Polyvinylidene chloride (PVDC), due to the symmetry and strong polarity of the two chlorine atoms in its monomer, makes its homopolymer have high crystallinity, so that the solubility of the gas in it is low, and the diffusion is slow, so that the barrier property of oxygen, water and water vapor is good. In addition, due to the high chlorine content, it also has the advantages of flame retardant, corrosion resistance and biodegradation resistance, so PVDC film is now widely used as packaging materials and protective fabrics. However, the two symmetric chlorine atoms in the vinylidene chloride molecule are extremely unstable to heat, and can only be used at 100 ° C, and HCl is released when heated to 125 ° C, forming conjugate double bonds, making the polymer yellow or brown, and finally black. In order to improve the thermal stability of PVDC, improve the processability and use performance, a variety of additives are usually added directly to PVDC before processing. The commonly used auxiliaries for film formation are plasticizers, stabilizers, etc. 1 Plasticizer PVDC film often used plasticizer are dibutyl sebacate (DBS), dioctyl sebacate (DOS), dioctyl adipate (DOA), tributyl citrate (TBC), acetyl-tributyl citrate (ATBC). Its main function is to reduce intermolecular forces in order to facilitate plasticization. In the selection, it is mainly required to have good compatibility with resin and meet the needs of food hygiene. Different plasticizers have different characteristics, so in actual use, two different plasticizers are often used to complement each other, to meet the requirements of processing performance and product performance, the amount of addition is generally 5 ~ 7phr, the amount of plasticizer is low, will produce a reverse plasticizer effect, so that it is rigid; If the amount of addition is too much, the barrier property and mechanical property of the product are greatly reduced. 2 Stabilizer PVDC usually adds some epoxy compounds with heat stability during film formation, such as epoxy soybean oil (ESO), epoxy linseed oil (ESL), etc. As a heat stabilizer, the epoxy structure of these epoxy compound molecules can interact with HCl, prevent or delay thermal decomposition, and have obvious plasticizing effect. The addition amount of epoxy compounds is generally 0.5 ~ 2.5phr, and the amount is too much, which is easy to migrate to the surface of the film, causing the film to be sticky and affecting the film formation. Glycidyl methacrylate can also be used as a heat stabilizer. The function of lubricant is to reduce the mutual friction between PVDC resin and extruder cylinder and screw due to mechanical shear force during film formation, reduce the PVDC material stagnated in the screw and die head, effectively prevent thermal decomposition, which is conducive to the improvement of film formation rate, and also make the film surface glossy. Commonly used lubricants are metal salts of stearic acid, stearic acid glycerides, stearic acid amides, etc., the general amount of addition is 011 ~ 1phr, and too much lubricant will affect the self-viscosity of the film. When PVDC film is formed, it is usually necessary to add a small amount of inorganic filler, commonly used calcium carbonate, talc powder, magnesium oxide, kaolin, calcium hydroxide, titanium dioxide and so on. The addition of filler can not only adjust the different barrier properties, but also improve the processing properties and mechanical properties of the film. For example, when improving the printability of the film and the smoothness of the surface, 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 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 a higher temperature, which can make the PVDC resin with a wider molecular weight distribution have a larger extrusion rate. In addition, the addition of talc can play the role of nucleating agent and accelerate the crystallization rate. 5 Polymer modifiers Although PVDC has excellent barrier properties, but there are still defects in the processing performance of the resin, thermal stability and film strength, in order to better improve a performance or adapt to some special uses, in addition to the commonly used, small molecular weight additives, but also often according to the need to add polymer blending to improve its performance. 511 Improve thermal stability and processing performance PVDC due to its poor thermal stability, easy to decompose, so that the processing performance is poor. In order to improve the processing performance, it is necessary to improve the thermal stability. For this purpose, the modifiers that need to be added are: elastomer or rubber body of ethylene alkane copolymer, the amount of addition is 2% to 20%; EVA copolymer containing 5% to 18% vinyl acetate and melting flow of 011 to 110dg/min, adding 5% to 40%. The modifiers used to improve the processability of resin include styrene copolymer, vinylidene chloride copolymer and methyl acrylate copolymer; In addition, vinylidene chloride with different molecular weights can also be blended with vinylidene chloride copolymer resins [16], such as vinylidene chloride polymer 100phr, styrene content >20% softening temperature 50 ~ 180℃ polymer 0101 ~ 5phr, plasticizer or stabilizer 0.1 ~ 3phr formula, can be obtained high barrier, good processing performance group The thing. A PVDC resin with a molecular weight of 50,000 ~ 300,000 and another PVDC resin with a molecular weight of ≥5000 can be blended to obtain a copolymer with excellent processing properties. 512 Improving film strength Blend modifiers used to improve film strength are styrene copolymers, such as styrene-isobutene, styrene-acrylonitrile, styrene-methyl acrylate, styrene-butadiene, etc. Butadiene - methyl methacrylate, ethylene - vinyl acetate, polyamide, grafted acrylates and other copolymers or these elastomers. For example, the addition of polyamide can improve the impact strength at low temperatures and has higher barrier properties. 513 Improve the softness of the film PVDC film itself is poor, adding ordinary plasticizers can be improved, but due to the migration of plasticizers during the film formation process, it is not appropriate to use special heat sealing such as high-frequency heat sealing. If 10% ~ 15% ethylene-acrylic alkyl ester copolymer is used, the film can have softness, cold resistance, heat sealing and barrier properties, and improve the processing performance. 513 To improve the transparency of the film using vinyl chloride-vinyl acetate copolymer, the chlorine content is 1% ~ 50%, the dosage is 1% ~ 40%; Or 1%-40% copolymer of ethylene chloride-methyl methacrylate is blended with PVDC; Or by blending two kinds of PVDC with different molecular weight, the film with high transparency can be prepared. 514 Improve the self-adhesive and adhesive properties of the film to improve the self-adhesive and adhesive properties of the PVDC film, adding a liquid plasticizer (such as citric acid ester) can improve the self-adhesive and adhesive properties, but also can be used as a plasticizer. However, the solubility of the liquid plasticizer in PVDC is limited, and it often migrates to the surface of the film or even to the vessel. Although this method can sometimes increase the self-adhesive and adhesive properties of the film, there are still problems of adhesion between films. If the ethylene content is 50% to 65%, the molecular weight is 1000 to 4000 ethylene-vinyl acetate copolymer, the addition amount is 011% to 70%, and can be used with plasticizer. Responsible Editor: Qiao Tong