Barry Bauer, David Johnsonbaugh, D. W. Liu, and Kalman Migler

Objectives

We plan to transfer the technologies of light scattering and microscopy from the laboratory environment to the processing environment. This will enable us to carry out real time characterization of structure and morphology of polymer blends during mixing/extrusion. We are synthesizing and testing a variety of model compatibilizers to assess their relative merits in stabilizing immiscible polymers.

Accomplishments

Blends of immiscible polymers often require the addition of a polymer that improves the dispersion and adhesion of the phases. Such "compatibilizers" are widely used but poorly understood in the manufacture of polymeric materials.

The processing of polymer blends involves the application of complex shear, temperature and pressure profiles to polymeric resins. While most experiments isolate these effects in controlled laboratory conditions, we need to understand the mixing and morphology under actual processing conditions.

Optical microscopy and light scattering are useful tools in the characterization of polymer blends. Recently, the Polymer Blends Group developed an instrument for real time microscopy and light scattering in simple shear flow. The next step is to transfer this technology onto a laboratory scale polymer processing device. This will allow measurements of how actual processing conditions affect the morphology, the mixing and the phase behavior. Furthermore real time measurements of the effects of model compatibilizers in the processing of polymer blends will be carried out.

To test the relative advantages of compatibilization strategies, a variety of model compatibilizers were synthesized. The mixer/extruder will be used to test these compatibilizers in mixtures of immiscible polymers. Both on-line testing, via the microscope and light scattering apparatus, as well as off-line testing, via physical properties and scanning electron microscopy will be employed. The model system chosen includes polystyrene (PS), poly(methylmethacrylate) (PMMA), poly(methacrylic acid) (PMAA), and poly(ethylene oxide) (PEO).

The design and construction of the slit die / optical flow cell was completed. The die features an open optical pathway through the slit which allows either light scattering or optical microscopy to be carried out. The die is temperature controlled through cartridge heaters located in the body. The width of the die is adjustable between 0.2mm - 1.0mm. There is a bypass valve which allows adjustment of the flow rate of polymer through the slit. Also completed is the optical setup which features both phase contrast microscopy and light scattering. Switching from one mode to the other is carried out via translation of an optical element.

Quantities of PMMA-g-PS, PMMA-r-PS, PMAA-g-PS, and PMAA-r-PS (g, r designate graft and random, respectively) have been synthesized and blended into mixtures of PS and PEO. This will elucidate the relative merits of two important compatibilization strategies, graft vs random and weakly vs strongly interacting. Small angle neutron scattering has proven that the combination PMAA-PEO has a much stronger interaction than PMMA-PEO. Blends have been made with and without these four compatibilizers and characterization is underway. Preliminary results indicate that the compatibilizers modify the resultant morphologies, giving better dispersions.