Cellulose fatty acid ester coated papers for stand-up pouch applications

Solventless Photopolymerizable Paper Coating Formulation for Packaging Applications

Nowadays, packaging applications require the use of advanced materials as well as production methods that have a low environmental impact. In this study, a solvent-free photopolymerizable paper coating was developed using two acrylic monomers (2-ethylhexyl acrylate and isobornyl methacrylate). A copolymer, with a molar ratio of 2-ethylhexyl acrylate/isobornyl methacrylate of 0.64/0.36, was prepared and used as the main component of the coating formulations (50 and 60 wt%). A mixture of the monomers with the same proportion was used as a reactive solvent, yielding formulations with 100% solids. The coated papers showed an increase in the pick-up values from 6.7 to 32 g/m² depending on the formulation used and the number of coating layers (up to two). The coated papers maintained their mechanical properties and presented improved air barrier properties (Gurley's air resistivity of ≈25 s for the higher pick-up values). All the formulations promoted a significant increase in the paper's water contact angle (all higher than 120 °) and a remarkable decrease in their water absorption (Cobb values decrease from 108 to 11 g/m²). The results confirm the potential of these solventless formulations for fabricating hydrophobic papers with potential application in packaging, following a quick, effective, and more sustainable approach.

A facile strategy to fabricate antibacterial hydrophobic, high-barrier, cellulose papersheets for food packaging

As a traditionally used packaging material, natural cellulose-based paper has poor barrier properties to water and oxygen, which severely limits its wide application in food packaging. In this study, we report a new sustainable approach to producing hydrophobic, high-barrier, and antibacterial packaging materials from cellulose paper. In this process, commercially available microcrystalline cellulose was first modified by long-chain stearic acid to form hydrophobic microcrystalline cellulose ester and then mixed with stearic acid as filler in the subsequent surface coating of bagasse fibre paper. The microcrystalline cellulose ester/stearic acid-coated paper (MSP) exhibited good water repellency and oxygen barrier activity due to a continuous hydrophobic film that formed, which completely covered the pores of the original bagasse fibre paper. The coated MSP sample also showed excellent dimensional stability in water and a good wet tensile strength of 16 MPa. In addition, poly(hexamethylene guanidine) (PHMG) was chemically grafted onto the free carboxyl groups of the MSP surface layer, and the resulting MSP-g-PHMG samples exhibited excellent antibacterial activity against Escherichia coli and Listeria monocytogenes. The biodegradable cellulose-based MSP-g-PHMG sample significantly delayed the decay of raspberry during storage, indicating its potential application in food packaging.

Bio-based materials for barrier coatings on paper packaging

Research into alternative packaging materials is becoming more and more popular as a result of growing eco-friendly concerns regarding the usage of some petroleum-based polymeric packaging materials and coatings, as well as growing buyer demands for products with nutritious quality and extended shelf lives. Barrier coatings made of naturally renewable biopolymers can be applied to paper packing materials. These biopolymer coatings have the potential to replace the current synthetic paper and paperboard coatings, are strong oxygen and oil barriers, and may prevent the unintended moisture transfer in food goods. An appealing method of controlling the growth and spread of microorganisms in food packaging is the integration of antimicrobial compounds into coatings to create active/functional paper-based packaging materials. Here, in this review of the oxygen/moisture barrier, mechanical, and other characteristics of paper coated with bio-based materials. Examples are used to discuss the current and future uses of bio-based material coatings on paper packaging materials to improve barrier performance.

Degradation of Cellulose Derivatives in Laboratory, Man-Made, and Natural Environments

Biodegradable polymers complement recyclable materials in battling plastic waste because some products are difficult to recycle and some will end up in the environment either because of their application or due to wear of the products. Natural biopolymers, such as cellulose, are inherently biodegradable, but chemical modification typically required for the obtainment of thermoplastic properties, solubility, or other desired material properties can hinder or even prevent the biodegradation process. This Review summarizes current knowledge on the degradation of common cellulose derivatives in different laboratory, natural, and man-made environments. Depending on the environment, the degradation can be solely biodegradation or a combination of several processes, such as chemical and enzymatic hydrolysis, photodegradation, and oxidation. It is clear that the type of modification and especially the degree of substitution are important factors controlling the degradation process of cellulose derivatives in combination with the degradation environment. The big variation of conditions in different environments is also briefly considered as well as the importance of the proper testing environment, characterization of the degradation process, and confirmation of biodegradability. To ensure full sustainability of the new cellulose derivatives under development, the expected end-of-life scenario, whether material recycling or "biological" recycling, should be included as an important design parameter.

Foamability of Cellulose Palmitate Using Various Physical Blowing Agents in the Extrusion Process

Polymer foams are widely used in several fields such as thermal insulation, acoustics, automotive, and packaging. The most widely used polymer foams are made of polyurethane, polystyrene, and polyethylene but environmental awareness is boosting interest towards alternative bio-based materials. In this study, the suitability of bio-based thermoplastic cellulose palmitate for extrusion foaming was studied. Isobutane, carbon dioxide (CO₂), and nitrogen (N₂) were tested as blowing agents in different concentrations. Each of them enabled cellulose palmitate foam formation. Isobutane foams exhibited the lowest density with the largest average cell size and nitrogen foams indicated most uniform cell morphology. The effect of die temperature on foamability was further studied with isobutane (3 wt%) as a blowing agent. Die temperature had a relatively low impact on foam density and the differences were mainly encountered with regard to surface quality and cell size distribution. This study demonstrates that cellulose palmitate can be foamed but to produce foams with greater quality, the material homogeneity needs to be improved and researched further.

