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Paper-based packaging materials are generally assembled using adhesives formulated with oil-based polymers. These adhesives make the recyclability of the materials more complex and may be the source of material contamination by mineral oil. In view of developing an adhesive-free process, the potential of ultrasonic compression was investigated in this study. 100% lignocellulosic papers were assembled using an ultrasonic welder dedicated to thermoplastic polymers. For papers containing lignin, the measured peeling strengths were equivalent to those achieved by hot-melt gluing, provided that the water content of papers was well adjusted. At the interface between bonded papers, the fiber network was dense and rather continuous. SEM examinations, 3D X-ray microtomography images, and temperature measurements suggested that the development of adhesion originated to a large extent from a thermoplastic welding mechanism: wood fiber polymers passed their glass transition temperatures, creeped and formed a matrix that coated fibers. Thus, ultrasonic welding appears as an efficient adhesive-free technique for assembling papers that are used in a broad range of packaging applications. [ABSTRACT FROM AUTHOR]

The modification of paper substrates by organic nanoparticle coatings offers an attractive alternative for creating hydrophobic and water-repellent surfaces without fluorinated chemicals. The nanoparticles were synthesized by imidization of poly(styrene-maleic anhydride) and applied to a standard paper grade by means of a laboratory bar-coating process. The effects of supplementary heat treatments of the coated papers were investigated in terms of coating morphology and hydrophobicity: a unique coating structure is formed with a combination of microdomains that are internally structured at the nanoscale. The relatively high glass transition temperature of the nanoparticles allows for good thermal stability of the coating with almost no morphological changes at heating up to 180°C. The changes in chemical composition were investigated by diffuse reflectance infrared spectroscopy (DRIFT) and UV/VIS spectroscopy. The latter techniques qualitatively describe the effects of thermal treatments on the imide and styrene moieties. Contact angle measurements indicate that there is an optimum curing temperature in order to obtain a maximum advancing contact angle of 133° to 150°. [ABSTRACT FROM AUTHOR]