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With China Plastic Machinery
With China Plastic Machinery
Rubber and plastic are collectively referred to as rubber and plastic industries. They are both byproducts of petroleum. They are the same in terms of source. However, in the process of making products, their physical properties are different, and their uses are even more different. Rubber is widely used in tires, and plastic is becoming more and more widely used with the needs of technology and the market. It is already inseparable from daily life.
Differences between rubber and plastic
Simply put, the most essential difference between plastic and rubber is that plastic deformation occurs when plastic is deformed, while rubber is elastic deformation. In other words, it is not easy for plastic to return to its original state after deformation, while rubber is much easier. The elasticity of plastic is very small, usually less than 100%, while rubber can reach 1000% or even more. In terms of plastic molding, most of the molding process is completed and the product process is completed; while rubber molding process needs to be vulcanized after completion.
Plastics and rubber are both polymer materials, mainly composed of carbon and hydrogen atoms, and some contain a small amount of oxygen, nitrogen, chlorine, silicon, fluorine, sulfur and other atoms. They have special properties and special uses. At room temperature, plastic is solid, very hard, and cannot be stretched or deformed. Rubber, on the other hand, is not very hard, is elastic, can be stretched and lengthened, and can return to its original shape when the stretching stops. This is due to their different molecular structures. Another difference is that plastic can be recycled and reused many times, while rubber cannot be directly recycled and reused. It can only be used after being processed into recycled rubber. The shape of plastic at more than 100 degrees to 200 degrees is similar to the shape of rubber at 60 to 100 degrees. Plastic does not include rubber.
To be complicated, in a broad sense, rubber is actually a type of plastic, and plastic includes rubber. Now let's introduce it in detail.
General industrial double-sided adhesives can be divided into two categories: acrylic adhesives and rubber adhesives. These two categories can be divided into two types: with substrate and without substrate (with substrate: add a layer of cotton to the adhesive to increase the amount and strength of the double-sided adhesive itself, without substrate: pure adhesive to ensure the transparency of the double-sided adhesive). Because the main body of the rubber adhesive is CR, it is very easy to react with the vulcanization system of rubber and turn purple when used in rubber products. Therefore, lighter colored rubber products all use double-sided adhesive with a base material in the acrylic adhesive system (double-sided adhesives of the same type, whether with a base material or without a base material, are distinguished by the thickness of their own adhesive.
Raw rubber can be divided into two categories: natural rubber and synthetic rubber.
1. Natural rubber: The raw rubber formed by collecting the rubber slurry flowing out from the cut of the rubber tree trunk, and undergoing processing procedures such as impurity removal, coagulation, smoking, and drying.
2. Synthetic rubber: A by-product produced by the petrochemical industry, which is synthesized into raw rubber with different physical properties according to different needs. Commonly used ones include: SBR, NBR, EPDM, BR, IIR, CR, Q, FKM, etc. However, due to differences in the synthesis method, the same type of rubber can be divided into There are several different kinds of raw rubbers, and through the setting of formulas, any type of rubber can be transformed into hundreds of raw rubbers that meet the needs of the products.
Natural rubber comes from tropical and subtropical rubber trees. Because rubber plays an important role in industry, agriculture, and national defense, it is an important strategic material, which has prompted countries lacking rubber resources to take the lead in researching and developing synthetic rubber.
By analyzing the chemical composition of natural rubber, it was found that its basic component is isoprene. This inspired people to use isoprene as a monomer for polymerization reaction to obtain synthetic rubber, called isoprene rubber. The structure and properties of isoprene rubber are basically the same as those of natural rubber. Because isoprene could only be obtained from turpentine at that time, the source of raw materials was limited. Due to the limitation of butadiene, a series of synthetic rubbers were developed based on butadiene. Such as butadiene rubber, styrene-butadiene rubber, nitrile rubber and chloroprene rubber.
With the development of petrochemical industry, various gases such as ethylene, propylene, butene, isobutylene, butane, pentene and isopentene can be obtained from oilfield gas and refinery gas through high-temperature cracking and separation and purification. They are good raw materials for making synthetic rubber.
Natural rubber accounts for only about 15% of the world's rubber production, and the rest is synthetic rubber. There are many varieties of synthetic rubber with different properties. They can replace or even exceed natural rubber in many occasions. Synthetic rubber can be divided into general-purpose rubber and special rubber. General-purpose rubber is used in large quantities. For example, styrene-butadiene rubber accounts for 60% of the output of synthetic rubber; secondly It is butadiene rubber, accounting for 15%; in addition, there are isoprene rubber, chloroprene rubber, sodium butadiene rubber, ethylene propylene rubber, butyl rubber, etc., which are all general-purpose rubbers.
The preparation of rubber raw materials can be divided into three basic processes.
1. Plastication: Plasticization is to cut the raw rubber, plasticize and homogenize the raw rubber, and help the mixing of the compounding agent. Its effect is to improve the dispersion of the drug, prevent the friction heat generated during the operation, and cause the rubber to burn, thereby changing the processability of the rubber.
2. Mixing: Mixing is to evenly mix the compounding drug into the raw rubber after plasticization, and the quality of mixing directly affects the quality of the product. If the drug is unevenly dispersed, the molecular structure cannot be completely cross-linked, and the rubber cannot achieve the ideal physical properties.
3. Extrusion: After the raw rubber is mixed, the excess air contained in the rubber is pressed out through the extrusion operation, and the required thickness is completed to facilitate the molding operation in the mold.
The molecular structure of raw rubber is an elastomer with unsaturated long bonds, so the molding requirements require appropriate drug additives and external environmental factors (such as time, temperature, pressure, etc.) to destroy its unsaturated bonds, re-combine them into saturated bonds, and use vacuum to completely force out the contained air.
