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ABSTRACT:The processing of poly(vinyl chloride) (PVC) consists of fusion, flow, and solidification processes. In this study, we examined how gelation in the fusion process affected the processability in the following flow process. We prepared sheets with adjusted degrees of gelation (Gs) by rolling a rigid-pipe-formulation PVC compound with a degree of polymerization of 1050 by changing the milling temperature and time. The rheological properties, including viscosity, die swell, melt fracture, and entrance pressure loss (⌬P ent ), of the sheets were measured with a capillary rheometer, and the effect of gelation on the flow processability was studied. The viscosity slightly increased as the milling temperature and time increased, and hence, G increased. The flow activation energy showed a maximum at a shear rate around 100 s Ϫ1 and increased with increasing gelation. The die swell was larger when a sheet with a more advanced gelation was extruded at a higher temperature. Melt fracture easily occurred when a sheet with an advanced gelation was extruded at a low temperature. The critical shear rate at the onset of melt fracture changed by over 3 decades, depending on G. ⌬P ent increased linearly with G. The dependence of the rheological properties on the gelation was in the following order: melt fracture Ͼ die swell Լ ⌬P ent Ͼ viscosity: The effect was larger for the elasticity than for the viscosity. The change in these rheological properties with increasing gelation was caused by a transition from particle flow to uniform molecular chain flow.

Section: Resultssupporting

confidence: 57%

“…Figure 13(a–d) shows the changes in D / D 0 of samples milled at 150, 160, 170, and 180°C with extrusion temperature. The change in D / D 0 with shear rate showed valleys or peaks, which is a characteristic of PVC 3, 4, 7, 20–23. The D / D 0 's of common resins, such as polypropylene and polyethylene, monotonously increase with shear rate.…”

Section: Resultsmentioning

confidence: 97%

Effect of gelation on the flow processability of poly(vinyl chloride)

Fujiyama

Kondou

2003

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“…Although the slope of decrease in ν of cat.‐B PPs is higher than that of cat.‐A PPs below 280°C, it tends to level off or turn to increase at high temperatures. The fact that ν decreases with temperature is generally observed for PP6, 7 and other polymers 8–17. As a large tendency, ν is higher as MFI is lower or the molecular weight is higher.…”

Section: Resultsmentioning

confidence: 71%

“…τ c values of 10 5 –10 6 Pa are reported for many polymers 37. As for the temperature dependence of τ c , that τ c scarcely changes or slightly increases with increasing temperature is reported for PP38–41 and most other polymers,11, 17, 38, 39, 42, 43 and is main stream, a reverse tendency being reported for PVC 15, 34, 44. As for the molecular weight dependence of τ c , a reduction of τ c with increasing molecular weight is reported for PP19, 29, 41, 45 and other polymers,9, 23, 29–33, 42, 44 some reports19, 20, 30 declaring τ c × M w = constant (3–4 × 10 10 Pa).…”

Section: Resultsmentioning

confidence: 87%

Rheological properties of polypropylenes with different molecular weight distribution characteristics

Fujiyama

Kitajima

Inata

2002

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ABSTRACT:Relationships between the rheological properties and the molecular weight distribution of two polypropylene series with different molecular weight distribution characteristics were studied. The end correction coefficient in capillary flow is determined by the molecular weight M w and the molecular weight distribution M w /M n , and is higher as both characteristic values are larger. The die swell ratio at a constant shear rate depends on M w , M w /M n , and M z /M w , and is higher as the three characteristic values are larger. The critical shear rate at which a melt fracture begins to occurs depends on the molecular weight M w and the molecular weight distribution M z /M w , and is proportional to M z /M w 2 in a log-log plot. The critical shear stress does not depend on the molecular weight, and is higher as M z /M w is higher. The zero-shear viscosity is determined by a molecular weight of slightly higher order than M w , and the characteristic relaxation time is determined by M z . The storage modulus at a constant loss modulus scarcely depends on the molecular weight, and is higher as the molecular weight distribution M w /M n is higher.

“…12,13,30 The fact that with increasing gelation the melt fracture occurs easily is fragmentarily reported by Berens and Folt, 1 Shinagawa, 26 and Fujiyama and Nagou. 27 According to Paradis, 31 the elastic energy that the PVC melt has stored when entering into the capillary from the reservoir is consumed by the elastic recovery of die swell.…”

Section: Melt Fracturementioning

confidence: 84%

Effect of degree of polymerization on gelation and flow processability of poly(vinyl chloride)

Fujiyama¹,

Kondou²

2004

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ABSTRACT:The effect of degree of polymerization (DP) on the gelation and flow processability of poly(vinyl chloride) (PVC) was studied. Sheets with adjusted degree of gelation were prepared by rolling rigid pipe formulation suspension PVC compounds with DPs of 800, 1050 and 1300 by changing the milling temperature. Their degrees of gelation were measured with DSC and their capillary flow properties were measured with a capillary rheometer at 150, 170 and 190°C and the effect of DP on the relation between gelation and flow processabilities was studied. Because of the higher shearing heat during milling, the sample with the higher DP had a higher history temperature and thus tended to show a higher degree of gelation. The viscosity increased as the gelation increased. The dependency of viscosity on DP was higher at higher milling and extrusion temperatures and thus at a higher degree of gelation and a lower shear rate. This was assumed to be attributed to the more prominent uniform molecular flow as against the particle flow. The die swell increased with increasing the milling and extrusion temperatures and hence with increasing the gelation. A sample with a lower DP tended to show a larger die swell and this tendency was even more pronounced at the higher extrusion temperature. The melt fracture easily occurred when a sample with advanced gelation was extruded at low temperature. Whereas at low milling temperatures a sample with the lower DP showed a lower critical shear rate at onset of melt fracture, and thus easily generating melt fracture, at high milling temperatures it showed a higher critical shear rate and hence scarcely generated melt fracture. These experimental results were explained by the fact and concept that a sample with a lower DP shows a higher increase in the gelation during extrusion and/or the slighter feature of particle flow as against the uniform molecular flow at the same gelation level.