Polyethylene physical properties influence

There are numerous variations on the basic linear structure of polymers. Returning to our example of polyethylene, we find short chain branches and long chain branches, as shown in Figs. 1.2 and 1.3, respectively. The number and type of these branches strongly influences the way that the molecules pack in the solid state, and hence affect the physical properties. Long... 

Figure 6.20). The carbon-carbon bonds are free to rotate, which allows the polymer chain to coil into ordered or disordered regions. Note that polyethylene, like all polymers, does not have a definite chemical formula. The number of (CH2) units in the chain is influenced by preparation conditions. Polymers with low average values of n have different physical properties from those in which n is larger (see below). 

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. 

Paraffin wax has been found to have an influence on the thermal and mechanical properties of low-density polyethylene (LDPE) [39,40]. It crosslinks to improve the mechanical properties of LDPE, short sisal fibres composites [42,43] and PVC. There is complete miscibility of the wax in LDPE at wax concentrations up to 10%, but only partial miscibility at higher wax concentrations. On blending an oxidised paraffin wax with LDPE, small wax concentrations improved the physical properties of the blends [40]. 

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

Gopakumar, T.G., Lee, J.A., Kontopoulou, M. etal. (2002) Influence of clay exfoliation on the physical properties of montmorillonite/polyethylene composites. Polymer, 43, 5483. 

The effect of such an additive on the UV degradation of polyethylene is shown in Fig. 3 which shows carbonyl formation in the polymer with time in the presence and absence of additive. It can be shown that carbonyl formation correlates directly with the physical properties of the polymer which rapidly loses strength and embrittles. Embrittlement and fragmentation are particularly rapid in the case of the more crystalline polymers which crumble even under the influence of wind and weather (see Fig. 4). The polymer particles so formed are chemically modified by oxidation to be now subject to attack by normal bacterial action and it is anticipated that these will quickly become part of the soil. 

The principal value of polyethylene lies in its desirable balance of physical properties in the solid state and its chemical inertness. These qualities in combination with its low cost and ready processability make it the material of choice for a wide variety of uses. The balance of physical properties can be controlled by judicious selection of the resin and processing parameters, thereby producing items useful in an extremely broad range of applications. In this chapter the macroscopic properties of polyethylene, with particular emphasis on commercially relevant attributes, are discussed with respect to the key molecular and morphological variables that influence them. 

---