Xylan Hemicellulose: A Renewable Material with Potential Properties for Food Packaging Applications

Xylan hemicelluloses are considered the second most abundant class of polysaccharides after cellulose which has good natural barrier properties necessary for foods packaging papers and films. Xylan exists today as a natural polymer, but its utilisation in packaging applications is limited and not sufficiently analysed. In this study, the performances of hardwood xylan hemicellulose in forming uniform films and as biopolymer for paper coatings were analysed. The xylan-coated paper and film samples were tested regarding their water, air, and water vapour permeability, water solubility, mechanical strength, and antimicrobial activity against pathogenic bacteria. Structural analyses of xylan hemicelluloses emphasised a high number of hydroxyl groups with high water affinity. This affects the functional properties of xylan-coated papers but can facilitate the chemical modification of xylan in order to improve their hydrophobic properties and extend their areas of application. The obtained results unveil a promising starting point for using this material in food packaging applications as a competitive and sustainable alternative to petroleum-based polymers.

Surface and optical properties of calcium carbonate paper

The article investigates the surface and optical properties of calcium carbonate paper obtained at the UzbekChinese enterprise Fergana stone paper company (Uzbekistan), in order to identify the possibility of their use at printing enterprises for printing multicolor products using traditional printing methods. According to the results of a quantitative assessment of the surface quality by the indirect Beck method, we can say that paper sample 1 has a smoothness like coated paper (750–1500 s), paper samples 2 and 3 – like calendered paper, so that these paper samples can be recommended for prints with increased quality requirements. Smaller values of roughness Ra and small depressions, expressed by darkening in the topographic AFM images, characterized sufficient homogeneity and density of the structure. It was also revealed that the surface of the paper samples has a high ability to specularly reflect the incident light, since the percentage of surface reflection is similar to that of coated papers. Samples of paper have a whiteness of about 90 % and do not have a tint, since the difference between the maximum and minimum values of the reflection coefficients on a white stack is not more than 10 %. The tested paper samples can be recommended without restrictions for double-sided printing, since the opacity index is more than 92 %.

Comprehensive Enhancement of Mechanical, Water-Repellent and Antimicrobial Properties of Regenerated Seaweed and Plant-Based Paper with Chitosan Coating

Regenerated papers made from discarded natural sources, such as seaweeds or non-wood plants, are viewed as promising eco-friendly alternatives relative to conventional wood-based paper. However, due to its limited mechanical strength and higher water absorption than compared to traditional wood paper, it often results in premature structural disintegration. In order to overcome this limitation, this research introduces an efficient and comprehensive strategy of coating seaweed and plant papers with varying concentrations and molecular weights of chitosan. Increased concentration and molecular weight resulted in a greater amount of chitosan deposition, while the highest molecular weight also shows increased dissolution of soluble components of the paper. Since plants and seaweeds contain high anionic polysaccharide contents, the cationic chitosan shows high binding affinity towards paper. The resulting chitosan-coated papers demonstrate significant enhancements in water repellency and mechanical properties. In addition, the chitosan-coated papers also show significant bacterial inhibition effects due to the natural anti-microbial activity of chitosan.

Fold cracking of coated papers: investigation on automated computer-aided visual assessment method

In this paper, white pixel percentage (WPP) value, as an overall measure of fold crack damages, has been analysed with respect to selected parameters of sample preparation and digitalization process, as well as the results of residual tensile strength. The WPP values were derived by an automated image processing algorithm, developed earlier, based on extensive comparative analysis of the existing computer-aided methods. Results indicate that WPP values correlate well with the extent of fold cracks on the coated samples, as far as the used parameters of sample preparation and digitalization are concerned. In the case of correlation with residual tensile strength, results for samples folded in cross direction revealed that the extent of the visually registered fold cracks agree well with the actual damage, while for samples folded in machine direction, the overall strength losses weren’t alarming, although the fold cracks were detected correctly. In addition, results pointed out that the simplest sample placement position (inner angle of 180°) is not applicable for realistic sample representation. Furthermore, scanners could provide a superior image quality in lab conditions, but for industry application, a camera-based solution would be more purposeful, while micrographs are more suitable for traditional visual analysis.

