Effects of long chain branching on melt fractures in capillary extrusion of metallocene‐catalyzed linear low‐density polyethylene melts

Abstract

To investigate the effect of long chain branching (LCB) on melt fractures of metallocene-catalyzed linear low-density polyethylene (mLLDPE), we prepared a series of sparsely long-chain-branched mLLDPEs with well-defined degrees of LCB. Gross melt fractures were observed to decrease as the degree of LCB increases. This is in accordance with a prediction based on the observation that LCB enhances chain entanglement and consequently increases the melt strength of a polymer. However, sharkskin melt fracture (SMF) was observed to be more severe with the degree of LCB. There have been debates over the effect of LCB on SMF. According to a well-known mechanism of SMF, SMF is expected to decrease with the degree of LCB. Therefore, the majority of research groups believe that SMF decreases with the degree of LCB. This study clearly shows that the SMF becomes more severe with an increase of the degree of LCB and suggests another possible mechanism for the SMF. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 126: E322-E329, 2012

A Comprehensive Review on Controlled Synthesis of Long‐Chain Branched Polyolefins: Part 3, Characterization of Long‐Chain Branched Polymers

“…The slope is also independent of MW, MWD, and the measurement conditions . The rheological properties discussed above are conventionally used for LCB characterization, but many other rheological parameters such as the first normal stress coefficient (ψ1) enhancement, the critical tensile stress ( σ c ) for the onset of gross melt fracture, the sharkskin periodicity and the stick‐slip flow in capillary extrusion experiments and so on can be also used.…”

An Intriguing Array of Extrudate Patterns in Long‐Chain Branched Polymers During Extrusion

“…[ 20 ] reported the opposite effect on a series of sparsely (less than two LCBs per 10 4 main chain carbons) long‐chain branched metallocene linear low‐density polyethylene (mLLDPE). [ 20 ] The surface patterns (cylindrical extrudates) identified included sharkskin and at higher shear rates gross melt fracture. [ 20 ] Filipe et al., [ 21 ] using an emerging state‐of‐the‐art high‐sensitivity piezoelectric pressure measurement system, included several LCB polymers in their study and reported surface and volume MFEI in some that they identified as sharkskin and stick‐slip.…”

“…However, Yoo et al [20] reported the opposite effect on a series of sparsely (less than two LCBs per 10 4 main chain carbons) long-chain branched metallocene linear low-density polyethylene (mLLDPE). [20] The surface patterns (cylindrical extrudates) identified included sharkskin and at b) typical extrudate patterns in a low-density polyethylene (LDPE). Both visualizations were performed on extrudates from Georgantopoulos et al [24] ).…”

“…higher shear rates gross melt fracture. [20] Filipe et al, [21] using an emerging state-of-the-art high-sensitivity piezoelectric pressure measurement system, included several LCB polymers in their study and reported surface and volume MFEI in some that they identified as sharkskin and stick-slip. [21] Gross melt fracture was reported as the main instability by Palza et al [22] in a LCB-PE using an upgraded version of the high sensitivity die, [22] later commercialized by Goettfert GmbH.…”

Thermoplastic biodegradable material elaborated from unripe banana flour reinforced with metallocene catalyzed polyethylene

“…Conversely, metallocene‐catalyzed polyethylenes (mPEs) exhibit superior physical and mechanical properties because the metallocene catalyst yields polyolefins with a narrow molecular‐weight distribution and sparse long‐chain branches . Metallocene catalysis produces PE with an excellent degree of control over the molecular structure and stereospecificity at the commercial scale . In manufacturing, mPE is considered to be a good option among the available plastics because it has good mechanical properties.…”