Development of Toughened Flax Fiber Reinforced Composites. Modification of Poly(lactic acid)/Poly(butylene adipate-co-terephthalate) Blends by Reactive Extrusion Process.

Jacek Andrzejewski,Michał Nowakowski

doi:10.3390/ma14061523

Abstract

The presented study focuses on the development of flax fiber (FF) reinforced composites prepared with the use of poly(lactic acid)/poly(butylene adipate-co-terephthalate)—PLA/PBAT blend system. This type of modification was aimed to increase impact properties of PLA-based composites, which are usually characterized by high brittleness. The PLA/PBAT blends preparation was carried out using melt blending technique, while part of the samples was prepared by reactive extrusion process with the addition of chain extender (CE) in the form of epoxy-functionalized oligomer. The properties of unreinforced blends was evaluated using injection molded samples. The composite samples were prepared by compression molding technique, while flax fibers reinforcement was in the form of plain fabric. The properties of the laminated sheets were investigated during mechanical test measurements (tensile, flexural, impact). Differential scanning calorimetry (DSC) analysis was used to determine the thermal properties, while dynamic mechanical thermal analysis (DMTA) and heat deflection temperature (HDT) measurements were conducted in order to measure the thermomechanical properties. Research procedure was supplemented with structure evaluation using scanning electron microscopy (SEM) analysis. The comparative study reveals that the properties of PLA/PBAT-based composites were more favorable, especially in the context of impact resistance improvement. However, for CE modified samples also the modulus and strength was improved. Structural observations after the impact tests confirmed the presence of the plastic deformation of PLA/PBAT matrix, which confirmed the favorable properties of the developed materials. The use of PBAT phase as the impact modifier strongly reduced the PLA brittleness, while the reactive extrusion process improves the fiber-matrix interactions leading to higher stiffness and strength.

Highlights

The results of the Differential scanning calorimetry (DSC) scans for the injection molded samples can be seen in the Figure 1, while Figure 2 presents the thermograms for the flax fiber (FF) reinforced composites
The 1st heating thermograms for all injection molded samples reveals the presence of the cold crystallization phenomenon, which suggest that the PLA structure was highly amorphous after the sample demolding
This kind of behavior is required for most of the thermoplastic polyesters, for PLA, since it helps in maintaining the transparent structure of the material, especially during processing of packaging items like foils or food containers

Summary

Introduction

In the case of many varieties of biopolymers, their performance does not match their petrochemical varieties This applies to most of the mechanical, thermomechanical and processing properties. The applications involving the production of films require only adequate puncture resistance and a high degree of elongation before tearing. Rheological properties are of particular importance, including characteristics, such as viscosity or melt strength [1,2,3,4]. Meeting such a wide range of requirements is usually difficult for traditional polymers, such a popular method of using polymer blends. We can expect an increasing share of biopolymer blends in the market, which makes the topic of using methods of compatibility of this type of systems very actual, in composite applications

Objectives

Methods

Results

Conclusion