Melt viscosity tensile strength

Molecular weight. The molecular weight influences the melt viscosity, tensile strength, the low temperature brittleness, and the resistance to tearing. 

The significance of such degradation is realized when one considers that any reaction which randomly breaks one carbon—carbon bond per thousand bonds in the polymer would reduce the average molecular weight by one-half (23). This effect would be observable in properties such as melt viscosity, tensile strength, and bulk modulus. 

MW of plastics influences their properties. As an example with increasing MW properties increase for abrasion resistance, brittleness, chemical resistance, elongation, hardness, melt viscosity, tensile strength, modulus, toughness, and yield strength. Decreases occur for adhesion, melt index, and solubility. 

EEDPE/PA- 10 X 100 X 1 RT vac, air X 50-400 Gel fraction, melt viscosity, tensile strength and modulus, elongation, impact strength, carbonyl and hydroxy group formation, SEM, DSC 12, 15, 16... 

Type MW Processing Temperature (°C) Melt viscosity Tensile strength Solubility rate ... 

HDPE or PP were compatibilized with EPDM by heating with dicumyl peroxide. This produced PE or PP radicals which added readily across the double bonds in the EPDM, increasing melt viscosity, tensile strength, and ultimate elongation [79]. 

Physical properties of polymers are influenced by the sizes of the molecules and by the nature of the primary and secondary bond forces. They are also influenced by the amount of symmetry or uniformity in molecular structures, and by arrangements of the macromolecules into amorphous or crystalline domains. This affects melting temperatures, solubilities, melt and solution viscosities, tensile strengths, elongation, flexibility, etc. ... 

Blends with styrenic block copolymers improve the flexibiUty of bitumens and asphalts. The block copolymer content of these blends is usually less than 20% even as Httie as 3% can make significant differences to the properties of asphalt (qv). The block copolymers make the products more flexible, especially at low temperatures, and increase their softening point. They generally decrease the penetration and reduce the tendency to flow at high service temperatures and they also increase the stiffness, tensile strength, ductility, and elastic recovery of the final products. Melt viscosities at processing temperatures remain relatively low so the materials are still easy to apply. As the polymer concentration is increased to about 5%, an interconnected polymer network is formed. At this point the nature of the mixture changes from an asphalt modified by a polymer to a polymer extended with an asphalt. 

The melt flow index describes the viscosity of a solid plastic. It is the weight in grams of a polymer extruded through a defined orifice at a specified time. The melt viscosity and the melt flow index can measure the extent of polymerization. A polymer with a high melt flow index has a low melt viscosity, a lower molecular weight, and usually a lower impact tensile strength. 

The PP is produced by melt-kneading PP, an isoprene monomer and a radical polymerisation initiator, which has a high melt viscosity and a high melt tensile strength and is difficult to cause drawdown. Foamed articles made therefrom have a low density, high closed cell content, good appearance and excellent heat resistance. 

Why does the melt viscosity increase faster with molecular weight increase than other properties such as tensile strength ... 

Figure 5.72 Dependence of ultimate tensile strength of polyethylene on molecular weight (melt viscosity) and crystallinity (density). From F. W. Billmeyer, Textbook of Polymer Science, 3rd ed. Copyright 1984 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

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