Viscosity and viscoelasticity measurements of low density polyethylene/poly(lactic acid) blends

The rheological properties and the viscoelastic behaviour of blends of polyethylene with different percentages of poly(lactic acid), ranging from 0 to 100 wt%, were studied. In a first part, all blends were examined under steady conditions using a capillary rheometer (at 180, 190 and 200 °C) and dynamic conditions using a parallel plate rheometer. The results showed that all blends behaved like pseudoplastic fluids, with the power–law index values varying between those of polyethylene and polylactide (0.45–0.75 at 180 °C, 0.49–0.77 at 190 °C and 0.54–0.81 at 200 °C). It was also observed that at low shear rate, pure poly(lactic acid) and polyethylene possessed, respectively, the highest and the lowest flow activation energy (66.9 and 48.3 kJ/mol); however, at high shear rate, the greater the content of poly(lactic acid), the lower the activation energy. In addition, poly(lactic acid) exhibited lower viscosity and lower melt elasticity than either polyethylene or the blends. The dynamic rheological study demonstrated that all formulations displayed shear thinning behaviour and only virgin poly(lactic acid) exhibited a clear Newtonian plateau. Also, mainly at low frequencies, polyethylene had the higher values of storage modulus (325 Pa), loss modulus (937 Pa) and complex viscosity (9,740 Pa.s). However, blends had values lying between those of the two homopolymers without any improvement in the storage modulus, loss modulus or complex viscosity. In a second part, the viscoelastic characteristics were investigated using dynamic mechanical thermal analysis (DMTA). DMTA spectra showed an increase in the storage modulus with the increase of poly(lactic acid) content but the opposite was observed for the loss modulus. A cold crystallization of poly(lactic acid) is observed around 87–100 °C and the temperature of glass transition of poly(lactic acid) did not depend on the composition of the blend. These results indicate that LDPE and PLA are immiscible in all proportions either in the melt state or in the solid state.

[1]  W. Orts,et al.  Binary and ternary blends of polylactide, polycaprolactone and thermoplastic starch , 2008 .

[2]  Howard Wang,et al.  Rheology and microstructures formation of immiscible model polymer blends under steady state and transient flows , 2005 .

[3]  H. Khonakdar,et al.  Tuning the processability, morphology and biodegradability of clay incorporated PLA/LLDPE blends via selective localization of nanoclay induced by melt mixing sequence , 2013 .

[4]  Xiaodong Wang,et al.  A polymer network based on thermoplastic polyurethane and ethylene–propylene–diene elastomer via melt blending: morphology, mechanical properties, and rheology , 2004 .

[5]  Christopher W. Macosko,et al.  Rheology: Principles, Measurements, and Applications , 1994 .

[6]  G. Jiang,et al.  Rheological Responses and Morphology of Polylactide/Linear Low Density Polyethylene Blends Produced by Different Mixing Type , 2011 .

[7]  C. Tiu,et al.  Rheological Behaviour of Polymer Blends Containing only Hyperbranched Polyesters of Varying Generation Number , 2001 .

[8]  J. Liang,et al.  Relationship between die swell ratio and melt flow index , 1997 .

[9]  Qi Wang,et al.  Properties, and Applications , 2005 .

[10]  Evaristo Riande,et al.  Polymer viscoelasticity : stress and strain in practice , 2000 .

[11]  H. Lobo,et al.  Handbook of Plastics Analysis , 2003 .

[12]  M. Rocha,et al.  Study of rheological behavior of elastomer/polypropylene blends , 2002 .

[13]  Jia Yang,et al.  Die-swell behavior of PP/Al(OH)3/Mg(OH)2 flame retardant composite melts , 2010 .

[14]  P. Cassagnau,et al.  Immiscible polymer blends stabilized with nano-silica particles: Rheology and effective interfacial tension , 2008 .

[15]  L. Utracki,et al.  Rheology of polycarbonate/linear low density polyethylene blends , 1990 .

[16]  C. Han.  Rheology and processing of polymeric materials , 2007 .

[17]  D. Romanini.  Synthesis Technology, Molecular Structure, and Rheological Behavior of Polyethylene , 1982 .

[18]  M. Jhon,et al.  Miscibility and rheological characteristics of biodegradable aliphatic polyester and linear low density polyethylene blends , 2001 .

[19]  Blends of two immiscible and rheologically different fluids , 1998 .

[20]  C. Carrot,et al.  Co-continuity interval in immiscible polymer blends by dynamic mechanical spectroscopy in the molten and solid state , 2004 .

