SynopsisAs-spun fibers of poly(ethy1ene terephthalate), PET, made at winding speeds ranging from 2000 to 6000 m/min exhibit quite different physical structures. Yarns wound at relatively low speeds are amorphous, whereas those spun at high speeds contain well-developed crystals of closely packed molecules. In this study the structures have been characterized by means of various techniques such as differential scanning calorimetry, x-ray diffraction, density, and pulse propagation measurements. Based on the results obtained, an arrangement of the molecules in the various yarns is proposed. It is shown that these arrangements can account for the extreme wide variety in contraction behavior found experimentally. Finally, the results obtained are compared with those of other investigations into orientation-induced crystallization.

SynopsisNylon 6 yarns were wound a t speeds varying from 700 to 5500 mpm. The effect of the winding speed on both a-and y-type crystals in these undrawn yarns was studied. Also the effects of dry heat, tension, and heating in saturated steam were included in this investigation, since they provide useful information for drawing and heat-setting processes. The emphasis was put on the characterization of the crystalline part of the yarns. By applying recently developed techniques, relative amounts of the two crystalline components, as well as their orientation factors, could be determined. Concerning the undrawn, conditioned yarns, it was found that the amount of y type increases with the winding speed. The y crystals are much better oriented than the a crystals, and the crystal dimensions of the y structure largely depend on the winding speed in contrast to those of the a crystals. Indications were found that y crystals are mainly generated from orientation-induced nuclei a t speeds higher than 2500 mpm and that a crystals grow slowly at relatively low temperatures after moisture pickup during conditioning. Drawing at high ratios causes a transition from y to a, while the thermal stability of the y crystals appears to be slightly below that of the a crystals, resulting in y crystal to a crystal transitions at extremely high temperatures or under usual autoclaving conditions.

SynopsisFrom an industrial point of view, it is effective to have a relation between process conditions and resulting product properties. In practice there are many possible process conditions, whereas properties are generally interrelated in a complex way. Thus, there is a strong need for a physical understanding of the product properties in terms of process settings. This comprehension should also allow one to predict possible consequences for the properties when new process conditions become available. To obtain that physical understanding for the development of production processes of PET yarns, use has been made of a simple two-phase model of crystalline and amorphous regions. As process parameters the spinning speed and the drawing temperature were chosen. As the drawing temperatures are only known as machine-setting values, they are simply referred to as "low" and "high." As mechanical properties the shrinkage, modulus, tenacity, and dynamic mechanical behavior are discussed.

In curve fitting the most commonly used technique is an iterative hill-climbing procedure that makes use of partial derivatives to calculate the steepest path to an optimum in solution space. However, reliable and accurate initial estimates of the number of peaks, individual peak positions, heights, and widths are necessary to find acceptable solutions. One of the main drawbacks involved is that as the number of overlapping peaks increases, the problem becomes progressively more ill-conditioned. Consequently, small errors in the data (e.g., noise or baseline distortions), errors in the mathematical model, or errors in the estimates can be magnified, leading to large errors in the parameters of the final model. In addition to this, more overlapping peaks can lead to ambiguous fitting results. Ambiguous fitting is a general problem in curve fitting and is not limited to the steepest hill-climbing methods only. In this article we present a method for peak detection using artificial neutral networks and a global search technique for curve fitting based on evolutionary search strategies which does not need accurate estimates and is less sensitive to local optima than steepest descent procedures. These statements are corroborated in our comparative case study, which involves the fitting of a seriea of spectra with strongly overlapping peaks X-ray equator diffractometer scans of poly(ethy1ene naphthalate) yams.If the underlying mathematical model of the peak pattern is not known, or proper estimates of the parameters in the model assumed cannot be obtained, curve fitting can be a long and complicated task. Apart from this, a good fit of an experimental spectrum does not always lead to parameters with a valid physical meaning because many overlapping peaks may lead to many sets of parameters that can give a close fit of the profile. Vandeginste and De Galan evaluated curve fitting in infrared spectrometry.' They investigated the influences of the degree of overlap, the number of unresolved bands in the profile, and the determination of the baseline position on the fitting results of theoretical and experimental spectra. They formulated conditions to be fulfilled in order to obtain reliable results from the fit of infrared data.Pierce et al. formulated the main sources of errors in curve fitting.2 These sources are used as a guideline throughout this article: (1) The exact number of peaks is not known, Error sources 1 and 2 originate from the experimental data, including the way the latter are collected and prepared for the subsequent optimization method used for curve fitting. In contrast, error source 3 originates from the optimization method. Traditionally, local searching optimization methods are most widely applied, e.g., the Gauss-Newton minimization method for nonlinear models. In contrast, globally searching optimization methods are more robust, i.e., less sensitive to initial estimates. Admittedly, globally searching optimization methods are computationally more intensive as well, but with the advent of increasi...

A wide‐angle x‐ray method has been developed by which quantitative structural information can be obtained on nylon‐6 yarns. To this end, experimental equatorial diffractometer scans measured in transmission were fitted to a mathematical model describing the profiles as the envelopes of three bell‐shaped functions. Four different models were investigated using, respectively, Gauss, Lorentz (Cauchy), Logistic, and Pearson‐VII functions. The last model, which can be regarded as a generalized Lorentz function, gave the best fit. On the basis of a statistical analysis of the results of well‐separated x‐ray peaks, two parameters could be fixed. Another reduction of the number of parameters was achieved by interrelating the peak areas of the two outer reflections. These reductions widened the applicability of a computer program based on the aforementioned model to highly overlapping x‐ray peaks. So the whole variety of x‐ray scans, which can be obtained from nylon‐6 yarns made under widely varying process conditions, can be well described. The fitting procedures provide unique solutions and hence objectively determined parameters.