# Poly(lactic acid)-Based Blends: A Comprehensive Review
## 2 Composites of Poly(lactic acid) with Poly(\(\varepsilon\)-caprolactone)
[39] have found that the size of the domains of the smaller phase (PCL) is affected by the crystallinity of the matrix (PLA), which in turn affects the mechanical properties of materials. With a significant increase in the crystallinity of the matrix, a clear decrease in the mechanical properties of composites has been revealed. It has been defined that the highly crystalline matrix of PLA can work effectively during hardening, provided that the PCL domains size should be 0.3-0.5 \(\upmu\)m. At the same time, PCL works as a plasticizer in the blend with PLA that increases the crystallinity of PLA [40]. Some researchers have found that the compatibility of PLA and PCL can be improved by using certain compounding technologies. The samples of PLA/PCL blends with a PCL content of 10 and 20 wt.% contains much smaller PCL domains when obtaining by injection moulding as opposed to hot pressing, regardless of the mixing method used [40]. Reducing the size of PCL domains increased the elasticity of materials under tension. Figure 2: The chemical structure of poly(\(\varepsilon\)-caprolactone). Like other mixtures of high-molecular compounds, the blends of PLA and PCL are incompatible; therefore, a number of works are devoted to the study of the effect of compatibilizers on the compatibility of PLA and PCL. [PERSON] et al. [41] investigated the process of reactive mixing of PLA/PCL using dicumyl peroxide as a crosslinking agent. They have observed an improvement in an elongation at break for the optimal ratio of PLA/PCL = 70/30. [PERSON] et al. [42] also have proven the effectiveness of peroxide crosslinking agents in the improvement of the compatibility of PLA and PCL phase; however, it has also been shown that the effect of the \(\beta\)-phase on the stability of PLA/PCL is not a significant effect. Figure 4: Change in impact strength from the composition of the blends of PLA/PCL [37]. Figure 3: SEM images of the blends of PLA/PCL: 90/10 (**a**), 70/30 (**b**), 30/70 (**c**), 10/70 (**d**) [33]. been found to decrease in the melt flow rate. In the papers [27; 28], tributyl citrate (3% by weight of PCL) was studied as a compatibilizer. [PERSON] et al. have shown that the PCL additive has a positive effect on the strength and plasticity of the composites with a low content of it. In the range of compositions of PLA/PCL = 99/1-95/5 wt.%, the mechanical properties of films with a compatibilizer exceeded the properties of films without it (an increase in the strength and elongation by 20-30%). [PERSON] and [PERSON] et al. [43] have found an improved interfacial adhesion between PLA and PCL in the presence of a reactive glycidyl methacrylate compatibilizer (up to 3 wt.%), which improved the impact strength. [PERSON] and [PERSON] [44] have used a copolymer (L-lactide-\(\epsilon\)-caprolactone) as a compatibilizer for the blend of PLA/PCL = 50/50. The effectiveness of this compatibilizer in improving polymer compatibility has been demonstrated. However, L-lactide-\(\epsilon\)-caprolactone causes a decrease in the hydrolysate interfacial surface in the blends of PLA and PCL that decreases the biodegradability.