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In this study, a biodegradable composite based on PLA reinforced with banana rachis fiber—derived from agricultural waste and forming the structural core of banana bunches—is developed. The fibers are evaluated with and without thermomechanical processing to enhance the properties of parts produced through material extrusion additive manufacturing (MEX), a technology with a screw feeding system. A preliminary study of the additive manufacturing process is conducted to ensure adequate processability of the matrix during the process. In addition, different composite formulations (0, 5, 10 and 15 wt.% fiber) are analyzed through morphological, thermal (TGA and DSC), rheological, and mechanical characterization, complemented by SEM analysis. This comprehensive characterization revealed that the incorporation of WTP fibers served to reinforce the PLA matrix for the tensile modulus, from 2273.54 ± 123.66 MPa to 2612.51 ± 95.16 MPa with 15% of WTP fiber. A similar trend was observed for the flexural modulus, which increased from 2456 ± 61.16 MPa in the neat PLA to 3189.68 ± 52.24 MPa for the PLA-15% WTP composite. The results demonstrate the feasibility of the process and the production of parts with acceptable quality under appropriate manufacturing conditions.

Nanocellulose-stabilized Pickering emulsions typically utilize oils that display high interfacial tension with water. For the first time, this work describes the stabilization of aniline (12 wt.%)-in-water emulsions, where the interfacial tension lies below 6 mN/m. The stabilizing agent consisted of oxidized cellulose nanofibrils (CNFs). While the density of aniline, alike to that of water, granted high kinetic stability with 0.18 wt.% CNFs (3 days), phase separation was avoided for at least 30 days if CNF concentration was 0.28 wt.% or higher. Easily dispersible polyaniline was attained by adding orthophosphoric acid (doping), sodium dihydrogen orthophosphate (pH adjusting), and ammonium persulfate (initiator) to a previously prepared aniline-in-water emulsion (dispersion polymerization). The resulting dispersions did not suffer from creaming or sedimentation. Polyaniline samples exhibited average molecular weights below 100 kDa. They were hardly electroconductive and possessed relatively low thermal stability, but they were chromogenic. Owing to the latter feature and to the suitable rheological behavior of the suspensions, packaging paper was coated on one side with those samples to produce visually responsive sheets. When their uncoated side was exposed to gaseous ammonia, volatile amines, or spoiled fish (cod, hake, and salmon), their green-colored surface (emeraldine salt) turned blue (emeraldine base). Electron microscopy assays ruled out diffusion of polyaniline from the coated side to the exposed side. Overall, the strategy presented here implies several innovative advantages: allowing for the high-concentration polymerization of aniline, keeping the polymer dispersed, and producing suspensions that can be readily applied to the manufacture of smart food packaging.

Achieving compatibility between biopolymers and natural fillers is a significant challenge in developing sustainable materials. PLA-lignin biocomposites frequently demonstrate poor interfacial adhesion, mostly due to polarity differences. Softwood (LS) and hardwood (LH) lignins vary in composition and reactivity, affecting PLA structure. This study evaluated the surface compatibilization of LS and LH through silylation at 1, 3, and 5 wt % using a GPS coupling agent. Silylation was validated by TGA, DSC (T_g increase of ∼3-7 °C), ash color, and EDX (increased silicon). FTIR assessed structural differences in lignins. Rheological tests and melt flow index indicated that unmodified lignin reduced PLA viscosity, while GPS-modified lignin increased it. DSC showed that LS enhanced crystallization more than LH, and GPS at 1 wt % promoted nucleation. Films containing LH at 10 and 1 wt % GPS exhibited improved mechanical properties. Barrier properties remained unchanged, though all films provided UV-blocking capability.