Comparison of Crystallization and Melting Characteristics of Quiescent and Melt-Spun Poly(ethylene-co-octene) Copolymers

An experimental study of crystallization and melting of polyethylene and its octene copolymers under quiescent conditions and their melt-spun fibers is presented. This includes copolymers produced by both Dow's Insite® Technology homogeneous catalyst and by a Ziegler heterogeneous catalyst. It is found that with increasing comonomer content, both isothermal and non-isothermal crystallization rate decrease. The melting peaks become broader and the melting temperatures decrease for polymers with more comonomer. Multiple melting peaks are observed for copolymers. Except the unchanged peak with the highest melting temperature, the other peaks move to higher temperature after being annealed under higher temperature. Attempts were made to correlate crystallization kinetics and melting behavior under quiescent conditions with melting temperatures and crystallinities determined for their melt-spun fibers. The results show that besides cooling effects, the melt temperatures and the crystallinities of the melt spun fibers are also affected by the degree of molecular orientation, which is mainly decided by the spin-line stress. These two competitive factors determine the final melt temperatures and crystallinities of the melt-spun fibers.