Elias Retulainen

Chemical modification of cellulosic fibers for better convertibility in packaging applications

Cellulose fiber has been modified by mechanical and chemical means in order to improve paper properties, which respond to moisture and temperature. When the cellulose is first refined and then etherified using hydroxypropylation under dry conditions, the paper sheets prepared from the hydroxypropylated cellulose show improved elongation. When the level of hydroxypropylation is high enough, the paper sheets also become transparent. Additionally, the effect of cellulose activation using different mechanical methods has been compared by esterification reactions. It is shown that removal of water is the most crucial step for the esterification reactions while other methods have a lesser impact. The paper sheets prepared from the esterified cellulose fibers show an increase in contact angles and high hydrophobicity.

Mechanically-induced dimensional extensibility of fibers towards tough fiber networks

The beneficial effect of materials with high aspect ratio as composite reinforcement has prompted continuous interest towards cellulosic fibers. Besides providing stiffness, fibers can potentially contribute to composite extensibility. While mechanical treatments are typically used to adjust the physical and surface properties of fibers, less is known about ensuing effects on their extensibility and that of associated networks. Fiber network dimensional extensibility of 16% was achieved by processing the precursor aqueous fiber dispersions following a simple mechanical treatment with a judicious combination of low (PFI refining) and high concentrations and temperatures (Wing defibrator). Consequently, deformation of fibers and increased inter-fiber bonding resulted in a three-fold increase in strength to rupture of the fiber network leading to the structures with unprecedented toughness.

Improving the extensibility of paper: Sequential spray addition of gelatine and agar

High extensibility of paper is of key importance for production of novel 3D-packaging materials. The application of agar onto a wet web has been shown to significantly improve the extensibility of dry paper as a result of shrinkage during drying while addition of gelatine strengthens inter-fibre bonding. In this work, these two bio-based materials were applied sequentially to yield paper with higher extensibility compared to that obtained by single component application. We studied the interactions between agar, gelatine and cellulose by using quartz crystal microgravimetry and atomic force microscopy. Agar adsorption was significantly improved after priming the cellulose surface with gelatine. This synergistic effect on extensibility only occurred if the protein was added first. It is hypothesized that the gelatine strengthens the interfibre bonds while the polysaccharide forms a film on the web surface, and reinforces it. The extensibility of webs treated with gelatine (4%) and agar (4%) was ca. 15% after unrestrained drying. Such remarkable level of extensibility allows production of tray-like shapes via conventional thermoforming machine to depths of up to 2 cm. Overall, a protocol based on the sequential application of two abundant biopolymers is proposed to enhance formability of paper.

The relationship between shrinkage and elongation of bleached softwood kraft pulp sheets

Abstract The relationship between shrinkage and elongation of hand sheets was examined. The results show that the same dimensional contraction brought about by shrinkage can be strained out in tensile testing. However, percentage-wise the elongation is greater than the shrinkage due to different reference points, and the difference increases strongly at higher shrinkage levels. Elongation of paper can be explained mainly by two factors: the shrinkage and the net elongation of paper. Here shrinkage refers to all kinds of in-plane contraction of the fiber network (drying shrinkage, in-plane-compaction and creping). The novel concept ‘net elongation’ was proposed in order to separate the effect of shrinkage from the total elongation of paper. Net elongation is the elongation of corresponding unshrunken paper dried under restraint. Sheets with high elongation were prepared from bleached softwood kraft pulp and the effects of shrinkage on elongation, strength and stiffness of the paper were investigated. Mechanical treatment methods of pulp fibers and chemical strength additives were applied in order to maximize the strength and elongation. In-plane compaction and creping were used to further boost shrinkage of the high basis weight (100 g/m2) sheets up to 160 percent. Experimental elongation data confirmed the proposed theoretical relationships.

The effect of oxyalkylation and application of polymer dispersions on the thermoformability and extensibility of paper

Wood fiber-based packaging materials, as renewable materials, have growing market potential due to their sustainability. A new breakthrough in cellulose-based packaging requires some improvement in the mechanical properties of paper. Bleached softwood kraft pulp was mechanically treated, in two stages, using high- and low-consistency refining, sequentially. Chemical treatment of pulp using the oxyalkylation method was applied to modify a portion of fiber material, especially the fiber surface, and its compatibility with polymer dispersions including one carbohydrate polymer. The results showed that the compatibility of the cellulosic fibers with some polymers could be improved with oxyalkylation. By adjusting mechanical and chemical treatments, and the thermoforming conditions, the formability of paper was improved, but simultaneously the strength and stiffness decreased. The results suggest that the formability of the paper is not a direct function of the extensibility of the applied polymer, but also depends on the fiber network structure and surface energy.

The effect of chemical additives on the strength, stiffness and elongation potential of paper - OPEN ACCESS

The effects of wet-end additions of cationic starches and/or carboxymethyl cellulose (CMC) on paper properties was determined by papermaking trials. The aim of this study was to mitigate the distinctive decrease in strength and stiffness due to unrestrained drying by addition of wet-end additives, while maintaining the extraordinarily high stretch potential of papers after unrestrained drying. Addition of the different polysaccharides increased the tensile index and density of the paper. The largest incgtreases in tensile index and stiffness were seen when combining cationic starches with CMC. With certain combinations of cationic starch and CMC, it was possible to increase the tensile index and stiffness of the paper, while maintaining the high elongation at break after unrestrained drying. To complement the results from the papermaking trials, adsorption of cationic starches and CMC onto cellulose nanofibril model surfaces was studied by QCM-D and SPR techniques. The additives adsorbed onto cellulose surfaces as soft gels, containing a large amount of coupled water. Adsorption of soft and malleable polysaccharide layers in the fiber-fiber joints enhanced the paper properties significantly on a macroscopic level. The softest and most swollen polysaccharide layers resulted in the largest increases in tensile index and stiffness of paper ADDRESSES OF THE AUTHORS: Anders Strand (anders.strand@abo.fi), Anna Sundberg (anna.sundberg@abo.fi), The Laboratory of Wood and Paper Chemistry, Åbo Akademi University, Porthaninkatu 3, FI-20500, Turku, Finland. Elias Retulainen (elias.retulainen@vtt.fi), Kristian Salminen (kristian.salminen@vtt.fi), Antti Oksanen (antti.oksanen@vtt.fi), Jarmo Kouko (jarmo.kouko@ vtt.fi), Annika Ketola (Annika.ketola@vtt.fi), VTT, Koivurannantie 1, FI-40400 Jyväskylä, Finland. Alexey Khakalo (alexey.khakalo@aalto.fi), Orlando Rojas (orlando.rojas@aalto.fi), Department of Bioproducts and Biosystems, School of Chemical Engineering, Aalto University, FI-00076, Espoo, Finland Corresponding author: Anders Strand

Changing Quality of Recycled Fiber Material – Part II. Characterization of the Strength Potential with Fiber Integrity Value and its Relationship with the Strength Properties of Paper

A novel method was introduced to evaluate the quality of fiber material from paper for recycling. The new concept, fiber integrity value, its components, and its relationship with paper strength properties were examined in more detail. The effect of deinking and screening on fiber integrity value, and its component parameters was shown. The fiber integrity value is closely connected to the strength potential of the pulp. It was shown that when the bonding degree was also considered, there was very good correlation with the tensile strength, tensile stiffness, and compressive strength (SCT) values. The fiber integrity value concept can be determined based on data from in-line analyzers.