Dale Earl Hauenstein

Photoreversible Polymeric Membranes

ABSTRACT A variety of advances have been made in the use of environmental factors to control the separation characteristics of polymeric membranes in real time. These systems work by incorporating membrane materials which respond to external stimuli such as temperature or pH by making changes in conformation, solubility, or phase. In this review we focus on the use of light (photons) as the external control stimulus. Specifically, we examine the ability to control polymeric membrane properties by incorporating reversible photochromic moieties into the polymer structure. The first section is a brief review of the chemistry of photochromic compounds, the second section focuses on photocontrol of the separation properties of nonporous and hydrogel membranes, and the third section discusses the photocontrol of release rates from synthetic bilayer membranes.

Photocontrol of Gas Separation Properties

Abstract Incorporation of photoresponsive moieties (phenylazobenzene) into a polymer (ethyl cellulose) has been shown to provide a method to reversibly modify the diffusivity of a non-porous membrane for gas separations. The diffusivity of N2 decreased by up to 18% upon exposure to UV light. No changes were observed for the other gases in this study (Ar, He, H2, CO, CO2, and O2). The anomalous behavior of N2 is explained in terms of an interaction between the N2 and cisazobenzene.

New Silicone Processing AIDS for the Extrusion of Linear Low Density Polyethylene

Various silicone process aid candidates were evaluated and compared to alternative process aids for their effect on surface properties of extruded linear low density polyethylene (LLDPE). Their performance was influenced by the silicone polymer structure and the concentration of the silicone polymer in the polyethylene resin. An increase in the polarity of functional groups on the silicone polymer resulted in an increase in the effect on surface properties of extruded LLDPE. Silicone concentrations in the range 220 to 3520 ppm in the polyethylene resin gave significant reduction in surface roughness caused by melt fracture during extrusion. Concentrations of 10000 ppm or less gave coefficient of friction values of 0.3 or below. Beneficial effects on extruder parameters, such as the reduction of extrusion pressure, current, and output were also observed.

Evaluation of Process Aids for Controlling Surface Roughness of Extruded LLDPE

Publisher Summary Surface irregularities are typically represented in terms of a degree of surface roughness. “Sharkskin” is characterized by the appearance of fine scale surface irregularities (transverse ridges similar to the design of a tire tread), about less than one-tenth the diameter of the extrudate, during steady pressure flow conditions. A number of techniques have been used for delaying or eliminating surface melt fracture. A number of techniques have been used for measuring the surface roughness of extrudates. These techniques have included observations with the naked eye and light microscopy, contact profilometry, fractal analysis, digital image analysis, fiber optic surface analyzer/pattern recognition, and atomic force microscopy. The more popular of these techniques is profilometry. In this chapter, a surface roughness analyzer is used to evaluate, offline, the surface roughness of samples produced from a single-screw extrusion tape line. Similar to a profilometer, a roughness average is used to quantify the extent of surface roughness. This analytical technique is used to compare the effectiveness of various silicone and commercial process aids in controlling the surface roughness of extruded thermoplastics. The measurement of average surface roughness of extruded tape at various extruder speeds differentiates the effectiveness of various process aids. Six commercial process aids and eleven new silicone process aid candidates are compared. A new silicone process aid is discovered which shows a significant reduction in surface roughness of both ethylene–octene and ethylene–hexene LLDPE copolymers. Beneficial effects on extruder parameters, such as reduction of pressure and current, are also observed.