Characteristics of PVC heat stabilizer
It is always desirable for PVC stabilizers to be easily dispersed in polymers and to be used for a long period of time without precipitation after being made into articles. However, when the stabilizer is not compatible, it will move from the inside to the outside of the product and remain on the surface of the product. If the spray is powdery, it is called frosting; if the spray is liquid, it is called perspiration
In general, some metal soap, lubricants and Organic Tin Maleate, easy to Cause Spray Frost; phosphite, phosphate and other PVC stabilizers will also increase spray frost. For metal soaps, the metal with less electronegativity is sprayed with less cream; the aromatic acid radical is sprayed with less cream than the fatty acid radical; the longer carbon chain in the fatty acid radical is, the more severe the Frost is sprayed.
TRANSPARENCY OF PVC STABILIZERS AND PRODUCTS
Organotin, especially maleate and Mercaptan Organotin, is a kind of transparent PVC stabilizer, mainly used in hard transparent products Only in opaque materials.
Transparent plastic products if the water immersion, or through the outdoor exposure, or by bending, stretching and other conditions, will produce albinism phenomenon loss of transparency. Immersion in water means that a transparent plastic board is opaque and opaque because it has been immersed in water for a certain period of time; exposure to sunlight means that a plastic hard board is placed in the air because of the moisture in the atmosphere, carbon dioxide, sulfur Dioxide and the role of light phenomenon; stress whitening refers to plastic products under external mechanical force, the crease appears white phenomenon.
3. Fish eye air bubble
When a transparent or semitransparent sheet of plastic is viewed against the light, transparent or translucent pellets similar to a fish's eye can be seen. "bubbles" are caused by an imbalance of volatile components or processability in a PVC STABILIZER
PVC is vinyl chloride monomer (vcm) initiated by free radical polymerization. In the reaction, during the growth of the molecular chain, a chain transfer reaction will take place and a tertiary carbon atom will be formed. The chlorine atom and the hydrogen atom, which are connected with the tertiary carbon atom, become active atoms due to the low density of the electron cloud distribution and the low bond energy It is easy to remove a portion of the HCL with the adjacent H and CL. The molecular structure of PVC Resin is arranged in the following order:
Primary Molecular Structure
Primary Molecular Structure
If the PVC resin is pure linear structure, and is secondary carbon atoms and chlorine atoms combined, then, its stability is better.
But in fact, even high purity PVC resin, at 100 °C above the beginning of the decomposition of HCL, which indicates that its molecular structure, there are still unstable factors.
The resulting unstable structure of PVC is thought to be a radical initiation polymerization of vinyl chloride in which the molecule may contain the following structure
The Molecular Structure Breaks Down
In the structure, there are secondary and tertiary chlorides at one end, unstable groups at the other end, and oxygen in the structure. The reason may be that part of the structure is formed by peroxide reduction of initiator, and the oxygen-containing structure may be formed by polymerization in the presence of trace oxygen or by post-oxidation of polymer.
Due to the poor thermal stability of PVC, the corresponding stabilizer must be added to repair the defects of PVC chain and absorb the HCL produced by PVC dechlorination in time. At the same time, due to the processing characteristics of PVC with high viscosity and shear, the corresponding lubricant such as polyethylene wax must be added when the stabilizer is added.
Polyethylene wax, Pe wax, low molecular weight polyethylene, is synthesized by direct polymerization of ethylene. The products synthesized by different synthesis processes and catalytic systems are different in molecular weight, molecular weight distribution and molecular chain structure The performance of the corresponding products will also have a significant difference. Pe Wax is usually white powder with an average molecular weight of 1500-5000 and a melting point of 100-120 degrees. It has excellent external lubrication effect in PVC processing, which can improve the fluidity, output, dispersion, surface brightness and stripping of PVC processing. Because of its high molecular weight, high melting point, high temperature stability is very good, in high temperature and high shear conditions show strong external lubrication.
Polyethylene wax can effectively improve the dynamic thermal stability and flowability of PVC products, increase the extrusion efficiency of PVC products, improve the surface gloss of products, and effectively reduce the precipitation phenomenon of PVC products during processing.
Pe Wax on the domestic market is mostly divided into several types:
Pe Wax is obtained by ethylene homopolymerization. The Pe wax produced by this method has good lubricity, high gloss, narrow molecular weight distribution and stable quality
The cracking process of low molecular weight polyethylene is simple and easy to operate, but the molecular weight distribution of the products fluctuates with the production process
Pe Wax, a by-product of ethylene polymerization, was purified by refining process. The PE WAX has low viscosity, high melting point, excellent lubricity and low price, but its quality fluctuates with the change of raw materials and process Due to the characteristics of refining process, it is inevitable that there will be more low melting point components in products.