Abstract
Sustainability has become the primary focus for researchers lately. Biopolymers such as polyhydroxyalkanoate (PHA) and polylactic acid (PLA) are biocompatible and biodegradable. Introducing piezoresistive response in the films produced by PLA and PHA by adding nanoparticles can be interesting. Hence, a study was performed to evaluate the mechanical, electrical and piezoresistive response of films made from PHA and PLA. The films were produced by solvent casting, and they were reinforced with graphene nanoplatelets (GNPs) at different nanoparticle concentrations (from 0.15 to 15 wt.%). Moreover, cellulose nanocrystals (CNC) as reinforcing elements and polyethylene glycol (PEG) as plasticizers were added. After the assessment of the nanoparticle distribution, the films were subjected to tests such as tensile, electrical conductivity and piezoresistive response. The dispersion was found to be good in PLA films and there exist some agglomerations in PHA films. The results suggested that the incorporation of GNPs enhanced the mechanical properties until 0.75 wt.% and they reduced thereon. The addition of 1% CNCs and 20% PEG in 15 wt.% GNPs’ tensile values deteriorated further. The PHA films showed better electrical conductivity compared to the PLA films for the same GNPs wt.%. Gauge factor (GF) values of 6.30 and 4.31 were obtained for PHA and PLA, respectively.
Highlights
To attend to the increasing demands of the markets and provide solutions for a constantly evolving society, a new generation of materials with multiple functionalities is emerging
The nanoparticles in PHA (Figure 2a) present a higher size than those in polylactic acid (PLA) (Figure 2d), with average diameter values of 16 μm and 9 mm, respectively. This bigger size of the graphene nanoparticles (GNPs) is related to the formation of clusters, which reveals a worse dispersion of the nanoparticles
The enhanced flow of the migrating and hopping electrons of the fillers is responsible for the increment in the electrical conductivity of the composite films [36]. These values of PLA composites agree with the results reported in the literature [41,47,56,57], where a GNP concentration between 7–10 wt.% is estimated as the percolation threshold
Summary
To attend to the increasing demands of the markets and provide solutions for a constantly evolving society, a new generation of materials with multiple functionalities is emerging. From a material science point of view, these materials may exhibit one or several properties that can activate a reaction as a response to environmental conditions or stimuli, which may be mechanical, electrical, magnetic, thermal and chemical, among others. This new generation of materials with advanced properties that allow the application and suitability of conventional materials to be enlarged are classified as smart materials. The conception of these products brings high costs associated with the difficulty of incorporating particles of different nature, turning them into an alternative with a high expense for commercialization
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