Flow and thermally induced birefringence in gas-assisted tubular injection moldings: Simulation and experiment

Various components of birefringence in polystyrene (PS) and polycarbonate (PC) tubular moldings, obtained by gas-assisted injection molding (GAIM), are measured and simulated considering both flow- and thermally induced stresses. The flow- and thermally induced stresses are calculated using nonlinear and linear viscoelastic theories, respectively, based on the flow and temperature histories that the polymer experiences during the GAIM cycle. Flow-induced birefringence components are calculated from flow stresses using the stress optical rule, while thermally induced birefringence components are calculated from thermal stresses using a photoviscoelastic model. The simulated total residual birefringence takes into account the contributions of both flow- and thermally induced birefringence generated during the melt injection, gas injection, and cooling stages of GAIM. The simulated results are in better agreement with the measured birefringence in PS moldings than in PC moldings. Considering both thermal and flow birefringence, simulations provides a better description of the experimental results indicating that, in GAIM moldings, the birefringence near the mold was caused mainly by flow stresses while that located towards the polymer/gas interface was caused mainly by thermal stresses. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

[1]  A. Carrillo,et al.  Birefringence in gas-assisted tubular injection moldings: Simulation and experiment , 2009 .

[2]  J. Sienz,et al.  Approximate prediction of gas core geometry in gas assisted injection molding using a short cut method , 2007 .

[3]  J. Sienz,et al.  Gas assisted injection molding of a handle: Three-dimensional simulation and experimental verification , 2005 .

[4]  H. S. Lee,et al.  Primary and secondary gas penetration during gas‐assisted injection molding. Part II: Simulation and experiment , 2004 .

[5]  Avraam Isayev,et al.  Primary and secondary gas penetration during gas-assisted injection molding. Part I: Formulation and modeling , 2004 .

[6]  Richard S. Graham,et al.  Simple constitutive equation for linear polymer melts derived from molecular theory: Rolie–Poly equation , 2003 .

[7]  C. Li,et al.  Residual thermal birefringence in freely quenched plates of amorphous polymers: Simulation and experiment , 2003 .

[8]  C. Li,et al.  Photoviscoelastic behavior of amorphous polymers during transition from the glassy to rubbery state , 2001 .

[9]  W. I. Patterson,et al.  Control of part weight in injection molding of amorphous thermoplastics , 1999 .

[10]  S. Chen,et al.  Simulations of primary and secondary gas penetration for a gas‐assisted injection‐molded thin part with gas channel , 1998 .

[11]  K. F. Hsu,et al.  Polymer melt flow and gas penetration in gasassisted injection molding of a thin part with gas channel design , 1996 .

[12]  K. F. Hsu,et al.  Analysis and experimental study of gas penetration in a gas-assisted injection-molded spiral tube , 1995 .

[13]  H. Potente,et al.  The Gas-assisted Injection Molding Process , 1993 .

[14]  A. Isayev.  Orientation development in the injection molding of amorphous polymers , 1983 .

[15]  C. A. Hieber,et al.  Toward a viscoelastic modelling of the injection molding of polymers , 1980 .

[16]  James L. White,et al.  Some relationships between injection molding conditions and the characteristics of vitrified molded parts , 1979 .

[17]  H. Janeschitz-Kriegl.  Injection moulding of plastics: Some ideas about the relationship between mould filling and birefringence , 1977 .

[18]  A. I. Leonov.  Nonequilibrium thermodynamics and rheology of viscoelastic polymer media , 1976 .

[19]  K. C. Rusch.  Time-temperature superposition and relaxational behavior in polymeric glasses , 1968 .

[20]  A. Carrillo,et al.  Thermal Stresses and Birefringence in Quenched Tubes and Rods: Simulation and Experiment , 2011 .

[21]  A. Cunha,et al.  Residual stresses in gas-assisted injection molding , 2009 .

[22]  James L White,et al.  Correlation of normal stresses in polystyrene melts and its implications , 1978 .

[23]  J. Wales,et al.  Some aspects of orientation in injection molded objects , 1972 .