Orientation development and relaxation in injection molding of amorphous polymers

Dietz, W.; White, James L.; Clark, Edward S.

doi:10.1002/pen.760180407

Cited by 71 publications

(19 citation statements)

References 55 publications

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“…By making a number of simplifying assumptions such as isothermal flow, the volume of the deposited surface layer S can be derived from a simple heat flow model :

S \approx 1.9 true(\frac{T_{T} - T_{W}}{T_{m} - T_{W}} true) \sqrt{α t_{c}}

where T T is the transition temperature ( T g 105°C); T w is the wall temperature of the mould; T m is the temperature of the injection moulded melt (180°C for setup J and L; 190°C for setup K); α is the thermal diffusivity of the polymer (2 × 10 −7 m 2 s −1 ) ; and t c is the contact time between the melt and the mould wall given by :

t_{c} = true(\frac{L - l}{U} true)

where L is the total mould length; l is the distance down the mould; and U is the melt velocity in the z direction.…”

Section: Resultsmentioning

confidence: 99%

Residual orientation in injection‐moulded plaques of atactic‐polystyrene I: The effect of processing conditions

Healy

Knott

Edward

2017

Polymer Engineering & Sci

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Injection moulded polymer articles often have residual macromolecular or crystalline orientation which can have a significant impact on the optical and mechanical properties of the moulded article. Small angle neutron scattering (SANS) was used to measure the molecular shape and orientation of deuterated blends of injection moulded polystyrene. For ∼1‐mm‐thick mouldings of uniform rectangular cross‐section, the eccentricity in the SANS pattern gave a direct measure of the residual molecular orientation over the length scale ∼100–1,500 Å. The residual orientation was found to vary significantly with injection moulding conditions with comparative residual orientation decreasing with decreasing mould fill‐time, and increasing with mould thickness and moulding temperatures. The orientation was found to be a minimum in the centre of the mould and highest near the surface and the average orientation at a particular position in the mould was found to be strongly correlated with the volume of material deposited as a solid skin layer during injection moulding. POLYM. ENG. SCI., 58:1322–1331, 2018. © 2017 Society of Plastics Engineers

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“…By making a number of simplifying assumptions such as isothermal flow, the volume of the deposited surface layer S can be derived from a simple heat flow model :

S \approx 1.9 true(\frac{T_{T} - T_{W}}{T_{m} - T_{W}} true) \sqrt{α t_{c}}

t_{c} = true(\frac{L - l}{U} true)

where L is the total mould length; l is the distance down the mould; and U is the melt velocity in the z direction.…”

Section: Resultsmentioning

confidence: 99%

Residual orientation in injection‐moulded plaques of atactic‐polystyrene I: The effect of processing conditions

Healy

Knott

Edward

2017

Polymer Engineering & Sci

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“…X,(wt % ) = AH/AHo (1) where AH = AHmelting -AHheating process and AH " is the heat of fusion of 100% crystalline P E T (AH O = 122 J/g). ' We also measured the nonisothermal crystallization behavior during the cooling process of extruded-and-quenched blends and neat PET by d.s.c.…”

Section: Resultsmentioning

confidence: 99%

Nonisothermal crystallization of poly(ethylene terephthalate) and its blends in the injection‐molding process

Okamoto

Shinoda

Kinami

et al. 1995

J of Applied Polymer Sci

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SYNOPSISWe investigated the nonisothermal crystallization during the cooling process of injection molding of poly(ethy1ene terephthalate) ( P E T ) , PET/talc, and PET/Surlyn blends. We applied the isothermal crystallization parameters obtained by the Hoffman-Lauritzen theory to the kinetics of nonisothermal crystallization and then calculated the relative crystallinity X / X , as a function of the mold temperature. X/X, were nicely interpreted by calculation without eff'ect of the pressure history on crystallization in PET and PET/talc (1 wt W ) blends. In contrast, in the PET/Surlyn ( 3 wt 96) blend, crystallization occurred at a lower mold temperature than predicted by our calculation. T h e transmission electron micrograph near t h e surface of the injection-molded PETfSurlyn blend showed deformation and stretching of dispersed Surlyn particles, suggesting that orientation of the PET matrix proceeds with the flow in processing. T h e orientation o f t h e PET matrix resulted in acceleration of the crystallization in the injection molding. CC

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“…'l JaneschitzKrieg144145 investigated the results of Wales by means of an analytical model for the heat transfer in the injection-moulded sarufle during filling. Another approximate theory was proposed by Dietz and White, Dietz et aZ., 21 and White and Dietz."' They applied a viscous model in the injection stage, calculating normal stresses from shear stresses by means of an empirical relation.…”

Section: L;d Approach For Flow-induced Stressesmentioning

confidence: 99%

The computation of properties of injection-moulded products

Douven

Baaijens

Meijer

1995

Progress in Polymer Science

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-Injection moulding is a flexible production technique for the manufacture of complex shaped, thin walled polymer products that require minimal finishing. During processing, the polymer experiences a complex deformation and temperature history that affects the final properties of the product.In a growing number of applications, injection-moulded products must meet high demands concerning their properties and dimensional stability. As a consequence, the ultimate aim of numerical simulations of the injection-moulding process is not only to analyse the processing stage but also to calculate the mechanical (and optical) properties of the product, starting from the material properties and the processing conditions. This also requires measurement techniques that can determine molecular orientation, residual stresses and density distributions.In all recent models of the injection-moulding process, the so-called 2iD approach is employed, referring to limitations of the mould geometry to narrow, weakly curved channels. Thus the ratio of the cavity thickness h and a characteristic length 1 in the mid-plane of the cavity must be much less than unity. In this paper an attempt is made to model all the stages of the production process, using this 2iD approach. The analysis is restricted to amorphous thermoplastics.Residual stresses in injection-moulded products stem from two main sources: first, the frozen-in flow-induced stresses, caused by viscoelastic flow of the polymer during the filling and post-filling stage of the injection-moulding process. These stresses correspond with the orientation of macromolecules; second, the thermally-and pressure-induced stresses, which are caused by differential shrinkage. In absolute value, the thermally-induced stresses are usually substantially larger than the frozen-in flowinduced stresses. However, the molecular orientation, as reflected in the frozen-in flow-induced stresses, determines the anisotropy of mechanical, thermal and optical properties and influences the long-term dimensional stability of an injection-moulded product.A decoupled method is proposed to calculate flow-induced stresses. Firstly, the kinematics of the flow field are determined, employing a viscous, generalized Newtonian constitutive law for the Cauchy stress tensor in combination with the balance laws. This is realized for all stages of the process: injection, packing, holding and cooling. The flow kinematics are subsequently substituted in a viscoelastic constitutive equation to calculate the transient stresses. Two constitutive models are used: a compressible version of the Leonov model (differential formulation) and a compressible version of the Wagner model (integral formulation). In the decoupled method, the flow kinematics are, consequently, supposed not to be influenced by the viscoelastic character of the flowing polymer melt. This decoupled method has a number of advantages compared to a coupled viscoelastic computation: the computation time is reduced considerably, an arbitrary viscoelastic c...

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Orientation development and relaxation in injection molding of amorphous polymers

Cited by 71 publications

References 55 publications

Residual orientation in injection‐moulded plaques of atactic‐polystyrene I: The effect of processing conditions

Residual orientation in injection‐moulded plaques of atactic‐polystyrene I: The effect of processing conditions

Nonisothermal crystallization of poly(ethylene terephthalate) and its blends in the injection‐molding process

The computation of properties of injection-moulded products

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