SYNOPSISThis study deals with the analysis of structure, physical properties, and dyeing behavior of silk fibers with different filament sizes. Fine and coarse silk fibers were obtained from Akebono and Ariake cocoon varieties, respectively. Both samples exhibited a fairly similar x-ray crystallinity, while the degree of molecular orientation increased with decreasing the fiber size. Tensile strength and energy of fine silk fibers were significantly higher, while elongation a t break did not change in relation to the fiber size. Fine silk fibers exhibited a slightly higher thermal stability, as shown by the upward shift of both the DSC decomposition temperature and the TMA final extension step a t above 300°C. The TGA and DMA (E") patterns remained unchanged regardless of fiber size. The amino acid analysis confirmed the absence of any difference of chemical structure between fine and coarse silk fibers, the content of acidic, basic, and other characteristic amino acid residues being exactly the same. Accordingly, both samples adsorbed the same amount of hydrochloric acid. Exhaustion dyeing tests with various direct, acid, and reactive dyes showed the occurrence of appreciable differences in the perceived color between fine and coarse silk fibers. The size of color difference was quantitatively evaluated by reflectance measurements and discussed in relation to silk fiber morphology, structure, as well as dyeing conditions. The kinetics of diffusion of two model dyes was not significantly affected by the different fiber size and structure.
Important differences arise when chemical demulsification strategies are implemented for heavy crude oils (°API ∼ 10). Traditional methods for screening and selecting an appropriate demulsifier based on bottle tests and lipophilic–hydrophilic parameters (i.e., HLB, RSN, and so on) tend to be less adequate because of the almost negligible density difference between the oil and the water phases. This situation leads to a detriment of the separated water often mixed with undesired dense-packed layers (DPLs) and emulsion layers. In this work, dehydration of heavy crude oil emulsions from a Colombian oilfield was assessed through the use of a wide range of chemical demulsifiers of different functionalities. Through the use of bottle tests and transmission/backscattering measurements, it was shown that the demulsification mechanisms involved in these limiting cases (low density difference) are different. Hence demulsifiers with functional groups that have traditionally performed very well for lighter oils fail when applied to the heavy crude oil cases. Poly(ethylene oxide)/poly(propylene oxide) block copolymer-based products (PEO/PPO) do not seem to have the ability to penetrate the asphaltene network/film at the liquid–liquid interface (separated water, <17%) while the alkylphenol-aldehyde resins seem to prevent the formation of DPLs/emulsion layers possibly through polar interactions, yielding a good quality water phase after separation.
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