In this way, the molded rubber can exert its due characteristics. If there are any deficiencies in the molding process (such as wrong formula, insufficient time, improper temperature, etc.), it may cause physical property loss, excess drug release, deformation, accelerated aging, and various serious adverse phenomena.
Depending on the environmental conditions of the rubber product, the phenomenon of cracking or hardening, degradation of rubber physical properties, etc. over time is called aging phenomenon. The cause of aging is internal factors.
Internal factors: Internal factors include the type of rubber, molding method, bonding degree, type of compounding drug, factors in processing engineering, etc.
To prevent aging, we should focus on the correct selection of rubber and formula design, as well as rigorous production concepts. Only in this way can the life of rubber products be increased and their special functions be brought into play.
1. When rubber products are molded, they are pressed under great pressure. Because the cohesive force of the elastic body cannot be eliminated, extremely unstable shrinkage often occurs when the rubber is released from the mold (the shrinkage rate of rubber varies with different rubber types). It takes a period of time before it can be stabilized. Therefore, when a rubber product is designed, no matter the formula or mold, it is necessary to calculate and match carefully. Otherwise, it is easy to produce unstable product size and low product quality.
2. Rubber is a hot-melt and thermosetting elastomer, while plastic is a hot-melt and cold-setting elastomer. Due to the different types of sulfide, the temperature range of rubber molding and curing is also quite different, and it can even be affected by climate changes and indoor temperature and humidity. Therefore, the production conditions of rubber products need to be adjusted appropriately at any time. If not, the quality of the products may be different.
3. The nine-vertical closed-cell structure of rubber and plastic can effectively prevent heat conduction
4. The thermal conductivity does not exceed 0.034W/m¡¤k at 0¡ãC.
5. The surface heat release coefficient is high, reaching 9W/mk
6. It has excellent resistance to water vapor penetration. The moisture resistance ¦Ì¡Ý5,000 constitutes a "built-in" waterproof vapor layer, making the insulation board as a whole both an insulation layer and a moisture-proof layer.
Long-term contact with rubber and plastic products is very harmful to human health. Many children like to chew this kind of eraser with strong fragrance and bright colors in their mouths. Children's resistance is relatively weak, so it is very harmful.
The pollution cost of plastic production is very high, especially for air pollution and emission pollution. The gas and sewage emitted contain very pungent chemical components, and the black smoke produced during the production process is highly toxic.
Rubber and plastic are also divided into two types: natural rubber and plastic and synthetic rubber and plastic. Synthetic rubber and plastic also have pollution emissions and are highly toxic. Now the country advocates the use of natural rubber and plastic for processing. Natural rubber and plastic are zero pollution and zero emission, which just meets the current international issues of low-carbon life. However, natural rubber and plastic also have performance differences for the above two types.
Due to the uniqueness of their chemical structure, rubber and plastic materials are flammable products and produce melt droplets during combustion. In order to meet the requirements of flame retardancy in use, the following methods are currently generally adopted internationally:
1. Increase the oxygen index. The oxygen index of a material refers to the minimum oxygen concentration that maintains the continuous combustion of the material. The higher the oxygen index, the better the flame retardant performance of the material, and vice versa. If the oxygen index is greater than 26, it will extinguish itself in the air. If the oxygen index is greater than 32, it is difficult to burn in the air. The methods generally used to improve the oxygen index of flammable materials are: copolymerization method - that is, introducing atoms such as X, P, and N on the molecular chain through copolymerization reaction. The HX, NH3, etc. produced when the material is burned and decomposed can dilute the density of small molecular olefins and alkanes produced by chain breaking, inhibiting the combustion reaction; grafting method - that is, monomers with good flame retardancy are grafted on flammable molecular chains to improve their flame retardancy; cross-linking method - that is, linear molecular chains are cross-linked to form a network structure between molecular chains to achieve the purpose of improving the oxygen index. The method to improve the oxygen index of rubber and plastic materials is the cross-linking method.
2. Add flame retardant additives to isolate the products of their combustion from air and combustible gases, thereby improving the flame retardant properties of the product. There are two types of flame retardant additives: halogen additives and metal hydroxide flame retardants.
Halogen additives refer to halogen-containing flame retardants, such as chlorine-based and bromine-based flame retardants. Under the action of flames, they release inert gases and isolate oxygen, thereby achieving the purpose of flame retardancy. However, on the other hand, under high temperature, halogen-based flame retardants will produce a large amount of toxic and corrosive gases because the condensed phase thermal decomposition products cannot be fully burned, forming secondary pollution. Although the combustion is prevented, the generated smoke concentration is large and the smoke density is high. The toxic gases produced once again harm people's health.
Metal hydroxide flame retardants refer to flame retardants containing hydroxides such as AL(OH)3 and Mg(OH)2. Such additives absorb heat and dehydrate at temperatures above 200¡ãC, taking away the generated combustion heat. The oxides produced by dehydration form a solid and dense flame retardant barrier on the surface of the material, which plays a role in heat insulation protection, thereby reducing the combustion speed, preventing the spread of flames, and achieving the purpose of inhibiting combustion. It does not produce droplets and has a low smoke concentration during combustion. It is an ideal flame retardant additive.
NBR-PVC nitrile rubber is a polar material. Adding hydroxide flame retardant will greatly reduce the physical and chemical properties of the material, increase the scrap rate, and cannot be produced continuously. In addition, due to the influence of production costs, Chinese rubber and plastic material manufacturers can only use halogen-containing flame retardants. This is the fundamental reason why those low-priced rubber and plastic materials produce a large amount of black, choking and toxic gases when burned. EPDM ethylene propylene rubber is a non-polar material. After adding hydroxide flame retardant, its physical properties will be greatly improved. Although the cost is high, the scrap rate is low and the smoke density is low when burning.
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