Abstract
Biodegradable blends and nanocomposites were produced from polylactic acid (PLA), poly(3-hydroxybutyrate) (PHB) and cellulose nanocrystals (NC) by a single step reactive blending process using dicumyl peroxide (DCP) as a cross-linking agent. With the aim of gaining more insight into the impact of processing methods upon the morphological, thermal and mechanical properties of these nanocomposites, three different processing techniques were employed: compression molding, extrusion, and 3D printing. The addition of DCP improved interfacial adhesion and the dispersion of NC in nanocomposites as observed by scanning electron microscopy and atomic force microscopy. The carbonyl index calculated from Fourier transform infrared spectroscopy showed increased crystallinity after DCP addition in PLA/PHB and PLA/PHB/NC, also confirmed by differential scanning calorimetry analyses. NC and DCP showed nucleating activity and favored the crystallization of PLA, increasing its crystallinity from 16% in PLA/PHB to 38% in DCP crosslinked blend and to 43% in crosslinked PLA/PHB/NC nanocomposite. The addition of DCP also influenced the melting-recrystallization processes due to the generation of lower molecular weight products with increased mobility. The thermo-mechanical characterization of uncross-linked and cross-linked PLA/PHB blends and nanocomposites showed the influence of the processing technique. Higher storage modulus values were obtained for filaments obtained by extrusion and 3D printed meshes compared to compression molded films. Similarly, the thermogravimetric analysis showed an increase of the onset degradation temperature, even with more than 10 °C for PLA/PHB blends and nanocomposites after extrusion and 3D-printing, compared with compression molding. This study shows that PLA/PHB products with enhanced interfacial adhesion, improved thermal stability, and mechanical properties can be obtained by the right choice of the processing method and conditions using NC and DCP for balancing the properties.
Highlights
The extensive use of petroleum-based plastics for industrial and consumer products along with ineffective waste management leads to serious environmental and economic issues [1,2,3]
Cellulose nanocrystals were synthesized from plum seed shells by acid hydrolysis and were successfully incorporated in the Polylactic acid (PLA)/PHB matrix by a reactive blending method
The best thermal stability and highest maximum degradation temperature were obtained for dicumyl peroxide (DCP) treated nanomaterials, especially in the case of PLA/PHB/NC nanocomposite filaments as compared with 3D printed meshes and films
Summary
The extensive use of petroleum-based plastics for industrial and consumer products along with ineffective waste management leads to serious environmental and economic issues [1,2,3]. Scientists are encouraged to seek for biodegradable materials derived from renewable resources which show comparable or enhanced properties to those of petroleum-based plastics. Polylactic acid (PLA) is considered the frontrunner of biodegradable polymers since it is already used in several commercial applications as an alternative to certain petroleum-based plastics. PLA is available on the market at a similar price with that of common plastics like polypropylene [6]. Biodegradability, renewability, and good mechanical strength, PLA has the important advantage of easy processability using common technologies for thermoplastic polymers (melt mixing, extrusion, and injection molding) or 3D printing [3,7,8]
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