Low-temperature thermal expansivities of polyethylene, polypropylene, mixtures of polyethylene and polypropylene, and polystyrene

✍ Scribed by Jacques L. Zakin; Robert Simha; Harry C. Hershey

• Publisher: John Wiley and Sons
• Year: 1966
• Tongue: English
• Weight: 829 KB
• Volume: 10
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/app.1966.070101006

✦ Synopsis

Length-temperature measurements on a seri-of polymer blends over the whole range of composition from pure polyethylene to pure polypropylene and one set of determinations on a 50:50 copolymer and on polystyrene are evaluated. The total crystallinity of the samples did not exceed 54%. The experimental procedure utilized a linear variable differential transformer without the use of a confining fluid, and the temperature ranged from about +20 to -185°C. A least-square numerical differentiation procedure based on moving arc9 is applied to yield directly the coefficients of thermal expansion as a function of temperature. The linear voltage differential transformer (LVDT) technique can detect transitions in which the change in thermal expansion coefficients is less than 10-6OC.-*. In polypropylene as well as the blends, the principal glass transition is clearly seen in the range observed by others, namely at about -9 to -14°C.

Its location varies only slightly with composition at polyethylene contents less than 88 mole-%. For polyethylene the transition region broadens noticeably.

The results are suggestive of two transitions for 0 > T > -40°C. A second transition region is observed for either pure component around -126OC. Its location varies somewhat with composition. However, our results do not indicate the appearance of an additional transition region characteristic of the mixture. The copolymer exhibits a major transition at -61°C. in good agreement with earlier workers. The thermal expansion decreases again around -150OC. In general our observations concerning transitions below T, are consistent with dynamic results.