Polyethylene temperature parameters

Plasticizers and Processing Aids. Petroleum-based oils are commonly used as plasticizers. Compound viscosity is reduced, and mixing, processing, and low temperature properties are improved. Air permeabihty is increased by adding extender oils. Plasticizers are selected for their compatibihty and low temperature properties. Butyl mbber has a solubihty parameter of ca 15.3 (f /cm ) [7.5 (cal/cm ) ], similar to paraffinic and naphthenic oils. Polybutenes, paraffin waxes, and low mol wt polyethylene can also be used as plasticizers (qv). Alkyl adipates and sebacates reduce the glass-transition temperature and improve low temperature properties. Process aids, eg, mineral mbber and Stmktol 40 ms, improve filler dispersion and cured adhesion to high unsaturated mbber substrates. 

Introduction of linear low density polyethylene in the 1970s and 1980s offered yet another design parameter, giving chlorosulfonated products with the advantages of linear types but with improved low temperature performance (8). 

There are thus no solvents at room temperature for polyethylene, polypropylene, poly-4 methylpent-l-ene, polyacetals and polytetrafluoroethylene. However, as the temperature is raised and approaches F , the FAS term becomes greater than AH and appropriate solvents become effective. Swelling will, however, occur in the amorphous zones of the polymer in the presence of solvents of similar solubility parameter, even at temperatures well below T. ... 

Since polyethylene is a crystalline hydrocarbon polymer incapable of specific interaction and with a melting point of about 100°C, there are no solvents at room temperature. Low-density polymers will dissolve in benzene at about 60°C but the more crystalline high-density polymers only dissolve at temperatures some 20-30°C higher. Materials of similar solubility parameter and low molecular weight will, however, cause swelling, the more so in low-density polymers Table 10.5). 

To illustrate the use of the gas sorption mode , we show in Figure 7 results of the supercritical ethylene sorption in low-density polyethylene (12,16). As seen in Figure 7, the theory is capable of fitting the ethylene sorption data. In this instance, the data at three temperatures can be fit within experimental precision using interaction parameters (p o) of 3235 atm, 3178 atm, or 3101 atm at 126°C, 140 0, and 155 C, respectively. 

A similar continuity in the Tj s through the melting temperature was previously reported for linear polyethylene. (17) We have now investigated the temperature dependence of this quantity, for this polymer, in more detail and have also studied a low density (branched) polyethylene. The results for the poly-ethylenes are summarized in Fig. 8. The new data reported here substantiate the conclusion previously reached for linear polyethylene. A similar conclusion can now be reached for the baclc-bone carbons of low density (branched) polyethylene. The melting temperature for this particular sample, under the crystallization conditions studied, is less than 110°C. (33) Thus, the spin-lattice relaxation parameters for the bac)cbone carbons are the same for both the linear and branched polymers over the temperature range studied here. Changes that occur in Tq as the temperature is reduced below 0°C involve other considerations and will be discussed in detail elsewhere. (22)... 

The major results described could be partially anticipated from those previously reported for linear polyethylene (17) as well as those for cis polyisoprene. (] ) For the latter polymer, by taking advantage of its crystallization kinetic characteristics, it was possible to compare the relaxation parameters of the completely amorphous and partially crystalline polymer (31% crystallinity) at the same temperature, 0°C. This is a unique situation and allows for some unequivocal comparisons. It was definitively observed that for all the carbons of cis polyisoprene the T] s did not change with crystallization. 

These results are reminiscent of and very similar to those reported here for the relaixation parameters of polyethylene oxide as illustrated in Figs. 5 and 7. We have found that the s are continuous with teit5>erature over a very wide molecular weight range. However, as is shown in Fig. 5, there are discontinuities in linewidths at the melting temperatures for the low molecular weight samples, but the linewidths are continuous... 

Since A i is proportional to the supercooling, the LH theory predicts that as the crystallization temperature is lowered to a value when Eq. (1.95) is satisfied, the lamellar thickness would diverge. This is referred to as the 8L catastrophe. By taking reasonable experimental values for the various parameters and assuming t / = 1 (no barriers for attachment of each stem), the necessary supercooling for the appearance of this catastrophe is 55 K for polyethylene. This is not observed experimentally. To fix this discrepancy, vf/ is taken to be zero so that... 

Composite-based PTC thermistors are potentially more economical. These devices are based on a combination of a conductor in a semicrystalline polymer—for example, carbon black in polyethylene. Other fillers include copper, iron, and silver. Important filler parameters in addition to conductivity include particle size, distribution, morphology, surface energy, oxidation state, and thermal expansion coefficient. Important polymer matrix characteristics in addition to conductivity include the glass transition temperature, Tg, and thermal expansion coefficient. Interfacial effects are extremely important in these materials and can influence the ultimate electrical properties of the composite. 

The same technique was applied to a mixture of polyethylene terephthalate and acrylic acid (34). The polymerizations were followed by looking at the acid number of the product the parameters studied were time, temperature, and monomer content see Fig.9a,b,c. The hydrophilicity, the solubility of the copolymer in benzyl alcohol, aniline, and a mixture of phenol and CHQ3 were increased by graft copolymerization. 

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