Spectra, Dyneema UHMWPE Flexible Polymer Chain

4 Spectra, Dyneema UHMWPE Flexible Polymer Chain 

The theoretical tensile modulus of polyethylene is 180-340 GPa. [165, 166] The extremely high tensile modulus of polyethylene is due to the small cross-sectional area of the chain, no side groups, and the planar zig-zag conformation in the orthorhombic crystal lattice. The theoretical tensile strength calculated from the C-C bond energy is in the order of 20-60 GPa. These theoretical values for polyethylene can happen if all the C-C bonds fracture simultaneously. This requires defect free, chain-extended structure, and infinite polymer chains which is a completely different situation from which is encountered [167]. 

Due to good film properties LDPE is extensively used for film making and nonwovens accounting for about 60% of polymer consumption [173]. Poltrusion and paper coating account for about 15%. Over 8 billion pounds of the polymer were produced in 2001 in the United States. 

Linear high-density polyethylene (HDPE) is mainly manufactured by using traditional Ziegler-Natta and metal oxide Philips-type initiators in suspension polymerization [173]. More expensive metallocene catalysts are also used but accoimted for less than 5% of the total HDPE production in 2002 [172]. About 14 billion pounds of high density polyethylene was produced in the United States in 2001. 

Since HDPE is nearly a linear polymer it has a higher density of 0.94-0.96 g/cm the melting point of 133-138°C as well as improved tensile strength, bending stiffness and chemical resistance. 

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