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Title: Coalescence in PLA-PBAT blends under shear flow: Effects of blend preparation and PLA molecular weight

Abstract

Blends containing 75 wt. % of an amorphous polylactide (PLA) with two different molecular weights and 25 wt. % of a poly[(butylene adipate)-co-terephthalate] (PBAT) were prepared using either a Brabender batch mixer or a twin-screw extruder. These compounds were selected because blending PLA with PBAT can overcome various drawbacks of PLA such as its brittleness and processability limitations. In this study, we investigated the effects of varying the molecular weight of the PLA matrix and of two different mixing processes on the blend morphology and, further, on droplet coalescence during shearing. The rheological properties of these blends were investigated and the interfacial properties were analyzed using the Palierne emulsion model. Droplet coalescence was investigated by applying shear flows of 0.05 and 0.20 s{sup −1} at a fixed strain of 60. Subsequently, small amplitude oscillatory shear tests were conducted to investigate changes in the viscoelastic properties. The morphology of the blends was also examined using scanning electron microscope (SEM) micrographs. It was observed that the PBAT droplets were much smaller when twin-screw extrusion was used for the blend preparation. Shearing at 0.05 s{sup −1} induced significant droplet coalescence in all blends, but coalescence and changes in the viscoelastic properties were much more pronounced for themore » PLA-PBAT blend based on a lower molecular weight PLA. The viscoelastic responses were also somehow affected by the thermal degradation of the PLA matrix during the experiments.« less

Authors:
 [1]; ;  [2];  [3];  [4]
  1. Center for High Performance Polymer and Composite Systems (CREPEC), Chemical Engineering Department, Polytechnique Montreal, Montreal, Quebec H3T 1J4, Canada and CREPEC, Department of Chemical Engineering, McGill University, Montreal, Quebec H3A 2B2 (Canada)
  2. Center for High Performance Polymer and Composite Systems (CREPEC), Chemical Engineering Department, Polytechnique Montreal, Montreal, Quebec H3T 1J4 (Canada)
  3. CREPEC, Department of Chemical Engineering, McGill University, Montreal, Quebec H3A 2B2 (Canada)
  4. NatureWorks LLC, 15305 Minnetonka Boulevard, Minnetonka, Minnesota 55345 (United States)
Publication Date:
OSTI Identifier:
22598951
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Rheology; Journal Volume: 60; Journal Issue: 4; Other Information: (c) 2016 The Society of Rheology; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; AMPLITUDES; BRITTLENESS; BUTENES; COALESCENCE; DROPLETS; EMULSIONS; EXTRUSION; MATRICES; MIXING; MOLECULAR WEIGHT; MORPHOLOGY; SCANNING ELECTRON MICROSCOPY; SHEAR; STRAINS; THERMAL DEGRADATION

