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The structure of the polyethylene

by:CSSSLD     2021-01-23
Relative molecular mass, copolymerization and processing conditions for all affect the crystallization of PE. 嗯- - - - - - WPE too big cause crystallization is difficult, the relative molecular mass of the branching degree of the small linear structures, but its crystallinity below HDPE. After ethylene copolymerization with other monomers, due to the increase in the number of branched macromolecules, crystallization ability greatly reduced. Processing in the rapid cooling can reduce the degree of crystallinity of the PE, this method is commonly used in production to improve the transparency of injection molding processing products.

the molecular structure of the PE major and polymerization methods, conditions, and the type of catalyst, state of aggregation structure is not only related to polymerization process, but also depends on the processing conditions. The chemical structure of PE, crystalline, relative molecular mass absolute three important aspects of its performance. From the chemical composition, PE is hydrocarbons, belongs to the polymer long chain fatty hydrocarbon, for non-polar polymers, small molecular inter-atomic forces, low mechanical strength, flammable.

the crystallization of PE influenced by molecular chain branching degree, with the increase of branching degree, reduced the regularity and the symmetry of macromolecular chain, crystallization ability decreases. Highly branched PE low crystallinity, molecular packing not close together, and therefore also density is small. In this sense, the density can be used as a measure of the degree of branching, is also a representation of crystallinity. Such as highly branched PE for LDPE, crystallinity is approximately 60%, branched degree is higher, the crystallinity of LDPE is only 40%, and the branching degree of low PE for HDPE, crystallinity of 80% 95%, LLDPE branched degree between LDPE and HDPE, its crystallinity is 65% 75%.

according to infrared spectra and magnetic resonance imaging (mri) findings suggest that PE is made up of the hydrocarbon of long chain branched, different types of PE molecules contained in the branched chain difference is very big. LDPE about every 1000 carbon atoms in the molecular chain has 50 or more side base, but also there is a long branches chain, this is caused by chain transfer reaction in the process of polymerization. Some branched chain can even reach the length of the main chain, the chain transfer reaction after can also occur on the branched chain, the branched chain also branched as main chain, and LDPE molecules form are often described dendritic.

HDPE macromolecular chain upper base is less, every 1000 atoms around five or fewer side group. LLDPE macromolecular chains with more short branched chain, almost no long branches chain. Thus HDPE and LLDPE for linear macromolecular chain structure. PE on the molecular main chain not only have a different number and length of branched chain structure, and there are double bond in molecular chain structure. Different types of PE contain a double bond in the molecular chain number and type is also different. The double bond structure and polymerization process residues in very small amounts of resin catalyst have a bad effect on electric properties and aging properties of PE.

slurry method of simple production process, operating conditions demand is low, easy to put into production. Using different kinds of catalyst and concentration, change the AI/Ti ratio can be obtained different performance of HDPE resin. Also can according to the needs of users to join different plastic additives, in the process of post-processing system of aggregate of different USES. PE polymerization technology development mainly due to the improvement of the catalyst is used in the production of HDPE product category of the catalyst to roughly three categories: titanium base catalyst, chrome base catalyst and metallocene catalyst. The application of metallocene catalyst for PE industry bring enormous changes, have led to the introduction of this new metallocene polyethylene.

PE intermolecular force is small, the molecular chain flexibility is good, the basic structure is simple, neat and crystallization ability. Either polymerization methods of PE has a crystalline structure. PE crystalline regions are usually spherulite structure, when the spherulite size close to or more than visible light wavelengths, due to the diffusing light has milk-white, and pure PE resin white translucent at room temperature. Above, the crystallinity of HDPE LDPE plastic processing, less its transparency.

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