Sizing Skin-core structure

Kevlar 149 has a substantially higher degree of crystallinity and larger crystal size than for Kevlar 49. The unit cell dimensions for the two also differ significantly. In addition, while there are present skin-core structure in both Kevlar 29 and Kevlar 49 fibers, there is no definable difference between the skin and core for Kevlar 149. 

It is seen that ultrasonic techniques have two major advantages high accuracy and the ability to determine the complete set of elastic constants for a sample of small size. As a result of these capabilities, all five independent stiffness constants have been obtained for extruded rods of PLC of high draw ratio (2 = 15) and small diameter (0.8 mm). Moreover, it has been possible to study the skin-core structure in injection molded PLC by monitoring the variation in stiffness with position. For blends of a PLC and a thermoplastic or glass fiber-reinforced PLC, successful correlation has been obtained between the modulus data and the orientation of the PLC fibrils or glass fibers. 

The higher-order structures (morphologies) of injection-molded polypropylene (PP), which should be considered, are crystalline form, lamellar thickness, spherulite size, crystallinity, molecular orientation, crystal orientation, dispersion state of a blended polymer, length and orientation of reinforcing fibers, crystalline texture (skin-core structure), etc. 

Fiber Structure. An extensive description of the structure of PPTA (Kevlar) fibers has been provided in a 1993 book (47), including a description of the crystal lattice (48), estimates of apparent crystallite size and percent ciys-tallinity, a description of fibrillar and pleat structure, and evidence of a skin-core structure. Crystal lattice structure and dimensions for PBA and MPDI (Nomex) fibers are also included, as shown in Table 3. The structure of Twaron is essentially the same (10), while the crystal structure ofTeijinconex is nearly identical to the MPDI fiber in Table 3. PPTA fibers are highly crystalline, ranging from 68 to 95% crystalline depending on the heat treatment of the fiber and the crystallinity measurement technique. MPDI fibers are also highly crystalline, although the crystal lattice is quite different from that of PPTA (30). 

Observation via SEM shows that the PCL foam has the typical skin-core structure. The size of the average cell is larger than 30 It may be caused by the... 

The study of the physical form and structure of a material. The overall physical form of the physical structure of a material on a submicron and micron scale. Common units are dispersed phase domains, lamellae, spherulites, etc. The term comprises notion of the global structure (e.g., stress-induced skin core), as well as shape, size, orientation, and distribution of the dispersed phase (solid, liquid, or gaseous). 

The model extends the structural hierarchy proposed by Dobb, Johnson and Saville [374] for the aramids. Three distinct fibrillar elements have been noted microfibrils, on the order of 50 nm in size fibrils, on the order of 500 nm in size and macrofibrils, about 5 pm (5000 nm) across. The importance of this structural model is that it not only describes the structure of uniaxially oriented fibrous materials, but it also shows the fine structure of the thicker LCP forms of moldings and extrudates. In these thicker materials, process history and temperature affects macrostructures, such as skin-core, bands and layering (Fig. 5.85). The fiber structural model shows the arrangement of the fine structure within those macro units. This structural model improves the understanding of relationships between processes, structure and properties in LCPs. 

The crystallinity and crystallite size of injection molded isotactic polypropylene was measured by wide angle X-ray diffraction(WAXD) and the distinct skin-core morphology was visible under a polarizing optical microscope. The results show that the crystal structures are dependent on the injection molding processing conditions. The crystallinity and crystallite size decreases with the distance from the gate. The skin layer thickness is thinner with the higher injection temperature. 

Liposomes were first proposed for drug topical administration to the skin more than 25 years ago by Mezei and Gulusekharam [1,2]. The basic components of liposomes are phospholipids (phosphatidylcholine, phophatidylethanolamine, phophatidylserine, dipalmitoyl phosphatidylcholine, and others), cholesterol, and water. Liposomes may vary significantly in terms of size (from tens of nm to microns) and structure. In liposomes, one or more concentric bilayers surround an aqueous core generating small or large unilamellar vesicles (SUV, LUV) or multilamellar vesicles (MLV), respectively [3]. 

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