Spherulitic crystallization behavior of linear low‐density polyethylene

Abstract

In this study the crystallization behavior of linear low‐density polyethylenes (LLDPEs) (ethylene‐α‐olefin copolymers) was studied by polarized light microscopy. A modified Hoffman‐Lauritzen (MHL) expression is proposed whereby the equilibrium melting temperature, T mH,∞ (T m0), is replaced with the melting temperature of the crystal stem is replaced with the maximum possible stem length, T mC,n*. It successfully describes the crystalline spherulitic growth kinetics for both homogeneous and heterogeneous LLDPEs. In addition to regimes III and II, another regime (IM) was found in the high crystallization temperature range. Linear growth behavior of crystalline spherulites was observed in regime III, and nonlinear growth behavior was found in regimes II and IM. The basal surface free energy can be estimated from the short chain branching polydispersity (SCBP) for LLDPEs with excluded comonomers. Polym. Eng. Sci. 45:74–83, 2005. © 2004 Society of Plastics Engineers.

Melting Temperature Characteristics for Polyethylenes from Crystal Size Distribution

“…The branching degrees were measured by nuclear magnetic resonance (NMR), and molecular weights were measured by gel permeation chromatography (GPC). The procedures for estimating the basal surface free energies may be found elsewhere [18,19].…”

“…Although the average crystal size of resin G (ZN-LLDPE) is lower than that of resin J (m-LLDPE) [8], the effective melting temperature of the former is higher. Because ZN-LLDPE has a high ethylene sequence polydispersity due to multi-active sites in the catalysts, the basal surface free energy of ZN-LLDPE is lower than that of m-LLDPE [19], when their short chain branching contents (SCBC) are the same. In m-LLDPEs and their blends, the effective melting temperature decreases as SCBC increases (as resin I weight content increases).…”

“…Based on analysis of the crystallization growth regime behavior, the regime transition temperatures between regimes III and II, T III -II , are 93.9 and 107.1°C for resins I and J, respectively [19] . It is interesting to note that these temperatures are roughly equal to the temperatures at which the inversion is observed in the relative intensities between the 2 nd and 3 rd peaks, as shown in Fig.…”

“…Intern [18] for HDPE and estimated from the Hoffman-Lauritzen secondary nucleation crystallization kinetics analysis for LLDPEs [19]. was from 0.01 to 2.01°.…”

Study on the Phase Behavior of High Density Polyethylene – Ethylene Octene Copolymer Blends

“…[22] However, because of the branching, more time is needed for ethylene sequences to fit into niches on the crystal substrates. Thus, the substrate completion rate in the EOC and its blends with HDPE is low and the chain folding time probably increases which determines the lower values of K g .…”