Adhesive and Flame-Retardant Properties of Starch/Ca2+ Gels with Different Amylose Contents.

Starch, being renewable and biodegradable, is a viable resource for developing sustainable and environmentally friendly materials. The potential of starch/Ca2+ gels based on waxy corn starch (WCS), normal corn starch (NCS), and two high-amylose corn starches, G50 (55% amylose content) and G70 (68% amylose content) as flame-retardant adhesives has been explored. Being stored at 57% relative humidity (RH) for up to 30 days, the G50/Ca2+ and G70/Ca2+ gels were stable without water absorption or retrogradation. The starch gels with increasing amylose content displayed increased cohesion, as reflected by significantly higher tensile strength and fracture energy. All the four starch-based gels showed good adhesive properties on corrugated paper. For wooden boards, because of the slow diffusion of the gels, the adhesive abilities are weak initially but improve with storage extension. After storage, the adhesive abilities of the starch-based gels are essentially unchanged except for G70/Ca2+, which peels from a wood surface. Moreover, all the starch/Ca2+ gels exhibited excellent flame retardancy with limiting oxygen index (LOI) values all around 60. A facile method for the preparation of starch-based flame-retardant adhesives simply by gelating starch with a CaCl2 solution, which can be used in paper or wood products, has been demonstrated.

Pre-gelatinized high-amylose starch enables easy preparation of flexible and antimicrobial composite films for fresh fruit preservation.

While high-amylose starch (HAS) possesses advantageous properties such as high resistant starch content and favorable mechanical attributes, its gelatinization constraints have limited its applicability. This study enhances its versatility by focusing on pre-gelatinized (PG) HAS with exceptional rehydratability, achieved by disorganizing native HAS granules (with amylose contents of 55 % and 68 %, respectively) using a 33 % CaCl2 solution, followed by water-ethanol precipitation and freeze-drying. The resulting PG-HAS exhibited elevated amylose content (61 % and 75 %) with minimal changes in amylose molecular weight. PG-HAS displayed superior water-absorption index (WAI) and water-soluble index (WSI) compared to native HAS, further improved by 2 % CaCl2 solution incorporation. Furthermore, composite films were prepared by mixing PG-HAS with PVA at a 6:4 (w/w) ratio. The PG-G50 (61 % amylose content)/PVA composite film exhibited remarkable elongation (131.1 ± 5.4 %), nearly three times that of a normal corn starch (NCS, with 27 % amylose)/PVA film, attributed to improved starch dispersity and higher amylose content. Nonetheless, the PG-G70 (75 % amylose content)/PVA film at the same ratio showed lower elongation (54.7 ± 8.0 %), potentially due to strong cohesive forces between amylose chains that impede starch-PVA interactions. Moreover, the PG-HAS/PVA composite films, enriched with antibacterial agents, demonstrated effective antibacterial properties with a gradual and sustained release of active compounds. Notably, the PG-G50/PVA/tannic acid (TA) film effectively preserved fresh apple slices by inhibiting bacteria growth and preventing browning. These findings underscore the excellent rehydration of PG-HAS and its potential as an inner packaging material for irregularly shaped foods, such as sliced fruits or meats, due to its nontoxic nature, softness and flexibility, which allows the film to maintain close contact with food surfaces.

Facile preparation of hydrogel glue with high strength and antibacterial activity from physically linked network.

Constructing plant-based hydrogel glues with outstanding adhesiveness, antibacterial activity and suitable mechanical properties has great practical importance in multiple areas. However, preparation of traditional antibacterial adhesive hydrogels usually requires of complex chemical reactions as well as expensive and toxic ingredients. Here, we develop a type of physically crosslinked hydrogel glues, which contains polyvinyl alcohol (PVA) for generating mechanical property, ß-cyclodextrin (ß-CD) for creating adhesion strength and acting as the drug carrier for curcumin (CUR), and silica nanoparticles for resolving the conflict between strength and adhesion within the gel matrix. The physically linked composite showed tunable mechanical strengths ranged from 150 kPa to 560 kPa, as well as high maximum strains up to 380%. Moreover, the composite gel exhibited high swelling ratio and significant antibacterial property. This study demonstrates that the pure physical strategy can be well used to prepare antibacterial hydrogel glues with high performance. The combining of the facile method with conventional and biocompatible materials provides a viable way for fabricating antibacterial hydrogel glues for practical applications.