Methods of testing the solidification point of fibres spun from a polymer melt

Abstract

The point on a spun fibre after which its diameter virtually does not change is called the solidification point. This determination is based on the fact that many fibres spun from a polymer melt are amorphous or their amorphous constituent is relatively large [1]. For such fibres, the transition from the liquid to the solid state is smooth.The position of the solidification point is used for evaluating the properties of a fibre and optimizing the spinning process parameters [2]. There are automatic methods of monitoring the solidification point based on the deviation of the fibre width caused by the effect of a short air pulse on it [2] and measurement of the diameter of the spun fibre at different distances from the spinneret [3]. However, according to the information sources, new methods of monitoring the solidification point have recently been proposed, involving a comparison of the errors of measurement and determination of the possibility of industrial implementation of these methods. It is also interesting to analyze the correlation of the nonuniformity of the fibre thickness with the position of the solidification point, i.e., the utility of utilizing a certain method. We will begin the analysis of the monitoring methods with an examination of their utility and informativeness.A diagram of spinning a fibre from a polymer melt is shown in Fig. 1. Polymer melt jet 3 forced from spinneret 1 through hole 2 expands, then is drawn in the cooling zone and fibre 4 is formed. An oiling liquid is applied to the fibre with wheel 5. The as-spun fibre is taken up in pack 6. When the solidification point is moved by quantity l from point a to b, for example, when the cooling conditions change, the volume of the polymer melt jet changes to the hatched part. Since feeding of the melt through the spinneret holes and removal of the fibre are constant, this alters the thickness of the spun fibre. Arbitrarily assuming that the profile of the change in the jet over the truncated cone and the change in the cooling conditions corresponds to a harmonic law [2], we will describe the correlation of the nonuniformity (H, %) of the fibre thickness with the zone of migration of the solidification point with the mathematical model 2 )/~(f)___k nl O0 ' H = 0.7l'~(dc max +dcmaxd f -2d 2 D s where d max is the maximum diameter of the polymer melt jet at the outlet from the spinneret hole, m; dfis the diameter of the spun fibre, m; l is the length of the solidification point migration zone, m; f is the solidification point migration frequency