completely replace natural rubber, such as styrene-butadiene rubber, cis-butadiene rubber and isoprene rubber. , mainly used for manufacturing tires and general industrial rubber products. General rubber is in great demand and is the main variety of synthetic rubber.
butadiene-styrene rubber
Styrene-butadiene rubber (SBR), which is polymerized from butadiene and styrene, is the most widely used synthetic rubber, including emulsion polymerized styrene-butadiene rubber, solution polymerized styrene-butadiene rubber and thermoplastic rubber (SBR).
Sisden
It is made of butadiene by solution polymerization. Cis-polybutadiene rubber has excellent cold resistance, wear resistance, elastic rubber tire performance and good aging resistance. Most of cis-polybutadiene rubber is used to produce tires, and a small part is used to make cold-resistant products, cushioning materials, adhesive tapes, rubber shoes and so on. The disadvantages of cis-polybutadiene rubber are poor tear resistance and wet skid resistance.
isoprene rubber
Isoprene rubber is the abbreviation of polyisoprene rubber, which is produced by solution polymerization. Like natural rubber, isoprene rubber has good elasticity and wear resistance, excellent heat resistance and good chemical stability. The strength of raw isoprene rubber (unprocessed) is obviously lower than that of natural rubber, but its quality uniformity and processability are better than that of natural rubber. Isoprene rubber can replace natural rubber to make truck tires and off-road tires, and can also be used to produce various rubber products.
ethylene propylene rubber
Ethylene-propylene rubber is synthesized from ethylene and propylene, which has outstanding aging resistance, electrical insulation and ozone resistance. Ethylene propylene rubber can be filled with a lot of oil and carbon black, and the product price is low. Ethylene propylene rubber has good chemical stability, and its wear resistance, elasticity and oil resistance are close to those of styrene butadiene rubber. Ethylene propylene rubber is widely used, which can be used as tire sidewall, rubber strip, inner tube and automobile parts, and can also be used as wire and cable sheath and high voltage and ultra-high voltage insulation material. You can also make light-colored products, such as rubber shoes and sanitary products.
chloroprene rubber
It is made of chloroprene as the main raw material by homopolymerization or polymerization of a small amount of other monomers. For example, rubber products with high tensile strength have excellent heat resistance, light resistance and aging resistance, and oil resistance is better than natural rubber, styrene-butadiene rubber and cis-butadiene rubber. It has strong flame retardancy and excellent flame retardancy, high chemical stability and good water resistance. The disadvantages of chloroprene rubber are poor electrical insulation and cold resistance, and the raw rubber is unstable during storage. Neoprene rubber has a wide range of uses, such as making covering materials for transportation belts and transmission belts, wires and cables, making oil-resistant hoses, gaskets and chemical-resistant equipment linings.
Structural introduction
Linear structure: the common structure of unvulcanized rubber. Because of its large molecular weight, it is fine spherical without external force. When external force is applied and removed, the entanglement degree of fine particles changes, and the molecular chain rebounds, resulting in a strong recovery tendency, which is the origin of rubber's high elasticity.
Branched chain structure: the branches of rubber macromolecular chain gather to form gel. Gel is not good for rubber properties and processing. When rubber is mixed, all kinds of compounding agents often cannot enter the gel zone, forming local blank, unable to form reinforcement and crosslinking, and becoming the weak part of the product.
Cross-linked structure: linear molecules are connected with each other through some atoms or atomic groups to form a three-dimensional network structure. With the progress of vulcanization, this structure has been continuously strengthened. In this way, the free movement ability of the chain segment decreases, the plasticity and elongation decrease, the strength, elasticity and hardness increase, and the compression set and swelling degree decrease.
Sources and application characteristics of different types of rubber
Rubber has good comprehensive properties and is widely used. Mainly includes: ① natural rubber. It is made from latex of Hevea brasiliensis, and its basic chemical composition is cis-polyisoprene. Good elasticity, high strength and comprehensive performance. ② Isoprene rubber. The full name is cis-1, 4- polyisoprene rubber, which is a high cis-synthetic rubber made of isoprene. Because its structure and performance are similar to natural rubber, it is also called synthetic natural rubber. ③ Styrene-butadiene rubber. Short for SBR, it is polymerized from butadiene and styrene. According to the production methods, it is divided into emulsion polymerized styrene-butadiene rubber and solution polymerized styrene-butadiene rubber. Its comprehensive performance and chemical stability are good. ④ Butadiene rubber. The full name is cis-1, 4- polybutadiene rubber, abBReviated as br, which is polymerized from butadiene. Compared with other general rubber, vulcanized cis-polybutadiene rubber has excellent cold resistance, wear resistance and elasticity, less heat generation under dynamic load and good aging resistance, and is easy to be used with natural rubber, chloroprene rubber and nitrile rubber.