Per- and polyfluoroalkyl substances and their alternatives in paper food packaging

Per- and polyfluoroalkyl substances (PFAS) have been used in food contact paper and paperboard for decades due to their unique ability to provide both moisture and oil/grease resistance. Once thought to be innocuous, it is now clear that long chain PFAS bioaccumulate and are linked to reproductive and developmental abnormalities, suppressed immune response, and tumor formation. Second-generation PFAS have shorter biological half-lives but concerns about health risks from chronic exposure underscore the need for safe substitutes. Waxes and polymer film laminates of polyethylene, poly(ethylene-co-vinyl alcohol), and polyethylene terephthalate are commonly used alternatives. However, such laminates are neither compostable nor recyclable. Lamination with biodegradable polymers, including polyesters, such as polylactic acid (PLA), polybutylene adipate terephthalate, polybutylene succinate, and polyhydroxyalkanoates, are of growing research and commercial interest. PLA films are perhaps the most viable alternative, but performance and compostability are suboptimal. Surface sizings and coatings of starches, chitosan, alginates, micro- and nanofibrilated cellulose, and gelatins provide adequate oil barrier properties but have poor moisture resistance without chemical modification. Plant proteins, including soy, wheat gluten, and corn zein, have been tested as paper coatings with soy being the most commercially important. Internal sizing agents, such as alkyl ketene dimers, alkenyl succinic anhydride, and rosin, improve moisture resistance but are poor oil/grease barriers. The difficulty in finding a viable replacement for PFAS chemicals that is cost-effective, fully biodegradable, and environmentally sound underscores the need for more research to improve barrier properties and process economics in food packaging products.

Nanofibrillated cellulose as coating agent for food packaging paper

Nanofibrillated cellulose (NFC), a promising bio-based nanomaterial, has received much attention in the field of coating preparation due to its unique properties. Herein, NFC was prepared from microcrystalline cellulose (MCC) via high-pressure homogenization process and deliberately employed as coating agent to enhance the properties of paper coatings and coated paper. The results demonstrated that the obtained paper coatings exhibited strong NFC concentration dependence on rheological behavior and displayed decreased water retention value with the increased NFC addition. Meanwhile, NFC addition was found to lead to the reduced Cobb value, improved air resistance, and enhanced tensile strength of coated paper. Under an optimized NFC addition of 0.30-0.40%, the properties of coated paper generally reached the optimum state. Moreover, SEM observation further confirmed that NFC addition imparted a relatively uniform surface structure to coated paper. Hence, NFC could be defined as an effective coating agent for developing high-performance coated paper for food packaging applications.

Reactive Water Vapor Barrier Coatings Derived from Cellulose Undecenoyl Esters for Paper Packaging

Paper packaging materials have been widely applied in our daily life. To maintain the quality of packed goods as well as the mechanical property, there is a need to enhance the paper water vapor barrier function. Although long-chain cellulose esters with saturated aliphatic chains have been employed as barrier coatings due to their excellent hydrophobicity as well as film-forming properties, the coated unsaturated cellulose esters would be beneficial to design reactive materials to further enrich their functionalities, e.g., antibacterial performance. Herein, solutions of cellulose undecenoyl esters (CUEs) were bar-coated to base papers. Obvious coating films were formed on the paper surfaces from the coating grammage of 6.25 g m−2. The resulting CUE-coated papers displayed good mechanical performance, hydrophobicity, and water vapor barrier property (the barrier ratio up to 66.35%), and the best coating grammage was 11.62 g m−2. Additionally, the reactivity of the coated paper was evaluated by further immobilization of the antibacterial agent (polyhexamethylene guanidine hydrochloride (PHGH)) using photo-click thiol-ene and condensation reaction. The generated paper exhibited good antibacterial and water vapor barrier performance. The obvious reactivity of our CUE-coated paper indicated the great possibility to design multi-functional paper packaging materials.

Review on Polysaccharides Used in Coatings for Food Packaging Papers

Paper and board show many advantages as packaging materials, but the current technologies employed to obtain adequate barrier properties for food packaging use synthetic polymers coating and lamination with plastic or aluminium foils—treatments which have a negative impact on packaging sustainability, poor recyclability and lack of biodegradability. Recently, biopolymers have attracted increased attention as paper coatings, which can provide new combinations in composite formulas to meet the requirements of food packaging. The number of studies on biopolymers for developing barrier properties of packaging materials is increasing, but only a few of them are addressed to food packaging paper. Polysaccharides are viewed as the main candidates to substitute oil-based polymers in food paper coating, due to their film forming ability, good affinity for paper substrate, appropriate barrier to gases and aroma, and positive effect on mechanical strength. Additionally, these biopolymers are biodegradable, non-toxic and act as a matrix for incorporation additives with specific functionalities for coated paper (i.e., active-antimicrobial properties). This paper presents an overview on the availability and application of polysaccharides from vegetal and marine biomass in coatings for foods packaging paper. The extraction methods, chemical modification and combination routes of these biopolymers in coatings for paper packaging are discussed.

Evaluation of esterification routes for long chain cellulose esters

Long chain cellulose esters are internally plasticized bio-based materials, which have good future potential in several applications such as coatings, films and plastics. The long chain cellulose esters with different side chain lengths were synthesized using different esterification methods. When homogeneous esterification was used, the acyl chloride method was the most effective esterification method and cellulose esters prepared using this method have the highest degree of substitution values (DS). In this case, the long chain cellulose esters showed DS values from 0.3 to 1.3 depending on the side chain length of cellulose esters. CDI activation, vinyl transesterification and anhydride routes resulted in somewhat lower DS values. The cellulose was also pretreated with ozone, which decreased cellulose molar mass, and resulted in synthesized cellulose esters having higher DS and better reaction efficiency than untreated cellulose. When heterogeneous esterifications were used, only acyl chloride method seemed to work.