Polylactic acid (PLA) is one of the most widely studied bio-based polymers for sustainable composite materials. However, its mechanical performance can limit its use in more demanding engineering applications. Combining PLA with lignocellulosic reinforcement and nanoscale additives offers one route toward improving these properties.
In our published research, we investigated how graphene nanosheets influence the physical and mechanical behavior of beech flour/PLA composites.
Why Graphene?
Graphene possesses an exceptional combination of mechanical and physical properties. Even at relatively low concentrations, graphene nanosheets can alter the behavior of polymer composites.
The objective of our study was therefore to determine how different graphene contents affect a hybrid composite consisting of PLA as the polymer matrix and beech flour as the lignocellulosic reinforcement.
Experimental Approach
Beech flour and graphene nanosheets were incorporated into a PLA matrix at different concentrations.
Graphene contents of 0, 0.5, 1.5, and 2.5 wt% were investigated. The composites were prepared using a solution-based method followed by pressing.
Their performance was evaluated through several mechanical and physical characterization techniques, including:
- Tensile testing
- Flexural strength
- Flexural modulus
- Impact resistance
- Differential scanning calorimetry (DSC)
- X-ray diffraction (XRD)
This combination of tests allowed us to examine not only changes in mechanical performance but also changes in the thermal and structural behavior of the PLA-based composites.
What Did We Find?
The addition of graphene produced significant changes in the mechanical properties of the composites.
The highest flexural strength, flexural modulus, and tensile strength were obtained in the formulation containing:
30 wt% beech flour + 67.5 wt% PLA + 2.5 wt% graphene.
Interestingly, maximum graphene content did not produce the highest value for every property.
The highest impact resistance was observed in a formulation containing only 0.5 wt% graphene, together with 20 wt% beech flour and 79.5 wt% PLA.
This illustrates an important principle in composite design: increasing the concentration of a nanofiller does not necessarily optimize every material property simultaneously.
Thermal Behavior
Differential scanning calorimetry showed that incorporating graphene nanosheets shifted the melting temperature of the PLA matrix toward higher temperatures.
This observation indicates that graphene influenced the thermal behavior of the polymer matrix in addition to its effects on mechanical performance.
Structural Analysis
X-ray diffraction revealed broadly similar peak patterns among the investigated treatments.
Increasing graphene concentration primarily changed the intensity of the diffraction peaks, rather than producing fundamentally different peak patterns.
Together with the mechanical and thermal results, these observations demonstrate that graphene nanosheets can modify several aspects of the behavior of beech flour/PLA composites.
Why This Matters
Bio-based polymers and lignocellulosic fillers are attractive components for developing more sustainable composite materials, but their performance must remain suitable for practical applications.
Our results showed that graphene nanosheets can enhance important mechanical and physical characteristics of beech flour/PLA composites.
At the same time, the different optimum concentrations observed for properties such as tensile/flexural performance and impact resistance highlight the importance of formulation-specific optimization when designing hybrid nanocomposites.
Original Research
Ghorbanpour, R., Ghasemi, I., & Naeimian, N.
Investigation of the effect of graphene nanosheets on the properties of beech/polylactic acid flour composites.
Journal of Thermoplastic Composite Materials, 36(6), 2582–2599.
First published online: 17 May 2022