Special rubber refers to rubber with some special properties. Mainly includes: ① chloroprene rubber. CR for short is polymerized from chloroprene. Have kindness
Good comprehensive performance, oil resistance, flame retardancy, oxidation resistance and ozone resistance. However, it has high density, easy crystallization and hardening at room temperature, poor storage and poor cold resistance. ② Nitrile rubber. NBR for short is polymerized from butadiene and acrylonitrile. Good oil resistance and aging resistance, and can be used in air at 120℃ or oil at 150℃ for a long time. In addition, it also has water resistance, air tightness and excellent bonding performance. ③ Silicone rubber. The main chain consists of silicon atoms and oxygen atoms alternately, and the silicon atoms have organic groups. High and low temperature resistance, ozone resistance and good electrical insulation. (4) fluororubber. Synthetic rubber with fluorine atoms in its molecular structure. It is usually expressed by the number of fluorine atoms of fluorine-containing units in * * * polymers, such as fluororubber 23, which is a * * * polymer of vinylidene fluoride and chlorotrifluoroethylene. Fluorine rubber is resistant to high temperature, oil and chemical corrosion. (5) polysulfide rubber. It is formed by condensation polymerization of dihalides of alkali metals or alkaline earth metals and polysulfides. It has excellent oil resistance and solvent resistance, but its strength is not high, its aging resistance and processability are not good, and its smell is unpleasant. It is mainly used with nitrile rubber. In addition, there are polyurethane rubber, chlorohydrin rubber, acrylate rubber and so on.
Rubber aging
(1) Rubber aging phenomenon: In the process of processing, storage or use, raw rubber or rubber products will gradually undergo physical and chemical changes under the influence of cleaning factors such as heat, oxygen and light, which will reduce their performance and lose their use value. This phenomenon is called rubber aging. The aging process of rubber is often accompanied by some remarkable phenomena. For example, natural rubber stored for a long time will appear soft, sticky and spotted. Rubber products are deformed, brittle, hardened, cracked, moldy, tarnished and discolored. In terms of physical properties, rubber has changes in swelling and rheological properties. In terms of mechanical properties, tensile strength, elongation at break, impact strength, bending strength, compression ratio, elasticity and other indicators will all decrease.
(2) Causes of rubber aging: The phenomenon of rubber aging is caused by external factors such as long-term heat, oxygen, light, mechanical force, radiation, chemical media and ozone in the air. The chemical change of its macromolecular chain destroys the original chemical structure of rubber, which leads to the deterioration of rubber properties. The external factors leading to rubber aging mainly include physical factors, chemical factors and biological factors. Physical factors include heat, light, electricity, pressure and so on; Chemical factors include oxygen, ozone, acid, alkali, salt and metal ions. Biological factors include microorganisms (mold, bacteria) and insects (termites, etc. ). These external factors often do not act alone in the rubber aging process, but interact with each other to accelerate the rubber aging process. For example, the tire sidewall will be affected by various factors such as heat, light, alternating stress and strain, oxygen, ozone and so on.
Different products have different functions under different conditions of use, and their aging conditions are also different. Even if the same product is used in different seasons and regions, the aging situation is different. So the aging of rubber is a comprehensive chemical reaction caused by many factors. Among these factors, the most common and important chemical factors are oxygen and ozone; Physical factors are heat, light and mechanical stress. Generally speaking, the aging of rubber products is the result of one or more factors. The most common aging is thermal oxidation, followed by ozone aging, fatigue aging and photooxidation aging. [2]
Break down the latest news
The futures market is very lively recently. In addition to the continuous record high of soybean meal, the trend of Hujiao has also attracted the attention of market participants. After hitting a five-year low, Hujiao futures actually showed a strong daily limit in May 19, and then fluctuated and rose.
Some market participants believe that it is geopolitical factors and the news that floods in Thailand may destroy about 15% of rubber trees that have become the source of speculation in the current Hujiao market.
"This year, the yield of rubber shorting has doubled. Making more rubber is like going to purgatory. Grab a rebound and lose once. I thought Monday's daily limit could establish the bottom. Now it seems that it is better to wait and see. " Mr. Wang, who has been losing money on rubber varieties this year, said in an interview that due to the tension between China and Vietnam and the floods in Thailand, Mr. Wang believes that there will be a wave of domestic rubber rebound. Now it seems that the bottom is far from being established.
