The Effects of Chain-Extending Cross-Linkers on the Mechanical and Thermal Properties of Poly(butylene adipate terephthalate)/Poly(lactic acid) Blown Films

Abstract

This study investigates the effects of four multifunctional chain-extending cross-linkers (CECL) on the processability, mechanical performance, and structure of polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA) blends produced using film blowing technology. The newly developed reference compound (M·VERA® B5029) and the CECL modified blends are characterized with respect to the initial properties and the corresponding properties after aging at 50 °C for 1 and 2 months. The tensile strength, seal strength, and melt volume rate (MVR) are markedly changed after thermal aging, whereas the storage modulus, elongation at the break, and tear resistance remain constant. The degradation of the polymer chains and crosslinking with increased and decreased MVR, respectively, is examined thoroughly with differential scanning calorimetry (DSC), with the results indicating that the CECL-modified blends do not generally endure thermo-oxidation over time. Further, DSC measurements of 25 µm and 100 µm films reveal that film blowing pronouncedly changes the structures of the compounds. These findings are also confirmed by dynamic mechanical analysis, with the conclusion that tris(2,4-di-tert-butylphenyl)phosphite barely affects the glass transition temperature, while with the other changes in CECL are seen. Cross-linking is found for aromatic polycarbodiimide and poly(4,4-dicyclohexylmethanecarbodiimide) CECL after melting of granules and films, although overall the most synergetic effect of the CECL is shown by 1,3-phenylenebisoxazoline.

Process-Induced Morphology of Poly(Butylene Adipate Terephthalate)/Poly(Lactic Acid) Blown Extrusion Films Modified with Chain-Extending Cross-Linkers

“…Due to the blown film extrusion with different draw ratios in ED and TD, anisotropic mechanical properties and corresponding differences in a morphological structure may be expected. Recently, Azevedo et al [ 28 ] showed (based on differential scanning calorimetry data of granules and films) that the chemical reactions were incomplete after compounding and that blown film extrusion intensified them even for rapidly cooled 25 µm films. This behavior can be explained by assuming that the CECL molecules are linked with one reactive site to polymer chains during compounding, whereas the other reactive sites remain unaffected.…”

“…Furthermore, chain scission and cross-linking altered viscosity and consequently the structure, e.g., dimensions of the dispersed phase and its geometry (spherical or fibrillar). According to dynamic mechanical analysis [ 28 ], for V1 CECLs, the T g of PLA and PBAT phases were hardly affected, whereas for V2 to V4, an increase of T g in the PBAT phase and a decrease in the PLA phase were observed. This means that cross-linking mainly occurred in the PBAT phase, whereas in the PLA phase, the free volume was mainly increased by partial reaction with CECL.…”

“…The vast majority of the studies available were carried out on samples prepared by compression or injection molding, thus not considering the process-induced changes introduced by blown film extrusion. In our previous study [ 28 ], we showed that the chemical reactions caused by CECLs incorporation into PBAT/PLA were incomplete after compounding and that the elongation during blow film extrusion brought appropriate molecular groups into reach and thus promoted crosslinking or chain scission. Therefore, the objective of this study was to investigate in detail the effect of four CECLs on the morphology of PBAT/PLA resulting from the molding route in order to optimize their processability and usage performance.…”

Development of Novel Blown Shrink Films from Poly(Lactide)/Poly(Butylene-Adipate-co-Terephthalate) Blends for Sustainable Food Packaging Applications

“…Promising results were obtained by the blending with poly(butylene-adipate-co-terephthalate) (PBAT), an aliphatic aromatic copolyester characterized by a good processability and mechanical properties quite similar to polyethylene, i.e., low elastic modulus and high ductility, [ 19 , 20 ]. Although PBAT is inherently not compatible with PLA, the two resins can be effectively compatibilized in situ by reactive extrusion, obtaining blends more suitable for the film blowing process [ 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. However, despite the numerous studies focused on production and characterization of blown films from PLA/PBAT blends, there is very little information on their use for development of shrink films by film blowing, and only reported in patent literature [ 28 , 29 ], therefore further investigations are needed.…”

A Sequenced Study of Improved Dielectric Properties of Carbon Nanotubes and Metal Oxide-Reinforced Polymer Composites

“…This problem has created the need for materials that have greater stability against environmental stresses. To resolve this issue, the fabrication of polymeric nanocomposites is under consideration, and especially the usage of inorganic nanofillers, which not only provide greater stability against the environment, but also enhance their electrical and dielectric properties [3][4][5]. Different morphologies of nanofiller are being explored to achieve a greater interface area.…”