Abstract
Results of the studies dealing with the toughness of polylactic acid/polycaprolactone (PLA/PCL) blends are analyzed with respect to the PCL particle size, PLA matrix crystallinity, and presence of a compatibilizer. It is shown that a high toughness or even »super-toughness« of PLA/PCL blends without a compatibilizer can be achieved for blends with the proper size of PCL particles. Nevertheless, the window for obtaining the super-tough PLA/PCL blends is quite narrow, as the final impact strength is very sensitive to multiple parameters: namely the blend composition, PLA matrix crystallinity, and PCL particle size. Available literature data suggest that the optimal composition for PLA/PCL blends is around 80/20 (w/w). The PLA/PCL(80/20) blends keep high stiffness of PLA matrix and the concentration of PCL particles is sufficient to achieve high toughness. The PLA/PCL(80/20) blends with low-crystallinity PLA matrix (below ca 10 %) exhibit the highest toughness for bigger PCL particles (weight average diameter above 1 μm), while the blends with high-crystallinity PLA matrix (above ca 30 %) exhibit the highest toughness for smaller PCL particles (weight average diameter below 0.5 μm). The addition of a compatibilizer may improve the toughness only on condition that it helps to achieve a suitable particle size. The toughness of both non-compatibilized and compatibilized PLA/PCL blends with optimized morphology can be more than 15 times higher in comparison with neat PLA.
Highlights
Poly(lactic acid) (PLA) is frequently reported as one of the most promising biodegradable polymers synthesized from natural resources as it can be used in many technical applications, especially in packaging (Lunt, 1998; Garlotta, 2002; Auras et al, 2004; Averous and Pollet, 2012)
Chee et al (2013) studied the reactive compatibilization of a PLA/PCL blend by the addition of glycidyl methacrylate (GMA) at blending. They found that the elongation at break and the unnotched Izod impact strength of PLA/PCL (85/15) blend increased with the amount of added GMA until 3%
Urquijo et al (2016) studied the effect of organically modified montmorillonite (OMMT) on the structure and the mechanical properties of PLA/PCL (80/20) blends. They found that the stiffness of PLA/PCL/OMMT nanocomposites increased, while the elongation at break and notched Izod impact strength decreased with the increasing content of OMMT
Summary
Poly(lactic acid) (PLA) is frequently reported as one of the most promising biodegradable polymers synthesized from natural resources as it can be used in many technical applications, especially in packaging (Lunt, 1998; Garlotta, 2002; Auras et al, 2004; Averous and Pollet, 2012). Kassos et al (2019) studied the effect of concentration of PCL on mechanical properties of samples of PLA/PCL blends prepared by the mixing in a twin screw extruder, followed by an injection molding They found that the notched Izod impact strength increased with increasing content of PCL. After addition of 1% of talc, the crystallinity of about 36% and Charpy notched impact strength almost 10 times higher in comparison with neat PLA were obtained (Table 1, the last row) This impact strength was substantially lower than that for PLA/PCL (80/20) blends having PLA crystallinity below 10% (compare Table 1 and Figure 3) but it could be sufficient for a number of applications
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