Crystallization of polypropylene, nylon‐66 and poly(ethylene terephthalate) at pressures to 200 MPa: Kinetics and characterization of products

He, Jian; Zoller, P.

doi:10.1002/polb.1994.090320610

Cited by 98 publications

(102 citation statements)

References 44 publications

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“…During a measuring cycle a steady state in the material is assumed, which implies that cooling and heating rates are restricted to 0.83 at maximum in a DSC (He [6]) and to 0.167[Ks −1 ] for the confining fluid or piston-die technique (due to the sample size). However, in injection moulding, cooling rates depend on the thickness of the product.…”

Section: The Confining Fluid Techniquementioning

confidence: 99%

“…The volume of the material is registered during the measuring cycle using the displacement of the piston. Both temperature and pressure can be varied, however the pressure applied is not hydrostatic because the material sticks to the wall (He [6]). According to Zoller [24] this technique only gives accurate results when the shear modulus of the material is much smaller than its bulk modulus, which is the case for polymer melts.…”

Section: Introductionmentioning

confidence: 99%

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Influence of cooling rate on pVT‐data of semicrystalline polymers

Zuidema

Peters

Meijer

2001

J of Applied Polymer Sci

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For numerical simulations of the injection moulding process, an accurate description of the specific volume is needed to predict differential shrinkage during and after moulding, which causes thermally induced stresses and controls the dimensional accuracy and long term dimensional stability. For amorphous polymers, for which often it can be assumed that cooling rate dependence can be ignored, standard techniques enable measurements of the specific volume as a function of temperature and pressure. For semi-crystalline polymers the situation is more complicated since the specific volume depends strongly on the degree of crystallinity which itself depends on the thermo-mechanical history, i.e. temperature and pressure (for quiescent crystallization). This requires the use of a combined experimental-numerical technique to interpret the data and to determine the specific volume. Standard equipment can only be used at relatively low cooling rates. Since high cooling rates are present during injection moulding, improved experimental techniques must be designed. A setup based on the confining fluid technique is build, which can reach cooling rates up to 60[Ks −1 ] and pressures up to 20 · 10 6 [P a]. During an experiment, the specific volume is measured together with the temperature history and pressure. Using an accurate model to calculate the crystalline structure, together with a specific volume model which depends on this structure, enables the determination of model parameters. Comparing both the measurements and the model predictions, leads to the conclusion that modeling of the crystallization kinetics, results in accurate predictions of the specific volume.

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Section: The Confining Fluid Techniquementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Influence of cooling rate on pVT‐data of semicrystalline polymers

Zuidema

Peters

Meijer

2001

J of Applied Polymer Sci

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“…During cooling, a shear pulse is applied with fixed duration of 1 s and varying shear rate of _ γ ¼ 0, 3, 10, 30, 100, 180 s À1 at undercooling of 30 C or 60 C. The undercooling is the difference between the temperature at which the shear pulse is applied and the melting temperature, taking into account the variation in melting temperature with pressure according the Clapeyron equation [86] (Eq. 34).…”

Section: Extended Dilatometrymentioning

confidence: 99%

“…The pressure dependence of the melting temperature ζ is 27.5 C/kbar [86]. The reference temperature T 0 ref is given at p ¼ 1 bar in Table 6.…”

Section: Crystallization Kineticsmentioning

confidence: 99%

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Modeling Flow-Induced Crystallization

Roozemond

Drongelen

Peters

2016

Polymer Crystallization II

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A numerical model is presented that describes all aspects of flow-induced crystallization of isotactic polypropylene at high shear rates and elevated pressures. It incorporates nonlinear viscoelasticity, including viscosity change as a result of formation of oriented fibrillar crystals (shish), compressibility, and nonisothermal process conditions caused by shear heating and heat release as a result of crystallization. In the first part of this chapter, the model is validated with experimental data obtained in a channel flow geometry. Quantitative agreement between experimental results and the numerical model is observed in terms of pressure drop, apparent crystallinity, parent/daughter ratio, Hermans' orientation, and shear layer thickness. In the second part, the focus is on flow-induced crystallization of isotactic polypropylene at elevated pressures, resulting in multiple crystal phases and morphologies. All parameters but one are fixed a priori from the first part of the chapter. One additional parameter, determining the portion of β-crystal spherulites nucleated by flow, is introduced. By doing so, an accurate description of the fraction of β-phase crystals is obtained. The model accurately captures experimental data for fractions of all crystal phases over a wide range of flow conditions (shear rates from 0 to 200 s À1 , pressures from 100 to 1,200 bar, shear temperatures from 130 C to 180 C). Moreover, it is shown that, for high shear rates and pressures, the measured γ-phase fractions can only be matched if γ-crystals can nucleate directly on shish.

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