Biodegradable binary blends of poly (butylene succinate) or poly (ε-caprolactone) with poly (butylene succinate-ran-ε-caprolactone)copolymers: Crystallization behavior

Poly (butylene succinate) (PBS) and polycaprolactone (PCL) are two immiscible biocompatible and biodegradable polymers. Aiming to combine the properties of these biodegradable polymers, this work explores for the first time blending PBS or PCL with PBS- ran -PCL copolymers (BS x CL y ) at 75/25, 50/50, and 25/75 wt% compositions, with various copolymer contents: BS 78 CL 22 , BS 46 CL 54 , and BS 15 CL 85 . The crystallization behavior of these novel binary blends was systematically studied with non-isothermal and isothermal differential scanning calorimetry (DSC), polarized light optical microscopy (PLOM), and simultaneous wide- and small-angle X-ray scattering (WAXS and SAXS). All the blends displayed a miscible character in the amorphous state, judging by a single glass transition temperature, and in the melt state (as indicated by SAXS), but their miscibility in the crystalline state depends on the specific blend. In both PBS/BS 78 CL 22 and PCL/BS 15 CL 85 evidences of co-crystallization between the matrix and the crystallizable fraction of the copolymer were found. However, high comonomer exclusion, higher in the BS 15 CL 85 than in the BS 78 CL 22 , greatly affects blend miscibility. Thus, the results show that the PBS/BS 78 CL 22 blend is miscible, in the crystalline state, at high PBS (homopolymer) content, i.e., 75/25 and 50/50 compositions, whereas its “counterpart”, the PCL/BS 15 CL 85 displays partial miscibility, even for high PCL (homopolymer) content. For the 25/75 blends, i.e., copolymer-rich, the homopolymer addition favors the crystallization of the copolymer-rich component. Blending PBS or PCL with BS 46 CL 54 leads to blends that exhibit a much lower miscibility in the crystalline state than the blends prepared with BS or CL-rich copolymers, independently of the composition. But, interestingly, a novel behavior is found, since the BS 46 CL 54 copolymer can crystallize either in PBS type crystals or in PCL type crystals depending on the polymeric matrix (PCL or PBS). The PBS favors the crystallization of the BS component, while the PCL favors the crystallization of the CL component within the random copolymer. The crystallization behavior found in this work evidences the interactions of the PBS or PCL with the BS x CL y copolymer, representing a potential strategy to combine the properties of the PBS and PCL through blending. • Combining properties of PBS and PCL by blending with their BS x CL y copolymers. • Novel binary blends of PBS or PCL with BS x CL y copolymers in various compositions. • Influence of the polymeric matrix on the BS 46 CL 54 crystallization. • How exclusion/inclusion balance affects matrix - BS x CL y copolymer interactions. • Tailoring properties of biodegradable binary blends: blend components and ratio.