Drawing and orientation

As the figures in ihis section show, molecules work similarly. Actually the real trouble in determining, for instance, whether two structures are enantiomers or diastereomers of each other stems from difficulty in drawing and orienting the pictures of the molecules so that the stcrcocenters can be compared in the first place. Let s look at an example. 

A related process is die-drawing. In this process the sample is pulled, not pushed, through the die. The important difference here is that the type of stress applied is quite different. In extrusion the polymer is under compressive stress, whereas in die-drawing it is largely under tensile or shear stress, with plane sections normal to the draw direction often remaining almost plane, giving rise to plug flow. This type of stress is necessary for some polymers in order to allow them to draw and orient. 

On drawing and orientation the man-made fibers become smaller in diameter and more crystalline, and imperfections in the fiber morphology are improved somewhat. Side-by-side bicomponent or biconstituent fibers on drawing become wavy and bulky. 

Thermoplastic man-made fibers can be permanently heat-set after drawing and orientation. The fiber will possess structural integrity and will not shrink up to that setting temperature. A1 so, thermoplastic fibers or yarns from these fibers can be texturized to give three dimensional loft... 

Lei s relurn fo bromochlorofluoromelhane as a simple example of a chiral mole cule The Iwo enanliomers of BrClFCH are shown as ball and slick models as wedge and dash drawings and as Fischer projections m Figure 7 6 Fischer projeclions are always generated Ihe same way Ihe molecule is oriented so lhal Ihe verlical bonds al Ihe chiralily center are directed away from you and Ihe horizonlal bonds poinl toward you A projeclion of Ihe bonds onto Ihe page is a cross The chiralily center lies al Ihe center of Ihe cross bul is nol explicilly shown... 

Mechanical Properties. Polyester fibers are formed by melt spinning generally followed by hot drawing and heat setting to the final fiber form. The molecular orientation and crystalline fine stmcture developed depend on key process parameters in all fiber formation steps and are critical to the end use appHcation of the fibers. 

Let s return to bromochlorofluoromethane as a simple example of a chiral molecule. The two enantiomers of BrCIFCH are shown as ball-and-stick models, as wedge-and-dash drawings, and as Fischer projections in Figure 7.6. Fischer projections are always generated the same way the molecule is oriented so that the vertical bonds at the chirality center are directed away from you and the horizontal bonds point toward you. A projection of the bonds onto the page is a cross. The chirality center lies at the center of the cross but is not explicitly shown. 

The melt blends exhibited the best mechanical properties, which could be still further improved with additional drawing. The composites Hel-He4 could not be drawn to improve the mechanical properties. In the case of the melt blends, even higher draw ratios than used in this study will increase the fibrillation and orientation of the LCP phase leading to significant improvements in strength and modulus [21,30]. 

The pinion shafts in this type of compressor are inside the housing. As a result, it is difficult to obtain radial measurements directly. A cross-sectional drawing of the compressor is required to determine the best location and orientation for the measurement points. 

Fibers are thin threads produced by extruding a molten polymer through small holes in a die, or spinneret. The fibers are then cooled and drawn out, which orients the crystallite regions along the axis of the fiber and adds considerable tensile strength (Figure 31.3). Nylon, Dacron, and polyethylene all have the semicrystalline structure necessary for drawing into oriented fibers. 

X-Ray diffraction analysis of oriented polysaccharide fibers has had a long history. Marchessault and Sarko discussed this topic in Volume 22 of Advances, and a series of articles by Sundararajan and Marchessault in Volumes 33, 35, 36, and 40 surveyed ongoing developments. The comprehensive account presented here by Chandrasekaran (West Lafayette, Indiana) deals with some 50 polysaccharides, constituting a wide range of structural types, where accurate data and reliable interpretations are available. The regular helical structures of the polysaccharide chains, and associated cations and ordered water molecules, are presented in each instance as stereo drawings and discussed in relation to observed functional properties of the polymers. 

The structure of the interface between two immiscible electrolyte solutions (ITIES) has been the matter of considerable interest since the beginning of the last century [1], Typically, such a system consists of water (w) and an organic solvent (o) immiscible with it, each containing an electrolyte. Much information about the ITIES has been gained by application of techniques that involve measurements of the macroscopic properties, such as surface tension or differential capacity. The analysis of these properties in terms of various microscopic models has allowed us to draw some conclusions about the distribution and orientation of ions and neutral molecules at the ITIES. The purpose of the present chapter is to summarize the key results in this field. 

Fig. 3.5 Representation of a scheme of an experiment (upper set of drawings) and the obtained experimental results presented as AFM images (middle part) and cross-sectional profiles (bottom) that provides evidence of silica nucleation and shell formation on biopolymer macromolecules. Scheme of experiment. This includes the following main steps. 1. Protection of the mica surface against silica precipitation. It was covered with a fatty (ara-chidic) acid monolayer transferred from a water substrate with the Langmuir-Blodgett technique. This made the mica surface hydrophobic because of the orientation of the acid molecules with their hydrocarbon chains pointing outwards. 2. Adsorption of carbohydrate macromolecules. Hydrophobically modified cationic hydroxyethylcellulose was adsorbed from an aqueous solution. Hydrocarbon chains of polysaccharide served as anchors to fix the biomacromolecules firmly onto the acid monolayer. 3. Surface treatment by silica precursor. The mica covered with an acid mono-...

The amorphous PEN resin pellets are first dried at 180 °C and then extruded at 290-300 °C through a die, formed into a sheet, which is then followed by a two-step orientation (forward draw and sideway draw process) just above the glass transition temperature (Tg) (>120°C). After the orientation process, the PEN film is conveyed between rollers at 210-220 °C to induce crystallization. At the end of the orientation and crystallization process, the film is cut and rolled into widths and lengths to suit individual customers [14-16], Two of the process used to produce such films are shown in Figure 10.3. 

Identity of the person taking the photograph Sketches, drawings, and plot plans to document the perspective of each photograph rapidly if needed to augment or as an alternative to the orientation entry... 

Conversion of copolymers to fibers and pertinent tensile date. Copolymers I-III described in Table I were melt extruded, and the extrudates were oriented by drawing and then annealed. The tensile properties of the unannealed and annealed fibers are summarized in Table II and III, respectively. 

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