Effects of zone heating on pet fibers structures and dynamics of melt spinning process.
Part I. Crystallinity and molecular orientation
Polimery 2005, No 1, 48
Effects of heating chamber temperature (TK) and take-up speed (VL) on crystallinity degree (XV), optical birefringence (Δn), crystalline orientation (fc), and amorphous orientation (fa) of PET fibers obtained in melt spinning with zone heating were investigated. Zone heating has been provided by thermostatic chamber with hot air in the temperature range 100-210°C. Take-up speed of fibers varied dependently on the type of spinning: conventional or high speed one (>4000 m/min). Crystallinity degree has been determined from density measured using gradient column, crystalline orientation factor was determined from WAXS diffraction patterns while amorphous orientation factor was determined on the basis of birefringence measurements as well as of crystalline orientation factor and crystallinity degree. Measurements have been carried out for small and big VL values, 2600 or 4800 m/min respectively, at low (135°C) or high (195°C) chamber temperature. Lower TK value is in the middle of the range between glass transition temperature (Tg) and the temperature of maximal crystallization rate (Tmax). It has been found PET fibers showing high XV value can be obtained using conventional VL speed at temp. TK >135°C while in case of high speed spinning XV increase requires high TK temperature close to Tmax ≈ 190°C. Molecular orientation is characterized by high values of crystalline orientation factor fc ≈ 0.9, independently on spinning conditions. It proves the constant critical level of fa orientation needed to oriented crystallization occurring. High amorphous orientation of the fibers is obtained during melt spinning with online crystallization induced in technological line. Zone heating is a factor inducing the crystallization in case of low take-up speeds while at high speed spinning high value of fa is this factor. Amorphous orientation is higher for low TK. High TK leads to decrease in fa value because of relaxation. The fibers showing the highest values of birefringence were obtained at high chamber temperature.
Key words: melt spinning, PET, zone heating, chamber temperature, take-up speed, amorphous orientation, crystalline orientation, oriented crystallization
Effects of zone heating on pet fibers structures and dynamics of melt spinning process. Part I. Crystallinity and molecular orientation