26 Segmental Orientation, Physical Properties, and Morphology of Poly-€-Caprolactone Blends
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D O U G L A S S. H U B B E L L and S T U A R T L . C O O P E R Department of Chemical Engineering, University of Wisconsin, Madison, W I 53706
The compatibility, mechanical properties, and segmental orientation characteristics of poly-e-caprofoctone (PCL) blended with poly (vinyl chloride) (PVC) and nitrocellulose (NC) are described in this study. In PVC blends, the amorphous components were compatible from 0-100% PCL concentration, while in the NC system compatibility was achieved in the range 50-100% PCL. Above 50% PCL concentration, PCL crystallinity was present in both blend systems. Differential IR dichroism was used to follow the dynamic strain-induced orientation of the constituent chains in the blends. It was found for amorphous compatible blends that the PCL oriented in essentially the same manner as NC and the isotactic segments of PVC. Syndiotactic PVC segments showed higher orientation functions, implying a microcrystalline PVC phase.
' " P h e objectives of the present study were to analyze polymer blends of poly-c-caprolactone with poly (vinyl chloride ) and nitrocellulose. The research included determination of compatibility and characterization of the morphological, mechanical, and orientation properties of the polycaprolactone blends. Experimental Poly-e-caprolactone designated as PCL-700 was supplied by J. V . Koleske of the Union Carbide Corp. This polymer has been used i n several other blend studies (1-6). The polymers blended with P C L were poly (vinyl chloride ) ( P V C ) and nitrocellulose ( N C ) . The poly0-8412-0457-8/79/33-176-517$05.00/0 © 1979 A m e r i c a n C h e m i c a l Society
Cooper and Estes; Multiphase Polymers Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
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MULTIPHASE
POLYMERS
(vinyl chloride) used was Union Carbide's QYTQ-387. The nitrocellu lose, supplied by Hercules Inc., was designated as RS % sec. The N C is reported to have 11.8-12.2% nitrogen ( 7 ) , which corresponds to 2.25 =fc 0.06 nitro groups per anhydroglucose ring. The molecular weights, densi ties, and solubility parameters for P C L , N C , and P V C appear i n Table I. The solubility parameters, when possible, have been calculated by the group contribution methods of Small (8) and H o y ( 9 ) . A small differ ence between solubility parameters of components i n a mixture is usually considered a necessary but not sufficient condition for compatibility. A f u l l discussion of the limitations of the solubility parameter approach to compatibility is given i n the review of polymer blend technology by Paul and Barlow i n Chapter 17. A l l samples for this study were prepared by spin casting from poly mer solutions (9,10). In this technique, a solution of polymer and solvent is forced against the walls of a spinning cylinder. The solvent is gradually evaporated under a slight vacuum and also by heat if desired, with the polymer precipitating onto a sheet of aluminum or paper lining the wall. W i t h this method, it has been demonstrated that unoriented films with thicknesses as small as 4 μ can be made. Tetrahydrofuran ( T H F ) was used as the spin-casting solvent. Films were cast at room temperature from approximately 15 m L of a 1 % solution. A l l samples were dried i n a constant stream of air for several hours and then dried for at least four days under vacuum at room temperature. After drying, the films were aged i n desiccators at room temperature for at least two weeks. This allows the P C L crystallinity to approach its equilibrium value (6). Throughout this chapter the blends are desig nated by the weight percent of the polymer blended with polycaprolactone. Thus 2 5 % P V C is a 25/75 blend of P V C / P C L . In favorable situations, segmental orientation i n polymer blends can be followed using the technique of I R dichroism. The results can be expressed i n terms of the Hermans orientation function shown i n E q u a tion 1. / — (3 cos