Generally speaking, due to the lack of substantial improvement in rubber fundamentals, short-term external bullish factors are still difficult to change the contradiction between supply and demand.
The Sino-Vietnamese conflict failed to stir the rubber market
In mid-May, serious violent incidents of beating, smashing, looting and burning Chinese-funded enterprises occurred in many places in Vietnam, causing casualties and property losses to Vietnamese citizens and undermining the atmosphere and conditions for exchanges and cooperation between Vietnam and China. A spokesman for the Ministry of Foreign Affairs said in May 18 that China has raised the level of travel safety tips for China citizens and suspended some bilateral exchange programs from now on.
As soon as this news is announced, the insiders believe that the deterioration of Sino-Vietnamese relations may lead to the market's fear that Vietnam's natural rubber imports will be blocked and the market supply will tighten in the short term. The main short positions that once continued to increase positions began to retreat sharply, which directly led to the futures market. Surge. In fact, at the end of April, Hujiao soared for two consecutive days, including many factors such as lightening positions before the holiday and drought speculation in Yunnan.
In the early morning of May 19, it seems that the main rubber contract 1409 is still looking for space. After consolidating at 13800- 13900 for about 1 hour, at about 10 in the morning, the rubber went straight to the daily limit in just 10 minutes. Subsequently, although the daily limit was opened many times, it finally closed at the daily limit.
However, the following four trading days still maintained a sideways upward trend. As of May 22nd, the closing price of the main natural rubber futures contract 1409 in the previous issue was 14375 yuan/ton, which was 0.48% lower than the settlement price of the previous trading day.
In this regard, Dong Shiguang, a rubber researcher in galaxy futures, believes that on May 19, the disk once again significantly reduced its position and went straight to the daily limit, with a single-day lightening range of 12%. At present, there are two kinds of rumors in the market: First, the situation in Vietnam is tense and there is an expectation of war; just look at the performance of other financial markets and you will know that domestic military stocks and emerging market stocks have not changed.
In addition, there are rumors that compound rubber will be subject to tariffs, that is, the zero tariff condition of compound rubber will be adjusted from 3% to 20%. The reason is that some enterprises say that importing rubber compound will disturb the domestic market. This matter has been circulating for a long time, but it actually belongs to the agreement of the six ASEAN countries. Even if it is improved, it will take a long time to negotiate. Natural rubber futures have always been characterized by skyrocketing and plunging, and the volatility is in the forefront of domestic futures varieties.
Although it has been in a bear market, it is not uncommon to rush to the daily limit halfway. This year, natural rubber has three daily limit in February 17, March 1 1 and March 12. The price rebounded sharply after a sharp drop. News often follows the price, and the fundamentals of large-scale rise are not supported, mainly because the accumulated supply and inventory in the early stage are too large. At present, the fundamentals of oversupply have not changed much. However, due to the low absolute price, the short positions in the futures market are too crowded and the price may fluctuate at the bottom.
In addition, from the overall supply and demand of rubber, the surplus is still a big pattern, and the long-term weak direction will not change. However, there are differences in a short period of time. Before the end of July, the supply of all latex in China was really not plentiful. At present, the stock of latex at the initial stage of rubber tapping is relatively small, and the price after rubber drying is 16000 yuan/ton, which is higher than the price of all latex. Therefore, Hainan private and self-operated rubber factories will mainly produce rubber latex.
However, Hainan rubber needs to be stored with new full latex after May, so the monthly output of more than 65438+100000 tons is basically used for storage, and the number of new full latex available for sale and delivery arbitrage is very small. This will lead to the short-selling pressure of industrial customers on 150 1, which will not be amplified in the short term, and the previous inventory will remain stable, which is a support for Hujiao.
Jia Min, an international futures rubber analyst, believes that from the performance of the internal and external markets, although the trend of Hujiao is strong, the trend of the external market and the spot market is relatively calm, and the price difference between Hujiao and compound rubber is rapidly enlarged, once again approaching the previous high point. On the one hand, it shows that the tire consumption is sluggish under the downward pressure of the economy, which leads to the cautious contraction of its raw material procurement. On the other hand, the rising price difference is more and more attractive to industrial arbitrage customers, and it is quite dangerous for futures to maintain excessive premium without physical support.
High inventory is still the fundamental problem.
