Today’s environmental concerns are pressuring industries to substitute paper-based materials in place of plastics in many sectors including packaging. However, assembling papers and paperboards using environmentally friendly solutions remains a technological challenge. In this context, ultrasonic (US) welding is an alternative to adhesives. In this work, the potential of US welding to assemble folding boxboards was investigated. Folding boxboards are commonly coated to enhance printability. This coating is generally composed of mineral pigments (85 to 90%) and polymer binders (10 to 12%). This study evaluated whether the presence of the coating layer allows the assembly of paperboards by US welding. Results indicated that welding coated folding boxboards is possible provided that coating weight and binder content are high enough. The mechanical performances of the welded boards met the requirements of most packaging applications. Adhesion in the welded joint resulted from a combination of thermoplastic (melting and flowing of the binder) and thermoset (degradation reactions) effects. However, it was not possible to assemble coated folding boxboards without degrading the welding zone. While the materials and process need to be optimized, this work represents a big step forward toward the adhesive-free assembling of paper-based materials.
Isolation and analysis of lignin and lignin-carbohydrate complexes (LCCs) were performed to understand the better delignification ability of prehydrolysed wood chips. Lignin analysis showed that prehydrolysis led to a slight depolymerisation and an increase in free phenolic group content. The yield measurement and composition analysis of LCCs of mixed softwoods (SWs) and mixed hardwoods (HWs) revealed essential differences. In the case of SW, the amounts of lignin and xylan involved in LCCs were significantly lowered, whereas in the case of HW, less cellulose, glucomannans, and xylans were detectable in the residual LCCs. The molecular mass distributions of glucomannan-lignin and xylan-lignin fractions were not changed significantly.
Paper board have very poor barrier properties to water, water vapour and grease that can be improved by coating a layer, in this work of PolyVinylAlcohol (PVA), which exhibits very good barrier to grease but limited resistance to water and water vapour. Chromatogeny is an hydrophobisation technique that allows to confer better barrier to water and water vapour with a technology implementable at the industrial scale. Several passages can be applied on the coated layer to improve the grafting densities. However, little is known about the molecular mechanisms and the distribution of the reagent among the coated layer or if it modified also the paper board. In this work, we demonstrated that the modification proceeds from the surface to the interior of the PVA layer by developing an imaging technique based on the labelling with Osmium Tetroxide (OsO4) of the double bond of an oleyl acyl chloride used as an unsaturated hydrophobisation agent. The result is a bright tagging of the modified PVA layer strictly limited to the upper surface, as revealed by SEM images. Calculations made on simple assumptions on the volume expansion due to the modification have been confronted to the experimental data, i.e. measurements of the thickness of the grafted layers. The results showed that in our experimental conditions, the reagent penetrates in a zone strictly restricted to the upper part of the PVA layer and never reached the paper board. Moreover, the second passage does not increase significantly the penetration depth of the reagent, but allows increasing notably the hydrophobicity of the grafted material, as shown by Cobb measurements. Paper board remains intact in all the experimental situations explored at pilot scale.
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