Cellulosic paper-based products, structurally known as hydrogen-bonded fiber networks or assemblies generated by processes typically involving filtration-based sheet formation, represent an aggregate of renewable, biodegradable, and recyclable materials [1,2]. Paper is a traditional material widely used in the food packaging industry due to its low cost, universal affordability and good mechanical performance [3]. The unique porous structure of paper is particularly suitable for fruit packaging. Because it can keep the fruit and the outside air exchange, maintain the respiratory function and keep it fresh [4,5]. However, the hydrophilicity and a porous structure make the paper have many problems, such as providing nutrition, suitable temperature and humidity for the growth of microorganisms, which limits its wide applications in many fields, especially in the development of food packaging industry [[6], [7], [8]]. As a result, special modifications are required to improve the antimicrobial properties and hydrophobic of paper substrates to meet the necessary criteria for some advanced applications.

Some nanometals or metal oxide nanoparticles, such as Ag, TiO2, ZnO and MOFs, have been used as antibacterial agents in various composites [[9], [10], [11], [12]]. However, these nanometals or metal oxide nanoparticles are prone to leaching from the filler matrix and cumulative toxicity, thus limiting their application in many fields, especially in food preservation. Chemical fungicides such as quaternary ammonium salts, hyperbranched polymers, penicillin, N-halamines and gentamicin have been widely used in the packaging field in order to prevent food contamination and extend its shelf life [[13], [14], [15], [16], [17]]. Nonetheless, long-term use of chemical synthetic antibacterial agents may increase antibacterial resistance of bacteria and lead to some potential side effects. Compared with chemical fungicides, nanometals and metal oxide nanoparticles, natural antimicrobials (e.g., thymol, quercetin, aloe-emodin, curcumin, tannin, ε-polylysine and CA) are better and safer agents for humans [[18], [19], [20], [21], [22], [23], [24]]. Among them, CA not only shows strong antimicrobial, antioxidant and excellent anti-mold properties but also is low cost, non-toxic, and harmless [25,26]. Many studies have been shown that the incorporation of CA can improve the antibacterial activity of the composite materials [[27], [28], [29]]. Polymers such as starch [30], poly (lactic acid) [31], and zein [32] have been combined with cinnamaldehyde as antimicrobial packaging films. Qin et al. [33] prepared PLA/poly(trimethylenecarbonate) films incorporated with CA by solvent casting method. The results showed that the composite films with 9 wt% CA exhibited a good antibacterial activity. CA has been regarded as a green and safe food additive and widely used in food preservative and fresh keeping [34]. However, the direct addition of CA to food can also affect the sensory properties of food. Therefore, adding CA into packaging may have supplementary application in food packaging [35,36]. Studies have shown that the materials composed of cellulose and CA have great prospects in antibacterial applications and can prolong the shelf life of food. However, the reaction process of these materials involves many complicated steps or uses catalysts or requires high temperature, which cannot meet the requirements of practical application [37,38]. Meanwhile, the preparation method of materials is mostly physical mixing, which leads to the antibacterial property as not durable. The CA structure contains aldehyde groups and can therefore be grafted onto cellulose by chemical reactions such as Schiff base. The bacteriostatic effect of Schiff base is mainly achieved by inhibiting the synthesis of bacterial proteins. Schiff bases can bind to the ribosomes of bacteria and prevent the process of protein synthesis in the bacteria, thus inhibiting the growth and reproduction of bacteria. Several cellulose-based Schiff base materials prepared by grafting some antimicrobial molecules such as chitosan and nisin with dialdehyde cellulose have shown good antimicrobial properties [39,40].

The inherent hydrophilicity of paper will lead to a significant decrease in the mechanical strength under wetting conditions, and the paper can only maintain 4 % ~ 10 % of its original strength after wetting. Giving food packaging paper a certain degree of water resistance can not only increase the wet strength of the paper and maintain the packaging performance of the paper, but also effectively reduce the probability of microbial adhesion. At present, the mature strategies for improving the hydrophobicity of paper mainly include sizing [[41], [42], [43], [44]], coating [45,46] and cellulose modification [[47], [48], [49]]. Therefore, it is necessary to endow cellulose paper with excellent antimicrobial properties along with hydrophobicity, which will greatly extend the service life of cellulose paper.

In this work, CA, a naturally derived material, was incorporated onto the surface of paper to prepare hydrophobic and antimicrobial packaging material for strawberry preservation through a simple synthetic route. The APS molecule acts as a chemical linker to form chemical bonds with cellulose and CA, increasing the water contact angle of paper samples from 0° to 119.7°. The antibacterial functionalization of cellulose paper is achieved through chemical binding whereby the CA molecules were bound to the surface of the paper via the imide reaction, which gives the paper excellent and long-term antibacterial activity without affecting the sensory properties of contact with food. Based on these advantages, multifunctional composite papers can prolong the shelf life of strawberries. Meanwhile, multifunctional composite papers have excellent biocompatibility and biodegradability. The structure, antimicrobial, hydrophobicity and mechanical properties of multifunctional composite paper were characterized, and the application of multifunctional composite paper in strawberry preservation was studied. This simple and sustainable strategy would direct green multifunctional cellulose paper toward diversified applications. Scheme 1 shows the fabrication schematic diagram and application of multifunctional paper.