Determination of antioxidants in polymeric materials.
A review of methods proposed for the analysis of antioxidants in polymeric materials, cast in the form of a step-by-step examination of the problems involved in any scheme of analysis, with a critical appraisal of the published procedures designed to overcome them.
The permeation of water vapor through polyethylene
A critical survey of the literature has been made relative to the permeation of water vapor through films of polyethylene. For conventional polyethylene, reported values of permeability range from 0.015 to 0.074 gm. mm./m.2 day cm. Hg at 25°C. Reported activation energies range from 6,590 to 14,540 cal./mole°C. It appears that the highest activation energies are associated with the lowest permeability coefficients. Recent investigations of the permeability of intermediate and high-density polyethylenes are not in agreement with one another The explanation is offered that part of the transport of water vapor through these materials occurs by Fickian diffusion through the amorphous fraction of the polymer and part occurs by passage through micropores in the polymer film. The expectation exists that a superior water-vapor barrier could be developed using ultralinear, crystalline polyethylene of high molecular weight. However, an incisive experimental test of this supposition would first have to be concerned with a more complete characterization of polyethylene in the solid state than has heretofore been employed in diffusion and permeability studies.
Submicron polymer structures with X-ray lithography and hot embossing
This article describes the process chain for replication of submicron structures with varying aspect ratios (AR) up to 6 in polymethylmethacrylate (PMMA) by hot embossing to show the capability of the entire LIGA process to fabricate structures with these dimensions. Therefore a 4.7 μm thick layer of MicroChem 950k PMMA A11 resist was spin-coated on a 2.3 μm Ti/TiOx membrane. It was patterned with X-ray lithography at the electron storage ring ANKA (2.5 GeV and λc ≈ 0.4 nm) at a dose of 4 kJ/cm3 using a Si3N4 membrane mask with 2 μm thick gold-absorbers. The samples were developed in GG/BDG and resulted in AR of 6–14. Subsequent nickel plating at 52°C resulted in a 200 μm thick nickel tool of 100 mm diameter, which was used to replicate slit-nozzles and columns in PMMA. Closely packed submicron cavities with AR 6 in the nickel shim were filled to 60% during hot embossing.