The papers summarized here are from the November 2017 issue, featuring special recycling content; and the January 2018 issue, featuring special coating content. TAPPI Journal is an online publication of relevant and timely peer-reviewed research delivered via email and free to all TAPPI members. To receive TAPPI Journal, join TAPPI at www.tappi.org.
Improved deinking and stickies removal
Previous work had shown that a novel flotation deinking reagent using modified kaolin was able to more efficiently separate and remove ink and dirt particles from recovered paper. The mechanism for this reagent is based on the ability of the modified kaolin to act as a collector for the fine ink, dirt, and contaminant particles.
Deinking mills using this reagent experienced deinked pulp with an increase in brightness and lower dirt count values. Further work has been carried out to determine whether this mechanism can be used to improve the removal of stickies in recovered pulp. Test results showed that use of this modified kaolin together with a reagent capable of effectively separating the sticky contaminants from the fiber improved the removal of stickies. The synergy of this reagent with the modified kaolin further improved ink and dirt removal.
New automated method for macrocontaminant analysis: industrial applications
Sylvie Ossard, Patrick Huber, Pascal Borel, Davy Soysouvanh, and Thierry Delagoutte
In recycled paper processes, stickies are the origin of many production disturbances. In this paper, we present how the recently developed method for macrocontaminant analysis was used with industrial samples for process analysis. The new automated stickies measurement method allows (i) determination of the three-dimensional (3D) morphology of screened particles (without any deformation) and (ii) classification of the particles as stickies among contaminants. This is achieved by a combination of laser triangulation and local near-infrared spectroscopy (NIR).
Measurement of macrocontaminants in pulp samples and their classification allow meaningful evaluation of their specific removal. Chemical nature and amount of the macrocontaminants coming from different raw materials were studied and were shown to be very different in two different mills. In an Asian mill, a low removal of pressure sensitive adhesives (PSAs) in the process (46 percent) was found in comparison with high removal of other stickies (99 percent). Applications of this device are shown in this study, while the new on-line sensor for macrocontaminant analysis is being developed.
This study demonstrates how mills can analyze stickies removal throughout the recycling process. As a consequence, they could control the process depending on the chemical nature of incoming stickies contamination.
Deinking process water flotation: An innovative solution to improve deinking and papermaking processes efficiency
Thierry Delagoutte, Bruno Carré, and Elisa Zeno
High and uncontrolled surface-active substances (SAS) concentrations in deinking line process waters strongly disturb flotation deinking. Indeed, their adsorption at air/water and ink/water interfaces stabilizes air bubbles and ink particles, reducing ink collection during flotation. In addition, foam stabilization promoted by SAS reduces froth drainage and consequently enhances suspended solids losses. All in all, selectivity of flotation is negatively affected by excessive SAS concentrations.
Floating process water with adapted technology, a patented solution, is an efficient way to decrease SAS concentration and thereby recover flotation deinking selectivity. Researchers successfully tested this concept at industrial scale. First-loop clear filtrates of a deinked pulp line (for newsprint production) were floated. At steady state, this treatment allows a 20 percent reduction of the SAS concentration in first loop process water. Evaluation of ink removal selectivity at pre-flotation and post-flotation showed a significant improvement in comparison with reference values.
During the trial, the mill could either produce pulp with lower ink content and consequently higher brightness (50 ppm effective residual ink concentration [ERIC] less, corresponding to a 1 brightness point increase) for similar losses, or similar pulp quality with 1-2 percent yield improvement, representing a huge cost reduction. The mill also reported beneficial side effects, such as reduced deinking chemicals consumption (soda, silicate, and bleaching agents) and better paper machine runnability, especially in terms of stickies breaks.
Mills may be able to increase brightness or yield in their deinking line using the process described in this study.
