Film forming properties of 3D printed polysaccharide based gels and development of CO2 monitoring labels

Polyvinyl alcohol (PVA) has good compatibility with polysaccharides and is suitable for 3D printing inks for preparing food packaging films or smart labels. In this work, the influences of different concentrations of PVA on the 3D printability and film-forming performance of six polysaccharide-based inks were investigated. PVA formed a strong cross-linked network with sodium alginate (SA) and carboxymethyl cellulose (CMC), which enhanced the 3D printability of the gel, and the addition of 7 % PVA increased the printing accuracy of SA by 20.83 times. PVA also facilitated the smooth extrusion of potato starch (PS), pectin (PE), konjac glucomannan (KGM), and xanthan gum (XG) inks in the printing operation and improved their flowability. The surface of 3D printed PVA- polysaccharide film had tiny print texture, no obvious roughness or graininess, smooth surface, soft texture and good shape. However, cracks and wrinkles were found on the surface of the PVA-PS membrane, which were likely related to inappropriate ratios and uneven shrinkage. FTIR and XRD analysis showed that PVA had excellent compatibility with polysaccharides and was fully distributed within the film. A 3 % PVA addition was found to be optimal, as the polysaccharide films exhibited appropriate hydrophilicity, mechanical strength, and flexibility. The color of polysaccharide-based labels containing bromothymol blue (BTB) and methyl red (MR) prepared with 3 % PVA content changed with the change of CO₂ concentration. 3D printed labels were successfully used to monitor the changes of CO₂ concentration in tomato packaging during storage. This research extends the applicability of 3D-printed smart labels for real-time monitoring environmental conditions of fruits and vegetables storage, particularly CO₂ concentration.