On additives, morphological evolution and dielectric breakdown in low density polyethylene

A series of low density polyethylene systems has been studied with respect to structural evolution and short-term dielectric breakdown behaviour. All materials were based upon a single polymer, that is commonly used in high voltage applications, but with different additives. In all three of these systems, multiple melting transitions were observed, as a result of molecular fractionation effects during crystallization. In the virgin polymer, a space-filling banded spherulitic morphology was found to develop at low temperatures (102 °C and below) whereas, at higher temperatures, only a few isolated axialites were observed. Inclusion of the antioxidant resulted in greatly increased nucleation densities, such that, at low temperatures, no evidence of spherulitic organisation remained. At higher temperatures, sheaf-like lamellar aggregates developed, which were much smaller and much more numerous than in the case of the virgin polymer. Further addition of dicumyl peroxide (DCP) resulted in the rapid formation of a crosslinked network at 200 °C. Some crosslinking also occurred at 150 °C, but over a much longer timescale. Where extensive crosslinking occurred prior to crystallization, the resulting gel inhibited structural development, such that only a few small, isolated sheaves were able to form at 102 °C. In view of the principal application area of this material, the breakdown strength of each of the above systems was then measured and the whole data set was analysed statistically. When structural factors were considered alongside the statistics, no clear trends emerged to indicate that either the compositional or morphological variations were reflected in the short-term electrical failure processes.     

A comparison of phosphated and sulfated beta-cyclodextrins as chiral selectors for capillary electrophoresis

The enantioseparation capabilities of three different functionalized beta-cyclodextrins, two sulfated beta-cyclodextrins with 4 and 15 nominal degrees of substitution and a phosphated beta-cyclodextrin with 8 degrees of substitution, were compared. While anodic detection was used with both sulfated cyclodextrins, the phosphated cyclodextrin required cathodic detection suggesting either lower ionization of the phosphated cyclodextrin or generally lower affinity of the analytes for the phosphated cyclodextrin. The effects of several experimental parameters were evaluated with respect to enantioseparation. The degrees of substitution of the cyclodextrin, pH of the background electrolyte as well as the concentration of the functionalized beta-cyclodextrin, each had a significant influence on the successful enantiomeric separation of the chiral drugs investigated.     

Determination of Monoterpenes in Oleoresin: A Chemosystematic Study of the Interaction between Fraser Fir (Abies fraseri) and Balsam Woolly Adelgid (Adelges piceae)

The Fraser fir (Abies fraseri), a conifer native to high elevation sites in the southern Appalachians, has suffered severe mortality attributed to an exotic insect, the balsam woolly adelgid (BWA) (Adelges piceae). Fraser fir, like many other plants, produce volatile organic compounds called monoterpenes in a variety of tissues, including the cortical oleoresin found in blisters on the bark. The purpose of this study was to perform a chemosystematic study to evaluate whether differences in monoterpene composition of Fraser fir oleoresin were observed as a function of the season sampled, the presence or absence of BWA infestation, the health of a tree, and the susceptibility of trees to BWA, based on geographic location. Oleoresin was collected in September and December, 1994, at two mountains, Mount Rogers, where the fir were relatively healthy, and Roan Mountain, where heavy to moderate mortality has been observed. The oleoresin samples were dissolved in methylene chloride, and the monoterpenes were determined by gas chromatography. This method was shown to have acceptable precision for chemosystematic studies for five monoterpenes and the total of all monoterpenes. The levels of monoterpenes in oleoresin were statistically the same for most compounds in September and December, although the total monoterpenes were higher in September at Mount Rogers and α-pinene was higher in December at Roan Mountain. Infested and uninfested fir had the same levels of oleoresin monoterpenes at both mountains. No differences in monoterpene levels were observed at Mount Rogers with healthy and unhealthy fir, but at Roan Mountain, the total monoterpene concentrations were different in these categories. A comparison of monoterpene concentrations in oleoresin from Mount Rogers and Roan Mountain showed statistically significant differences for 3-carene, β-phellandrene, and total monoterpenes.     

Preparative isolation of (+)-beta-eudesmol fromAmyris balsamifera

Summary Optically pure (+)-beta-eudesmol is a possible starting material for the synthesis of several termite defense compounds. A two step procedure for the isolation of gram quantities of (+)-beta-eudesmol from commercially availableAmyris balsamifera oil (syn. West Indian sandalwood oil), containing 8% beta-eudesmol, was developed. Step one consisted of an efficient vacuum distillation of the total oil. Step two was a medium pressure LC separation with an AgNO₃ impregnated silica gel stationary phase. Several other separation procedures failed due to the presence of many closely related sesquiterpene alcohols (75% of the oil).