Direction of draw

Miscibility or compatibility provided by the compatibilizer or TLCP itself can affect the dimensional stability of in situ composites. The feature of ultra-high modulus and low viscosity melt of a nematic liquid crystalline polymer is suitable to induce greater dimensional stability in the composites. For drawn amorphous polymers, if the formed articles are exposed to sufficiently high temperatures, the extended chains are retracted by the entropic driving force of the stretched backbone, similar to the contraction of the stretched rubber network [61,62]. The presence of filler in the extruded articles significantly reduces the total extent of recoil. This can be attributed to the orientation of the fibers in the direction of drawing, which may act as a constraint for a certain amount of polymeric material surrounding them. 

Obviously, the discrepancy between the experimental data [238-241] and predictions of the theory [236,237] can be attributed to the difference of the coefficients of thermal expansion. The polymer exerts pressure on the filler, thereby masking the effect of the strength of adhesion on the modulus. The pressure on the filler may be sufficiently high. In [243] it was found, for example, that in PP, quartz particles experienced a compression force of about 100 MPa after cold drawing of the composite the force reduces to 50 MPa in the direction of drawing but at the same time increases to 300 MPa in the perpendicular direction. 

Fig. 3. Apparent secant modulus (stress/strain) in tension at 0.1% strain and at various sample aspect ratios, measured at strain rate of 10 V. Highly oriented polyethylene (D. R. 28) measured in direction of drawing. (Sample cross section 0.2 mm x 2 mm)...

The lamellae slip rigidly past one another. Lamellae parallel to the direction of draw cannot slip thus, spherulites become anisotropic. At this stage, at which necking begins, the strain is accommodated almost entirely by the interlamellar amorphous component. 

The sprue is the channel from which the resin will flow through the gate and into the mold. Runners are perpendicular to the direction of draw, and the sprue is parallel to the direction of draw. This portion of the system is often recycled because typical OEMs allow up to 15% of regrind material (the use of polymer salvaged from the runner or sprue and not used in the original part). When injection molding takes place, automotive thermoplastics must be cooled under the Tm or T before ejection. 

Molecular and/or crystal orientation increases the yield stress in the direction of drawing (Fig. 8.16). However, the yield stress at right angles to the draw direction hardly changes or may even decrease. The resulting... 

Continuous formation of flat sheets sheet glass) can be performed by drawing a ribbon directly from the melt. Different commercial techniques involve variations in the method used to control the initial point of ribbon formation, and in the direction of draw. All commercial processes involve initial vertical draws, but the ribbon is subsequently... 

Drawing of filaments and fibers may result in an orientation of either or both polymer molecules and crystalline aggregates in the direction of draw. In crystalline aggregates, specimen drawing does not change the degree of crystallinity significantly. However, in amorphous or only partially crystallized material, crystallinity is likely to develop and increase. 

When the fiber is drawn, the crystals are oriented with the Z>-axis parallel to the direction of drawing. Drawing is an important process in the manufacture of PVA fiber. 

Particulate fillers are often used to improve the dimensional stability of polymeric manufacts. Several papers have been published on the effect of the draw ratio and glass filler contents on the recoil kinetics of unfilled and composites specimens (32,33). The presence of the filler, however, do not modify the recoil kinetics of composite samples, but significantly reduces the total extent of the lenght reversion ratio. This can be attributed to the orientation of the fibers in the direction of drawing, that act as a constrain for the matrix surrounding the fibers the fiber-filled specimens consequequently undergo partial sterss relaxation and partial creep. 

The draft specification controls the way the mold is built as the direction of draft normally indicates the direction of draw (removal of the part from the tool) since reverse draft would be an undercut condition. For injection molding, the mold designer will attempt to locate the core on the back, or movable, half of the mold. That is the side where the molding machine s ejector bars are located, and locating the core on that half makes the ejector mechanism available to push the part off the core. Part designs with cores from both sides of the part may require slight undercuts to keep them on the side of the mold which has the ejector mechanism. The draft specification will also control the location of the parting line, which should be indicated. 

The first hard elastic polymers were made from crystalline lamellar materials, and were processed via melt spinning and stress crystallization, followed by annealing under tension. The common morphology of these polymers is shown for hard elastic polypropylene [3] in Figure 2a. The structure consists of rows of lamellae oriented perpendicularly to the direction of draw, o Between these lamellae are microfibrils (ca. 100-500A... 

In one study. X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy and refractive index measurements were utilized to characterize the state of molecular orientation in one-way and two-way (bi-axially) drawn isotactic polypropylene (iPP) films [6]. It was shown that the use of all three techniques leads to much greater confidence in the orientation averages deduced than can be obtained by using any two of the techniques. It was observed that, with one-way drawing, the chain axes of both crystalline and amorphous regions orient towards the direction of drawing. The crystalline chains are more highly oriented than the amorphous chains and tend to orient towards the plane of the... 

As a result of stretching at 60°C, the film undergoes a transition to the polar phase I form. The amount of phase I form depends on the temperature and the elongation [12]. After stretching the film several times its original length, the lamellae orient in the direction of draw as shown in Fig. 4 (bottom). A poling treat-... 

Scheme 15.2. Morphology development scheme of microfibrillai blends (a) after extrusion, (b) alignment of the dispersed phase in the direction of draw, (c) coalescence of the dispersed phase, and (d) completion of formation of the microfibrils...

Birefringence bl-ri- frin-j9n(t)s n [ISV] (1898) (1) (double refraction) The difference between any two refractive indices in a single material. When the refractive indices measured along three mutually perpendicular axes are identical, the material is said to be optically isotropic. Orientation of a polymer by drawing may alter the refractive index in the direction of draw so... 

Studies of mechanical anisotropy in polymers have for the most part been restricted to drawn fibres and uniaxially drawn films, both of which show isotropy in a plane perpendicular to the direction of drawing. The number of independent elastic constants is reduced to five [3, p. 138]. Choosing the 3 direction as the axis of symmetry, the compliance matrix sy reduces to... 

Here 6 denotes the angle between the long axis of a monomer and the direction of drawing, i.e. the unique axis of the sample. has the advantage that it can be directly deduced from the birefringence An, using the relation... 

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