[21]  A. Adegbola,et al.  Rheological Properties of Polymers: Structure and Morphology of Molten Polymer Blends , 2011 .

[22]  T. K. Chaki,et al.  Effect of organo-montmorillonite addition on the dynamic and capillary rheology of LLDPE/EMA blends , 2012 .

[23]  Sabu Thomas,et al.  Melt elasticity and extrudate characteristics of polystyrene/polybutadiene blends , 2002 .

[24]  P. Chang,et al.  Influence of formamide and water on the properties of thermoplastic starch/poly(lactic acid) blends , 2008 .

[25]  Li-song Dong,et al.  Dynamic mechanical and thermal properties of plasticized poly(lactic acid) , 2006 .

[26]  S. Lim,et al.  Toughening of polylactide by melt blending with linear low‐density polyethylene , 2003 .

[27]  P. Dubois,et al.  Polylactide compositions. The influence of ageing on the structure, thermal and viscoelastic properties of PLA/calcium sulfate composites , 2008 .

[28]  A. Peacock.  Handbook of Polyethylene: Structures: Properties, and Applications , 2000 .

[29]  M. Gahleitner.  Melt rheology of polyolefins , 2001 .

[30]  Aroon Shenoy,et al.  Rheology of Filled Polymer Systems , 1999 .

[31]  Sabu Thomas,et al.  Melt elasticity and flow activation energy of nylon 6/polystyrene blends , 2002 .

[32]  M. Pluta.  Morphology and properties of polylactide modified by thermal treatment, filling with layered silicates and plasticization , 2004 .

[33]  J. Ness,et al.  The melt die-swell behaviour during capillary extrusion of LDPE/PP blends , 1998 .

[34]  Y. Li,et al.  REACTIVE BLENDING OF POLYETHYLENE AND POLY ( L-LACTIC ACID ) USING A HIGH-SHEAR EXTRUDER , 2011 .

[35]  P. Pisitsak,et al.  Rheological, morphological, thermal, and mechanical properties of blends of vectra A950 and poly(trimethylene terephthalate): A study on a high-viscosity-ratio system , 2009 .

[36]  P. Supaphol,et al.  Melt rheology and extrudate swell of low-density polyethylene/ethylene–octene copolymer blends , 2006 .

[37]  M. Hillmyer,et al.  Polyethylene-poly(L-lactide) diblock copolymers: synthesis and compatibilization of poly(L-lactide)/polyethylene blends , 2001 .

[38]  A. Penlidis,et al.  HDPE/LLDPE reactor blends with bimodal microstructures—Part II: rheological properties , 2002 .

[39]  D. Acierno,et al.  Flow properties of low density/linear low density polyethylenes , 1986 .

[40]  K. Menard.  Thermomechanical And Dynamic Mechanical Analysis , 2003 .

[41]  M. A. Barrera,et al.  Melt flow index on high molecular weight polyethylene : A comparative study of experiments and simulation , 2006 .

[42]  C. Han,et al.  Rheological behavior of polymer blends , 1984 .

[43]  M. Kaseem,et al.  Preparation and Characterization of Binary and Ternary Blends with Poly(Lactic Acid), Polystyrene, and Acrylonitrile-Butadiene-Styrene , 2012 .

[44]  Shiai Xu,et al.  Melt rheology of compatibilized polystyrene/low density polyethylene blends , 1999 .

[45]  Jens Rieger,et al.  The glass transition temperature Tg of polymers: Comparison of the values from differential thermal analysis (DTA, DSC) and dynamic mechanical measurements (torsion pendulum) , 2001 .

[46]  C. Han,et al.  RHEOLOGY OF MISCIBLE BLENDS OF POLY(METHYL METHACRYLATE) WITH POLY(STYRENE-CO-ACRYLONITRILE) AND WITH POLY(VINYLIDENE FLUORIDE) , 1994 .

[47]  Y. Grohens,et al.  Structural, morphological and mechanical characteristics of polyethylene, poly(lactic acid) and poly(ethylene-co-glycidyl methacrylate) blends , 2013, Iranian Polymer Journal.

[48]  Azman Hassan,et al.  Mechanical, Thermal, and Morphological Properties of Polylactic Acid/Linear Low Density Polyethylene Blends , 2010 .

[49]  L. Salmén,et al.  Comparison of dynamic mechanical measurements and Tg determinations with two different instruments , 1994 .