Effect of miscibility on mechanical and thermal properties of poly(lactic acid)/ polycaprolactone blends

Abstract

In this work, binary blends based on poly(lactic acid)-PLA and poly(caprolactone)-PCL were prepared by melt mixing in a twin screw co-rotating extruder in order to increase the low intrinsic elongation at break of PLA for packaging applications. Although PLA and PCL show low miscibility, presence of PCL leads to a remarkable increase in ductile properties of PLA.Different mechanical properties were evaluated in terms of PCL content up to 30 weight % PCL. Additionally to tensile and flexural properties, the Poisson's ratio was obtained by using bi-axial extensometry to evaluate transversal deformations when axial loads are applied. Very slight changes in the melt temperature (T m ) and glass transition temperature (T g ) of PLA were observed thus indicating low miscibility of the PLA-PCL system. Field emission scanning electron microscopy (FESEM) revealed some interactions between the two components of the blend since the morphology is characterized by non-spherical poly(caprolactone) drops dispersed into the PLA matrix. In addition to the improvement of mechanical ductile properties, PCL provides higher degradation rates of blends under conditions of composting for contents below 22.5% PCL.Keywords: Poly(lactic acid)-PLA; poly(caprolactone)-PCL; binary blends; FESEM; mechanical properties; disintegrability. 1.-Introduction.Nowadays, polymers find a broad number of applications in the fields of packaging, medical and automotive industries due to an excellent balance between processing and overall properties [1]. Among all these polymers, aliphatic polyesters from both renewable and/or fossil fuel resources [2] Poly(lactic acid) is one of the most used biocompostable polymers in packaging applications due to its high mechanical performance and balanced barrier properties [16,17].PLA is widely used in the manufacturing of biodegradable/biocompostable films for food applications. The main drawback related to PLA is its high intrinsic fragility that is still accentuated as degradation occurs. PLA has low ductility at room temperature because its glass transition temperature (T g ) is located at around 60 ºC; so that, below its T g , it behaves as a glass characterized by high mechanical resistance and modulus and high fragility together with low elongation at break (due to restricted polymer chain mobility below T g ). Conventional plasticizers could potentially be used to allow some elongation at break but typical plasticizers can migrate and this could be responsible for a toxicity as well as a decrease in mechanical properties [18][19][20]. Another alternative is copolymerization. By using copolymerization processes with appropriately selected monomers it is possible to tailor PLA properties to desired performance. Some examples of PLA-based copolymers are poly(lactic acid-co--caprolactone)-PLACL, poly(lactic acid-co-ethylene glycol)-PLAEG, poly(hydroxibutirate-cohydroxivalerate)-PHBV, etc [21,22]. Nevertheless these copolymers are expensive. One attracting solution is manufacturing of binary or ternary...

Poly(lactic acid) blends in biomedical applications

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