Structural and Thermo-Mechanical Properties of Poly(ε-Caprolactone) Modified by Various Peroxide Initiators

Abstract

The modification of poly(ε-caprolactone) (PCL) was successfully conducted during reactive processing in the presence of dicumyl peroxide (DCP) or di-(2-tert-butyl-peroxyisopropyl)-benzene (BIB). The peroxide initiators were applied in the various amounts of 0.5 or 1.0 pbw (part by weight) into the PCL matrix. The effects of the initiator type and its concentration on the structure and mechanical and thermal properties of PCL were investigated. To achieve a detailed and proper explication of this phenomenon, the decomposition and melting temperatures of DCP and BIB initiators were measured by differential scanning calorimetry. The conjecture of the branching or cross-linking of PCL structure via used peroxides was studied by gel fraction content measurement. Modification in the presence of BIB in PCL was found to effectively increase gel fraction. The result showed that the cross-linking of PCL started at a low content of BIB, while PCL modified by high DCP content was only partially cross-linked or branched. PCL branching and cross-linking were found to have a significant impact on the mechanical properties of PCL. However, the effect of used initiators on poly(ε-caprolactone) properties strongly depended on their structure and content. The obtained results indicated that, for the modification towards cross-linking/branching of PCL structure by using organic peroxides, the best mechanical properties were achieved for PCL modified by 0.5 pbw BIB or 1.0 pbw DCP, while the PCL modified by 1.0 pbw BIB possessed poor mechanical properties, as it was related to over cross-linking.

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

“…It is worth noting that limited reinforcement of crosslinks is expected after the glass transition, as previously observed in similar systems [24]. However, PCL damping factor decreases with increasing peroxide amount, indicating a more elastic behavior of the polymer after REx.…”

“…The radicals are then expected to propagate by proton abstraction from the α-carbon relative to the carbonyl group of PCL [ 17 ]. Finally, PCL macroradicals can recombine, resulting in branching/crosslinking, or undergo β-scission ( Figure 1 c) [ 24 , 25 ]. Water can also stabilize the radical structures, suppressing the scission reactions and enhance recombination thus increasing the overall reaction rate [ 29 , 30 ].…”

“…The use of peroxides as radical initiators has been previously reported for PCL backbone modification [ 17 , 18 ] or PCL blends compatibilization [ 19 , 20 , 21 ]. However, to our knowledge only few works have explored the effect of the only peroxide on PCL branching/crosslinking in solvent casting [ 15 , 22 ] or during melt processing [ 9 , 23 , 24 , 25 ]. Gandhi et al [ 23 ] studied the PCL crosslinking with dicumyl peroxide during melt processing, in comparison with radiation crosslinking.…”

“…Dynamic rheology of the modified PCL shows an increase in viscosity and melt elasticity with higher amounts of dicumyl peroxide. Structural PCL modification via REx comparing two types of peroxide was investigated by Przybysz et al [ 24 ]. The results point out that different degrees of branching/crosslinking can be achieved as a function of the peroxide structure and amount.…”

Different Influences of Two Peroxide Initiators on Structure and Properties of Poly(Lactic Acid)

“…According to the mechanisms of free‐radical reactions, during the process of reactive extrusion/blending, the reactions occur not only at the interfaces but also in polymer matrix, which alter the structure of the macromolecules and the properties of the material. There have been some reports on the influences of initiators on polymers [28–30]. However, researches focusing on different influences of peroxide initiators on the structure and properties of PLA are still very limited.…”