Common additives and formula design of the hottest

2022-08-09
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Common additives and formula design for PVC profiles (I)

the formula for PVC plastic profiles is mainly composed of PVC resin and additives, in which additives are divided into: heat stabilizer, lubricant, processing modifier, impact modifier, filler, aging inhibitor, colorant, etc. according to their functions. Before designing PVC formula, we should first understand the performance of PVC resin and various additives

raw materials and additives

PVC resin

the resin used to produce PVC plastic profiles is polyvinyl chloride resin (PVC), which is a polymer polymerized from vinyl chloride monomer. The output is second only to PE

pvc resin can be divided into loose type (XS) and tight type (XI) due to different dispersants in polymerization. The loose particle size is 0.1-0.2mm, the surface is irregular, porous, cotton ball, easy to absorb plasticizer, and the compact particle size is less than 0.1mm, the surface is regular, solid, ping-pong ball, not easy to absorb plasticizer. At present, more loose types are used

pvc can be divided into ordinary grade (toxic PVC) and sanitary grade '(non-toxic PVC). The hygienic level requires that the content of vinyl chloride (VC) is lower than LOXL, which can be used in food and medicine. PVC can be divided into suspension PVC and lotion PVC with different synthetic processes. According to the national standard GB/T "inspection standard for general PVC resin by suspension method", PVC by suspension method is divided into PVC SGL to pvc-sg8jk resins, of which the smaller the number, the greater the degree of polymerization, the greater the molecular weight and the higher the strength, but the more difficult the melt flow is, the more difficult the processing is. When making soft products, pvc-sgl, pvc-sg2 and pvc-sg3 are generally used, and a large amount of plasticizers need to be added. For example, the PVC film uses SG to make the automobile lightweight project -2 resin and add 50~80 parts of plasticizer. When processing hard products, plasticizers are generally not added or added in a small amount, so pvc-sg4, vc-sg5, pvc-sg6, pvc-sg7 and pvc-sg8 are used. For example, SG-4 resin is used for PVC hard pipes, SG-5 resin is used for plastic door and window profiles, sg-6 resin is used for hard transparent sheets, and SG-7 and SG-8 resins are used for hard foaming profiles. The lotion PVC paste is mainly used for artificial leather, wallpaper, floor leather and dipped plastic products. PVC resins from some PVC resin manufacturers are classified according to the degree of polymerization (the degree of polymerization is the number of unit chain links, and the degree of polymerization multiplied by the molecular weight of the chain links is equal to the molecular weight of the polymer). For example, the PVC resin produced by Shandong Qilu Petrochemical plant, the ex factory product is sk-700; S if the speed of data collection is not high enough, k-800; SK—1000; SK—1100; Sk-1200, etc. The corresponding polymerization degree of SG-5 resin is 1000-1100. P all future Polaris cars will adopt an all electric driveline. The physicochemical properties of VC resin can be seen in Chapter 4

pvc powder is a white powder with a density of 1.35-1.45g/cm3 and an apparent density of 0..5g/cm3. Depending on the content of plasticizer, it can be divided into soft and hard products. Generally, the content of plasticizer is divided into hard products, semi-hard products, and soft products greater than 25 parts

pvc is an amorphous, polar polymer. The softening temperature and melting enterprise production cost are long and the temperature is high. Pure PVC generally can be plasticized at 160-210~c. due to the polar bond between macromolecules, PVC shows hard and brittle properties. Moreover, PVC molecules contain chlorine groups. When the temperature reaches 120~c, pure PVC begins to undergo a dehydrochlorination reaction, which will lead to the thermal degradation of PVC. Therefore, various additives must be added to PVC for processing modification and impact modification, so that it can be processed into useful products

pvc resin is mainly used to produce all kinds of films (such as daily printing film, industrial packaging film, agricultural greenhouse film and heat shrinkable film, etc.), all kinds of plates, sheets (the sheets can be used for Blister products), all kinds of pipes (such as non-toxic water supply pipes, building threading pipes, transparent hoses, etc.), all kinds of profiled materials (such as doors, windows, decorative plates), hollow bottle blowing (for cosmetics and beverages), cables, all kinds of injection molding products and artificial leather, floor leather Plastic lined toys, etc

stabilizer

pure PVC resin is extremely sensitive to heat. When the heating temperature reaches above 90Y, a slight thermal decomposition reaction will occur. When the temperature rises to 120c, the decomposition reaction will intensify. At 150C, 10 minutes, the PVC resin will gradually change from the original white to yellow red brown black. The decomposition process of PVC resin is a series of chain reactions caused by the dehydrochlorination reaction, which finally leads to the breaking of macromolecular chains. The thermal stability mechanism of preventing PVC thermal decomposition is realized through the following aspects

prevent the catalytic degradation of HCl by capturing HCl produced by the thermal decomposition of PVC

lead salts mainly act according to this mechanism, in addition to metal soaps, organotin, phosphite esters and epoxides

· replace the active allyl chlorine atom. Metal soaps, phosphite esters and organotin can act according to this mechanism

· react with free radicals and terminate the reaction of free radicals. Organotin and phosphite act according to this mechanism

· addition with conjugated double bonds inhibits the growth of conjugated chains

organotin and epoxy act according to this mechanism

· decompose peroxides and reduce the number of free radicals. Organotin and phosphite act according to this mechanism

· passivate metal ions with catalytic dehydrochlorination

the same stabilizer can achieve the purpose of thermal stability according to several different mechanisms

varieties of common stabilizers:

1. Lead salts

lead salts are the most commonly used heat stabilizers for PVC, and they are also very effective heat stabilizers. Their dosage can account for more than 70% of PVC heat stabilizers

advantages of lead salt stabilizer: excellent thermal stability, long-term thermal stability, excellent electrical insulation, good weather resistance and low price

disadvantages of lead salt stabilizer: poor dispersion, high toxicity, initial coloring, it is difficult to get transparent products, it is difficult to get bright colored products, lack of lubricity, and it is easy to produce sulfur pollution

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