Crystallization kinetics as a sensitive tool to detect degradation in poly(lactide)/poly(ε-caprolactone)/ PCL-co-PC copolymers blends

Abstract

Poly(lactide)/poly(-caprolactone) blends (PLA/PCL) with composition 80/20 (w/w%) are immiscible but biodegradable and therefore often studied in the literature. We have prepared 80/20 PLA/PCL blends with and without poly(ε-caprolactone)-co-poly(carbonate) copolymers (block and random). The blends were prepared both by melt extrusion and by solution blending. The concentration of PCL-co-PC copolymers added to the blends was 2 wt%. Compression molded sheets and solvent cast films were evaluated by GPC (Gel Permeation Chromatography), TGA (Thermogravimetric Analysis), SEM (Scanning Electron Microscopy), PLOM (Polarized Light Optical Microscopy) and DSC (Differential Scanning Calorimetry). Copolymer addition causes a reduction of molecular weight in melt mixed blends. In particular, the random copolymer (PCL-ran-PC) causes the highest molecular weight reduction, since it has lower thermal stability, as shown by TGA. PLOM experiments show that these degraded PLA chains in melt-mixed blends can nucleate and grow faster than similar but undegraded PLA chains in solution-mixed blends. As a result, the PLA phase within melt mixed blends containing PCL-co-PC copolymers shows a higher tendency to crystallize during both isothermal and non-isothermal DSC experiments. Upon molecular weight reduction in melt mixed blends containing copolymers, PLA chains have a higher mobility resulting in faster diffusion towards the growing crystal front. Our results show crystallization kinetic measurements, performed by PLOM or DSC, are useful tools to qualitatively detect molecular weight changes produced by degradation of PLA chains, when the molecular weight reduction is not large enough to decrease Tm values.

Accelerating the crystallization kinetics of linear polylactides by adding cyclic poly ( -lactide): Nucleation, plasticization and topological effects

“…The addition of both nucleating and plasticizers agents has also been reported in the literature [10]. Another alternative to improve the crystallization of PLA is blending with other polymers [14,18,19].…”

Competition between Chain Extension and Crosslinking in Polyamide 1012 during High-Temperature Thermal Treatments as Revealed by Successive Self-Nucleation and Annealing Fractionation

“…Figure 6b shows the overall crystallization rate for PA1012 as a function of T c with different isothermal times at 250 °C. Some studies 50 have demonstrated that the overall crystallization rate first increased as the molecular weight increased, then reached a maximum, and finally decreased. For most commercial polymers, such as polyamides, molecular weights are high enough that they are in the molecular weight range in which the overall crystallization rate decreases with increasing molecular weight.…”

Biodegradation and performance of poly(ɛ‐caprolactone)/macaíba biocomposites

“…Upon biodegradation T d5% for neat PCL decreases from 350 to 323 C, related to the biocomposites decreases even higher were verified all of them presented T d5% lower than neat PCL corroborating with the lower thermal stability of PCL/MF. 59,60 Related to the biodegradation time for longer time the decreasing in the thermal stability was intensified and specimens presented lower T d5% , T d50% , and T dmax after 90 days of biodegradation. Related with the fiber treatment PCL/MF-T presented lower TG parameters than PCL/MF-P.…”