"Now for our rubber enterprises, the biggest problem is not profit, but inventory. How to go to inventory has become the biggest problem. " Manager Li of a large rubber company in Qingdao said in an interview with the reporter of China Times, "With the continuous downturn in rubber prices, the company's trade volume has dropped sharply this year. Last year, the trade volume was 200,000 tons, and this year may be less than 6.5438+10,000 tons. "
In this regard, Jia Min believes that only through thorough premium repair and seizing the composite rubber market can the fundamental problem of high price difference and high inventory of Hujiao be solved. Therefore, the existence of these contradictions also shows that the low point of rubber in the year did not appear, but it is more important to grasp the rhythm in the overall empty atmosphere.
Judging from the fluctuation performance of Hujiao, since May, the amplitude has narrowed and the directionality has weakened. The effective contribution of intraday fluctuation to the price trend is decreasing, and the downward momentum is weakened. Bears need to accumulate energy again.
In Jia Min's view, in May and June, when the supply of new whole milk labels was less, the market was still dominated by low shocks. After the delivery of 1405 contract, the market lacks new short positions, and the problems of high price difference and high inventory may last until July and August when 1409 contract is changed to 150 1 contract.
In addition, the latest inventory report of Zhou Du shows that the natural rubber warehouse receipt is reduced by 680 to 1236 10 tons compared with the previous week, and the inventory is reduced by 3755 to 163097 tons compared with the previous week. The latest data of the bonded area increased by 1.200 tons to 362,200 tons, including 7,000 tons of natural rubber, 5,500 tons of composite rubber and 300 tons of synthetic rubber. The amount of standard rubber that can be delivered has exceeded the historical high point in mid-February.
In this regard, Dong Shiguang believes that the operating rate of all-steel tires and semi-steel tires is 76.5% and 8 1.3% respectively in the downstream eastern Shandong area. At present, all-steel construction is generally around 70%, and semi-steel is higher. The operating rate of old factories and big factories is high, and the inventory of raw materials is still not high. According to the daily normal consumption, most of them did not increase the inventory, and the overall inventory remained low. On the whole, if we simply look at the downstream situation, it is not bad, even good.
"Although Hujiao's rebound did not effectively break through the high point on April 29, it is still in the game stage of frequent hand changes. The weakness of the spot market has become an important resistance to the upward trend of futures prices. Traders are actively shipping at the rebound node, but the insufficient consumption of finished products in tire factories limits the procurement of raw materials, and the main participants in the industrial chain are still bearish. At present, the macro environment lacks further stimulus policies for commodities, and the volatility of futures prices has been entrenched at a low level for a long time, and prices will remain weak and volatile. " Dong Shiguang said.
At the same time, Jia Min said that from the perspective of industrial chain structure, for small and medium-sized traders, it is still the dishwashing period. Normal rubber trade is bound to lose money, and it is difficult for private traders with short capital chains to turn around. However, the market has never lacked fresh blood. Some state-owned enterprises with strong financial strength choose to re-enter the market share during the industrial downturn, and transfer industrial risks to speculators through futures arbitrage and hedging operations, and still achieve profitability [1].
merits and demerits
natural rubber
Natural rubber is a polymer of isoprene, which is made of latex collected from rubber trees. It has good wear resistance, high elasticity, breaking strength and elongation. Easy to age in air, sticky when heated, easy to swell and dissolve in mineral oil or gasoline, alkali-resistant but not strong acid-resistant. Advantages: good elasticity, acid and alkali resistance. Disadvantages: no weather resistance and oil resistance (vegetable oil resistance). It is a raw material for manufacturing adhesive tapes, rubber hoses and rubber shoes, and is suitable for manufacturing shock-absorbing parts and products used in hydroxyl-containing liquids such as automobile brake oil and ethanol.
butadiene-styrene rubber
(Styrene-butadiene copolymer) Compared with natural rubber, the * * * polymer of butadiene and styrene has uniform quality, less impurities, better wear resistance and aging resistance, but weaker mechanical strength, and can be blended with natural rubber. Advantages: low-cost non-oil resistant material, good water resistance, good elasticity below hardness 70, and poor compressibility at high hardness. Disadvantages: Strong acid, ozone, oil, grease and most hydrocarbons are not recommended. Widely used in tire industry, shoe industry, cloth industry and conveyor belt industry.
