Thermal and mechanical modification of LDPE in single‐screw extruder

Ono, Kaori; Yamaguchi, Masayuki

doi:10.1002/app.29980

Cited by 11 publications

(6 citation statements)

References 36 publications

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“…Moreover, some LDPE samples are known to be thermocomplex materials,45, 46, 49 although Stadler et al54 reported that LDPE used in their research obeys the time‐temperature superposition principle. This is reasonable because relaxation mechanism associated with long‐chain branches has different activation energy from that of entanglement couplings for a linear polyethylene 5, 52, 53. We confirmed that the present LDPE is also a thermocomplex material as demonstrated by a well‐known van Gurp–Palmen plot in our previous work 49…”

Section: Resultssupporting

confidence: 90%

“…The flow activation energy is calculated to discuss the branch structure assuming that the time‐temperature superposition principle is applicable to the virgin LDPE and found to be ∼ 53 kJ/mol. The value, however, has no/little relation with, at least, long‐chain branch structure for a commercial LDPE,16 although it is known that longer branches provide higher activation energy employing model star‐branch polyethylenes 52, 53. This could be attributed to the complicated branch structure for a commercial LDPE.…”

Section: Resultsmentioning

confidence: 99%

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Effect of shear history on flow instability at capillary extrusion for long‐chain branched polyethylene

Siriprumpoonthum

Mieda

Doan

et al. 2011

J of Applied Polymer Sci

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Effect of applied processing history on flow instability at capillary extrusion is studied using a commercially available low-density polyethylene (LDPE) having long-chain branches. It is found that processing history in an internal mixer in a molten state depresses long-time relaxation mechanism associated with long-chain branches, which is known as ''shear modification.'' Consequently, the onset of output rate for melt fracture increases greatly. Furthermore, it should be noted that the sample having intense shear history shows shark-skin failure without volumetric distortion, although it has been believed that LDPE exhibits gross melt fracture at capillary extrusion. The reduction of elongational viscosity by the alignment of long-chain branches along to the main chain is responsible for the anomalous rheological response. As a result, the sample shows shark-skin failure like a linear polyethylene at a lower output rate than the critical one for gross melt fracture.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Effect of shear history on flow instability at capillary extrusion for long‐chain branched polyethylene

Siriprumpoonthum

Mieda

Doan

et al. 2011

J of Applied Polymer Sci

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“…The question arises as to whether amylose could undergo shear scission purely because its branches are long, as distinct from being a much smaller molecule than amylopectin (which as explained is susceptible to shear scission because it is so large and relatively inflexible, being comprised only of short highly connected branches). However, the branches in amylose, although long (say, DP ∼ 500), are much shorter than those in synthetic polymers which susceptible to shear scission . Thus, the individual branches of amylose will not be strongly prone to shear scission, although as noted above there can be some preferential scission of longer chains.…”

Section: Resultsmentioning

confidence: 99%

“…Some work has been conducted on degradation of polyethylene and polypropylene during extrusion where scission of long chain branches in polyethylene and chain scission of polypropylene has been reported, but as stated in these papers more detailed knowledge of macromolecular branching structure and degradation chemistry needs to be understood in explaining the degradation processes. The present study provides useful insight into these processes.…”

Section: Resultsmentioning

confidence: 99%

Mechanism of Degradation of Starch, a Highly Branched Polymer, during Extrusion

2010

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An investigation of the mechanisms of degradation of a branched polymer in extrusion was performed using starch as substrate. Starch has the advantage that the distribution of degree of polymerization of individual branches can be readily obtained using a debranching enzyme and also that it does not undergo any reaction except scission during extrusion, thereby aiding mechanistic interpretation. Various starches, containing a range of the highly branched amylopectin component and the much less branched amylose component, were extruded in the presence of water and glycerol as plasticizers with extruder barrel temperatures ranging from 50 °C at the hopper zone through to 140 °C near the die exit. Analysis by size-exclusion chromatography of both whole and debranched samples subject to various levels of extrusion showed that the extrusion degradation process involved preferential cleaving of larger molecules, while causing the size distribution to narrow and converge toward a maximum stable size. This is analogous to a similar effect of shear degradation of droplets in emulsions. It was also found that the susceptibility of polymer molecules to shear degradation is not only dependent on the size of the molecule but also extensively influenced by the branching structure. High branching density and short branch length were associated with higher susceptibility to shear degradation. This is explained by the hypothesis that a short-chain hyperbranched polymer has a relatively inflexible structure, leading to a higher susceptibility to shear scission. The degradation process is not significantly selective toward the length of individual branches when the polymer is in a molten state but it preferentially breaks longer branches when the starch polymer is in a semicrystalline granular form. These inferences are generally applicable and use the additional information from the branch length distribution and absence of side reactions, which is generally not available for synthetic polymers.

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“…Finally, it was found that the rheological properties and processability of the polymer composite containing PTFE fibers are dependent on the processing history to a great extent [15], which is similar to shear modification behavior of long-chain branched polymers [39][40][41][42]. The change of shape and dispersion state of PTFE fibers during processing would affect the rheological properties.…”

Section: Introductionmentioning

confidence: 99%

Morphology development of polytetrafluoroethylene in a polypropylene melt (IUPAC Technical Report)

Ali

Nobukawa

Yamaguchi

2011

Pure and Applied Chemistry

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Morphology development of polytetrafluoroethylene (PTFE) caused by applied flow history in molten isotactic polypropylene (PP) is investigated, employing a cone-andplate rheometer and a capillary rheometer as mixing devices. Since the flow history is applied at 190 °C, PTFE is in the solid state whereas PP is in the molten state. It is found that primary PTFE particles tend to be agglomerated together by mechanical interlocking. Then they are fragmented into fibers by hydrodynamic force with reorganization process of crystalline phase. The diameter of the fragmented fibers is the same as that of the original ellipsoidal particles. Further, fine fibers whose diameter is in the range from 50 to 100 nm are also generated by yielding behavior of the particles. The prolonged shearing leads to a large number of fibers, although the diameter and length are hardly affected by the exposure time of shearing and shear stress. Moreover, the flow type (i.e., drag or pressure flow) does not affect the morphology to a great extent, although the drag flow is not efficient to reduce large agglomerated particles. The fibers form an interdigitated network structure, which is responsible for the marked melt elasticity.

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Thermal and mechanical modification of LDPE in single‐screw extruder

Cited by 11 publications

References 36 publications

Effect of shear history on flow instability at capillary extrusion for long‐chain branched polyethylene

Effect of shear history on flow instability at capillary extrusion for long‐chain branched polyethylene

Mechanism of Degradation of Starch, a Highly Branched Polymer, during Extrusion

Morphology development of polytetrafluoroethylene in a polypropylene melt (IUPAC Technical Report)

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