Substantial Effect of Water on Radical Melt Crosslinking and Rheological Properties of Poly(ε-Caprolactone)

Abstract

One-step reactive melt processing (REx) via radical reactions was evaluated with the aim of improving the rheological properties of poly(ε-caprolactone) (PCL). In particular, a water-assisted REx was designed under the hypothesis of increasing crosslinking efficiency with water as a low viscous medium in comparison with a slower PCL macroradicals diffusion in the melt state. To assess the effect of dry vs. water-assisted REx on PCL, its structural, thermo-mechanical and rheological properties were investigated. Water-assisted REx resulted in increased PCL gel fraction compared to dry REx (from 1–34%), proving the rationale under the formulated hypothesis. From dynamic mechanical analysis and tensile tests, the crosslink did not significantly affect the PCL mechanical performance. Dynamic rheological measurements showed that higher PCL viscosity was reached with increasing branching/crosslinking and the typical PCL Newtonian behavior was shifting towards a progressively more pronounced shear thinning. A complete transition from viscous- to solid-like PCL melt behavior was recorded, demonstrating that higher melt elasticity can be obtained as a function of gel content by controlled REx. Improvement in rheological properties offers the possibility of broadening PCL melt processability without hindering its recycling by melt processing.

Reactive melt crosslinking of cellulose nanocrystals/poly(ε-caprolactone) for heat-shrinkable network

“…We developed a novel simultaneous green REx and sustainable bionanocomposites production grounded on the hypothesis of a synergy between water-assisted PCL crosslinking [27] and CNC wet-feeding. Therefore, water was exploited for the first time in two simultaneous key roles: booster of radical crosslinking and dispersant for CNCs.…”

Can 3D-Printed Bioactive Glasses Be the Future of Bone Tissue Engineering?

“…PCL is a biodegradable polymer with a melting point of 60 • C and has a glass transition temperature of −60 • C [81]. It has excellent mechanical properties, biocompatibility, and thermal stability.…”

Crystal Nucleation and Growth in Cross-Linked Poly(ε-caprolactone) (PCL)

“…Crosslinking influences the crystallization behavior of the polymer. Under non-isothermal conditions, the crystallization temperature of PCL changes due to cross-linking [8,9]. Optimizing the processing of such modified polymers requires knowledge of their crystallization behavior under different conditions.…”

“…The viscosity of the polymer increases with increasing cross-linking [17]. The cross-linking of PCL has a strong effect on the rheological properties of the polymer, and already at a relatively low cross-link density, the behavior of the polymer changes from viscous to elastic [8]. These variations affect crystal nucleation and growth via variations of the kinetic coefficients in the expressions for the nucleation and growth rates.…”