Structure and physical properties of PVC
Polyvinyl chloride is a product of polymerization of vinyl chloride, whose chemical formula is CH 2-CHCl.In the process of polymerization formed slaborazvetvlennye linear (branched macromolecules is 2-5 per 1000 carbon atoms, main chain) of a macromolecule c elementary link in the form of a flat zigzag.
Nature of relations between elementary links allows several options for building a molecular chain that, in practice, with industrial production of polyvinyl chloride, resulting in low regularity (sindiotaktichnosti) to macromolecules:in a macromolecule are implemented for various types of elementary links of links, and regular sequence of elementary units are not created and the designs have a low degree of crystallinity.
PVC is characterized by a very broad molecular weight distribution (polydispersity).The degree of polymerization for different fractions of the polymer of the same brand can vary by several orders of magnitude (from 100 to 2500).Therefore, in practice, the molecular weight of PVC is often characterized not by its numerical value, and the constant Fikentchera Kf, which is determined by the equation:
Cp = 1000 * k
lg ?;RH = [(75k2S) / (1 KC 1.5)] + Kc,
where ?;RH - relative viscosity at 25 ° C, C - concentration of polyvinyl chloride, usually 0.5 or 1 per 100 ml of solvent (usually ethylene dichloride, or cyclohexanone).The value of Kf is nearly constant for solutions of different concentrations of polyvinyl chloride, slightly dependent on temperature measurements, however, varies greatly with the nature of the solvent.
Chemical formula:[-CH2-CHCl-] n.
The molecular weight of 10-150 thousand.Density - 1,35-1,43 g./ Mass Media.Glass transition temperature of 75-80 ° C (heat-resistant grades for up to 105 ° C), melting point - 150-220 ° C.
At temperatures above 110-120 ° C is prone to decomposition with liberation of hydrogen chloride, HCl.
is soluble in cyclohexanone, tetrahydrofuran (THF), dimethylformamide (DMF), dichloroethane, limited - in benzene, acetone.Does not dissolve in water, alcohols, hydrocarbons;resistant to alkaline solutions, acids, salts.
Tensile strength - 40-50 MPa, flexural - 80-120 MPa.Specific electrical resistance - 1012-1013 ohm • m.
Dissipation of the order of 0.01-0.05.
PVC is resistant to moisture, acids, alkalis, salt solutions, industrial gases (eg, NO2, Cl2), gasoline, kerosene, grease, alcohol.Insoluble in its own monomer.Limited soluble in benzene, acetone.Soluble in dichloroethane, cyclohexanone, nitrobenzene and chloro-.Physiologically harmless
Pure PVC is a hornlike material, which is difficult to processed.Therefore, it is usually mixed with plasticizers.The properties of the final product ranges from hard to very flexible plastic, depending on the percentage of added plasticizer, which can reach up to 30% by weight.