SLOT DIE COATING
Slot die coating of nanocellulose on paperboard
Vinay Kumar, Douglas W. Bousfield, and Martti Toivakka
Constantly growing interest in nanocellulose use and applications is pushing the scientific community to search for suitable production and processing techniques. One example is use of nanocellulose as a barrier material in packaging applications, which requires processing of nanocellulose into films and coatings. It is challenging to coat nanocellulose suspensions using conventional pigment coating techniques due to their yield stress behavior and very high viscosity, even at low solids concentration.
This study demonstrates a novel roll-to-roll coating method of nanocellulose on paperboard using slot die geometry. The rheology of nanocellulose suspensions in pressure-driven flow is found to play a critical role in enabling their coating using the said process. In this work, the slot die is used in an unconventional manner: the shearing and metering elements are combined to aid wet film formation and application of nanocellulose suspension onto the paperboard. Barrier performance of the nanocellulose coated paperboards against air, water, heptane vapor, grease, and oils was found to be reasonable and warrants further research on the subject.
The modified slot die coating method reported in this study could be used for roll-to-roll coating of web materials with a large variety of highly viscous materials such as cellulose nanofibers.
Experimental setup for roll-to-roll slot die coating of cellulose nanofibers suspension.
Contrasting underlying mechanisms of different barrier coating types
Bryan Mcculloch, John Roper, and Kaitlin Rosen
Barrier coatings are used in applications including food packaging, dry goods, and consumer products to prevent transport of different compounds either through or into paper and paperboard substrates. These coatings are useful in packaging to contain active ingredients, such as fragrances; or to protect contents from detrimental substances, such as oxygen, water, grease, or other chemicals of concern. They also are used to prevent visual changes or mechanical degradation that might occur if the paper becomes saturated. The performance and underlying mechanism depends on the barrier coating type and, in particular, on whether the barrier coating is designed to prevent diffusive or capillary transport.
Estimates on the basis of fundamental transport phenomena and data from a broad screening of different barrier materials can be used to understand the limits of various approaches to construct barrier coatings. These estimates also can be used to create basic design rules for general classes of barrier coatings, and barrier coatings can be designed with unique performance profiles optimized for customer requirements.
Print quality of flexographic printed paperboard related to coating composition and structure
E. Bohlin and C. Johansson
Ink transfer and setting influence the achievable print quality and visual appearance. The pressure in the printing nip and the porosity of the substrate regulate the amount of ink that penetrates into a porous coating structure. The purpose of this study was to understand how print quality aspects could be related to ink penetration of water-based flexographic ink into coatings of differently engineered structures: calcium carbonate (GCC) of various particle size distribution (PSD), coatings with different amounts of latex binder, and coatings with various blends of GCC and kaolin.
Calcium carbonate with broad pigment PSD resulted in a lower print density compared to coatings of narrowly distributed particle sizes. Coatings of larger pore volume and greater dominating pore radius showed a higher amount of z-directional ink penetration. A high ratio of uncovered areas could be detected for samples with a high amount of latex. However, increased printing force eliminated these artifacts.
Increased printing force increased the print density to a higher degree than did a reduced ink viscosity for coatings with pure GCC. For coating layers containing both GCC and kaolin clay, decreased ink viscosity had a stronger impact on the print density than increased printing force. Print density was also affected by ink penetration, suggesting that the optical response is sensitive to the ink-substrate interaction layer. The result presented in this study also suggests that the print gloss decreases with increased amount of penetrated ink due to a higher rate of ink vehicle removal.
By fine-tuning the coating composition and structure and by a proper selection of printing parameters, it was demonstrated that print quality defects can be addressed by fundamental studies of ink transfer and subsequent ink setting. The detailed understanding of mechanisms of ink-substrate interactions is a requirement for maintaining competitiveness in the packaging industry based on renewable materials.
OTHER RESEARCH APPEARING IN TAPPI JOURNAL’S NOVEMBER 2017 ISSUE:
Innovative technology for making improved paper from the poorest fibers
Marion Sterner and Mikael Magnusson
OTHER RESEARCH APPEARING IN TAPPI JOURNAL’S JANUARY 2018 ISSUE:
Discrete element method to predict coating failure mechanisms
Daniel H. Varney and Douglas W. Bousfield