WAXS, orientational process

The amorphous halos existing in the WAXS patterns reveal the significance of the amorphous phase in the orientation process. Due to this good orientation of the crystalline phase (k > 3), NR exhibits SIC, which increases with increasing strain ratios, as clearly represented in Figure 22.2. 

An orientation process to enhance the elastic recovery and stiffness of propylene-based elastomers is described. Elastomers fabricated during this process have virtually complete elastic recovery, and are up to ten times stiffer than unoriented controls. The structural development during orientation is explored with WAXS. A relationship between crystal structure, strain recovery, and modulus is described. 

Overall, DSC is an excellent method to measure the wax appearance and crystallization temperatures of vegetable oils. Due to the complexity of the vegetable oil composition with respect to their FA distribution, the situation is not as simple as pure triacylglycerol molecules. Moreover, there is significant influence of the nature, relative abundance, and orientation of C=C bonds on the wax appearance temperatures. Further, presence of other saturated short-chain-length FAs in vegetable oil structure is found to affect the crystallization process. Statistical analysis of NMR-derived vegetable oil structure support the influence of several predictor variables associated with FA unsaturation on the crystalhzation process. 

After solid-state processing, a very different crystalline structure was found, compared to melt-processed PHB, as revealed by WAXS and, in spite of a certain orientation due to solid-state processing, a slight decrease of crystallinity was also reported. The mechanical properties of the solid-state extruded PHB depends substantially on the initial molecular weight of the polymer, as well as on the processing temperature, as seen in Tables 22.9 and 22.10. 

Hand Layup (Contact Molding or Open Mold Process). The oldest and simplest technique is primarily manual. An open mold is waxed to lubricate it. The surface of the proposed product is applied to the mold, usually as an unreinforced gel coat or sometimes as a thermoformed plastic sheet. A layer of fabric is hand cut and hand laid into the mold. Catalyzed resin is poured over the fabric and worked into it with brush, roUer, and squeegee to eliminate air bubbles. Another layer of fabric is laid over this, often oriented in a specific direction to optimize properties. Again, catalyzed resin is poured over it and worked into it. The process is repeated as many times as required to build up the desired thickness and optimum orientation of the layers. If the cure reaction is inhibited by air, a wax may be dissolved in the resin it exudes to the surface and forms a barrier to exclude air and permit complete cure. The resin may be allowed to cure at room temperature, or the assembly may be heated to complete or hasten the cure reaction. 

In the SAXS regime, typical nanostructures (e.g., domain sizes and long periods in semicrystalline materials, thermoplastic elastomers) are observed, while the ultra small angle X-ray scattering (USAXS) extends the accessible structure towards the micrometer range (e.g., spherulites). In addition to size and orientation of domains as determined by WAXS, the arrangement of crystalline domains within SMPs could be characterized by SAXS. The programming and recovery processes performed... 

---