TABLE OF CONTENTS Polyethylenes (PE) are semi-crystalline materials with excellent chemical resistance, good fatigue and wear resistance, and a wide range of properties (due to differences in structure and molecular weight). PE are easy to distinguish from other plastics because they float in water. Their properties permit both their identification and differentiation from other polymeric materials and also determine the end use of the products made from them. PE provide good resistance to organic solvents, degreasing agents, and electrolytic attack. They are resistant to water, acids, alkalis, and most solvents. They have a higher impact strength but lower working temperatures and tensile strength than polypropylene (PP). They are of low weight, are resistant to staining, and have low moisture absorption rates. The mechanical and thermal properties of PE, a viscoelastic material, are dependent on structure, molecular weight and its distribution, crystallinity and the type and amount of comonomer, temperature, and stress. Long-chain branches are important in the structure of low-density PE (LDPE). The size of long branches increases with increasing number average molecular weight ( M n) of PE, but the mean size of long branches relative to M n decreases with increasing molecular weight. Logarithmic plots of storage modulus ( G ?) v ersus loss modulus ( G") strongly depend on the molecular weight distribution (MWD) and the degree of side-chain branching, but are only weakly sensitive to temperature and weight average molecular weight ( M w).
The properties of most known commercial grades of...
