Rheology⁻Microstructure Relationships in Melt-Processed Polylactide/Poly(vinylidene Fluoride) Blends.

Reza Salehiyan,Suprakas Ray,Vincent Ojijo,Florian Stadler

doi:10.3390/ma11122450

Abstract

In this study, small amplitude oscillatory shear tests are applied to investigate the rheological responses of polylactide/poly(vinylidene fluoride) (PLA/PVDF) blends and to correlate their viscoelastic properties with the morphological evolutions during processing. Although the analysis of the elastic moduli reveals some changes as a function of blend composition and processing time, the weighted relaxation spectra are shown to be more useful in detecting changes. The analysis demonstrates that when PVDF, i.e., the more viscous phase, is the matrix, the blend relaxes cooperatively and only a single relaxation peak is observed. By contrast, blends with highly concentrated morphologies do not fully relax, showing instead an upward increasing trend at longer times. This outcome is attributed to the broad distribution of highly concentrated droplets with a high probability of droplet–droplet contacts. Dynamic mechanical analysis (DMA) reveals that crystalline segmental motions attributed to the α-relaxation of PVDF at around 100 °C are restricted by the highly concentrated morphology of the 50/50 PLA/PVDF blend processed for 10 min. Relaxation analyses of the blends via dynamic oscillatory shear tests and DMA are shown to be powerful tools for investigating small microstructural changes in immiscible polymer blends.

Highlights

The blending of two or more polymers is an economically efficient strategy for the development of materials with interesting characteristics
It is known that the final morphology of an immiscible polymer blend is governed by the balance between droplet breakage and coalescence [27,28]
In the case of the 70/30 PLA/poly(vinylidene fluoride) (PVDF) blends (Figure 1b), the storage modulus G0 (ω) is higher when the blend is processed for 5 min

Summary

Introduction

The blending of two or more polymers is an economically efficient strategy for the development of materials with interesting characteristics. Most chemically different polymers are immiscible, and their blending leads to phase-separated morphologies with weak interfacial adhesion and poor mechanical performances. The studies reported to date have shown that various morphologies can be developed by altering the dynamic and kinetic parameters, such as the blend ratio [2,3,4], the viscosity ratio [5], compatibilization [6,7,8], the mixing time [9,10], and the mixer type [11,12]. Among the bio-based polymers available, polylactide (PLA) has attracted significant attention owing to its green characteristics (bio-degradable and biomedical) and reasonable modulus.

Methods

Results

Conclusion