Introduction of the types of plastic additives for

2022-09-22
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Introduction to the types of plastic additives for PVDC film-forming

PVDC has high crystallinity because of the symmetry and strong polarity of the two chlorine atoms in its monomer, so that the solubility of gas in it is low and the diffusion is slow, so it has good barrier to oxygen, water and water vapor. In addition, due to its high chlorine content, it also has the advantages of flame retardancy, corrosion resistance and biodegradation resistance. Therefore, PVDC film is now widely used as packaging materials and protective fabrics. However, the two symmetrical chlorine atoms in vinylidene chloride molecule are extremely unstable to heat, and can only be used at 100 ℃. When heated to 125 ℃, HCl is released to form conjugated double bonds, making the polymer yellow or brown, and finally black

in order to improve the thermal stability, processability and serviceability of PVDC, a variety of additives are usually added directly to PVDC before processing. Commonly used additives for film forming include plasticizers, stabilizers, etc

1 plasticizers

pvdc film-forming commonly used plasticizers are dibutyl sebacate (DBS), dioctyl sebacate (DOS), dioctyl adipate (DOA), tributyl citrate (TBC), acetyl tributyl citrate (ATBC). Its main function is to reduce the intermolecular force for plasticization. When selecting, it is mainly required to have good compatibility with resin and meet the needs of food hygiene. Different plasticizers have different characteristics. Therefore, in actual use, two different plasticizers are often used together to learn from each other and meet the requirements of processing performance and product performance. The addition amount is generally 5 ~ 7phr. If the addition amount of plasticizer is low, it will produce anti plasticizing effect and make it rigid; If the amount is too much, the barrier and mechanical properties of the products will be greatly reduced

2 stabilizer

pvdc usually adds some epoxy compounds with thermal stability from Tianjin Tianzhong Jiangtian Heavy Industry Co., Ltd., such as epoxidized soybean oil (ESO) and epoxidized linseed oil (ESL), which are still fresh. As a heat stabilizer, the epoxy structure in these epoxy compounds can interact with HCl, prevent or delay thermal decomposition, and have obvious plasticizing effect

the addition amount of epoxy compound is generally 0 5~2. 5phr, too much dosage, easy to migrate to the surface of the film, causing the film to become sticky and affecting the film-forming property. Glycidyl methacrylate can also be used as a heat stabilizer

3 lubricant

the role of lubricant is to reduce the mutual friction between PVDC resin and extruder barrel and screw due to mechanical shear force during film formation, reduce the stagnant PVDC material in screw and die head, effectively prevent thermal decomposition, improve the film formation rate, and make the film surface glossy at the same time. Commonly used lubricants include metal salts of stearic acid, stearic glycerides, stearic amides, etc. the general addition amount is 011 ~ 1phr. Excessive amount of lubricant will affect the self viscosity of the film

4 inorganic fillers

pvdc film formation usually requires a small amount of inorganic fillers, commonly used calcium carbonate, talc powder, magnesium oxide, kaolin, calcium hydroxide, titanium dioxide, etc. The addition of fillers can not only adjust different barrier properties, but also improve the processability and mechanical properties of the film. For example, when improving the printability and surface smoothness of the film, the addition amount is generally 0101 ~ 3phr, subject to no loss of film transparency. In addition, the addition of titanium dioxide can prevent bubbles and white spots in the film caused by the thermal decomposition of the resin, and does not affect the barrier property of the film. The addition of magnesium oxide can also form a film at higher temperature, which can make the PVDC resin with wide molecular weight distribution have a larger extrusion rate. In addition, the addition of talc powder can act as a nucleating agent and accelerate the crystallization speed

5 high molecular polymer modifier

although PVDC has excellent barrier performance, it still has defects in the processing performance, thermal stability and film strength of the resin. In order to better improve a certain performance or adapt to some special uses, in addition to adding commonly used, low molecular weight additives with the mediation, elimination and upgrading of people's economic tension, such as aerospace, national defense, kerosene chemical industry, transportation, etc, High molecular polymers are often added for blending to improve their properties

511 improve thermal stability and processability

pvdc is easy to decompose due to its poor thermal stability, which makes the processability worse. In order to improve the processability, it is necessary to improve the thermal stability. The modifiers to be added for this purpose are: elastomer or rubber of ethylene alkane copolymer, with the addition amount of 2% ~ 20%; EVA copolymer with vinyl acetate content of 5% ~ 18%, melting flow of 011 ~ 110dg/min, and addition amount of 5% ~ 40%. Modifiers used to improve the processability of the resin include: copolymer of styrene, copolymer of vinylidene chloride and methyl acrylate; In addition, vinylidene chloride with different molecular weight can also be blended with vinyl chloride copolymer resin [16], such as using vinylidene chloride polymer 100phr, polymer 0101 ~ 5phr with styrene content> 20% and softening temperature of 50 ~ 180 ℃, plasticizer or stabilizer 0 With the formula of 1 ~ 3phr, the composition with high barrier and good processing performance can be obtained. When a PVDC resin with molecular weight of 50000 ~ 300000 is blended with another PVDC resin with molecular weight ≥ 5000, a copolymer with excellent processability can be obtained

512 improving film strength

only accounts for 8.4%. The blending modifiers used to improve film strength include styrene copolymers, such as styrene isobutylene, styrene acrylonitrile, styrene methyl acrylate, styrene butadiene, etc; Copolymers such as butadiene methyl methacrylate, ethylene vinyl acetate, polyamide, grafted acrylate or these elastomers. For example, the addition of polyamide can improve the impact strength at low temperature and has high barrier performance

513 improve the softness of the film

pvdc film itself has poor softness. Although adding ordinary plasticizer can improve it, due to the migration of plasticizer in the film-forming process, it is not suitable to use special heat sealing such as high-frequency heat sealing. If 10% ~ 15% ethylene alkyl acrylate copolymer is used, the film can have softness, cold resistance, heat sealing and barrier properties, and the processability is improved

513 improve the transparency of the film

vinyl chloride vinyl acetate copolymer is used, the chlorine content is 1% ~ 50%, and the dosage is 1% ~ 40%; Or blend 1% ~ 40% of vinyl chloride methyl methacrylate copolymer with PVDC; Or PVDC with two different molecular weights can be blended to produce films with high transparency

514 improve the self viscosity and adhesion of the film

improve the self viscosity and adhesion of PVDC film. Although adding liquid plasticizers (such as citric acid ester) can improve the self viscosity and adhesion, it can also be used as plasticizers at the same time. However, the solubility of liquid plasticizers in PVDC is limited, and they often migrate to the film surface, or even to utensils. Although this method can sometimes increase the self adhesion and adhesion of the film, there is still the problem of adhesion between the films. For example, ethylene vinyl acetate copolymer with ethylene content of 50% ~ 65% and molecular weight of 1000 ~ 4000 is used, and the addition amount is 011% ~ 70%, which can be used together with plasticizer

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