Physical properties of polyethylene

The effect of these two parameters on mechanical and physical properties of polyethylene and polypropylene are shown in Tables 3.44 and 3.45. The copolymer grade is usually propylene with a little ethylene (5%), wliich considerably improves the impact strength while causing only a slight loss in stiffness. 

The principal difference in the physical properties of polyethylene and paraffin wax is based on both chain entanglement and total intermolecular dispersion forces per molecule (chain). 

M. Gr0tH, . H. Gotfredsen, J. Rademann, J. Buchardt, A. J. Clark, J. O. Duus and M. Meldal, Physical properties of polyethylene glycol) (PEG)-based resins for combinatorial solid phase organic chemistry A comparison of PEG-cross-linked and PEG-grafted resins, J. Comb. Chem., 2000, 2, 108 119. 

Grotli M, Grotfredsen CH, Radermann J, Buchardt J, Clark AJ, Duus J, Meldav M, Physical properties of polyethylene glycol) (PEG)-based resins for... 

Some physical properties of polyethylene ionomers are compared with those of polyethylene and the acid copolymer, poly(ethylene-co-methacrylic acid) in Table 5.15. lonomer is generally tougher and, as shown in Table 5.15, relative to the acid copolymer, its tensile strength is increased by 27—53% and its stiffness is nearly tripled. 

TABLE 5.15 Comparative Physical Properties of Polyethylene Ionomers and Their Acid Precursor... 

FIGURE 15.8 Influence of crystallinity and chain length on the physical properties of polyethylene. (After Richards, R.B., J. Appl. Chem., 1, 370, 1951.) The percentage crystallinity c is plotted against molar mass M. 

Note that gel-spinning is not so much a modification of polyethylene as it is a technique to change the orientation, or physical properties, of polyethylene. Since it is not modifying the chemical structure of polyethylene but only the microscopic orientation of the polyethylene chains, it is not included among the above polyethylene modification techniques. 

The physical properties of polymers are also related to their molecular weights. Melt viscosity, hot strength, solvent resistance, and overall toughness increase with molecular size. Table 2.4 illustrates the effect of molecular weights (size) upon physical properties of polyethylene [64]. 

S. Sheshmani, A. Ashori, Y. Hamzeh, Physical properties of polyethylene-wood fiber-clay nanocomposites. Journal of Applied Polymer Science 118 (6) (2010) 3255-3259. 

MOLECULAR WEIGHT INFLUENCES ON THE PHYSICAL PROPERTIES OF POLYETHYLENE ADIPATE-BASED ELASTOMERS (WITH NDI)... 

Table 1-2. Comparison of the Physical Properties of Polyethylene and crosslinked Polyethylene.

Table 7.5 Physical properties of polyethylene terephthalate fibres at room temperature...

The first commercial manufacture of polyethylene, using high-pressure ethylene gas in the presence of trace amounts of oxygen that acted as a free-radical source for the initiation of the polymerization process, was due to the important physical properties of polyethylene for electrical applications at the beginning of World War 11. In 1940 about 90 metric tons of polyethylene was produced by Imperial Chemical Industries (ICI) in Great Britain in support of the war effort. 

The properties listed in Table 5.8 were responsible for the rapid replacement of cellophane or other cellulose-based packaging materials by polyethylene. Utilizing polyethylene in food packaging applications, such as fresh produce, provided much longer shelf-life and a reduction in waste and spoilage. As can be seen from the physical properties of polyethylene relative to cellulose, polyethylene was more elastic, less likely to tear, heat sealable and much less permeable to water vapor. 

The lack of polyethylene samples with tailored architectures, controlled molecular weight, low PDI, and absence of branching defects has hmited a systematic study of the relationships between molecular structure and physical properties of polyethylene. Several notable exceptions include cyclic polyethylene that has been synthesized by ring-opening metathesis polymerization (ROMP) (PDI of 2) (Bielawski et al., 2002 Bielawski et al., 2003) and star, comb, H-shape and pom-pom polyethylenes, containing 17—25 ethyl branching defects per 1000 carbons, which were produced by anionic polymerization (Hadjichristidis et al., 2000). 

Cross-linking involves the formation of chemical bonds between adjacent chains to create a molecular network. The chemistry of cross-linking, the processes used to accomplish it, and its effect on the physical properties of polyethylene are addressed in Chapter 7. 

FIGURE 1.10 Physical properties of polyethylene as a function of molecular weight and crystallinity. (Adapted from Richards, R. B., Journal of Applied Chemistry, 1, 370, 1951.)... 

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