Effect of Overlapping Eco-Friendly Cellulose Nanofibrils and Nanoclay Layers on Mechanical and Barrier Properties of Spray-Coated Papers

This work proposes to evaluate the effect of spray-coating in papers using eco-friendly cellulose nanofibrils (CNFs) and nanoclay (NC) on mechanical and barrier properties for application as reinforced bags. Sack kraft papers of 60 g m-² (C60) were coated with CNFs + CNFs/NC in 4 layers (L5), 40 g m-² of CNFs + CNFs/NC in 3 layers (L4), 30 g m-² with CNFs/NC in 2 layers (L3) and 10 g m-² of CNFs in 1 layer (L2), and compared to uncoated sack kraft papers with basis weight of 60 g m-² (C60), 80 g m-² (C80) and 120 g m-² (C120). The coated papers L2; L3; L4 and L5 obtained a decrease in water vapor transmission rate (WVTR) of 3.5%; 17%; 14% and 14%, respectively, when compared to C60. Comparing L2 and L3, CNF layer induced lower contact angles on the coated paper than CNF/NC layer. When compared coated papers with C120, it was observed an increase of around 66% in tensile strength for L2, around 44% for L3, and decrease of ~ 18% for L5 coated papers. L4 achieved the same tensile strength (when divided by basis weight) than C120. L2 and L3 coated papers led to the highest values of Young’s modulus, with increase of 56% and 38%, respectively, when compared to C60. Spray-coating in the present conditions improved the mechanical and barrier properties of the coated papers, being a possible alternative to produce papers with lower basis weight and using renewable raw materials.

Synergetic Effect of Cationic Starch (Ether/Ester) and Pluronics for Improving Inkjet Printing Quality of Office Papers

Improving the printability of paper is still a relevant challenge, despite the fast development of digital communications. While it is well-known that cationic starches enhance ink density, their commercial paper-grade forms are limited to ethers with low degree of substitution. This work addresses the underexplored potential of highly substituted cationic starch for paper coating and its combination with tri-block polymers, namely Pluronics (P123 and F127), taking advantage of their supramolecular interactions with amylose chains. For that purpose, cationic starch ether and ester (starch betainate), both with a degree of substitution of 0.3, were synthesized by alkaline etherification and by transesterification, respectively. Paper without any surface treatment was subjected to one-side bar coating with suspensions encompassing those products and Pluronics, besides other common components. Black, cyan, yellow and magenta inks were printed on all coated papers through an inkjet printer. Key properties of printing quality such as the gamut area, gamut volume, optical density, print-through, inter-color bleed and circularity were measured in a controlled temperature-humidity environment. For instance, a formulation with cationic starch (ether/ester) and P123 improved the gamut area by 16–18% in comparison to native starch-coated paper sheets. Interestingly, the individual assessment of each component showed that cationic starch ether, starch betainate and P123 only improved the gamut area by 5.6%, 8.9% and 6.8%, respectively. Finally, but not less importantly, starch betainate was found to quench optical brightening agents to a lesser extent than cationic starch ethers.

Back-trap mottle: A review of mechanisms and possible solutions

Print mottle is a serious and common uneven printing defect that occurs when printing coated paper by the offset multicolor printing process. It is characterized by a non-uniform appearance in terms of brightness, gloss, or color density that appears mostly in solid printed areas. Back-trap print mottle and water-interference print mottle occur when the quality of the paper substrate, especially the coating layer quality, is not satisfactory. To cope with this quality problem of coated papers, the understanding of the offset printing process, the requirements of coated-paper quality, and the reasons for this problem should be addressed. In this review, the basic process of offset printing and the mechanisms of print mottles were explored, the importance of coating uniformity in both the coating structure and process was reviewed, and the approaches to cope with print mottle were introduced.