Butyl rubber IIR
Butyl rubber is polymerized from isobutylene and a small amount of isoprene. Because the movement of sterically hindered molecules of methyl group is less than that of other polymers, it has less air permeability, stronger heat resistance, sunlight resistance and ozone resistance, and better electrical insulation. Resistant to polar solvents, the general temperature range is -54- 1 10℃. Advantages: impermeable to most general gases, good resistance to sunlight and odor, and contact with animals or vegetable oils or evaporable chemicals. Disadvantages: It is not recommended to use it together with petroleum solvent, colloidal kerosene and aromatic hydrogen. Used for inner tube, leather bag, rubber paste paper, window frame glue, steam hose, heat-resistant conveyor belt, etc. Car tires.
Hydrogenated nitrile rubber HNBR
Hydrogenated nitrile rubber is a kind of nitrile rubber with partial double chains removed after hydrogenation. After hydrogenation, the temperature resistance and weather resistance are much higher than those of ordinary nitrile rubber, and the oil resistance is similar to that of ordinary nitrile rubber. The general temperature range is -25- 150℃. Advantages: Compared with NBR, it has better wear resistance and excellent corrosion resistance, tensile strength, tear resistance and compressibility.
It has good resistance under atmospheric conditions such as ozone, and is generally suitable for washing clothes or washing dishes. Disadvantages: It is not recommended to be used in air conditioning and refrigeration industry in alcohol, ester or aromatic solution, but widely used in environmental protection refrigerants, seals in R 134a systems and seals in automobile engine systems.
ethylene propylene rubber
EPDM (ethylene propylene rubber) is polymerized from ethylene and propylene, so it has excellent heat resistance, aging resistance, ozone resistance and stability, but sulfur cannot be added. In order to solve this problem, EPDM can be obtained by introducing a small amount of the third component with double chains into the main chain of EP, and the general use temperature is -50- 150℃. Excellent resistance to polar solvents such as alcohols and ketones: good weather resistance and ozone resistance, excellent water resistance and chemical resistance, both alcohols and ketones, high temperature steam resistance and good air tightness. Disadvantages: Not recommended for food or contact with aromatic hydrogen. Seals, sanitary ware seals or parts in high temperature steam environment. Rubber parts in braking system. Seals in radiator (automobile water tank).
nitrile rubber
(NBR) is polymerized from acrylonitrile and butadiene, and the acrylonitrile content ranges from18% to 50%. The higher the acrylonitrile content, the better the hydrocarbon fuel oil resistance of petrochemical oil, but the lower the temperature performance. Generally, the temperature range is -25- 100℃. Nitrile rubber is one of the most commonly used rubbers for oil seals and O-rings at present: it has good oil resistance, water resistance, solvent resistance and high-pressure oil resistance.
It has good compressibility, wear resistance and elongation.
Disadvantages: Not suitable for polar solvents, such as ketones, ozone, nitrohydrocarbons, methyl ethyl ketone and chloroform. It is used to manufacture fuel tanks, lubricating oil tanks and rubber parts, especially seals, and is used in fluid media such as petroleum hydraulic oil, gasoline, water, silicone oil and diester lubricating oil. It can be said that it is the most widely used rubber seal with the lowest cost at present.
Neoprene CR
(chloroprene rubber, polychloroprene) is polymerized from chloroprene monomer. Vulcanized rubber has good elasticity and wear resistance, not afraid of direct sunlight, especially good weather resistance and strong distortion, refrigerant, dilute acid and silicone ester lubricating oil, but not phosphate ester hydraulic oil. It is easy to crystallize and harden at low temperature and has poor storage stability. It has great expansion in mineral oil with low aniline point, and the general temperature range is -50~ 150℃. Advantages: good elasticity, good compression deformability, no sulfur in the formula, so it is very easy to make, has the characteristics of animal and vegetable oil resistance, will not be affected by neutral chemicals, fat, grease and solvents, and has the characteristics of flame retardant.
Disadvantages: It is not recommended to use R 12 refrigerant-resistant seals in chemicals such as strong acids, nitro-hydrocarbons, esters, chloroform and ketones, and rubber parts or seals on household appliances. Suitable for making all kinds of parts that are in direct contact with the atmosphere, sunlight and ozone. Suitable for all kinds of rubber products with fire resistance and chemical corrosion resistance.
Composition of synthetic rubber: Synthetic rubber is a polymer polymerized from petroleum and natural gas as well as dienes and olefins as monomers.
The polymer of rubber has broken through the process of monomer polymerization, and the world's leading rubber factory has begun to use rubber with higher strength, which is made of ultra-high molecular polymer, and the cost is quite low.