Citation Formats

Nofar, M., Heuzey, M. C., Carreau, P. J., E-mail: pierre.carreau@polymtl.ca, Kamal, M. R., and Randall, J. Coalescence in PLA-PBAT blends under shear flow: Effects of blend preparation and PLA molecular weight. United States: N. p., 2016. Web. doi:10.1122/1.4953446.
Nofar, M., Heuzey, M. C., Carreau, P. J., E-mail: pierre.carreau@polymtl.ca, Kamal, M. R., & Randall, J. Coalescence in PLA-PBAT blends under shear flow: Effects of blend preparation and PLA molecular weight. United States. doi:10.1122/1.4953446.
Nofar, M., Heuzey, M. C., Carreau, P. J., E-mail: pierre.carreau@polymtl.ca, Kamal, M. R., and Randall, J. 2016. "Coalescence in PLA-PBAT blends under shear flow: Effects of blend preparation and PLA molecular weight". United States. doi:10.1122/1.4953446.
@article{osti_22598951,
title = {Coalescence in PLA-PBAT blends under shear flow: Effects of blend preparation and PLA molecular weight},
author = {Nofar, M. and Heuzey, M. C. and Carreau, P. J., E-mail: pierre.carreau@polymtl.ca and Kamal, M. R. and Randall, J.},
abstractNote = {Blends containing 75 wt. % of an amorphous polylactide (PLA) with two different molecular weights and 25 wt. % of a poly[(butylene adipate)-co-terephthalate] (PBAT) were prepared using either a Brabender batch mixer or a twin-screw extruder. These compounds were selected because blending PLA with PBAT can overcome various drawbacks of PLA such as its brittleness and processability limitations. In this study, we investigated the effects of varying the molecular weight of the PLA matrix and of two different mixing processes on the blend morphology and, further, on droplet coalescence during shearing. The rheological properties of these blends were investigated and the interfacial properties were analyzed using the Palierne emulsion model. Droplet coalescence was investigated by applying shear flows of 0.05 and 0.20 s{sup −1} at a fixed strain of 60. Subsequently, small amplitude oscillatory shear tests were conducted to investigate changes in the viscoelastic properties. The morphology of the blends was also examined using scanning electron microscope (SEM) micrographs. It was observed that the PBAT droplets were much smaller when twin-screw extrusion was used for the blend preparation. Shearing at 0.05 s{sup −1} induced significant droplet coalescence in all blends, but coalescence and changes in the viscoelastic properties were much more pronounced for the PLA-PBAT blend based on a lower molecular weight PLA. The viscoelastic responses were also somehow affected by the thermal degradation of the PLA matrix during the experiments.},
doi = {10.1122/1.4953446},
journal = {Journal of Rheology},
number = 4,
volume = 60,
place = {United States},
year = 2016,
month = 7
}
  • Binary blends of four different high molecular weight poly(styrene-b-isoprene) (SI) diblock copolymers with a lower molecular weight poly(styrene-b-isoprene-b-styrene) (SIS) triblock copolymer were prepared, and their morphology was characterized by transmission electron microscopy and ultra-small-angle X-ray scattering. All the neat block copolymers have nearly symmetric composition and exhibit the lamellar morphology. The SI diblock copolymers had number-average molecular weights, Mn, in the range 4.4 x 10{sup 5}--1.3 x 10{sup 6} g/mol and volume fractions of poly(styrene), {Phi}{sub PS}, in the range 0.43--0.49, and the SIS triblock had a molecular weight of Mn 6.2 x 10{sup 4} g/mol with {Phi}{sub PS} =more » 0.41. The high molecular weight diblock copolymers are very strongly segregating, with interaction parameter values, {chi}N, in the range 470--1410. A morphological phase diagram in the parameter space of molecular weight ratio (R = M{sub n}{sup diblock}/1/2M{sub n}{sup triblock}) and blend composition was constructed, with R values in the range between 14 and 43, which are higher than previously reported. The phase diagram revealed a large miscibility gap for the blends, with macrophase separation into two distinct types of microphase-separated domains for weight fractions of SI, w{sub SI} < 0.9, implying virtually no solubility of the much higher molecular weight diblocks in the lower molecular weight triblock. For certain blend compositions, above R 30, morphological transitions from the lamellar to cylindrical and bicontinuous structures were also observed.« less
  • In situ rheo-SAXS (small-angle X-ray scattering) and rheo-WAXD (wide-angle X-ray diffraction) techniques were used to investigate the role of high molecular weight species on the evolution of oriented microstructure in isotactic polypropylene (iPP) melt under shear flow. The two iPP samples, designated as PP-A and PP-B, respectively, had the same number-average (M{sub n}) but different weight-average (M{sub w}) and Z-average (M{sub z}) molecular weights. Molecular weight distribution (MWD) of PP-A and PP-B was such that for MW<10{sup 5} the MWD curves overlapped; whereas in the high MW tail region, the amount of high molecular weight species was higher in PP-Bmore » than PP-A. Both samples were subjected to an identical shear condition (rate=60 s{sup -1}, duration=5 s, T=155 degC). In situ 2D SAXS and WAXD images allowed the tracking of shear-induced oriented structures in the melt. It was found that the shish structures evolved much earlier, and the degree of crystal orientation and oriented crystal fractions were higher in PP-B than PP-A. Moreover, PP-B exhibited faster crystallization kinetics than PP-A. These results, along with the predictions of double reptation models of chain motion and experimental studies of chain conformation dynamics in dilute solutions under flow, suggest the following: When a polymer melt that consists of entangled chains of different lengths is deformed, the chain segments aligned with the flow eigenvector can undergo the abrupt coil-stretch-like transition, while other segments would remain in the coiled state. Since, flow-induced orientation decays much more slowly for long chains than for short chains, oriented high molecular weight species play a prominent role in formation of the stretched sections, where shish originates. Our experimental results are strong evidence of the hypothesis that even a small increase in the concentration of high molecular weight species causes a significant increase in the formation, stability and concentration of the flow-induced oriented microstructure.« less